Research On Surface Modification Of Metal Bipolar Plates Of PEMFC

Fuel Cells, as a highly efficient and clean power generation technology, can convert the chemical energy of the active material to electrical energy directly through electrochemical reaction. Due to the properties of high energy conversion rate(40% ~ 60%), environmental friendly, low noise, almost no emissions of nitrogen and sulfur oxide, lower carbon dioxide emissions, is known as the fourth generation after hydraulic, thermal and nuclear power plant. Proton Exchange Membrane Fuel Cells(PEMFC), as the fifth generation of fuel cells, use the solid polymer as electrolyte, has the advantages of high energy conversion efficiency, noise free, zero pollution, corrosion free, low working temperature, fast cold start, long service life and high power density, possesses the extremely broad application prospect, especially suitable for electric vehicles, submarines, and all kinds of mobile power supply, has become one of the research highlights in the world.Bipolar plates is one of the key components of PEMFC. Usually Bipolar plates can be divided into two types, graphite plate and metal plate. Compared with graphite material, Metal material possesses better thermal conductivity, better electrical conductivity, better mechanical strength and better machining performance, is considered to be the inevitable choice of bipolar plates in PEMFC. But in the high temperature and acid hydrogen electrode side of PEMFC, metal bipolar plates are prone to corrosion and dissolution. And the corrosion cation can decrease the activity of electric catalyst, pollute polymer electrolyte membrane and increase the membrane resistance; In the oxygen electrode side of PEMFC, superficial passive film increases interfacial contact resistance between the gas diffusion layer and bipolar plates, enhances the ohm polarization effect, reduces the power output of fuel cells.In this paper, Zr and Zr C nanocrystalline coating were deposited onto Ti-6Al-4V alloy and 316 stainless steels bipolar plates by double cathode glow discharge technique. The coatings as-prepared consisted of the outer deposition layer and the inner diffusion layer. The microstructure of coatings was continuous, dense and well adherent. The corrosion resistance of Zr and Zr C nanocrystalline coating, Ti-6Al-4V alloy and 316 stainless steel in simulated PEMFC environment and the influence of temperature changes(25 ℃, 40 ℃, 55 ℃, 70 ℃) on the corrosion resistance were analyzed by potentiodynamic polarization, Potentiostatic polarization, open circuit potential(OCP) and electrochemical impedance spectroscopy(EIS). The electrochemical corrosion results indicated that corrosion potential, the values of capacitance semicircle, phase angle maximum as well as the frequency range of Zr, Zr C nanocrystalline coating were larger than those of Ti-6A1-4V alloy and 316 stainless steel in simulated PEMFC environment. At applied cathode(+0.6 V) potentials for PEMFC, Zr, Zr C nanocrystalline coating were in the passive region, 316 stainless steel is in the transpassivation region, and the passive current density of the as-deposited Zr, Zr C nanocrystalline coating was four orders of magnitude lower than that of Ti-6A1-4V alloy; At applied anode(-0.1 V) potentials, Zr,Zr C nanocrystalline coating exhibited the characteristic of cathodic protection. The higher the temperature, the worse the corrosion resistance, and the temperature corrosion susceptibility of Zr C nanocrystalline coating < Zr nanocrystalline coating < Ti-6A1-4V alloy, 316 stainless steel. Moreover, Zr, Zr C nanocrystalline coating could effectively improve electrical conductivity and hydrophobicity of Ti-6A1-4V alloy and 316 stainless steel bipolar plate.