Water splitting-biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis

Artificial photosynthetic systems can store solar energy and chemically reduce CO₂. We developed a hybrid water splitting-biosynthetic system based on a biocompatible Earth-abundant inorganic catalyst system to split water into molecular hydrogen and oxygen (H₂ and O₂) at low driving voltages. When grown in contact with these catalysts, Ralstonia eutropha consumed the produced H₂ to synthesize biomass and fuels or chemical products from low CO₂ concentration in the presence of O₂. This scalable system has a CO₂ reduction energy efficiency of ~50% when producing bacterial biomass and liquid fusel alcohols, scrubbing 180 grams of CO₂ per kilowatt-hour of electricity. Coupling this hybrid device to existing photovoltaic systems would yield a CO₂ reduction energy efficiency of ~10%, exceeding that of natural photosynthetic systems.