CuNiZn vs CuZn Electrodes: Electrochemical CO₂ Reduction, Role of Metal Elements, and Insights for C–C Coupling Chemistry

Abstract

Exploring bi-and trimetallic catalysts in electrochemical CO 2 reduction (EC CO 2 R) has been a focal point for discovering reduction products. This study investigates the distinct roles of metal elements in the CO 2 R using CuNiZn and CuZn electrodes. Bimetallic CuZn exhibits superior electrochemical activity, yielding substantial amounts of CO, CH 4 , C 2 H 4 , and various liquid products, including formate, ethanol, acetate, propanol, and isopropanol. The study on trimetallic CuNiZn suggests potential connections to Fischer−Tropsch (FT) synthesis, indicating their capability to produce long-chain hydrocarbons (C n H 2n and C n H 2n+2 , n = 2−7) from CO 2 . EC CO reduction validated the FT process over the bi-and trimetallic catalysts. The discussion explores mechanisms for the formation of CO, CH 4 , and C−C coupled C 2+ products, considering potential-and concentration-dependent Faradaic efficiencies (FEs). Recycling tests emphasize the influence of metal composition on FEs. Surface analyses reveal oxidation states and compositional changes, while the dissolution of metals during electrochemistry highlights dynamic surface characteristics. This work provides insights into the metal composition of bi-and trimetallic catalysts, surface states, and electrochemical conditions, advancing our understanding of these electrodes and their role in CO 2 recycling through electrochemistry.

Electrocatalytic CO2 Reduction for Dynamic C1, C2, and C3+ Chemistry over Electrodeposited Zn on Cu and CuZn Mesh Supports

“…Cu 2p XPS and corresponding Cu LMM Auger profiles prior to sputtering are depicted in Figure a,b, respectively. For all samples, two characteristic Cu 2p 3/2 peaks were observed at 934.0 and 932.5 eV, corresponding to CuO and Cu 2 O/Cu species, respectively. ,, Corresponding Cu 2p 1/2 peak for Cu 2 O/Cu species was appeared at 952.5 eV. The presence of a shakeup peak above 940 eV confirmed the existence of Cu(II) oxidation states. ,, Given that Cu served as the support material, variations in Cu 2p intensity were influenced by carbon impurities and the Zn overlayer on the mesh supports.…”

“…Figure a,a1 display selected CV curves for Zn/CuZn electrodes in CO 2 -saturated 0.1 M KHCO 3 and 0.1 M K 2 CO 3 electrolytes, respectively. As the scan rate increased, the curve width also expanded, suggesting an increase in the associated electrical double-layer capacitance. , The cathodic and anodic currents ( i c and i a ) were measured, and the capacitive current density (| i a – i c |) was plotted against scan rates, as shown in Figure b for the tested electrodes. The slopes of these plots were halved to calculate the electric double-layer capacitance ( C dl ).…”

“…Previously, due to their low FE levels, these reaction pathways were often overlooked. However, they have recently been recognized as important in EC FT synthesis, − which is analogous to traditional FT synthesis. , …”

“…We analyzed the production of C 2–5 hydrocarbons over a selected CuZn electrode using the Anderson–Schulz–Flory (ASF) equation: ln( w n / n ) = n ln α + constant, where w n represents the weight distribution of a hydrocarbon, the y -axis is ln( w n / n ), and the chain growth probability (α) is derived from the slope of ln α. − The x -axis, n , represents the carbon number. In Figure d, the C n H 2 n +2 hydrocarbons exhibited high linearity, suggesting a production mechanism similar to conventional FT synthesis using thermal catalysts.…”

“…The slopes of these plots were halved to calculate the electric double-layer capacitance ( C dl ). ECSA was determined using the formula ECSA (cm 2 ) = C dl / C s , where C s is the specific double-layer capacitance, assumed to be 40 μF/cm 2 for a flat metal surface. , The resulting ECSA values are presented in Figure c. Under CO 2 conditions, ECSA values generally increased compared to those under N 2 conditions, indicating the involvement of CO 2 adsorption in CO 2 reduction.…”