Superior Photocatalytic H2 Production with Cocatalytic Co/Ni Species Anchored on Sulfide Semiconductor

Downsizing transition metal-based cocatalysts on semiconductors to promote photocatalytic efficiency is important for research and industrial applications. This study presents a novel and facile strategy for anchoring well-dispersed metal species on CdS surface through controlled decarboxylation of the ethylenediaminetetraacetate (EDTA) ligand in the metal–EDTA (M–EDTA) complex and CdS mixture precursor to function as a cocatalyst in the photocatalytic H₂ evolution. Microstructure characterization and performance evaluation reveal that under visible light the resulting pentacoordinated Co(II) and hexacoordinated Ni(II) on CdS exhibits a high activity of 3.1 mmol h⁻¹ (with turnover frequency (TOF) of 626 h⁻¹ and apparent quantum efficiency (AQE) of 56.2% at 420 nm) and 4.3 mmol h⁻¹ (with TOF of 864 h⁻¹ and AQE of 67.5% at 420 nm), respectively, toward cocatalytic hydrogen evolution, and the cocatalytic activity of such a hexacoordinated Ni(II) even exceeds that of platinum. Further mechanistic study and theoretical modeling indicate that the fully utilized Co(II)/Ni(II) active sites, efficient charge transfer, and favorable kinetics guarantee the efficient activities. This work introduces a promising precursor, i.e., M–EDTA for planting well-dispersed transition metal species on the sulfide supports by a facile wet-chemistry approach, providing new opportunities for photocatalytic H₂ production at the atomic/molecular scale.

Well-dispersed Co(II) species with pentacoordination and Ni(II) species with hexacoordination are anchored on CdS surface by using metal–ethylenediaminetetraacetate complex as precursor, both of which function as efficient cocatalysts in the photocatalytic H₂ evolution, even the activity of Ni(II) species exceeding that of platinum with apparent quantum efficiency of 67.5% at 420 nm.

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