Facet-Control versus Co-Catalyst-Control in Photocatalytic H 2 Evolution from Anatase TiO 2 Nanocrystals.

Titanium dioxide (TiO 2 ) and, in particular, its anatase polymorph, is widely studied for photocatalytic H 2 production. In the present work, we examine the importance of reactive facets of anatase crystallites on the photocatalytic H 2 evolution from aqueous methanol solutions. For this, we synthesized anatase TiO 2 nanocrystals with a large amount of either {001} facets, that is, nanosheets, or {101} facets, that is, octahedral nanocubes, and examined their photocatalytic H 2 evolution and then repeated this procedure with samples where Pt co-catalyst is present on all facets. Octahedral nanocubes with abundant {101} facets produce >4 times more H 2 than nanosheets enriched in {001} facets if the reaction is carried out under co-catalyst-free conditions. For samples that carry Pt co-catalyst on both {001} and {101} facets, faceting loses entirely its significance. This demonstrates that the beneficial role of faceting, namely the introduction of {101} facets that act as electron transfer mediator is relevant only for co-catalyst-free TiO 2 surfaces.