The operation active sites of O 2 reduction to H 2 O 2 over ZnO

The two-electron oxygen reduction reaction (2e − ORR) in neutral media is a promising method to achieve hydrogen peroxide (H 2 O 2 ) from oxygen (O 2 ) directly in a sustainable way. Here, we show an ideal ZnO@ZnO 2 electrocatalyst for efficient O 2 reduction to H 2 O 2 in a neutral medium. The in situ growth of ZnO 2 on ZnO forms the operation active sites, namely the heterogeneous interface between tetrahedral ZnO and octahedral ZnO 2 , weakening the binding energies of both OOH* and O*. In a 0.1 M K 2 SO 4 electrolyte, ZnO@ZnO 2 shows a H 2 O 2 selectivity of nearly 100.0% via the ORR, while it can convert O 2 to H 2 O 2 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.