Dye-sensitized semiconductors: from photovoltaics to hydrogen evolution and back

Semiconductors such as TiO2 nanoparticles can be functionalized with metals like Pt to create catalytic sites for hydrogen evolution reaction (HER) from a protic sacrificial electron donor (SED) once light shines on the system. Unfortunately, most semiconductors have a wide bandgap requiring photoexcitation with UV light, which reduces the system efficiency under solar irradiation. By functionalizing of the nanocomposite with organic molecules, we improved visible-light-driven H2 generation. The dye affected both the spectral response toward the visible region and the possibility to use a wide range of compounds as SED. In our work, we developed three-component heterogeneous photocatalysts by sensitizing Pt/TiO2 nanoparticles with organic dyes inspired by the ones used in the dye-sensitized solar cells (DSSC) photovoltaics. The modular design D-?-A was employed to systematically alternate features like steric bulk, hydrophobicity, and hydrophilicity in different parts of the molecules to accommodate for the aqueous environment of the HER. The choice of SED and reaction conditions largely altered the overall hydrogen production efficiency. Best results were found with ascorbic acid and promising ones with EtOH, paving the way for using biomass-derivative as SED. Presently, we are reversing the technology transfer exploiting the insights in dyes compatible with the water environment to develop DSSC with aqueous electrolytes.