Utilization of platinum nanoclusters (Ptn (n ≤ ca. 15)) as a co-catalyst for photocatalytic hydrogen evolution

Abstract

To solve the global energy and environmental problems, there has been active research on heterogeneous particulate photocatalysts for hydrogen (H₂) production by water splitting. Although such photocatalysts are typically composed of a semiconductor photocatalyst and a noble metal co-catalyst, there has not been sufficient studies on the effects of the sizes of co-catalysts as small as nanoclusters consisting of a few to tens of atoms. In this study, we have fabricated a new type of particulate photocatalysts deposited with platinum (Pt) nanoclusters consisting of approximately 15 atoms or fewer as a co-catalyst and evaluated the H₂ evolution activities from an aqueous solution. The Pt nanoclusters were generated by a dry fabrication method using magnetron sputtering (MSP), which simplifies the synthetic process, and they were directly embedded on photocatalyst powders, titanium(IV) oxide (TiO₂) and graphitic carbon nitride (g-C₃N₄). The Pt nanoclusters could work as a photocatalytic co-catalyst equivalent to ordinary Pt nanoparticles by a well-known photodeposition method (wet process). Furthermore, the optimal amount of Pt co-catalysts to improve the rate of H₂ production was found to be 0.1 wt% in the diluted sample from photocatalyst powders deposited with Pt co-catalysts of 1 wt%, and the improvement in activity by diluting samples was more pronounced for the Pt-nanocluster-deposited photocatalyst than for the Pt-nanoparticle-deposited photocatalyst. Our method will be extended to the design of functional materials with Pt (including alloys) co-catalysts/catalysts for the widespread use by reducing the amount and cost of precious metals.