Interfacial capture-electroreduction cascade enables cathodic Cu²⁺ removal in energy-storing microbial fuel cells

Heavy metal contamination is persistent due to non-biodegradability and toxicity. Here, a hierarchical MXene/NiCo₂O₄/PANI-modified carbon felt anode was developed to enhance extracellular electron transfer (EET) and thereby improve cathodic Cu²⁺ removal in microbial fuel cells (MFCs). The engineered anode reduced interfacial charge-transfer resistance, promoted electroactive biofilm formation, and reshaped the microbial community toward exoelectrogenic taxa (e.g., Geobacteraceae), leading to a markedly improved power output (P_max = 2.47 ± 0.08 W m^-2). In the cathode chamber, rapid Cu²⁺ remediation was achieved (99.2 ± 0.1% within 15 h at 30 mg L^-1), following a dual-pathway process involving initial interfacial capture and subsequent electroreduction to insoluble Cu⁰/Cu₂O. Moreover, stable Cu²⁺ removal under intermittent operation was enabled by the pseudocapacitive charge-buffering behavior of the NiCo₂O₄/PANI framework. This work clarifies how anodic interfacial engineering governs cathodic metal reduction and provides a scalable strategy for coupling metal remediation with energy recovery.