Study On The Materials And Process Optimization Of Surface Modified Coatings In Metallic Bipolar Plates Of Fuel Cell

The proton exchange membrane fuel cell(PEMFC)has the advantages of no pollution,low noise,high conversion efficiency and swift start up at room temperature and it is widely applied in many fields such as transportation and energy.The poor comprehensive performance and high cost of the key components of the bipolar plate are the main reasons that limit the commercialization of PEMFC.Coating modification on the surface of the bipolar plates is an effective way to solve the problem.Based on the cluster-plus-glue-atom model of alloy composition design,the optimal composition point of Cr-C binary material system as a modified coating material was designed theoretically,the corresponding optimal composition formula was Cr_0.22C_0.78.The C_0.77Cr_0.23amorphous modified coating which was highly consistent with one of the best components and the best comprehensive performance,had been prepared on the surface of 316L stainless steel bipolar plate used by our pulse bias arc ion plating equipment.The indexes were far better than the technical standards of DOE.However,the serious corrosion occurred on the coating after about 3000 hours of stacking operation.The main reason for the failure of the coating was that there were defects such as pinholes and looseness on the surface of the coating.The corrosive liquid would contact the stainless steel substrate through these defects and cause chemical and electrochemical corrosion.After long-term operation,the coating would gradually develop from local corrosion to ulcers,and finally the coating would crack and the bipolar plate failed.In response to this problem,two materials and process schemes were designed to further improve the corrosion resistance of the bipolar plates.The modified coatings were prepared on the 316L stainless steel substrate by the pulse-biased arc ion plating equipment independently developed by our research group,The material characterization and comprehensive performance test analysis of the coatings were carried out.The main results are as followed:The Scheme one is to add Cr and four corrosion-resistant titanium alloys:TA1,TA9,TA10,Ti35 as the transition layer and deposit the corresponding metal-carbon composite films between them.The structure of the coatings is Me/Me-C/Me/Me-C/Me/Me-C.The conductivity of all the coatings before and after the test is better than Cr_0.23C_0.77single-layer coating.The corrosion resistance of multi-layer coatings with Cr,TA1 and TA10 as the transition layer is also improved,and the hydrophobic properties of the six groups of coatings are not much different.It is proved that the multi-layer structure and the design of adding a transition layer in Scheme one can slightly improve the overall performance of the bipolar plates.The Scheme two is to deposit a layer of carbon film with the nitrides of the above four titanium alloys as the transition layer.The structure of the coatings is(Ti Alloy)N_X/C.The results show that the contact resistance of the four groups of samples before and after corrosion is not much different from that of Cr_0.23C_0.77.The contact resistance of(TA10)N_X/C coating before and after corrosion is the lowest,which are 1.38 m?·cm²and 2.66 m?·cm²,respectively.Compared with Cr_0.23C_0.77single-layer coating,the electrical conductivity of the four groups of samples is improved.Among them,the corrosion current density of the dynamic potential and constant potential of the 9#sample(Ti35)N_X/C coating are the lowest,which are 0.142?A·cm^-2and 0.0627?A·cm^-2respectively,about 1/4-1/3 of the Cr_0.23C_0.77coating.The corrosion resistance is significantly improved and the water contact angle reaches 100.28°.It is verified that(Ti Alloy)N_X/C composite coatings can improve the overall performance of bipolar plates.Among them,(Ti35)N_X/C has the best corrosion resistance and can be used for subsequent stacking operations and further improvement programs.