Synergistic modulation of PPy and CeO₂ in hollow carbon nanocage bimetal catalysts for enhanced extracellular electron transfer.

The low efficiency of extracellular electron transfer (EET) at the anode of microbial fuel cells (MFCs) is a key bottleneck limiting their performance improvement. In this study, a polypyrrole (PPy)-assisted metal-organic framework (MOF) pyrolysis strategy was employed to successfully construct bimetallic (FeMn) sites embedded in hollow nitrogen-doped carbon nanocages, which were further decorated with CeO₂ nanoclusters to obtain a highly efficient bio-electrocatalyst, FeMn-IDMs/H-NC@CeO₂. The PPy coating induces cavitation of the precursor, maximizing the exposure of active sites and providing biocompatible anchoring sites for microorganisms. CeO₂ coordinates and adsorbs electron mediators such as riboflavin through Lewis acid sites, establishing a new Fe-O-Ce-O-Mn electron transport channel and optimizing the interfacial electron coupling efficiency. Experimental results show that the MFC with the FeMn-IDMs/H-NC@CeO₂ anode achieves a maximum power density of 5.11 ± 0.21 W m⁻², which is 1.74 and 1.22 times higher than those of FeMn-DMs-NC and FeMn-IDMs/H-NC, respectively, demonstrating excellent electrocatalytic activity and stability. 16 S rRNA sequencing confirms the selective enrichment of Geobacter (69.4%), promoting electron transfer at the biofilm-electrode interface. This study provides new insights into the synergistic regulation of EET by rare-earth oxide and bimetallic nitrogen-carbon materials.