Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction

5 years ago

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction

Alexis T. Bell, Yanwei Lum, Joel W. Ager, Binbin Yue, Peter Lobaccaro

Copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO₂ and better selectivity toward C₂ and C₃ (C₂₊) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO₂ reduction, with particular attention given to the selectivity to C₂₊ products. All catalysts were tested for CO₂ reduction in 0.1 M KHCO₃ and 0.1 M CsHCO₃ at applied voltages in the range from −0.7 to −1.0 V vs RHE. The best performing oxide-derived catalysts show up to ∼70% selectivity to C₂₊ products and only ∼3% selectivity to C₁ products at −1.0 V vs RHE when CsHCO₃ is used as the electrolyte. In contrast, the selectivity to C₂₊ products decreases to ∼56% for the same catalysts tested in KHCO₃. By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C₂₊ products is attained at an overpotential of −1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO₂. On the basis of recent theoretical studies, a high pH suppresses the formation of C₁ relative to C₂₊ products. At the same time, however, a high local CO₂ concentration is necessary for the formation of C₂₊ products.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b03673

DOI: 10.1021/acs.jpcc.7b03673