FUEL CELLS-WHERE
ARE WE NOW?
A sharp look at deuelopments in f u e l cell technology and application. H o w f a r have w e progressed toward economic application R J
since IHEC’s April 7959 symposium feature?
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ost of the development of fuel cells has been comIn 1956, exploratory work on fuel cells was being carried out at only a few places around the world. In the U.S., only five companies were interested, and the military program was modest. Since then, growth of the world-wide effort has been exponential-in 1961, over 50 companies in the U.S. were actively engaged in fuel cell research. Confidence in the fuel cell concept is shown by the money laid out on research. In 1961, companyfunded research investment is estimated at 15 million dollars. This is matched by $4 million spent by the Government on fuel cells for military and space applications. What progress has been made using this investment? Fuel cells have not yet been devised to light our homes or power our automobiles. But two developments during the last two years stand out as major advances :
M pacted into the last few years.
--Not just one, but several companies have demonstrated their abzlzty t o produce hydrogen-oxygen fuel cells, useful for certain applications -Research woik now includes evaluation of medzum cost fuels such as methanol, propane, and ammonia. This zs a j r s t step toward Lehicula? power
s Military and Special Uses
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The first applications of fuel cells will be in areas where cost is of major importance. Progress on the hydrogenoxygen fuel cell is most advanced. Several variations have been built, ranging up to 20 hp. in size. These cells have made space flights, powered communications systems, and served as the engine for a tractor. Among the companies which have shown considerable progress in producing hydrogen-oxygen cells are : -General Electric -United Aircraft -Allis Chalmers
-Electro-Ojtzcal -Union Carbide -Thompson-Ramo- Wooldridge
The technology for these cells is quite well worked out. It is possible to predict size and weight, and evaluate the
possibilities and limitations of the cell for any application. They can be described as in the “hardware” stage of development. As far as production is concerned, however, even this system is in the preprototype stage. Though adapted to special uses, refinements are required to improve efficiency and dependability, and to reduce costs. It is predicted that in-flight space applications will be found within the next year or two, and that submarines may be powered by these systems in about three years. Utilizing Cheap Fuels and Oxidizers
For generating domestic and industrial power, cost of producing power becomes very important. Economics dictate use of such fuels as methane, propane, and kerosene, oxidized by air. Substantial progress has taken place in the development of high temperature systems, using molten-salt electrolyte. High temperature fuel cells using molten-carbonate electrolyte are under development at Sondes Place Research Institute and the Institute of Gas Technology. These systems are not as advanced as the hydrogen-fueled cells. There is still much to learn about the mechanism of the reactions, and it is not yet possible to predict what the power system will look like. The cell is in the stage of component testing; sizes approach 10 kw. Some of the problems of endurance, corrosion, reliability, and materials which plagued the pioneers have been solved. The economic goals which this system must reach are outlined on page 68, from C. G. von Fredersorff’s work. Handling, storage, logistic, and economic problems limit the utility of fuel cells using oxygen at the cathode. This is an I&EC StaffFeature, prepared with the assistance of: A . M . Moos, Vice President and General Manager of Leesona Moos Laboratories C. G. von Fredersdorff, Senior Chemical Engineer at the Illinois Institute of Gas Technology M . J . Schlatter, Senior Research Chemist in the Petroleum Products Division of California Research Cor$, AUTHOR.
VOL. 5 4
NO.
1
JANUARY
1962
65
Significant progress has been made in 1960 and 1961 as a result of fundamental work on the oxidizer electrode. A better understanding-of both fuel cell-electrode reaction mechanisms and structural requirements bas advanced the development of useful, practical air electrodes. Little information is available, because of the potential economic importance of this discovery.
Two general conclusions from methanol product studzes are: -Intermediates and prodwts formed at the anode are in no more reactive form than the Same substances added to the cell -A molecule need not be 6ompletelj oxidized, or even oxidiud to a relatively stable slate, before it is desorbed from thc electrode
U l i l i z i n ~ M d i u mCost Fuels
Future Implicolions
At the 1959 symposium, although methanol was mentioned as an "ideal fuel," no results were reported on low temperature fuel cells using medium cost fuels such as hydrazine, ammonia, ethylene, ethylene oxide, ethylene glycol, or methylamines. Recently, significant results have been reported here and abroad. Use of such fuels with air may be economically sound in a number of applications, ranging from replacement of industrial storage batteries to vehicular power. Further progress in this area depends on continued basic and fundamental work in electrode reactions, kinetics, and surface catalysis leading to a better understanding of the rate-determining processes. Recent work of the California Research Gorp., summarized on page 61, points out many possibilities and also debunks several beliefs-or hopes. Little is known of reaction paths of many of these oxidations. The graph helow shows the importance of the reaction path.
The advances in knowledge, the increase in research, development, and engineering hat have taken place in the last two years assure us that fuel cells will become successful and competitive power sources. The practical and commercial criteria for a fuel cell power plant can be defined as a function of intended application: high efficiency, low cost, minimum upkeep, long life, etc. Some of these criteria are met hy existing alreadyengineered systems. Although it is impossible to predict the progress of new knowledge, it seems certain that fuel cells will be competitive in some commercial applications within the next five to six years. However, it also seems certain that furl cells will not be used to power automobiles in that time interval. Five years from now, fuel cells will probably cost about 10 times as much as conventional internal combustion engines. Wider scale application will follow reduction in costs.
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The Methrmol Fuel Cell:
8
Hopes and Limitalionr
Methanol has been suggested as an ideal liquid fuel for fuel cells. Although good current densities have been achieved in such cells, there are problems which still must be solved before practical low temperature methanol fuel cells can be developed. In hasic electrolyte, formate is formed which is less reactive than methanol. This limits the performance of the cell. To be practical, either formate must be removed, with attendant loss of more than one third of the energy of the methanol fuel, or means must be found to accelerate the electrolytic oxidation of formate to carbonate. Furthermore, methods must be developed to remove product and rrplace hydroxide. In acidic electrolytes, on the other hand, complete oxidation of methanol to carbon dioxide and water and the removal of these products can be achieved without difficulty. However, the lower over-all cell potentials mean low efficiencies. Methanol cells with acidic electrolyte, designed for special uses, are approaching the development stage. But higher potentials and higher current densities must be obtained before cells likely to compete with oresent mobile powen witscan be produced. %
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F p r a 1. F u l cell pcrformarufs.af methanol and rodiumfarmate at 50° C. Mrthanol, 2% by volume; sodium 9o by weight; sodium hydroxide elccholvte, IS'% by weight *!
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.--66
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
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A t California Research Cor?. fuel cell performance o j many substances was determined at 250 ++80' C., using platinized porous carbon anodes. The reactiuity sequence (Table I ) shows several dzstinct grou$s. Some compounds which do not require catalytic electrodes (not
Table 1.
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Relative Reactivities of Reductants in Baric Electrolyte Fuel Cell
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shown in the table) are hydroquinone, p-aminophnol, mercaptides, and some inorganic sulfur compounds. The data collected in this study can be put together to deriue the gross effects of chemical structure on reactivity (Table I I ) .
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PRODUCING CHEMICALS AND POWER
Since no commercial application of this type of processing is in the ofiing, stBements regarding recovery of valuable chemicals as intermediates in fuel cell operation must be considered as strictly “blue-sky.” Some important work has been done, however. M. J. Schlatter has determined the products which can be separated from some fuel cell reactions. In a few cases, special circumstances may overcome economic objections. The most likely of these is the production of anhydrous hydrogen bromide from hydrogen and bromine, or production of large volumes of dilute sulfuric acid.
Household Power from Fuel Cells
A methane fuel cell power pack is potentially attractive for domestic use. The high temperature fuel cell was selected for economic analysis, to establish the goal for further cost reduction studies. Because of the steep voltage-current characteristics of fuel cells in general, and the normal variations of household loads, extreme voltage regulation would probably be needed. If the cells could be operated continuously to charge storage batteries, say at a load factor of 90%, the power pack capacity could be reduced by a factor of 4 or 5. One or more direct-current inverter units would be required to supply 60-cycle a x . service. Further, hightemperature fuel cel
IN BASIC ELECTROLYTE
-Secondary alcohols give electrochemically unreactive ketones -Primary alcohols yield stable carboxylates via renctive aldehydes -Formate is an exception-it can be slowly oxidired to carbonate -Mucaptides oxidize to d i d j i d e s -Sodium su@de converted to thiosulfate via polysuljde
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IN ACIDIC ELECTROLYTE
-Ethylene and propane give carbon dioxide --Sulfur dioxide yields sulfuric acid. But rates decrease sharply when the acid roncentration is inmeused above 5N -Hydrogen su@de gives sulfur, not sulfuric acid -Hydrogen and bromine can be reacted to give hydrogen bromide heat, and for maintaining the power pack at operating temperature. Ample waste heat would be available. For this system concept using natural gas, general mathematical relations were developed which involve costs, efficiencies, and payout time, based on a survey of the present state of the art. Figure 2 shows, for example, how investment cost would be related to payout time for several cost values of purchased electricity. Recovery of waste heat improved the economics equivalent to 20 to 30% reduction in payout time. For example, if the power pack investment must be paid out in 10 years, fuel cell investment cost can be no more than about $300 per kilowatt, based on reasonable assumptions. This goal seems attainable if recent manufacturing cost estimates for high-temperature molten carbonate fuel cells are confirmed. (Moos, A. M., “Evaluation Criteria for Fuel Cell Systems,’’ Spring Meeting, Electrochemical Society, Indianapolis, Ind., April 30 to May 3, 1961.) The effects of over-all system efficiency on payout time were also explored, for a fixed purchased power cost of 2.5 cents per kilowatt hour (Figure 3). With waste heat recovery, the effect of improving fuel cell efficiency from 30 to 60% is not of great significance, except that it mav determine the amount of waste heat available.
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ASSEMBLY INSTRUCTIONS
OTHER SIDE
You need only scissors, a razor blade and
a dress snap-fastener
CORRELATIONS FOR
i E A T TRANSFER COEFFICIENTS This chert giver the importmnt equations used in d c u l ~ t i n g reffirientr for man9 ond Row I ~ I
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IN5 JRUfilONS FOR ASSEMBLING 1. Using rduorr, cut out both dirks a l e q outline 2 Carefully cut out black areas M w c h disk with a rhorp stencil knife or ringle-edge razor blade.
3 Fw added proledion brush or spray (I coot of &ella< or pl.. -
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tic on both sides of disks.
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4. Fasten the Ewo dirks together with a dressmaker's mapfastener. If you prefer to a 3/16'' eyelet cut out center hole indicated by dotted line. Snap-fasteners and eyelets may be obtained d the notions counter of (I deportment store.
CUT ON OTHER $ID€ ON1r . .-
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