Crystal-Plane Dependence of Nb-Doped Rutile TiO2 Single Crystals on Photoelectrochemical Water Splitting

Abstract

The crystal-plane dependence of the photoelectrochemical (PEC) water-splitting property of rutile-structured Nb-doped TiO2 (TiO2:Nb) single-crystal substrates was investigated. Among the crystal planes, the (001) plane was a very promising surface for attaining good photocurrent. Under 1 sun illumination at 1.5 V vs. a reversible hydrogen electrode, the TiO2:Nb(001) single-crystal substrate showed the highest photocurrent (0.47 mA/cm2) among the investigated substrates. The doped Nb ions were segregated inward from the top surface, and the TiO2 ultrathin layer was formed at the surface of the crystal, resulting in the formation of a heterointerface between the TiO2 and the TiO2:Nb. The enhancement of the PEC properties of the TiO2:Nb(001) single-crystal substrate originated from favorable atomic configurations for water molecule absorption and facilitation of transport of photoexcited electron–hole pairs in the depletion layer formed around the heterointerface of TiO2 thin layers on the base crystal.