Mechanistic study of paired H2O2 electrosynthesis by coupling oxygen reduction with two-electron water oxidation in a membrane-free electrolyzer

The two-electron water oxidation reaction (2e − -WOR) offers a sustainable route for hydrogen peroxide production, yet its practical application remains constrained by the low Faradaic efficiency of catalysts. In this work, we demonstrate a dual-path H 2 O 2 production mechanism using a novel membrane-free electrolyzer, integrating oxygen reduction at a commercial carbon cloth (cathode) and WOR at zinc-vacancy-rich Zn x TiO 3 (anode). Furthermore, through in situ spectroscopic characterization, we reveal how the zinc vacancy concentration in the Zn x TiO 3 anode modulates the adsorption strength of *OOH intermediates, where Zn 0.66 TiO 3 exhibits optimal binding energy for *OOH intermediates while avoiding over-stabilization that would trigger the competing four-electron pathway, leading to a H 2 O 2 Faradaic efficiency of 69% at 3.2 V vs. RHE and delivers a H 2 O 2 partial current density up to 223 mA cm −2 at 3.3 V vs. RHE. Ultimately, by combining defect engineering with optimized electrolyzer design, the integrated system demonstrates synergistic enhancement through continuous cathodic ORR and WOR, reaching an exceptional overall efficiency of 152% at 240 mA cm −2 , demonstrating remarkable efficacy for the degradation of tetracycline contaminants, with a degradation rate reaching 80%. This study establishes defect engineering as a powerful strategy for designing selective H 2 O 2 electrocatalysts.