Studies On Preparation And Electrocatalytic Properties Of Cobaltite Spinel Composite Anodes For Water Electrolysis

In this research, the preparation and electrocatalytic properties of cobaltite spinel composite electrodes for alkaline water electrolysis were discussed. In order to overcome the shortages of the traditional alkaline water electrolysis as high overpotential and bad electrocatalytic stability of the metal nickel anode for oxygen evolution reaction (OER), the purpose of the present research is to develop new anodic materials with low overpotential for OER, high energy-efficiency, and good stability. The research includes the preparation and characterization of cobaltite spinel oxides, the preparation of cobaltite/nickel composite electrodes and their electrocatalytic properties for OER. The mechanism of OER in cobaltite was also discussed. The physicochemical properties of the four cobaltites spinels MCo2O4 (M=Ni, Cu, Zn, Mn) and the preparation methods of cobaltite/nickel composite electrodes were investigated. Electrochemical measurement methods were used to evaluate the surface roughness factors and the electrocatalytic properties such as cyclic voltammograms, overpotentials for OER. The prepared cobaltite composite electrodes show good electrocatalytic properties for OER. When tested at a current density of 100 mAcm-2, the electrodes prepared by surface coating method have the overpotentials of 0.454 V, 0.469 V, 0.476 V, and 0.510 V for ZnCo₂O₄, Cu_0.9Co_2.1O₄, NiCo2O4, and MnCo2O4, respectively, while the overpotential of nickel on the same testing condition is more than 0.65V. In addition, the electrodes prepared by electrophoretic deposition method show smaller overpotentials than that prepared by thermal decomposition method. The overpotential for electrophoretic electrodes is 0.447 V, 0.468 V, and 0.472 V at the current density of 100 mAcm-2 for ZnCo₂O₄, Cu_0.9Co_2.1O₄, and NiCo2O4, respectively. All the composite electrodes show good stability for OER during the testing. It is also found that electrophoretic deposition method is more suitable than surface coating method as to prepare cobaltite composite electrodes, which provides a new technique for preparation of cobaltite/nickel composite electrode. The transition of CoO2/CoOOH redox couple on the electrode surface is confirmed to be useful for OER. The role of other metal cations in the spinel shows no or less electrocatalytic roles for OER. The quantity of cobalt ions that occupy the octahedral sites on the electrode surface determines the electrocatalytic properties of the composite electrode. ZnCo2O4 has the best electrocatalytic properties for OER because of its highest content of cobalt ions on the surface.