Alkali-metal cations steer the product selectivity of O reduction on M-N sites.

The oxygen reduction reaction (ORR) to either HO or HO generation is important to meet diverse application demands. The product selectivity of the ORR is strongly correlated with the nature of the catalyst. We report herein that alkali-metal cations (AM) can steer the product selectivity of the ORR catalysed on a molecular model catalyst with Co-N sites. The electron-transfer number of the ORR increases with Li ≈ Na < K < Rb < Cs. A series of electrochemical measurements reveal the 2e+2e ORR pathway in large AM electrolytes at neutral pH. electrochemical scanning tunneling microscopy resolves the formation of high-contrast species in the cobalt octaethylporphine (CoOEP) monolayer on Au(111) in large AM electrolytes when the ORR occurs. The high-contrast species is assigned to the HO , as the 2e ORR product, adsorbed on CoOEP. Combined electrochemical scanning tunneling microscopy, electrochemical measurements and theoretical calculations reveal that large AM can stabilize HO on CoOEP and promote its further reduction, which accounts for the AM-dependent selectivity of the ORR. Revealing the unrecognized effect of AM on ORR selectivity opens up new avenues for modulating the distribution of ORR products by adjusting the electrolyte composition.