Photocatalytic reduction of CO2 to produce fuels is a promising way to reduce CO2 emission and address energy crisis. However, the H2 evolution reaction competes with the CO2 photoreduction, which would lower the overall selectivity for carbonaceous products. Cu2O has emerged as a promising material for suppressing the H2 evolution. However, it suffers from poor stability, which is commonly regarded as the result of the electron induced reduction of Cu2O. This work demonstrates a simple strategy using Cu2O as a dark cathode and TiO2 as a photoanode to achieve stable aqueous CO2 reduction with a high Faradaic efficiency of 87.4% and a selectivity of 92.6% for carbonaceous products. We have shown that the photogenerated holes, instead of electrons, primarily account for the instability of Cu2O. Therefore, Cu2O was used as a dark cathode to minimize the adverse effects of holes, by which an improved stability was achieved compared to Cu2O photocathode under illumination. Another consideration for CO2 reduction is product distribution. Compared to gas products, liquid fuels, such as CH3OH, that are suitable for storage and transport is more desired and remains a grand challenge. We introduce metallic Cu nanoparticles (NPs) on Cu2O films to change the product distribution from gas products on bare Cu2O to predominant CH3OH via CO2 reduction in aqueous solutions. The specifically designed Cu/Cu2O interfaces could balance the binding strength of H* and CO* intermediates, which plays a key role in CH3OH production. With TiO2 model photoanode to construct a photoelectrochemical cell, Cu/Cu2O dark cathode exhibited a Faradaic efficiency up to 53.6% for CH3OH production.

Cu2O-based electrodes for photocatalytic CO2 reduction in aqueous solutions

2019 Spring National Meeting

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