Fuel cell is a device that converts chemical energy to electrical energy. In this way, a fuel cell is similar to a battery. However, a battery contains all of the components required to produce electric power. A fuel cell, however, must constantly be fed a fuel and an oxidizer to produce power. An oxidizer is a substance that removes electrons in a chemical reaction.
It costs more to produce a given amount of power using a fuel cell than using a battery. However, a fuel cell’s electrodes (electric terminals) remain largely unchanged during its operation. A battery’s electrodes, on the other hand, can be gradually used up. After battery electrodes are consumed, the battery will stop producing power. It must be discarded or recharged. But a fuel cell will continue to produce power as long as the fuel and oxidizer are provided.
The United States Gemini and Apollo space programs of the 1960’s used fuel cells to provide electrical energy for spacecraft. Today, many scientists are working to produce cost-effective fuel cells to power automobiles.
How a fuel cell works.
In a fuel cell, the fuel is fed from outside the cell to one of two electrodes, called the anode. There, an oxidation reaction releases electrons. The electrons, which are negatively charged, travel outside of the fuel cell through an external circuit. The flow of electrons powers one or more devices, such as motors or lights, that are included in the circuit. The electrons then travel to the other electrode, called the cathode. There, they are involved in a reduction reaction with the oxidizer, which is fed from outside the cell. In a typical fuel cell, the anode and cathode each contain a catalyst. A catalyst is a substance that speeds a chemical reaction. If the catalysts were not present to enable efficient reactions, the fuel cell would produce little or no power. Platinum is commonly used as a catalyst in fuel cells.
Between the anode and the cathode is an electrolyte. An electrolyte is a substance that conducts electric current. The electrolyte in a fuel cell may be a solid or a liquid. The electrolyte does not allow electrons to pass through it. However, it acts as an internal circuit by conducting positively charged ions. Ions are atoms or molecules that carry a positive or negative electric charge. The ions in a fuel cell are also involved in the oxidation and reduction reactions.
Different devices require different voltages and current to operate. By electrically connecting several fuel cells, voltage and the current may be tuned to satisfy the requirements of various devices. A group of electrically connected fuel cells is called a fuel cell stack.
A common fuel cell
is the polymer electrolyte membrane (PEM) fuel cell. It is also called a proton exchange membrane fuel cell. This device is named for the electrolyte it uses. Its electrolyte is a thin, solid membrane composed of long chains of molecules called polymers. The two electrodes sit on either side of the membrane. The fuel is hydrogen gas. The oxidizer is either oxygen gas or air. At the anode, hydrogen is oxidized at a platinum catalyst to produce electrons and hydrogen ions. The hydrogen ions pass through the membrane. The electrons are forced through the external circuit. At the cathode, the hydrogen ions and electrons are combined with the oxygen in the presence of platinum. This reaction produces heat, along with water. The water is removed.
