Electrical, optical and photoelectrochemical properties of BaSnO3-δ Applications to hydrogen evolution

Photoactive BaSnO3-delta is synthesized at 1253 K under air free atmosphere. The oxygen deficiency leads to a concomitant reduction of Sn4+ ions and the transport properties suggest low lattice polaron conduction with activation energy of 0.16 eV. Above 445 K, a plateau region is observed in the thermal variation of the conductivity caused by oxidation process, i.e. oxygen capture. The absence of the electrochemical peak Sn2+/4+ in the intensity-potential curve corroborates the delocalization of the stereo chemical pair Sn2+:5s(2). From photoelectrochemical measurements, the band gap is 2.80 eV and the transition is directly allowed. Moreover, indirect transition occurs at 2.60 eV. The material exhibits a long-term chemical stability over the whole pH range. In KOH (0.5 M) solution, the semi-logarithmic plot gave a current density of 24 mu A cm(-2) and a corrosion potential of -0.447 V-SCE. The capacitance measurements and cyclic voltammetry indicate that the photoresponse of BaSnO3-delta is characteristic of n-type conductivity with a flat band potential of -0.87 V-SCE and an electron density of 1.2 x 10(20) cm(-3). The best quantum efficiency occurs at 400 nm and is attributed to a depletion width (15 nm) and a diffusion length (57 nm) compared to a large penetration depth (820 nm). The electrochemical impedance spectroscopy (EIS) reveals the presence of bulk contribution effect and the Nyquist response has been decomposed on R-C parallel circuit. As application, BaSnO3-delta has been tested successfully for the hydrogen evolution under visible illumination when combined with the delafossite CuFeO2 as sensitizer. (C) 2010 Elsevier B.V. All rights reserved.