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 (H-2 and O-2) at low driving voltages. When grown in contact with these catalysts, Ralstonia eutropha consumed the produced H-2 to synthesize biomass and fuels or chemical products from low CO2 concentration in the presence of O-2. This scalable system has a CO2 reduction energy efficiency of similar to 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 similar to 10%, exceeding that of natural photosynthetic systems.