Hollow Mn3O4 nanospheres on graphene matrix for oxygen reduction reaction and supercapacitance applications: Experimental and theoretical insight

This work demonstrates the synthesis, characterization and electrochemical application of hollow-like Mn3O4 nanostructures well-dispersed on graphene matrix (MnH/G). The as-synthesized MnH/G shows favorable electrochemical properties for energy conversion application towards oxygen reduction reaction (ORR) and energy storage towards supercapacitor. The MnH/G efficiently catalyzes the ORR at lower potential and possesses the methanol tolerance activity that may find promising application as an alternative to Pt/C, which is susceptible to tolerance towards methanol crossover. Also, MnH/G exhibits the supercapacitance properties with 97% of capacitance retention over 2000 cycles. The MnH/G shows the practical usefulness by fabricating the coin-cell type supercapacitor towards powering the light-emitting diode (LED) light. Further, the density functional theory (DFT) simulations investigate the geometry and electronic properties of Mn3O4, and with graphene matrix. The theoretical calculation computes the overpotential for ORR activities of the hybrid structures from the adsorption energy of O, OH, and OOH species. The experimentally obtained overpotential is in good agreement with the theoretically calculated overpotential. The enhanced quantum capacitance for the hybrid structures obtained from DFT simulations supports experimental findings. The present report demonstrates a new and reasonable design of preparing non-precious nanomaterials with complex structures towards the methanol tolerance ORR and supercapacitor applications.