The operation active sites of O2 reduction to H2O2 over ZnO

Abstract

The two-electron oxygen reduction reaction (2e⁻ ORR) in neutral media is a promising method to achieve hydrogen peroxide (H₂O₂) from oxygen (O₂) directly in a sustainable way. Here, we show an ideal ZnO@ZnO₂ electrocatalyst for efficient O₂ reduction to H₂O₂ in a neutral medium. The in situ growth of ZnO₂ on ZnO forms the operation active sites, namely the heterogeneous interface between tetrahedral ZnO and octahedral ZnO₂, weakening the binding energies of both OOH* and O*. In a 0.1 M K₂SO₄ electrolyte, ZnO@ZnO₂ shows a H₂O₂ selectivity of nearly 100.0% via the ORR, while it can convert O₂ to H₂O₂ with a production rate of 5.47 mol g_cat⁻¹ h⁻¹ at 0.1 V vs. RHE and a Faraday efficiency (FE) of ∼95.5%, tested using a gas diffusion electrode device. The pulse voltage-induced current (PVC) was utilized in conjunction with a number of in situ characterization techniques and electrochemical studies to disclose the transformation of the ZnO surface and the production process of operational catalytic active sites on ZnO.