Isostructural Co/Ni-containing banana-shaped polyoxometalates for visible-light-driven hydrogen production

Isostructural Ni/Co-containing banana-shaped polyoxometalates, (C₂H₈N)₁₀[Ni₃W₂O₂(OH)₄(P₂W₁₅O₅₅)₂]·20H₂O (Ni3P4) and (C₂H₈N)₁₀[Co₃W₂O₂(OH)₄(P₂W₁₅O₅₅)₂]·26H₂O (Co3P4), which exhibit novel structural features, were successfully synthesized through a one-pot hydrothermal method. The synthesized compounds were characterized by various techniques to determine their composition, crystal structure, and elemental oxidation states. Single-crystal X-ray diffraction confirms that the two isostructural compounds differ solely in the metal-oxo cluster cores: {Ni₃W₂} and {Co₃W₂}, respectively. The title complexes Ni3P4 and Co3P4 have been investigated as noble-metal-free catalysts for visible-light-driven hydrogen evolution in a three-component system. Under otherwise identical catalytic conditions, Ni3P4 displayed significantly enhanced hydrogen evolution catalytic activity relative to Co3P4, achieving a 6.5-fold higher catalytic efficiency. Comprehensive mechanistic studies reveal that the superior hydrogen evolution activity of Ni3P4 does not originate from a more favorable photoinduced electron-transfer rate, but rather from the intrinsically higher proton reduction catalytic activity of the Ni center compared to that of Co.