Efficient Suppression of Electron-Hole Recombination in Oxygen-Deficient Hydrogen-Treated TiO₂ Nanowires for...

There is an increasing level of interest in the use of black TiO₂ prepared by thermal hydrogen treatments (H:TiO₂) due to the potential to enhance both the photocatalytic and the light-harvesting properties of TiO₂. Here, we examine oxygen-deficient H:TiO₂ nanotube arrays that have previously achieved very high solar-to-hydrogen (STH) efficiencies due to incident photon-to-current efficiency (IPCE) values of >90% for photoelectrochemical water splitting at only 0.4 V vs RHE under UV illumination. Our transient absorption (TA) mechanistic study provides strong evidence that the improved electrical properties of oxygen-deficient TiO₂ enables remarkably efficient spatial separation of electron-hole pairs on the submicrosecond time scale at moderate applied bias, and this coupled to effective suppression of microsecond to seconds charge carrier recombination is the primary factor behind the dramatically improved photoelectrochemical activity.