Study Of Surface Modification On Ti Bipolar Plate For Proton Exchange Membrane Fuel Cell

Bipolar plate(BP)is one of the key components of proton exchange membrane fuel cell(PEMFC).Its cost and weight account for about 45%and 80%of PEMFC stack,respectively,looking for cheap and excellent bipolar.The board material and preparation method,reducing its cost and weight,are of great significance for promoting the large-scale application of PEMFC.The thin titanium plate with low density,high strength,good corrosion resistance and the like has significant advantages in improving the weight specific power of the PEMFC stack,and has broad application prospects in the commercialization process of the PEMFC.The surface of the titanium plate is prone to passivation film,which leads to an increase in contact resistance and must be modified before use.Based on the review of the status quo of titanium plate modification,the Nb-based sandwich structure coating was prepared on industrial pure titanium by multi-arc ion plating technology with the aim of improving corrosion resistance and reducing contact resistance.The chemical testing technique optimizes the preparation process.(1)A complete and dense NbN coating was prepared on the surface of the titanium substrate.The coating composition was mainly NbN0.95 phase.The bias voltage has little effect on the morphology during the preparation process,but the increase of the nitrogen flow rate will increase the defects.The test results show that the best performance is obtained when the bias voltage is 300 V and the nitrogen flow rate is 200 seem.At this time,the simulated cathode and anode side corrosion current densities are 22.89 ?A cm-2(@0.6 V,vs.SCE)and-8.12 ?A cm-2(@-0.1 V,vs.SCE),respectively;the contact resistance at 1.5 MPa is 7.2 m?cm2,and there is no high rise after constant polarization of the anode and cathode.(2)With the introduction of Ti,a(Ti,Nb)N coating was prepared on the surface of the titanium substrate.The introduction of Ti transforms the NbN0.95 phase in the NbN coating into the NbN phase,and the corrosion resistance is greatly improved.When preparing,the Nb target current is reduced and the defects are correspondingly reduced.The performance of the Nb target current is 50 A,and the simulated cathode and anode corrosion currents reduced to 14.8 ?A cm-2(@0.6 V,vs.SCE)and-0.83 vA cm-2(@-0.1 V,vs.SCE).The pitting phenomenon is also significantly weakened;the contact resistance at 1.5 MPa drops to 3.6 mQ cm2,which is close to the commercial level and less than 10 m? cm2 after constant potential polarization.(3)NbC coating was prepared on the surface of titanium substrate,and the surface composition was mainly graphite-like carbon and amorphous NbC.The surface is completely dense and has fewer defects,and tends to be flat as the C content increases.The performance of the C target current is 70 A,and the simulated cathode and anode corrosion current densities reduced to 19.8?A cm-2(@0.6 V,vs.SCE)and-3.2 ?A cm-2(@-0.1 V,respectively).Vs.SCE),the corresponding dynamic potential is slightly insufficient;while its durability is greatly improved,the corrosion current density continues to decrease with time,and the cathode and anode are reduced to 2.0?A cm2 and-1.3 ?A cm-2,respectively;The contact resistance at MPa drops to 4.0 mQ cm2.