HISTORY | Fuel Cells

Fuel Cells P Kurzweil, University of Applied Sciences, Amberg, Germany & 2009 Elsevier B.V. All rights reserved.

Early Insights into Energy Conversion Together with the electric motor, the dynamo, the gas turbine, the internal combustion engine, and the fused salt electrolysis of aluminum, the industrial revolution of the nineteenth century brought about the fuel cell – the silent or cold combustion of fossil fuels by the electrochemical oxidation with atmospheric oxygen to water and carbon dioxide. Fuel cells convert the chemical energy stored in the fuel directly into electricity, without any detour using heat. Wilhelm Ostwald, in 1894, emphasized the high efficiency and the nonpolluting properties of the direct conversion of chemical energy into electricity – in contrast to the then combination of steam engine and dynamo, which reached only about 10% efficiency at that time. Direct coal fuel cells designed for the propulsion of ships, however, have not become a reality so far. Instead of fuel cells and batteries, internal combustion engines determined the twentieth century. Against the background of the oil crisis and the long-term scarcity of natural gas, crude oil, and coal, new hopes have focused on fuel cell technology, which saw the first splendid applications during the space programs of the 1960s, in submarines since the 1980s, and in experimental zeroemission vehicles (ZEVs) since the 1990s. Scho¨nbein’s Pioneering Work At the time when there was no general understanding of electricity, when the physical meaning of voltage, current, and power was not yet clear, when electricity’s strength was measured by the sensation of electric shocks, the length of an arc, or the amount of gas liberated by electrolysis, in 1839, Christian Friedrich Scho¨nbein (1799– 1868), professor at the University of Basel, discovered the fuel cell effect during his studies on the electrolysis of diluted sulfuric acid and other matters. Scho¨nbein presented his discovery at the 1839 meeting of the British Association for the Advancement of Science at Birmingham, from which he received a grant of 40 Pounds Sterling ‘‘for defraying the expenses of certain Experiments on the connexion between Chemical and Electrical Phenomena.’’ His article appeared in the January 1839 edition of ‘The London, Edinburgh, and Dublin Philosophical Magazine’, in short, ‘Philosophical Magazine’. During his electrochemical studies, Scho¨nbein noticed a strange ‘electric smell’ that followed the passage of the

generated electricity in electric arcs. With the aid of a platinum zinc battery, which Scho¨nbein had purchased from his friend Grove during his visit to England, he was able to generate enough substance to announce the discovery of ozone in October 1839. Moreover, Scho¨nbein applied for an English patent protection of his gun cotton (nitrocellulose); his patent attorney was Sir William Grove. The news of a horrible explosion at the factory of his English license holder in 1847 is said to have inspired Alfred Nobel’s own developments of nitroglycerin and, subsequently, of dynamite. Scho¨nbein was born in the German town of Metzingen and spent his youth compulsorily under Napoleon’s occupation. He, who was on friendly terms with Michael Faraday, could not help noting in a postscript to Grove on 12 February 1858: ‘‘I was rather vexed to see the other day a misprint in my letter to Faraday published in the last number of the Philosophical Magazine. Instead of Academy of Munich they put Academy of Paris and you know perhaps that on purpose I abstain from communicating even the slightest note to the French Institutions. I won’t have any thing to do with the ‘savants’ there.’’ Scho¨nbein and Grove used to have a lively correspondence and familial visits for almost 30 years. Grove’s First Practical Fuel Cell Welsh lawyer and physics professor William R. Grove (1811–1896), in a one-page postscript to an unrelated paper that appeared in February 1839, described that an electrolytic cell, consisting of two platinum strips surrounded by closed tubes containing hydrogen and oxygen in sulfuric acid, provided electricity for a short time after the electrolytic current was switched off (Figure 1). Meanwhile, German chemist Robert Wilhelm Bunsen, in 1841, created the nonpolarizing carbon–zinc cell, replacing the expensive platinum used in Grove’s cell by the cheaper carbon. This battery found large-scale use for powering arc lights, and in electroplating. Between 1842 and 1845, Grove demonstrated his ‘gas battery’, a hydrogen–oxygen secondary battery, which delivered electricity during the consumption of gases produced before by electrolysis or steam pyrolysis of water. Grove was ever the practical thinker and built fuel cells working on hydrogen and chlorine, camphor, vegetable oils, ether, and alcohol. Grove became a high court judge in 1880. He is also famous for his galvanic cell using zinc and sulfuric acid for the anodic reaction, and platinum in nitric acid for

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Grove 1839

Figure 1 Grove’s discovery of the hydrogen–oxygen fuel cell was based on insights into electrolysis. Detail from Philosophical Magazine (1839). Sources: www.wbzu.de/infopool/images/grove. jpg; http://www.diebrennstoffzelle.de/zelltypen/geschichte/ grove.gif.

the cathode. The device provided nearly double the voltage of the first Daniell cell. Early American telegraph office systems were reported to be filled with poisonous nitrous fumes from rows of Grove batteries, before advanced Daniell batteries emerged victoriously by the time of the American Civil War. Grove narrated in a letter to Scho¨nbein dated 20 August 1842: ‘‘A friend of mine in the neighbourhood has with me been getting up a boat which goes at about 3 miles an hour by Electro Magnetism with only 8 pairs of 6 inch plates of my battery & carries several hundred weights.’’ In the 1840s, Prussian engineer Moritz H. von Jacobi, financed by Czar Nicholas, powered the first electric boat using 128 Grove cells. Jacobi’s theorem about load matching is known to every electrochemist. The Phantom of Direct Conversion of Coal The direct conversion of coal, the most important primary resource of the nineteenth century, has not been successful up to the present. In 1855, A. C. Becquerel and A. E. Becquerel experimented with a carbon rod in molten sodium nitrate, and a vessel of platinum or iron as the counter electrode. In 1860, M. Vergnes (US 28317) realized a sulfuric acid cell using platinized coke electrodes. C. Westphal (Germany, 1880) explored as well the direct conversion of fossil fuels. L. Mond and C. Langer (England, 1889) discovered the overpotential at the oxygen electrode and recognized carbon monoxide as an electrode poison during their experiments with hydrogen–oxygen fuel cells, having platinized platinum electrodes in sulfuric acid and diaphragms of gypsum, clay, cardboard, or asbestos. Their Swiss patent of 1889 (CH 492) is entitled ‘gas battery’.

In 1896, American engineer William W. Jacques succeeded in producing electricity directly from coal. Jacques’ passion was the propulsion of ships. He placed a hundred cells with carbon electrodes in molten alkali hydroxide on top of a coal-fired furnace and injected air into the heated electrolyte (400–500 1C). Actually, he was able to measure an electric current of 16 A at 90 V. Jacques initially claimed 82% efficiency for the carbon ‘battery’, but he forgot to account for the addition of heat and the energy demand of the air pump. The real efficiency was a meager 8%. Further research revealed that the current originated partly from thermoelectric action. In 1897, C. Liebenow and L. Strasser (Accumulatorenfabrik AG, later Varta in Germany) studied the potentials at carbon and iron electrodes in molten potassium hydroxide, but could not realize a practical battery. In 1904–06, Fritz Haber and coworkers (Germany) investigated in more detail the temperature and pressure dependence of the cell voltage of the direct carbon conversion reaction. They used a glass frit coated with platinum or gold on both sides. Finally, the direct coal fuel cell turned out to be a hydrogen–oxygen fuel cell, because carbon is not simply oxidized to carbonate in fused alkali hydroxide, but hydrogen is generated in a preceding chemical reaction in the molten electrolyte.

Cathodic reaction :

C þ 2OH þ H2 O-CO3 2 þ 2H2 2H2 þ 4OH -4H2 O þ 4e O2 þ 2H2 O þ 4e -4OH

Overall reaction :

C þ O2 þ 2OH -CO3 2 þ H2 O

Anodic reaction :

A similar so-called CE reaction mechanism explained the direct conversion of CO and generator gas. Carbon dissolves slowly in molten alkali salts. Carbonate and the ash content of the coal form a steadily increasing amount of undesired impurities in the electrolyte. Between 1918 and 1920, K. A. Hofmann (Germany) investigated the direct conversion of carbon monoxide at copper plates in molten alkali at platinum–air electrodes. However, the time was ripe for genuine hydrogen–oxygen fuel cells (Figure 2). Since the beginning of the twenty-first century, research groups have once again been concentrating on direct fuel cells. The Lawrence Livermore National Laboratory (USA), in 2005, reported 0.8 V cell voltage at 1–2 kA m2 in a self-feeding carbon/air fuel cell, based on molten alkali carbonate electrolyte and the internal pyrolysis of cleaned coal. Since 2005, further activities have been reported by university and industry research groups in the USA, Europe, and China. Sparsely Prosperous Indirect Fuel Cells In 1912, Walter Nernst (DE 264026) oxidized and reduced multivalent ions such as iron, titanium, thallium, and

History | Fuel Cells

PAFC

AFC Space programs (USA, SU)

ONSI/IFC 1992

Elenco 1976 Kordesch/ Union Carbide 1963−69

Siemens 1961/85 VARTA 1959

Japan 1981

PEFC

DMFC

Vaillant 1998 Ballard/ DaimlerChrysler 1994

Siemens 1994

General Electric 1962−66

Dornier 1987

Hitachi 1983 Bosch 1963 Shell, Exxon 1960−70

FCE/ERC

Broers 1958−69

Müller 1922

Justi/Winsel 1948/53 Bacon 1937

Baur 1910−44

Reid 1902

Schönbein 1839 Grove 1839/42

Coal conversion

Mond/Langer 1889 Vergnes 1860

Becquerel 1855

Westphal 1880

Jacques 1896

Accumulatorenfabrik 1897

SOFC

Sulzer 1990

MTU

Westinghouse 1967 UTC/IFC 1967−86

MCFC

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Haber 1904

Beutner 1911

Siemens Westinghouse

Davtyan 1946−71 Baur 1937 Schottky 1935

Figure 2 Historical development of fuel cell technology. Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg. AFC, alkaline fuel cell; PAFC, phosphoric acid fuel cell; PEFC, polymer electrolyte fuel cell; DMFC, direct methanol fuel cell; MCFC, molten carbonate fuel cell; SOFC, solid oxide fuel cell.

cerium in acid solution with oxygen and hydrogen, respectively. His redox fuel cell formed a two-electrode flow battery, which generated electricity by redox reactions taking place at ‘unassailable’ electrodes such as graphite electrodes. Nernst mentioned earlier attempts of French researchers (FR 345118). In 1955–58, E. K. Rideal and coworkers (Great Britain), despite intensive research, did not find any rapid redox system appropriate for a fuel cell. Owing to the poor power density, such indirect fuel cells had no market and are currently not under investigation.

Historical Roots of Alkaline Fuel Cells The Discovery of Gas Diffusion Electrodes J. H. Reid (US 736016), in 1902, and P. G. L. Noe¨l (FR 350111), in 1904, experimented with alkaline fuel cells (AFCs) in KOH solution. The three-phase boundary between electrodes, electrolyte, and gas space was already mentioned by Grove at platinum electrodes, the performance of which declined considerably when wet. It was found later that porous electrode structures could be prevented from flooding by applying hydrophobic coatings such as polytetrafluoroethylene (PTFE). In 1919, E. W. Jungner (Sweden, e.g., GB 145018) developed electrodes that were rendered hydrophobic by a

treatment with paraffin. His recipe for preparing graphite electrodes sounds quite modern: ‘‘A meal-fine amorphous carbon powder is kneaded together with a liquid binding agent, as for instance tar or molasses for obtaining a great porosity, suitably mixed with a volatile liquid as for instance water, to a plastic paste, which firstly is burned in usual manner and then is heated in an electric furnace to such a temperature (3000 1C or more) that the carbon is graphitized.’’ A. Schmid (Germany), in 1923, described the fundamentals of the gas diffusion electrode (Figure 3). At that time, M. Raney (US 1563587 of 1925) developed highly dispersed nickel for chemical hydrogenations – later used as electrode material. Heise and Schumacher (Germany 1932) were the first among those who used hydrophobic diffusion electrodes for high-pressure cells. In the late 1930s, first practical AFCs with porous nickel electrodes were demonstrated by English mechanical engineer Francis Thomas Bacon – a direct descendant of philosopher Sir Francis Bacon. In 1937, Bacon and E. K. Rideal designed a system of electrolyzer, hydrogen tank, and fuel cell. In 1939, an AFC delivered 0.89 V at 13 mA cm2 in 27% potassium hydroxide at 100 1C and a pressure of 220 bar. Cylindrical sintered nickel electrodes and oxygen electrodes of lithiated nickel oxide followed in 1946. In 1952, a 5 kW system provided 0.78 V at 0.8 A cm2 in 30% potassium hydroxide (200 1C, 45 bar).

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History | Fuel Cells Large pores

Fine pores

Low-Pressure AFCs Conquer Spacecrafts and Submarines The 1960s

Gas

Electrode

Electrolyte

Figure 3 Principle of the gas diffusion electrode as described by Schmid (1923). Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

A 150 W stack of six cells in ‘filter press design’ working at 200 1C and 41 bar reached a power density of 355 W L1 in 1954. Between 1956 and 1959, Bacon constructed 6 kW stacks of 40 cells for forklifts and welding equipment. With the manned missions to the moon, AFCs found their first specific application in space. Conventional batteries would have been too heavy; cost and life projections were not imperative at that time. In the Bacon cells, sintered nickel electrodes operated in 30% potassium hydroxide at 200 1C and pressures up to 50 bar. The pores at the gas side were 10–30 mm in diameter and were 1.5–16 mm at the electrolyte side. The pores at the gas side were rendered hydrophobic with paraffin or polysiloxanes. The electrolyte was fixed by capillary forces in the small pores, whereas the wider pores were blown free by the operating pressure. A thin electrolyte film creeping on the walls of the wider pores at the gas side allowed high current densities at the three-phase boundary between electrode, alkaline electrolyte, and gas space. The oxygen electrode was coated with lithium nickel oxide; intercalated lithium improved the conductivity of the p-type semiconducting nickel oxide. Reaction water was condensed at cooling fins outside the cell. Since the end of the Apollo flights, high-pressure cells have no longer been used. Gas diffusion electrodes based on active platinum on porous carbon materials allowed henceforth the operation of low-pressure AFCs at 50–80 1C.

In 1959, Allis Chalmers in Milwaukee, Wisconsin, powered a tractor with the help of a 750 V/15 kW hydrogen– oxygen fuel cell based on bipolar porous metal electrodes coated with platinum, and potassium hydroxide soaked in an asbestos separator. Between 1962 and 1967, in cooperation with NASA, a bipolar fuel cell with nickel electrodes and platinum–palladium catalysts was developed. The bipolar plates were of nickel-plated magnesium. Product water was removed from the hydrogen gas stream by static water-vapor control, that is, through the diffusion of water through a supported membrane. The ‘immobile’ electrolyte solution, fixed by capillary forces in a microporous medium, quickened later developments of fixed AFCs and electrolyzers. The manned ‘Apollo’ missions to the moon between 1961 and 1970 were equipped with Pratt & Whitney hydrogen–oxygen fuel cells (Figure 4). Platinum-activated double-layer electrodes of sintered nickel, 20 cm in diameter and about 2 mm in thickness, were integrated in a nickel housing, together with sealing and insulating rigs of fluoropolymers, at a system pressure of 3.3 bar. The operating temperature of 200–230 1C was maintained by Joule heat in the molten electrolyte of 85% potassium hydroxide. Hydrogen and oxygen were supplied by cryo stores; water was separated from the residual hydrogen stream by condensation. The temperature of the cell stack was controlled by electric heating in a jacket of nitrogen, and a radiator outside the spacecraft. A module of 31 single cells weighing 109 kg delivered a rated power of 1120 W at 28 V. The total 810 kg system consisting of three cell stacks and a tank generated 500 kWh during the 10day mission, corresponding to an energy density of 620 Wh kg1. Conventional lead–acid batteries would have required a mass of 10–12 tonnes, and silver–zinc accumulators of 4 tonnes. A total of 54 such stacks accompanied nine flights to the moon, three Skylabs, and the Apollo-Sojus mission, and operated altogether for 10 750 h. The life of the stack, about 400 h, was determined by corrosion of the nickel oxide electrode, impurities in the fuel gases, and drying up at the hydrogen side. Around 1965: AFCs were developed among others by Siemens (since 1961), who powered its electric boat ‘Eta’ with AFCs in 1965. E. W. Justi, between 1948 and 1965, and A. Winsel (since 1961 by Varta) developed the double-skeleton electrode using Raney nickel. K. Kordesch (Union Carbide, 1963–69) favored activated carbon on sintered nickel supports, and powered his ‘Austin A40’ by a 90 V/6 kW fuel cell between 1970 and 1973. Union Carbide’s thin carbon/fixed zone electrode (1965) consisted of a wettable carbon layer at the electrolyte side that was impregnated with the electrocatalyst; thereupon

History | Fuel Cells

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The electrodes were mounted in injection-molded acrylonitrile butadiene styrene plastic (ABS) frames. The electrolyte of potassium hydroxide was ‘mobile’, that is, it was circulated in the gaps between the electrodes. In the later EUREKA project (1989–94), together with Air Products, Ansaldo, and Saft, an 80 kW fuel cell system fueled by LH2 was combined with a nickel–cadmium battery in a 180 kW/800 V propulsion system for city buses. The 1980s

Figure 4 Alkaline fuel cell system for the Apollo space program (Pratt & Whitney, 1.12 kW module of 31 single cells). Reproduced from Sandstede G, Cairns EJ, Bagotzky VS, and Wiesener K (2003) History of low temperature fuel cells. In: Vielstich W, Lamm A, and Gasteiger HA (eds.) Handbook of Fuel Cells – Fundamentals, Technology, and Applications, vol. 1, ch. 12, p. 145. Chichester: John Wiley & Sons Ltd.

followed several hydrophobic layers and finally a sintered nickel layer. General Motors’ ‘Electrovan’ (1967) was powered by a Union Carbide 400 V/160 kW AFC with mobile electrolyte and fueled by liquid hydrogen (LH2); the early lifetime was a meager 1000 h (Figure 5). The 1970s

In Japan, Fuji Electric demonstrated a 10 kW AFC (1972). Around 1976, Elenco, a Belgian–Dutch consortium, built fuel cell stacks of 24 monopolar alkaline cells (for cell characteristics, see Figure 6). The hydrogen and oxygen electrodes were based on nickel mesh. At the electrolyte side, a layer of activated carbon–PTFE–platinum was rolled on, and at the gas side, a layer of porous PTFE. Heat treatment or sinter processes were not required.

Varta in Germany developed the EloFlux cell based on PTFE-bonded gas diffusion electrodes (DE 2941774). By ‘reactive mixing’ in a mill, the catalyst powder was surrounded by PTFE fibers and then the mass was rolled in a calender onto a wire gauze to yield a continuous band electrode. The hydrogen electrode was made of PTFEbonded Raney nickel on a nickel-plated copper support as the current collector. The oxygen electrode used a PTFE-bonded silver catalyst on a silver-plated copper mesh. The EloFlux stack consisted of alternating hydrogen electrodes and oxygen electrodes that were separated by a sheet of asbestos or polyolefin. Mobile and immobile cells were developed. Water and heat were removed at the electrode rear side. United Technologies Corporation (UTC), in cooperation with NASA, further developed the Apollo fuel cell in 1974. In April 1982, the space shuttle was launched with three 12 kW stacks (32 bipolar cells, 465 cm2, 91 kg, 27.5 V at 436 A). In 7 days, electricity and water for the astronauts were produced from 750 kg hydrogen and oxygen. The advanced fuel cell technology comprised the following: oxygen flow plates of nickel-plated plastic; an oxygen electrode of 90% gold (as catalyst) and 10% platinum (as a sintering inhibitor) on a gilt nickel mesh; the electrolyte of 25–45% potassium hydroxide in a matrix of butyl-bonded potassium titanate; a hydrogen electrode of PTFE-bonded carbon, pressed into a silverplated nickel mesh, and activated by 10 mg cm2 platinum–palladium (80:20); a hydrogen flow field plate of metallized plastic; and cell frames of polyphenylene sulfide. The 1990s

The fuel cell system ‘Foton’, produced by Ural Electrochemical Integrated Plant (also KVANT) after the collapse of the former Soviet Union, has been used in the Energia-Buran space programs since 1960. The 40 kW AFC system consisted of four modules. Between 1984 and 1993, the European Space Agency projected a regenerative fuel cell system (RFCS) for the space glider ‘Hermes’, which was not realized, however. One and the same aggregate should alternately work both as an electrolyzer driven by solar energy and as a fuel cell in the dark phase of the orbit. The fixed alkaline water

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History | Fuel Cells

Liquid hydrogen tank Liquid oxygen tank Motor controls

Water condenser

Electrolyte radiator AC induction motor Gearbox Electrolyte reservoir 32 Fuel cell modules

Figure 5 General Motors Electrovan powered by a 150 kW alkaline fuel cell (AFC) (Union Carbide, 1967). Source: Kordesch K (2006) Fuel Cells and Their Applications. Weinheim, Germany: VCH Publishers.

1.2

Cell voltage (V)

1.0 0.8 A

1

0.6

B 2

0.4

C 3

0.2 0

25

50

75

100

125

150

titanium. The oxygen electrode contained silver with additions of nickel, titanium, and bismuth. Eight modules, a heat exchanger, and a gas supply unit formed a 48 kW fuel cell system (192 V, 250 A). By mid-1990s, the AFC was silently replaced by a system that promised better power densities and the use of ambient air instead of pure oxygen. Traces of carbon dioxide in the oxidants have always been a major problem of the AFC, leading to the formation of potassium carbonate (K2CO3) in the electrolyte.

Current density (mA cm−2)

Figure 6 Current–voltage characteristics after the data of Elenco alkaline fuel cells (6.6 mol L1 KOH, 70 1C): 1 ¼ H2/O2 (platinum), 2 ¼ H2/air (platinum), 3 ¼ H2/air (without catalyst). A ¼ activation polarization, B ¼ ohmic drop in the electrolyte, C ¼ mass transport controlled region at high current densities. Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

electrolysis at nickel/IrO2 electrodes was further developed for the oxygen production in space by European Aeronautic Defence and Space Company (EADS) in Germany. Alkaline fuel cells for submarines have been developed by Siemens since the 1970s. The advanced 6 kW stacks of 1990 combined 60 monopolar cells (340 cm2) electrically connected in series. With the ‘mobile’ technology, potassium hydroxide solution was circulated through the electrolyte gaps filled with asbestos and connected in parallel. Reaction water was evaporated from the electrolyte by heating. The hydrogen electrode consisted of Raney nickel including a certain amount of

The twenty-first century

In Germany, GASKATEL, since 1998, has been further developing the ‘Eloflux’ AFC based on carbon and nickel. Until 2002, ZEVCO Ltd. and ZETEC continued the ELENCO Electronics Inc. technology in boats, in a pickup truck (63 kW AFC), and in a ‘Millennium Taxi’ (5 kW AFC plus battery). Independent Power Technology (IPT), a Russian company established in 2002, is further developing the 6 kW ‘KVANT’ AFC system used in the Soviet space programs for auxiliary power units (APUs) in buildings and ships. ‘Cascade-6’ employs a regenerative carbon dioxide purification system. ASTRIS, a young Canadian company, which unfortunately had to close for financial reasons in 2007, demonstrated in 2004 its portable 2.5 kW AFC generator ‘E8’ having a system efficiency of about 55% at a cell voltage of 0.7 V. The US company Apollo Energy Systems in Florida with pioneer K. Kordesch is developing advanced ‘mobile’ AFC systems (2004). Hydrogen is generated by the cracking of ammonia, NH3-3H2 þ N2.

History | Fuel Cells

SPE

H2

Anode

Fuel gas

(a)

V

O2 Cathode

V Valve outlet

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2

3 5

Oxygen

Grubb 1955

(b)

Niedrach 1959

Figure 7 Historical embodiments of solid polymer fuel cells as disclosed in patents (US 2913511, US 3134697). SPE, solid polymer electrolyte.

Polymer Electrolyte Fuel Cells Revolutionary Polymer Technology Recent developments favor the proton-exchange membrane fuel cell (PEMFC) system, which exhibits a compact cell design and a high power density, although the technology faces strict cost requirements. Environmental concerns and forced legislation in California in the 1990s initiated a unique wave of worldwide research on fuel cells and ZEVs. The first solid polymer fuel cells were developed by General Electric (USA). Willard Thomas Grubb, a chemist working for General Electric, explained in US patent 2913511 filed in 1955: ‘‘A cell employing a gaseous fuel has two electrodes separated by and in contact with a hydrated ion exchange synthetic resin membrane which constitutes the electrolyte. [y] The electrodes may consist of platinum, palladium, platinum or palladium black deposited on a base metal such as steel or nickel, or of iridium, rhodium, copper, nickel, metal oxides, or activated carbon, and may be in the form of sheets, screens or porous bodies.’’ In 1958, Leonard Niedrach (US 3134697) devised a way of depositing platinum onto ion-exchange membranes. The ‘Grubb–Niedrach fuel cell’, between 1962 and 1966, equipped the Gemini space project – NASA’s first manned space vehicles (Figures 7–9). The early membranes were of sulfonated polystyrene, which, however, dried out quickly. Product water at the cathode was removed with the help of a wick in every cell. Three stacks of 32 cells delivered a power of 1 kW (0.038 W cm2 at 0.83 V per cell). The total system, including pressure reservoirs for deep-cold hydrogen and oxygen sufficient for 160 kWh electrical energy, weighed about 250 kg – not more than one-sixth the mass of a then commercial battery. Fuel and oxygen were preheated in a heat exchanger by use of the cooling water of the fuel cell and an additional electric heater. Critical points were the low power density, and the desiccation and stability of the polystyrene membrane, so that AFCs instead of PEFCs were launched in the later Apollo program and the Space Shuttle.

1

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CM SCALE

Figure 8 The Grubb cell. Source: Smithsonian Institution, http://scienceservice.si.edu/pages/copyright.htm

Nafion, a trademark of Du Pont, was introduced in 1968 and promptly employed in the 350 W proton exchange membrane (PEM) fuel cell in the ‘Biosatellite’. In the early 1980s, UTC, Hamilton Standard Division, and UTC’s subsidiary International Fuel Cells Corp. (IFC) continued the General Electric technology. A number of technical improvements – carbon-supported platinum catalysts, humidification of the gases, elevated differential pressure at the oxygen side, and higher operating temperature – quickened the PEMFC technology. Finally, cell voltages of 0.825 V at 300 mA cm2 and 0.5 V at 1 A cm2 were reached (at 105 1C, 10 bar O2, 2 bar H2). The operation with air, despite high pressures, however, allowed not more than 300 mA cm2. The US Navy and Siemens in Germany, based on a UTC license of 1983, developed fuel cells for submarines. Between 1985 and 1988, Energetic Power Systems (EPSI), a subsidiary of Ergenics, presented 2 kW proton-exchange membrane (PEM) fuel cells for space applications (Engelhard technology). Water was removed by wicks, and a current density of 1.5 A cm2 was obtained at a cell voltage of 0.6 V.

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History | Fuel Cells Cooling water 3 Stacks (each 32 cells)

H2O

O2

− Electrolyte

+

+

H2

O2

−

+

H2

O2

H2O

Heat exchanger Radiator

H2

17 bar

O2

58 bar

Cooling water

Waste heat

Water tank

Separator

Absorbent Water

Figure 9 Solid polymer fuel cell system in the Gemini spacecraft (1965). Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

Fuel Cells Power Electric Vehicles and Submarines Since 1983, Ballard in Canada has been developing fuel cells operated by ambient air. The heavy niobium plates used earlier by NASA were replaced by graphite. Protonexchange membrane fuel cell systems in combination with gas generators based on steam reforming and CO oxidation were demonstrated in 1985. In 1987, ‘Mark IV’ delivered 4.3 A cm2 at 0.53 V using a Dow membrane and H2/O2 at a pressure of 7 bar. A submarine was equipped in 1989 (Perry Energy). Between 1990 and 1994, city buses were powered by 24 water-cooled 5 kW stacks fueled by a 210 bar Hydrogen tank. A stationary 250 kW power system followed in 1999. ‘Mk500’ stacks (5 kW, 150 W L1) powered DaimlerBenz’ experimental vehicle ‘Necar 1’ in 1994. Around 1988, researchers with Los Alamos National Laboratory (LANL) succeeded in reducing the platinum load on the electrodes below 1 mg cm2. Wilson and Gottesfeld (1992) pressed films of 20% platinum/carbon powders bonded by 5% Nafion suspension at elevated temperatures on PEM. In 1987–90, the US Department of Energy (DOE) promoted projects on fuel cell vehicles. Early developments took place at General Motors, Giner, Analytic Power, and DeNora (Italy). Energy Partners Inc. presented its ‘Green Car’ powered by a 15 kW/125 V PEM fuel cell in 1993 (Figure 10). In 1994, supported by public funding in Germany, a number of companies (BASF, Heraeus, Axiva, Hoechst,

Bosch, SGL, Sachsenring, and Siemens) and research institutes (DLR, FhG, FZ Ju¨lich, and MPI) turned their attention to PEM fuel cells. Advanced ion exchange membranes and solid polymer electrolytes (SPEs) were developed at that time by DuPont, Ballard, Gore, Hoechst, Dow, and Asahi. Dow’s PEM (1988) was a copolymer of tetrafluoroethene and a vinylether monomer, but with a shorter side chain than that in Nafion. DaimlerBenz (Germany) started its fuel cell vehicle program in 1994. ‘Necar 4’ of 1999 was powered by two Ballard stacks (together 70 kW, 330 V, 200 W kg1). The California Fuel Cell Partnership – a consortium of DaimlerChrysler (since 1998), Ford, Shell, Texaco, ARCO, Honda, Volkswagen (1999), Nissan, US Department of Energy (2000), General Motors, Hyundai, Toyota, BP, Exxon, IFC, and others – has been testing a fleet of fuel cell vehicles in daily practice and public transit since. Table 1 gives an overview of early R&D activities on fuel cell vehicles. In 2000, MAN, Siemens, and Linde (Germany) operated a public transit bus for nearly 1 year in the city of Nurnberg. The 120 kW PEM fuel cell consisted of 640 single cells. A total of 1548 l of hydrogen was stored at 250 bar in nine compressed gas cylinders made of aluminum and a carbon fiber jacket. In 2002, Howaldswerke Deutsche Werft (Germany) launched its submarine ‘U212’, which was equipped with a Siemens PEM fuel cell system (50 kW). Hydrogen was supplied by metal hydride stores that were loaded with

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Figure 10 Proton-exchange membrane fuel cell (PEMFC) systems in electric vehicles and submarines. Source: Daimler AG, ¨ V Su¨d Industrie Service GmbH. Reproduced from Kurzweil P (2003) Howaldtswerke Deutsche Werft GmbH, Toyota, TU Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

low-temperature, high-pressure hydrogen. Later, ‘U214’ had 120 kW stacks. Around 2007, fleets of up to a hundred electric vehicles were tested all over the world. Fuel cells are employed by Daimler, Audi, Ford, Daihatsu, GM, General Motors, Honda, Mazda, Lada, Nissan, PSA, Suzuki, Toyota, VW, Volkswagen, and other companies. The European projects CUTE (Clean Urban Transport for Europe, 2001–06) and HyFleet:CUTE supported field tests of fuel cell buses in Amsterdam, Barcelona, Hamburg, Stockholm, Reykjavik, Madrid, Stuttgart, Luxemburg, Porto, and London. By July 2005, 30 CITARO buses of DaimlerChrysler, powered by Ballard 250 kW PEM fuel cells, covered a total distance of 850 000 km within 62 000 h. Hydrogen has been generated from various natural and regenerative sources. Table 1 compiles historical highlights of PEMFC systems in electric vehicles. Direct Methanol Fuel Cell For nearly six decades, researchers have been trying to improve the direct conversion of methanol into electricity – a fascinating idea, which, however, has to meet the high activation overpotential of the oxidation step to carbon dioxide in which six electrons are involved.

Similar direct fuel cells were proposed based on glucose to supply electrical power for artificial hearts and vital parts in the human body. In 1910, Taitelbaum (Germany) investigated the anodic oxidation of solved fuels. R. Mu¨ller, in 1922, reported on the electrochemical oxidation of methanol. K. Kordesch and A. Marko, in 1951, proposed the direct methanol fuel cell (DMFC) in alkaline electrolyte, although serious investigations did not commence immediately. In the 1960s, Esso Research and Engineering developed a 100 W system for use in communication systems of the US Army. The initial unit gave 55 mA cm2 at 0.4 V, using noble metal electrocatalysts, but durability was limited. K. R. Williams and D. P. Gregory, working with Shell, obtained a power of 300 W from a series connection of 40 DMFCs in 1963. In the same year, engineers at Bosch (Germany) investigated ‘methanol–oxygen batteries’, especially as methanol has attracted most interest as an inexpensive, and widely available fuel. Both Shell and Esso terminated their research on DMFC catalysts in the late 1970s. The platinum/ruthenium system was among the most active of the ones tested, but it did not meet the activity targets for automotive applications. Around 1972, ruthenium was discovered as the electrocatalyst for the oxidation of methanol. Other DMFC

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History | Fuel Cells

Table 1 1990 1993 1995 1997–2000 1997 1998 1999 2000

2001

2002

2003 2005

Early milestones of fuel cell vehicles Energy Partners (USA): ‘Green Car’ Ballard (Canada): PEM fuel cell bus ‘P1’ (120 kW) Ballard (Canada): ‘Mark 900’ delivers 250 V/75 kW from 440 single cells Ballard: Six fuel cell buses in Chicago and Vancouver carry 200 000 passengers along 118 000 km dbb Fuel Cell Engines (later Xcellsis), a consortium of DaimlerBenz, Ford, and Ballard (Germany): methanol fuel cell car ‘NECAR 3’. Ansaldo: bus (45 kW PEMFC and lead–acid battery). Daimler-Benz: ‘Nebus’ (250 kW PEMFC) Toyota ‘RAV4’ with methanol reformer Ford ‘P2000’ with CGH2. First hydrogen gas station in the USA; DaimlerChrysler: NECAR 4; Xcellsis: 200 kW fuel cell engine ‘P4’ for buses DaimlerChrysler: NECAR 5 and hybrid vehicle ‘Jeep Commander 2’; Ford ‘Focus FCV’ (355 bar CGH2); General Motors’ ‘Opel Zafira HydroGen1’ with LH2 PEMFC establishes a record in speed and range; Munich airport (Germany) opens a hydrogen gas station. MAN: fuel cell bus (120 kW PEMFC) Mercedes ‘Sprinter’ vans (75 kW H2 PEMFC) for Hermes-Versand; first zero-emission bus of SunLine Transit Agency, Palm Springs, achieves 24 000 km; Chrysler ‘Natrium’ van with NaBH4 store; Fiat ‘Seicento Elettra H2 fuel cell’; Honda ‘FCX V3’ and ‘FCX V4’ including Ballard fuel cell, hydrogen store, double-layer capacitor; Mazda ‘Premacy’ with methanol reformer; Toyota ‘FCHV-3’ with titanium hydride store, ‘FCH-4’ with 350 bar CGH2, ‘FCH-5’ with methanol reforming DaimlerChrysler ‘Mercedes F-Cell’ and Ford ‘Focus FCV Hybrid’ (65 kW, NiMH battery, Ballard ‘Mark 902’ fuel cell, 350 bar CGH2). ‘Necar 5’ runs 5250 km from San Francisco to Washington; Evobus ‘CITARO’ fuel cell bus; General Motors’ Chevrolet-Pickup ‘S10’ with gasoline reformer; Volkswagen and Volvo: ‘Golf Variant’ with methanol reformer, ‘Bora Hy.Motion’ with LH2. A ‘Bora Hy.Power’ with 320 bar CGH2 and 350 V/60 kW double-layer capacitor crosses the Swiss-Italian Simplon pass; Audi ‘A2’ with 58 kW PEMFC and 6.5 Ah NiMH battery US Government: 1.2 billion US$ for hydrogen technology; Nissan: ‘X-Trail FCV’; Clean Energy Partnership; General Motors: Opel ‘Zafira’ with PEMFC and 4.6 kg LH2; Reykjavik (Iceland): public hydrogen gas station DaimlerChrysler: ‘F600 Hygenius’ (85 kW) powered by a 60 kW PEMFC and a Li-ion battery; 4 kg hydrogen (700 bar); Toyota: ‘Fine-X’, 80 kW PEMFC plus battery, CGH2 (700 bar)

CGH2, compressed gaseous hydrogen. PEM, proton-exchange membrane; PEMFC, proton-exchange membrane fuel cell.

systems have been investigated by Brown Boveri (around 1964), Cathro and Weeks (1971), the US Army for military communication systems, and the Royal Institute of Technology, Stockholm, for electric wheelchairs (1977–80). Hitachi (Japan, 1983) applied acid electrolytes in DMFCs. Applications were foreseen in the leisure and domestic markets. A hybrid system with lead–acid batteries was demonstrated in a golf cart. Platinum was used as the cathode catalyst and a combination of platinum and ruthenium in the anode. In 1993, Siemens reported cell voltages of 0.5 V at 400 mA cm2 (O2, 4 bar, 130 1C). UTC’s membrane cells of 1994 delivered 0.7 V. The Jet Propulsion Laboratory reduced the platinum load to 0.5 mg cm2 and achieved a cell voltage of 0.4 V at 0.1 A cm2 and 60 1C. In the same year, Ballard (Canada) started R&D on DMFC systems. Johnson-Matthey (Great Britain, 1995) developed carbonsupported PtRu electrodes bonded with a Nafion film. In 2001, DaimlerChrysler (Germany) powered a gocart by a 3 kW pure oxygen DMFC (Figure 11). Ballard demonstrated portable DMFC having a power density of 500 W L1. In 2002, Smart Fuel Cell (Germany) presented the ‘Remote Power System SFC 25’ for outdoor power supply and camping. Toshiba’s 100 mW DMFC of 2004, weighing 8.5 g, was small enough to power mobile phones and MP3 players for about 20 h by 2 cm3 of methanol (0.1 W from 22  56  4.5 mm).

Small companies such as Smart Fuel Cell (SFC), PlugPower, Hydrogenics, FC Energy, Voller, MIT Micro, and Medis have been improving DMFC technology for portable applications, for example, in mobile telephones, PDAs, and MP3 players. SFC’s ‘EFOY’ generators of 2006–07 delivered 25, 50, and 65 W of power, and capacities in the range of kilowatt hours. Mobile applications suffer from the low power density of the DMFC. However, Veloform commercialized the bicycle-like ‘CityCruiser’ and ‘DeliveryCruiser’ powered by a DMFC (SFC). Stationary Power Systems In the 1990s, stationary PEM fuel cells were investigated with respect to supply of electric power and heat for private households. Hydrogen is generated by steam reforming of natural gas, followed by partial oxidation of residual CO to CO2 – or the combination of both processes, the so-called autothermal reforming. Fraunhofer Institute (ISE, Germany) and Energy Partners (USA) built a 7.5 kW system in 1996. Vaillant and Plug Power, since 1998, have equipped heating systems in the USA and Germany. In 2002, a combined heat and power unit based on natural gas and a PEM fuel cell was demonstrated. European Fuel Cell (EFC) and Dais Analytic Power (USA), since 2000, furthermore Viessmann, and since around 2003, RWE Plus (Germany) and Nuvera Fuel Cells (USA), as well as Buderus and UTC (USA) have established

History | Fuel Cells

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Figure 11 Go-cart, ‘CityCruiser’ and ‘DeliveryCruiser’ powered by direct methanol fuel cells (DMFCs). Source: Daimler AG, kfpn GmbH (Germany). Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

PEMFC systems in the range of 1.5–5 kW in houses. In the USA, Plug Power/GE, UTC, and Ida Tech have been active in the field of 10 kW electric power generation. In 2005, Ballard in Canada sold 315 ‘Mark 1030’ stacks (1.3 kW) for different clients, among others, in Japan. In Japan, since 2005, a large field test program of several hundred 1 kW PEM fuel cell systems for household energy and heat supply is under way, borne by Ebara-Ballard, Sanyo, Panasonic, Toshiba, and Toyota. Town gas, kerosene, and liquefied petroleum gas (LPG) have been used as primary fuels. Fuel cells in uninterruptible power supply (UPS) systems have been employed by P21, a company established in Brunnthal in 2001, in its ‘Premion T’ (3 kW, 48 V, including a supercapacitor) and by PlugPower in its ‘GenCore’ (5 kW, 48/230 V, including a battery).

Portable Proton-Exchange Membrane Fuel Cell Systems Portable fuel cells as nearly unlimited power sources for handheld devices have been developed since the 1990s. Portable ‘power packs’ attracted attention for military use before. Mini fuel cells (500 W–2 kW) for portable power generators have been presented by Ballard for use in UPS emergency generators, forklifts, baggage tractors, floor scrubbers, and small electric vehicles. Ballard’s ‘Nexa’ 1.2 kW PEMFC module of 2001 and the ‘AirGen Fuel Cell Generator’ of Coleman Powermate were designed for emergency power supply. In 2002, Smart Fuel Cell (Germany) presented its portable DMFC. Midi fuel cells (50–500 W) have been investigated for novel applications in communication systems and photovoltaic plants. Masterflex supplied its light traction applications, ‘Veloform’ and ‘Cargo-Bike’, with 250 W

PEM fuel cells, which were tested in the European Hychain Minitrans project (2006–07). Micro fuel cells (o50 W) have been integrated in camcorders, notebooks, and torches, for example, by NEC, ISE Freiburg, and ZSW in Ulm. The Fraunhofer Institute, in 2003, presented hydrogen PEMFCs for powering mobile computers and cameras, which were fueled from metal hydride stores.

Phosphoric Acid Fuel Cell Acid Fuel Cells – Forerunner of the PEMFC System Grove’s sulfuric acid fuel cell of 1839 was the basis for the experiments of Mond and Langer in 1889, which, however, did not result in a commercial gas battery. In 1983, Exxon and Occidental Chemical completed the rediscovered sulfuric acid fuel cell with bipolar plates of soot-filled polypropylene. Fruitless attempts to convert gasoline in a sulfuric acid fuel cell into electricity ultimately led to the invention of phosphoric acid fuel cell (PAFC). Hydrocarbons react with sulfuric acid at 80–100 1C, whereas there is no reaction with phosphoric acid up to 200 1C. Moreover, the higher temperature simplifies the removal of product water, and the PAFC tolerates 1–3% carbon monoxide and hydrogen sulfide (H2 S), so that hydrogen-rich gases from fossil fuels can be used without elaborate purification. In 1967, UTC in the USA built the first water-cooled PAFC, based on a PTFE-bonded platinum black catalyst in a tantalum mesh, and 85% phospheric acid (H3PO4) absorbed in a glass fiber separator. The ‘fuel cell generator’ of 1971 comprised PTFE-bonded platinum–carbon electrodes on carbon paper, and 95% phospheric acid

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History | Fuel Cells

(H3PO4) absorbed in a silicon carbide (SiC) separator. The first 1 MW plant was demonstrated in South Windsor, Connecticut (1977); 4.5 MW plants followed in Manhattan (1978–83) and Tokyo (1980–85). A current density of 270 mA cm2 was achieved at a cell voltage of 0.65 V (pressure 3.4 bar) and a system efficiency of 40–45%. In 1979–80, a ribbed cell design was introduced. In 1985, IFC was established as a consortium of UTC and Toshiba, and renamed as ONSI in 1990. A field test of 42 ‘PC18’ systems between 1982 and 1986 proved a useable lifetime of 9–15 months. An 11 MW PAFC plant was established in Tokyo thereafter (1989–94). Westinghouse (USA) has been developing air-cooled PAFCs since 1967, based on the technology of Energy Research Corporation (ERC). The design of 1987–90 comprised four cell stacks arranged crosswise vertically around the integrated feed of fuel, air, and cooling air. Between 1971 and 1973, Pratt & Witney Aircraft Co. (USA) built 65 experimental 12.5 kW natural gas PAFC in the USA, Canada, and Japan. A 10-year study of Gas Research Institute (GRI) and DOE stated a mean lifetime of 6500 h (1976–86). In the 1980s, the US Navy tested PAFCs for use in submarines. Japan launched the pathbreaking ‘moonshine program’ (1981) for the development of energy-saving technologies. A number of companies built PAFC power plants: Westinghouse (1980), Engelhard (1986), Toshiba (1982), Mitsubishi (1984), Fuji (1990), Sanyo (1986), and Hitachi (1990). Engelhard (1980–83) powered forklifts and buses by liquid-cooled PAFCs that were fed by the hydrogen from a methanol reformer. The liquid coolant was more effective than air. ERC and LANL, between 1987 and 1991, powered a city bus by a 36 kW PAFC, fueled by reformer methanol; it was a hybrid system of fuel cell and Ni–Cd accumulator. Kinetics Technology (KTI) built the first European PAFC plant (25 kW) in 1989. Since 1990, ONSI, the sales company of UTC, Toshiba, and Ansaldo (Italy), has delivered 200 kW ‘PC25’ units. By 1998, 160 plants were established worldwide, with 19 in Europe. The lifetime was estimated beyond 6800 h. The advanced types, PC25B and PC25C, were introduced in 1993 and 1997, respectively. Stationary PAFC plants have since delivered both electrical energy and useful heat, for example, in hospitals and for indoor swimming pools. In 1994, H-Power and Fuji powered a city bus by a 50 kW methanol PAFC and an additional lead–acid battery. Applications in vehicles were undertaken by Mitsubishi and by Nissan (2003). No other technology but the PAFC has influenced the development of solid polymer fuel cells so strongly, especially with respect to carbon materials and catalysts.

Phosphoric Acid Fuel Cell Plants in Japan Japan is the worldwide leader of commercial PAFC utilization, although the PEM fuel cell has been favored since 1995. Megawatt plants, 2 MW and more, have not been realized with any other fuel cell technology but the PAFC. In 1970, Tokyo Gas and Osaka Gas established 12.5 and 40 kW PAFCs, imported from the USA. Fuji Electric Co. started to develop PAFC in 1973. Between 1989 and 1999, Fuji installed 25 PAFC plants rated at 50, 100, and 500 kW at Tokyo Gas, Osaka Gas, and Toho Gas, respectively. The latter three companies operated an additional 20 ‘PC25A’ of Toshiba/IFC. By the end of the 1980s, the time was ripe for a megawatt plant. Toshiba/IFC set up an 11 MW PAFC for Tokyo Electric Power Co. (1989–97; Figure 12). The world’s largest PAFC plant consisted of eighteen 650 kW stacks and reached, after a year of construction and a short period of testing, its rated power in April 1991. In 7 years, the plant operated for 23 140 h and generated 77 842 MWh of energy. Net AC electric efficiency reached an impressing 41.8% (at 11 MW), and 83% of the feedstock (methane) was converted into electricity; waste heat utilization was 32.2%. The degradation of the cell stacks was >10% in 40 000 h. Critical points were the corrosion of stack housing and air electrodes, and the reliability of the gas generation system. In 1994, Fuji had gathered testing experience on various plants from 50 to 500 kW and up to 15 000 operating hours. In addition, a hybrid city bus powered by a PAFC was available. In 1996–97, Kansai Electric Power Co. reported a life of 6410 h for a 5 MW PAFC.

Figure 12 Impression of the 12 MW phosphoric acid fuel cell (PAFC) of Tokyo Electric Power Station Company (TEPCO), based on 18 IFC 670 kW stacks and a Toshiba infrastructure, generated 77.8 GWh of electric energy in 23 140 operating hours between 1991 and 1997.

History | Fuel Cells

In 1999, 70 of 162 PAFC plants ever installed in Japan were still running: 500 kW (2), 200 kW (46), and 50– 100 kW (22). In 2001, Mitsubishi and Fuji offered commercial PAFC plants. Gasoline Fuel Cells Usually, natural gas is employed as the fuel, although hydrogen has been successfully used. Naphtha, kerosene, butane, and biogas were tested in PAFC by Fuji and Toshiba in the mid-1990 s. Unfortunately, the conversion of light petroleum fractions and liquid gas requires complicated desulfurization and steam reforming processes. Mobile Applications A research group at Georgetown University realized zwei buses powered by PAFC stacks. The first generation (1994) combined a 50 kW PAFC of Fuji with a 40 kWh Ni–Cd battery. The second generation (1998) used a 100 kW PAFC of UTC and a 50 kWh lead–acid battery. Hydrogen was provided by methanol reforming. The later development focused on PEM fuel cells.

High-Temperature Fuel Cells Molten Carbonate Fuel Cell The generation of electricity in molten electrolytes dates back to the early twentieth century. In 1911, R. Beutner, a scholar of F. Haber, investigated palladium foil as a hydrogen diffusion electrode in fused KF/NaCl at 600–800 1C. Until 1939, E. Baur (Germany) and coworkers developed fuel cells using fused salts and air electrodes. The basic cell of 1910 comprised an iron vessel containing molten sodium hydroxide (380 1C) and a magnesium oxide (MgO) diaphragm and was fueled by sugar, carbon monoxide, lignite, town gas, saw dust, and heavy oil. Molten silver to improve oxygen reduction was added in 1912. The anode was of coal or platinum. The electrolyte was chosen from soda, potash, borax, or kryolith. The fuel gas was hydrogen or carbon monoxide. In 1921, an iron rod anode and iron oxide or magnetite as cathode were used in molten alkali carbonate, which was absorbed in a porous magnesium oxide ceramics (at 800 1C). Platinized graphite as hydrogen electrode was rendered hydrophobic by paraffin (1933). In 1935, the discovery followed that carbon dioxide in the airstream improves the concentration polarization at the cathode in molten carbonate – an important result for later molten carbonate fuel cells (MCFCs). Between 1958 and 1969, G.H.J. Broers and Ketelaar (Amsterdam) developed a fuel cell with molten alkali carbonate covered on a magnesia plate or adsorbed in a magnesium oxide pellet at 650 1C. The catalyst was silver

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on the cathode side and nickel powder on the anode side, each plated on a perforated steel plate to allow the access of humidified natural gas. A cell voltage of 0.7–0.8 V was achieved at current densities of 50–100 mA cm2. Early work on the MCFC was done by S. Baker, Institute of Gas Technology, Chicago (1960), and promoted by the DOE and Electric Power Research Institute (EPRI, 1975–85). In 1981, Mitsubishi, Fuji, Hitachi, and Toshiba reported cell voltages of 0.74–0.69 V at current densities of 150 mA cm2 in a 10 000 h test. Around 1990, screen-printed lithium aluminate (LiAlO2) layers were introduced. Prior to this, hotpressed electrolyte tiles and pastes had been used. Developments were under way with MTU, RWE, and Ruhrgas in Germany. On the contrary, Siemens-KWU stopped its MCFC program at that time. Between 1991 and 1996, M-C Power built a 250 kW module with ‘internally manifolded heat exchanger’. In 1992, ECN (Netherlands) and Chicago Institute of Gas Technology achieved 5000 h life with a 2 kW MCFC stack. Energy Research Corporation (ERC, later Fuel Cell Energy (FCE)) operated a 70 kW MCFC for 2000 h (1992). A 120 kW system with internal reforming of natural gas was tested for 250 h (1993). A 2 MW plant was installed in Santa Clara in 1995. Around 2000, MCFC was investigated in Europe by MTU Friedrichshafen (Germany), ECN (Netherlands), and Ansaldo (Italy); in the USA, by ERC/FCE and IFC/ UTC and others; in Japan, by Hitachi, IHI, Mitsubishi, and Toshiba. In 2004, MTU and FCE manufactured 250 kW combined heat and power plants. The MCFC can directly be fueled by natural gas, thanks to an internal reforming process at a catalyst in the anode chamber (CH4 þ 2H2O-CO2 þ 4H2 at 650 1C). Electric efficiencies of 47% were reported; total system efficiencies of up to 90% are possible, when the exhaust gas temperature of 400 1C is used in a gas turbine. About 35 000 operating hours were reached. Critical points are the sulfur content of the fuel, the circulation of carbon dioxide, corrosion and phase changes, short circuits by dissolution of the nickel oxide cathode, and deposition of nickel at the anode. In Japan, IHI is developing a 300 kW system with external gas refinement. Marubeni Corporation is operating 250 kW modules with internal reforming at atmospheric pressure. There is a close cooperation between Marubeni and FCE. The latest FCE power stations provide several megawatts of electrical energy and can be combined with a gas turbine (Figure 13). Ansaldo (Italy) is developing 100 kW modules for electric power plants in the range of 500 kW–5 MW. The MCFC must reach a cost limit of about 1.500 h kW1 to compete with conventional block heat and power plants.

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History | Fuel Cells O2

−

O2 1

2 3 4

Figure 13 Molten carbonate fuel cell (MCFC), manufacturer’s label ‘DFC’, direct fuel cell of Fuel Cell Energy (FCE) combined with a gas turbine. Rated electric power was from 300 kW to 2.4 MW, and electric efficiency 65%. Fuel was natural gas.

Solid Oxide Fuel Cell

+

5

Figure 14 Carbon–oxygen cell of Baur and Preis (1937): 1, carbon rod; 2, carbon powder; 3, solid electrolyte tube; 4, magnetite; 5, cathode vessel. Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

Technology and power plants

Modern solid oxide fuel cells (SOFCs) have been manufactured in three designs: tubular, flat, and monolithic. The solid electrolyte dates back to 1897, when W. Nernst invented the ‘Nernst pin’ (ZrO2/15% Y2O3 ¼ yttrium-stabilized zirconium dioxide (YSZ)) as a source of light. In 1935, W. Schottky, a student of Nernst, who was working by Siemens, suggested the SOFC using Nernst’s ceramic mass. E. Baur (Germany) recognized in 1939 the SOFC as a current source ‘without polarization’. However, conductivity and stability of solid electrolytes were poor at that time. Between 1937 and 1939, E. Baur and H. Preis investigated clay, kaoline, and ‘Nernst mass’ in cells with cathodes of coke or iron, through which air was blown, and anodes of magnetite. The fuel gas was hydrogen, carbon monoxide, or town gas. They observed opencircuit potentials of 0.7–0.83 V. In their carbon–oxygen element of 1937, a carbon rod anode was surrounded by carbon powder in a tube of solid electrolyte (Al2O3 þ WO3 þ CeO2), and dipped in a vessel filled with magnetite, in which air was blown (cathode), as shown in Figure 14. O. K. Davtyan (Russia, 1938–71) improved the Baur cell. In 1946, he was able to measure 0.79 V at 20 mA cm2 (at 700 1C, town gas). In 1951, the addition of 15% calcium oxide (CaO) was found to improve the conductivity of the Nernst mass decisively. In 1958, Westinghouse Electric Corp. (USA) introduced the tubular design, which allowed 0.7 V at 1 A cm2. Later, ‘Air Electrode Supported Design’ completed porous cathode tubes. In 1986, a 400 W stack of 24 cells was successfully operated for 1760 h with H2/CO. A year later, 3 kW stacks were delivered to Tokyo Gas and Osaka Gas, which survived the operation under natural gas for 5000–15 000 h; degradation was 2% per 1000 h.

The 25 kW plant for Osaka Gas and Tokyo Gas endured 7064 h (1992–94) (Figure 15). In 1980, thermal spraying (chemical vapor deposition (CVD)) allowed the fabrication of laminated layers. In 1983, Argonne National Lab. (USA) introduced the monolithic design, which did not require any supporting structure. Cathode, solid electrolyte, and anode formed a wavelike composite, which was terminated by an upper and a lower current collector (interconnect). Fuel and air were flown in the space between the current collector and the pressed honeycomb laminate. Allied Signal Corp., after further development, reported 1.0 V at 0.1 A cm2 and 1050 1C with this design in 1992. In Japan, Fuji Electric Corp. demonstrated 0.22 W cm2 and 1.07 V in 1990. Developments in Germany were under way at Siemens-Westinghouse, Dornier, MBB, and research institutes (DLR, FhG, and FZ Ju¨lich). Siemens flat cell design – a variant was also developed by Dornier (1988–97) – employed a bipolar stack of single cells. The bipolar plate (interconnector) was of hightemperature superalloy (such as CrLa2O31); the anode consisted of nickel ceramic metal, the cathode for example of LaSrMnO3, screen-printed on the solid electrolyte of ZrO2/Y2O3/CaO. Siemens obtained 0.6 V at 100 mA cm2 (20% H2 in N2 at 950 1C) in 1988, and improved the design to 0.8 V at 500 mA cm2 in 1993. A Westinghouse 110 kW SOFC plant, which was installed in the Netherlands in the late 1990s and run later in Essen (Germany) and Turin (Italy), has been operated for more than 35 000 h. In 1999, a 220 kW hybrid plant of SOFC and gas turbine was realized in California, which was fueled by natural gas or town gas and delivered an electric efficiency of 53% – a world record. Later, 250 kW plants followed in Toronto and 300 kW in Pittsburg.

History | Fuel Cells Nickel felt (+) Cathode

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Cathode collector

Interconnector Anode

1/ 2 O2

+2e

O2− −2e

H2 H2O

Solid electrolyte

Anode collector

Figure 15 Tubular solid oxide fuel cell (SOFC) design of Siemens-Westinghouse. Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

In 2002, H-Power and Siemens-Westinghouse presented a 5 kW propane-fueled SOFC for use in Alpine huts and national parks. Hybrid power plants of a 1152-cell SOFC and a gas turbine endured over 3700 h (in 2001). Later, 1 MW plants followed for EnBW and Electricite´ de France. In 2003, 250 kW plants (called ‘e|cell CHP 250’) were field-tested at E.ON and municipal utilities. In 2005, Siemens-Westinghouse installed in Hannover a 125 kW system, which was the basis for the later ‘SFC200’, providing 125 kW of electrical energy and 100 kW of thermal energy at an electric efficiency of 44% and a total efficiency of 80%. In Japan, Mitsubishi Heavy Industries (MHI) and Chubu Electric Power Co. are active in the field of 200–300 kW SOFC plants. Smaller systems are in development by Hitachi, TOTO, Acumentrics Japan, Sumitomo, Sanyo, New Nippon Steel, and Mitsubishi Materials. Rolls-Royce is developing a 1 MW SOFC gas turbine hybrid. ZTEK (USA) is arranging 25 kW stacks to 200 kW SOFC hybrid plants. In the USA, the SOFC is attracting increasing attention for a future utilization of coal with CO2 sequestration (Figure 16). Solid oxide fuel cell heating systems

In 2000, Sulzer-Hexis (Switzerland) employed SOFC for energy and heat supply in private households. Flat circular cells (12 cm in diameter, B0.15 mm in thickness) having an inner hole of 2 cm diameter were stacked to the ‘heat exchanger integrated stack’. The self-supporting YSZ electrolyte was coated with an anode layer and a cathode layer. The metallic interconnector (a chromium alloy) between the single cells and including flow channels served simultaneously both as a heat exchanger and a current collector. The 70-cell stack was operated with natural gas (inside) and air (outside) and delivered a rated power of 1053 W (27 A, at 950 1C). The life was reported to be lower than 6 months around 2003. More than a hundred such systems have been tested. In 2006, the development was transferred to the Swiss ‘Hexis’ foundation, because the market launch was not foreseeable.

The ‘Galileo 1000 N’ system provides 1 kW of electrical energy and 2.5 kW of heat energy; with the use of an additional burner, a heat output of 20 kW is possible. In Germany, Vaillant, in cooperation with Webasto as well as EBZ, is developing SOFC heating systems for houses. In Japan, from 2005 to 2008, Kyocera, MitsubishiKansai El., NGK, TOHO Gas, and Sumitomo developed 10 kW SOFC systems. In Australia, Ceramic Fuel Cells Limited (CFCL) has been developing 1 kW stacks (Gennex) in planar technology for domestic use. Versa Power Systems (US/Canada), since 2000, has been developing a stationary 3–10 kW SOFC system using natural gas. FC Technologies (Canada), supported by Siemens-Westinghouse, is developing a 5 kW system. Propane, natural gas, and town gas are considered as the most important fuels at present. Smaller SOFC systems are investigated by Wa¨rtsila¨ (Finland), in cooperation with Haldor Topsoe (Denmark), as well as by FUCELLCO AG (Switzerland), HTceramix (CH), and CERES Power (UK). Auxiliary power units

The US Solid State Energy Conversion Alliance (SECA), a public–private partnership since 1999, pursues the commercialization of SOFC systems for stationary, mobile, and military applications; members in this program include Siemens-Westinghouse, Delphi, GE, Cummins Power Generation, Acumentis, and FCE. In 2001–02, BMW, Delphi Automotive Systems, and DLR developed an onboard APU for cars including an SOFC. Ce0.9Gd0.1O2 was introduced as electrode material. Auxiliary power units are designed as stationary and mobile power supplies, for example, for engine starting and high-efficiency automotive onboard electrical systems in automobiles, ships, and aircrafts. In Germany, besides BMW, Staxera Dresden is active; ALPPS is active in Austria. Delphi’s ‘Gen 2 A’ of 2003 delivered 220 W of electrical energy, followed by ‘Gen 2B/2 C’ in 2004 (423 W, 3.3% efficiency), ‘SPU 1 A’ in 2005 (1180 W, 17%

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History | Fuel Cells

Figure 16 Left: Siemens-Westinghouse 110 kW solid oxide fuel cell (SOFC) plant. Right: CEFL (Australia): 1, stack; 2, pre-reformer, steam generator, burner, heat exchanger; 3, air supply and filter; 4, water supply; 5, high-temperature insulation. Reproduced from Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.

efficiency), and ‘SPU 18’ in 2006 (2160 W, 38% efficiency). A useable life of 5000 h has been reported. The start-up from room temperature to 750 1C lasts 3 h. Portable SOFC units

The SOFC technology opens up the utilization of ‘logistic fuels’ such as propane, butane, kerosene, and diesel, and the SOFC is attractive owing to the higher power densities and efficiencies in comparison with the DMFC. Portable systems are developed in the USA by ITN Energy Systems, Microcell, Nanodynamics, Mesoscopic Devices, Adaptive Materials, in Europe by Allps (Austria), Adelan (GB), Swiss institutions (OneBath/ETH, Dantherm, EPF Lausanne, and HTceramix), and in Japan by TOTO/Hitachi and AIST. For example, NanoDynamics’ ‘Revolution 50’ provides 50 W/12 V and can be operated for a period of 36 h by a 410 ml tank of propane. Mesoscopics Devices (Protonex Technology Corporation) has developed 75 and 250 W ‘MesoGen’ units for military applications, which are fueled by 770 and 2110 ml of kerosene per day, respectively.

Nomenclature Abbreviations and Acronyms ABS AFC APU CFCL

acrylonitrile butadiene styrene plastic alkaline fuel cell auxiliary power unit Ceramic Fuel Cells Limited

CGH2 CH CUTE CVD DE DFC DMFC DOE EADS EFC EPRI EPSI ERC FCE FR GB GRI IFC IPT KTI LANL LPG MCFC MHI PAFC PEM PEMFC PTFE RFCS SECA

compressed gaseous hydrogen Swiss patent Clean Urban Transport for Europe chemical vapor deposition German patent direct fuel cell direct methanol fuel cell Department of Energy European Aeronautic Defence and Space Company European Fuel Cell Electric Power Research Institute Energetic Power Systems Energy Research Corporation Fuel Cell Energy French patent British patent Gas Research Institute International Fuel Cells Corp. Independent Power Technology Kinetics Technology Los Alamos National Laboratory liquefied petroleum gas molten carbonate fuel cell Mitsubishi Heavy Industries phosphoric acid fuel cell proton-exchange membrane proton-exchange membrane fuel cell polytetrafluoroethylene regenerative fuel cell system Solid State Energy Conversion Alliance

History | Fuel Cells SFC SOFC SPE UPS US UTC ZEV

Smart Fuel Cell solid oxide fuel cell solid polymer electrolyte uninterruptible power supply US-American patent United Technologies Corp. zero-emission vehicle

Further Reading Bacon FT (1952) GB Patent 667298; (1955) GB Patent 725661. Baur E and Preis H (1937) Zeitschrift fur Elektrochemie 43: 727--732. (1938) 44: 695–698; (1939) Bull. Schweiz. Elektrochem. Verein 30: 478–481 Baur E, et al. (1910) Zeitschrift fur Elektrochemie 16: 286--302; (1912) 18: 1002–1011; (1921) 27: 199–208; (1933) 39: 148–167, 168–180; (1934) 40: 249–252; (1935) 41: 794–796; (1937) 43: 725–726 (on MCFC). Blomen LJ and Mugerwa MN (eds.) (1993) Fuel Cell Systems. New York: Plenum Press. Bossel U (2000) The Birth of the Fuel Cell, 1835–1845 including the first publication of the complete correspondence from 1839 to 1868 between Christian Friedrich Scho¨nbein (discoverer of the fuel cell effect) and William Robert Grove (inventor of the fuel cell). Oberrohrdorf, Switzerland: European Fuel Cell Forum. Davtyan OK, et al. (1946) Bull. Acad. Sci. USSR, Dept. Sci. Technol 1: 107--114. (1946) 2: 215–218; (1970) Soviet Electrochemistry 6: 773–776. Euler K-J (1974) Entwicklung der elektrochemischen Brennstoffzellen. Munich: Thieme.

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Grove WR (1839) Philosophical Magazine III 14: 127--130. (1842) 21: 417– 420; (1854) 8: 405; (1833) Proceedings of the Royal Society of London 4: 463–465; (1845) 5: 557–559. Haber F, Brunner L, and Moser A (1904) Zeitschrift fur Elektrochemie 10: 697--713. (1904) 11: 593–609; (1906) 12: 78–79; (1906) Zeitschrift fur Anorganische und Allgemeine Chemie 51: 245–288, 289–314, 356–368; (1907) Austrian patent 27,743. Jacques WW (1896) Harpers Magazine 26: 144--150. Justi EW (1963) Seventy years fuel cell research. British Journal of Applied Physics 14: 840--853. Kordesch K, Gsellmann J, Cifraina M, et al. (1999) Intermittent use of a low-cost alkaline fuel cell-hybrid system for electric vehicles. Journal of Power Sources 80(1–2): 190--197. Kordesch K and Simader G (1996) Fuel Cells and Their Applications. Weinheim: Wiley VCH. Kurzweil P (2003) Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg. McNicol BD, Rand DAJ, and Williams KR (1999) Direct methanol–air fuel cells for road transportation. Journal of Power Sources 83(1–2): 15--31. Mu¨ller E (1922) Zeitschrift fur Elektrochemie 28: 101. Posner AM (1955) Fuel 34: 330--338. Rideal EK (1958) Zeitschrift fur Elektrochemie 62: 325--327. Sandstede G, Cairns EJ, Bagotzky VS, and Wiesener K (2003) History of low temperature fuel cells. In: Vielstich W, Lamm A, and Gasteiger HA (eds.) Handbook of Fuel Cells – Fundamentals, Technology, and Applications, vol. 1, ch. 12, p. 145. Chichester: John Wiley & Sons Ltd. Schmid A (1923) Die Diffusionsgaselektrode. (1924) Helvetica Chimica Acta 7: 370–373. Stuttgart: Enke. Spengler H (1956) Brennstoffelemente. Angewandte Chemie 68: 689. Strasser K (1990) The design of alkaline fuel cells. Journal of Power Sources 29: 149--166. Yokokawa H and Sakai N (2003) History of high temperature fuel cells. In: Vielstich W, Lamm A, and Gasteiger HA (eds.) Handbook of Fuel Cells – Fundamentals, Technology, and Applications, vol. 1, ch. 13, p. 219. Chichester: John Wiley & Sons Ltd.