Understanding the MXene Pseudocapacitance

作者：Zhan, Cheng; Naguib, Michael; Lukatskaya, Maria; Kent, Paul R. C.; Gogotsi, Yury; Jiang, De-en^*

来源：Journal of Physical Chemistry Letters, 2018, 9(6): 1223-1228.

DOI：10.1021/acs.jpclett.8b00200

• TI3C2TX MXENE
• AB-INITIO
• CAPACITANCE
• INTERCALATION
• MECHANISMS
• NANOSHEETS
• ANODE

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.

• 出版日期2018-3-15