Hollow N-doped bimetal carbon spheres with superior ORR catalytic performance for microbial fuel cells

Herein, we report the fabrication of bimetal ZIF-derived Cu/Co/N co-doped hollow spheres as effective oxygen reduction reaction (ORR) catalysts by the pyrolysis of core-shell polystyrene@Cu/Co-ZIFs (PS@Cu/Co-ZIFs) composite precursors. As a thermally degradable template, PS spheres are a key to determine the catalyst size. The bimetal ZIF hollow spheres were synthesized via a simple carbonization reaction, where ZIFs shells formed on PS spheres after the addition of metal sources, (Co(NO₃)₂ and Cu(NO₃)₂), and organic ligand 2-methylimidazole. Benefiting from the hollow structural and abundant catalytic sites, the as-prepared Cu/Co/N-doped hollow spheres showed superior electrocatalytic performances and excellent durability than commercial Pt/C catalysts. The on-set and half-wave potentials of the Cu/Co/N-HS-3 catalyst were 0.25 and 0.13 V (vs Ag/AgCl), respectively, which were greater than those of 20% Pt/C catalysts (0.24 and 0.12 V). Moreover, the Cu/Co/N-HS-3 catalyst-based air-cathode microbial fuel cells (MFCs) exhibited maximum output voltage and power density of 620 mV and 1016 mW/m², respectively, demonstrating superiority to commercial Pt/C catalyst-based MFCs (586 mV and 908 mW/m²).