Electrochemical oxygen reduction to hydrogen peroxide at practical rates in strong acidic media.

Electrochemical oxygen reduction to hydrogen peroxide (HO) in acidic media, especially in proton exchange membrane (PEM) electrode assembly reactors, suffers from low selectivity and the lack of low-cost catalysts. Here we present a cation-regulated interfacial engineering approach to promote the HO selectivity (over 80%) under industrial-relevant generation rates (over 400 mA cm) in strong acidic media using just carbon black catalyst and a small number of alkali metal cations, representing a 25-fold improvement compared to that without cation additives. Our density functional theory simulation suggests a "shielding effect" of alkali metal cations which squeeze away the catalyst/electrolyte interfacial protons and thus prevent further reduction of generated HO to water. A double-PEM solid electrolyte reactor was further developed to realize a continuous, selective (∼90%) and stable (over 500 hours) generation of HO via implementing this cation effect for practical applications.