Biomass-Derived Porous Fe3C/Tungsten Carbide/Graphitic Carbon Nanocomposite for Efficient Electrocatalysis of Oxygen Reduction.

The oxygen-reduction reaction (ORR) draws an extensive attention in many applications, and there is a growing interest to develop effective ORR electrocatalysts. Iron carbide (Fe3C) is a promising alternative to noble metals (e.g., platinum), but its performances need further improvement, and the real role of the Fe3C phase remains unclear. In this study, we synthesize Fe3C/tungsten carbide/graphitic carbon (Fe3C/WC/GC) nanocomposites, with waste biomass (i.e., pomelo peel) serving as carbon source, using a facile, one-step carbon thermal-reduction method. The nanocomposite is characterized by a porous structure consisting of uniform Fe3C nanoparticles encased by graphitic carbon (GC) layers with highly dispersed nanosized WC. The Fe3C provides the active sites for ORR, while the graphitic layers and WC nanoparticles can stibilize the Fe3C surface, preventing it from dissociation in the electrolyte. The Fe3C/WC/GC nanocomposite is highly active, selective, and stable toward four-electron ORR in pH-neutral electrolyte, which results in a 67.82% higher power density than that of commercial Pt/C and negligible voltage decay during a long-term phase of a 33 cycle (2200 h) operation of a microbial fuel cell (MFC). The density functional theory (DFT) calculations suggest high activity for splitting the O-O bond of molecular oxygen on the surface of Fe3C.