Bioinspired artificial photosynthesis has resulted in efficient solutions for many areas of science and technology spanning from solar cells to medicine. Owing to rapid development of synthesis and nanofabrication methods we are able to engineer advanced materials at atomic and molecular levels and assemble them into functional devices. Copper compounds are very promising as photocatalysts with good multielectron transfer properties due to their loosely bonded d electrons. Cu₂O is an inexpensive material with near-ideal electronic properties for solar energy conversion into fuels. Importantly, Cu₂O shows intrinsic p-type conductivity due to the presence of negative-charged Cu vacancies with one of the lowest electron affinities, identifying Cu₂O as an optimal candidate for reduction of CO₂. However, crystalline Cu₂O is photocathodically unstable and therefore unsuitable for multielectron reductive photocatalysis, unless strong adsorption of the reactants that modifies active sites and kinetically enhances reduction reactions occurs. Herein, we report atomic level study of the active sites in Cu₂O that lead to the discovery of the facet specific adsorption and subsequent light induced reduction of CO₂ exclusively into liquid fuel – methanol. The activity of these sites was unraveled using operando multimodal correlated characterization of a single particle, and in situ activity measurements. We also show the interplay between strain and photocatalytic reaction for CO₂ reduction on Cu₂O single particles that leads to high yield of facet-selective photocatalytic reduction of CO₂ to methanol.

Tijana Rajh

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