Phototrophic carbon dioxide reduction in highly saline microbial fuel cell

Microbial fuel cells integrating photosynthetic microorganisms hold promise for sustainable bioelectricity generation but their operation in real matrices remains underexplored. Here, we report the development of a polydopamine-coated polyhydroxybutyrate‑carbon nanofibers electrode colonized by the purple non‑sulfur bacterium Rhodobacter capsulatus enabling simultaneous light-driven current production, CO₂ sequestration, and long-term stability in real highly saline environments. Specifically, the artificial bioelectrode demonstrated high operational durability over one month of continuous fed-batch operation, maintaining stable current generation across repeated 6-day analytical cycles. Under stressful conditions (50:50 growth medium:seawater), the biophotoelectrode achieved a current density of 32±1 μA cm^-2 alongside a Coulombic efficiency of 7.2±1.2%. Headspace gas chromatography analysis revealed CO₂ depletion over time, with formate identified among the major products in the investigated conditions, particularly under moderate salinity (80:20 growth medium:seawater). In contrast, hydrogen evolution was detected only under high-salinity stress (50:50 growth medium:seawater), suggesting activation of alternative metabolic pathways. These findings demonstrate that R. capsulatus-modified electrodes can harness light energy and drive carbon conversion in complex saline environments. By leveraging stress-responsive metabolic flexibility and electroactive biofilm engineering, this platform paves the way for self-sustaining systems capable of simultaneous renewable electricity generation in highly saline environments, and production of value-added chemicals.