Effect of current flow on bipolar plate/gas diffusion layer interfacial contact resistance in Proton Exchange Membrane fuel cells (PEMFC)

摘要

Stainless steel bipolar plates can be excellent alternative to graphite bipolar plates since they display better mechanical properties and the manufacturing procedure is easier and cheaper. However, they are chemically instable in the corrosive environment of PEMFCs, and a thin oxide layer is developed on the plate’s surface. This layer causes a significant increase in the interfacial contact resistance (ICR) between the plates and gas diffusion layers. In an effort to characterize various stainless steel samples, before and after their exposure to the corrosive environment of a PEMFC, the interfacial contact resistance (ICR) between the plates and a commercial gas diffusion layer (GDL) was studied as a function of the pressure applied on the assembly. The ICR was studied in the range of 0-500 N/cm2 of pressure applied to the assembly; the ICR value was determined by means of galvanostatic potentiometry, where a constant current is applied to the assembly and the average value of the potential over time is recorded. The ICR is then calculated, after appropriate simplifications, as:ICR = Rtot = Iapplied / Vmonitored (1)It was observed that, besides the expected exponential reduction of ICR versus pressure, the value of the current applied to the assembly impacted greatly the obtained values for the ICR, irrespective of the applied pressure. This indicates that the observed phenomenon is not caused by any morphological changes on the interface. A possible explanation is that, at higher currents, the temperature increases locally due to ohmic heating, inducing thus changes in the GDL’s resistivity.