Sn-CuO single atom catalyst for electrochemical reduction of CO2 to C2H4

Abstract

Currently, various kinds of nanoscale catalysts are utilized for the electrochemical re-duction of CO2. Throughout several studies on the nanoscale catalyst, numerous works have reported catalysts showing good performance in reducing CO2. However, for further improvement in metal utilization efficiency and catalyst activity, research on downsizing nanoscale catalysts to the atomic scale has emerged. Single-atom catalysts (SACs) contain metal atoms singly located on supports and isolated from each other. SACs have ad-vantages when applied as catalysts. First, they maximize metal utilization efficiency, which alleviates the cost of metals. Second, downsizing them to the atomic scale forms low-coordination environments and induces quantum size effects, opening new strategies for catalyst design. Thus, research on SACs has attracted great attention in recent years. Various types of supports such as carbon materials (e.g., graphene, CNT, graphene oxide), metal oxides, and metals are selected for fabricating SACs. From the perspective of cata-lysts for the electrochemical reduction of CO2, metal oxide possesses good properties. Metal oxide contains abundant defects (vacancies, edges, steps) and OH- on the surface, which can act as host sites for anchoring single atoms. Most importantly, the interaction between single isolated atoms and metal oxide supports can lead to a synergistic effect and enhance catalyst properties. Thus, applying metal oxide supports for CO2 reduction can be a good choice. In this work, we synthesized SACs using CuO as a support and Sn as a single atom via wet chemical oxidation. While most SACs show high selectivity towards C1 products (CO, CH4, HCOOH), we utilized the synergistic effect between the single metal atoms and metal oxide supports to improve productivity of the C2 product. We also employed a flow cell, which is relatively more advantageous for C2 production than an H-cell. The faradaic efficiency of C2H4 increased from 32% to 43% at -0.8 VRHE. XANES and XAFS reveal that Sn atoms are singly dispersed on CuO supports. By calculating the D-band center from the valence spectrum, we found that the electronic structure change in our catalyst improved the performance of C2H4.