Photocatalytic reactions could enhance the share of chemicals produced through renewable sources. The efficiency of photocatalysts drastically depends on light absorption, on the surface energy of the crystals, and on the properties of the nanobuilding blocks assembled in devices. Here, we show that photoelectrochemical water oxidation on brookite TiO2 nanorods is greatly enhanced by engineering the location of Au nanoparticles deposition. Brookite photoanodes show a very low onset potential for water oxidation to H2O2 of −0.2 VRHE due to energetics of exposed crystal facets. By combining electrochemical measurements and ultrafast optical spectroscopy, we link the water oxidation activity with electron–hole recombination phenomena. The preferential Au decoration at the electrode/water interface produces highly enhanced photocurrent, while when Au is distributed along the whole film thickness, the activity is depressed with respect to pure brookite. In the latter case, Au nanoparticles act as recombination centers with plasmonic carriers recombining on the same time scale of their generation (fs). Conversely, Au surface decoration enables a hot electrons lifetime 4 orders of magnitude longer (ns) due to efficient hopping on brookite lateral facets, thus providing an efficient path for plasmon-enhanced solar water oxidation

In this article we present the first comparative study of the transient decay dynamics of photo-generated charges for the three polymorphs of TiO2. To our knowledge, this is the first such study of the brookite phase of TiO2 over timescales relevant to the kinetics of water splitting. We find that the behavior of brookite, both in the dynamics of relaxation of photo-generated charges and in energetic distribution, is similar to the anatase phase of TiO2. Moreover, links between the rate of recombination of charge carriers, their energetic distribution and the mode of transport are made in light of our findings and used to account for the differences in water splitting efficiency observed across the three polymorphs.

No abstract

Hydrogen evolution is among the most investigated catalytic processes given the importance of H2 from an industrial and an energy perspective.