Biochar-supported Fe3C nanoparticles with enhanced interfacial contact as high-performance binder-free anode material for microbial fuel cells

•The Fe3C nanoparticles were embedded into biochar as the binder-free anode.•The carbon layers inhibited the dissolution and over-aggregation of nanoparticles.•The nanostructure of Fe3C nanoparticles had enhanced interfacial contacts.•The nano-Fe3C anode with a fast start-up time enriched the Geobacter genus.•The nano-Fe3C anode achieved a superior power density of 2316 mW m−2.