Transforming Single‐Cluster Hybrids Into Single‐Atom CoN 4 Se 2 Motifs on Carbon Nitride for Efficient Photocatalytic H 2 Evolution

ABSTRACT 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.