Enhancing oxygen reduction and evolution reactions on multi-metal N-doped graphene catalysts through catalytic activity and selectivity tuning

Metal-nitrogen-carbon (M-N-C) catalysts exhibit promising electrocatalytic properties for oxygen reduction and evolution reactions (ORR/OER) and are potential substitutes for precious metal catalysts. However, the underlying reaction mechanisms are still debated. To investigate the connection between atomic microstructures and catalytic performance, this study employs density functional theory (DFT) calculations to analyze 10 different M-N-C catalysts with varying metal atom types and ratios (Fe, Co, and Ni) on three active centers. The activities of all active sites are computed, showing notable variations in ORR/OER performance among different sites. For homonuclear M-N-C catalysts, the ORR overpotentials of Fe, Co, and Ni are 0.69, 0.26, and 1.03 V, respectively. These values change to 0.79, 0.31, and 1.00 V, respectively, for the heteronuclear M-N-C catalysts with trimetallic active centers when the reaction occurs at the Fe, Co, and Ni site. Similar trends are observed for the OER of both homonuclear and heteronuclear M-N-C catalysts in molecular models. Among Fe, Co, and Ni atoms, the Co site exhibits the most favorable ORR/OER bifunctional activity. This study provides valuable insights into selecting catalytic active sites and understanding the structure-performance relationship of M-N-C structures at a microscopic level.