Highly efficient charge transfer in Co/Co₂P Schottky junctions embedded in nitrogen-doped porous carbon for enhancing...

Exploration of noble-metal free catalysts with high oxygen reduction reaction (ORR) activity and durability as alternatives for platinum/carbon (Pt/C) in microbial fuel cells (MFCs) remains a great challenge. This study reports the preparation of nitrogen-doped cobalt/cobalt phosphide/carbon (Co/Co₂P/NC) catalysts via an in situ simultaneous doping/reduction method by using residual cornstalks as carbon source. Effects of carbonization temperature on structural characteristics and catalytic activity of Co/Co₂P/NC catalysts are investigated. Co/Co₂P/NC-850 with regular network structure obtains the maximum power density of 972 ± 5mWm^-2, which is higher than that of Pt/C (808 ± 5mWm^-2). The highest Coulombic efficiency (23.1%) and the lowest charge transfer resistance (0.93Ω) are also obtained by Co/Co₂P/NC (850°C). ORR catalyzed by Co/Co₂P/NC-850 is mainly via 4e^- reduction pathway. The better durability of Co/Co₂P/NC (850°C) is detected from long-term operation of MFCs. The promising catalytic activity for ORR is attributed to the introduction of Co/Co₂P nanoparticles/Schottky junctions and N species in porous carbon skeleton, which are served as active sites to trap and consume electrons. Biomass-derived carbon with good electrical conductivity can provide large specific surface area and abundant interconnected holes, which contribute to efficient permeation and transport of O₂. The synergistic effects between porous structure and sufficient active sites can energetically boost catalytic activity to improve ORR efficiency. These Co/Co₂P/NC catalysts with durable power outputs are expected to have more extensive applications in MFCs.