41 Fuel Cells a Real Option

Fuel cells are hardly a new idea. They were invented in about 1840, but they are yet to really make their mark as a power source for electric vehicles. However, this might be set to change over the next 20 or 30 years. Certainly most of the major motor companies are spending very large sums of money developing fuel cell powered vehicles.

The basic principle of the fuel cell is that it uses hydrogen fuel to produce electricity in a battery-like device to be explained in the next section. The basic chemical reaction is:

The product is thus water, and energy. Because the types of fuel cell likely to be used in vehicles work at quite modest temperatures (~85°C) there is no nitrous oxide produced by reactions between the components of the air used in the cell. A fuel cell vehicle could thus be described as zero-emission. Furthermore, because they run off a fairly normal chemical fuel (hydrogen), very reasonable energies can be stored, and the range of fuel cell vehicles is potentially quite satisfactory. They thus offer the only real prospect of a silent zero-emission vehicle with a range and performance broadly comparable with IC engined vehicles. It is not surprising then that there have, for many years, been those who have seen fuel cells as a technology that shows great promise, and could even make serious inroads into the domination of the internal combustion engine. Such ideas regularly surface in the science and technology community, and Figure 4.1, showing a recent cover of the prestigious Scientific American magazine, is but one example.

Many demonstration fuel cell powered cars of very respectable performance have been made, and examples are shown in Figures 1.14 and 1.15. However, there are many problems and challenges for fuel cells to overcome before they become a commercial reality as a vehicle power source. The main problems centre around the following issues.

1. Cost: fuel cells are currently far more expensive than IC engines, and even hybrid IC/electric systems. The reasons for this are explained in Section 4.4, where we consider how a fuel cell system is made, and in Section 4.7, where we show the extent of the equipment that needs adding to a fuel cell to make a working system.

Electric Vehicle Technology Explained James Larminie and John Lowry © 2003 John Wiley & Sons, Ltd ISBN: 0-470-85163-5

Figure 4.1 The front cover of the October 2002 issue of the magazine Scientific American.

Articles within outline the possibilities presented by fuel cell powered electric vehicles. (Reproduced by kind permission of Scientific American.)

Figure 4.1 The front cover of the October 2002 issue of the magazine Scientific American.

Articles within outline the possibilities presented by fuel cell powered electric vehicles. (Reproduced by kind permission of Scientific American.)

2. Rival technology: hydrogen is a fuel, and it can be used with exactly the same overall chemical reaction as equation (1.1) in an IC engine. Indeed, cars have been produced with fairly conventional engines running off hydrogen, notably by BMW in Germany. The emissions from these vehicles are free from carbon monoxide, carbon dioxide, hydrocarbons, and virtually all the unpleasant pollution associated with cars; the only pollutant is a small amount of nitrous oxide. Considering the reduced cost and complexity, is this a better solution? To answer this question we need to look at the efficiency of a fuel cell, and see how it compares with an IC engine. This basic thermodynamics are covered in Section 4.3.

3. Water management: it is not at all self-evident why water management should be such an important and difficult issue with automotive fuel cells, so Section 4.5 is devoted to explaining this important and difficult problem.

4. Cooling: the thermal management of fuel cells is actually rather more difficult than for IC engines. The reasons for this, and the solutions, are discussed in Section 4.6.

5. Hydrogen supply: hydrogen is the preferred fuel for fuel cells, but hydrogen is very difficult to store and transport. There is also the vital question of 'where does the hydrogen come from?' These issues are so difficult and important, with so many rival solutions, that we have dedicated a whole chapter to them, Chapter 5.

Figure 4.2 A fuel cell powered bus in use in Germany. Vehicles like this, used all day in cities, and refueling at one place, are particularly suited to being fuel cell powered (Reproduced by kind permission of MAN Nutzfahrzeuge AG.)

However, there is great hope that these problems can be overcome, and fuel cells can be the basis of less environmentally damaging transport. Many of the problems are more easily solved, and the benefits are more keenly felt, with vehicles such as buses that run all day in large cities. Such a vehicle is shown in Figure 4.2, and they have been used in several major cities in Canada, the USA and Europe. Many thousands of people will have taken journeys in a fuel cell powered vehicle, though many of them will not have noticed it. So before we consider the major problems with fuel cells, we will explain how these interesting devices work.

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