Accelerating water reduction towards hydrogen generation via cluster size adjustment in Ru-incorporated carbon nitride

The metal cluster size and its interaction with the support has a strong impact on charge separation, water dissociation performance as well as durability of a heterogeneous catalyst. However, recent research on heterogeneous catalysis is predominantly devoted to enhancing the water splitting performance, but overlooks the fundamental concepts of relating cluster size as well as metal-support interaction with charge transfer ability and catalytic stability of electrocatalyst. Here, we report density functional theory along with experimental investigation that probe the relationship between particle size, intermediate structures, and energetics of water reduction on Rux (Ruthenium) clusters (x = 6, 13 and 55) on the g-CN support. The electrocatalytic activity for water reduction is found to dramatically oscillate as a function of the 'Ru' cluster size; the Ru55@CN catalyst shows the highest turnover rate 0.75 s-1 at 100 mV of H2 production. Density function theory (DFT) and experimental studies show a better stability and durability of Ru55@CN substrate due to its direct connection with five nitrogen atoms near the hole, along with one nitrogen at the hole center. In contrast, smaller clusters (Ru6 and Ru13) lead to greater distortion as they interact with only two neighboring nitrogen atoms in the pores of g-CN. The DFT study supported the Ru-N interaction in novel nitrogen-rich 2D g-CN structure which facilitates water dissociation and prohibits the undesired adsorption of active *OH groups. We hope optimization of metal's cluster size and its interaction with the substrate might be an interesting approach for designing an electrocatalyst system.