Highly Efficient Acidic Electrosynthesis of Hydrogen Peroxide at Industrial-Level Current Densities Promoted by Alkali Metal Cations.

Acidic H 2 O 2 synthesis through electrocatalytic 2e - oxygen reduction presents a sustainable alternative to the energy-intensive anthraquinone oxidation technology. Nevertheless, acidic H 2 O 2 electrosynthesis suffers from low H 2 O 2 Faradaic efficiencies primarily due to the competing reactions of 4e - oxygen reduction to H 2 O and hydrogen evolution in environments with high H + concentrations. Here, we demonstrate the significant effect of alkali metal cations, acting as competing ions with H + , in promoting acidic H 2 O 2 electrosynthesis at industrial-level currents, resulting in an effective current densities of 50-421 mA cm -2 with 84-100 % Faradaic efficiency and a production rate of 856-7842 μmol cm -2  h -1 that far exceeds the performance observed in pure acidic electrolytes or low-current electrolysis. Finite-element simulations indicate that high interfacial pH near the electrode surface formed at high currents is crucial for activating the promotional effect of K + . In situ attenuated total reflection Fourier transform infrared spectroscopy and ab initio molecular dynamics simulations reveal the central role of alkali metal cations in stabilizing the key *OOH intermediate to suppress 4e - oxygen reduction through interacting with coordinated H 2 O.