Bipolar plate properties

Boyaci SFC, Isik-Gulsac I, Osman OO (2013) Analysis of the polymer composite bipolar plate properties on the performance of PEMFC (polymer electrolyte membiane fuel cells) by RSM (response surface methodology). Eneigy 55 1067-1075... 

Porvair Progress Toward Meeting DOE Bipolar Plate Property and Cost Targets ... 

GB/T 20042.6-2011 Proton exchange membrane fuel cell—Test method of bipolar plate properties (China)... 

Properties and Estimated Cost of Nb-Clad SS430 Plates and Ni-Clad SS430 Plates with Boronized Layer Made by U.S. Pacific Northwest National Lab to Compare with U.S. DoE Bipolar Plate Technical Targets... 

Bipolar plates in PEMFCs were conventionally made of graphite with excellent corrosion resistance, chemical stability, and high thermal conductivity. However, graphite has a high cost, poor mechanical properties, and very little formability due to its microstructural nature. This limits its further applications as plate material and forces a search for alternative solutions. Nevertheless, the performance, durabilify, and cosf of fhe graphite plate (e.g., POCO graphite and graphite plates) have been taken as benchmark references to compare with those of alternative materials. 

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. 

In PEMFCs working at low temperatures (20-90 °C), several problems need to be solved before the technological development of fuel cell stacks for different applications. This concerns the properties of the components of the elementary cell, that is, the proton exchange membrane, the electrode (anode and cathode) catalysts, the membrane-electrode assemblies and the bipolar plates [19, 20]. This also concerns the overall system vdth its control and management equipment (circulation of reactants and water, heat exhaust, membrane humidification, etc.). 

Fuel cell assembly requires that considerable compression be applied to the stack to ensure tight gas seals and good electrical conductivity at the GDM-bipolar plate interface. This compression leads to reduced porosity, smaller average pore size, and possibly other microstructure changes in the GDM. Since capillary properties... 

For the HTE process, the electrochemical cell consists of a tri-layer ceramic, well known for its brittleness, which limits applied loads. In addition, the relatively low ionic conduction properties of the electrolyte materials (3% yttrium-stabilised zirconia) requires an operating temperature above 700°C to reduce ohmic losses. This creates difficulties for the involved metallic materials, including bipolar plates and seals. 

An additional component in a fuel cell is the interconnects or bipolar plates. This is a vital component in SOFC development, since it forms the connection between the anode of one cell and the cathode of the next in a stacked arrangement. That is, these components operate as connections between individual fuel cells in a fuel cell stack [128], Then, the interconnects have to be electronically conductive and also possess good impermeability, chemical stability, and good mechanical properties since these components seal the gas chambers for the oxygen and fuel gas feed at either the anode or the cathode [66,137],... 

Overall, the component reliability is a challenge to fnel cell mannfactnrers as well as their component snppliers. The stack is only one of several snbsystems in a PEM fuel cell system with hundreds of parts and components. Component compatibility, which includes both chemical and mechanical properties, plays an important role in system reliability and overall performance. To select the best materials/design for a system component, one mnst first stndy its properties (physical, chemical, mechanical, and electrochanical) nnder relevant conditions snch as temperature, pressure, and composition. Eor example, the reactant side of a PEM fuel cell bipolar plate (all sealing materials and plate components) mnst be able to tolerate high humidity, temperature... 

Oh, M.H., Yoon, Y.S., and Park, S.G., The electrical and physical properties of alternative material bipolar plate for PEM fuel cell system, Electrochim. Acta, 50, 111, 2004. 

During this period, the mechanical properties of the carbon composite bipolar plate material were assessed, including measurements of uniformity and defect distribution by infrared imaging. The results indicate good material uniformity and substantial resistance to torsional stresses. Significant improvement in the wetting of the material was demonstrated after a simple oxidation treatment. 

Develop carbon/carbon composite materials for bipolar plates that meet or exceed target property criteria... 

Developed two-sided embossed bipolar plates with excellent material properties, exhibiting the potential for low-cost production... 

Developed improved bipolar plate materials, exhibiting improved material properties and low-cost ingredients... 

The potential of embossing flow field patterns in the preform materials has also been investigated. A two-sided proprietary flow field pattern has been successfully transferred to the carbon/carbon material yielding near-net-shape bipolar plates. Subsequent materials property testing has confirmed adequate material properties. 

Table 1 shows preliminary materials properties measured on non-optimized bipolar plate materials produced through initial development work at PFCT Comparisons with published DOE goals are made in the table. Sealing of the plate through - through plate permeability is accomplished through the application... 

Preliminary work completed in this project includes laboratory and equipment setup and installation, and preliminary rounds of material optimization and process development. Full size bipolar plate prototypes have been produced with full double-sided flow patterns, demonstrating the potential of the manufacturing process. Process and material development has resulted in the characterization of material properties under a variety of composition levels. Material properties meeting or exceeding DOE targets have been measured, and bipolar plates, both machined and pattern-embossed, have been submitted to UTC Fuel Cells for in and out of cell testing. Phase I work will... 

In addition to the earlier described state of the art, nanotechnology plays a role in the development of micro fuel cells the realisation of special properties of surfaces and the enhancement of functionalities by nanostrnctnres, nanolayers as coatings and nanoparticles raise increasing interest. Nanostructnred electrolytes, carbon snp-ports or coatings for bipolar plates are examples. 

The materials for bipolar plates have to fulfil several requirements. The most important properties are the electrical and thermal conductivity. A review about the present state is given in [97]. The resistance of a PFM fuel cell usually is dominated by the membrane electrolyte, and thus the bipolar plate shall not significantly contribute to this value. Besides the bulk resistance of the material the contact resistance between bipolar plate and GDL has to be considered. A second important aspect is... 

The material properties of a bipolar plate, as summarized by Ruge and Buchi [6], must take into account several important factors ... 

As matrix polymers for the bipolar plate standard thermoplastic and technical polymers can be considered. For the developments at the Fraunhofer ICT polypropylene (PP) was used as a suitable polymer because of its material properties and also its low material price. With a service temperature of 100 °C PP is in the uncritical temperature range for the operating conditions in a PEMFC. 

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