Balancing Activity and Selectivity in Two-Electron Oxygen Reduction through First Coordination Shell Engineering in...

The electrochemical two-electron oxygen reduction reaction (2e^- ORR) offers a potentially cost-effective and eco-friendly route for the production of hydrogen peroxide (H₂O₂). However, the competing 4e^- ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective H₂O₂ production under low voltage conditions remains challenging. Herein, guided by first-principles density functional theory (DFT) calculations, we show that modulation the first coordination sphere in Co single atom catalysts (Co-N-C catalysts with Co-N_xO_4-x sites), specifically the replacement of Co-N bonds with Co-O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards H₂O₂ (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N-doped carbon-supported catalysts with Co-N_xO_4-x active sites, we were able to validate the DFT findings and explore the trade-off between catalytic activity and selectivity for 2e^- ORR. A catalyst with trans-Co-N₂O₂ sites exhibited excellent catalytic activity and H₂O₂ selectivity, affording a H₂O₂ production rate of 12.86  $$ and an half-cell energy-efficiency of 0.07  $$ during a 100-hours H₂O₂ production test in a flow-cell.