Characterization of LaNiO3 prepared by sol–gel: Application to hydrogen evolution under visible light

The semi conducting properties of LaNiO3, elaborated by sol–gel, have been investigated for the first time by the photocurrent technique and capacitance measurements. The oxide crystallizes in a distorted perovskite structure and the transport properties indicate degenerate conductivity with activation energy of 18 meV. The infrared spectrum allowed us to evaluate the band gap at 88 meV. The electrochemical behaviour has been studied in alkaline electrolyte (KOH, 0.5 M). The corrosion potential (−0.204 VSCE) and the exchange current density (0.103 mA cm−2), determined from the semi logarithmic plot, indicate long lived oxide. The slope and the intercept to C−2 = 0 of the Mott Schottky plot, characteristic of n type behaviour, gave respectively an electron density (ND) of 2.3 × 1019 cm−3 and a flat band potential (Vfb) of −0.61 VSCE. The nature of the Nyquist plot, measured over a wide frequency range (10−3–105 Hz), shows the predominance of the bulk contribution. The arc is not centred on the real axis (−6.3°), an evidence of a constant phase element. The straight line at low frequencies is due to Warburg diffusion and the data are interpreted thanks to the Randles model. The absorption of light promotes electrons into LaNiO3–CB with a potential (−0.62 VSCE) sufficient to reduce water (−0.50 VSCE). As application, the oxide has been tested successfully for hydrogen evolution upon visible light with a rate evolution of 1.73 μmol min−1 (g catalyst)−1 and a quantum efficiency of 0.042% under full light (29 mW cm−2).