Targets bipolar plate

Source U.S. Department of Energy. 2007. Technical targets Bipolar plates. Multiyear research, development and demonstration plan, http //wwwl.eere.energy.gov/hydrogenand-fuelcells/mypp/pdfs/fuel cells.pdf (accessed Dec. 2008). 

J62 I 73 Materials and Coatings for Metallic Bipolar Plates in Polymer Electrolyte Membrane Fuel Cells Table 13.1 US DOE technical targets bipolar plates [9]. 

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. 

Although it is difficult to determine the quantitative requirements of plate and plate materials appropriately for various fuel cells and different applications in a development phase, such a target would be helpful to direct the development effort and make necessary trade-offs. The cascaded performance requirement targets in 2010 and 2015 for bipolar plates of fuel cells in transportation applications were set by the U.S. DoE (Department of Energy) according to functions of the plate mentioned before and overall requirements of performance, reliability, manufacturability, and cost of a stack, as shown in Table 5.1 [7]. The technical target in the DoE s multiyear research, development, and demonstration plan has been popularly and worldwide... 

DoE 2010/2015 Performance Targets of Bipolar Plates for Transportation Fuel Cells ... 

Many alternative materials have been investigated to replace graphite in the fabrication of bipolar plates. The major candidate materials with potential to overcome the technical barriers and reach the targets mentioned in... 

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... 

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

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 summary, both TiN coating and surface plasma modification require suitable substrates with good corrosion resistance in PEMFC environments. These combinations provide economical ways to overcome the technical and cost barriers associated with PEMFC bipolar plates. Both substrate SSs and surface modification methods are cost-effective. It is considered that the DOE targets will be matched with such methods. 

Stainless steels, as well as A1-, Ni-, and Ti-based alloys have been studied extensively as possible candidates for bipolar plates. One of the most well-studied materials for bipolar plates is SS 316/316L (16-18% Cr, 10-14% Ni, 2% Mo, rest Fe) other candidates are 310,904L, 446, and 2205. Bare stainless steel plates form a passive 2-A nm chromium oxide surface layer under PEMFC conditiOTs that leads to unacceptably high ICRs. A similar trend is observed for the other alloys and therefore surface modification or surface coatings on selected substrate material has to be considered as a pathway to meet the technical targets of low ICR and high corrosion resistance. 

An additional requirement that has to be satisfied is a high level of surface hydrophilicity. Non-wettable plate surfaces result in unstable reactant flows that have to be countered with higher pressure drops and gas stoichiometries and hence higher parasitic power drains. This requirement has lead to the development of hybrid coatings that can provide the low ICR and high wettability. At this time, the bipolar plates account for 75% of the total stack weight and x% of the stack cost. Table 15.4 summarizes some of the targets for bipolar plates for automotive fuel cells. 

Table 15.4 Technical targets for automotive PEMFC bipolar plates [48]...

Direct hydrogen-fuel-cell-powered vehicles have reached a level of development where the major automotive companies have publicly announced that initiation of commercialization is imminent around 2015. The targets of performance, durability, and cost agreed upon by various organizations, including the US DOE, appear to be achievable in the specified time frame. Well-delineated pathways and strategies have been established to address the barriers of cost and durability of PEMFC stacks and achieve the automotive targets. The principal directions for reduction of cost and enhancement of durability of key fuel cell components, i.e., electrocatalysts, membranes, and bipolar plates are briefly summarized in this section. 

Trends in short- and lOTiger-term directions for key fuel cell components including electrocatalysts/supports, membranes, and bipolar plates have been elaborated in this section improvement of the performance and durability of these components will directly impact the entire automotive fuel cell system requirements, complexity, and cost. Durable catalysts with enhanced ORR activity, durable membranes that perform at very low humidity and durable bipolar plates that have low contact resistance will not only increase the power density and cost of the fuel cell stack but also simplify and lower/eliminate system component costs of the air compressor, humidification systems, recycle pumps, radiator, start-up/shutdown and freeze-start-related components, etc. A combination of advances in all the fuel cell components discussed above, system simplification, governmental policies that are sensitive to sustainable clean energy, and development of a hydrogen infrastructure will enable achieving the projected technical and cost targets needed for automotive fuel cell commercialization. 

Based on the technical functions described above, the US Department of Energy (DoE) suggested development targets for fuel cell components as shown in Table 19.1 for bipolar plates. These data are apparently based on communication with and input from conventional low temperature PEM fuel cell developers. Some of the data are directly transferred to the HT-PEM fuel cell technology. This has also been discussed by DoE [4] and Liao et al. [5]. However, depending on the specific application in HT-PEM fuel cells, priorities of the target values may significantly differ. 

Additionally, the chemical resistance of the bipolar plate can be characterized by measuring the corrosion current under a potential typical for fuel cell operation and using 85 % phosphoric acid as an electrolyte. The relevance, detailed parameters, and development targets of this corrosion test are still subject to technical discussions and depend on the anticipated application of the plate. The accepted corrosion current under reference conditions is lower for long... 

Table 19.1 Target specifications for bipolar plates in HT-PEM fuel cell applications...

Hence, technical and bipolar plate specific targets in the form of measurable values can be obtained from the current international literature today. The change of bipolar plate criteria for PEMFC can be shown by the well-established and documented targets of the United States Department of Energy (DOE). 

TABLE 6.1 Change of Technical Targets Concerning PEMFC Bipolar Plates (2003-2009)... 

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

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