The Electrochemical Behaviors Of Stainless Steel Bipolar Plate In High Temperature PEMFC

Proton exchange membrane fuel cell (PEMFC) has been undergoing rapid development for portable applications, particularly for electric vehicles due to the characteristics of high efficiency and power density and environmental friendliness. Compared with the traditional low temperature (below80℃) PEMFC, the high temperature PEMFC(HT-PEMFC)(above100℃), which can increase the reaction kinetics and energy density, make water and heat management more easy, enhance CO tolerance, is the main development trends of PEMFC. Bipolar plate, which accounts for the dominant share of the total stack weight and cost, is significant multifunctional component of the PEMFC stack. The previous studies mostly focus on the proton exchange membrane and catalyst, however, the studies on bipolar plate in HT-PEMFC are rarely reported. In this paper, the HT-PEMFC environment is simulated when polybenzimidazole membrane with phosphoric acid (PBI/H3PO4) is used as proton exchange membrane. The electrochemical behaviors of stainless steel as bipolar plate in simulated HT-PEMFC environment are investigated.This paper first explored the simulation of high temperature corrosive environment. Then, evaluated the corrosion resistance of304,316,430stainless steel(SS) in different temperatures by potentiodynamic polarization, potentiostatic polarization and observation on surface morphology. In order to improve the corrosion resistance and surface conductivity of uncoated stainless steel, a TiN coating was deposited on the surface of304SS by multi-arc ion plating technology. The corrosion resistance and surface conductivity of TiN coated304SS(TiN-304SS) was also investigated in simulated HT-PEMFC environment, at110℃. Following are the main study and results:1. The boiling point of the simulated corrosion solution can be enhanced up to116℃by adding10M organic solvent N,N-dimethyl formadide (DMF) into0.5M H3PO4solution. The variation of current density obtained in the DMF added solution is similar to that in0.5M H3PO4solution without DMF added. Therefore, it is deduced that the corrosion solution of10M DMF+0.5M H3PO4at110℃can be used to simulate the HT-PEMFC corrosive environment.2. As the temperature rises, the corrosion current density of stainless steel increases, the stability of surface passivation film decreased in both the corrosive environment of0.5M H3PO4without DMF and0.5M H3PO4+10M DMF solutions. The intergranular corrosion occurred on stainless steel at110℃.3. The corrosive current density of TiN-304SS lower than that of uncoated304SS, which means the corrosion resistance increases; Interfacial contact resistance of TiN-304SS lower than uncoated304SS as well means the modification enhanced the surface conductivity of304SS.