Hierarchical meso/macroporous N-doped biocarbon architectures with synergistic dual-pathway electron transfer for high-performance microbial fuel cells

Advancing anode materials with rational pore architecture and optimized electron transfer pathways remains pivotal for developing high-efficiency microbial fuel cells (MFCs) towards sustainable wastewater treatment and energy harvesting. While macroporous biocarbon anodes (>50 μm) effectively maintain biofilm vitality, their inherent lack of bacterial-adhesive nanostructures fundamentally limits extracellular electron transfer (EET) efficiency. Here we demonstrate a breakthrough hierarchical architecture through layer-by-layer Fe(OH)₃templating on silk-derived biocarbon, achieving synergistic meso/macroporous structures (4.3 nm mesopores/∼130 μm macropores) with tailored pyrrolic-N configurations. Advanced characterization reveals three key innovation points: (1) The mesoporous network exhibits exceptional riboflavin adsorption capacity (1.6-fold enhancement vs. conventional biocarbons), establishing continuous redox-mediating pathways for indirect EET; (2) N-induced charge redistribution creates electron-conducting “highways” between outer membrane cytochromes and carbon matrix; (3) The hierarchical porosity enables simultaneous optimization of bacterial colonization (macropores) and interfacial electron exchange (mesopores), resolving the long-standing surface area-transport limitation trade-off. The resultant anode delivers high power density (4.4-fold enhancement vs. CC baseline) and COD removal (91.43 %), with coulombic efficiency of 21.84 % over 60 days. This work provides fundamental insights into pore hierarchy-mediated EET mechanisms while establishing a universal biomass templating strategy for next-generation bioelectrochemical systems.