Design Requirements for Bipolar Plates and Stack Hardware for Durable Operation
The main requirements for the bipolar plate are electrical contacting of electrodes, current conduction, supply of gases and cooling media, removal of products, and the separation of reactant gases and cooling media. Another important factor for efficient operation and high durability is a homogeneous gas distribution. The homogeneity of the local reactant partial pressures is influenced by the depletion of oxygen and the accumulation of water and is locally affected by covered contact areas (landings) of the bipolar plate. Degradation effects in connection with hydrogen or oxygen undersupply and starvation are strongly influenced by bipolar plate design. Bipolar plate design may be influenced by the material, the production process, the gas diffusion layer properties, the membrane properties, the temperature profile requirements, the temperature level requirements, the interaction of the anode and the cathode, and especially by the liquid water transport through the membrane electrode assembly. As a result, different cell types have been established, e.g., gases can be conducted by a porous structure or in channels. Nonoptimized bipolar plate structures reduce the performance or involve the danger of increased degradation of the membrane electrode assembly and the bipolar plate. Requirements for an efficient and durable stack operation are a homogeneous distribution of fluids and a homogeneous and defined cell compression. The manifold of a fuel cell stack has the function to carry reactants and cooling media to the stack or to different cell rows and to carry off products and cooling media; therefore, the design of the manifold has an impact on the distribution of gas and cooling media. The stack-compression hardware has the function to lock the stack components into position with a defined and homogeneous pressure. Too high, too low, or inhomogeneous compressions have negative effects on the performance and durability of the stack.
KeywordsContact Resistance Liquid Water Membrane Electrode Assembly Bipolar Plate Leaf Spring
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