Coupling effect of nitrogen-doped carbon black and carbon nanotube in assembly gas diffusion electrode for H2O2 electro-generation and recalcitrant pollutant degradation

Abstract The generation of H2O2 on cathode is a pivotal and rate-limiting step in the electrocatalytic oxygen reduction reaction process. In this work, carbon nanotube (CNT) and nitrogen-doped carbon black (NCB) was assembled on carbon fiber cloth to achieve high oxygen reduction reaction (ORR) efficiency in gas diffusion electrode (GDE). An excellent and stable H2O2 generation capacity of 42.15 mg L-1 h-1 cm-2 was achieved, and 39.6% TOC removal and complete decolorization over a wide pH range were realized for recalcitrant Reactive Red X-3B in modeling wastewater. The involved reactive oxygen species were found to be H2O2, 1O2 and •OH. Besides density functional theory calculations, the coupling effect of various components in the GDE on electrocatalytic activity was investigated based on characterization and electrochemical examinations. It was revealed that pyridinic N and pyrrolic N in NCB and electron transfer of CNT increased the electrocatalytic activity and selectivity for two-electron ORR. In addition, the gradient hydrophobic three-phase-boundary increased oxygen retention and ORR activity for H2O2 generation. The reusability test of CNT/NCB-GDE showed its great applicability for H2O2 electro-generation and wastewater treatment.