Copper is the only pure metal electrocatalyst capable of producing hydrocarbons and oxygenated products with high Faradaic efficiency via the electrochemical reduction of CO2 (CO2RR). Previous work has shown that the activity and selectivity of Cu are largely dependent on the surface morphology of the metal, as well as its local reaction environment (electrolyte composition and pH). Cu(100) and Cu(211) surfaces have been found to be more active than Cu(111) surfaces and to be more effective in promoting C-C bond formation, resulting in multi-carbon products. More recently, concave defects with respect to Cu(100) planes have been identified as active sites for C-C bond formation. By contrast, there is a continuing discussion about the role of partially oxidized Cu sites, stabilized by subsurface oxygen, nitrogen, or halide atoms, and their role in promoting C-C bond formation. We will report the results of our experiments aimed at addressing this issue. The activity and product selectivity of electrochemically polished Cu will be compared with those of roughened Cu surfaces prepared by different plasma bombardment treatments and characterized ex situ by SEM, AFM and cross-section FIB-TEM. We will show that differences in overall CO2RR activity due to different plasma pretreatments are attributable changes in the electrochemically active surface area. While we observe differences in product current densities for different plasma pretreatments, the ratio of current densities for hydrogen evolution to CO2RR and the ratio of current densities for C2+ to C1 product formation depend on the duration of plasma treatment and are nearly independent of plasma composition. Therefore, our work suggests that the distribution of products produced by CO2RR on metallic Cu of changes Cu surface topology created by plasma pretreatment.

Surface topology effect of under-coordinated Cu sites on electrochemical CO2 reduction

2019 Fall National Meeting

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