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

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/CoP/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/CoP/NC catalysts are investigated. Co/CoP/NC-850 with regular network structure obtains the maximum power density of 972 ± 5mWm, which is higher than that of Pt/C (808 ± 5mWm). The highest Coulombic efficiency (23.1%) and the lowest charge transfer resistance (0.93Ω) are also obtained by Co/CoP/NC (850°C). ORR catalyzed by Co/CoP/NC-850 is mainly via 4e reduction pathway. The better durability of Co/CoP/NC (850°C) is detected from long-term operation of MFCs. The promising catalytic activity for ORR is attributed to the introduction of Co/CoP 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 O. The synergistic effects between porous structure and sufficient active sites can energetically boost catalytic activity to improve ORR efficiency. These Co/CoP/NC catalysts with durable power outputs are expected to have more extensive applications in MFCs.