A fuel cell is an electrochemical energy conversion device that works similar to a battery. Fuel cells differ from batteries in that they consume reactants and must be replenished, while batteries store electrical energy chemically in a closed system.

The fuel cell has two ‘sides’ an anode and cathode side that react in the presence of an electrolyte. Fuel cells can operate continuously as long as the necessary flow is maintained.

There are many combinations of processes and fuels possible. The most well-known, the hydrogen fuel cell uses hydrogen, other fuels include hydrocarbons, alcohols, air, chlorine and chlorine dioxide.

With the hydrogen cells, the anode, or negative post of the fuel cell, conducts the electrons that are freed from the hydrogen molecules. The cathode conducts the electrons back, where it recombines with the hydrogen ions and oxygen to form water.

The reaction in a single fuel cell produces only about 0.7 volts, so to increase the voltage fuel cells are combined to form a fuel-cell stack.

Types of fuel cells
There are several different types of fuel cells, and are usually classified by the type of electrolyte used. 

Proton exchange membrane fuel cell (PEMFC)
PEMFCs operate at a fairly low temperature which means they don't require expensive containment structures. Improvements in the engineering and materials have increased the power density to where a device the size of a small piece of luggage can power a car. Alkaline fuel cell (AFC): This type of fuel cell was used in the U.S. space program. It requires pure hydrogen and oxygen making it very expensive.

Phosphoric-acid fuel cell (PAFC)
The phosphoric-acid fuel cell has potential for use in small stationary power-generation systems. It operates at higher temperatures creating a long warm-up time making it unsuitable for use in cars.

Solid oxide fuel cell (SOFC)
These fuel cells are best suited for large-scale stationary power generators. This type of fuel cell operates at very high temperatures that in turn can produce steam then channeled into turbines in order to generate more electricity.

Molten carbonate fuel cell (MCFC)
These fuel cells are also best suited for large stationary power generators. They operate at 1,112 F, so they also generate steam that can be used to generate more power. They have a lower operating temperature than the SOFC, which means they don't need such exotic materials making the design less expensive.

Controversy
A great deal of the technology surrounding fuel cells is focused on hydrogen and hydrogen, although abundant is difficult to store and distribute. Despite being plentiful, hydrogen is derived from raw material, which until recently has mostly been fossil fuels like oil, coal and natural gas. Most of the hydrogen is produced by the combustion of fossil fuels, which have well-known environmental issues therefore the production of hydrogen is going to need greater focus in the future.

Information resources:

Fuel cell commercialization—Ohio Fuel Cell Coalition

Clean Fuels Ohio

Wright Fuel Cell Group

Department of Energy