Facet-Dependent Selectivity of Cuprous Oxide/Silver Tandem Catalysts for Promoting C2H4 Production from Electrochemical CO2 Reduction

The over-exploitation of fossil fuels and the consequent increase of atmospheric CO 2 concentration have aroused people's attention to energy and environmental issues. (1) In terms of reducing CO 2 content, the electrocatalytic CO 2 reduction reaction (CO 2 RR) can effectively solidify CO 2 and convert it into high value-added chemicals. There are many CO 2 RR reduction products, including CO, HCOOH, C 2 H 5 OH, CH 4 ,C 2 H 4 , etc. (2) However, in the CO 2 RR process, the hydrogen evolution reaction (HER) in the water phase has a lower reduction potential, making the CO 2 RR products less selective, which has become the most important problem restricting its practical application. Therefore, improving the selectivity and activity of CO 2 RR products has important research significance and practical application value. In this work, a series of Cu 2 O/Ag nanocrystals (NCs) with different crystal faces were prepared by hydrothermal method. Specifically, cubic Cu 2 O (c-Cu 2 O) enclosed with {100} facets, rhombic dodecahedral Cu 2 O (d-Cu 2 O) enclosed with {110} facets, and octahedral Cu 2 O (o-Cu 2 O) enclosed with {111} facets, are mixed with Ag nanospheres to form c-Cu 2 O/Ag, d-Cu 2 O/Ag, and o-Cu 2 O/Ag bimetallic tandem catalysts. The catalysts can improve the high activity and selectivity of CO 2 RR to produce C 2 H 4 product by adjusting different crystal faces. We can find from Figure 1 that o-Cu 2 O/Ag tandem catalyst exhibits an impressive Faradaic efficiency (66.8%) and partial current density (17.8 mA cm -2 ) for C 2 H 4 product at -1.2 V RHE . This result provides a new strategy for improving the selectivity of CO 2 RR to produce C 2+ products by adjusting the crystal facet engineering. Figure 1 . (a) SEM images of o-Cu 2 O/Ag, (b) LSV curves of three Cu 2 O/Ag catalysts in Ar and CO 2 -saturated 0.5 M KHCO 3 solutions, (c) Partial current density of C 2 H 4 formation on the three Cu 2 O/Ag catalysts at -1.2 V, (d) Faradaic efficiencies of C 2 H 4 on the three Cu 2 O/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). Figure 1