Semi-artificial leaf interfacing organic semiconductors and enzymes for solar fuel synthesis

Photoelectrochemical biohybrids combine the advantages of light harvesting semiconductors and biocatalysts into a single compact device. However, limited device stability, the use of toxic elements and non-innocent external components (buffers, mediators or sacrificial reagents) makes a sustainable artificial photosynthetic reaction, where fuel production is coupled to water oxidation, difficult to achieve. Here, we introduce organic photoelectrodes connected to an inverse opal TiO2 matrix that hosts efficient hydrogenase or formate dehydrogenase, driving direct solar fuel synthesis. By co-immobilising carbonic anhydrase, supported by simulations and spectroscopic investigations, the PCE10:EH-IDTBR photobiocathodes generate unprecedented photocurrent densities of up to −8 mA cm−2 in a pH neutral bicarbonate solution, attaining stable H2 production or selective CO2-to-formate conversion over 10 h. Semi-artificial photosynthesis is achieved by assembling the photobiocathode with a BiVO4 photoanode in an artificial leaf device for unassisted CO2 reduction coupled to O2 evolution, attaining a faradaic yield of 87% over 24 h of operation.