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 via 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.