K 4Ce 2M 10O 30 (M = Ta, Nb) as visible light-driven photocatalysts for hydrogen evolution from water decomposition

Abstract

A series of single-phase metal oxide photocatalysts K 4Ce 2M 10O 30 (M = Ta, Nb), capable of evolving H 2 and O 2 from aqueous solutions containing a sacrificial electron donor (Na 2SO 3) and acceptor (AgNO 3), respectively, under visible light irradiation ( λ > 420 nm) without any co-catalyst were presented. The activities were greatly enhanced by the incorporation of Pt, RuO 2 and NiO (NiO x ) as co-catalysts on the prepared oxides. The photocatalysts have an appropriate band gap energy ca. 1.8–2.3 eV (corresponding to absorption edge of 540–690 nm) and excellent chemical potential level for utilization of solar energy, representing candidates of photocatalysts for hydrogen evolution from water decomposition. Density function theory (DFT) calculation indicated that while their valence bands are composed of hybridization with O 2p + Ta 5d (or Nb 4d) and occupied Ce 4f orbitals, the conduction bands of these photocatalysts K 4Ce 2M 10O 30 (M = Ta, Nb) are mainly attributable to the Ta 5d (or Nb 4d) orbitals. Although the unoccupied Ce 4f orbitals have overlap in the bottom of conduction band, they are less effective in transferring electrons and photocatalytic activities for their high localized nature. The contribution of these orbitals to the energy bands affects the electronic structure of the both photocatalysts and gives rise to their differences in light absorption and photocatalytic activities.