A fuel cell combines hydrogen and oxygen to produce electricity, heat, and water. Fuel cells are often compared to batteries. Both convert the energy produced by a chemical reaction into usable electric power. However, the fuel cell will produce electricity as long as fuel (hydrogen) is supplied, never losing its charge.
Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed, and they were the first type widely used in the U.S. space program to produce electrical energy and water on-board spacecraft. These fuel cells use a solution of potassium hydroxide in water as the electrolyte and can use a variety of non- precious metals as a catalyst at the anode and cathode.
A regenerative fuel cell or reverse fuel cell (RFC) is a fuel cell run in reverse mode, which consumes electricity and chemical B to produce chemical A. By definition, the process of any fuel cell could be reversed. However, a given device is usually optimized for operating in one mode and may not be built in such a way that it can be operated backwards. Standard fuel cells operated backwards generally do not make very efficient systems unless they are purpose-built to do so as with high-pressure electrolyzers.
Zinc Air Fuel Cells (ZAFCs) combine zinc pellets and air with an electrolyte to create electricity, generating significantly more power than lead-acid batteries of the same weight. ZAFC systems have potential use in transport applications.
Microbial Fuel Cells (MFCs) use the catalytic reaction of microorganisms to convert virtually any organic matter (e.g. glucose, acetate, wastewater) into fuel. Enclosed in oxygen-free anodes, organic compounds are consumed by bacteria or other microbes. As part of the digestive process, electrons are pulled from the fuel and conducted into a circuit with the help of inorganic mediator chemicals. MFCs operate in mild conditions between 68-104 ⁰ F. These systems are capable of efficiencies up to 50 percent, and will be suitable for small to miniature applications such as medical devices.
The Hydrogen, Zinc and Alkaline Fuel Cells are similar because they all create energy. Another way that these fuel cells are similar is they all work in quite similar ways.
The Hydrogen, Alkaline and Zinc Fuel Cells are different because they use different things to make them run. The Hydrogen Fuel Cell takes hydrogen and oxygen, the Alkaline Fuel Cell uses potassium and hydroxide, whereas the Zinc Fuel Cell combines zinc pellets with air.