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

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

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

Advanced system analysis for indirect methanol fuel cell power plants for transportation applications

The indirect methanol cell fuel concept actively pursued by the USDOE and General Motors Corporation proposes the development of an electrochemical engine'' (e.c.e.), an electrical generator capable for usually efficient and clean power production from methanol fuel for the transportation sector. This on-board generator works in consort with batteries to provide electrical power to drive propulsion motors for a range of electric vehicles. Success in this technology could do much to improve impacted environmental areas and to convert part of the transportation fleet to natural gas- and coal-derived methanol as the fuel source. These developments parallel work in Europe and Japan where various fuel cell powered vehicles, often fueled with tanked or hydride hydrogen, are under active development. Transportation applications present design challenges that are distinctly different from utility requirements, the thrust of most of previous fuel cell programs. In both cases, high conversion efficiency (fuel to electricity) is essential. However, transportation requirements dictate as well designs for high power densities, rapid transients including short times for system start up, and consumer safety. The e.c.e. system is formed from four interacting components: (1) the fuel processor; (2) the fuel cell stack; (3) the air compression and decompression device; and (4) the condensing cross flow heat exchange device. 2 figs

Heat transfer through coals and other naturally occurring carbonaceous rocks

The understanding of heat transfer through solid fossil fuels is essential to the phenomenology of pyrolysis, gasification and combustion of these fuels. While coals have thermal conductivities of 0.1 to 0.5 W/mK at 300/sup 0/K, heat transfer measurements are complicated by the changes found in these fuels caused by the heating processes. Such complications are clearly shown when one looks at thermal conductivity differences between virgin and heat-treated materials. Coals, upon heating, undergo a variety of chemical and physical modifications. Initially, these materials lose low molecular weight gases; additional heating removes moisture. Such pyrolytic processes result not only in a significant mass decrease (as much as 50 percent for low-rank coals), but a marked alteration in the internal structure of the material. In virgin coals, mass transfer is dominated by a system of pores. Drying these materials typically alters the flow mechanisms and consequently the permeability. Heat transfer becomes dominated by the convective transport of products generated within the specimen during the heating process. Studies are described that explore the concurrent and counter-current heat and mass transfer problems through semiporous materials such as coals and other model specimens

Kinetic behavior of subbituminous coal drying; effects of confining pressure

A model is developed which explains the drying behavior of a subbituminous coal. This model, a variation of the moving-boundary approach, has the vapor-liquid interface in the macropores receding from the exterior surface of the coal as drying progresses. On the liquid side of the interface, liquid water exists in all three pore systems - macropores, transitional pores, and micropores. On the vapor side of the interface, in the transitional and micropore systems branching off the macropores, the moisture essentially is in equilibrium with the water vapor in the macropore system. Water diffuses from the liquid interface in the macropores through these pores to the exterior surface of the coal. Experiments with a Washington State subbituminous coal are described which test this model. The predictions of the model match the behavior of experimental drying curves. The effective diffusivities obtained were within the range expected for the constricted pore systems which coal possesses. Higher initial stresses apparently decrease the total porosity and increase the severity of pore constrictions. Disparities between model prediction and experimental behavior, which occurred at a late drying time, result from the assumed water adsorption isotherm