CO₂-Reductive, Copper Oxide-Based Photobiocathode for Z-Scheme Semi-Artificial Leaf Structure

Green plants convert sunlight into high-energy chemicals by coupling solar-driven water oxidation in the Z-scheme and CO2 fixation in the Calvin cycle. In this study, formate dehydrogenase from Clostridium ljungdahlii (ClFDH) is interfaced with a TiO2-coated CuFeO2 and CuO mixed (ClFDH-TiO2|CFO) electrode. In this biohybrid photocathode, the TiO2 layer enhances the photoelectrochemical (PEC) stability of the labile CFO photocathode and facilitates the transfer of photoexcited electrons from the CFO to ClFDH. Furthermore, inspired by the natural photosynthetic scheme, the photobiocathode is combined with a water-oxidizing, FeOOH-coated BiVO4 (FeOOH|BiVO4) photoanode to assemble a wireless Z-scheme biocatalytic PEC device as a semi-artificial leaf. The leaf-like structure effects a bias-free biocatalytic CO2-to-formate conversion under visible light. Its rate of formate production is 2.45 times faster than that without ClFDH. This work is the first example of a wireless solar-driven semi-biological PEC system for CO2 reduction that uses water as an electron feedstock.