Atomic Co decorated free-standing graphene electrode assembly for efficient hydrogen peroxide production in acid

Abstract

Electrochemical oxygen reduction reaction (ORR) in acids via a selective 2e⁻ pathway offers great opportunities for electrosynthesis of H₂O₂, allowing on-site environmental treatment in industry. Unfortunately, despite some progress, the apparent activity of most electrocatalysts (especially in a flow cell reactor) still requires further improvement to meet the industrial demands, where high H₂O₂ productivity with low energy input is desired. Herein, we report a free-standing ORR electrode comprising cobalt single atoms on a vertically aligned graphene nanosheet assembly (CoN₄/VG), which is demonstrated to exhibit a hierarchical porous structure maximizing the utilization of catalytic active atoms without sacrificing the mass/charge transport efficiencies. Within a H-cell setup, the as-prepared ORR electrode gives a H₂O₂ selectivity close to 100% from 0.3 to 0.5 V versus reversible hydrogen electrode (RHE) in 0.1 M HClO₄, sustaining a record-breaking H₂O₂ productivity of 706 mmol_H2O2 g_catalyst⁻¹ h⁻¹ at 0.3 V vs. RHE for 36 hours. Further employing this electrode in a gas-diffusion flow reactor yields a peroxide concentration of 1100 mg L⁻¹ (4000 mmol_H2O2 g_catalyst⁻¹ h⁻¹) continuously at −1.8 V of cell voltage, corresponding to an energy consumption of 3.81 W h g_H2O2⁻¹, which represents the most energy-efficient flow system for rapid H₂O₂ generation in acidic media.