Metal Cluster Catalysts for Electrochemical CO₂ Reduction

The manufacturing industry plays a critical role in the global economy, producing goods and materials essential for everyday life. However, this sector is also responsible for a significant environmental impact due to the overreliance on petrochemicals and fossil fuels. To mitigate CO2 emissions in the manufacturing industry, electrochemical CO2 reduction (ECR) is a potential solution, as it allows the production of many industrial chemicals using CO2 waste and renewable electricity. In ECR, metal catalysts for the CO2 reduction reaction have been the subject of intensive research in the last few decades. Theoretically, when the size of metal catalysts decreases, i.e., from bulk to nanoparticles, to polynuclear clusters, and to single atoms, the mass efficiency increases as more atoms are exposed and available for catalysis. Polynuclear metal clusters are a special case, as they straddle between the atomic world and the nanoscale materials. Unlike nanoparticles with a distribution of sizes, polynuclear metal clusters can have a well-defined structure. They often contain a few to tens of metal atoms/ions, which allows them to facilitate C–C couplings to obtain C2+ products in ECR─a feat unattainable with single atoms. In this Perspective, we aim to bring together the knowledge from the field of polynuclear metal clusters and ECR, providing the background, the synthesis, and the characterization of polynuclear metal clusters before assessing their current applications in ECR. We discuss key insights from recent studies, with the focus on catalyst performance, selectivity, and the mechanisms driving these processes. Additionally, we highlight the major challenges and outline the steps needed to develop more efficient CO2 reduction catalysts. Our aim is to encourage further research into the design of highly active and selective catalysts for ECR using polynuclear metal clusters.