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

Abstract

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 towards C2 and C3 (C2+) products than metallic copper that has not been pre-oxidized. 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 of -0.7 V 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. Based on 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.3

Zn–Cu Alloy Nanofoams as Efficient Catalysts for the Reduction of CO2 to Syngas Mixtures with a Potential‐Independent H2/CO Ratio

“…The electrocatalytic activity of the Zn|ZnSO 4 (100− X ) % CuSO 4 X % electrodes for the production of syngas was investigated in a two‐compartment H‐type electrolyzer equipped with an anion exchange membrane under constant CO 2 flow (20 mL min −1 ). To limit the competitive H 2 production and explore a broader range of H 2 /CO ratios, the electrolysis was performed in 0.1 m CsHCO 3 electrolyte (pH 6.8) because previous reports demonstrated hat large cations in the electrolyte favor the reduction of CO 2 instead of protons . We used 1 cm 2 working electrodes because the properties measured on very small electrodes (<0.5 cm 2 ) do not appear to scale up correctly when increasing the geometric surface area of the electrode, likely as a consequence of the significant thickness of the deposit (≥100 μm for X≥5).…”

Stability of Residual Oxides in Oxide‐Derived Copper Catalysts for Electrochemical CO2 Reduction Investigated with 18O Labeling

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Oxide-derived (OD) Cu catalysts have high selectivity towards the formation of multi-carbon products (C 2 /C 3 ) for aqueous electrochemical CO 2 reduction (CO 2 R). [6][7][8][9][10][11][12][13] OD Cu catalysts are formed by oxidizing Cu and subsequently reducing it. 60 %) for up to 5hin 0.1m KHCO 3 at À1.0 Vv s. RHE.

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A Disquisition on the Active Sites of Heterogeneous Catalysts for Electrochemical Reduction of CO2 to Value‐Added Chemicals and Fuel

“…The study discovered that enhancing the thickness of Cu 2 O film would lead to an increase in amount of C 2 H 4 generated and that the various Cu 2 O facets did not present any effect on the product selectivity. In fact, OD‐Cu can be shown to be selective in generating more C 2 products . A similar study further elaborated on this understanding and found out that by altering the thickness of Cu 2 O overlayer between 1.7 and 3.6 µm, it is possible to maximize the selectivity for C 2 H 4 (FE C2H4 of 34–39)% and C 2 H 5 OH (FE C2H5OH of 9–16%) at an applied potential of −0.99 V .…”