Electroactive bimetallic CoNi and CNT modified carbon felt cathode promotes microbial CO₂ electroreduction

Efficiently reducing carbon dioxide (CO₂) to high-value organic chemicals in microbial electrosynthesis (MES) systems hinges on the electrochemical performance of electrode materials. This study increased the efficiency of CO₂ reduction to acetic and formic acids by creating a carbon felt (CF) cathode co-modified with nickel‑cobalt bimetallic oxide (NiCo₂O₄) and carbon nanotubes (CNT) coupled with an enriched mixed microbial community derived from anaerobic sludge. Compared to NiCo₂O₄/CF and CF cathodes, the CNT-NiCo₂O₄/CF cathode increased acetate yield by 1.3- and 2.3-fold, and formate yield by 1.1- and 2.4-fold, respectively. Within 8 days, the system achieved 742.98 mg/L acetate and 566.37 mg/L formate. Performance gains stem from: (1) the synergistic effect of CNT and NiCo₂O₄, which increased electrode surface area and electron transfer efficiency; (2) enhanced hydrophilicity, which improved microbe-electrode interactions; and (3) the presence of Co/Ni ions, which boosted CF conductivity and the selective enrichment of electroactive microbes (e.g., Sporomusa and Cupidesulfovibrio). This study provides an innovative strategy for developing high-performance MES electrode materials. Through the synergistic design of bimetallic oxides and nanocarbon materials, the conversion of CO₂ to acetic acid and formic acid was achieved, offering a feasible technical pathway toward carbon neutrality.