A Living Semiartificial Photoelectrocatalytic Biohybrid for Solar CO ₂ Fixation and Fermentation to Fatty Acids

To address the global climate and energy crisis, innovative strategies are urgently needed to transform CO₂ into sustainable fuels and chemicals. We present a semiartificial biophotoelectrochemical (BPEC) platform, combining solar energy conversion with naturally evolved microbes to develop solutions for transforming CO₂ and water into multicarbon products─without sacrificial additives or precious materials. This remains extremely challenging for fully artificial photocatalytic systems. Our system features a scalable and low-cost CuBi₂O₄ photocathode, stabilized by a thin MgO interlayer, in direct contact with the CO₂-fixing bacterium <i>Sporomusa ovata</i> grown on the electrode surface. This interface enables direct electron uptake, eliminating the need for diffusible redox mediators or externally supplied H₂─limitations commonly seen in bionic leaf systems. The BPEC operated stably for 140 h (5.5 days), a record duration for a Cu-based system, producing 673.2 ± 71.4 μM cm^-2 acetate and 683 ± 55.2 μM cm^-2 of ethanol with a Faradaic efficiency of 69% for C₂ products. Subsequent addition of <i>Clostridium kluyveri</i> enabled biological chain elongation, producing 1.31 ± 0.2 μmol butyrate (C₄) and 0.6 ± 0.1 μmol caproate (C₆), with 0.72 ± 0.2 μmol H₂ as a fermentation byproduct. To our knowledge, this represents the longest-chain solar-driven CO₂-derived product reported to date, highlighting a critical advance in artificial photosynthesis. This approach demonstrates the power of pairing stable photoelectrochemical interfaces with microbial consortia to utilize CO₂ as a feedstock for solar chemical production.