Design and testing criteria for bipolar plate materials for PEM fuel cell applications

Bipolar plates for proton exchange membrane (PEM) fuel cells are currently under development. These plates separate individual cells of the fuel cell stack, and thus must be sufficiently strong to support clamping forces, be electrically conducting, be fitted with flow channels for stack thermal control, be of a low permeability material to separate safely hydrogen and oxygen feed streams, be corrosion resistant, and be fitted with distribution channels to transfer the feed streams over the plate surface. To date, bipolar plate costs dominate stack costs, and therefore future materials need to meet strict cost targets. A first step in the bipolar plate development program is an assessment of design constraints. Such constraints have been estimated and evaluated and are discussed here. Conclusions point to promising advanced materials, such as conductive, corrosion resistant coatings on metal substrates, as candidates for mass production of fuel cell bipolar plates. Possible candidate materials are identified, and testing procedures developed to determine suitability of various materials

The rate of isothermal hydration of polyperfluorosulfonic acid membranes

Water transport rates through polyperfluorosulfonic acid membranes at relatively low water content (close to the fuel cell failure mode) were investigated using dynamic thermogravimetry. A model was developed to describe water transport within the membrane during the dynamic thermogravimetry experiment. Using the model, the experimental data, and a nonlinear regression technique, values for the effective diffusion coefficient of water in the Dow Chemical Company's experimental membrane samples of the same equivalent weight but of two different thickness, 10.16 µm and 17.78 µm, were obtained for temperatures of 60oC, 80oC, and 90oC. Results show that the effective diffusion coefficient of water in the membrane increases with water content and temperature. Values for the partition coefficient of water in these membranes at these temperatures are determined and found to be in close agreement with published values. Finally, rehydration of polyperfluorosulfonic acid membranes is found to be controlled by both the gas/solid interface and the diffusion of water into the inner structure of the membrane

Primary and secondary electrical space power based on advanced PEM systems

For new space ventures, power continues to be a pacing function for mission planning and experiment endurance. Although electrochemical power is a well demonstrated space power technology, current hardware limitations impact future mission viability. In order to document and augment electrochemical technology, a series of experiments for the National Aeronautics and Space Administration Lewis Research Center (NASA LeRC) are underway at the Los Alamos National Laboratory that define operational parameters on contemporary proton exchange membrane (PEM) hardware operating with hydrogen and oxygen reactants. Because of the high efficiency possible for water electrolysis, this hardware is also thought part of a secondary battery design built around stored reactants - the so-called regenerative fuel cell. An overview of stack testing at Los Alamos and of analyses related to regenerative fuel cell systems are provided in this paper. Finally, this paper describes work looking at innovative concepts that remove complexity from stack hardware with the specific intent of higher system reliability. This new concept offers the potential for unprecedented electrochemical power system energy densities

Recent trends and developments in pyrolysis-gas chromatography: review

Pyrolysis-gas chromatography (Py-GC) has become well established as a simple, quick and reliable analytical technique for a range of applications including the analysis of polymeric materials. Recent developments in Py-GC technology and instrumentation include laser pyrolysis and non-discriminating pyrolysis. Progress has also been made in the detection of low level polymer additives with the use of novel Py-GC devices. Furthermore, it has been predicted that future advances in separation technology such as the use of comprehensive two-dimensional gas chromatography will further enhance the analytical scope of Py-GC

Synthesis of hydrocarbons in the earth's crust

This report suggests an alternative theory for the generation and migration of petroleums. Considerable evidence supports the conclusion that life processes persist deep within terrestrial and marine environments. Such in vivo processes may survive in photon-free ecologies using mechanisms that both reduce carbon dioxide and oxidize sulfides. These in vivo conversions create petroleums

Recovery of minerals from US coals

Projections show that domestic coal will serve for the majority of energy supplies during the next decades. Thorough chemical cleaning of this coal can be accomplished in long residence time, slurry transport systems to produce high-quality fuel product. Concurrently, mineral recovery from coals will supplement existing ores. This paper describes this concept and given preliminary engineering considerations for mineral recovery during transport operations

The effects of light intensity on epipelic algae and associated fauna.

Our research examined the effect of light intensity on this benthic FPOM community. The primary goal of this study was to examine the benthic FPOM community and describe the assemblage of algae, diatoms, and meiofauna found there. Effects of light on this community wass assessed by surveying these habitats in different regions of a stream with different light levels and by experimentally manipulating light in artificial streams. The research was begun with several predictions; first, at higher irradiances production of epipelic algae and diatoms will increase. Second, this increase in primary productivity may in turn generate greater densities of meiofaunal grazers, larger grazers, and a shift in the community structure of meiofauna. Third, the alga assemblages may shift from one dominated by the more shade tolerant diatoms in the lowest light treatments to a chlorophyte dominated assemblage in the highest light treatment. Finally, this shift in the alga assemblage should be accompanied by a corresponding shift in the associated fauna. Chlorophytes often support their own community of diatoms and organisms.http://deepblue.lib.umich.edu/bitstream/2027.42/54640/1/3080.pdfDescription of 3080.pdf : Access restricted to on-site users at the U-M Biological Station

Characterization of PEM fuel cell membrane-electrode-assemblies by electrochemical methods and microanalysis

Characterization of Membrane Electrode Assemblies (MEAs) is used to help optimize construction of the MEA. Characterization techniques include electron microscopies (SEM and TEM), and electrochemical evaluation of the catalyst. Electrochemical hydrogen adsorption/desorption (HAD) and CO oxidation are used to evaluate the active Pt surface area of fuel cell membrane electrode assemblies. Electrochemical surface area measurements have observed large active Pt surface areas, on the order of 50 m{sup 2}/g for 20% weight Pt supported on graphite. Comparison of the hydrogen adsorption/desorption with CO oxidation indicates that on the supported catalysts, the saturation coverage of CO/Pt is about 0.90, the same as observed in H{sub 2}SO{sub 4}. The catalyst surface area measurements are nearly a factor of 2 lower than the Pt surface area calculated from the 30 {angstrom} average particle size observed by TEM. The electrochemical measurements combined with microanalysis of membrane electrode assemblies, allow a greater understanding and optimization of process variables

Night storage and backup generation with electrochemical engines

Li/I/sub 2/ electrochemical engines both store and generate electric power. These dual capabilities complement solar photovoltaic generation in critical areas: Photovoltaics need backup storage at least for nights and, if possible, for two or three days' needs. Such storage must be relatively cheap and compact--aqueous batteries would have trouble filling these requirements. Likewise, photovoltaics need backup generation based on combustion of fossil fuels for periods of bad weather--solar residences or communities will probably have to supply their own backup generation because central generating stations cannot be expected to keep large amounts of equipment on standby for solar users. Li/I/sub 2/ engine designs are described which could be developed to fill these needs of solar users, i.e., storing electricity generated by photovoltaics and generating additional electricity from fossil fuels as needed. Calculations based on laboratory performance indicate that the devices could be simple to manufacture, economically competitive, and efficient both in storage and generation. These engines also could directly use solar energy from focused and tracking solar collectors, or they could indirectly use solar energy through the combustion of biomass materials

Evaluation of the humidification requirements of new proton exchange membranes for fuel cells

Measurements of PEM fuel cell device performance were made with different gas inlet temperatures and relative humidity using a newly-designed test fixture. Significant improvement in device performance was observed when the fuel inlet temperature was increased above the operating temperature of the cell. These measurements were then correlated to a model to describe energy and mass transport processes. Proton exchange membrane (PEM), fuel cells--the focus of this study--use an ion conducting polymer, especially polyperfluorosulfonic acid materials. These polymer materials, when imbibed with water, exhibit solution-like properties, but because the anions are chemically bound to the polymeric structure, the electrolyte is contained. Importantly, product water removal is simplified, as electrolyte dilution is not a concern. However, the proton transport rate is a function of the polymer geometry, which is set, in part, by the polymer water content. Consequently, dynamics of water flow are essential to understand the design of efficient conversion devices