Bipolar plate design

The bipolar plate design is illustrated in Fig. 47. It consists of a cross-flow arrangement where the gas-tight separation is achieved by dense ceramic or metallic plates with grooves for air and fuel supply to the appropriate electrodes. A porous cathode, a dense and thin electrolyte and a porous anode form a composite flat layer placed at the top of the interconnected grooves. The deposition of the porous electrodes can be achieved by mass production methods. Moreover, the bipolar plate configuration technology makes it possible to check for defaults, independently and prior to assembly of the interconnection plate and the anode-electrolyte-cathode structure. 

Grigoriev S.A., Kalinnikov A.A., Fateev V.N., Porembsky V.I., Blach R. Numerical and experimental study of current collector and bipolar plate design for PEM fuel cells. Book of abstracts of C European Hydrogen Energy Conference (2-5 September 2003, Grenoble, France), p.92. 

The third design is a compromise between the first two and is often encountered in bipolar plate designs. The channels are typically about 1 mm in width and depth. The pressure difference between the start and end of a channel must be engineered to overcome the surface tension of water droplets forming on the channel walls, in order to clear blockages. 

M. Ruge and F.N. Btichi, PE fuel cells evaluation of concepts for a bipolar plate design and construction. Proceedings - Electrochemical Society, 2001, pp. 165-173. 

The method of connecting cells in series. The bipolar plate designs vary greatly, and some fuel cells use altogether different methods. We discuss these in Section 4.6. 

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. 

One of the major challenges in the bipolar plate design is to house reduced-size and highly complex gas flow channels with complex patterns for both fuel and oxidant gas flows as well as house cooling/heating channels if required. Additionally, it has to integrate well with the internal supply and return manifolds. 

Metallic bipolar plate design with conventional channels and use of metal foams in the flow fields are also considered (Kumar and Reddy, 2004). Results show a superior performance of the fuel cell with the use of metal foam bipolar plates with lower permeability. Bipolar plates with conventional channels are restricted to higher permeability owing to machining limitations. 

The use of SS-316 bipolar plates with multiple-parallel straight channels is very common in the fabrication of PEM fuel cell stack. A porous bipolar plate design to transport liquid water from the cell to the coolant stream is also considered (Wheeler et al., 2001). Reviews of bipolar plate design and materials are given by Ajersch et al. (2003) and Kumar and Reddy (2004). 

There are two major considerations for the design of the bipolar plate (1) selection of materials for bipolar plafes and (2) gas flow-field design. A detailed description of fhese two aspecfs of the bipolar plate design is given in the following section. 

The mathematical model for studying the hydro-dynamically developing flow-field and developing heat and mass transport phenomena is solved for different bipolar plate designs (Boddu and Majumdar, 2008). Figure 10.17 shows a three-dimensional model for simulation and a typical computational mesh size distribution in the feeder section of the channels. 

FIGURE 12.27. Bipolar plate design of solid oxide fuel cell. 

In the following the reqniranents for the bipolar plate are described as this is the basis for the understanding of bipolar plate designs. Then different types of flow fields are described, illustrating the difficulty to fulfill all requirements at the same time. 

Other methanol-tolerant catalysts have been found in iron poiphyiine-type materials supported on high surface area carbon [69,70]. These catalysts were tested in fuel cell conditions and it was found that no deterioration of the electrode performance could be seen when utilizing methanol in the ceU. The catalysts are insensitive to methanol. These catalysts were also combined with a new cell concept whereby the anode and the cathode reside in the same compartment. Both electrodes are in contact with the same side of the membrane, thus eliminating most of the ohmic resistance in the cell. The fuel efficiency in the ceU at low current densities was much higher than for a normal bipolar plate design. A methanol-tolerant cathode is a prerequisite to make this concept feasible. 

Some of the abovementioned requirements may contradict each other therefore, selection of the material involves an optimization process. The resulting material may not be the best in any of the property categories, but it is the one that best satisfies the optimization criteria (typically the lowest cost per kWh of electricity produced). Table 4-4 summarizes bipolar plate design criteria. 

Table 3. Summary of PEMFC bipolar plate design requirements (from Cooper, 2004)...

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