Solar-Driven Paired CO₂ Reduction–Alcohol Oxidation Using Semiartificial Suspension, Photocatalyst Sheet, and Photoelectrochemical Devices

Fuel-forming enzymes can display excellent performance, achieving high rates of catalysis with unity selectivity at minimal overpotentials, but they are generally considered to be fragile and difficult to handle in combination with synthetic semiconductors in light-driven chemical synthesis. Here, we demonstrate a biohybrid platform that is assembled from cyanamide-functionalized carbon nitride (CN_<i>X</i>) as a scalable and inexpensive photosensitizer that selectively photo-oxidizes 4-methyl benzyl alcohol (MBA) to its aldehyde (MBAld), indium tin oxide (ITO) nanoparticles as electron conduit and biocatalyst support material, and the enzyme formate dehydrogenase (FDH) for selective CO₂-to-formate reduction. This integrated semiartificial multicomponent system can be assembled and used in several configurations to drive bias-free operation, including (i) a photocatalytic suspension, (ii) a photocatalyst sheet, and (iii) a photoelectrochemical cell. The unprecedented adaptability and robustness of the assembled biohybrid systems motivated us to select the best performing and scalable system in practical solar chemical production by deploying a 50 cm² CN_<i>X</i>-ITO|FDH photosheet device for 3 days under natural sunlight to produce 41 (mmol formate) m^-2 and 35 (mmol aldehyde) m^-2. We have therefore demonstrated that CN_<i>X</i>-ITO|FDH provides a robust and versatile platform that enables solar chemical synthesis for several days in outdoor operation using natural sunlight.