Fuel cell technology is "space-age technology" brought down to earth. Fuel cell technology dates back to the 1800s, but it was not until the end of the 20th century that it was used successfully in spacecraft to provide electricity and water. The technology can be used to make electricity to power vehicles, homes, and businesses. And if you use a renewable energy source as the main source of hydrogen, a fuel cell can be considered a renewable energy source. In California, fuel cell electricity systems using renewable resources are eligible for funding under the state's Emerging Renewables Rebate Program.
Unlike conventional technologies, fuel is not "burned" but is combined in a chemical process. A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water, and heat.
Hydrogen fuel is fed into the "anode" of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a separate current that can be utilized before they return to the cathode, to be reunited with the hydrogen and oxygen in a molecule of water.
A fuel cell system that includes a "fuel reformer" can obtain hydrogen from any hydrocarbon fuel - from natural gas, methanol, and even gasoline. Other possible fuels include propane, hydrogen, anaerobic digester gas from wastewater treatment facilities, and landfill gas.
Fuel cells are being designed for use in stationary electric power plants to provide reliable, clean, high quality electricity for distributed power generation. These small systems can provide primary or backup power to commercial and industrial customers such as hotels, hospitals, manufacturing facilities, and retail shopping centers. Eventually, smaller fuel cells will be sold for use in homes, most of which will connect to natural gas supplies.
For industries that require high quality uninterruptable power, such as the computer technology industry, fuels cells can provide power without disruptions or voltage distortions.
In addition to electricity, customers can take advantage of the heat from the fuel cell and use it for hot water, space heating and cooling, and industrial processes.
Fuel Cell Types
Fuel cells are categorized according to the type of electrolyte used. Some of the these include:
- Proton Exchange Membrane (PEM) fuel cells were used in the "Gemini" space craft missions and designed by DuPont. A solid polymer ion exchange membrane is used as an electrolyte. Platinum Ruthenium is used as the catalyst. PEM fuel cells are being tested in mobile sources such as buses and smaller vehicles.
- Platinum is used as the catalyst in Phosphoric Acid fuel cells, one of the most mature fuel cells (and which relies upon aqueous phosphoric acid as an electrolyte).
- Alkaline fuel cells are one of the oldest types of fuel cells. They, too, rely upon platinum (or palladium) as the catalyst for a potassium hydroxide electrolyte.
All three of the above fuel cell types operate at temperatures that require that conversion of fuel to hydrogen occur outside of the fuel cell. This approach introduces a level of complexity avoided by the following two fuel cell designs:
- Molten carbonate fuel cells rely upon nickel-based catalysts (and molten carbonates as electrolytes) and can operate at higher temperatures. Reforming the fuel into hydrogen can occur inside the fuel cell. Most of the larger fuel cells on the market today rely upon this approach.
- The Solid Oxide fuel cell relies upon a coated zirconia ceramic as the electrolyte, which translates into the ability to operate at even higher temperatures that can support fuel formulation within the fuel cell. No catalyst at all is required. This technology is the least mature of the fuel cell types currently on the market. Nevertheless, it offers the promise of reduced cost and greater quantities of thermal heat for use at the installation site.