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DOE OSTI · 1484259

Understanding the MXene Pseudocapacitance

Zhan, Cheng·Naguib, Michael·Lukatskaya, Maria·Kent, Paul R. C.·Gogotsi, Yury·Jiang, De-en
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Abstract

MXenes have attracted great attention as next-generation capacitive energy-storage materials, but the mechanisms underlying their pseudocapacitive behavior are not well understood. Here we provide a theoretical description of the surface redox process of Ti3C2Tx (T = O, OH), a prototypical MXene, in 1 M H2SO4 electrolyte, based on joint density functional theory with an implicit solvation model and the analysis of Gibbs free energy under a constant-electrode potential. From the dependence of the O/OH ratio (or the surface H coverage) and the surface charge on the applied potential, we obtain a clear picture of the capacitive energy-storage mechanism of Ti3C2Tx that shows good agreement with previous experimental findings in terms of the integral capacitance and Ti valence change. We find a voltage-dependent redox/double-layer co-charging behavior: the capacitive mechanism is dominated by the redox process, but the electric double-layer charge works against the redox process. This new insight may be useful in improving the capacitance of MXenes.

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Zhan, Cheng, Naguib, Michael, Lukatskaya, Maria, Kent, Paul R. C., Gogotsi, Yury, Jiang, De-en. 2018-02-20. Understanding the MXene Pseudocapacitance. https://doi.org/10.1021/acs.jpclett.8b00200

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