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10 Fuel-Cell Chemistry Overview 10.1 IntroductIon Companies such as Daimler, Ford, GM, Honda, Peugeot–Citroen, Toyota, and Renault–Nissan have long known the limitations of internal combustion engines. The efficiency of petroleum-fueled engines is expected to peak at around 30% [1]. Efficiency is not the only limitation for internal combustion engines. As detailed in Chapter 9, combustion of gasoline produces emissions that are environmentally harmful. Hydrocarbons, CO 2 emissions, nitrogen oxides, and carbon monoxide are released into the atmosphere during combustion. Predictions are that fuel-cell vehicles will be twice as efficient as internal combustion engines and have only byproducts of water and heat [1]. With advances in technology such as direct fuel injection, improvements in EGR valves, and improvement in cylinder sealing, internal combustion engines have greatly improved in efficiency. Since the 1960s, CO 2, hydrocarbon emissions, and nitrogen oxides have decreased by over 90% [1]. Despite these improvements, CO 2 emissions remain a cause for concern due to their global warming potential (discussed in Chapter 9). One of the benefits of fuel-cell vehicles is that they produce no polluting emissions and utilize a renewable source of energy. General Motors and Toyota are also aggressively pursuing battery-operated vehicles; however, these have certain drawbacks as well. Battery-powered vehicles only store a finite amount of energy. Range for these vehicles is limited typically to about 100 miles, and cooling of the lithium ion battery is currently an issue [1]. The hybrid vehicles currently being produced are a great help with fuel efficiency and environmental issues are only a stop-gap measure. With these technologies, a fundamental paradigm shift in automotive as well as world thinking around energy and its efficient use is currently occurring. 10.2 Future marKet and usage Recent studies by the WBCSD (World Business Council for Sustainable Development) have been published and some very interesting findings noted [2]. For instance, with a current population of motor vehicles of approximately 600 million, the WBCSD points out that the world population is urbanizing; it projects 8 billion people living in urban areas by 2030 and fuel use to be 3.8 trillion L by 2030 [2]. If population predictions are accurate, then as many as 1.2 billion persons will have vehicles by 2030 [3]. As countries like China and India develop their middle class, we can expect 151
152 The Role of the Chemist in Automotive Design table 10.1 Personal transportation activity by region—average annual growth rates 2000–2030 (%) 2000–2050 (%) Africa 1.90 2.10 Latin America 2.80 2.90 Middle East 1.90 1.80 India 2.10 2.30 Other Asia 1.70 1.90 China 3.00 3.00 Eastern Europe 1.60 1.80 Former Soviet Union 2.20 2.00 OECD Pacific 0.70 70.00 OECD Europe 1.00 80.00 OECD North America 1.20 1.10 Total 1.60 1.50 Source: Sustainable Mobility Project calculation. http://www.wbcsd.org/templates/Template WBCSD5/Layout.asp?MenuID=1 that the corresponding increase in income will be followed by a demand for personal vehicles. Table 10.1 shows the average annual growth rate as predicted by the Sustainable Mobility Project, which is part of the WBCSD [2]. 10.3 Fuel cells as automotIve ProPulsIon There are many types of different fuel cells; however, for our purposes we will focus on proton exchange membrane (PEM) fuel cells because they are most applicable to automobiles. A PEM basically consists of an anode and cathode in a thin cell separated by a polymer membrane. There is a platinum catalyst, which is electrochemically active. Also, of course, hydrogen and oxygen are in the circuit. Figure 10.1 illustrates the process of how fuel cells work. Hydrogen enters the fuel cell from the source and is exposed to the anode, where an electron is extracted, leaving a proton via H2→ 2H + 2e + − (10.1) The electrons are now free to go to work in the vehicle by driving an electric motor. Stripped of their electrons, the protons travel across a membrane of perfluorosulfonic acid (Nafion by DuPont). Proton conductivity is enhanced by impregnation with an acidic solid. The resulting solution will provide a higher concentration of protons. The catalyst on the cathode interface will combine the protons with oxygen from the air, producing a potential and causing the electrons to move through the
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THE ROLE OF THE CHEMIST IN AUTOMOTI
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CRC Press Taylor & Francis Group 60
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Contents Preface...................
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Contents ix 6.6 Thermal Properties
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Contents xi 11.4 Glass Microspheres
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The Author Herman Phlegm was born i
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2 The Role of the Chemist in Automo
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10 The Role of the Chemist in Autom
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3 3.1 IntroductIon Component Materi
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Component Materials in Automobiles
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Engineering and Structural Polymers
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