Fuel Cell Stack, Bipolar Plate, and Gas Flow Channel

Fuel Cell Stack, Bipolar Plate, and Gas Flow Channel 

The efficiency of a fuel cell depends on fhe overall kinetics of the electrochemical process and the performance of its components such as MEA and bipolar plate. As we have mentioned before, the success of fuel cells as an alternative power generation system requires reduced cost, reduced volume and weight, and improved performance and durability of both MEA and bipolar plates. Other components that contribute significantly to these requirements in a fuel cell are gaskets or seals, current collector, end plates, and gas flow manifolds. 

Research and development effort has been concentrated on the bipolar plate designs to reduce the cost and increase the performance of the fuel cell. Improvements can occur in the performance of a fuel cell through optimization of the channel dimensions and shape in the flow field of bipolar plates. The contact surface area of the reactant gas on the bipolar plates has an effective contribution on the overall reaction of the gases. The reactant gas pressure has an important role in the overall functioning of the fuel cell. Consideration of fluid flow, heat, and mass transfer phenomenon is impor-fanf while designing the bipolar plate channels. 

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Forms the connection between MEAs in a fuel cell stack. The bipolar plate includes the gas flow channels and may also include cooling channels. Bipolar plates are also called flow plates. 

A fuel cell stack is formed by connecting a number of tri-layer single fuel cell units or MEA units separated by interconnect or bipolar plates in series to meet the required power output. The MEAs are placed in good contact on both anode and cathode sides with the electrically conducting plates, often referred to as thefluid flow-field plates or bipolar plates or interconnect plates, which have integrated flow channels. Liquid- or gas-phase fuel and oxidant streams are fed through external and internal manifolds and distributed into the... 

Figure 2a illustrates a representative bipolar plate with its associated inlet and outlet ports, and serpentine flow field channel. Figure 2b shows a generalized cross section of a complete unit ceU taken along the different lines indicated in Fig. 2a. The essential difference between these cross sections is the composition of the environment contacting the external part of the seal leading to either a port or the atmosphere (Fig. 2a). As a result of seal degradation or breakage, fuel or coolant can penetrate into the porous gas-diffusion electrode and subsequently the airstream. A similar situation can arise as a result of a bipolar plate or membrane breakage. Component failure is not a necessary requirement for the fuel stream to interact with the airstream since the membrane is permeable to gases, liquids, and cations. The airstream can also be contaminated by any fuel cell stack components...

A bipolar plate that serves to connect individual cells together. Gas channels are usually machined, or moulded, into both sides of the plate to introduce fuel and oxygen/air to the respective electrodes and to remove the reaction products, i.e., pure water in the case of hydrogen fuel. This component is commonly known as a flow-field plate because it serves to smooth the current across the area of the cell stack. 

Beside the MEA the bipolar plates are the key components in a PEMFC stack in terms of their contribution to weight, volume, and costs. Bipolar plates contain a fine mesh of gas channels called the flow-field, to ensure a uniform distribution of the process gasses (hydrogen and oxygen) of fuel and air across both sides of the MEA and the removal of the reaction products. Furthermore, the bipolar plates in PEM fuel cells separate the individual cells from each other and guarantee an electrical connection between them in series. Substantial requirements for the bipolar plates are a high electrical conductivity and corrosion resistance. 

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