Transforming Single-Cluster Hybrids Into Single-Atom CoN4Se2 Motifs on Carbon Nitride for Efficient Photocatalytic H2 Evolution.

Engineering single-atom cocatalysts on semiconductors holds great prospects for boosting the photocatalytic hydrogen evolution reaction (HER). Herein, we report an innovative strategy to transform Co-based hybrid precursors containing CoOx clusters and atomic Co-N4 moieties into uniform single-atom Co-N4Se2 motifs on carbon nitride (CN) via H2-assisted thermal selenization, yielding a novel Co1N4Se2/CN photocatalyst. We unveil that high spin density and charge accumulation enable the Se atoms within the Co-N4Se2 configuration to function as sites for H2O dissociation with a markedly reduced energy barrier, while the coordinated Co atoms play a decisive role in activating Se atoms. Moreover, the unique single Co-N4Se2 moieties on CN facilitate n→π* and d-d electron transitions, thus significantly improving the photoelectric properties of Co1N4Se2/CN. Consequently, the as-achieved Co1N4Se2/CN catalyst delivers an exceptional HER rate of 5.4 mmol h-1 gcat -1 under visible-light irradiation, and the activity normalized to Co content even reaches 2.36 mmol h-1 mgCo -1, far exceeding reported non-precious and even most precious metal single-atom co-catalysts on CN. This work provides a new avenue for the design of efficient Pt-free cocatalysts toward solar H2 production.