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

Abstract

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-NxO4-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-NxO4-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 (Formula presented.) and an half-cell energy-efficiency of 0.07 (Formula presented.) during a 100-hours H2O2 production test in a flow-cell.