A Semi-Artificial Photoelectrocatalytic Biohybrid for Efficient and Selective Carbon Dioxide Conversion to Medium Chain Fatty Acids

Converting atmospheric carbon dioxide emissions and water into value-added liquid multi-carbon products (e.g medium-chain fatty acids (MCFA’s)) and O₂ remains a difficult undertaking. Here, we present a semi-biological photoelectrochemical (PEC) system consisting of a scalable and cheap CuBi₂O₄ photocathode (stabilized by MgO), with <i>Sporomusa ovata</i> grown on the electrode surface, a known CO₂-fixing acetogenic and electrotrophic bacteria^1-3. The PEC biohybrid effectively produces acetate and ethanol (as well as H₂ and O₂) after 140 hours of stable operation (&gt;5.5 days), without the need for any sacrificial organic additives. The PEC system splits water into its core elements forming O₂ on the anode and providing H₂ and electrons via the photocathode to living <i>S. ovata</i> cells to utilize as reducing equivalents for synthesis of acetate and ethanol from waste carbon dioxide. Chain elongation was then performed on the photosynthesised acetate and ethanol via fermentation using Clostridium kluyveri which produced butyrate (C4) and caproate (C6). Spectroelectrochemistry (cyclic voltammetry and UV-Vis spectroscopy), transient absorption spectroscopy, and attenuated total reflection infrared spectroscopy were also used to probe the biointerface and gain a deeper mechanistic understanding of these biohybrid systems. This semi-artificial photosynthetic approach demonstrates the advantages of synergistically pairing biotechnology with materials science as a promising method to use waste carbon dioxide as a feedstock for solar chemical production.<br/><br/><b>References:</b><br/>Wang et al., 2022 Nat. Catal. 5 633-641<br/>Yang et al., Nano Lett. 2021, 21, 5453–5456<br/>Su et al., Joule 4, 800–811