Differentiating interfacial water structures via alkali metal cation promotor for H2O2 electrosynthesis in acid

Abstract Electrocatalytic oxygen reduction reaction (ORR) for H 2 O 2 production represents a sustainable alternative route to the energy-intensive anthraquinone process. Nevertheless, under industrially-relevant acidic conditions, excessive protons at the reaction interface exacerbate low H 2 O 2 selectivity and severe H 2 O 2 reduction. Herein, we propose a universal alkali metal cation (AMC: Li + , Na + , K + , or Cs + ) dosing strategy to markedly boost the acidic H 2 O 2 electrosynthesis. Upon Cs + addition, 2e − ORR selectivity increases from 20% to 80%, concurrently suppressing an H 2 O 2 reduction current by 50% and achieving an H 2 O 2 production rate of 9.2 mol g −1 h −1 at 500 mA cm −2 . Microelectrode hydrogen evolution measurements witness impeded proton diffusion in AMC-dosed acidic electrolytes, directly restricting proton supply to catalytic active sites. In situ spectroscopic analysis combined with molecular dynamics simulation demonstrate AMCs help reconfigure interfacial water networks via cation hydration shells, thereby disrupting proton-hopping pathways. The efficacy trend (Li + <Na + <K + <Cs + ) originates from distinct cation-specific interfacial water restructure, delivering mechanistic insights into cation-promoted selective H 2 O 2 electrosynthesis in acidic media.