Vertical graphene array for efficient electrocatalytic reduction of oxygen to hydrogen peroxide

Abstract

Hydrogen peroxide (H2O2) is a green chemical oxidant that finds widespread use in the chemical industry. The electrocatalytic oxygen reduction reaction (ORR) is presently attracting a lot of attention as an environmentally friendly synthetic route towards H2O2. However, the efficient reduction of O2 to produce H2O2 at high current densities (> 100 mA cm−2), thereby achieving viable H2O2 yields, remains a challenge. Herein, we demonstrate that vertical graphene arrays grown on carbon paper (denoted herein as VG array) via plasma-enhanced chemical vapor deposition show outstanding activity for ORR to H2O2 in alkaline media at high current densities. The VG array electrode delivered a Faradaic efficiency of 94% and a H2O2 production rate of 61.3 mg h−1 cm−2 at 100 mA cm−2, and similarly impressive performance at 200 mA cm−2 (81% and 102.8 mg cm−2 h−1, respectively), outperforming most catalysts reported to date for electrochemical H2O2 synthesis. The remarkable performance of the VG array electrode is ascribed to the interconnected network of graphene nanosheets which ensures a high availability of graphene edge active sites (thus a high H2O2 selectivity) and fast electron transfer during ORR. Further, gas-liquid-solid three-phase interfaces formed between the graphene nanosheets facilitate a steady supply of O2 from the gas phase when the electrode was applied in a flow cell. Results encourage the application array electrodes in electrochemical H2O2 synthesis, whilst also offering a roadmap to future industrial H2O2 production.