Bio-electro-catalytic reduction of carbon dioxide to acetate on a bio-cathode colonized by Geobacter sulfurreducens
摘要
This study demonstrates the first pure-culture microbial electro-synthesis (MES) system employing Geobacter sulfurreducens as a bio-cathode catalyst for the selective reduction of CO₂ to acetate. Operated in a dual-chamber reactor with a carbon felt cathode poised at −0.7 V vs. SHE, the system achieved a stable cathodic current density of −15.2 A/m2 and a final acetate titer of 4.6 g dm−3 (76.7 mM) over 25 days. The volumetric and areal acetate production rates reached 0.184 g dm−3 d−1 and 230 g m−3 d−1, respectively, with an average Faradaic efficiency of 88.5 ± 4.2%, confirming the highly selective utilization of electrons for biosynthesis. Electrochemical characterization using cyclic voltammetry revealed a pronounced catalytic wave with an onset potential of −0.45 V, supporting a direct electron transfer (DET) mechanism. SEM imaging confirmed the development of a dense, multi-layered biofilm encasing the cathode fibers, while FT-IR and XPS analyses identified abundant protein and polysaccharide components, including redox-active moieties critical for extracellular electron transfer. A reversed oxidative TCA (roTCA) cycle is proposed as the carbon fixation route, leveraging bi-directional citrate synthase and ferredoxin-driven reductive reactions to generate acetyl-CoA and ultimately acetate. This work establishes G. sulfurreducens as a genetically tractable, high-performing biocatalyst for cathodic CO₂ valorization, providing a foundational platform for sustainable bio-electrochemical production of fuels and chemicals.
Graphical abstract