The Study Of CrMoN Coatings Preparation And Its Application In PEMFC Bipolar Plates

Proton exchange membrane fuel cell(PEMFC)is ideal new clean energy source,bipolar plates is one of the most important components of it.However,the processing cost and weight of bipolar plate limits the commercial application of fuel cells.The bipolar plate must possesses excellent electrical conductivity,good mechanical strength,high corrosion resistance and good gas impermeability.Although the traditional graphite bipolar plates have good electrical conductivity,The brittleness and gas permeability of graphite hinder the large-scale application of graphite bipolar plates.Metal bipolar plates are expected to replace graphite as a preparation material for bipolar plates due to their excellent mechanical properties and low processing costs,but ions generated by corrosion of metal bipolar plates in PEMFC environments can contaminate membrane electrodes and catalysts.The use of surface modification technology to improve corrosion resistance of metal bipolar plates is the focus of current research.In this experiment,closed-field magnetron sputtering technology was used to deposition coatings,and SS316L was chose as the substrate.CrMoN coatings with different Mo contents were deposited on the surface.The morphology,structure and phase composition of the CrMoN coatings were analyzed by SEM and XRD techniques.The corrosion resistance,contact resistance and hydrophobicity of the surface-modified bipolar plates were tested in a simulated PEMFC environment,and the wear resistance of the coatings was tested by friction and wear and nanoindentation to comprehensively evaluate the advantages and disadvantages of the coatings.And the adhesion strength and wear resistance of coatings are tested by nanoindentation test,friction-wear test to evaluate the overall performance of coatings.The SEM results show that the CrMoN coating has a dense structure without obvious crack on the surface,and the coating column crystal growth mode is not obvious.The XRD structure indicates that the CrMoN coating forms a solid solution phase.Electrochemical test results in simulated cathode and anode PEMFC environments(0.5M H₂SO₄+5ppm HF,70?)show the corrosion resistance of CrMoN coating is better than Cr N coating,the potentiodynamic test results also show that the corrosion potential of the CrMoN coating is positive than SS316L,and CrMoN-4A coating sample has the highest corrosion potential.The potentiostatic polarization test results prove that CrMoN-4A coating has the lowest corrosion current density,which is two orders of magnitude lower than the SS316L substrate.The interface contact resistance test result show that the doping of Mo element significantly improve the conductivity of the Cr N coating.The water contact angle test shows that the doping of Mo reduce the hydrophobicity of Cr N coating.The contact angle of the CrMoN coating is significantly lower than that of the Cr N coating,but it still has better hydrophobic properties than SS316L.In order to optimize the performance of the coating and improve the preparation process,the corrosion resistance of the coating in the simulated PEMFC environment was further studied by changing the parameters such as test potential,temperature and immersion time.The results show that CrMoN-4A coating still has good corrosion resistance in complex environment.At the same time,the corrosion mechanism of the coating is also discussed.In order to optimize the performance of the coating and improve the preparation process,the corrosion resistance of the coating in the simulated fuel cell environment was further studied by changing the parameters such as test potential,temperature and immersion time.The potentiostatic polarization test at high potential showed that the corrosion resistance of the CrMoN-4A coating decreases with the increase of potential;the increase of temperature will also lead to the decrease of corrosion resistance of the coating.At the same time,the corrosion mechanism of CrMoN coating is also discussed.The doping of Mo element effectively reduces the electrochemical reaction between the layers/substrate.