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

Hydrogen peroxide (H 2 O 2 ) 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 H 2 O 2 . However, the efficient reduction of O 2 to produce H 2 O 2 at high current densities (> 100 mA cm −2 ), thereby achieving viable H 2 O 2 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 H 2 O 2 in alkaline media at high current densities. The VG array electrode delivered a Faradaic efficiency of 94% and a H 2 O 2 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 H 2 O 2 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 H 2 O 2 selectivity) and fast electron transfer during ORR. Further, gas-liquid-solid three-phase interfaces formed between the graphene nanosheets facilitate a steady supply of O 2 from the gas phase when the electrode was applied in a flow cell. Results encourage the application array electrodes in electrochemical H 2 O 2 synthesis, whilst also offering a roadmap to future industrial H 2 O 2 production. • The vertical graphene array (VG array) delivered a high faradaic efficiency and H 2 O 2 production rate at large current densities (100 and 200 mA cm −2 ). • TheVG array ensured high availability of graphene edge active sites and fast electron transfer during ORR. • The VG array possessed abundant gas-liquid-solid interfaces, which promoted efficient O 2 supply from the gas phase to the catalytic sites.