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

The electrochemical two-electron oxygen reduction reaction (2e ORR) offers a potentially cost-effective and eco-friendly route for the production of hydrogen peroxide (HO). However, the competing 4e ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective HO 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-NO sites), specifically the replacement of Co-N bonds with Co-O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards HO (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N-doped carbon-supported catalysts with Co-NO 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-NO sites exhibited excellent catalytic activity and HO selectivity, affording a HO production rate of 12.86  and an half-cell energy-efficiency of 0.07  during a 100-hours HO production test in a flow-cell.