Greatly boosted H2O2 activity in two-electron water oxidation reaction on Zn-based catalysts by doping engineering

Abstract

Electrocatalytic production of hydrogen peroxide (H₂O₂) by two electron water oxidation reaction (2e-WOR) is an environmental process with low cost and devoid of H₂O₂ storage and transportation. ZnO is one of the important promising 2e-WOR catalysts with relatively high activity and selectivity of H₂O₂. However, the active sites and the effects of oxygen defects of ZnO remain unknown, which hampers the further improvement in H₂O₂ formation. To explore the active sites and develop Zn-based catalysts with high performance, Ni, Cu and Co ions are chosen to form M_0.1Zn_0.9O (M = Ni, Cu and Co) catalysts. Combining the experimental results with density functional theory (DFT) calculations, the active site of 2e-WOR on Zn-based catalysts is first discovered to be the 3-coordinated surface Zn without surface oxygen defects since oxygen defects result in a strong interaction of ·OH with catalyst and then impede the 2e-WOR process. Catalysts with high activity and selectivity for 2e-WOR should have small nano-particle sizes without oxygen defects. Co_0.1Zn_0.9O is obtained with high activity (35.3 mmol min⁻¹·g_cat⁻¹) and selectivity (82%) of H₂O₂ at 3.2 V vs RHE. This work provides valuable perspectives for designing and developing high-performing catalysts in 2e-WOR reaction.