Preparation And Surface Modification Of The High Entropy Alloy/Nitride Co-deposition Coating For Stainless Steel Bipolar Plate

Bipolar plate is one of key component in proton exchange membrane fuel cell(PEMFC).Traditional graphite bipolar platehas been seriously restrictedon the application of PEMFCdue toits high cost,fragile,large volume and high permeability.Metalsare the promising candidate materials for PEMFC because of their high mechanical strength,ease processing,good conductivity and low material cost,which provide a new way for the fabrication and application of the bipolar plates.However,the metals have poor corrosion resistance and high interface contact resistance(ICR)in the operation environment of PEMFC,which reduces the electrical performance of PEMFC during the working condition.The results show that the surface modification with transition metal nitrides is one of the effective ways to improve the corrosion resistance and electrical conductivity of metal substrate materials.Based on the high entropy alloy and its nitride have excellent corrosion resistance and electrical conductivity,the high entropy alloynitride film was deposited on 304 stainless steel bipolar plates with magnetron sputtering technology for the surface modification in this study.Throughthe electrochemical performance test and ICR analysis,the effects of different sputtering process parameters(substrate temperature,nitrogen flow ratioRN)on the high entropy alloy nitride film formation and the surface modified properties were sysytematically investigated in the simulated environment of PEMFC.The main results are listed as follows.1.The morphology,chemical composition and microstructure of the deposited films were characterized by scanning electron microscopy(SEM),Energy dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD).The study showedthe substrate temperature had a significant effect on the surface morphology and microstructure of the FeCrCoNiMnNx films.With the increase of substrate temperature,the particles/grain size of the films increased gradually.The structure of the films change from face-centered cubic(FCC)+body centered cubic(BCC)to face-centered cubic(FCC)solid solution.Nitrogen flow ratio RN had a significant effect on nitrogen content of the FeCrCoNiMnNx films.With the increase of RN,nitrogen content of the film increased gradually.There was no obvious influence on the cross-section morphology and structure of the films.The films stucture still FCC solid solution and the filmswere island-like growth.2.The properties of FeCoNiCrMnNx films deposited at the nitrogen flow rate RN of 16.7% and different substrate temperatures(40°C,300°C,500°C)were investigated.The results of electrochemical and conductivity analysis showed that in the simulated anode/cathode environment of PEMFC,compared to the corrosion resistance and conductivity of uncoated 304 stainless steel substrate,the corrosion resistance of the FeCoNiCrMnNx films prepared increased 15 times and their conductivity improved 4 times at substrate temperature 300℃ respectively.Therefore the FeCoNiCrMn high entropy alloy nitride film materials exhibited better corrosion resistance and electrical conductivity.3.The FeCoNiCrMn high entropy alloy nitride films were deposited at substrate temperature 300°C and different nitrogen flow rate RN(0.0%,16.7%,28.6%,37.5%).Electrochemical properties and interfacial contact resistance test results showed that in the PEMFC cathode/anode environment,the corrosion current density and the interfacial contact resistance value before and after potentiostatic polarization of the alloy nitride film at nitrogen flow rate RN = 28.6% were smaller than the films of other nitrogen flow rate,the film showed better corrosion resistance and conductivity.The high entropy alloy nitride film deposited at the substrate temperature of 300℃ and the nitrogen flow rate RN of 28.6% was more conducive to improving the corrosion resistance and conductivity of 304 stainless steel.