Band gap engineering of Gd and Co doped BiFeO3 and their application in hydrogen production through photoelectrochemical route

Abstract

The present report deals with the synthesis of Gd and Co doped BiFeO3 (BFO) i.e. Bi1-xGdxFe1-yCoyO3 (BGFCO, x = 0.0, 0.1; y = 0, 0.05, 0.10, 0.20, 0.25) nanoparticles by sol–gel method. The co-doping leads to band gap engineering of BiFeO3 with the band gap varying from 2.23 eV to 1.77 eV. The band gap engineering coupled with UV–Vis spectroscopy has been used to find the optimum material. The significant lowering in the band gap of the doped BFO is attributed to the deformation produced in Fe–O octahedron geometry as well as rearrangement in its molecular orbitals. The band gap engineering leads to materials with improved solar spectral response which in turn results in better harvesting of solar energy. X-ray diffraction (XRD) patterns indicate the formation of pure phase of BiFeO3 and its doped variants. The surface morphologies and particle sizes of different compositions have been investigated through scanning electron microscope (SEM). The as synthesized BFO as well as its doped variants have been used as photoanodes for hydrogen production through photoelectrochemical (PEC) splitting of water. The optimum material Bi0.9Gd0.1Fe0.75Co0.25O3 (BGFCO-25) with band gap of 1.77 eV has been used as photoanode having PEC configuration of 1 mol/L NaOH as the electrolyte solution and the Pt as cathode using 1.5 AM UV–Vis illumination. This has produced the photocurrent density of 2.03 mA/cm2 and hydrogen production rate of 74.57 μmol cm−2 h−1. The maximum photo-conversion efficiency has been found to be 2.29% for BGFCO-25 which is higher than that of BFO in which it is 0.76%. This noteworthy enhancement in the photoelectrochemical properties is ascribed to narrowing of the band gap which improves the solar spectral response and allows the absorption of higher density of photons. The stability test of the photoanode has been done through chronoamperometry technique.