The abandonment of noble metals as cocatalysts and the use of visible light are two important aspects in the field of photocatalytic H2 Evolution with polyoxometalates (POMs) as photosensitizers. Here we introduce two new POM-based materials: [CuII5(2-ptz)6(H2O)4(GeW12O40)]· 4H2Ö (1) and [CuI2(ppz)4][H2GeW12O40]· 8H2Ö (2) (2-ptz = 5- (2-pyridyl) -tetrazole, ppz = 3- (pyrid-4-yl) -pyrazole) synthesized with the Keggin type [GeW12O40]4− (GeW12th) Polyanion and copper-azole complexes. The optimal photocatalytic H2 Evolution rate of the compound 1 without a noble metal cocatalyst is 3813 μmol g-1 Ha-1, which is 7.6 times higher than that of the compound 2 and more than 27 times higher than with mere GeW12th Polyanions. The improved photocatalytic H2 Evolution rate of the compound 1 is mainly attributed to: (i) the formation of stable heteropolybla species that can absorb visible light, (ii) the large differences in the reduction potentials of GeW12th Polyanion and the copper complexes that inhibit the photogenerated electron-hole pair recombination and (iii) the good dispersion of the GeW12th Polyanions, thanks to the presence of [CuII5(2-ptz)6(H2O)4]No4n + Layers that exclude their aggregation. To the best of our knowledge, Compound 1 is the photosensitizer for H2 Evolution with the highest photocatalytic performance of all classic POM-based materials.

Graphic summary: Improvement of the photocatalytic H2 evolution activity of Keggin polyoxometalates that anchor copper-azole complexes


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