Boosting wastewater bioelectricity recovery via solvent mediation and zinc fencing: Dual regulation for catalyst spatial structure and active sites

[Display omitted] •Solvent mediation and zinc fencing dually regulated cathode catalyst efficacy.•Methanol dosage mediated the particle size of bimetallic ZIFs over a wide range.•Zinc fence dispersed hybrid cobalt active sites onto the porous carbon skeleton.•Coexistence of micro/mesopores ensured active site exposure and mass transfer.•Optimized cobalt active sites embedded porous carbon BES exhibited 2057 mW m−2. Bioelectrochemical systems (BESs) are promising in self-sustaining energy recovery of wastewater. Cathode catalysts are crucial to enhancing the oxygen reduction reaction (ORR) process in BESs. In this study, a dual regulation strategy including solvent mediation and zinc fencing was proposed for regulation of catalyst spatial structure and active sites. The particle size of catalysts derived from bimetallic zeolitic imidazolate frameworks (ZIFs) was tuned over a wide range via solvent mediation while the dispersion of cobalt active sites was achieved via zinc fencing. As-optimized cobalt active sites embedded nitrogen-doped porous carbon with a Co/Zn molar ratio of 1/20 (Co1/20@NPC) directed a four-electron transfer pathway in ORR process. The BES employing Co1/20@NPC as cathode catalyst produced a maximum power density of 2057 ± 21 mW m−2, 40% higher than the BES using Pt/C as cathode catalyst. Co1/20@NPC BES displayed fast organic elimination and efficient energy recovery with a coulombic efficiency of 73 ± 1% and a normalized energy recovery of 0.361 ± 0.006 kWh m−3. The outstanding ORR activity, high bioelectricity generation and operation stability made Co1/20@NPC a prospective cathode catalyst. This dual regulation strategy provides implications for controllable synthesis of ZIF-derived catalysts with tailored structures and characteristics, and demonstrates potential in improving wastewater energy recovery performance in BESs.