Photoelectrochemical hydrogen production by water splitting over dual-functionally modified oxide: p-Type N-doped Ta2O5 photocathode active under visible light irradiation

Doping of nitrogen into tantalum pentoxide (Ta2O5) drastically modifies two semiconductor characteristics simultaneously; first is activation toward visible light region from 320 to 520 nm in wavelength and second is reversed polarity in photoresponse from n-type to p-type conduction. N-doped Ta2O5 (N-Ta2O5) was also found to possess highly negative energy position of conduction band minimum (-1.3 V vs NHE) compared to those of Ta2O5 and TaON (-0.3 V), which was originated from surface dipole effect as recently clarified by DFT calculation reported in a literature. Here, we exhibit the first demonstration of photoreaction over N-Ta2O5 in an aqueous solution. The surface of N-Ta2O5 was found to be almost inert for hydrogen production by water splitting. However, the hydrogen generation rate was highly enhanced by surface modification with Pt, Rh or Au, which was assessed by photocathodic current over N-Ta2O5 films under visible light irradiation (lambda >= 410 nm). Among them, loading with either Pt or Rh greatly enhanced the H-2 evolution rate in an aqueous solution by two orders of magnitude compared to that over unmodified N-Ta2O5 for both films and powders. These results imply that the dual functional modification by single doping of N has a potential to generate new photocathodes for water splitting reaction under visible light irradiation. (C) 2016 Elsevier B.V. All rights reserved.