Fuel Cells

Paul Breeze

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780081010396
• eBook ISBN: 9780128095157
• Topic: Economics
• Subtopic: Economic Theory
• Index: Economics

Fuel Cells is a concise, up-to-date and accessible guide to the evolution of the use of electrochemistry to generate power. The author provides a comprehensive exploration of the history of fuel cells, the environmental concerns which came into prominence in the 1980s and the economic factors associated with this method of power generation.Examples discussed include Alkaline Fuel Cells, Phosphoric Acid Fuel Cells, Molton Carbonate Fuel Cells and Solid Oxide Fuel Cells, making this a valuable and insightful read for those in the power generation market and those in electrochemistry, such as engineers, managers and academics.- Explores multiple variations of fuel cell technology and evaluates their cost and application- Provides detailed historical context, beginning in 1839 with the development of electrolysis- Discusses the most up-to-date advancements and methods of fuel cell technology today

Chapter 1

An Introduction to Fuel Cells

Abstract

The fuel cell is an electrochemical device, similar to a battery, that exploits a chemical reaction to provide electrical power. In contrast to a battery, the chemicals needed to generate the power are provided externally. For most fuel cells the reactants are hydrogen and oxygen. The hydrogen is usually made from natural gas while air supplies the oxygen. Early adopters of fuel cell technology included NASA which used them for its Gemini and Apollo programs. However, these fuel cells were very expensive to manufacture. It was not until the 1990s that a commercial fuel cell was launched. Today, there are six major fuel cell types under development or available commercially. Global generating capacity based on fuel cells is between 1000 MW and 2000 MW.

Keywords

Fuel cell; hydrogen; oxygen; natural gas; electrochemical device; hydrogen economy; phosphoric acid fuel cell; alkaline fuel cell

The fuel cell is an electrochemical device, similar in concept to a battery, that exploits a chemical reaction in order to generate electricity. Batteries are designed as portable sources of electrical power and so they must carry all the chemicals necessary to provide that power within them. Once those chemicals are exhausted, the battery can no longer provide any power. A fuel cell, in contrast, contains no chemical fuel itself. It simply provides a reaction chamber in which the fuel cell reaction takes place. The actual reactants that are needed to generate the electricity are provided externally. So long as there is a source of the chemical fuel, the fuel cell can generate power. Some fuel cells are still designed to be portable, like batteries. However, many are designed for stationary applications and have very limited portability.

In order for a chemical reaction to be able to provide electrical power, it must be a reaction that releases energy as it proceeds. Such reactions are called exothermic. When a reaction of this type takes place under normal conditions, by mixing the ingredients together in a test tube for example, this energy is released in the form of heat. By manipulation of the reaction conditions, the battery and the fuel cell both release most of that energy as electrical energy instead of heat energy.

There are a wide variety of exothermic chemical reactions that have proved suitable for battery construction, reactions such as that between lead and sulfuric acid that forms the basis of the lead-acid battery used to start motor vehicles. Fuel cells, however, virtually all rely on a single reaction, that between hydrogen and oxygen to produce water. (The one variation involves a reaction between methanol and oxygen that produces carbon dioxide and water.)

The simplicity of the fuel cell reaction and the benign reaction product, water, makes the fuel cell extremely attractive environmentally. In addition, the fact that the driving force is electrochemical rather than thermodynamic means that fuel cells are not limited by heat-engine physics and are potentially more efficient than most alternative fuel-based forms of power generation. So while the best efficiency for a simple heat engine is that achieved by the diesel engine at around 50% fuel-to-electricity efficiency, the best fuel cell can reach 60%. In fact the theoretical maximum efficiency for a fuel cell operating at room temperature is 83%.

While the fuel cell reaction is simple, the practical realization of a fuel cell is not so straight-forward. In the first place the reaction between hydrogen and oxygen will not take place spontaneously at ambient temperature,¹ so the reaction must be catalyzed in low temperature fuel cells. In addition, while the oxygen that is required by a fuel cell can be provided from air, there is no ready source of hydrogen today. This means that the hydrogen for a fuel cell must be manufactured and in most fuel cells this is achieved by carrying out a process called reforming with natural gas. Reforming natural gas produces hydrogen but also generates carbon dioxide so that one of the clear environmental benefits of the fuel cell reaction, that it produces only water, is no longer applicable. In addition, the reforming of natural gas has an energy penalty, so that a fuel cell using natural gas is not as efficient as one that is fueled with pure hydrogen.

In the future there may be ready sources of hydrogen available. In the meantime, fuel cells remain environmentally attractive because of other advantages they possess. The device itself has no moving parts making it inherently quiet and relatively maintenance free. (Some fuel cell systems require pumps which will generate noise.) And even when fueled with natural gas the fuel cell generates little in the way of atmospheric or other pollutants excepting carbon dioxide. This makes it easy to site fuel cell power plants in urban areas where systems based on rotating machines such as gas turbines, steam turbines, or reciprocating engines are often less suitable.

While fuel cells offer some major advantages over other power generation technologies, one factor has held them back commercially, their cost. The principle of the fuel cell has been known since the first half of the 19th century but it was not until the middle of the 20th century that a practical fuel cell was built. The first cells were very efficient alkaline fuel cells. These demonstrated the potential for fuel cell technology but also highlighted its weakness. In order to make a fuel cell work, it was necessary to provide a catalyst that was formed from a very expensive material such as platinum. Partly as a result of this, the first fuel cells proved prohibitively expensive to make and operate.

Early fuel cells were adopted by NASA for its manned space program, an application where cost was immaterial provided the device could function efficiently and reliably. Meanwhile research during the second half of the 20th century led to the development of a range of new fuel cell technologies. Eventually a commercial fuel cell for stationary power applications was launched in 1992 based on one of these new technologies, the phosphoric acid fuel cell. Costs were still high but continued development has brought the costs of this technology down. In addition, the automotive industry has identified another type of fuel cell, the proton exchange membrane fuel, cell as a potential automotive power source to replace the piston engine and this has led to heavy investment into this area of fuel cell research. Meanwhile other technologies including two high-temperature fuel cells, the solid oxide fuel cell, and the molten carbonate fuel cell are being developed for stationary power applications and the direct methanol fuel cell has potential for portable power use.

In spite of continued investment, fuel cells have not yet had a major impact on global power generation. The global installed capacity of stationary fuel cells was over 1000 MW, but probably well under 2000 MW, at the end of 2015 based on shipment data.² This may be compared to a global installed power generating capacity from all technologies of around 6,200,000 MW at the end of 2014³: fuel cells provide 0.02% of this. It may require the development of a clean energy economy built around hydrogen rather than fossil fuels to boost growth rates significantly. Such an economy would allow fuel cells to achieve their full potential. The development of this economy is likely to be tied to the growth in the use of fuel cells in automotive applications.

1.1 The History of Fuel Cells

The history of the fuel cell can be traced to experimental studies of the origins of electricity and its connection to chemical reactions, studies that were taking place at the end of the 18th and the beginning of the 19th centuries. One of the scientists involved in this endeavor was the British scientist Sir Humphry Davy. Davy studied the effect of an electric current on water and showed that the passage of a current could split water into hydrogen and oxygen, the process now known as the electrolysis of water. In 1802 he also devised a very simple electrochemical cell using oxygen that was able to deliver a small electric shock. This device had a carbon anode and nitric acid electrolyte but Davy did not publish his findings.

While Davy’s device is now recognized as a crude form of fuel cell, the first fuel cell that conforms to the modern description was a device that was developed independently by the German scientist Christian Friedrich Schonbein and the British scientist William Grove. Both men were exploring the idea that if water could be split into its constituent elements by an electrical current, then the process could be reversed and hydrogen and oxygen used to generate a current. Grove’s letter on the subject was published in The Londo...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1. An Introduction to Fuel Cells
• Chapter 2. The Fundamentals of Fuel Cell Operation
• Chapter 3. The Alkaline Fuel Cell
• Chapter 4. The Proton Exchange Membrane Fuel Cell
• Chapter 5. The Phosphoric Acid Fuel Cell
• Chapter 6. The Molten Carbonate Fuel Cell
• Chapter 7. The Solid Oxide Fuel Cell
• Chapter 8. Direct Methanol Fuel Cell
• Chapter 9. Fuel Cells and the Environment
• Chapter 10. The Cost of Electricity From Fuel Cells