Microbial Electrosynthesis with NiFe-Layered Double Oxide and Carbon Nanotube Modified Cathode for CO ₂ Reduction to Acetate: Electron Transfer and Carbon Metabolism

Microbial electrosynthesis (MES) is an emerging bioelectrochemical technology for converting carbon dioxide (CO 2 ) into valuable organic chemicals. However, its performance is often constrained by ineffective electron transfer between microbes and the electrode. In this study, we developed a hybrid cathode composed of carbon nanotubes (CNTs) and NiFe-layered double oxide (NiFe-LDO) coated on carbon felt (NiFe-LDO/CNTs@CF) to enhance the MES performance. The integration of NiFe-LDO with CNTs increased its specific surface area to 332.85 m 2 ·g –1, 4.4 times larger than that of CF modified solely with NiFe-LDO. The lower charge transfer resistance (3.76 Ω) of the NiFe-LDO/CNTs@CF cathode facilitated efficient interfacial electron transfer. Results demonstrated that MES with the NiFe-LDO/CNTs@CF cathode achieved significantly higher acetate production of 92.8 mg·L –1 ·d –1 (1.5 mmol·L –1 ·d –1 ) compared to control cathodes (CF, CNTs@CF, and NiFe-LDO@CF), along with improved coulombic efficiency (51.0 ± 18.2%). Enhanced secretion of protein-dominant extracellular polymeric substances (EPS) supported biofilm development. Microbial community analysis revealed that Acetobacterium (54.1%) was selectively enriched in the NiFe-LDO/CNTs@CF biofilm, with significant upregulation of key functional units (such as K05299, K15022, K00198, K00925, etc.) associated with the Wood-Ljungdahl pathway for acetate synthesis. These findings provide a theoretical basis for improving the MES performance and preliminary insights for advancing CO 2 bioelectrochemical reduction technologies.