NH₄Cl-tailored ZIF-67-derived Co/N carbon for enhanced neutral oxygen reduction in microbial fuel cells

Developing non-precious cathode catalysts for neutral oxygen reduction is critical to improving microbial fuel cell performance. Here, NH₄Cl-assisted secondary pyrolysis was used to reconstruct ZIF-67-derived Co/N-doped carbon and regulate Co/N surface environments. The optimized CoNC-1 combined an open porous framework, abundant defects, improved wettability, and favorable pyridinic N/Co-N_x-containing surface configurations. Density functional theory indicated adsorbate-induced Co 3d redistribution and a theoretical overpotential of 0.244 V for the four-electron oxygen reduction pathway at the Co-N-C model site. In PBS condition, CoNC-1 delivered a half-wave potential of 0.592 V vs. RHE, a limiting current density of 6.37 mA·cm^-2, an H₂O₂ yield of 5.18%, and an electron-transfer number of approximately 3.90. As an air-cathode catalyst, CoNC-1 achieved a maximum power density of 681.5 ± 5.99 mW m^-2, 87.2% COD removal, and 15.3% coulombic efficiency. These results demonstrate that coupling framework reconstruction with surface Co/N regulation improves neutral ORR and wastewater-to-electricity conversion.