Transforming Single‐Cluster Hybrids Into Single‐Atom CoN 4 Se 2 Motifs on Carbon Nitride for Efficient Photocatalytic H 2 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 CoO x clusters and atomic Co‐N 4 moieties into uniform single‐atom Co‐N 4 Se 2 motifs on carbon nitride (CN) via H 2 ‐assisted thermal selenization, yielding a novel Co 1 N 4 Se 2 /CN photocatalyst. We unveil that high spin density and charge accumulation enable the Se atoms within the Co‐N 4 Se 2 configuration to function as sites for H 2 O 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‐N 4 Se 2 moieties on CN facilitate n→π* and d ‐ d electron transitions, thus significantly improving the photoelectric properties of Co 1 N 4 Se 2 /CN. Consequently, the as‐achieved Co 1 N 4 Se 2 /CN catalyst delivers an exceptional HER rate of 5.4 mmol h −1 g cat −1 under visible‐light irradiation, and the activity normalized to Co content even reaches 2.36 mmol h −1 mg Co −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 H 2 production.