Synergistic Modulation of PPy and CeO₂ in Hollow Carbon Nanocage Bimetal Catalysts for Enhanced Extracellular Electron Transfer

Microbial fuel cells (MFCs) are constrained by sluggish anodic extracellular electron transfer (EET) and cathodic reaction kinetics under mild, near‑neutral conditions. In this study, utilizing a polypyrrole (PPy)-assisted MOF pyrolysis strategy, we constructed isolated metal active sites (IDAs) embedded within hollow N‑doped carbon nanocages and further precisely modified them with CeO₂ nanoclusters, successfully preparing an efficient FeMn‑IDAs/H‑NC@CeO₂ catalyst. The hollow porous structure and abundant active sites of the catalyst enhance anodic EET. The PPy coating simultaneously triggers precursor cavitation, maximizing the exposure of active sites and providing biocompatible anchoring points for anodic microorganisms. This modification enriches more electroactive bacteria on the anode and strengthens synergistic interactions, further promoting efficient EET. The incorporation of CeO₂ not only supplies additional active sites but also optimizes the adsorption behavior of electron intermediates through enhanced metal‑support interactions, improves electron‑transfer pathways, and significantly boosts electrocatalytic activity and stability, while facilitating electron transfer via cellular electron mediators. High‑throughput sequencing confirmed that FeMn‑IDAs/H‑NC@CeO₂ functions to selectively enrich highly efficient electrogenic microorganisms, promoting electron transfer between the biofilm and the electrode. With dual regulation by PPy and CeO₂, FeMn‑IDAs/H‑NC@CeO₂ exhibits high‑level, efficient bio‑electrocatalytic performance. The MFC equipped with a FeMn‑IDAs/H‑NC@CeO₂ anode achieved a maximum power density of 5.11±0.21 W m⁻², which is 1.74 and 1.22 times higher than those of MFCs with FeMn‑DAs‑NC (2.93±0.16 W m⁻²) and FeMn‑IDAs/H‑NC (4.19±0.31 W m⁻²) anodes, respectively. This study provides new insights into the design of efficient bio‑electrocatalysts and offers a feasible strategy for advancing the practical application of MFCs.