Performance Research On The Corrosion Resistance And Surface Conductivity Of Metal Bipolar Plates For Proton Exchange Membrane Fuel Cells

Proton Exchange Membrane Fuel Cells（PEMFCs）are power supply devices with high energy density and cause no pollution,the development of the cell technology has an important strategic significance to realize the"double carbon"goal in our country at an early date.As one of the most important key components of PEMFCs,the corrosion resistance and surface conductance of bipolar plates（BPPs）directly affect the overall output performance and service life of the cells.Compared with the traditional graphite plates,the metal BPP has the advantages of higher volume/weight ratio power and lower processing cost,but it also substains the weaknesses of poor surface conductance and insufficient corrosion resistance.Therefore,the effects of surface modification and external magnetic field intervention on the corrosion resistance and surface conductivity of titanium plate were investigated,and the feasibility of using zirconium based amorphous alloy as the material of BPPs without coating treatment was explored in this paper.To evaluate the corrosion resistance and surface conductivity of the metal bipolar plate,a simulated PEMFC solution was used to replace the electrolyte environment inside the cell,and an experimental program based on the microstructure characterization,electrochemical corrosion performance testing and electrical characteristics measurement of the metal BPP materials was developed.The testing platforms for the corrosion resistance and interfacial contact resistance（ICR）of the metal BPP were built,and the accuracy of the test results was improved by ameliorating the structure of the ICR test device,which laid a foundation for the research of the corrosion resistance and surface conductance of the metal BPPs.In terms of the surface modification of titanium BPPs,in view of the poor long-term corrosion resistance to dissolution of conventional metal-based coatings such as titanium nitride（TiN）,while the existing gold（Au）coatings with high resistance generally have the problem of high preparation cost resulting from the excessive thickness（micron level）.On the premise of ensuring the high corrosion resistance and surface conductivity of titanium plates,an ultra-thin Au coating with a thickness of 50 nm was successfully prepared on the surface of metal titanium by Magnetron Sputtering,and the overall preparation cost of titanium plates was reduced to the standards for commercial applications(≤$3·k W^-1).The performance research results show that the corrosion current density and ICR value of the Au coating meet the application standard,and its ICR value is close to that of the TiN coating,but the corrosion current density and cathodic dissolution current density are only about 1/2 and 1/3 of that of TiN respectively,which effectively solves the dissolution and peeling of the TiN coating under various unusual working conditions.The research shows that the Au coating has longer theoretical service life and higher operation stability,and reveals its higher commercial application value.In terms of the influence of magnetic field intervention on the performance of BPPs,since the corrosion resistance of the metal electrode plate not only depends on the substrate and coating materials,but related to the internal chemical environment and operating conditions of the PEMFC,among which the influence of the magnetic field generated by the operating current of the cell stack on the performance of BPPs is often ignored.For this reason,this paper first focused on this issuse and simulate the internal magnetic field environment of the cell by loading magnets,and the influence of magnetic field on the performance of titanium plates as well as the microscopic influence mechanism was explored.The results show that the simulated internal magnetic field of 160 m T can promote the passivation of bare titanium plate and significantly reduce its corrosion rate（≥50%）,but has no obvious effect on the corrosion of the Au coating.However,since the gold coating will eventually peel off and expose the titanium substrate during operation and continue to serve before complete failure,the influence mechanism of magnetic field on the performance of titanium plates is more focused on changing the passivation behavior of titanium substrates.The research shows that the stronger internal magnetic field（0～30 m T）can improve the passivation rate of titanium by promoting the enrichment of dissolved oxygen on its surface,so that titanium can form a thicker surface passivation film with lower roughness and exhibit the optimum comprehensive performance under the magnetic field of about 20 m T,which also reflects that dissolved oxygen is the important medium for magnetic field to promote the passivation of titanium.The further experiment comfirms that dissolved oxygen and magnetic field can synergistically increase the content of oxides of high valent titanium in the passivation film on titanium,reduce the concentration of inside oxygen vacancies and thus enhance its corrosion resistance,but magnetic field alone can reduce the corrosion resistance of titanium.It follows that the evaluation on the performance of titanium plates without considering the internal magnetic field effect are negative,and appropriate positive correction to obtain a more accurate conclusion is necessary.This study also provides a more complete analytical idea and a new realization way for improving the electrochemical performance of the metal plate.In the exploration of new metal BPP material,in view of the problems of high inherent ICR value and low corrosion resistance of existing titanium or stainless steel（SS）materials,and various anti-corrosion coatings are subjected to varying degrees of insufficient long-term durability,the feasibility of using amorphous alloys as high-performance BPP materials without coating treatment was explored and four kinds of bulk zirconium based amorphous alloys with different compositions were prepared based on the vacuum suction casting.The evaluation results show that all the amorphous alloy materials exhibit low corrosion rates under simulated PEMFC environments,where the bulk metallic glass,Vitreloy 1(Vit1,Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5)not only exhitited better pitting resistance,but has an annual corrosion rate of 1/30 of SS 304 under the same conditions under anode and cathode environments.ICR value of Vit1（18.6 mΩ·cm²）is 1/5 of SS 304;The output power density of the single cell with Vit1 BPPs reaches 473 m W·cm^-2,1.7 and 1.8 times that of the single cell with uncoated SS 304 and pure titanium TA2 plates,respectively.It not only proves the feasibility of Vit1 amorphous as a new metal BPP material,but provides a new research interest for obtaining high-performance metal BPP substrate without coating.