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(Invited) Single Atom Co-Catalysts in Photocatalytic H2 Generation

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.