(79e) Electrochemical Reduction of CO2 over Phase-Segregated Cuag Bimetallic Electrodes with Enhanced Oxygenate Selectivity By CO Spillover

The use of solar energy to produce fuels and commodity chemicals from water and carbon dioxide (CO₂), present either in the atmosphere or dissolved in seawater, represents an opportunity to obtain these products in a sustainable manner. One approach to this goal would be to convert solar energy into electrical energy using a photovoltaic device and to then utilize the generated electricity to drive an electrochemical cell for CO₂ reduction (CO₂R).^1â??4 Within such an electrochemical cell water is oxidized at the anode and CO₂ is reduced at the cathode. The electrocatalyst used as the cathode will largely define the overall efficiency of the process as well as the composition of the generated products. To date, extensive research has shown that the only metal capable of producing hydrocarbons and oxygenated products from CO₂ with Faradaic efficiencies (FEs) in excess of 1% is Cu.⁵ The principal products formed over Cu with high FEs (> 10%) are H₂, HCOO^-, CO, CH₄, C₂H₄, and C₂H₅OH.^6,7 The distribution of these products is sensitive to many variables, including the surface morphology of the Cu cathode, the electrolyte composition, and the applied potential. While alloying Cu with other transition metals has been identified as a promising method of tuning the product distribution obtained during CO₂R,⁸ no studies in the current literature have observed a positive effect of doing so on the FEs of potential fuels.

Herein we report our investigations of electrochemical CO₂ reduction over phase-segregated CuAg bimetallic electrodes, which we have observed to be the only metallic electrocatalysts yet discovered that are more selective for the formation of multi-carbon oxygenates than hydrocarbons. The selectivity of oxygenates relative to hydrocarbons is found to scale with the relative distribution of Cu and Ag facet terminations present at the electrode surface at steady state. The unique selectivity observed over these bimetallic electrodes is explained in terms of CO spillover from the Ag phase to the Cu phase, which results in an enhanced steady state coverage of CO adsorbed to the Cu facet terminations present at the electrode surface. The enhanced coverage of this key reaction intermediate on Cu increases the rate of C-C coupling at the expense of C-H bond formation, resulting in an improved selectivity to multi-carbon oxygenated products at the expense of hydrogen and hydrocarbons.

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