Breaking the Scaling Relationship in Two-Electron Water Oxidation via Designing Dual Active Centers for Efficient H₂O₂ Electrosynthesis

A two-electron water oxidation reaction (2e-WOR) over nonprecious and environmentally friendly electrocatalysts like SnO2 holds great promise to replace the traditionally energy-intensive anthraquinone process for valuable hydrogen peroxide (H2O2) synthesis, while it is subjected to poor activity and selectivity due to the inherent scaling limitation of intermediate adsorption on active sites. Herein, we report a theory-guided dual active center engineering of SnO2 quantum dots, achieved by introducing oxygen vacancy (OV) and Zn dopant (ZnD), to break the scaling limitation for promoting 2e-WOR. Physicochemical characterizations, including operando infrared spectroscopy, isotope-labeling mass spectrometry, quasi in situ electron paramagnetic resonance, 119Sn Mössbauer spectroscopy, and X-ray absorption spectroscopy, along with theoretical calculations, unveil that OV activates the water molecule to dissociate it to *OH, and ZnD facilitates the subsequent *OH coupling, collectively boosting H2O2 production. Consequently, the resulting Zn/SnO2–x exhibits a high Faradaic efficiency of 87.5% at 200 mA cm–2, a fast production rate of 52.7 μmol cm–2 min–1, and robust stability of 60 h for H2O2 generation, superior to most reported 2e-WOR electrocatalysts. In addition, the on-site generated H2O2 can be used as a typical oxidant for ciprofloxacin pollutant degradation and selective propylene oxidation to propylene glycol feedstock.