Majid Beidaghi

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Scholarly Contributions

Chapters

• Jamshidi, E., Woods, M., Davis, V., & Beidaghi, M. (2024). Three-Dimensional (3D) Printing of MXenes. In Transition Metal Carbides and Nitrides (MXenes) Handbook: Synthesis, Processing, Properties and Applications. wiley. doi:10.1002/9781119869528.ch14
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  This chapter provides a review of the advancements in the preparation and application of MXene inks for three-dimensional (3D) printing by direct ink writing (DIW). MXenes, two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have garnered interest in many fields due to their exceptional properties like high electrical conductivity and versatile surface chemistry. These qualities make MXenes promising for applications in energy storage devices, electromagnetic interference shielding, and flexible electronics, among others. The chapter details the development of 3D printable MXene-based inks, focusing on their rheological properties essential for DIW. It discusses various approaches for ink formulation and highlights the significant role of viscoelastic properties in determining the printability and performance of the final 3D structures. The chapter reviews specific studies on MXene inks used for fabricating 3D energy storage devices, such as micro-supercapacitors (MSCs), emphasizing the benefits of 3D architectures over conventional 2D planar structures. Despite recent advances, challenges such as the limited shelf life of MXene inks, the predominance of one MXene composition in printing, and the need for improved delamination and etching yields in synthesis remain and need to be addressed in future studies. The chapter concludes by suggesting that further research is required to develop functional MXene inks and novel preparation processes to broaden the application range of 3D MXene-based devices.
• Anasori, B., Xie, Y., Beidaghi, M., Lu, J., Hosler, B. C., Hultman, L., Kent, P. R., Gogotsi, Y., & Barsoum, M. W. (2023). Two-dimensional, ordered, double transition metals carbides (MXenes). In MXenes From Discovery to Applications of Two-Dimensional Metal Carbides and Nitrides. Jenny Stanford Publishing.
• Mishra, M., Behura, S. K., Beidaghi, M., Verma, K., & Singh, S. (2021). MXene: A Non-oxide Next-Generation Energy Storage Materials for Batteries and Supercapacitors. In Advanced Applications of 2D Nanostructures. Springer Nature. doi:10.1007/978-981-16-3322-5_6
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  MXenes, represented by Mn+1XnTx, are an emerging class of two-dimensional (2D) nitrides, carbides and carbonitrides (X) of transition elements (M) containing terminations of free surface-active groups (T). These are derived by selective etching out ‘A’ from their corresponding MAX phases. MXene, like their other 2D material counterparts, has exceptional electrical, electrochemical, mechanical and structural properties which make them a formidable candidate for electrode materials in energy storage systems like rechargeable lithium-ion batteries, supercapacitors and microsupercapacitors. They have excellent metal-ion storage capacity due to large interlayer space, low ion diffusion barrier, metal-like conductivity, high thermal stability and hydrophilic surface. Also, increased electrochemical performance has been observed when MXenes are used in conjuncture with graphene and carbon nanotubes (CNT) or dopants like silver, silicon, etc., as heterostructures or hybrid composites of 2D materials synthesized via innovative mix of processes. Thus, MXenes have been successfully identified and demonstrated as future sustainable energy material for energy storage application in the upcoming battery technology revolution.
• VahidMohammadi, A., Kayali, E., Orangi, J., & Beidaghi, M. (2019). Techniques for MXene delamination into single-layer flakes. In 2D Metal Carbides and Nitrides (MXenes). Springer International Publishing. doi:10.1007/978-3-030-19026-2_11

Journals/Publications

• Baek, Y., Singh, P. G., Prorok, B. C., & Beidaghi, M. (2025). Effect of Synthesis Conditions on the Morphology and Electrochemical Properties of Nb₂ CT _x MXenes. ACS Appl. Electron. Mater., 7(22), 10411-10420.
• Pakravan, K., Esfahani, M. R., Prorok, B. C., & Beidaghi, M. (2025). Understanding the Role of Microstructure in Ti3C2Tx MXene Membrane Performance. ACS applied materials & interfaces, 17(Issue 31). doi:10.1021/acsami.5c10055
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  Ti3C2Tx MXene membranes have attracted considerable interest for separation technologies owing to their well-defined and tunable interlayer channels. However, reported water permeability values vary widely, suggesting the presence of additional, unrecognized factors influencing water transport. In this study, we demonstrate that both the dynamic microstructure of MXene membranes under pressure and the flake size of Ti3C2Tx, used in fabrication play critical roles in determining water flux. We observed a substantial decline in water permeability, from tens of L/m2·bar·h to below 5 L/m2·bar·h, during filtration, attributed to compaction of the initially loose membrane structure. Notably, the change in the microstructure is reversible, with the disordered microstructure recovering after drying. Moreover, MXene flake size is found to impact the tortuosity of water pathways, where membranes constructed from smaller flakes exhibit higher permeability. For example, membranes fabricated with an average flake size of 4 μm achieved water permeabilities 2.15 times lower than those made with 0.17 μm flakes. These findings underscore the complex interplay between microstructure dynamics, flake size, and liquid transport, offering key insights for the rational design of high-performance MXene-based separation membranes.
• Pala, J., Al, M. A., Pakravan, K., Gurdev, S. P., Awasthi, V. D., Beidaghi, M., & Esfahani, M. R. (2025). Perfluorooctanesulfonic Acid Removal by Delaminated Titanium Carbide MXene: Impact of MXene Surface Chemistry on Adsorption Mechanisms and Removal Efficiency. ACS Applied Engineering Materials, 3(10), 3442-3454.
• Stratulat, A., Nesterova, V., Korostelev, V., Beidaghi, M., Mochalin, V., & Klyukin, K. (2025). Defect-Driven Degradation of MXenes in Aqueous Environments and Mitigation Strategies: Insights from First-Principles. ACS Nano, 19(42), 36994-37003.
• Thakur, A., Chandran, B. N., Wyatt, B. C., Gurdev, S. P., Bedford, A., Nemani, S. K., Beidaghi, M., & Anasori, B. (2025). Cation Exchange and Systematic Evaluation of M4C3Tx MXenes for Hydrogen Evolution Reaction Electrocatalysis. Chem. Mater..
• Woods, M., Beidaghi, M., & Davis, V. (2024). Phase Behavior and Rheological Properties of Size-Fractionated MXene (Ti3C2Tx) Dispersions. Langmuir, 40(6). doi:10.1021/acs.langmuir.3c02851
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  Understanding the dispersion behavior of MXenes is interesting from a fundamental colloid science perspective and critical to enabling the fluid-phase manufacturing of MXene devices with controlled microstructures and properties. However, the polydispersity, irregular shape, and charged surfaces of MXenes result in a complex phase behavior that is difficult to predict through theoretical calculations. As two-dimensional (2D) nanomaterials, MXenes can form lyotropic liquid crystal phases, gels, and aggregates. This work aims to elucidate the effects of MXene (Ti3C2Tx) sheet size on their phase behavior and associated rheological properties. Aqueous dispersions of large sheets with an average lateral dimension of 3.0 μm, small sheets with an average lateral dimension of 0.3 μm, and a bimodal mixture of the two sizes were investigated by using cross-polarized optical microscopy and rheology. At low concentrations, the large MXene dispersions exhibited lyotropic liquid crystal behavior and extended aligned textures, but increasing concentration resulted in the formation of dense flocs. Dispersions of small sheets formed small birefringent domains with increasing concentration but lacked long-range ordering. A bimodal mixture of these sizes enabled the formation of liquid crystalline phases with extended aligned textures with less floc formation. These results provide insights into using polydispersity to tune dispersion microstructure and rheological properties that can be applied to designing dispersions for fluid-phase manufacturing methods, such as direct ink writing.
• Wu, G., Du, H., Pakravan, K., Kim, W., Cha, Y. L., Beidaghi, M., Zhang, X., Pan, X., & Kim, D. J. (2024). Wearable room-temperature ethanol sensor based on Ti3C2Tx/Polypyrrole functionalized face mask for drunk driving monitoring. Carbon, 216(Issue). doi:10.1016/j.carbon.2023.118565
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  As one of the most encountered volatile organic compounds (VOCs), ethanol, especially with high blood concentrations, could cause adverse effects such as nausea, vomiting, skin allergies, low blood pressure, low blood sugar, and Parkinson's disease, seriously threatening human health and safety driving. In this study, we demonstrate a wearable ethanol sensor through drop-coating Ti3C2Tx suspension followed by chemical polymerization of pyrrole on a disposable face mask substrate. The as-fabricated PP/Ti3C2Tx/PPy composite sensor exhibited a rapid response/recovery speed (49s/18s), a good sensing response of 76.3 % toward 400 ppm ethanol, an admirable theoretical limit of detection of 2.21 ppm, reliable flexibility, high selectivity, and excellent reproducibility. The outstanding sensing characteristics of the composite sensor are ascribed to the abundant functional groups (e.g., amino groups in PPy, terminal groups in Ti3C2Tx) and the formation of the Schottky junction between Ti3C2Tx and PPy. Moreover, the composite sensor exhibits stable sensing performance around room temperatures (20–40 °C), and even at different bending states (0–150°). In addition, we developed a portable and wearable Bluetooth sensor module for human alcohol breath detection, suggesting the PP/Ti3C2Tx/PPy composite sensor can be used for human drunk driving monitoring and health assessment.
• Beidaghi, M., Huang, S., & Mochalin, V. (2023). Properties and applications of two-dimensional MXenes. Diamond and Related Materials, 139(Issue). doi:10.1016/j.diamond.2023.110255
• Beidaghi, M., Huang, S., & Mochalin, V. (2023). Properties and applications of two-dimensional MXenes. Diamond and Related Materials, 139, 110255.
• Wu, G., Du, H., Pakravan, K., Kim, W., Cha, Y. L., Chiang, S., Beidaghi, M., Zhang, X., Kim, S. H., Pan, X., & Kim, D. (2023). Polyaniline/Ti3C2Tx functionalized mask sensors for monitoring of CO2 and human respiration rate. Chemical Engineering Journal, 475, 146228.
• Wu, G., Wu, G., Du, H., Du, H., Pakravan, K., Pakravan, K., Kim, W., Kim, W., Cha, Y. L., Cha, Y. L., Chiang, S. T., Chiang, S. T., Beidaghi, M., Beidaghi, M., Zhang, X., Zhang, X., Kim, S. H., Kim, S. H., Pan, X., , Pan, X., et al. (2023). Polyaniline/Ti3C2Tx functionalized mask sensors for monitoring of CO2 and human respiration rate. Chemical Engineering Journal, 475(Issue). doi:10.1016/j.cej.2023.146228
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  Flexible and wearable gas-sensing devices have become increasingly crucial for monitoring air quality and human health. Disposable masks, mainly composed of polypropylene (PP) fibers, can serve as a potential flexible substrate for sensing devices yet have been largely overlooked during the COVID-19 pandemic. In the present work, flexible Ti3C2Tx/PANI-PP composite gas sensors were fabricated by spray-coating delaminated Ti3C2Tx MXene and in-situ polymerization of aniline on a disposable mask substrate. The resulting hybrid gas sensor displayed a wide detection range (25–1500 ppm), reliable reproducibility, long-term stability, and excellent flexibility and selectivity, a remarkable response (15.2%) towards 500 ppm CO2 gas, which is 6.5 times higher than pristine Ti3C2Tx and 2.4 times higher than pristine PANI. The enhanced sensing performance of the composite sensor is mainly attributed to the synergistic effects of the heterojunctions between Ti3C2Tx and PANI, the improved conductivity, and the enlarged specific surface area. We further investigated the influence of various parameters, including humidity, temperature, bending angles, and folding times on the sensing performance of the composite gas sensor. Finally, a wearable wireless Bluetooth sensing device was fabricated for human exhaled breath monitoring at room temperature, demonstrating the potential application of this Ti3C2Tx/PANI-PP composite sensor for respiratory disease diagnosis.
• Fathi-Hafshejani, P., Orangi, J., Beidaghi, M., & Mahjouri-Samani, M. (2022). Laser-assisted growth of hierarchically architectured 2D MoS2 crystals on metal substrate for potential energy applications. International Journal of Extreme Manufacturing, 4(4), 045102.
• Fathi-Hafshejani, P., Orangi, J., Beidaghi, M., & Mahjouri-Samani, M. (2022). Laser-assisted growth of hierarchically architectured 2D MoS2 crystals on metal substrate for potential energy applications. International Journal of Extreme Manufacturing, 4(Issue 4). doi:10.1088/2631-7990/ac8f73
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  Recently, there has been substantial interest in the large-scale synthesis of hierarchically architectured transition metal dichalcogenides and designing electrodes for energy conversion and storage applications such as electrocatalysis, rechargeable batteries, and supercapacitors. Here we report a novel hybrid laser-assisted micro/nanopatterning and sulfurization method for rapid manufacturing of hierarchically architectured molybdenum disulfide (MoS2) layers directly on molybdenum sheets. This laser surface structuring not only provides the ability to design specific micro/nanostructured patterns but also significantly enhances the crystal growth kinetics. Micro and nanoscale characterization methods are employed to study the morphological, structural, and atomistic characteristics of the formed crystals at various laser processing and crystal growth conditions. To compare the performance characteristics of the laser-structured and unstructured samples, Li-ion battery cells are fabricated and their energy storage capacity is measured. The hierarchically architectured MoS2 crystals show higher performance with specific capacities of about 10 mAh cm−2, at a current rate of 0.1 mA cm−2. This rapid laser patterning and growth of 2D materials directly on conductive sheets may enable the future large-scale and roll-to-roll manufacturing of energy and sensing devices.
• Le, T., Jamshidi, E., Beidaghi, M., & Esfahani, M. R. (2022). Functionalized-MXene Thin-Film Nanocomposite Hollow Fiber Membranes for Enhanced PFAS Removal from Water. ACS Applied Materials & Interfaces.
• Le, T., Jamshidi, E., Beidaghi, M., & Esfahani, M. R. (2022). Functionalized-MXene Thin-Film Nanocomposite Hollow Fiber Membranes for Enhanced PFAS Removal from Water. ACS Applied Materials and Interfaces, 14(Issue 22). doi:10.1021/acsami.2c03796
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  Due to adverse health effects and the broad sources of per- and polyfluoroakyl substances (PFAS), PFAS removal is a critical research area in water purification. We demonstrate the functionalization of thin-film composite (TFC) hollow fiber nanofiltration (HFN) membranes by MXene nanosheets during the interfacial polymerization (IP) process for enhanced removal of perfluorooctane sulfonic acid (PFOS) from water. A MXene-polyamide (PA) selective layer was fabricated on top of a polysulfone (PSF) hollow fiber support via IP of trimesoyl chloride (TMC) and a mixture of piperazine (PIP) and MXene nanosheets to form MXene-PA thin-film nanocomposite (TFN) membranes. Incorporating MXene nanosheets during the IP process tuned the morphology and negative surface charge of the selective layer, resulting in enhanced PFOS rejection from 72% (bare TFC) to more than 96% (0.025 wt % MXene TFN), while the water permeability was also increased from 13.19 (bare TFC) to 29.26 LMH/bar (0.025 wt % MXene TFN). Our results demonstrate that both electrostatic interaction and size exclusion are the main factors governing the PFOS rejection, and both are determined by PA selective layer structural and chemical properties. The lamella structure and interlayer of MXene nanosheets inside the PA layer provided different transport mechanisms for water, ions, and PFAS molecules, resulting in enhanced water permeability and PFAS rejection due to traveling through the membrane by both diffusions through the PA layer and the MXene intralayer channels. MXene nanosheets showed very promising capability as a 2D additive for tuning the structural and chemical properties of the PA layer at the permeability-rejection tradeoff.
• Tetik, H., Orangi, J., Yang, G., Zhao, K., Mujib, S. B., Singh, G., Beidaghi, M., & Lin, D. (2022). 3D Printed MXene Aerogels with Truly 3D Macrostructure and Highly Engineered Microstructure for Enhanced Electrical and Electrochemical Performance. Advanced Materials, 34(2), 2104980.
• Orangi, J., Tetik, H., Parandoush, P., Kayali, E., Lin, D., & Beidaghi, M. (2021).

  Conductive and highly compressible MXene aerogels with ordered microstructures as high-capacity electrodes for Li-ion capacitors

  . Materials Today Advances. doi:10.1016/j.mtadv.2021.100135
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  Assembling two-dimensional (2D) materials into functional three-dimensional (3D) structures can enable their use in a wide variety of applications. For energy storage devices, 3D electrodes with high ionic and electronic transport properties and decent mechanical properties are expected to prompt the fabrication of the next generations of devices with high energy and power densities. Herein, we report a simple, efficient, and scalable process based on unidirectional freeze casting to fabricate ordered and porous 3D aerogels from 2D Ti3C2Tx MXene flakes. The fabricated aerogels show excellent mechanical, electrical, and electrochemical properties. Our studies show that the processing conditions significantly affect the properties of MXene aerogels. The electrical conductivity and mechanical properties of fabricated aerogels directly correlate with their structural features. The mechanical test results showed that MXene aerogels with ordered structures could withstand almost 50% of strain before recovering to their original shape and maintain their electrical conductivities during continuous compressive cycling. As electrode materials for lithium-ion capacitors, the fabricated aerogels delivered a significantly high specific capacity (~1210 mAh/g at 0.05 A/g), excellent rate capability (~200 mAh/g at 10 A/g), and outstanding cycling performance. We believe that the MXene aerogels with ordered structures have promising properties for a broad range of applications, including energy storage devices and strain sensors.
• Orangi, J., Tetik, H., Parandoush, P., Kayali, E., Lin, D., & Beidaghi, M. (2021). Conductive and highly compressible MXene aerogels with ordered microstructures as high-capacity electrodes for Li-ion capacitors. Materials Today Advances, 9, 100135.
• Tetik, H., Orangi, J., Yang, G., Zhao, K., Mujib, S. B., Singh, G., Beidaghi, M., & Lin, D. (2021).

  3D Printed MXene Aerogels with Truly 3D Macrostructure and Highly Engineered Microstructure for Enhanced Electrical and Electrochemical Performance

  . Advanced Materials. doi:10.1002/adma.202104980
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  Assembling 2D materials such as MXenes into functional 3D aerogels using 3D printing technologies gains attention due to simplicity of fabrication, customized geometry and physical properties, and improved performance. Also, the establishment of straightforward electrode fabrication methods with the aim to hinder the restack and/or aggregation of electrode materials, which limits the performance of the electrode, is of great significant. In this study, unidirectional freeze casting and inkjet-based 3D printing are combined to fabricate macroscopic porous aerogels with vertically aligned Ti3 C2 Tx sheets. The fabrication method is developed to easily control the aerogel microstructure and alignment of the MXene sheets. The aerogels show excellent electromechanical performance so that they can withstand almost 50% compression before recovering to the original shape and maintain their electrical conductivities during continuous compression cycles. To enhance the electrochemical performance, an inkjet-printed MXene current collector layer is added with horizontally aligned MXene sheets. This combines the superior electrical conductivity of the current collector layer with the improved ionic diffusion provided by the porous electrode. The cells fabricated with horizontal MXene sheets alignment as current collector with subsequent vertical MXene sheets alignment layers show the best electrochemical performance with thickness-independent capacitive behavior.
• VahidMohammadi, A., Liang, W., Mojtabavi, M., Wanunu, M., & Beidaghi, M. (2021). 2D titanium and vanadium carbide MXene heterostructures for electrochemical energy storage. Energy Storage Materials, 41, 554-562.
• Ahmadi, Z., Fathi-Hafshejani, P., Kayali, E., Beidaghi, M., & Mahjouri-Samani, M. (2020). Rapid laser nanomanufacturing and direct patterning of 2D materials on flexible substrates???2DFlex. Nanotechnology, 32(5), 055302.
• Ahmadi, Z., Fathi-Hafshejani, P., Kayali, E., Beidaghi, M., & Mahjouri-Samani, M. (2020). Rapid laser nanomanufacturing and direct patterning of 2D materials on flexible substrates—2DFlex. Nanotechnology, 32(Issue 5). doi:10.1088/1361-6528/abc285
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  Direct synthesis, large-scale integration, and patterning of two-dimensional (2D) quantum materials (e.g. MoS2, WSe2) on flexible and transparent substrates are of high interest for flexible and conformal device applications. However, the growth temperatures (e.g. 850 °C) of the emerging 2D materials in the common gas-phase synthesis methods are well beyond the tolerances limit of flexible substrates, such as polydimethylsiloxane (PDMS). In addition, random nucleation and growth process in most growth systems limits the predicted integration and patterning freedoms. Here, we report a rapid direct laser crystallization and mask-free large-scale patterning of MoS2 and WSe2 crystals on PDMS substrates. A thin layer of stoichiometric amorphous 2D film is first laser-deposited via pulsed laser deposition (PLD) system onto the flexible substrates followed by a controlled crystallization and direct writing process using a tunable nanosecond laser (1064 nm). The influences of pulse duration, number of pulses, and the thickness of the deposited amorphous 2D layer on the crystallization of 2D materials are discussed. Optical spectroscopy and electrical characterizations are performed to confirm the quality of crystallized 2D materials on flexible substrates. This novel method opens up a new opportunity for the crystallization of complex patterns directly from computer-aided design models for the future 2D materials-based wearable, transparent, and flexible devices.
• Orangi, J., & Beidaghi, M. (2020).

  A Review of the Effects of Electrode Fabrication and Assembly Processes on the Structure and Electrochemical Performance of 2D MXenes

  . Advanced Functional Materials. doi:10.1002/adfm.202005305
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  Abstract MXenes are 2D materials with relatively high surface areas, high electrical conductivities, functional transition metal surfaces, tunable surface chemistries, and solution processability. Due to these properties, 2D MXenes have attracted widespread attention as electrode materials for energy storage devices, including electrochemical capacitors, with high power and energy densities. However, many studies have shown that the electrochemical performance of MXene electrodes is considerably affected by their structure and morphology. These properties are, for the most part, controlled by the method used for the assembly of 2D MXene flakes and the electrode fabrication methods. A successful electrode assembly and fabrication method should address several challenges, such as the restacking of 2D flakes, to achieve electrode structures and morphologies that deliver high ionic transport properties, electrical conductivity, and mechanical stability. This review aims to provide insight into the current state‐of‐the‐art assembly and fabrication methods used to design and fabricate high performance electrodes based on MXenes. The major challenges to be addressed and possible future directions in the fabrication of MXene electrodes for practical energy storage applications are highlighted.
• Orangi, J., & Beidaghi, M. (2020). A review of the effects of electrode fabrication and assembly processes on the structure and electrochemical performance of 2D MXenes. Advanced Functional Materials, 30(47), 2005305.
• Thakur, R., Hoffman, M., VahidMohammadi, A., Smith, J., Chi, M., Tatarchuk, B., Beidaghi, M., & Carrero, C. A. (2020). Multilayered Two-Dimensional V2CTx MXene for Methane Dehydroaromatization. ChemCatChem, 12(Issue 14). doi:10.1002/cctc.201902366
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  We report a thermally stable multilayered two-dimensional vanadium carbide (V2CTx) MXenes catalyst for the direct conversion of methane (CH4) into benzene (C6H6). The multilayered carbide structure shows state-of-the-art CH4 conversion 11.8 % with a C6H6 formation rate of 1.9 mmol gcat−1h−1 (4.84 % C6H6 yield) at 700 °C, which is comparable to the benchmark Mo/ZSM-5 catalyst. The structure-activity relationship was explored by numerous characterization techniques including in-situ/operando Raman-MS, ex-situ X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and ammonia temperature programmed desorption (NH3-TPD). This work provides a new platform to design and explore multilayered two-dimensional catalysts demonstrating confinement effect to convert CH4 into *C2H3 intermediates which further oligomerize inside multilayered structures producing C6H6 as the final product.
• Thakur, R., Hoffman, M., VahidMohammadi, A., Smith, J., Chi, M., Tatarchuk, B., Beidaghi, M., & Carrero, C. A. (2020). Multilayered Two???Dimensional V2CTx MXene for Methane Dehydroaromatization. ChemCatChem, 12(14), 3639-3643.
• Thakur, R., VahidMohammadi, A., Smith, J., Hoffman, M., Moncada, J., Beidaghi, M., & Carrero, C. A. (2020). Insights into the genesis of a selective and coke-resistant MXene-based catalyst for the dry reforming of methane. ACS Catalysis, 10(9), 5124-5134.
• Thakur, R., Vahidmohammadi, A., Smith, J., Hoffman, M., Moncada, J., Beidaghi, M., & Carrero, C. A. (2020). Insights into the Genesis of a Selective and Coke-Resistant MXene-Based Catalyst for the Dry Reforming of Methane. ACS Catalysis, 10(Issue 9). doi:10.1021/acscatal.0c00797
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  We report the use of a multilayered vanadium carbide MXene (m-V2CTx) as a precursor for a robust oxy-carbide catalyst to convert CH4 and CO2 into syngas via dry reforming of methane (DRM). The in situ generated V2O3-V8C7/m-V2CTx catalyst undergoes a redox (oxidation-carburization) mechanism that results in attractive reactivity, selectivity (H2/CO ratio close to unity), and unprecedented stability (negligible formation of coke). The oxy-carbide species (V2O3 and V8C7) growing in situ under reaction conditions decorate the layers of m-V2CTx and provide a better utilization of V sites in such a way that the resulting V2O3-V8C7/m-V2CTx catalyst exhibits four times higher activity than its bulk counterparts, V2AlC MAX phase and commercial vanadium carbide (VC). These kinetic findings combined with spectroscopy, microscopy, and isotopic labeling experiments reveal that while dehydrating the pristine m-V2CTx, an oxy-carbide (V2O3-V8C7/m-V2CTx) material is produced which oxidizes further in the presence of CO2 to generate additional V2O3 nanocrystals on the surface and in-between the multilayered structure. These oxide particles are further carburized in situ by reaction with CH4 and transforming into V8C7 nanocrystals. This study provides kinetic, structural, and mechanistic insights into the genesis of m-V2CTx as a selective and coke-resistant catalyst for DRM. We foresee m-V2CTx, and MXenes in general, as promising precursors, supports, and/or catalysts for various other catalytic applications at relatively high temperatures (≥500 °C).
• Lee, E., VahidMohammadi, A., Yoon, Y. S., Beidaghi, M., & Kim, D. (2019). Two-dimensional vanadium carbide MXene for gas sensors with ultrahigh sensitivity toward nonpolar gases. ACS sensors, 4(6), 1603-1611.
• Lee, E., Vahidmohammadi, A., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2019). Two-Dimensional Vanadium Carbide MXene for Gas Sensors with Ultrahigh Sensitivity Toward Nonpolar Gases. ACS Sensors, 4(Issue 6). doi:10.1021/acssensors.9b00303
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  The sensitive detection of explosive and flammable gases is an extremely important safety consideration in today's industry. Identification of trace amounts of nonpolar analytes at ambient temperatures, however, is still a challenge because of their weak adsorption, and very few studies have been able to achieve it via a chemiresistive mechanism. Herein, we demonstrate the high performance of 2D vanadium carbide MXene (V2CTx) gas sensors with ultrahigh sensitivity toward nonpolar gases. The fabricated 2D V2CTx sensor devices consisting of single-/few-layer 2D V2CTx on polyimide film were able to detect both polar and nonpolar chemical species including hydrogen and methane with a very low limit of detection of 2 and 25 ppm, respectively, at room temperature (23 °C). The performance of the fabricated V2CTx gas sensors in detection of nonpolar gases surpasses that of previously reported state-of-the-art gas sensors based on other 2D materials.
• Mojtabavi, M., VahidMohammadi, A., Liang, W., Beidaghi, M., & Wanunu, M. (2019). Single-molecule sensing using nanopores in two-dimensional transition metal carbide (MXene) membranes. ACS nano, 13(3), 3042-3053.
• Mojtabavi, M., Vahidmohammadi, A., Liang, W., Beidaghi, M., & Wanunu, M. (2019). Single-Molecule Sensing Using Nanopores in Two-Dimensional Transition Metal Carbide (MXene) Membranes. ACS Nano, 13(Issue 3). doi:10.1021/acsnano.8b08017
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  Label-free nanopore technology for sequencing biopolymers such as DNA and RNA could potentially replace existing methods if improvements in cost, speed, and accuracy are achieved. Solid-state nanopores have been developed over the past two decades as physically and chemically versatile sensors that mimic biological channels, through which transport and sequencing of biomolecules have already been demonstrated. Of particular interest is the use of two-dimensional (2D) materials as nanopore substrates, since these can in theory provide the highest resolution readout (
• Orangi, J., Hamade, F., Davis, V. A., & Beidaghi, M. (2019). 3D printing of additive-free 2D Ti3C2T x (MXene) ink for fabrication of micro-supercapacitors with ultra-high energy densities. ACS nano, 14(1), 640-650.
• Orangi, J., Hamade, F., Davis, V. A., & Beidaghi, M. (2019).

  3D Printing of Additive-Free 2D Ti₃C₂T_x (MXene) Ink for Fabrication of Micro-Supercapacitors with Ultra-High Energy Densities

  . ACS nano. doi:10.1021/acsnano.9b07325
• Thakur, R., VahidMohammadi, A., Moncada, J., Adams, W. R., Chi, M., Tatarchuk, B., Beidaghi, M., & Carrero, C. A. (2019). Insights into the thermal and chemical stability of multilayered V 2 CT x MXene. Nanoscale, 11(22), 10716-10726.
• Thakur, R., Vahidmohammadi, A., Moncada, J., Adams, W. R., Chi, M., Tatarchuk, B., Beidaghi, M., & Carrero, C. A. (2019). Insights into the thermal and chemical stability of multilayered V2CT: X MXene. Nanoscale, 11(Issue 22). doi:10.1039/c9nr03020d
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  We report on the thermal stability of multilayered V2CTx MXenes under different atmospheres by combining in situ Raman spectroscopy with ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to elucidate and monitor the molecular, electronic, and structural changes of both the surface and bulk of the V2CTx MXene which has recently received much attention. The MXene samples were heated up to 600 °C in inert (N2), oxidative (CO2, air), and reductive (H2) environments under similar conditions. In situ Raman showed that the VO vibration for two-dimensional vanadia is preserved up to 600 °C under N2, while its intensity reduces under H2. When heated above 300 °C under either CO2 or air, V2CTx slightly oxidizes or transforms into V2O5, respectively. Furthermore, SEM revealed the presence of an accordion-like layered structure for the MXene under N2 and H2, while under CO2 and air the layered structure collapses and forms VO2 (V4+) and V2O5 (V5+) crystals, respectively. XPS reveals that, regardless of the gas, surface V species oxidize above 300 °C during the dehydration process. Finally, we demonstrated that the partial dehydration of V2CTx results in the partial oxidation of the material, and the total dehydration is achieved once 700 °C is reached. We believe that our methodology is a unique alternative to tune the dehydration, oxidation, and properties of V2CTx, which allows for the expansion of applications of MXenes.
• Tian, W., VahidMohammadi, A., Reid, M. S., Wang, Z., Ouyang, L., Erlandsson, J., Pettersson, T., Lars, W., Beidaghi, M., & Hamedi, M. M. (2019). Multifunctional nanocomposites with high strength and capacitance using 2D MXene and 1D nanocellulose. Advanced Materials, 31(41), 1902977.
• Tian, W., VahidMohammadi, A., Reid, M. S., Wang, Z., Ouyang, L., Erlandsson, J., Pettersson, T., Wågberg, L., Beidaghi, M., & Hamedi, M. M. (2019). Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose. Advanced Materials, 31(Issue 41). doi:10.1002/adma.201902977
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  The family of two-dimensional (2D) metal carbides and nitrides, known as MXenes, are among the most promising electrode materials for supercapacitors thanks to their high metal-like electrical conductivity and surface-functional-group-enabled pseudocapacitance. A major drawback of these materials is, however, the low mechanical strength, which prevents their applications in lightweight, flexible electronics. A strategy of assembling freestanding and mechanically robust MXene (Ti3C2Tx) nanocomposites with one-dimensional (1D) cellulose nanofibrils (CNFs) from their stable colloidal dispersions is reported. The high aspect ratio of CNF (width of ≈3.5 nm and length reaching tens of micrometers) and their special interactions with MXene enable nanocomposites with high mechanical strength without sacrificing electrochemical performance. CNF loading up to 20%, for example, shows a remarkably high mechanical strength of 341 MPa (an order of magnitude higher than pristine MXene films of 29 MPa) while still maintaining a high capacitance of 298 F g−1 and a high conductivity of 295 S cm−1. It is also demonstrated that MXene/CNF hybrid dispersions can be used as inks to print flexible micro-supercapacitors with precise dimensions. This work paves the way for fabrication of robust multifunctional MXene nanocomposites for printed and lightweight structural devices.
• Tian, W., VahidMohammadi, A., Wang, Z., Ouyang, L., Beidaghi, M., & Hamedi, M. M. (2019). Layer-by-layer self-assembly of pillared two-dimensional multilayers. Nature Communications, 10(Issue 1). doi:10.1038/s41467-019-10631-0
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  We report Layer-by-Layer (LbL) self-assembly of pillared two-dimensional (2D) multilayers, from water, onto a wide range of substrates. This LbL method uses a small molecule, tris(2-aminoethyl) amine (TAEA), and a colloidal dispersion of Ti3C2Tx MXene to LbL self-assemble (MXene/TAEA)n multilayers, where n denotes the number of bilayers. Assembly with TAEA results in highly ordered (MXene/TAEA)n multilayers where the TAEA expands the interlayer spacing of MXene flakes by only ~ 1 Å and reinforces the interconnection between them. The TAEA-pillared MXene multilayers show the highest electronic conductivity of 7.3 × 104 S m−1 compared with all reported MXene multilayers fabricated by LbL technique. The (MXene/TAEA)n multilayers could be used as electrodes for flexible all-solid-state supercapacitors delivering a high volumetric capacitance of 583 F cm−3 and high energy and power densities of 3.0 Wh L−1 and 4400 W L−1, respectively. This strategy enables large-scale fabrication of highly conductive pillared MXene multilayers, and potentially fabrication of other 2D heterostructures.
• Tian, W., VahidMohammadi, A., Wang, Z., Ouyang, L., Beidaghi, M., & Hamedi, M. M. (2019). Layer-by-layer self-assembly of pillared two-dimensional multilayers. Nature communications, 10(1), 1-10.
• VahidMohammadi, A., Mojtabavi, M., Caffrey, N. M., Wanunu, M., & Beidaghi, M. (2019). Assembling 2D MXenes into highly stable pseudocapacitive electrodes with high power and energy densities. Advanced Materials, 31(8), 1806931.
• Kayali, E., VahidMohammadi, A., Orangi, J., & Beidaghi, M. (2018).

  Controlling the Dimensions of 2D MXenes for Ultrahigh-Rate Pseudocapacitive Energy Storage

  . ACS applied materials & interfaces. doi:10.1021/acsami.8b07397
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  The capacitive properties of two-dimensional (2D) transition metal carbides/nitrides (MXenes) have been the focus of much research in recent years. MXenes store charge by the pseudocapacitance mechanism (fast surface redox reactions) but can deliver their stored charge at much higher rates compared to other pseudocapacitive materials. Herein, the dependence of the electrochemical properties of MXenes on their lateral dimensions is reported. We show that synthesizing MXenes with controlled dimensions enables the design and fabrication of electrodes with high electronic and ionic conductivities. At low scan rates, electrodes fabricated using a mixture of small and large flakes could deliver very high specific gravimetric and volumetric capacitances of about 435 F g–1 and 1513 F cm–3, respectively. At a very high scan rate of 10 V s–1, the performance of the electrodes remained capacitive, demonstrating their ultrahigh-rate energy storage capability. This work outlines an effective method for the design and fabrication of MXene electrodes with high energy and power densities.
• Kayali, E., VahidMohammadi, A., Orangi, J., & Beidaghi, M. (2018). Controlling the dimensions of 2D MXenes for ultrahigh-rate pseudocapacitive energy storage. ACS applied materials & interfaces, 10(31), 25949-25954.
• VahidMohammadi, A., Mojtabavi, M., Caffrey, N. M., Wanunu, M., & Beidaghi, M. (2018).

  Assembling 2D MXenes into Highly Stable Pseudocapacitive Electrodes with High Power and Energy Densities

  . Advanced Materials. doi:10.1002/adma.201806931
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  Abstract Electrochemical capacitors (ECs) that store charge based on the pseudocapacitive mechanism combine high energy densities with high power densities and rate capabilities. 2D transition metal carbides (MXenes) have been recently introduced as high‐rate pseudocapacitive materials with ultrahigh areal and volumetric capacitances. So far, 20 different MXene compositions have been synthesized and many more are theoretically predicted. However, since most MXenes are chemically unstable in their 2D forms, to date only one MXene composition, Ti 3 C 2 T x , has shown stable pseudocapacitive charge storage. Here, a cation‐driven assembly process is demonstrated to fabricate highly stable and flexible multilayered films of V 2 CT x and Ti 2 CT x MXenes from their chemically unstable delaminated single‐layer flakes. The electrochemical performance of electrodes fabricated using assembled V 2 CT x flakes surpasses Ti 3 C 2 T x in various aqueous electrolytes. These electrodes show specific capacitances as high as 1315 F cm −3 and retain ≈77% of their initial capacitance after one million charge/discharge cycles, an unprecedented performance for pseudocapacitive materials. This work opens a new venue for future development of high‐performance supercapacitor electrodes using a variety of 2D materials as building blocks.
• VahidMohammadi, A., Moncada, J., Chen, H., Kayali, E., Orangi, J., Carrero, C. A., & Beidaghi, M. (2018). Thick and freestanding MXene/PANI pseudocapacitive electrodes with ultrahigh specific capacitance. Journal of Materials Chemistry A, 6(44), 22123-22133.
• Vahidmohammadi, A., Vahidmohammadi, A., Moncada, J., Moncada, J., Chen, H., Chen, H., Kayali, E., Kayali, E., Orangi, J., Orangi, J., Carrero, C. A., Carrero, C. A., Beidaghi, M., & Beidaghi, M. (2018). Thick and freestanding MXene/PANI pseudocapacitive electrodes with ultrahigh specific capacitance. Journal of Materials Chemistry A, 6(Issue 44). doi:10.1039/c8ta05807e
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  Two-dimensional (2D) titanium carbide MXene (Ti3C2Tx) has shown great promise as a high-performance electrode material for electrochemical capacitors (ECs). However, similar to other 2D materials, processing MXenes into freestanding films results in their restacking, thus decreasing the ion transport inside the electrodes. This problem significantly hinders the specific capacitance and rate capability of freestanding electrodes, particularly for those with thicknesses higher than a few microns. Here, we demonstrate a strategy based on surface modification of MXene sheets to fabricate electrodes with highly accessible structure and improved electrochemical performance even at very high electrode thicknesses. 2D Ti3C2Tx and polyaniline (PANI) hybrid materials were synthesized through oxidant-free in situ polymerization of PANI on the surface of MXene sheets and were assembled into freestanding films with various thicknesses. Thin MXene/PANI hybrid electrodes delivered outstanding gravimetric and volumetric capacitances as high as 503 F g-1 and 1682 F cm-3, respectively. As the electrode thicknesses and mass loadings were increased, the hybrid electrodes still showed high electrochemical performance. For example, an electrode with a thickness of 90 μm and a mass loading of 23.82 mg cm-2 could deliver a specific capacitance of about 336 F g-1 (∼888 F cm-3 volumetric capacitance). The hybrid electrodes also showed a high cycle lifetime with a capacitance retention of 98.3% after 10000 cycles. This paper explains a simple and fast approach for the fabrication of MXenes/conducting polymer hybrid electrodes with superior electrochemical performance.
• Alhabeb, M., Beidaghi, M., Van Aken, K. L., Dyatkin, B., & Gogotsi, Y. (2017). High-density freestanding graphene/carbide-derived carbon film electrodes for electrochemical capacitors. Carbon, 118(Issue). doi:10.1016/j.carbon.2017.03.094
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  Freestanding films of reduced graphene oxide (rGO) have attracted much attention as electrodes for electrochemical capacitors, especially for flexible device applications. Here, for the first time, we report binder-free supercapacitor electrodes made of highly porous carbide-derived carbon (CDC) nanoparticles as spacers between thermally reduced graphene oxide (rGO) sheets. The addition of CDC between the rGO layers increases the wettability and accessibility of active material to the electrolyte ions, which improves electrochemical performance. The resulting electrodes exhibit high capacitance of over 210 F/g, high power densities at 100 mV/s and 10 A/g charge/discharge rates, and long stability of over 10,000 cycles in an aqueous electrolyte. Moreover, hybrid rGO/CDC electrodes, in contrast to solely rGO-based counterparts, maintained high gravimetric capacitance as the electrode thickness increased from 5 μm to ∼50 μm. This hybrid electrode material design is greatly viable in high-power energy storage devices.
• Alhabeb, M., Beidaghi, M., Van, A., Dyatkin, B., & Gogotsi, Y. (2017). High-density freestanding graphene/carbide-derived carbon film electrodes for electrochemical capacitors. Carbon, 118, 642-649.
• Jiang, J., Yang, W., Wang, H., Zhao, Y., Guo, J., Zhao, J., Beidaghi, M., & Gao, L. (2017). Electrochemical Performances of MoO2/C Nanocomposite for Sodium Ion Storage: An Insight into Rate Dependent Charge/Discharge Mechanism. Electrochimica Acta, 240(Issue). doi:10.1016/j.electacta.2017.04.103
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  MoO2/C nanocomposite has been prepared by simultaneously reducing as-prepared MoO3 nanosheets and introducing an amorphous carbon matrix in the combination of facile hydrothermal and post-annealing processes. MoO2 nanoparticles are uniformly embedded in the carbon framework, resulting in porous nanostructured MoO2/C composite material. The MoO2/C electrodes exhibit varied electrochemical working mechanisms for sodium ion storage that is dependent on charge/discharge rates. At low charge/discharge rate conditions, MoO2/C nanocomposite shows dominant battery performances for sodium ion storage involving reversible conversion reaction of MoO2. The MoO2/C anode material can deliver high initial charge capacity of 557.2 mAh/g at 0.1C (1C = 600 mA/g), along with good cycling stability in comparison with bare MoO2 material. At high rate situations, cyclic voltammetric (CV) results indicate distinct pseudocapacitive behaviors of MoO2/C materials when the scanning rate is higher than 0.5 mV/s. Specific capacitances of 123.25, 85.47 and 49.90 F/g can be obtained from CV measurements conducted at 1, 2 and 5 mV/s, respectively. These electrochemical performances illustrate remarkable capabilities of MoO2/C nanocomposite as anode material for sodium ion storage involving varied conversion reactions and pseudocapacitive sodiation/desodiation reactions depending on charge/discharge rates.
• Jiang, J., Yang, W., Wang, H., Zhao, Y., Guo, J., Zhao, J., Beidaghi, M., & Gao, L. (2017). Electrochemical performances of MoO2/C nanocomposite for sodium ion storage: an insight into rate dependent charge/discharge mechanism. Electrochimica Acta, 240, 379-387.
• Lee, E., VahidMohammadi, A., Prorok, B. C., Yoon, Y. S., Beidaghi, M., & Kim, D. (2017). Room temperature gas sensing of two-dimensional titanium carbide (MXene). ACS applied materials & interfaces, 9(42), 37184-37190.
• Lee, E., Vahidmohammadi, A., Prorok, B. C., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2017). Room Temperature Gas Sensing of Two-Dimensional Titanium Carbide (MXene). ACS Applied Materials and Interfaces, 9(Issue 42). doi:10.1021/acsami.7b11055
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  Wearable gas sensors have received lots of attention for diagnostic and monitoring applications, and two-dimensional (2D) materials can provide a promising platform for fabricating gas sensors that can operate at room temperature. In the present study, the room temperature gas-sensing performance of Ti3C2Tx nanosheets was investigated. 2D Ti3C2Tx (MXene) sheets were synthesized by removal of Al atoms from Ti3AlC2 (MAX phases) and were integrated on flexible polyimide platforms with a simple solution casting method. The Ti3C2Tx sensors successfully measured ethanol, methanol, acetone, and ammonia gas at room temperature and showed a p-type sensing behavior. The fabricated sensors showed their highest and lowest response toward ammonia and acetone gas, respectively. The limit of detection of acetone gas was theoretically calculated to be about 9.27 ppm, presenting better performance compared to other 2D material-based sensors. The sensing mechanism was proposed in terms of the interactions between the majority charge carriers of Ti3C2Tx and gas species.
• Vahidmohammadi, A., Hadjikhani, A., Shahbazmohamadi, S., & Beidaghi, M. (2017). Two-Dimensional Vanadium Carbide (MXene) as a High-Capacity Cathode Material for Rechargeable Aluminum Batteries. ACS Nano, 11(Issue 11). doi:10.1021/acsnano.7b05350
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  Rechargeable aluminum batteries (Al batteries) can potentially be safer, cheaper, and deliver higher energy densities than those of commercial Li-ion batteries (LIBs). However, due to the very high charge density of Al3+ cations and their strong interactions with the host lattice, very few cathode materials are known to be able to reversibly intercalate these ions. Herein, a rechargeable Al battery based on a two-dimensional (2D) vanadium carbide (V2CTx) MXene cathode is reported. The reversible intercalation of Al3+ cations between the MXene layers is suggested to be the mechanism for charge storage. It was found that the electrochemical performance could be significantly improved by converting multilayered V2CTx particles to few-layer sheets. With specific capacities of more than 300 mAh g-1 at high discharge rates and relatively high discharge potentials, V2CTx MXene electrodes show one of the best performances among the reported cathode materials for Al batteries. This study can lead to foundations for the development of high-capacity and high energy density rechargeable Al batteries by showcasing the potential of a large family of intercalation-type cathode materials based on MXenes.
• Li, T., Beidaghi, M., Xiao, X., Huang, L., Hu, Z., Sun, W., Chen, X., Gogotsi, Y., & Zhou, J. (2016). Ethanol reduced molybdenum trioxide for Li-ion capacitors. Nano Energy, 26(Issue). doi:10.1016/j.nanoen.2016.05.004
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  Orthorhombic molybdenum trioxide (α-MoO3) is a layered oxide with promising performance as electrode material for Li-ion capacitors. In this study, we show that expansion of the interlayer spacing (by ~0.32 Å) of the structure along the b-axis, introduced by partial reduction of α-MoO3 and formation of MoO3-x (x=0.06-0.43), results in enhanced diffusion of Li ions. Binder-free hybrid electrodes made of MoO3-x nanobelts and carbon nanotubes show excellent electrical conductivity. The combination of increased interlayer spacing and enhanced electron transport leads to high gravimetric and volumetric capacitances of about 420 F/g or F/cm3 and excellent cycle life of binder-free MoO3-x electrodes.
• Li, T., Beidaghi, M., Xiao, X., Huang, L., Hu, Z., Sun, W., Chen, X., Gogotsi, Y., & Zhou, J. (2016). Ethanol reduced molybdenum trioxide for Li-ion capacitors. Nano Energy, 26, 100-107.
• Zhang, C., Beidaghi, M., Naguib, M., Lukatskaya, M. R., Zhao, M. Q., Dyatkin, B., Cook, K. M., Kim, S. J., Eng, B., Xiao, X., Long, D., Qiao, W., Dunn, B., & Gogotsi, Y. (2016). Synthesis and Charge Storage Properties of Hierarchical Niobium Pentoxide/Carbon/Niobium Carbide (MXene) Hybrid Materials. Chemistry of Materials, 28(Issue 11). doi:10.1021/acs.chemmater.6b01244
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  Orthorhombic niobium pentoxide (T-Nb2O5) offers high capacitance and fast charging-discharging rate capabilities when used as an electrode material for Li-ion capacitors. A homogeneous distribution of T-Nb2O5 nanoparticles in a highly conductive matrix represents a promising approach to maximize its energy and power densities. Here we report a one-step CO2 oxidation of two-dimensional (2D) Nb2CTx, a member of the MXenes family of 2D transition metal carbides, which leads to a hierarchical hybrid material with T-Nb2O5 nanoparticles uniformly supported on the surface of Nb2CTx sheets with disordered carbon. The oxidation temperature, duration, and CO2 flow rate determine the T-Nb2O5 crystallite size as well as the structure, composition, and the charge storage properties of the hybrid material. Fifty micrometer thick electrodes of the hybrid material exhibit high capacitance (330 C g-1 and 660 mF cm-2 at a charge-discharge time of 4 min) and good cycling performance in a nonaqueous lithium electrolyte. The charge storage kinetics are dominated by a surface-controlled process. The observed electrochemical performance is attributed to the intrinsic pseudocapacitive response and excellent energy storage capability of T-Nb2O5 coupled with the fast charge transfer pathways provided by the conductive 2D Nb2CTx sheets and the as-formed disordered carbon.
• Zhang, C., Beidaghi, M., Naguib, M., Lukatskaya, M. R., Zhao, M., Dyatkin, B., Cook, K. M., Kim, S. J., Eng, B., & Xiao, X. (2016). Synthesis and charge storage properties of hierarchical niobium pentoxide/carbon/niobium carbide (MXene) hybrid materials. Chemistry of Materials, 28(11), 3937-3943.
• Anasori, B., Xie, Y., Beidaghi, M., Lu, J., Hosler, B. C., Hultman, L., Kent, P. R., Gogotsi, Y., & Barsoum, M. W. (2015). Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes). ACS Nano, 9(Issue 10). doi:10.1021/acsnano.5b03591
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  The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), M′2M″C2 and M′2M″2C3, where M′ and M″ are two different early transition metals. In these solids, M′ layers sandwich M″ carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes' chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties.
• Anasori, B., Xie, Y., Beidaghi, M., Lu, J., Hosler, B. C., Hultman, L., Kent, P. R., Gogotsi, Y., & Barsoum, M. W. (2015). Two-dimensional, ordered, double transition metals carbides (MXenes). ACS nano, 9(10), 9507-9516.
• Byeon, A., Boota, M., Beidaghi, M., Aken, K. V., Lee, J. W., & Gogotsi, Y. (2015). Effect of hydrogenation on performance of TiO2 (B) nanowire for lithium ion capacitors. Electrochemistry Communications, 60, 199-203.
• Byeon, A., Boota, M., Beidaghi, M., Aken, K. V., Lee, J. W., & Gogotsi, Y. (2015). Effect of hydrogenation on performance of TiO2(B) nanowire for lithium ion capacitors. Electrochemistry Communications, 60(Issue). doi:10.1016/j.elecom.2015.09.004
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  TiO2(B) nanowires have shown excellent capacitance and energy density with a very low charge transfer resistance in 80-μm thick lithium ion capacitor electrodes. Nanowires hydrogenated by heat treatment at 500°C showed improved Li ion diffusion and an increase in capacitance from 148 to 194 F/g as well as energy density from 23 to 30 Wh/kg. Hydrogenation of oxides as a way to improve their capacitance is critically discussed.
• Come, J., Black, J. M., Lukatskaya, M. R., Naguib, M., Beidaghi, M., Rondinone, A. J., Kalinin, S. V., Wesolowski, D. J., Gogotsi, Y., & Balke, N. (2015).

  Controlling the actuation properties of MXene paper electrodes upon cation intercalation

  . Nano Energy. doi:10.1016/j.nanoen.2015.07.028
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  Atomic force microscopy was used to monitor the macroscopic deformation in a delaminated Ti3C2 paper electrode in situ, during charge/discharge in a variety of aqueous electrolytes to examine the effect of the cation intercalation on the electrochemical behavior and mechanical response. The results show a strong dependence of the electrode deformation on cation size and charge. The electrode undergoes a large contraction during Li+, Na+ or Mg2+ intercalation, differentiating the Ti3C2 paper from conventional electrodes where redox intercalation of ions (e.g. Li+) into the bulk phase (e.g. graphite, silicon) results in volumetric expansion. This feature may explain the excellent rate performance and cyclability reported for MXenes. We also demonstrated that the variation of the electromechanical contraction can be easily adjusted by electrolyte exchange, and shows interesting characteristics for the design of actuators based on 2D metal carbides.
• Come, J., Black, J. M., Lukatskaya, M. R., Naguib, M., Beidaghi, M., Rondinone, A. J., Kalinin, S. V., Wesolowski, D. J., Gogotsi, Y., & Balke, N. (2015). Controlling the actuation properties of MXene paper electrodes upon cation intercalation. Nano Energy, 17, 27-35.
• Levi, M. D., Lukatskaya, M. R., Sigalov, S., Beidaghi, M., Shpigel, N., Daikhin, L., Aurbach, D., Barsoum, M. W., & Gogotsi, Y. (2015). Solving the capacitive paradox of 2D MXene using electrochemical quartz-crystal admittance and in situ electronic conductance measurements. Advanced Energy Materials, 5(Issue 1). doi:10.1002/aenm.201400815
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  Fast ion adsorption processes in supercapacitors enable quick storage/delivery of significant amounts of energy, while ion intercalation in battery materials leads to even larger amounts of energy stored, but at substantially lower rates due to diffusional limitations. Intercalation of ions into the recently discovered 2D Ti3C2Tx (MXene) occurs with a very high rate and leads to high capacitance, posing a paradox. Herein, by characterizing the mechanical deformations of MXene electrode materials at various states-of-charge with a variety of cations (Li, Na, K, Cs, Mg, Ca, Ba, and three tetraalkylammonium cations) during cycling by electrochemical quartz-crystal admittance (EQCA, quartz-crystal microbalance with dissipation monitoring) combined with in situ electronic conductance and electrochemical impedance, light is shone on this paradox. Based on this work, it appears that the capacitive paradox stems from cationic insertion, accompanied by significant deformation of the MXene particles, that occurs so rapidly so as to resemble 2D ion adsorption at solid-liquid interfaces. The latter is greatly facilitated by the presence of water molecules between the MXene sheets.
• Levi, M. D., Lukatskaya, M. R., Sigalov, S., Beidaghi, M., Shpigel, N., Daikhin, L., Aurbach, D., Barsoum, M. W., & Gogotsi, Y. (2015). Solving the capacitive paradox of 2D MXene using electrochemical quartz???crystal admittance and in situ electronic conductance measurements. Advanced Energy Materials, 5(1), 1400815.
• Van Aken, K. L., Beidaghi, M., & Gogotsi, Y. (2015). Formulation of ionic-liquid electrolyte to expand the voltage window of supercapacitors. Angewandte Chemie - International Edition, 54(Issue 16). doi:10.1002/anie.201412257
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  An effective method to expand the operating potential window (OPW) of electrochemical capacitors based on formulating the ionic-liquid (IL) electrolytes is reported. Using model electrochemical cells based on two identical onion-like carbon (OLC) electrodes and two different IL electrolytes and their mixtures, it was shown that the asymmetric behavior of the electrolyte cation and anion toward the two electrodes limits the OPW of the cell and therefore its energy density. Also, a general solution to this problem is proposed by formulating the IL electrolyte mixtures to balance the capacitance of electrodes in a symmetric supercapacitor.
• Van Aken, K. L., Pérez, C. R., Oh, Y., Beidaghi, M., Joo Jeong, Y., Islam, M. F., & Gogotsi, Y. (2015). High rate capacitive performance of single-walled carbon nanotube aerogels. Nano Energy, 15(Issue). doi:10.1016/j.nanoen.2015.05.028
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  Single-walled carbon nanotube (SWCNT) aerogels produced by critical-point-drying of wet-gel precursors exhibit unique properties, such as high surface-area-to-volume and strength-to-weight ratios. They are free-standing, are binder-free, and can be scaled to thicknesses of more than 1. mm. Here, we examine the electric double layer capacitive behavior of these materials using a common room temperature ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI). Electrochemical performance is assessed through galvanostatic cycling, cyclic voltammetry and impedance spectroscopy. Results indicate stable capacitive performance over 10,000 cycles as well as an impressive performance at high charge and discharge rates, due to accessible pore networks and enhanced electronic and ionic conductivities of SWCNT aerogels. These materials can find applications in mechanically compressible and flexible supercapacitor devices with high power requirements.
• Van, A., Beidaghi, M., & Gogotsi, Y. (2015). Formulation of ionic???liquid electrolyte to expand the voltage window of supercapacitors. Angewandte Chemie, 127(16), 4888-4891.
• Van, A., P??rez, C. R., Oh, Y., Beidaghi, M., Jeong, Y. J., Islam, M. F., & Gogotsi, Y. (2015). High rate capacitive performance of single-walled carbon nanotube aerogels. Nano Energy, 15, 662-669.
• Zhang, C. J., Maloney, R., Lukatskaya, M. R., Beidaghi, M., Dyatkin, B., Perre, E., Long, D., Qiao, W., Dunn, B., & Gogotsi, Y. (2015). Synthesis and electrochemical properties of niobium pentoxide deposited on layered carbide-derived carbon. Journal of Power Sources, 274, 121-129.
• Zhang, C., Maloney, R., Lukatskaya, M. R., Beidaghi, M., Dyatkin, B., Perre, E., Long, D., Qiao, W., Dunn, B., & Gogotsi, Y. (2015). Synthesis and electrochemical properties of niobium pentoxide deposited on layered carbide-derived carbon. Journal of Power Sources, 274(Issue). doi:10.1016/j.jpowsour.2014.10.018
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  Herein we report on the hydrothermal synthesis of niobium pentoxide on carbide-derived carbon (Nb2O5/CDC) with a layered structure. The presence of phenylphosphonic acid guides the deposition during preparation, leading to the formation of amorphous Nb2O5 particles which are 4-10 nm in diameter and homogeneously distributed on the CDC framework. Electrochemical testing of the Nb2O5/CDC electrode indicated that the highest capacitance and Coulombic efficiency occurred using an electrolyte comprised of 1 M lithium perchlorate in ethylene carbonate/dimethyl carbonate. Subsequent heat treatment of Nb2O5/CDC in CO2 environment led to crystallization of the Nb2O5, allowing reversible Li+ intercalation/de-intercalation. For sweep rates corresponding to charging and discharging in under 3 min, a volumetric charge of 180 C cm-3 and Coulombic efficiency of 99.2% were attained.
• Anasori, B., Beidaghi, M., & Gogotsi, Y. (2014). Graphene - Transition metal oxide hybrid materials. Materials Today, 17(Issue 5). doi:10.1016/j.mattod.2014.04.043
• Anasori, B., Beidaghi, M., & Gogotsi, Y. (2014). Graphene???transition metal oxide hybrid materials. Mater. Today, 17(5), 253-254.
• Beidaghi, M., & Gogotsi, Y. (2014).

  Capacitive energy storage in micro-scale devices: recent advances in design and fabrication of micro-supercapacitors

  . Energy and Environmental Science. doi:10.1039/c3ee43526a
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  Miniaturized energy storage is essential for the continuous development and further miniaturization of electronic devices. Electrochemical capacitors (ECs), also called supercapacitors, are energy storage devices with a high power density, fast charge and discharge rates, and long service life. Small-scale supercapacitors, or micro-supercapacitors, can be integrated with microelectronic devices to work as stand-alone power sources or as efficient energy storage units complementing batteries and energy harvesters, leading to wider use of these devices in many industries. In recent years, the research in this field has rapidly advanced and micro-supercapacitors with improved storage capacity and power density have been developed. The important factors affecting the performance of micro-supercapacitors are the intrinsic properties of electrode materials and electrolyte, architectural design of the device and the fabrication methods. This paper reviews the recent advances in fabrication of materials and devices and provides a critical analysis of reported performances of micro-supercapacitors.
• Beidaghi, M., & Gogotsi, Y. (2014). Capacitive energy storage in micro-scale devices: recent advances in design and fabrication of micro-supercapacitors. Energy & Environmental Science, 7(3), 867-884.
• Boota, M., Hatzell, K. B., Beidaghi, M., Dennison, C. R., Kumbur, E. C., & Gogotsi, Y. (2014).

  Activated Carbon Spheres as a Flowable Electrode in Electrochemical Flow Capacitors

  . Journal of The Electrochemical Society. doi:10.1149/2.072406jes
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  Here, we report modified carbon spheres (CS) as a high energy and power density flowable electrode for use in electrochemical flow capacitors – a new energy storage concept proposed by our group. Activated CS with high specific surface area (SSA) of 1157 m2 g−1 were obtained by CO2 activation. The electrochemical performance of the flowable electrodes as tested in both aqueous (KOH) and organic (TEABF4/PC) electrolytes. It was observed that both the morphology and electrochemical performance of the flowable electrodes are strongly dependent on the activation conditions. Among tested samples, flowable electrode composed of CS activated at 1000°C for one hour yielded the highest capacitance, rate handling ability, and lowest equivalent series resistance (ESR) values. When tested in a static configuration, these suspension electrodes showed a specific capacitance of 139 Fg−1, which is comparable to the performance of traditional film electrodes. The performance of the CS-1000 was further investigated under intermittent flow condition using slurry containing 16 wt% of CS. It was observed that CS-1000 showed significantly enhanced performance due to its high surface area, decreased ohmic resistance, and enhanced conductivity, both in static and under intermittent flow conditions as compared to the flowable electrodes previously reported by our group.
• Boota, M., Hatzell, K. B., Beidaghi, M., Dennison, C. R., Kumbur, E. C., & Gogotsi, Y. (2014). Activated carbon spheres as a flowable electrode in electrochemical flow capacitors. Journal of The Electrochemical Society, 161(6), A1078.
• Dennison, C. R., Beidaghi, M., Hatzell, K. B., Campos, J. W., Gogotsi, Y., & Kumbur, E. C. (2014). Effects of flow cell design on charge percolation and storage in the carbon slurry electrodes of electrochemical flow capacitors. Journal of Power Sources, 247(Issue). doi:10.1016/j.jpowsour.2013.08.101
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  The electrochemical flow capacitor (EFC) is an electrical energy storage concept recently introduced for grid-scale energy storage applications. The EFC utilizes flowable carbon-based electrodes as the active material in a flow battery type architecture for capacitive storage and recovery of energy. Charged slurry can be stored in external reservoirs until it is needed, enabling scalable energy storage to satisfy a variety of large-scale applications. Here, the capacitance and conductivity of EFC slurry electrodes were measured as a function of flow rate (from 0 to 10 ml min-1) and flow cell channel depth (electrode 'thickness', ranging from 0.5 to 3 mm). The effect of salt concentration in the electrolyte was also explored. The interfacial resistance associated with the current collector|slurry interface was found to constitute a large portion of the total cell resistance. Bulk slurry conductivity was found to vary significantly with changes in electrolyte concentration, flow rate and channel depth. Very respectable capacitance values of up to ∼30 F ml -1 (150 F g-1) were obtained during intermittent flow operation. However, significant underutilization of the slurry due to increased ohmic losses at larger channel depths was observed, as evidenced by a rapid decay in capacitance with increasing channel depth. © 2013 Elsevier B.V. All rights reserved.
• Dennison, C. R., Beidaghi, M., Hatzell, K. B., Campos, J. W., Gogotsi, Y., & Kumbur, E. C. (2014). Effects of flow cell design on charge percolation and storage in the carbon slurry electrodes of electrochemical flow capacitors. Journal of Power Sources, 247, 489-496.
• Ghassemi, H., Harlow, W., Mashtalir, O., Beidaghi, M., Lukatskaya, M. R., Gogotsi, Y., & Taheri, M. L. (2014). In situ environmental transmission electron microscopy study of oxidation of two-dimensional Ti 3 C 2 and formation of carbon-supported TiO 2. Journal of Materials Chemistry A, 2(35), 14339-14343.
• Ghassemi, H., Harlow, W., Mashtalir, O., Beidaghi, M., Lukatskaya, M. R., Gogotsi, Y., & Taheri, M. L. (2014). In situ environmental transmission electron microscopy study of oxidation of two-dimensional Ti3C2 and formation of carbon-supported TiO2. Journal of Materials Chemistry A, 2(Issue 35). doi:10.1039/c4ta02583k
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  Two-dimensional Ti3C2, also known as "MXene", was oxidized in air under two different oxidizing regimes in order to produce carbon-supported TiO2. In situ TEM analysis coupled with Raman spectroscopy revealed the formation of either anatase nanoparticles or planar rutile nanocrystals, which were controlled by the time, temperature and heating rate. © the Partner Organisations 2014.
• Hatzell, K. B., Fan, L., Beidaghi, M., Boota, M., Pomerantseva, E., Kumbur, E. C., & Gogotsi, Y. (2014).

  Composite Manganese Oxide Percolating Networks As a Suspension Electrode for an Asymmetric Flow Capacitor

  . ACS applied materials & interfaces. doi:10.1021/am501650q
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  In this study, we examine the use of a percolating network of metal oxide (MnO2) as the active material in a suspension electrode as a way to increase the capacitance and energy density of an electrochemical flow capacitor. Amorphous manganese oxide was synthesized via a low-temperature hydrothermal approach and combined with carbon black to form composite flowable electrodes of different compositions. All suspension electrodes were tested in static configurations and consisted of an active solid material (MnO2 or activated carbon) immersed in aqueous neutral electrolyte (1 M Na2SO4). Increasing concentrations of carbon black led to better rate performance but at the cost of capacitance and viscosity. Furthermore, it was shown that an expanded voltage window of 1.6 V could be achieved when combining a composite MnO2-carbon black (cathode) and an activated carbon suspension (anode) in a charge balanced asymmetric device. The expansion of the voltage window led to a significant increase in the energy density to ∼11 Wh kg–1 at a power density of ∼50 W kg–1. These values are ∼3.5 times and ∼2 times better than a symmetric suspension electrode based on activated carbon.
• Hatzell, K. B., Fan, L., Beidaghi, M., Boota, M., Pomerantseva, E., Kumbur, E. C., & Gogotsi, Y. (2014). Composite manganese oxide percolating networks as a suspension electrode for an asymmetric flow capacitor. ACS applied materials & interfaces, 6(11), 8886-8893.
• Shi, C., Beidaghi, M., Naguib, M., Mashtalir, O., Gogotsi, Y., & Billinge, S. J. (2014). Structure of nanocrystalline Ti 3 C 2 MXene using atomic pair distribution function. Physical review letters, 112(12), 125501.
• Xiao, X., Peng, Z., Chen, C., Zhang, C., Beidaghi, M., Yang, Z., Wu, N., Huang, Y., Miao, L., & Gogotsi, Y. (2014). Freestanding MoO3??? x nanobelt/carbon nanotube films for Li-ion intercalation pseudocapacitors. Nano Energy, 9, 355-363.
• Xiao, X., Peng, Z., Chen, C., Zhang, C., Beidaghi, M., Yang, Z., Wu, N., Huang, Y., Miao, L., Gogotsi, Y., & Zhou, J. (2014). Freestanding MoO3-x nanobelt/carbon nanotube films for Li-ion intercalation pseudocapacitors. Nano Energy, 9(Issue). doi:10.1016/j.nanoen.2014.08.001
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  Molybdenum trioxide (MoO3) is known as a promising pseudocapacitive material, but low conductivity limits its applications. Hydrogenation is demonstrated to increase the conductivity of MoO3 and hence improve its electrochemical performance. Hydrogenated MoO3 (MoO3-x) shows enhanced conductivity based on, both first principle calculations and single nanobelt measurements. Freestanding MoO3-x/carbon nanotubes (CNT) composite films have been fabricated and showed much improved electrochemical performance compared to composites of CNT and as-synthesized MoO3 (MoO3/CNT). Electrodes showed a specific capacitance of 337F/g (based on the mass of MoO3-x) and a high volumetric capacitance of 291F/cm3 (based on the whole electrode) with excellent rate capability. Also we confirmed that the improved intercalation kinetics and the increased intercalation pseudocapacitance could be attributed to the higher electronic conductivity of MoO3-x, which results in better and faster intercalations of Li+ ions. This electrochemical behavior implies that MoO3-x can serve as a very good negative electrode with high capacitance at high mass loading levels.
• Zhang, C., Hatzell, K. B., Boota, M., Dyatkin, B., Beidaghi, M., Long, D., Qiao, W., Kumbur, E. C., & Gogotsi, Y. (2014). Highly porous carbon spheres for electrochemical capacitors and capacitive flowable suspension electrodes. Carbon, 77(Issue). doi:10.1016/j.carbon.2014.05.017
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  In flowable and conventional electrochemical capacitors, the energy capacity is largely determined by the electrode material. Spherical active material, with high specific surface area (SSA) represents a promising material candidate for film and flow capacitors. In this study, we synthesized highly porous carbon spheres (CSs) of submicrometer size to investigate their performance in film and suspension electrodes. In particular, we studied the effects of carbonization and activation temperatures on the electrochemical performance of the CSs. The CSs activated at optimum conditions demonstrated narrow pore size distribution (
• Zhang, C., Hatzell, K. B., Boota, M., Dyatkin, B., Beidaghi, M., Long, D., Qiao, W., Kumbur, E. C., & Gogotsi, Y. (2014). Highly porous carbon spheres for electrochemical capacitors and capacitive flowable suspension electrodes. Carbon, 77, 155-164.
• Campos, J. W., Beidaghi, M., Hatzell, K. B., Dennison, C. R., Musci, B., Presser, V., Kumbur, E. C., & Gogotsi, Y. (2013). Investigation of carbon materials for use as a flowable electrode in electrochemical flow capacitors. Electrochimica Acta, 98(Issue). doi:10.1016/j.electacta.2013.03.037
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  A recently introduced, novel electrical energy storage concept, the electrochemical flow capacitor (EFC), holds much promise for grid-scale energy storage applications. The EFC combines the principles behind the operation of flow batteries and supercapacitors, and enables rapid charging/discharging and decoupled energy/power ratings. Electrical charge is stored in a flowable carbon slurry composed of low-cost and abundantly available carbon particles in pH-neutral, aqueous electrolyte. Charge storage and transfer is analogous to solid carbon electrodes in conventional supercapacitors. Here, the effects of carbon particle solid fraction, shape, and size on the electrochemical and rheological properties of slurry electrodes are investigated. A static cell configuration is utilized for studying the electrochemical properties of the flowable electrodes. The electrochemical properties of the slurry electrodes tested in a static cell are found to be similar to that of solid electrodes in conventional supercapacitors for both, large spherical and anisometric activated carbons. Flow properties of the slurry electrodes are obtained for shear rates corresponding to pumping shear rates by rheometry. Results indicate that electrochemical and rheological properties of slurries depend on their concentration, shape and size of the carbon particles used in the slurries. For a range of concentrations, slurries based on spherical carbon particles show lower viscosities compared to anisometric activated carbon based slurries while performing similar electrochemically. © 2013 Elsevier Ltd. All rights reserved.
• Campos, J. W., Beidaghi, M., Hatzell, K. B., Dennison, C. R., Musci, B., Presser, V., Kumbur, E. C., & Gogotsi, Y. (2013). Investigation of carbon materials for use as a flowable electrode in electrochemical flow capacitors. Electrochimica Acta, 98, 123-130.
• Dyatkin, B., Presser, V., Heon, M., Lukatskaya, M. R., Beidaghi, M., & Gogotsi, Y. (2013). Development of a green supercapacitor composed entirely of environmentally friendly materials. ChemSusChem, 6(12), 2269-2280.
• Dyatkin, B., Presser, V., Heon, M., Lukatskaya, M. R., Beidaghi, M., & Gogotsi, Y. (2013). Development of a green supercapacitor composed entirely of environmentally friendly materials. ChemSusChem, 6(Issue 12). doi:10.1002/cssc.201300852
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  Owing to recent power- and energy-density advances, higher efficiencies, and almost unlimited lifetimes, electrical double-layer capacitors (EDLCs, also known as supercapacitors) are now used in a wide range of energy harvesting and storage systems, which include portable power and grid applications. Despite offering key performance advantages, many device components pose significant environmental hazards once disposed. They often contain fluorine, sulfur, and cyanide groups, which are harmful if discarded by using conventional landfill or incineration methods, and they are constructed by using multiple metallic parts, which contribute to a high ash content. We explore designs for a fully operational supercapacitor that incorporates materials completely safe to dispose of and easy to incinerate. The components, which include material alternatives for the current collector, electrolyte, separator, particle binder, and packaging, are all mutually compatible, and most of them exhibit better performance than commonly used materials. We selected a graphite foil as current collector, sodium acetate as electrolyte, an ester as porous membrane based on acetate cellulose, and polymers based on polyvinyl alcohol as environmentally benign solutions for device components. The presented materials all originate from simple and inexpensive source compounds, which decreases the environmental impact of their manufacture and renders them more viable for integration into commercial devices for large-scale stationary and transportation energy storage applications. Green machine: Every single component of the electrical energy storage system presented is environmentally friendly and can be safely disposed of or incinerated after use. Moreover, the performance of the proposed alternatives meets or exceeds that offered by most materials in traditional supercapacitors. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
• Hatzell, K. B., Beidaghi, M., Campos, J. W., Dennison, C. R., Kumbur, E. C., & Gogotsi, Y. (2013). A high performance pseudocapacitive suspension electrode for the electrochemical flow capacitor. Electrochimica Acta, 111, 888-897.
• Hatzell, K. B., Beidaghi, M., Campos, J., Dennison, C. R., Kumbur, E. C., & Gogotsi, Y. (2013).

  A high performance pseudocapacitive suspension electrode for the electrochemical flow capacitor

  . Carbon. doi:10.1016/j.electacta.2013.08.095
• Penmatsa, V., Ruslinda, A. R., Beidaghi, M., Kawarada, H., & Wang, C. (2013). Platelet-derived growth factor oncoprotein detection using three-dimensional carbon microarrays. Biosensors and Bioelectronics, 39(Issue 1). doi:10.1016/j.bios.2012.06.055
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  The potential of aptamers as ligand binding molecule has opened new avenues in the development of biosensors for cancer oncoproteins. In this paper, a label-free detection strategy using signaling aptamer/protein binding complex for platelet-derived growth factor (PDGF-BB) oncoprotein detection is reported. The detection mechanism is based on the release of fluorophore (TOTO intercalating dye) from the target binding aptamer's stem structure when it captures PDGF. Amino-terminated three-dimensional carbon microarrays fabricated by pyrolyzing patterned photoresist were used as a detection platform. The sensor showed near linear relationship between the relative fluorescence difference and protein concentration even in the sub-nanomolar range with an excellent detection limit of 5. pmol. This detection strategy is promising in a wide range of applications in the detection of cancer biomarkers and other proteins. © 2012 Elsevier B.V..
• Penmatsa, V., Ruslinda, A. R., Beidaghi, M., Kawarada, H., & Wang, C. (2013). Platelet-derived growth factor oncoprotein detection using three-dimensional carbon microarrays. Biosensors and bioelectronics, 39(1), 118-123.
• Shi, C., Beidaghi, M., Naguib, M., Mashtalir, O., Gogotsi, Y., & Billinge, S. (2013). Structure of nanocrystalline Ti3 C2 MXene using atomic pair distribution function. Physical Review Letters, 112(12). doi:10.1103/PhysRevLett.112.125501
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  The structures of nanocrystalline pristine, potassium hydroxide and sodium acetate intercalated new two-dimensional materials Ti3C2 MXenes were studied using the x-ray atomic pair distribution function technique. Pristine MXene has a hexagonal structure with a=b=3.0505(5)Å, c=19.86(2)Å (S.G. P63/mmc No. 194). Both hydroxyl and fluoride terminating species are present. The intercalation of K+ or Na+ ions expands the Ti3C2 layers perpendicular to the planes but shrinks the in-plane a and b lattice parameters. © 2014 American Physical Society.
• Beidaghi, M., & Wang, C. (2012). Micro-supercapacitors based on interdigital electrodes of reduced graphene oxide and carbon nanotube composites with ultrahigh power handling performance. Advanced Functional Materials, 22(Issue 21). doi:10.1002/adfm.201201292
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  A novel method for fabricating micro-patterned interdigitated electrodes based on reduced graphene oxide (rGO) and carbon nanotube (CNT) composites for ultra-high power handling micro-supercapacitor application is reported. The binder-free microelectrodes were developed by combining electrostatic spray deposition (ESD) and photolithography lift-off methods. Without typically used thermal or chemical reduction, GO sheets are readily reduced to rGO during the ESD deposition. Electrochemical measurements show that the in-plane interdigital design of the microelectrodes is effective in increasing accessibility of electrolyte ions in-between stacked rGO sheets through an electro-activation process. Addition of CNTs results in reduced restacking of rGO sheets and improved energy and power density. Cyclic voltammetry (CV) measurements show that the specific capacitance of the micro-supercapacitor based on rGO-CNT composites is 6.1 mF cm -2 at 0.01 V s -1. At a very high scan rate of 50 V s -1, a specific capacitance of 2.8 mF cm -2 (stack capacitance of 3.1 F cm -3) is recorded, which is an unprecedented performance for supercapacitors. The addition of CNT, electrolyte-accessible and binder-free microelectrodes, as well as an interdigitated in-plane design result in a high-frequency response of the micro-supercapacitors with resistive-capacitive time constants as low as 4.8 ms. These characteristics suggest that interdigitated rGO-CNT composite electrodes are promising for on-chip energy storage application with high power demands. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
• Beidaghi, M., & Wang, C. (2012). Micro???supercapacitors based on interdigital electrodes of reduced graphene oxide and carbon nanotube composites with ultrahigh power handling performance. Advanced Functional Materials, 22(21), 4501-4510.
• Beidaghi, M., Wang, Z., Gu, L., & Wang, C. (2012). Electrostatic spray deposition of graphene nanoplatelets for high-power thin-film supercapacitor electrodes. Journal of Solid State Electrochemistry, 16(10), 3341-3348.
• Beidaghi, M., Wang, Z., Gu, L., & Wang, C. (2012). Electrostatic spray deposition of graphene nanoplatelets for high-power thin-film supercapacitor electrodes. Journal of Solid State Electrochemistry, 16(Issue 10). doi:10.1007/s10008-012-1777-5
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  Thin-film electrodes of graphene nanoplatelets (GNPs) were fabricated through the electrostatic spray deposition (ESD) technique. The combination of a binder-free deposition technique and an open pore structure of graphene films results in an excellent power handling ability of the electrodes. Cyclic voltammetry measurements of 1-μm-thick electrodes yield near rectangular curves even at a very high scan rate of 20 V s -1. Thin-film electrodes (1 μm thickness) show specific power and energy of about 75.46 kW kg -1 and 2.93 W h kg -1, respectively, at a 5 V s -1 scan rate. For the thin-film electrode, about 53% of the initial specific capacitance of electrodes at low scan rates was retained at a high scan rate of 20 V s -1. Although the thickness of the thin-film electrodes has influence on their rate capability, an electrode with an increased thickness of 6 μm retained about 30% if its initial capacitance at a very high scan rate of 20 V s -1. The results show that the ESD-fabricated GNP electrodes are promising candidates for thin-film energy storage for applications that require moderate energy density and very high power and rate handling ability. © Springer-Verlag 2012.
• Penmatsa, V., Kim, T., Beidaghi, M., Kawarada, H., Gu, L., Wang, Z., & Wang, C. (2012). Three-dimensional graphene nanosheet encrusted carbon micropillar arrays for electrochemical sensing. Nanoscale, 4(12), 3673-3678.
• Penmatsa, V., Kim, T., Beidaghi, M., Kawarada, H., Gu, L., Wang, Z., & Wang, C. (2012). Three-dimensional graphene nanosheet encrusted carbon micropillar arrays for electrochemical sensing. Nanoscale, 4(Issue 12). doi:10.1039/c2nr30161j
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  Integrating graphene onto three-dimensional (3D) microelectrodes is a plausible technique to significantly improve the sensitivity of electrochemical devices. However, the construction of graphene coated 3D microstructures has been a considerable challenge. In this paper, we present a simple methodology using electrostatic spray deposition (ESD) to conformally coat graphene onto 3D carbon micropillars that are fabricated by pyrolyzing finely patterned photoresist. During the ESD, changes in the critical parameters such as substrate temperature, deposition time, and nozzle to substrate distance have shown a significant effect on the morphology of the deposited graphene film. The amperometric response of graphene/carbon micropillar electrode arrays exhibited higher electrochemical activity, improved charge transfer and a linear response towards H2O2 detection between 250 μM and 5.5 mM. The ESD technique, with the flexibility of integrating a wide variety of functional nanomaterials onto complex 3D microstructures, is attractive in the field of electrochemistry and biotechnology. © 2013 The Royal Society of Chemistry.
• Beidaghi, M., & Wang, C. (2011). Micro-supercapacitors based on three dimensional interdigital polypyrrole/C-MEMS electrodes. Electrochimica Acta, 56(25), 9508-9514.
• Beidaghi, M., & Wang, C. (2011). Micro-supercapacitors based on three dimensional interdigital polypyrrole/C-MEMS electrodes. Electrochimica Acta, 56(Issue 25). doi:10.1016/j.electacta.2011.08.054
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  Symmetric micro-supercapacitors with three dimensional (3D) interdigital electrode structures have been designed and fabricated through Carbon-microelectrochemical system (C-MEMS) technology. The micro-supercapacitor consists of a 3D C-MEMS structure which serves as a high effective surface area current collector and conformal polypyrrole (PPy) films deposited on the carbon structures as electroactive materials. The electrochemical performance of single electrodes and symmetric micro-supercapacitor cells were evaluated by cyclic voltammetry (CV) at different scan rates and galvanostatic charge/discharge tests. The effect of the 3D electrode structure on the performance of the micro-supercapacitor was studied. Single PPy/C-MEMS electrodes presented a specific capacitance of 162.07 ± 12.40 mF cm -2 and a specific power of 1.62 ± 0.12 mW cm-2 at 20 mV s-1 scan rate. The symmetric micro-supercapacitor cells exhibited an average specific capacitance of 78.35 ± 5.67 mF cm -2 and a specific power of 0.63 ± 0.04 mW cm-2 at 20 mV s-1 scan rate, demonstrating that 3D micro-supercapacitors are promising for applications that require high power in a limited footprint area of the device. © 2011 Elsevier Ltd. All rights reserved.
• Beidaghi, M., Chen, W., & Wang, C. (2011). Electrochemically activated carbon micro-electrode arrays for electrochemical micro-capacitors. Journal of Power Sources, 196(Issue 4). doi:10.1016/j.jpowsour.2010.09.050
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  Interdigitated carbon micro-electrode arrays for micro-capacitors are fabricated through the carbon microelectromechanical systems (C-MEMS) technique which is based on the carbonization of patterned photoresist. To improve the capacitive behavior, electrochemical activation is performed on carbon micro-electrode arrays. Cyclic voltammetry (CV) and galvanostatic charge-discharge results demonstrate that the electrochemical activation effectively increases the capacitance of the micro-electrode arrays by three orders of magnitude. Although the charge-discharge experiments show the non-ideal behavior of micro-capacitors, the specific geometric capacitance reaches as high as 75 mF cm-2 at a scan rate of 5 mV s-1 after electrochemical activation for 30 min. The capacitance loss is less than 13% after 1000 CV cycles. These results indicate that electrochemically activated C-MEMS micro-electrode arrays are promising candidates for on-chip electrochemical micro-capacitor application. © 2010 Elsevier B.V.
• Beidaghi, M., Chen, W., & Wang, C. (2011). Electrochemically activated carbon micro-electrode arrays for electrochemical micro-capacitors. Journal of power sources, 196(4), 2403-2409.
• Chen, W., Beidaghi, M., Penmatsa, V., Bechtold, K., Kumari, L., Li, W. Z., & Wang, C. (2010). Integration of carbon nanotubes to C-MEMS for on-chip supercapacitors. IEEE Transactions on Nanotechnology, 9(Issue 6). doi:10.1109/tnano.2010.2049500
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  Carbon nanotubes (CNTs)/carbon microelectromechanical systems (C-MEMS) composites were fabricated as electrode materials for on-chip supercapacitors. By using photolithography and pyrolysis process, 3-D C-MEMS architectures were prepared. The iron catalyst particles were conformally coated on the C-MEMS by electrostatic spray deposition (ESD) and CNTs were synthesized on the surfaces of C-MEMS by catalytic CVD method. The CNT/C-MEMS composites exhibited higher specific capacitance than C-MEMS. Furthermore, the composites with more homogeneous CNTs showed better capacitance. After treatment of oxygen plasma, the specific capacitance of the composite increased due to the contribution of oxygen functional groups. © 2010 IEEE.
• Chen, W., Beidaghi, M., Penmatsa, V., Bechtold, K., Kumari, L., Li, W. Z., & Wang, C. (2010). Integration of carbon nanotubes to C-MEMS for on-chip supercapacitors. IEEE transactions on nanotechnology, 9(6), 734-740.

Proceedings Publications

• Horikawa, S., Du, S., Liu, Y., Lu, X., Chen, I., Wikle, H., Chen, P., Beidaghi, M., Suh, S., Feng, Y., Cheng, Z., & Chin, B. (2017). Effects of surface-scanning detector position on the response of a wireless magnetoelastic biosensor. In 232nd ECS Meeting, 80.
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  This paper investigates the measurement accuracy of a wireless magnetoelastic (ME) biosensor for direct pathogen detection on solid surfaces. The experiments were conducted on the surface of a polyethylene (PE) plate as a model study. An ME biosensor (1mm × 0.2 mm × 30 µm) was placed on the PE surface, and a surface-scanning detector was positioned in the proximity of the sensor for wireless resonant frequency measurement. The detector position was accurately controlled by using a motorized three-axis translation system. The results showed that the resonant frequency variations of the sensor were 125 to +150 Hz for X and Y detector displacements of ± 600 µm and Z displacements of +100 to +500 µm. These resonant frequency variations were small compared to the sensor's initial resonant frequency (< 0.007% of 2.2 MHz initial resonant frequency) measured at the detector home position, indicating high accuracy of the measurement.
• Chen, C., Agrawal, R., Kim, T. K., Li, X., Chen, W., Yan, Y., Beidaghi, M., Penmatsa, V., & Wang, C. (2014). Nanostructured electrodes via electrostatic spray deposition for energy storage system. In Symposium on Battery and Energy Technology Joint General Session - 225th ECS Meeting, 61.
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  Energy storage systems such as Li-ion batteries and supercapacitors are extremely important in today's society, and have been widely used as the energy and power sources for portable electronics, electrical vehicles and hybrid electrical vehicles. A lot of research has focused on improving their performance; however, many crucial challenges need to be addressed to obtain high performance electrode materials for further applications. Recently, the electrostatic spray deposition (ESD) technique has attracted great interest to satisfy the goals. Due to its many advantages, the ESD technique shows promising prospects compared to other conventional deposition techniques. In this paper, our recent research outcomes related to the ESD derived anodes for Li-ion batteries and other applications is summarized and discussed.
• Beidaghi, M., & Wang, C. (2012). Recent advances in design and fabrication of on-chip micro-supercapacitors. In Energy Harvesting and Storage: Materials, Devices, and Applications III, 8377.
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  Recent development in miniaturized electronic devices has increased the demand for power sources that are sufficiently compact and can potentially be integrated on a chip with other electronic components. Miniaturized electrochemical capacitors (EC) or micro-supercapacitors have great potential to complement or replace batteries and electrolytic capacitors in a variety of applications. Recently, we have developed several types of micro-supercapacitors with different structural designs and active materials. Carbon- Microelectromechanical Systems (C-MEMS) with three dimensional (3D) interdigital structures are employed both as electrode material for electric double layer capacitor (EDLC) or as three dimensional (3D) current collectors of pseudo-capacitive materials. More recently, we have also developed microsupercapacitor based on hybrid graphene and carbon nanotube interdigital structures. In this paper, the recent advances in design and fabrication of on-chip micro-supercapacitors are reviewed. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Penmatsa, V., Ruslinda, A. R., Beidaghi, M., Kawarada, H., & Wang, C. (2012). Functionalized three-dimensional carbon microarrays for cancer biomarker detection. In Symposium on Nano/Bio Sensors - 221st ECS Meeting, 45.
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  A label-free detection strategy for the detection of platelet-derived growth factor (PDGF-BB) oncoprotein detection using signaling aptamer/protein binding complex is reported. The 3D carbon microarrays detection platform was fabricated by pyrolyzing patterned photoresist and surface functionalized using directamination technique. The detection strategy is based on the release of TOTO intercalating dye from the target binding aptamer's stem structure when it captures PDGF. The sensor showed near linear relationship between the relative fluorescence difference and protein concentration with a very good detection limit of 5 pmol. This detection strategy is promising for the potential detection of different cancer biomarkers and proteins.
• Beidaghi, M., Chen, W., & Wang, C. (2011). Design, fabrication, and evaluation of on-chip micro-supercapacitors. In Energy Harvesting and Storage: Materials, Devices, and Applications II, 8035.
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  Development of miniaturized electronic systems has stimulated the demand for miniaturized power sources that can be integrated into such systems. Among the different micro power sources micro electrochemical energy storage and conversion devices are particularly attractive because of their high efficiency and relatively high energy density. Electrochemical micro-capacitors or micro-supercapacitors offer higher power density compared to micro-batteries and micro-fuel cells. In this paper, development of on-chip micro-supercapacitors based on interdigitated C-MEMS electrode microarrays is introduced. C-MEMS electrodes are employed both as electrode material for electric double layer capacitor (EDLC) or as three dimensional (3D) current collectors of EDLC or pseudo-capacitive materials. Recent advancements in fabrication methods of C-MEMS based micro-supercapacitors are discussed and electrochemical properties of C-MEMS electrodes and it composites are reviewed. © 2011 SPIE.
• Beidaghi, M., & Wang, C. (2010). On-chip micro-power: Three-dimensional structures for micro-batteries and micro-supercapacitors. In Micro- and Nanotechnology Sensors, Systems, and Applications II, 7679.
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  With the miniaturization of portable electronic devices, there is a demand for micro-power source which can be integrated on the semiconductor chips. Various micro-batteries have been developed in recent years to generate or store the energy that is needed by microsystems. Micro-supercapacitors are also developed recently to couple with microbatteries and energy harvesting microsystems and provide the peak power. Increasing the capacity per footprint area of micro-batteries and micro-supercapacitors is a great challenge. One promising route is the manufacturing of three dimensional (3D) structures for these micro-devices. In this paper, the recent advances in fabrication of 3D structure for micro-batteries and micro-supercapacitors are briefly reviewed. © 2010 Copyright SPIE - The International Society for Optical Engineering.