A fuel cell is nothing but an electrochemical energy conversion device that converts hydrogen and oxygen into water, producing electricity and heat in the process. Every fuel cell has two electrodes, one positive, termed as cathode, and one negative, called the anode. The production of electricity takes place at the electrodes.
It has an electrolyte that carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes. It is just like a battery that can be recharged while you are drawing power from it. It can be recharged using electricity; however, a fuel cell uses hydrogen and oxygen.
In an ordinary combustion reaction, as in a flame or an internal combustion engine, essentially all the energy released in the reaction is converted to heat. In a fuel cell, the reaction is done electrochemically, meaning that in the anode compartment the fuel is oxidized and in the cathode compartment, oxygen from the air is reduced to water.
The two compartments are connected by an electrolyte that allows hydrogen ions (protons) to move from the anode to the cathode. A single fuel cell can generate a very small amount of direct current (DC) electricity. Generally they are assembled in a stack.
Fuel Cell-Powered Electric Car
A fuel cell using pure hydrogen has the potential to be up to 80% efficient. But hydrogen is difficult to store in a car. Adding a reformer to convert methanol to hydrogen drops the overall efficiency to about 30 to 40%. To convert the electrical energy into mechanical energy, an electric motor and inverter are required.
The motor/inverter is about 80% efficient. Converting methanol to electricity is about 30 to 40% efficient, and converting electricity to mechanical power is 80% efficient. This gives an overall efficiency of about 24 to 32%. It provides direct current voltage that can be used to power motors, lights, or any number of electrical appliances.
Classification of Fuel Cells
PEM Fuel Cell
This technology was invented at General Electric in the early 1960s, through the work of Thomas Grubb and Leonard Niedrach. This company announced initial success in mid-1960 when they developed a small fuel cell for a program with the U.S. Navy's Bureau of Ships (Electronics Division) and the U.S. Army Signal Corps.
Proton exchange membrane fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet. Thomas Grubb and Leonard Niedrach ran a fan with a small diesel-powered PEM fuel cell in April 1963. The PEM technology served as part of NASA's Project Gemini.
Alkali Fuel Cell
These devices work on compressed hydrogen and oxygen, and generally use a solution of potassium hydroxide in water as their electrolyte. The working temperature inside alkali cells are around 150 to 200 degrees C.
NASA preferred alkali fuel cells for the Space Shuttle fleet, as well as the Apollo program, mainly because of power generating efficiencies that approach 70%. These cells also provide drinking water for the astronauts.
Solid Oxide Fuel Cell
A solid oxide fuel cell makes use of a hard ceramic electrolyte instead of a liquid and operates at temperatures up to 1,000 degrees C. Solid oxide and molten carbonate fuel cells are high temperature devices.
During recent years the climbing energy prices and advances in materials technology have reinvigorated work on SOFCs, and a recent report noted about 40 companies working on these fuel cells.
Recent research has proved that using readily available hydrocarbon fuels like methane would avoid the logistical problems of storing and refueling with hydrogen. Such fuel cell cars will start to replace gas and diesel engine cars in the coming 2 to 3 years. It will be very similar to an electric car but with a fuel cell and reformer instead of batteries.
In future, you will fill your fuel-cell car up with methanol, but some companies are working on gasoline reformers. Some companies hope to do away with the reformer completely by designing advanced storage devices for hydrogen.
The fuel cell will fight with many other types of energy conversion devices―including the gas turbine in our city's power plant, the gasoline engine in our car, and the battery in our laptop―and will prove superior.