Cobalt‑nitrogen‑carbon nanotube co-implanted activated carbon as efficient cathodic oxygen reduction catalyst in microbial fuel cells

Abstract

The low catalytic activity of activated carbon (AC) toward oxygen reduction reaction (ORR) in air cathode severely limits the electricity production of microbial fuel cells (MFCs). In this work, a novel cobalt‑nitrogen‑carbon nanotube co-implanted activated carbon catalysts ([email protected]) were prepared by growth of Co/Zn-based metal organic frameworks on AC followed by thermal pyrolysis. The [email protected] catalyzed ORR via an efficient four-electron pathway in pH-neutral medium, and exhibited superb ORR catalytic activity comparable to commercial Pt/C. As compared with pristine AC, implantation of Co, N and carbon nanotubes into [email protected] improved the ORR current density and exchange current density of air cathodes by 120% and 73% respectively. The maximum power density of MFCs achieved 2045 ± 43 mW m−2 by using the optimized [email protected] pyrolyzed at 850 °C, which was 65% higher than that of pristine AC. The superb ORR performance of [email protected] originated from the synergistic effect of abundant Co-Nx, Pyridinic-N and Graphitic-N active sites, high graphitization degree, well dispersed Co nanoparticles and improved micro-mesoporous coexistence structure, which enabled high ORR catalytic activity and rapid mass transfer at the three-phase boundary. This work provides a new routine for large-scale synthesis of highly-efficient ORR electrocatalysts based on AC and metal organic frameworks, which has promising potential for the application in practical MFCs.