Improving the photocatalytic H2 evolution activity of Keggin polyoxometalates anchoring copper-azole complexes

Eliminating the use of precious metals as cocatalysts and using visible light are two important aspects in the field of photocatalytic H-2 evolution with polyoxometalates (POMs) as photosensitizers. Here we present two new POM-based materials: [Cu-5(II)(2-ptz)(6)(H2O)(4)(GeW12O40)]center dot 4H(2)O (1) and [Cu-2(I)(ppz)(4)][H2GeW12O40]center dot 8H(2)O (2) (2-ptz = 5-(2-pyridyl) tetrazole, ppz = 3-(pyrid-4-yl) pyrazole) synthesized with the Keggin type [GeW12O40](4-) (GeW12) polyanion and copper-azole complexes. The optimum photocatalytic H-2 evolution rate of compound 1 without a noble metal cocatalyst is 3813 mu mol g(-1) h(-1), which is 7.6 times higher than that of compound 2 and more than 27 times higher than that of bare GeW12 polyanions. The improved photocatalytic H-2 evolution rate of compound 1 is mainly attributed to: (i) the formation of stable heteropoly blue species that can absorb visible light, (ii) the large differences in the reduction potentials of the GeW12 polyanion and the copper complexes that inhibit photogenerated electron-hole pair recombination and (iii) the good dispersion of the GeW12 polyanions, thanks to the presence of [Cu-5(II)(2-ptz)(6)(H2O)(4)](n)(4n+) layers that preclude their aggregation. To the best of our knowledge, compound 1 is the photosensitizer for H-2 evolution with the highest photocatalytic performance of all the classical POM-based materials.

Automated summary

In this study, two new POM-based materials were developed for photocatalytic H-2 evolution, with compound 1 showing significantly higher efficiency compared to compound 2 and bare GeW12 polyanions. The improved performance of compound 1 is attributed to the formation of stable heteropoly blue species, differences in reduction potentials, and good dispersion of GeW12 polyanions.