The role of metal-doping on the enhanced electrocatalytic properties of -MnO2 during oxygen reduction reaction

Metal-doping is a common strategy for improving the performance of alpha-MnO2 during oxygen reduction reaction (ORR) in metal-air batteries (MABs). Understanding the role of dopants in an atomic level is crucial to develop this cathode's performance, which is required to study. This work presents the insight effects of metal-doping (Co, Ni, and Pd) in alpha-MnO2 during ORR, investigated through density functional theory and computational hydrogen electrode calculations. As a result, all dopants enhance the adsorption strength of surface species during ORR due to the induction of electron accumulation at the Mn site, modifying the d-band center of the doping site. Unfortunately, Ni doping had an inhibiting effect on specific ORR elementary steps, leading to lower activity. In the volcano plot of theoretical overpotential, Co and Pd doping play as the promoter, where enhanced ORR activity is found on the Mn-site. The insight information reveals that the enhanced alpha-MnO2 catalysts are achieved by Co and Pd doping at interstitial sites rather than substitution on Mn sites. These findings emphasize the critical role of both well-controlled dopant concentration and the atomic dispersion of a dopant at the interstitial sites on the electrocatalytic activity for MABs.