Fuel cells for automotive application

Index of contents

1 Introduction

2 Basics

3 Fuel cells in automotive application

3.1 Fuel cells as main drive

3.2 Fuel Cells as range extender

3.3 Fuel cells as Auxiliary Power Unit (APU)

4 Problems of fuel cells

4.1 Storage of hydrogen

4.2 Hydrogen infrastructure

4.3 Exhaustible raw materials dependence

5 Conclusion

6 References

1 Introduction

In the last 20 years, the automotive industry had to adopt itself to the rapidly changing market. Environmental awareness gets more and more important in the western but also in the emerging countries. Due to the global warming governments all over the world enact laws to protect the environment. The European Union (EU) for example limited the emission of CO2 from 2015 to 120 g/km and from 2020 even to 95 g/km for each new car that is licensed in the EU.¹

Particularly air pollution in China’s cities is extremely high. 20 of the 30 cities with worldwide highest pollution are located in China. Not only industry but also individual transportation grows extremely year by year. China’s government enacted emission standards for vehicles according to European model in several cities like the capital Beijing or Shanghai. Despite big efforts to advance air quality, there is no significant improvement because of 1.300 new registered vehicles daily.²

Due to the different ecological laws, car manufacturers spend big efforts in developing fuel saving technology and alternative drives. On the one hand, systems like direct fuel injection, engine start-stop, that turns off the engine while idling, or intelligent energy control are just some examples for reducing fuel consumption in commercial vehicles. Toyota on the other hand released their Prius on Japanese market in 1997 which was the first commercial available hybrid car. Especially in Germany many car manufacturers realized their failure in this technology and now spend big efforts in development of hybrid cars.

To reduce emission of greenhouse gases, there is another key technology which is actually very old but because of the development of combustion engine it was buried in oblivion. DaimlerChrysler with the NECAR 1 proved that Fuel Cells generally can be implemented in cars to provide the needed electrical energy for propulsion. Nowadays many companies try to push this technology forward, but 15 years later there is still no commercial car available which is equipped with a fuel cell. The following pages give a short overview of fuel cells, implementation of them into individual mobility and problems companies have to face.

2 Basics

A fuel cell converts chemical energy directly, which means without a thermal expansion process, into electricity. In principle such a cell works with a reduction and oxidation element. Both have to be continuously supplied to the fuel cell, unlike a battery or accumulator fuel cells stay unchanged. A fuel cell consists of two electrodes sandwiched around an electrolyte, which assure that both gases do not contact and due to that not react. Encouraged by catalyst hydrogen atoms split into a proton and an electron, which take different paths to the cathode.

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Only the resulted proton can cross the electrolyte, while electrons create a separate current that can be utilized before reaching the cathode, to be reunited with hydrogen and oxygen in a molecule of water. At the cathode the following reaction proceeds:

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Figure 1 shows the electrochemical process of a fuel cell in principle.

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Figure 1: Configuration of a PEMFC[3]

A fuel cell system which includes a "fuel reformer" can utilize the hydrogen from any hydrocarbon fuel - from natural gas to methanol, and even gasoline. Since the fuel cell relies on chemistry and not combustion, emissions from this type of a system would still be much smaller than emissions from the cleanest fuel combustion processes.[4]

Because of the existence of several different types of fuel cells they are listed and classified in table 1 and 2. Usually fuel cells are classified by the electrolyte material and their working temperature which also specifies the area of application.