Study On The Crystal Structure And Electrochemical Properties Of Rare Earth Films

By using magnetron sputtering technique, the rare earth films including Ce-rich mischmetal, La-rich mischmetal, lanthanum and yttrium were prepared on glass, ITO glass and Si substrates under the vacuum environment. The crystal structure, surface morphology, electrochemical properties and optical performances during the hydriding/dehydriding process were investigated, the reaction mechanism and invalidation reason were analyzed as well.The optimum parameters for the preparation of rare earth films by magnetron sputtering technique are as follows: substrate temperature of 150"C and sputtering pressure of 4.5 x 10 -1 Pa Ar+. The contamination of the different target, the oxidation and the carbonization during the sputtering process and the crystal structure of Pd all have the significant influence in the performance of the rare earth films.The research of the Pd/Mm films show that the Pd cover layer on the Mm films is of island structure with a grain of 150~200nm in size. During the electrochemical hydridation/ dehydridation the invalidation of the films are caused by the corrosion of films in KOH electrolyte. The presence of a thin Pd layer can provide sufficient high electrocatalytic activity for the electrochemical reaction. The electrochemical reduction and oxidation reaction occurs on the Pd layer and the diffusion of H into the Mm film is the rate-controlled step.For Pt/Ml films, it was found that Pt layer on the Ml films is of island structure tending to smoothen with the increase of Pt thickness. The potential of the Pt/Ml films electrode during the electrochemical hydridation have three regions corresponding to the formation of different La hydride phase. The electrochemical reduction and oxidation reaction occur on the Pt layer and the diffusion of H into the Mm film is the rate-controlled step. The crystal structure and electrochemical properties results show that the Pt cover layer can protect the rare earth films against oxidation in the air effectively and provide sufficient high electrocatalytic activity for the electrochemical hydridation/dehydridation in replace with the Pd cover layer.Pd/Y films show different corrosion mechanism during the different hydrogen loading process. The films exhibit the switchable optical properties during the air hydridation/dehydridation, however, there no optical properties were investigated during the electrochemical hydrogen loading process. The galvanostatic charging plot of the Pd/Y films show two plateau corresponding to the formation of YH2 and YH3 respectively. YH3 is unstable in air and can easily transform into YH2- Due to the band gap the absorption edge of YH3 is found at Xa400nm. YH2 shows a maximum transmittance windows at =689nm.