Competition and synergistic effects of Ru-based single-atom and cluster catalysts in electrocatalytic reactions

Single-atom catalysts (SACs) and cluster catalysts are increasingly recognized as powerful materials for electrocatalysis, especially in the field of sustainable energy storage and conversion. SACs have the advantages of low metal loading and high atom utilization efficiency, but the free energy of the surface area tends to make individual atom unstable, making them prone to agglomeration during synthesis and catalytic reactions. Cluster catalysts with high atom utilization and different active sites can overcome the limitations of single-atom catalysts for continuous and collective adsorption as well as activation of reactants or intermediates. The synergistic effect resulting from the competition between single-atom and cluster catalysts can significantly improve the performance of the catalysts. Ru-based catalysts have important application prospects in catalysis. Accurate design of the geometrical and electronic structures of Ru-based single-atom and cluster catalysts and the unraveling of their structure-property relationships face great challenges. Herein, we classify and compare these catalysts, with a special focus on Ru-based homologous and heterologous catalysts. Next, we show several major breakthroughs in electrocatalysis catalyzed by Ru-based single-atom and clusters. In recent years, Ru-based catalysts have made significant progress in hydrogen evolution reaction (HER), so we focus on the application of Ru-based catalysts in HER and cover other electrocatalytic reactions, bifunctional reactions (HER/oxygen evolution reaction, HER/hydroxide oxidation reaction), and electrochemical organic reactions. In addition, the review summarizes the catalytic mechanism of HER on Ru-based single-atom and clusters. Finally, challenges and prospects in the development of strategies for complex Ru-based catalysts for industrial applications are highlighted.