Characterization of LaNiO_3 prepared by sol-gel: Application to hydrogen evolution under visible light

摘要

The semi conducting properties of LaNiO_3, 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 (-0.204V_(SCE)) and the exchange current density (0.103 mAcm~(-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 (No) of 2.3 x 1019cm~3 and a flat band potential (V_(fb)) of -0.61 V_(sce).The nature of the Nyquist plot, measured over a wide frequency range (10~(-3)-10~5 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 Randies model. The absorption of light promotes electrons into LaNiO_3-CB with a potential (-0.62 V_(SCE)) sufficient to reduce water (-0.50 V_(SCE)). 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)).