Polyoxometalate-based catalysts for visible-light-driven hydrolytic hydrogen production: coordinatively unsaturated Cu-based active sites enhance performance

Hydrolytic hydrogen production can serve as a pollution-free solution to mitigate the energy crisis. However, many catalysts suffer from issues such as ambiguous structural definitions, which hinder nanoscale modifications aimed at enhancing their performance. In this work, two polyoxometalate-based photocatalysts, [Cu₄(C₈H₆N₃)₄(CH₃COO)₂]₂Na(H₂O)₂PW_11.5Cu_0.5O₄₀ (1) and [Cu₄(C₈H₆N₃)₆(H₂O)₂]₃H₂SiW₁₁CuO₄₀·20H₂O (2), were successfully synthesized for visible-light-driven H₂ production. We thoroughly investigated the structure-activity relationship (SAR) by taking advantage of the polyoxometalate-based catalyst as a crystalline material. To achieve unsaturated coordination of Cu sites and preserve the reactive active centers of the catalysts, the tridentate ligand 2-(1<i>H</i>-pyrazol-3-yl) pyridine (pzpy) was employed. The hydrogen production rates reached 16 831.6 (for 1) and 11 040.8 μmol g^-1 h^-1 (for 2). These catalysts contain four- and five-coordinated Cu active sites, respectively, clearly demonstrating performance enhancement attributed to the unsaturated coordination of metal sites.