The over-exploitation of fossil fuels and the consequent increase of atmospheric CO₂ concentration have aroused people's attention to energy and environmental issues.⁽¹⁾ In terms of reducing CO₂ content, the electrocatalytic CO₂ reduction reaction (CO₂RR) can effectively solidify CO₂ and convert it into high value-added chemicals. There are many CO₂RR reduction products, including CO, HCOOH, C₂H₅OH, CH₄,C₂H₄, etc.⁽²⁾ However, in the CO₂RR process, the hydrogen evolution reaction (HER) in the water phase has a lower reduction potential, making the CO₂RR products less selective, which has become the most important problem restricting its practical application. Therefore, improving the selectivity and activity of CO₂RR products has important research significance and practical application value.

In this work, a series of Cu₂O/Ag nanocrystals (NCs) with different crystal faces were prepared by hydrothermal method. Specifically, cubic Cu₂O (c-Cu₂O) enclosed with {100} facets, rhombic dodecahedral Cu₂O (d-Cu₂O) enclosed with {110} facets, and octahedral Cu₂O (o-Cu₂O) enclosed with {111} facets, are mixed with Ag nanospheres to form c-Cu₂O/Ag, d-Cu₂O/Ag, and o-Cu₂O/Ag bimetallic tandem catalysts. The catalysts can improve the high activity and selectivity of CO₂RR to produce C₂H₄ product by adjusting different crystal faces. We can find from Figure 1 that o-Cu₂O/Ag tandem catalyst exhibits an impressive Faradaic efficiency (66.8%) and partial current density (17.8 mA cm^-2) for C₂H₄ product at -1.2 V_RHE. This result provides a new strategy for improving the selectivity of CO₂RR to produce C₂₊ products by adjusting the crystal facet engineering.

Figure 1. (a) SEM images of o-Cu₂O/Ag, (b) LSV curves of three Cu₂O/Ag catalysts in Ar and CO₂-saturated 0.5 M KHCO₃ solutions, (c) Partial current density of C₂H₄ formation on the three Cu₂O/Ag catalysts at -1.2 V, (d) Faradaic efficiencies of C₂H₄ on the three Cu₂O/Ag NCs.

Reference

[1] P. De Luna, C. Hahn, D. Higgins, S. A. Jaffer, T. F. Jaramillo and E. H. Sargent, Science, 364 (2019).

[2]Y. Zheng, A. Vasileff, X. Zhou, Y. Jiao, M. Jaroniec and S. Z. Qiao, J Am Chem Soc, 141, 7646 (2019).