Visible-light driven photoreduction of carbon dioxide to syngas with decatungstate-based metal–organic frameworks

The application of solar energy to catalyze the photoreduction of carbon dioxide (CO₂) into sustainable fuels and value-added chemicals offers a promising approach to enhance the natural carbon cycle and address global warming. Herein, two isostructural polyoxometalate-based metal-organic frameworks (POMOFs), Co₂(3,5-dmp)₈(W₁₀O₃₂) (CoW10) and Ni₂(3,5-dmp)₈(W₁₀O₃₂) (NiW10), assembled from decatungstate clusters and M(3,5-dmp)₄ (M = Co and Ni) units, were synthesized under solvothermal conditions. Both compounds exhibit two-dimensional grid structures featuring M-POM-M linkage conducive to efficient electronic conduction. CoW10 and NiW10 demonstrate strong visible-light absorption and effective photogenerated charge separation, conferring high catalytic activity and recyclability in CO₂ photoreduction. Under a pure CO₂ atmosphere, CoW10 achieves a high syngas (CO/H₂) production rate of 44.08 mmol g^-1 h^-1, while NiW10 shows high CO selectivity (88%). This activity divergence stems from distinct electronic configurations: high-spin Co²⁺ (t52ge2g) facilitates electron transfer <i>via</i> π-bonding in W-O-Co linkages, while Ni²⁺ (t62ge2g) exhibits suboptimal orbital alignment. Mott-Schottky and photoelectrochemical analyses confirm CoW10's superior charge separation and lower interfacial resistance. This work demonstrates transition-metal-dependent activity modulation in POMOFs and proposes a design approach for efficient CO₂-to-syngas photocatalysts.