Stainless Steel Bipolar Plates.- Double-Channel Serpentine Flow Field Design

Abstract

The performances of two gas-channel designs of bipolar plates were investigated by numerical simulations and experimental incell tests. The experimental study examined the performances of two gas-channel geometries and materials under cathode and anode flooding conditions. Design 1 consisted in straight-parallel channels with graphite monopolar plates. On the other hand, Design 2 was made of a double-channel serpentine flow field pattern with stainless steel monopolar plates. Design 1 did not provide a uniform flow distribution over the gas diffusion layer, so liquid water was accumulated in certain regions. The flow velocity in Design 2 was higher and produced more uniform electrical current distributions than the straight-parallel channels design. This design, using 304 SS plates, diminished the effect of the electrical resistance related to the mass transfer rate. IntroductionThe principal components of proton exchange membrane fuel cells (PEMFC) are current collectors, anodic/cathodic catalysts layers, gaskets and an electrolyte (proton exchange membrane). The current collectors, also known as the monopolar plate (single cell) and bipolar plate (stack), supply fuel and oxidant to the catalyst layer, removes water, collects generated electrical current and provides mechanical support for the membrane electrode assembly (MEA) in the stack.The membrane and catalysts layers usually are the most expensive parts of the fuel cell. However, current collectors would be the most costly element if the material or manufacturing processes have a high cost. Therefore, an inexpensive material like stainless steel could be used instead, and it would be the preferred material for the mass production of current collectors. Several types of stainless steels have been evaluated in order to develop a material capable of satisfying the requirements set by the US Department of Energy (DOE). Currently, there is a consensus that bare stainless steels are far from reaching the DOE's specifications (1-2). Therefore, several stainless steel coatings have been evaluated and some of them show a satisfactory performance (1-2).In our previous papers (3-4), the corrosion resistances of several electrical current metallic collectors were evaluated by the out-cell test (5). However, in this study only bare stainless steel 304 was tested using the in-cell test. Monopolar plates of stainless steel 304 were evaluated under real PEMFC environments in order to determine a reference performance for a fuel cell, which later allowed comparisons with other cell performances. In addition, studies are in progress in our laboratory using 444 steel coatings.