Visible light hydrogen production on the novel ferrite NiFe_2O_4

摘要

The spinel type compounds represent a new family of photocatalysts that can be used as photoelectrodes capable to produce hydrogen under visible light. In the current study, the NiFe_2O_4 spinel, which is prepared by the sol-gel method, is investigated as a possible candidate, and the structure, opto-electronic, electrochemical and photoactive properties are characterized. NiFe_2O_4 exhibits a p-type semiconductor behaviour with a hole mobility of 1.57 × 10 ~(10) cm~2 (V s)~(-1). The conduction at 300 K is found to take place by electron-hopping mechanism with an activation energy ΔE_0~1 = 0.12 ev, and the lowest optical transition is observed at 1.56 eV. The valence band is of cationic character and derives from the Ni-3d orbital (5.23 eV/vacuum). On the other hand, the conduction band, E_(GB) = -1.62 V_(SCE). Is located above the H_2O/H_2 potential (-0.98 V_(SCE)which allows for the H_2-evolution under illumination. The effects of NiFe_2O_4 amount, pH level and S_2O_3~2 concentration are optimized. Under these ideal conditions, the rate of H2 involvement attains 0.68 × 10~(-3) mL mg~(-1) min~(-1) with a quantum efficiency η(H_2) = 0.53%. Electrochemical impedance spectroscopy is also used to model the photosystem and an electronic equivalent circuit is proposed.