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Hydrogen Fuel Cell, by Tyler Osgood

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  • Bashir Syed
    Hydrogen Fuel Cell Hydrogen Fuel Cell Tyler Osgood Georgetown University School of Foreign Service Program in Science, Technology, & International Affairs The
    Message 1 of 1 , May 2, 2006
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      Hydrogen Fuel Cell
       


      Hydrogen Fuel Cell
      Tyler Osgood
      Georgetown University School of Foreign Service
      Program in  Science, Technology, & International Affairs

      The Hydrogen Fuel Cell could revolutionize the world. This ingenious technology, which creates electricity from the chemical reactions of hydrogen and oxygen has, in its 150-year history, passed many of the critical tests along the path from invention to innovation. Recent developments in fuel cell technology and concurrent developments within the energy and automotive industries have brought the world to brink of the fuel cell age and the hydrogen economy.

      The future is, however, inherently murky. Fuel cells still face significant technological, political and economic hurdles before they can realize their truly awesome potential. An examination of these hurdles, set to the backdrop of an explanation of the current state of the art in fuel cell technology and the current and developing economic and regulatory landscape, will provide insights into much touted future of the fuel cell. In the near future, the fuel cell will come to play a much more prominent role in the world energy economy. The extent to which this innovation will revolutionize the world will depend on any number of technological, economic and political factors.

      In order to understand the potential impact and resulting policy implications of the fuel cell, it is first necessary to explain the technology of the fuel cell. The fuel cell utilizes the chemical properties of hydrogen to produce an electrical current. "...[T]hey produce an electric current by intercepting the electrons that flow from one reactant to the other in an electrochemical reaction."1 Fuel cells require only a fuel containing hydrogen and oxygen, usually from atmospheric air, to produce electricity. A fuel cell that utilizes pure hydrogen produces this electricity leaving water and heat as the only waste by-products. Recent interest in the hydrogen fuel cell stems from its ability to produce electricity without the producing any pollutants, including carbon dioxide, associated with the burning of fossil fuels.

      A fuel cell is, in principle, a very simple electrochemical device. The chemical reaction that powers hydrogen fuel cells is the same as that which occurs when hydrogen burns. The chemical equation for this reaction is: 2H2 + O2 ( 2H2O + energy. "Normally hydrogen burns, reacting with oxygen from the air, producing water, heat and light. ... In the fuel cell the chemical reaction is exactly the same, but instead of producing light and heat energy, electrical energy is produced."2 All fuel cells consist of an electrolyte (a substance that allows only the passage of ions) sandwiched between two electrodes. When a fuel containing hydrogen is passed over the negative electrode, otherwise known as an anode, it is ionized. Ionization of the fuel, often accomplished with the assistance of a catalyst, removes electrons from the hydrogen creating positively charged hydrogen ions and negatively charged free electrons. Since only the ions can pass through the electrolyte situated between the electrodes, the electrons must find another route to the positive electrode or cathode, where they will be reunited with the hydrogen ions and combined with oxygen atoms to form water. The electrons passing around the electrolyte constitute an electric current, and thus can be used to provide power during their journey from anode to cathode.3

      The basic principles of the fuel cell have been understood since its invention more than 150 years ago. The hydrogen fuel cell was first demonstrated in 1839 by British physicist William R. Grove.4 It was not for more than one hundred years that the fuel cell found its first major application, as power sources for all US manned spacecraft since Project Gemini in 1965. 5 Despite a number of experimental applications such as a fuel cell tractor developed in 1959, until the 1990s, the space program remained the only large-scale user of fuel cells. Throughout the 1990s, however, interest in the fuel cell has increased significantly.

      While the same simple overall basic design is common to all fuel cells, fuel cells vary widely in their specific choices of electrolytes and catalysts. These factors have large effects in terms of the efficiency, price and operating characteristics of fuel cells. Thus, while the basic principle of the fuel cell has been understood for close to 150 years, future advances in this technology will be determined by improvements to its constituent parts, such as electrolytes and catalysts. The choice of electrolyte is the factor that differentiates the major types of hydrogen fuel cells now being researched. Current fuel cell research can be divided into three categories based on the type of application for which the cell is intended: mobile applications such as automobiles, fixed applications such as power sources for homes and businesses and miniature portable applications such as power sources for laptop computers and personal electronics.

      The internal combustion engines of the world's automobiles are a major source contributing to rising levels of atmospheric carbon dioxide levels, which have been linked to increasing global temperature. Automobiles, burning petroleum products (gasoline and diesel fuel) also produce high levels of other pollutants such as sulfur dioxide and particulate matter that contribute to the production of smog. The fuel cell has been identified as a possible alternative power source for automobiles, due to the fact that it can produce power with little or no pollution. Current research has focused on the Proton Exchange Membrane (PEM) fuel cell, a type of Solid Polymer fuel cell as the leading type of cell for automotive use.

      The PEM fuel cell, named for the thin polymer membrane that acts as the cell's electrolyte, possesses characteristics favorable to mobile implementations such as low operating temperatures, compact size and lack of volatility.6 As the term membrane implies, the electrolyte in this type of fuel cell is extremely thin, allowing the key components of such a cell to be compact enough to make mobile applications practical. "The membrane-electrode assembly of a modern cell is as little as 2.5 millimeters (0.1 inch) thick."7 Numbers of these individual fuel cell assemblies are connected in series with a plate containing channels for the two reactants, hydrogen and oxygen, and channels to siphon off wastewater wedged between each cell, creating what is known as a fuel cell stack.8 Stacks can then be used as the source of electricity for the electric motors that could provide an automobile's motive force.

      While the PEM fuel cell's low operating temperatures of approximately 80 degrees Celsius9, opposed to more than 1000 degrees C for certain other types of fuel cells, allows for car installation without heavy thermal shielding, low operating temperatures necessitate expensive platinum catalysts. "Because it is low temperature cell, the electrodes need a platinum catalyst to promote the reactions."10 The platinum catalyst speeds the ionization/deionization process at the center of the fuel cell's electrochemical reactions, creating more current per unit fuel. Platinum is among the world's most rare and most valuable metals, thus the need for significant quantities in PEM fuel cells has presented a significant obstacle to their development. While a detailed accounting of the reduction of platinum requirements will be given in relation to the economics of the automotive fuel cell, costs have dropped to the point where widespread research and development along with early commercialization efforts have become practical. One of the most successful development efforts to date has been pioneered by Ballard Power Systems of Vancouver, British Columbia. In 1995 Ballard produced a single stack weighing 45Kg (99 lbs) and occupying 30 liters (1.06 cubic ft) of space that produces 32.3 kilowatts or approximately 43 horsepower with an efficiency of 54 percent.11 This level of efficiency is very impressive when compared to the average internal combustion engine operating at an efficiency of 15 percent with a theoretical limit of 35 percent.12 "Various generations of Ballard's stacks are now powering buses in Vancouver and Chicago as well as several experimental DaimlerChrysler vehicles."13

      Currently fuel cells are not price competitive with gasoline or diesel fired internal combustion engines as automotive power plants. While the cost of fuel cell generating capacity has rapidly fallen and at the current price of between $3000 and $4000 per kilowatt of capacity14 is only a fraction of what it was just a few years ago, experts estimate that the price per kilowatt of power generating capacity must fall to between $50 and $100 per kilowatt to be competitive with gasoline. As stated before one of the major material costs of producing PEM fuel cells is platinum. While no substitute for the platinum catalyst in PEM fuel cells has yet been found, extensive research and development efforts have reduced the quantity needed for effective cells by a factor of 30 since 1986, with an additional halving seen as readily achievable.15 Accordingly, the amount of platinum necessary to manufacture a fuel cell capable of producing one kilowatt of power has fallen from nearly $180 worth to between six and eight dollars worth.16 According to The Economist: "Five years ago, for example, the amount of platinum required by a stack of PEM fuel cells cost $30,000; now it needs about $500-worth."17 At the same time, advances are being made in the in the plates that separate the membrane-electrode assemblies, allowing their construction from inexpensive carbon composites instead of expensive graphite.18 "On their own, these and similar economies should bring the cost of a kilowatt of output down to around $20, if as many as 250,000 engines a year were produced."19 Therefore, if we factor in the efficiency gains from mass production, PEM fuel cell stacks should be able to compete on price with the internal combustion engine as a power source for automobiles.

      As The Economist observes, however, "...a fuel cell engine is more than a stack of cells."20 The largest issue associated with the use of fuel cells is the question of fuel. Fuel cells rely on hydrogen. While hydrogen is extremely easy to produce and is found in a high percentage of chemical compounds (hydrocarbons), its production requires energy. As almost any inquisitive 12 year old knows (the author performed the experiment at that age) hydrogen can be produced by passing an electric current through water, leaving oxygen as the only by-product, 2H2O + energy ( 2H2 + O2. This process of electrolysis of water is the exact reversal of the electrochemical reaction that drives the fuel cell. "So it looks like a zero-sum game: you have to invest at least as much energy in making the fuel as get back from burning it."21 If the generation source of the electricity used to create hydrogen burns fossil fuels, almost all the emissions gains from moving away from the internal combustion engine will be offset by the increased emissions resulting from increased electrical production. Even if higher efficiencies of fuel cells, in terms of translating fuel to power, make their use a net improvement in terms of pollution when using fossil fuel produced electricity22, producing hydrogen from water makes it very expensive.

      Per unit energy, hydrogen produced electrically costs ten times as much as natural gas and three times as much as petroleum based fuels.23 As a result, even if the manufacturing costs of fuel cells can be made competitive on a per kilowatt capacity basis with internal combustion engines, the high cost of hydrogen fuel could still leave fuel cells much more expensive than conventional engines on a per kilowatt generated basis. Also if reduction of carbon dioxide is the primary concern, hydrogen fuel cell powered vehicles using hydrogen produced with nuclear, solar, wind, hydro or geothermal power would achieve this goal. All of these power generation methods, however, have severe limitations. Nuclear power has widely been shown both politically and economically untenable whatever one thinks of it environmentally. At the same time, both solar generation and wind power remain prohibitively expensive. Hydroelectric power is viable in some areas, but has been coming under greatly increased environmental criticism of late. Finally, geothermal power is only viable in those limited areas that are geologically active. While all these sources could be used to generate emission's free electricity to create hydrogen for fuel cells, all other problems aside, they are unlikely to be able to produce cheaply enough to create cost competitive hydrogen. Also, the amount of electricity necessary to produce fuel for even a small portion of the world's cars would be immense. The number of new plants needed and the additional demand for electricity would raise the price of electricity and consequently the price of hydrogen. A large leap in the price of electricity could have unforeseen consequences far removed from the automotive industry.

      It should be noted that a potential breakthrough in hydrogen production would be the discovery of an efficient and cheap photocatalyst, a substance that directly harnesses the energy in solar radiation to electrolyze water and thus produce hydrogen.24 This type of hydrogen generation systems could allow hydrogen power to realize its full potential of emissions reduction in a presumably cheaper and more efficient manner than any other non-polluting generating technique. While several such photocatalysts are known, it was reported in the October 1999 that researchers in Japan have discovered the most effective photocatalyst yet.25

      There is an alternative to using hydrogen produced from the electrolysis of water to power fuel cells. Reforming hydrocarbons such as methane, natural gas or methanol through a series of chemical reactions can produce hydrogen. Reforming can be done either centrally, such as at a natural gas well head, necessitating a hydrogen infrastructure, or onboard the fuel cell vehicle. Reformation results in the release of CO2, whether done centrally or onboard. Central reformation from natural gas has the potential to be very cost competitive with gasoline, all infrastructure and storage questions aside. "It is very easy to make hydrogen from natural gas. Hydrogen with an energy content equal to a gallon of gasoline might cost $1.20 - $1.50, which - because a fuel cell vehicle can operate more than twice as efficiently as today's autos - could provide very low fuel costs per kilometer."26

      Onboard reformation presents problems due to the efficiency losses from the power needed to run the reformer and the inability to contain or avoid the CO2 emissions from the reformers. Still many industry officials have advocated the use of onboard reformation of fuels other that hydrogen, such as methanol and even gasoline. The use of gasoline while attractive for its ability to use existing infrastructure, operates at an efficiency only marginally better than that of the internal combustion engine, releases the same amount of CO2 and cannot be used in today's automotive fuel cells.27 Another option is to use methanol fuel, but methanol requires many of the same infrastructure and storage upgrades needed for hydrogen. It seems that direct use of hydrogen is the most plausible scenario for the future of the fuel cell.

      If an effective, efficient and competitive method for the production of hydrogen can be found, there are a number of issues relating to the infrastructure needed to deliver that hydrogen to vehicles and how the hydrogen should be stored on board the vehicles. Assuming the decision to directly use hydrogen and not onboard reformation, the first question that arises is in what from, liquid or gas, should the hydrogen be distributed and stored. Each form of the fuel has unique properties. Liquid hydrogen can be stored more compactly than gaseous hydrogen, but it must be stored cryogenically. Moreover, liquid hydrogen requires 30% more energy to produce than gaseous hydrogen28, further raising fuel costs. On the other hand, gaseous hydrogen occupies approximately 1.8 times the space of the liquid, even when stored at high pressure, creating problems for mobile installations.29 Gaseous hydrogen, however, as opposed to the liquid form of the element can easily be distributed through the existing natural gas infrastructure.30 This ability to rely at least to some degree on an existing infrastructure combined with its 30% price advantage give gaseous hydrogen the edge over the liquid form as the form for hydrogen fuel.

      One interesting and plausible scenario for the production and distribution of hydrogen fuel is that of central reformation from natural gas at the wellhead. The main advantage of natural gas lies in the fact that it is relatively plentiful and thus cheap. Central reformation of the gas would yield economies of scale from the large amounts of gas processed. Furthermore, by tying the production of hydrogen with the production of natural gas, it would be possible to fully use the existing natural gas distribution infrastructure for the hydrogen. By using an existing infrastructure instead of building a new infrastructure, both economic and social costs can be avoided. The most exciting aspect of the wellhead reformation scenario is the possibility of preventing the release of the carbon dioxide produced by the reformation. By capturing the CO2 produced by the reformer and pumping it back into the ground, the CO2 could be kept from entering the atmosphere and contributing to the greenhouse effect.31 While pumping CO2 into the ground may sound fanciful, it is currently being done in at least one location. Since 1996, the Norwegian state-owned oil and gas company, Statoil has been disposing up to a million metric tons of CO2 a year, produced as a by-product of the Sleipner West gas field, into the rock beneath the North Sea.32 The same disposal techniques in use at Sleipner West could be used with CO2 produced from hydrogen production. This scenario could allow fuel cells to reach their full potential in terms of emissions reductions.

      In the Kyoto protocol signed in December 1997 (check fact find citation) the world's major industrialized nations agreed to cut their rates of carbon dioxide emissions by the year 2010. The United States agreed to reduce its emissions by 7% by 2010 with the European Union agreeing to an 8% cut.33 International law now compels Kyoto to not act in any way contrary to the general purpose or nature of the protocol, even if they have not ratified the treaty. Having constrained themselves in Kyoto, it is obvious that domestic governments are serious about reducing CO2 emissions. However, non-emitting technologies such as the fuel cell are not yet cost competitive with traditional emitting energy sources, nor are they likely to be in the near future. The carbon tax, a tax on the carbon dioxide released from any given energy source, is one possible method of overcoming the price differential between emitting and non-emitting energy sources. "...[R]emember that the easiest way to reduce something is to tax it-in this case, by taxing the carbon content of power."34 By directly taxing only that which is to be reduced, carbon emissions, the highest levels of economic efficiency will be achieved because the market will determine all other factors, such as the choice of technology. The market will still determine what technologies and what fuels are used, but the carbon tax will introduce an economic cost for the previously external factor of environmental degradation caused by CO2 release. The overall effect of such a tax would be a fall in the production of CO2 and an overall rise in the price of energy.

      The carbon tax, while perhaps the most economically efficient method for directly tackling the release of CO2, has been politically unpopular in many countries. If a tax is going to be an effective method of reducing CO2 it must be unambiguous and without exception. While a few countries, specifically those in Scandinavia, have implemented carbon taxes, the have undercut them by exempting certain industries that consume large amounts of power, but are politically powerful. According to The Economist: "This is perverse. If the idea is to reduce consumption, exempting big consumers makes a nonsense of it."35 In the US, where energy has always been taxed minimally, there is almost no serious political consideration of such taxes, as the issue is considered to be "certian death"36 for politicians. Even the comparatively regulation rich European Union has finally given up on its plans to institute such a tax. The main reason for opposition to such a tax is the perceived high cost imposed by any form of energy tax. However, any increase or imposition of an energy tax could be accompanied by a corresponding decrease in other forms of broad based tax such as payroll, sales or even capital gains taxes. Further complaints that a carbon tax is regressive in that it effects, can also be overcome by tinkering with other existing taxes.37 Other programs can be used to offset the immediate cost of a carbon tax, such as granting tax credits to companies that reduce emissions with indirect methods such as planting trees to absorb CO2 or bussing their employees to and from work.

      Since automobiles are responsible for a large portion of many nations' CO2 emissions, the use of even a small percentage of zero-emission vehicles would aid a country in meeting its emissions reduction goals. For example, in the US approximately 30 percent of all CO2 emissions are produced by the transport sector.38 As previously explained, the fuel cell is one propulsive mechanism that could fill the role of the internal combustion engine, but it is not yet cost competitive. By raising the price of fuels that release CO2 such as gasoline, relative to the price of non-emitting fuels like cleanly produced hydrogen, the carbon tax could make the fuel cell a cost competitive propulsion system for road borne vehicles.

      Precedent and anecdotal evidence suggests that the carbon tax would be effective. Many nations phased out leaded gasoline by taxing it more heavily than its unleaded equivalent. In addition, those countries that have implemented carbon taxes have seen a diminished growth rate in the use of energy by those industries subjected to the tax.39 While not all agree, many sources suggest that the Statoil CO2 reinjection program at Sleipner West came in response to Norway's carbon tax. "The release of CO2 from Sleipner West... would be enough to increase Norway's CO2 emissions by 3 per cent. And as Norway was imposed a carbon tax it would cost Statoil about pounds 35 million a year."40 If it can ever be made politically acceptable a carbon tax can work.

      For more than 150 years, the fuel cell has gathered dust on the shelves of laboratories around the world. Now, however, something has changed drastically in favor of the fuel cell, that much is clear. Fuel cell research is one of the hottest areas of applied science. Three of the world's largest automobile manufacturers, Ford, General Motors and DiamlerChrysler, have all promised to bring fuel cell powered cars to market by 2004 41 and have undertaken aggressive research to make it happen. Even the world's largest oil companies, traditionally portrayed as a conservative force feverishly working to undercut alternative fuels, have jumped on to the fuel cell bandwagon. According to Don Huberts head of Shell Hydrogen as quoted in The Economist, "The stone age did not end because the world ran out of stones, and the oil age will not end because we run out of oil."42

      "The fuel cell has been around for 150 years, so why is it attracting attention now? The reason is a happy coincidence of greenery, market liberalization and technology is finally making fuel cells cheap."43 The largest single factor inducing the rush to develop fuel cell powered automobiles has been the automotive and oil companies' recognition that due to environmental sensitivities, an alternative to the conventionally fueled internal combustion engine must be found to power automobiles. This realization has grown out of agreements such as the Kyoto protocol and earlier government regulation such as California's Zero Emission Vehicle mandate. The popularity of such environmental legislation and current science establishing the theory of global warming on solid scientifically accepted ground have convinced the auto and oil industries that the development of non-polluting energy sources makes economic sense. Industry would not be spending money on the fuel cell unless it believed it would be profitable to do so.

      The success of the initial fuel cell research undertaken as a result of government regulation has lead to the current focus on fuel cells as the most plausible power source for zero and ultra-low emissions vehicles. Now identified as the leader of the pack in the diverse world of alternative fueled vehicles, fuel cells are poised to receive the majority of research funding in this area, and increased funding will in turn produce more breakthroughs. "Such have been the advances that market incentives, not mere regulation are now motivating firms."44 The imposition of additional incentives, such as a tax on the carbon content of fuel, will further reinforce the economic benefits of the fuel cell, both for producers and consumers.

      The fuel cell is currently the nearest alternative to the internal combustion engine as a viable alternative power source for automobiles. The fuel cell's unique properties, in that it can operate extremely efficiently, without any polluting emissions have led to increased development in the face of industry's recognition that increased environmental regulation is forthcoming. When that increased regulation manifests itself is a question of politics, but agreements like the Kyoto Protocol illustrate that governments around the globe have recognized the need for such regulation. The form of such regulation is also a matter of debate. Whatever policy is adopted, it should be independent of any particular technology and it should seek to accomplish its environmental goals with the minimum loss of economic efficiency. Since economic efficiency is best achieved through the market mechanism, a policy such as a carbon tax that directly addresses the problem, in this case CO2 emissions, while leaving all other factors in the hands of the market makes the most sense. A carbon tax, introducing an economic cost for the previously external factor of environmental degradation, could help close the price gap between traditional and alternative power sources for automobiles. The fuel cell, as the current leader in alternative engine technology, could thus receive the final push it needs to become an economically viable technology, thus ushering in the era of the fuel cell car.

      Works Cited

      Appleby, A. John. "The Electrochemical Engine for Vehicles," Scientific American, July 1999, 74-79.

      "Carbon Tax leads to burial at sea," New Scientist, 3 August 1996, 11.

      "Cleaner Energy," The Economist. 18 April 1998, 17.

      "Climate Change Information Sheet 24," UNFCCC Climate Change Information Kit.

      http://www.unfccc.de/resource/iuckit/fact24.html

      Lloyd, Alan C. "The Power Plant in Your Basement," Scientific American, July 1999, 81-86.

      Electro-Chem-Technic Corp. "Fuel Cell Types,"

      http://www.i-way.co.uk/~ectechnic/FCTYPES.HTML Downloaded 10/31/99.

      Electro-Chem-Technic Corp. "How does a fuel cell work?,"

      http://www.i-way.co.uk/~ectechnic/BASICS.HTML Downloaded 10/31/99.

      "Emission Summary for CO2 in United States of America," United Nations Framework Convention of Climate Change. 11/18/99.

      http://www.unfccc.de

      "English Conference of the Parties," Kyoto Protocol to the United Nations Framework Convention on Climate Change." Downloaded 10/10/99.

      http://www.cnn.com/SPECICALS/1997/global.warming/stories/treat/index4.html

      "Fill'er Up: With Hydrogen," Reuters, 16 August, 1999. Available on Wired News http://www.wired.com/news/technology/0,1282,21293,00.html

      "Fuel cells hit the road," The Economist. 24 April 1999.

      "Fuel cells meet big business," The Economist. 24 July 1999.

      "The Future of Fuel Cells," Scientific American, July 1999, 72-73.

      "Here comes the sun battery," FT Asia Intelligence Wire, 10/28/99.

      Houlder, Vanessa, "Fuel for thought: Environment Hydrogen Power." Financial Times, 10/05/99.

      Endnotes

      1. Lloyd, Alan C. "The Power Plant in Your Basement," Scientific American, July 1999, 81.
      2. Electro-Chem-Technic Corp. "How does a fuel cell work?," http://www.i-way.co.uk/~ectechnic/BASICS.HTML Downloaded 10/31/99.
      3. "The Future of Fuel Cells," Scientific American, July 1999, p73.
      4. Ibid, 72.
      5. Appleby, A. John. "The Electrochemical Engine for Vehicles," Scientific American, July 1999, p74.
      6. Ibid, 76.
      7. Ibid, 76.
      8. Ibid, 76.
      9. Ibid, 76.
      10. Electro-Chem-Technic Corp. "Fuel Cell Types", http://www.i-way.co.uk/~ectechnic/FCTYPES.HTML Downloaded 10/31/99.
      11. Appleby, 76.
      12. Ibid, 75.
      13. Ibid, 76.
      14. Llyod, p80.
      15. Appleby, p76.
      16. Ibid, p 76.
      17. The Economist. 24 July 1999.
      18. "Fuel cells hit the road," The Economist. 24 April 1999.
      19. Ibid.
      20. Ibid.
      21. "Here comes the sun battery," FT Asia Intelligence Wire, 10/28/99.
      22. Houlder, Vanessa, "Fuel for thought: Environment Hydrogen Power." Financial Times, 10/05/99.
      23. FT Asia Intelligence Wire, 10/28/99.
      24. Ibid.
      25. Ibid.
      26. Appleby, 77.
      27. Ibid, 79.
      28. Ibid, 77.
      29. Ibid, 77.
      30. Houlder.
      31. Ibid.
      32. "Carbon Tax leads to burial at sea," New Scientist, 3 August 1996.
      33. "English Conference of the Parties," Kyoto Protocol to the United Nations Framework Convention on Climate Change." http://www.cnn.com/SPECICALS/1997/global.warming/stories/treat/index4.html
      34. "Cleaner Energy," The Economist. 18 April 1998. p17.
      35. Ibid.
      36. Ibid.
      37. "Climate Change Information Sheet 24," UNFCCC Climate Change Information Kit. http://www.unfccc.de/resource/iuckit/fact24.html
      38. "Emission Summary for CO2 in United States of America," United Nations Framework Convention of Climate Change. 11/18/99. http://www.unfccc.de
      39. The Economist. 18 April 1998.
      40. New Scientist, 3 August 1996.
      41. "Fill'er Up: With Hydrogen," Reuters, 16 August, 1999. Available on Wired News, http://www.wired.com/news/technology/0,1282,21293,00.html.
      42. "Fuel cells meet big business," The Economist. 24 July 1999.
      43. Ibid
      44. Ibid

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