Facet Dependence of CO2 Reduction Paths on Cu Electrodes

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• 作者：Wenjia Luo ; Xiaowa Nie ; Michael J. Janik ; Aravind Asthagiri
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：January 4, 2016
• 年：2016
• 卷：6
• 期：1
• 页码：219-229
• 全文大小：557K
• ISSN：2155-5435

文摘

Experimental results have shown that CO₂ electroreduction is sensitive to the surface morphology of Cu electrodes. We used density functional theory (DFT) to evaluate the thermodynamics and kinetics of CO₂ reduction pathways on Cu(100) and Cu(111) with the aim of understanding the experimentally reported differences in CO₂ reduction products. Results suggest that the hydrogenation of CO* to hydroxymethylidyne (COH*) or formyl (CHO*) is a key selective step. Cu(111) favors COH* formation, through which methane and ethylene are produced via a common CH₂ species under high overpotential (<?0.8 V vs RHE). On Cu(100), formation of CHO* is preferred and ethylene formation goes through C–C coupling of two CHO* species followed by a series of reduction steps of the C₂ intermediates, under relatively lower overpotential (?0.4 to ?0.6 V vs RHE). Further reduction of these C₂ intermediates, however, require larger potentials (～?1.0 V vs RHE) and conflicts with the experimentally observed low potential pathway to C₂ products on Cu(100). Calculations show that the presence of (111) step sites on the flat (100) terrace can reduce the overpotential for C₂ production on the Cu electrode, which may be present on Cu(100) due to reconstruction. On Cu(100), a change in CO* coverage from low to high with increasing negative applied potential can trigger a switch from ethylene/ethanol to methane/ethylene as the reduction products by affecting the relative stability of CHO* and COH*.