Preparation And Properties Of Cr And Nitride Coatings On 316L Stainless Steel Bipolar Plates

Proton exchange membrane fuel cell(PEMFC) is considered to be one of the best power systems with many superior performance in the future market development prospect. Bipolar plate is the core parts of the PEMFC multifunction, which occupies the vast majority of battery weight and cost.Compared with the conventional graphite material,the metal material possess excellent strength, gas permeability, a largen scale production processing plate and improving the batter power. Itowever the corrosion problem of metal bipolar plates has been an important factor restricting of its application. Chromium coating was deposited on the surface of 316L stainless steel bipolar plate by magnetron sputtering and the corrosion resistance was studied in this dissertation.In order to explore the nitriding mechanism of molten salt electrochemistry on the surface of the Cr coating,studying the electrochemical nitride for surface of the stainless steel bipolar plates in the molten salt system firstly, this have established the study foundation for preparing excellent Cr/CrxN coating on the surface of the 316L stainless steel,and acquire the following major results.Chromium coating is deposited on the 316L stainless steel by magnetron sputtering.Microstructure of Cr coating on the 316Lstainless steel by scanning electron microscopy(SEM) was observed.The results show that the grain of the chromium coating increase when the sputtering current increases 0.2A to 0.25A,the 316L/Cr coating is more uniform and dense with the extension of depositing time.The electrochemical test that 316L/Cr coating with Sputtering at different times in 0.5mol/L H2SO4 solution,corrosion potential increase and corrosion current density decrease with the increase of the sputtering time;When 316L/Cr coating in corrosion solution soaked after 720h by Sputtering current at 0.25A and time for 3h,the corrosion potential of coating remains high,and coating remains very good stability, the corrosion of the matrix alloy is inhibit effectively.Nitriding process on the surface of 316L stainless steel in the LiCl-KCl-KNO2 molten salt system was studied using electrochemical methods.Firstly,analysis of the nitrogen deposition potential is confirmed by the cyclic voltammetry, and the nitrogen coating was deposited on the surface of 316L stainless steel using potentiostatic method.The results showed that reducing of the potential that N3+reverts into N is significantly lower than the ions of potassium and lithium reverting to the corresponding potential of alkali metal in the electro-oxidation system of LiCl-KCl-KNO2 When the LiCl-KCl-KNO2 molten salt system is 480℃,N3+is reduced into N atoms and that seeping into the surface of stainless steel,it show that the nitriding layer is uniform density,and thickness can achieve about 10μm.