Photocatalytic H₂ generation has been a highly investigated topic ever since Fujishima und Honda (1972) reported on the use of TiO₂ as a solar-illuminated semiconductor for the splitting of water into H₂ and O₂. Generally, in a fully photocatalytic setting (when photogenerated electron and hole are transferred from a solution-suspended TiO₂ nanoparticle to an aqueous electrolyte), a reasonable electron transfer rate can only be established when a noble metal co-catalyst is attached to the TiO₂. Mostly this is a Pt nanoparticle that is deposited onto the TiO₂ by various reductive treatments.

Over the years numerous efforts have been devoted to the shrinkage of the particle to enhance the usage of the noble metal. Evidently the most extreme case shrinkage is the use of an insulated single atom of Pt. The use of such isolated atoms as a co-catalyst in photocatalysis has in recent years attracted strong interest, not only because the single atom state represents a maximized surface to volume efficiency, but also because single atom reactivity allows for unprecedented reaction pathways.

In the presentation we discuss the use of Pt dispersed and anchored as single atoms on TiO₂ nanocrystallites, powders and nanotubes as a co-catalyst in photocatalytic H₂ generation.

We discuss various trapping and stabilization approaches of SAs on photocatalysts and report on a SA-Pt photocatalyst with a higher photocatalytic activity than observed for classic arrangements of co-catalyst on the semiconductive substrate. Moreover, we show that a small fraction of the totally deposited Pt that is stably trapped SAs provides virtually all photocatalytic reactivity of a Pt decorated catalyst.