Bipolar plate production

Evaluate pilot line performance and estimate pilot and mass bipolar plate production costs... 

The experimental dependence between the current density and width of air channels of bipolar plate has been obtained [3, 4]. Based on these data optimal width of channels 0.4-0.7 mm and current transfer prominent elements 0.2-0.7 mm was prescribed (exact values are determined by technological and material aspects of bipolar plate production, and also by gas diffusion layer parameters (thickness, porosity, mechanical characteristics, electric resistance). 

Fig. 13 Injection mold tool with two cavities for bipolar plate production...

FIGURE 6.2 Schematic view for bipolar plate production via compression molding. (Adapted from Hamilton P. J. and Pollet B. G. 2010. Fuel Cells 10(4) 489-509.)... 

Owing to the chemically nearly inert nature, low costs and sustainable availability of the substance class of carbon-based fillers are preferred as filler materials for bipolar plates and carbon composite bipolar plates have been extensively investigated. The following section is structured in the different ways of composite bipolar plate production and the resulting eligible materials. 

Institute of Gas Technology Deyeloping low cost composite bipolar plates Production of much thinner plates... 

Since a typical voltage output from one cell is around 0.4-0.8 V, many cells must be connected together in series to build up a practical voltage (e.g., 200 V). A bipolar plate performs this cell-connecting function and also helps to distribute reactant and product gases to maximize power output. 

Cost targets exist for all parts of the fuel cell for bipolar plates, from 10/kW (2004) to 3/kW in 2015 for electrocatalysts, from 40/kW (2005) to 3/kW in 2015 and for membrane electrode assemblies (MEA), from 50/kW (2005) to 5/kW in 2015 (Freedom Car, 2005 these cost targets are somewhat different from those mentioned by the IEA (2005)). Since 2004, the number of fuel-cell cars has been growing and at the time of writing they numbered approximately 1000 worldwide there are also around 100 fuel-cell buses in use worldwide in several demonstration projects. But these cars are produced as individual (hand-built) models and are extremely expensive, with production costs per vehicle currently estimated at around one million large-scale production is not expected before 2015, see Section 13.1. 

The major function of a bipolar plate, or simply called "plate," is to connect each cell electrically and to regulate the reactant gas (typically, hydrogen and air in a hydrogen fuel cell) or reactant liquid (typically, methanol in a DMFC) and liquid or gas coolant supply as well as reaction product removal in desired patterns. This plate must be at least electrically conductive and gas and/or liquid tightened. Considering these important functions and the larger fraction of volume, weight, and cost of the plate in a fuel cell, it is worthwhile to construct this chapter with emphasis on the current status and future trend in bipolar plate research and development, mainly for the plate materials and fabrication process. 

The importance of materials characterization in fuel cell modeling cannot be overemphasized, as model predictions can be only as accurate as their material property input. In general, the material and transport properties for a fuel cell model can be organized in five groups (1) transport properties of electrolytes, (2) electrokinetic data for catalyst layers or electrodes, (3) properties of diffusion layers or substrates, (4) properties of bipolar plates, and (5) thermodynamic and transport properties of chemical reactants and products. 

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. 

Thus, the heat release is directly related to the amount of product water. The next consideration is the amount of heat needed to raise fuel cell temperature from, for example, -30 to 0°C (AT = 30 K). The thermal mass of the fuel cell components comes in large part from the bipolar plates (BPPs), neglecting the end plates. With graphite bipolar plates of 1 mm thickness each, and assuming an adiabatic system, the required heat is... 

Bipolar plates are currently made from milled graphite or gold-coated stainless steel. Ongoing research is aiming to replace these materials with polymers or low-cost steel alloys, which will allow the use of low-cost production techniques. Even today, bipolar plates can be produced at 200 /kW, if the production volume... 

A special stainless steel was developed in Australia and patented (Jaffray, 1999). Production costs and endurance of the resulting flat plate design (Foger etal, 2000) were improved relative to that of the firm s initial all-ceramic design. The bipolar plates and interconnects were stainless steel. The cell had operational difficulties, and has been discontinued. The firm has just established a UK division, to compete in Europe. 

It should be noted that the products of this decomposition are water, carbon dioxide, and HF. While PFSA membrane FCs have been demonstrated for many thousands of hours, the flux of HF is significant enough so that uncoated metallic bipolar plates are precluded. Hard to machine graphite bipolar plates must be used or an electrically conducting corrosively resistive coating must be developed for easily fabricated metal bipolar plates. Lifetime studies of PEM... 

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