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Solar formate production from CO2 and H2O was achieved with no external electrical bias by combining an InP/RuCP semiconductor/metal-complex hybrid photocathode with a reduced SrTiO3 (r-STO) photoanode. The conversion efficiency from solar to chemical energy was improved from 0.03 to 0.14% compared to a previous system utilizing a TiO2 photoanode. Stimulated electron transfer from the photoanode to the photocathode is the main cause for the observed improvement, due to an enlarged difference in the band-energy position between r-STO and InP. Since r-STO showed high H2O oxidation selectivity even in the presence of formate, a r-STO/InP/RuCP wireless device successfully performed solar CO2 reduction in a one-compartment reactor with no proton exchange membrane, yielding a solar conversion efficiency of 0.08%.
Arai et al. (Tue,) studied this question.