Molybdenum Induced Modifications in the Quantum Capacitance of Graphene-Based Supercapacitor Electrodes: First-Principle Calculations

Herein, spin-polarized calculation is performed based on density-functional theory in the frame of generalized gradient approximation to examine the quantum capacitance (C_Q) and surface charge storage of graphene(G)-based supercapacitor electrodes modified with molybdenum, sulfur, nitrogen, and monovacancy. In total, 15 electrode models, including graphitic doping, monovacancy doping, and Mo adsorption on pristine and single-vacancy graphene structures are analyzed. In the results, it is demonstrated that vacancy defects and N/S/Mo doping enhances the C_Q of graphene. Among all configurations, pyrrolic-S (d1S) shows the lowest C_Q performance due to few states at the Fermi level. Electrodes with Mo adsorption exhibit the highest C_Q, particularly when Mo is adsorbed at the top site of graphene. However, formation and adsorption energy calculations suggest that Mo is more likely to adsorb at hollow sites. Optimally, Mo can be most effectively utilized by loading it onto vacancy or N/S-decorated vacancy sites. The significant contribution of Mo's 4dz² and 4s states to C_Q, along with the charge-redistribution around the Mo complexes, may facilitate proton-coupled electron transfer to enhance pseudocapacitance. In these findings, valuable insights into designing high quantum capacitance of 2D materials with electroactive sites for improved energy storage are offered.