NonPt Catalysts
The high perceived cost and relatively high overpotentials associated with Pt-based cathode catalysts has led to an intense investigation of alternative non-precious-metal catalyst systems, both initially for PAFC and now for PEMFC. Recent literature has shown that Ru-based chalcogenides, pyrolyzed Fe and Co macrocycles, and metal carbides all show significant oxygen reduction. In addition, many of these catalysts show good selectivity towards oxygen in the presence of methanol, which may allow...
The Fueling Problem Fuel Cell Systems
Trier University of Applied Sciences, Umwelt-Campus Birkenfeld Pressure Cylinders Liquid Hydrogen Metal Hydrides Fuel Storage Capacities Reformer Technology Steam Reforming SR Partial Oxidation POX Autothermal Reforming ATR Comparison of Reforming Technologies Methanation Preferential Oxidation Palladium Membranes Anode Solutions The Right Fuel Fuel Cell Power Systems Primary Fuels and Fuel Cleanup Fuel Cell Technology Based on Renewables Renewable Hydrogen from Water Electrolysis Biomass and...
Use of Air Bleeds
The alternative to the use and development of CO-tolerant anode catalysts has been the practice of adding an oxygen or air bleed to the fuel stream, prior to contacting the MEA. The residual CO is then oxidized by the anode catalyst layer to a level that does not degrade anode performance Gottesfeld, 1990 Gottesfeld and Pafford, 1988 see Fig. 6.7 . Although this practice is effective, it has some disadvantages. The exotherms resulting from the gas-phase oxidation of CO and H2 in the vicinity of...
General Design Features
The proton exchange membrane fuel cell, PEMFC, takes its name from the special plastic membrane used as the electrolyte. Robust cation exchange membranes were originally developed for the chlor-alkali industry by DuPont and have proved instrumental in combining all the key parts of a fuel cell, anode and cathode electrodes and the electrolyte, in a very compact unit. This membrane electrode assembly MEA , not thicker than a few hundred microns, is the heart of a PEMFC and, when supplied with...
Molten Carbonate Fuel Cell
Alkali metal carbonates were among the many compounds used during the development of the direct coal fuel cell, but they emerged from the other salts because of their compatibility with the products of the oxidized fuel. The work was influenced by Baur and Preis 1937 in Switzerland, Davtyan beginning in 1946 in Russia, Broers and Ketelaar 1960 in the Netherlands, Baker et al. beginning in 1960 at the Institute of Gas Technology, and Douglas 1960 at General Electric Company. With the goal of...
Electrovan by General Motors
General Motors developed the Electrovan to evaluate the fuel cell as a power system for transportation vehicles Marks et al., 1967 . The alkaline fuel cells were manufactured by Union Carbide Corporation, incorporating the thin-electrode design Fig. 2.12 , and were capable of producing 32 kW continuous and 160 kW for short durations. Thirty-two fuel cell modules were installed in a section of the body of the vehicle, mostly under the floor, as shown in Fig. 2.18. The electrolyte was aqueous...
Bipolar Plates
Flow field plates in early fuel cell designs and still in use in the laboratory were usually made of graphite into which flow channels were conveniently machined. These plates have high electronic and good thermal conductivity and are stable in the chemical environment inside a fuel cell. Raw bulk graphite is made in a high-temperature sintering process that takes several weeks and leads to shape distortions and the introduction of some porosity in the plates. Hence, making flow field plates is...
Japanese Companies and the Moonlight Project
At the same time that phosphoric acid fuel cells were being demonstrated in Japan, Japanese companies were developing their own fuel cell technology with support from the government as reviewed by Appleby and Foulkes, 1989 . The goal of the Moonlight Project in Japan was to develop energy conversion systems with efficiencies higher than those attainable in 1974. In 1981, fuel cell technology was transferred from the Sunshine Project to the Moonlight Project as part of a ten-year plan to develop...
Ballard Power Systems
Ballard Power Systems Prater, 1990 began development of solid polymer fuel cell technology in 1984 under contract to the Canadian Department of National Defense, which had determined in 1983, with the Canadian National Research Council, that the technology could be applicable in the military as well as commercial products. The first goal was to develop stack hardware to operate on hydrogen and air as well as pure oxygen , and the second goal was to demonstrate operation on products of reformed...
Fueling Options
Hydrogen is required for all low- and medium-temperature fuel cells, i.e., the alkaline fuel cell AFC , the proton exchange membrane fuel cell PEMFC , and the phosphoric acid fuel cell PAFC see Table 1.1 in Chapter 1 . Generally, the demand for hydrogen purity decreases with increasing operating temperature. While the PEMFC cannot operate when carbon monoxide CO is present in the fuel gas at concentrations of more than a few ppm Cooper et al., 1997 Hoogers and Thompsett, 1999 , the PAFC, with...
Domestic Heat and Power Generation
The majority of currently active fuel cell developers are focusing on the residential and small commercial power market in the range 1 to 20 kWel. These include traditional, leading fuel cell companies and startups that sometimes originate from a university laboratory or have some other technology base. A number of these companies have substantial financial backing from leading utilities see below . One of the attractions of this market lies in the belief that target cost, approximately 1000...
The Nernst Equation and Open Circuit
The general expression in Eq. 3.63 , which was derived for gas mixtures, can be converted to an expression for electrochemical equilibrium by using the work relationship presented earlier in Eq. 3.36 . where We is the electrochemical work, ne is the number of electrical charges electrons or protons transferred in the reaction, F is the charge carried by a mole of electrons or protons , and E is the voltage difference across the electrodes. The change in Gibbs energy is equal to the negative of...
Voltage EfficiencyandPowerDensity
Figure 4.3 shows a typical current voltage curve, broken down into the respective performance losses. The cell voltage at open circuit, the open circuit voltage OCV , usually does not reach the theoretical value of the reversible cathode potential at the given temperature and pressures as discussed in Chapter 3, for standard conditions, this would be 1.23 V . When no current is drawn from the cell, parasitic electrochemical processes show up next to the main two reactions, hydrogen oxidation...
Autothermal Reforming ATR
Attempts have been made to combine the advantages of steam reforming and partial oxidation. Ideally, the exothermal reaction Eq. 5.4 would be used for start-up and for providing heat to the endothermal FIGURE 5.7 Johnson Matthews modular HotSpot fuel processor. Each unit generates 6000 liters of hydrogen per hour, equivalent to 750 liters of hydrogen per hour per HotSpot module. Courtesy of Johnson Mattthey. FIGURE 5.7 Johnson Matthews modular HotSpot fuel processor. Each unit generates 6000...
Nafion Electrolyte Jet Propulsion Laboratory
Development of the direct methanol fuel cell DMFC was revived after the success of the solid polymer fuel cell SPFC . Jet Propulsion Laboratory began developing a DMFC with a Nafion membrane around 1992 with Giner Inc. and the University of Southern California Surampudi et al., 1994 Narayanan et al., 1998 . Because of the solid polymer electrolyte, the methanol fuel was delivered to the anode liquid-feed rather than through the electrolyte as had been done with the sulfuric acid electrolytes....
Kinetic Performance
When operating on pure hydrogen, the anode stays at a potential close to the theoretical reversible potential of a hydrogen electrode, i.e., Er 0 V compare Eq. 4.1 . In electrochemical terminology, this corresponds to a low overpotential indicative of a kinetically facile reaction. For the moment, we will therefore neglect the anode contribution towards the cell voltage, assuming an anode potential of 0 V. Since the cell voltage is the difference between anode and cathode potential, the cell...
Outlook
Based on what has been said in this chapter, the following certainly subjective conclusions may be drawn. Large central power generation using fuel cell technology will only be viable when sufficiently high electric efficiencies particularly operating on coal gas can be obtained. Currently, only SOFC technology in combined cycle processes with gas turbines offers this potential, but cost reduction still has a long way to go. A number of developers are competing for the 100- to 100- kW...
Stationary Power Generation
8.1 Fuel Cell Technology for Stationary Power Generation The PAFC The MCFC The SOFC Fuel Impurities 8.2 Large-Scale Central Power Generation and Small-Scale CHP Systems The PEMFC as a CHP System The PAFC as CHP System The MCFC as Small-Scale CHP System and Large Central Power Plant The SOFC as Small-Scale CHP System and Large Central Power Plant Trier University of Applied Sciences, Umwelt-Campus Birkenfeld 8.3 Domestic Heat and Power Generation The PAFC for Domestic Heat and Power Generation...
Supports
The requirements of a support for an active electrocatalyst were outlined above. It must provide structural, conductive, and durable support for the active metal particles. By far the most common support materials used in PEMFCs are carbon blacks. For an in-depth review of carbons, their properties and uses, the reader is directed towards the excellent book by Kinoshita 1988 . A brief summary of the typical carbons used in PEMFC will be provided here. 4Or NEXAFS near edge x-ray adsorption line...
Membranes and Ionomers
The strong interest in the PEM fuel cell stems from the advantages of using a solid polymer electrolyte. Solid polymer electrolytes form a thin but sound electronic insulator and gas barrier between the two electrodes while allowing rapid proton transport and high current densities. This, in turn, allows the high cell and stack power densities vital for automotive applications. Once put in place, the solid electrolyte does not redistribute, diffuse, or evaporate, making intermittent operation...
Methanation
When looking at the reformer gas composition, an obvious first thought might be the removal of CO by reacting it with hydrogen according to the methanation reaction, i.e., the reversal of Eq. 5.3 . CO 3H2 CH4 H2O g AH -206 kJmol-1 5.5 Although viable in principle, this reaction is not suited to the task of removing CO from reformer gas for two major reasons. First, each CO molecule is removed at the expense of three hydrogen molecules. At CO levels around 2 , this technique painfully cuts into...
References Jlc
Adams, A.A., Coleman, A.J., and Joyce, L.S., Fuel Cell Seminar, Orlando, FL, November 13-16, 1983, p. 118. Adams, R. and Shriner, R.L., J. Am. Chem. Soc., 45, 2171, 1923. Alonso-Vante, N. and Tributsch, H., Nature, 323, 431, 1986. Alonso-Vante, N. and Tributsch, H., in Electrochemistry of Novel Materials, Vol. 3, Lipkowski, J. and Ross, P.N., Eds., VCH, New York, 1994, p. 1. Appleby, A.J., J. Electroanal. Chem., 357, 117, 1993. Atanassova, P. et al., Abstract 333, Proceedings of the 200th ECS...
Fuel Cell Electrodes and Gas Diffusion Layers
Modern fuel cell electrodes are gas diffusion electrodes GDEs that consist of a gas porous layer of high surface area catalyst and a gas porous, electrically conducting gas diffusion layer, or electrode substrate or electrode backing material compare Fig. 4.1. Two similar electrodes, anode and cathode, are in intimate contact with the polymer electrolyte membrane. Views differ on whether the term electrode' denotes just the layered catalyst structure attached to the membrane or whether it...
Davtyan
As well as developing a high-temperature fuel cell Section 2.4.1 , Davtyan also experimented with a low-temperature fuel cell that used an alkaline electrolyte and operated at atmospheric temperature and pressure Davtyan, 1946, in Bacon, 1954 . The electrolyte was an aqueous solution of potassium hydroxide 35 , the hydrogen oxidation catalyst was activated carbon impregnated with silver, and the oxygen reduction catalyst was activated carbon impregnated with nickel. The catalyst was bound by...
Broers and Ketelaar
Testing the electrolyte formulations of Davtyan was the starting point for Broers and Ketelaar 1960 in their work on molten carbonate fuel cells at the University of Amsterdam. The conclusion of their investigation begun in 1951 was that the state of the electrolyte, which was supposed by Davtyan to have been solid, was actually two phases a molten phase consisting of carbonates, phosphates, tungstates, and silicates a eutectic salt mixture and a solid phase of rare earth oxides. The solid...
LargeScale Central Power Generation and SmallScale CHP Systems
Table 1.1 in Chapter 1 gives an estimate of the electric efficiencies to be expected from various fuel cell systems. For low-temperature PEMFC- and PAFC-based systems, these range between 35 and 45 . The efficiency is probably best known for the ONSI more recently IFC and lately UTC Fuel Cells PC25C system, which to date is the most commercially successful fuel cell system, with close to 250 units sold worldwide. The electric efficiency starts at a maximum of 42 at the beginning of life and...
Reformer Technology
Hydrogen is currently produced in large quantities primarily for two applications. Roughly 50 of the world hydrogen production is used for the hydroformulation of oil in refineries producing mainly automotive fuels. Approximately 40 is produced for subsequent reaction with nitrogen to ammonia, the only industrial process known to bind atmospheric nitrogen. Ammonia is used in a number of applications, especially fertilizer production. It is useful, however, to put the current industrial output...
Grubb and Niedrach at General Electric
Grubb and Niedrach 1960 developed a fuel cell with a solid ion-exchange membrane electrolyte in 1960. The ion-exchange membrane was a polymer sheet, 0.06 cm thick, made of cross-linked polystyrene with sulfonic acid HSO3 groups at the ends of the side chains and bound with an inert binder. According to Grubb 1959, in Grubb and Niedrach, 1960 , the membranes, in the hydrogen form, had a conductivity equivalent to that of a solution of 0.1 N Normal, 0.5 M sulfuric acid, H2SO4. But to maintain...
Haber and Bruner
Haber and Bruner 1904 worked on direct coal fuel cells, which were called the Jacques element, investigating the electrical potential of iron electrodes in molten alkaline electrolytes and finding that the coal first reacted with the electrolyte, which made it an indirect coal fuel cell. Haber and Bruner pointed out that caustic soda sodium hydroxide, NaOH contained manganese as an impurity, and even technicalgrade iron also contained manganese. This manganese would become oxidized in the...
Maximum Thermal Efficiencies
The thermal efficiency of a heat engine is determined by the amount of work the engine can perform with the thermal energy supplied to the system. The heat, Qin, is released from the fuel when it is oxidized and is transferred to the working fluid in the case of an external combustion engine . The expansion of the working fluid the combustion gases themselves in an internal combustion engine is harnessed by machinery and converted to mechanical work, Wnet. Equation 3.34 is the general...
Prototypes and Examples
The purpose of this section is not the in-depth discussion of business opportunities for new fuel cell start-ups. For each potential application, one is advised to do a thorough technical, market, and cost analysis that goes well beyond the scope of this book. It would appear that existing developers have not always done this. The intent here is merely to show typical examples within this rapidly developing set of fuel cell applications and name leading developers. The list of developers is far...
Technological Challenges Prior to DMFC Commercialization
Although the DMFC relies on thermodynamically favorable reactions, in practice both the anode and the cathode electrodes are kinetically limited due to the irreversible nature of the reactions. While this is also the case for the cathode reaction of the H2 PEMFC, which is identical to Eq. 7.2 , the anode reaction of the PEMFC is not performance limiting. In the DMFC, however, both anode and cathode suffer from similarly large overpotentials as shown in Fig. 7.4 later in this chapter. The key...
References
Alder Wright, C.R. and Thompson, C., Note on the development of voltaic electricity by atmospheric oxidation of combustible gases and other substances, Proceedings of the Royal Society of London, 46, 372-376, 1889. Anahara, R., Research, development, and demonstration of phosphoric acid fuel cell systems, in Fuel Cell Systems, Blomen, L.J.M.J. and Mugerwa, M.N., Eds., Plenum Press, New York, 1993, pp. 271-343. Andrew, M.R. and Glazebrook, R.W., Electrolyte-soluble fuels, in Introduction to Fuel...
The PEMFC as a CHP System
Ballard is currently the only developer of PEMFC-based power systems in the 250-kW range. Ballard has developed these systems since the mid-1990s, and stationary power systems below 1 MW are now being developed by Ballard Generation Systems BGS , a partnership between Ballard Power Systems, GPU International, Alstom, and Ebara Corporation. GPU International is an international energy company based in New Jersey. Alstom is a world leader in the design and manufacture of equipment and systems for...
References Epu
Anderson, A.B. and Grantscharova, E., J. Phys. Chem., 99, 9149, 1995. Arico, A.S. et al., Electrochim. Acta, 39, 691, 1994. Burstein, G.T. et al., Catalysis Today, 38, 425, 1997. Cameron, D.S. et al., Direct methanol fuel cells recent developments in search of improved performance, Platinum Metal Rev., 31, 173, 1987. Christensen, P.A., Hamnett, A., and Potter, R.J., Ber. Bunsenges. Phys. Chem., 94, 1034, 1990. Chrzanowski, W. et al., J. New Mater. Electrochem. Syst., 1, 31, 1998. Franaszczuk,...
References Tdt
Antonlini, E. et al., Influence of nafion loading in the catalyst layer of gas diffusion electrodes for PEFC, J. Power Sources, 77, 3, 1999. Bahar, B. et al., U.S. Patent 5,547,551, 1996. Barbir, F., Braun, J., and Neutzler, J., Effect of Collector Plate Resistance on Fuel Cell Stack Performance, 1997. Basura, V.I., Beattie, P.D., and Holdcroft, S., Solid-state electrochemical oxygen reduction at Pt Nafion 117 and Pt BAM3G 407 interfaces, J. Electroanalyt. Chem, 458, 1, 1998. Buchi, F.N.,...
Metal Hydrides
Most elements form ionic, metallic, covalent, or polymeric hydrides or mixtures thereof Greenwood and Earnshaw, 1984 . The ionic and metallic types are of particular interest because they allow reversible storage of hydrogen Sandrock, 1994 . FIGURE 5.3 The package study for MINI Cooper Hydrogen has a hydrogen tank that fits into the body of the MINI. Photograph coutesy of BMW. FIGURE 5.3 The package study for MINI Cooper Hydrogen has a hydrogen tank that fits into the body of the MINI....
Baur and Brunner
Baur and Brunner 1935 returned to the problem of the direct coal air chain despite the problems associated with it high temperatures, ash formation, dilution of the fuel gases by carbon dioxide and water vapor , focusing their efforts on carbonate electrolytes. The electrolyte was a mixture of salts containing eight parts of K2CO3, seven parts of Na2CO3, and six parts of NaCl with some borates. With carbon as the anode electrode and platinum the cathode, they operated the cell at 500 to 600 C...
Baur and Preis
Baur and Preis 1937 , in the article immediately following that of Baur and Brunner 1937 , reported on investigations into suitable solid electrolytes and a design of a cell. According to Baur and Preis, earlier, in 1916, Baur and Treadwell had applied for a patent, but it seemed at the time that coal chains would work only with molten electrolytes. After the investigation by Baur and Brunner, it was decided that solid conductors deserved serious developments to lower their resistance, and Baur...
Pratt Whitney Aircraft Division and the TARGET Program
The culmination of the TARGET program Team to Advance Research for Gas Energy Transformation in 1975 was the demonstration in homes of phosphoric acid fuel cells operating on natural gas Appleby and Foulkes, 1989 . The program was initiated in 1967 by Pratt amp Whitney Aircraft Division of the United Technologies Corporation, responsible for developing the fuel cell, with sponsorship from 32 U.S. gas companies that wanted a share of the electricity market at a time when heating for homes was...
Partial Oxidation POX
The second important reaction for generating hydrogen on an industrial scale is partial oxidation POX . It is generally employed with heavier hydrocarbons Dams, 1996 or when special preferences exist because certain reactants for example, pure oxygen are available within a plant. It can be seen as oxidation with less than the stoichiometric amount of oxygen for full oxidation to the stable end products, carbon dioxide and water. For example, for methane CH4 1 2O2 CO 2H2 AH -36 kJmol-1 5.4a CH4...
The ButlerVolmer Equation
The heterogeneous rate coefficient, k, in Eq. 3.76 is a function of the Gibbs energy of activation, and its expression is derived from the Transition State theory see Atkins, 1998, Chapter 27 . Because an electrochemical reaction occurs in the presence of an electric field, the Gibbs energy of activation in Eqs. 3.77 and 3.78 includes both chemical and electrical terms A G AGc n_FA reduction 3.77 AG AGc - n 1 - oxidation 3.78 The subscript c is the chemical component. The electrical component...
The MCFC as SmallScale CHP System and Large Central Power Plant
FuelCell Energy is based in Danbury, CT, and has a second facility in Torrington. The company was formed out of Energy Research Corporation founded in 1969 , which is probably best known for setting up the largest fuel cell power plant ever operated in the North America the Santa Clara Demonstration Project, with a nominal electric power output of 2.5 MW. Like other demonstration plants, it was based on 300-kW MCFC stack technology called Model 9000. Current plant sizes are 300 kW, 1.5 MW, and...
Justi and Winsel and the DSK Electrodes
Justi and Winsel 1961 started their research in 1943 and focused on the electrodes for hydrogen and oxygen fuel cells operating at temperatures below 100 C and pressures below 4 atm. Their gas diffusion electrodes were named Doppelskelett-Katalysator Double Skeleton Katalyst, DSK electrodes because the catalyst, considered a skeleton itself, was held by a skeleton that provided mechanical stability, form, and electrical conductivity. The hydrogen electrode was developed before the oxygen...
The Gaseous Voltaic Battery
Before it went by the name fuel cell Rideal and Evans, 1922 , it was first known as the gaseous voltaic battery Grove, 1842 . The gaseous voltaic battery of Grove used platinum electrodes and sulfuric acid electrolyte, with hydrogen and oxygen as reactants. At that time, platinum was already known to be a catalyst for the reaction between hydrogen and oxygen, and the first published experimental results of Grove were an important illustration of that principle Grove, 1839 . Schoenbein had...
The Phosphoric Acid Fuel Cell
The phosphoric acid fuel cell was developed to use natural gas, but with the fuel first chemically reformed to produce hydrogen. Because a byproduct of the reforming reaction was carbon monoxide, which would lower the efficiency of the anode, the fuel cell temperature was raised to increase the rate of carbon monoxide removal. Phosphoric acid could be used with platinum electrodes at temperatures above 100 C, but sulfuric acid could not because it would be chemically reduced in the presence of...
Baur and Ehrenberg
Baur and Ehrenberg 1912 followed the work of Taitelbaum 1910, in Baur and Ehrenberg, 1912 , selecting molten silver as the cathode for a coal cell because of its good oxygen-dissolving properties. With one electrode having been selected, they investigated different electrolytes, which they identified as having to be melts in order to maintain the temperature. The anode material could be either the carbon itself or, for gaseous fuels such as hydrogen and carbon monoxide, a metal but,...
Mond and Langer
The new form of gas battery described by Ludwig Mond and Carl Langer in 1889 was more than an improvement it was the prototype for the practical fuel cell. These researchers considered their main contribution as being a solution to the problem of electrode flooding, caused by a liquid electrolyte. The sulfuric acid could be held in place by using a matrix Grove , as well as later investigators, overlook one important point, viz., the necessity of maintaining the condensing power of the...
Apollo Space Missions
Pratt amp Whitney Aircraft began developing the fuel cell power plant for the Apollo Command and Service Module in March 1962 Morrill, 1965 . The fuel cell was model PC3A-2, and three were used to supply the electricity for life support, guidance, and communications for the module, as well as water for the crew throughout the two-week missions to the moon. The PC3A-2 had a mass of 109 kg 240 pounds , and the dimensions were approximately 57 cm 22.5 inches in diameter and 112 cm 44 inches in...
Liquid Fuel The Direct Methanol Fuel Cell
No doubt one of the most elegant solutions to the fueling problem would be to make fuel cells operate on a liquid fuel. This is particularly so for transportation and the portable sector. The direct methanol fuel cell DMFC , a liquid- or vapor-fed PEM fuel cell operating on a methanol water mix and air, therefore deserves careful consideration. The main technological challenges are the formulation of better anode catalysts to lower the anode overpotentials currently several hundred millivolts...