We demonstrate the ability to convert CO2 to acetate with 80% Faradaic efficiency using a mixed Fe–Cu oxide catalyst at −0.4 V bias vs. Ag/AgCl during visible light illumination. Analysis shows that the selective catalyst is a mixed phase material consisting of CuFeO2 and CuO. By varying the Fe:Cu atomic fraction from 1.3 to 0.1, it is possible to tune the selectivity for CO2 reduction from primarily acetate to primarily formate. These results identify a new low cost, earth abundant material capable of synthesizing an energy-dense liquid directly from CO2 and show that selectivity for CO2 reduction can be tuned by controlling catalyst composition in mixed Fe–Cu oxide catalysts. To better understand the photo-physics of this catalyst leading to high selectivity, we are performing ultrafast soft x-ray spectroscopy of this and related catalytic materials. We demonstrate that soft x-ray reflection-absorption spectroscopy provides element, oxidation, and spin state specific dynamics with femtosecond time resolution. These measurements are also surface sensitive, probing only the top several nm of a catalytic material. This work demonstrates the ability to probe ultrafast carrier dynamics with chemical state specificity and surface sensitivity, and the results provide important insights on the mechanism of charge transfer and energy conversion at the surface of photo-excited metal oxide catalysts.

Photo-electrochemical CO2 reduction to acetate on iron–copper oxide: Understanding electron dynamics in catalysts showing high selectivity for CO2 reduction

254th National Meeting (2017)

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