Electrocatalytic oxygen reduction to hydrogen peroxide through a biomass-derived nitrogen and oxygen self-doped porous carbon metal-free catalyst

Abstract

The electrocatalytic oxygen reduction reaction (ORR) to hydrogen peroxide (H₂O₂) by a two-electron pathway is regarded as a green and substitute technique to the anthraquinone method. However, an important challenge in H₂O₂ electrogeneration is to design selective and economic electrocatalysts. Herein, nitrogen and oxygen self-doped porous carbon (NO/PC) was prepared using low-cost alfalfa as a raw material without nitrogen sources and strong oxidants. NO/PC prepared at 500 °C (NO/PC-500) showed the highest H₂O₂ selectivity of 85.1%. The H₂O₂ electrogeneration performance and stability of a composite gas diffusion electrode with NO/PC-500 as an electrocatalyst were significantly improved at high current density by introducing a polytetrafluoroethylene (PTFE) hydrophobic layer. A NO/PC-500 (g) to PTFE binder (mL) ratio of 1 : 3 was selected as an optimal value to fabricate the composite gas diffusion electrode. X-ray photoelectron spectroscopy combined with density functional theory calculations demonstrated that the OOH adsorption energy on most N/O functional groups (graphitic N, the co-doping of graphitic N and C–O–C, and the co-doping of pyrrolic N and C–O–C) in NO/PC was lower than the H₂O₂ adsorption energy, which promoted the two-electron ORR and reduced H₂O₂ decomposition. However, the co-doping of pyridine N and C–O–C in NO/PC is not conducive to H₂O₂ electrogeneration due to the lowest OOH adsorption energy and the highest H₂O₂ adsorption energy. Overall, these results have offered insights into the potential application of biomass-derived heteroatom-doped porous carbon as an effective electrocatalyst for H₂O₂ generation.