Preparation Of Protective Film For Metal Bipolar Plate Of Proton Exchange Membrane Fuel Cell And Its Conductivity And Corrosion Resistance

Proton exchange membrane fuel cell（PEMFC）stands out among various fuel cells with the advantages of high efficiency,fast start-up,low working temperature and near zero emission.Bipolar plate is the most important part of PEMFC,which has important functions such as supporting membrane electrode assembly,providing electronic connection,water transfer and gas flow channel.Therefore,corrosion resistance and conductivity are very important for bipolar plates.Graphite bipolar plate is most widely used among many bipolar plate materials,but the disadvantages of the difficulties of preparing and the high cost is unfavourable for large-scale production.Therefore,it is urgent to develop a low-cost and easy processing alternative bipolar plate material.Metal bipolar plate has good conductivity,easy processing and low cost.It is the best candidate material for bipolar plate.However,in the acidic environment of PEMFC,metals are prone to corrosion.The released metal ions will not only lead to the decline of conductivity,but also affect other components of the battery stack.Therefore,the surface modification of metal bipolar plates is needed to solve this problem.In view of the challenges faced by metal bipolar plates at present,the surface of metal bipolar plates is modified by coatings,which greatly improves the performance of metal bipolar plates.The specific contents and results are as follows:（1）LaB₆ doped carbon films were prepared on the surface of SS316L by magnetron sputtering.The effect of LaB₆doping on the properties of carbon film coated bipolar plates was studied.It was found that LaB₆doping was conducive to obtaining carbon films with denser structure and promoted the graphitization of carbon films.When the content of LaB₆was 5%and the bias voltage was 100 V,the carbon films exhibited the best corrosion resistance and conductivity properties.（2）TiN thin films were deposited on the surface of SS316L by high power pulsed magnetron sputtering.Firstly,the effect of pulse width on the corrosion resistance and interfacial conductivity of TiN thin films was studied.It was found that the corrosion resistance and conductivity of thin films were the best when the pulse width was 500μs.On this basis,the preparation process was further optimized by changing the nitrogen flow rate.The results showed that when the nitrogen flow rate was 8 sccm,the film has the densest section structure and the best corrosion resistance.In the simulated PEMFC environment,the corrosion current density is 0.52μA·cm^-2,and the interfacial conductivity of the film is the best,with ICR of 3.51 mΩ·cm²（1.4 MPa）.（3）CrN thin films were prepared on the surface of Ti substrates by high power impulse magnetron sputtering（HiPIMS）,and compared with CrN thin films prepared by medium frequency magnetron sputtering.The corrosion resistance mechanism of CrN thin films prepared by HiPIMS was studied.The results show that HiPIMS can improve the smoothness and density of CrN thin films compared with medium frequency magnetron sputtering,so as to improve the interfacial conductivity of the films.On the other hand,HiPIMS is conducive to the growth of small-size Cr₂N nanoclusters.The structure of amorphous wrapped Cr₂N nanoclusters gives CrN films excellent corrosion resistance.In addition,the CrN films prepared by HiPIMS have high conductivity and strong corrosion resistance under wide process conditions（nitrogen flow rate of 2 to 8 sccm）.The films prepared at nitrogen flow rate of 4 sccm have very low ICR（6.82 mΩ·cm²,1.4 MPa）and corrosion current density(0.086μA·cm^-2,simulating PEMFC environment,0.6 V),with the best comprehensive performance.