Facile preparation of the spinel CuCo 2 O 4 Application to hydrogen photo-production

For the first time, we proposed a simple method by co-precipitation for the preparation of the spinel CuCo2O4 at 140 °C in KOH medium, using sulfates as precursors. The oxide crystallizes in a cubic symmetry (SG: F d $$\overline{3}$$ m) with a lattice constant of 8.0590 A and has been characterized by physical and photoelectrochemical techniques. The X-ray diffraction (XRD) indicates a single phase with a high purity. The SEM analysis shows a porous nature with an average grains size of 0.1 µm. The UV–Visible spectroscopy of the black product indicates an optical transition of 1.38 eV, due to the degeneracy lifting of Co3+: 3d orbital in octahedral cavities. The thermal dependence of the electrical conductivity displays a semiconducting behavior. The electrochemistry carried out at pH ~ 13 shows the peak of the redox couple Co3+/Co2+. The capacitance-potential (C−2–E) characteristic exhibits a negative slope characteristic of p-type semiconducting behavior with a flat band potential (+ 0.28 VSCE). Further, the electrochemical impedance spectroscopy (EIS) plot shows two semicircles at high and low frequencies, due to no diffusion process. To show the photocatalytic performance, predicted from the energy diagram, we have tested our product for the hydrogen production upon visible light irradiation. H2 evolution rate of 7 µmol h−1 mg−1 and quantum efficiency of 1.1% were obtained upon visible light illumination (15 mW cm−2).