Visible light induced H2 evolution on the hetero-junction Ag/NiO prepared by nitrate route

Abstract

The photo-electrochemical study of the hetero-junction Ag/NiO (5/95 wt%) prepared in situ by nitrate route was investigated to assess its photoactivity for the hydrogen production upon visible light. The X-ray diffraction pattern shows narrow peaks of Ag and NiO. The direct optical gap of the sensitizer NiO (1.51 eV) is well matched to the solar spectrum. It acts as n-type semiconductor and the potential of its conduction band (−0.35 VSCE), determined from the capacitance measurement, is more negative than the H2O/H2 level (∼−0.3 VSCE), yielding water reduction under visible light; the photoactivity peaks at pH ∼ 13. The excited electrons are transferred to Ag clusters, to reduce water into gaseous hydrogen owing to the low H2-over-voltage (∼160 µmol). A quantum conversion efficiency of 0.11% is reported under visible light (3.42 × 1018 photons s−1) within ∼10 min with an evolution rate of 96 µmol h−1 mg−1. The catalyst was tested for several successive photocatalytic cycles, a deactivation effect of ∼7% per cycle is observed, thus proving its stability and repeatability. The heating of the catalyst under dynamic vacuum at 250 °C restores the initial photoactivity.