Theoretical Investigation of Quantum Capacitance of M2C MXenes as Supercapacitor Electrode

MXenes are promising electrode materials due to their excellent performance. However, the quantum capacitance ( C diff ) and surface storage charge ( Q ) of bare M 2 C are little reported theoretically up to now. Herein, C diff and Q of 12 M 2 C MXenes related with 3d, 4d, and 5d transition metal (TM) atoms are investigated in aqueous and ionic/organic systems. All M 2 C MXenes are metallic. M 2 C with 5d TM are cathode materials. M 2 C with 4d TM are also cathode materials except Y 2 C MXene. For M 2 C with 3d TM, Sc 2 C and Mn 2 C are cathode materials, while Ti 2 C, V 2 C, and Cr 2 C are anode materials, especially for Ti 2 C and V 2 C with larger | Q p |/| Q n | and Q p . The broadened voltage maintains the type of electrode materials. W 2 C is the least promising cathode material in broad voltage.