Influence of Temperature on the Shape Evolution of IrO2-SiO2 coating and Its Electrochemical Activity for Oxygen Evolution

The surface structure of IrO₂-SiO₂/Ti anode was modified by thermal decomposition of non-aqueous solution of iridium chloride (IrCl₃) and tetraethoxysilane (TEOS) with different calcination temperatures. The surface morphology and microstructure of these anodes were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray-photoelectron spectroscopy (XPS). At low calcination temperature, the surface was dominated by biphase solid solution, in which the IrO₂-rich phase, spiculate IrO₂-SiO₂ crystal, was encircled by the SiO₂-rich phase, the amorphous SiO_2­-IrO₂ solution. As the calcination temperature increase, more amorphous IrO₂ from the SiO₂-rich phase converted into rutile nanothorn, then into nanoparticle composed by fine crystallites nanosheet aggregated on the surface of coatings and grew larger constantly. The electrochemical behaviors of the oxygen evolution reaction (OER) were evaluated by cyclic voltammetry (CV) and quasi steady-state polarization. The results showed that the electrocatalytic activities and the electrochemically active sites on the surface of the oxide electrodes for OER decreased with the increase of calcination temperature. This could be explained by the decrease of amorphous IrO₂ and the surface active sites, such as surface OH groups and crystal edges. The onset potentials of IrO₂-SiO₂/Ti anode were significantly affected by the calcinations temperature. The onset potential of amorphous film was shifted toward the negative side from that of the crystalline ones. The Tafel slopes indicated that the electron charge transfer process is the rate determining step of IrO₂-SiO₂/Ti electrodes for the OER.