The efficiency of sunlight-driven reduction of carbon dioxide (CO2), a process mimicking the photosynthesis in nature that integrates the light harvester and electrolysis cell to convert CO2 into valuable chemicals, is greatly limited by the sluggish kinetics of oxygen evolution in pH-neutral conditions. Current non-noble metal oxide catalysts developed to drive oxygen evolution in alkaline solution have poor performance in neutral solutions. Here we report a highly active and stable oxygen evolution catalyst in neutral pH, Brownmillerite Sr2GaCoO5, with the specific activity about one order of magnitude higher than that of widely used iridium oxide catalyst. Using Sr2GaCoO5 to catalyze oxygen evolution, the integrated CO2 reduction achieves the average solar-to-CO efficiency of 13.9% with no appreciable performance degradation in 19 h of operation. Our results not only set a record for the efficiency in sunlight-driven CO2 reduction, but open new opportunities towards the realization of practical CO2 reduction systems.
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