Formation and activity mechanisms of a carbon-nitride-supported single-atom catalyst for photocatalytic hydrogen evolution

Single-atom catalysts (SACs), which feature isolated single atoms (SAs) of a metal adsorbed on a support, have garnered significant attention as catalysts for a wide range of reactions due to the complete utilization of their active metal sites. However, the fundamental mechanisms governing their formation and exceptional catalytic activity remain largely unelucidated. A major challenge in SAC preparation lies in controlling residual SA precursors and mitigating the aggregation of SAs, particularly at high metal loadings. A comprehensive understanding of these mechanisms is therefore paramount for developing rational design principles to overcome these limitations. In this study, we combined in situ X-ray absorption fine structure analysis with density functional theory calculations to elucidate these critical mechanisms. Our findings reveal that i) the key factors in successful SAC formation are the destabilization of the SA precursor and the suppression of neutral-metal-atom formation; and ii) the high catalytic activity of SACs is primarily attributed to their maximized number of surface-active sites and that SAs exhibit an optimal hydrogen adsorption energy. These insights provide valuable design guidelines for the future development of diverse and highly active SACs.