A Semi-artificial Photoelectrochemical Tandem Leaf with a CO -to-Formate Efficiency Approaching 1 .

Semi-artificial photoelectrochemistry can combine state-of-the-art photovoltaic light-absorbers with enzymes evolved for selective fuel-forming reactions such as CO reduction, but the overall performance of such hybrid systems has been limited to date. Here, the electrolyte constituents were first tuned to establish an optimal local environment for a W-formate dehydrogenase to perform electrocatalysis. The CO reductase was then interfaced with a triple cation lead mixed-halide perovskite through a hierarchically structured porous TiO scaffold to produce an integrated photocathode achieving a photocurrent density of -5 mA cm at 0.4 V vs. the reversible hydrogen electrode during simulated solar light irradiation. Finally, the combination with a water-oxidizing BiVO photoanode produced a bias-free integrated biophotoelectrochemical tandem device (semi-artificial leaf) with a solar CO -to-formate energy conversion efficiency of 0.8 %.