Dual promotional effect of Cu x O clusters grown with atomic layer deposition on TiO 2 for photocatalytic hydrogen production.

The promotional effects on photocatalytic hydrogen production of Cu x O clusters deposited using atomic layer deposition (ALD) on P25 TiO 2 are presented. The structural and surface chemistry study of Cu x O/TiO 2 samples, along with first principles density functional theory simulations, reveal the strong interaction of ALD deposited Cu x O with TiO 2 , leading to the stabilization of Cu x O clusters on the surface; it also demonstrated substantial reduction of Ti 4+ to Ti 3+ on the surface of Cu x O/TiO 2 samples after Cu x O ALD. The Cu x O/TiO 2 photocatalysts showed remarkable improvement in hydrogen productivity, with 11 times greater hydrogen production for the optimum sample compared to unmodified P25. With the combination of the hydrogen production data and characterization of Cu x O/TiO 2 photocatalysts, we inferred that ALD deposited Cu x O clusters have a dual promotional effect: increased charge carrier separation and improved light absorption, consistent with known copper promoted TiO 2 photocatalysts and generation of a substantial amount of surface Ti 3+ which results in self-doping of TiO 2 and improves its photo-activity for hydrogen production. The obtained data were also employed to modify the previously proposed expanding photocatalytic area and overlap model to describe the effect of cocatalyst size and weight loading on photocatalyst activity. Comparing the trend of surface Ti 3+ content increase and the photocatalytically promoted area, calculated with our model, suggests that the depletion zone formed around the heterojunction of Cu x O-TiO 2 is the main active area for hydrogen production, and the hydrogen productivity of the photocatalyst depends on the surface coverage by this active area. However, the overlap of these areas suppresses the activity of the photocatalyst.