Crystal structure and electrochemical behaviors of Pt/mischmetal film electrodes

The Ml(La-rich mischmetal) films with a thin Pt layer on the substrate of chemically coarsen ITO glass or silicon slices were prepared by magnetic sputtering technique. The crystal structure and surface morphology of the films were investigated by X-ray diffraction(XRD) analysis and atomic force microscopy(AFM), respectively. The electrochemical hydridation/dehydridation behaviors of the films in KOH solution were studied by using cyclic voltammagraph and electrochemical impedance spectrum(EIS) as well. The AFM results show that the Pt cover layer on the Ml films is of island structure with a grain of 150200 nm in size. The presence of a thin Pt layer can provide sufficient high electrocatalytic activity for the electrochemical charge-transfer reaction. The electrochemical reduction and oxidation reaction occur on the Pt layer, and the diffusion of H into the Ml film is the rate-controlled step. The Pt coatings also act as protective layers, preventing oxidation and/or poisoning of the underlying Ml films in air.