Interfacial Electronic Structures and the Fischer–Tropsch Synthesis Path by Electrochemical CO₂/CO Reduction for Ternary CuNiZn Alloys

Abstract

Metal alloy electrocatalysts are commonly used in electrochemical (EC) CO 2 reduction. In this study, we demonstrate the application of a ternary CuNiZn alloy as an electrocatalyst for both CO 2 and CO reductions. Our results show that formate, CO, CH 4 , and C 2−7 hydrocarbons were produced through the process of initial CO 2 adsorption followed by subsequent stepwise reactions. Interestingly, we also observed the production of CH 4 and C 2−7 hydrocarbons (C n H 2n+2 and C n H 2n ) through EC CO reduction, which occurred via direct CO adsorption, followed by hydrogenation reactions. Furthermore, we discovered an electrochemically-induced surface reaction that mimics the Fischer−Tropsch (F−T) synthesis, resulting in the formation of long-chain hydrocarbons through C−C coupling/polymerization. We utilized X-ray photoelectron spectroscopy with Ar + ion sputtering depth to investigate the interfacial electronic structures and surface elemental composition distributions of Cu, Ni, and Zn. Our results indicate that these properties are highly dependent on both the applied potential and the depth at which they are measured. These unique observation provides significant insights into the EC F−T synthesis process, C−C coupling mechanism, the design of efficient metal alloy electrodes, and the theoretical modeling of alloys in both electrochemical CO 2 reduction and CO reduction.

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

“…The reductions in Zn and Ni were most pronounced, with Zn reduced more than 10 times in amount. This suggests that the EC CO 2 reduction process could be influenced by the altered elemental ratios …”

Ag–Sb/Cu by Galvanic Replacement: Electrochemical CO2 Reduction and Unveiling C3+ Hydrocarbon Pathways

“…H 2 production, a well-known path initiated from H + + e – → H*, is a common dominant route. The two-electron process for CO involves the reactions CO 2 + H + + e – → *COOH, followed by *COOH + H + + e – → *CO + H 2 O. − ,,, Similarly, the two-electron process for formate is known to occur through CO 2 + H + + e – → OCHO* and OCHO* + e – → HCOO – . − , The adsorption of two intermediate species, *COOH and *CHO*, determines the final products and is highly dependent on the nature of the developed electrodes and the experimental conditions. The initiation of C 1 products, CH 4 , and methanol appears to involve the hydrogenation of surface *CO, following reactions such as *CO + H + + e – → *CHO or *COH.…”

“…Metallic Sb appeared after sputtering for the electrode after EC (Figure 9f2). This indicates that the overlaid species were metallic Sb covered by Sb 2 O 3 .The VB profiles became broader after EC tests (Figure 9e3 [39][40][41][42][43]45,55,56 Similarly, the two-electron process for formate is known to occur through CO 2 + H + + e − → OCHO* and OCHO* + e − → HCOO − . [35][36][37][38]47 The adsorption of two intermediate species, *COOH and *CHO*, determines the final products and is highly dependent on the nature of the developed electrodes and the experimental conditions.…”

“…In the 0.5 M condition, the FEs of liquid products were significantly diminished, in good consistency with the literature. 45,47 The C 2 H 6 FE was highest in the 0.05 M condition but lower in higher concentrations (Figure 5b2). On the other hand, the C 3 H 6 FE was highest in the 0.2 M condition, similar to the C 2 H 4 FE.…”

“…Electrodes incorporating three different metals have been increasingly explored to enhance CO 2 reduction efficiency further and explore new dominant reaction pathways. − The utilization of the three metals offers increased opportunities to customize favorable adsorption sites and augment active sites for EC CO 2 reduction. This intricate interplay between multiple metals not only enhances the catalytic efficiency but also introduces a rich diversity of reaction pathways, contributing to the intricate landscape of CO 2 electroreduction.…”