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 (Cdiff) and surface storage charge (Q) of bare M2C are little reported theoretically up to now. Herein, Cdiff and Q of 12 M2C MXenes related with 3d, 4d, and 5d transition metal (TM) atoms are investigated in aqueous and ionic/organic systems. All M2C MXenes are metallic. M2C with 5d TM are cathode materials. M2C with 4d TM are also cathode materials except Y2C MXene. For M2C with 3d TM, Sc2C and Mn2C are cathode materials, while Ti2C, V2C, and Cr2C are anode materials, especially for Ti2C and V2C with larger |Q(p)|/|Q(n)| and Q(p). The broadened voltage maintains the type of electrode materials. W2C is the least promising cathode material in broad voltage.