Preparation of the Spinel CuCo2O4 at Low Temperature. Application to Hydrogen Photoelectrochemical Production

We reported for the first time a facile method for the preparation of the spinel CuCo2O4 at 140 °C by using sulfates of copper and cobalt in KOH. The compound crystallizes in a cubic system (SG: F d \( \bar{3} \) m) with a lattice constant of 8.0590 A. The material was characterized by physical and photo-electrochemical techniques. The X-ray diffraction (XRD) pattern confirms the single phase with a high purity. The UV–Visible spectroscopy of the black product revealed a direct optical transition of 1.38 eV. The capacitance-potential (C−2-E) displays a negative slope and a flat band potential (+0.28 VSCE) characteristic of p-type semiconductor behavior. Further, the Nyquist plot shows a semicircle followed by straight line at low frequencies, indicating a diffusion process. To show effectively the photocatalytic performance, we tested our product in the hydrogen production upon visible light irradiation. H2 evolution rate of 7 µmol h−1 mg−1 and a quantum efficiency of 1.1% were obtained upon visible light illumination.