There are several types of fuel cells. These are categorized in 5 main parts as below:
- Solid oxide fuel cell (SOFC)
- Alkaline fuel cell (AFC)
- Phosphoric acid fuel cell (PAFC)
- Molten carbonate fuel cell (MCFC)
- Polymer electrolyte fuel cell (PEFC or PEM)
In addition to the above categories, there is one more type named direct methanol fuel cell or DMFC. But this type is commonly included in 5th group. The working temperature of fuel cells can vary between 80 degrees Celsius for PEFCs and 1000 degrees for SOFCs. Low temperature cells have H+ and OH– carriers that exchange ions through electrolyte and electrons through an external circuit. In high temperature cells like MCFCs and SOFCs, electric current is carried by CO32- and o22- .
1. Solid Oxide fuel cell:
These cells use a metal oxide as electrolyte. Ion conductivity is carried out using oxygen ions traveling through a crystal network. Zirconium is a common electrolyte used in these cells and usual working temperature is between 100 to 900 degrees Celsius.
2. Alkaline fuel cell
This kind of fuel cells works in relatively high temperatures about 250 degrees Celsius with concentrated 85 wt% potassium hydroxide. Newer systems use 35-50 wt% potassium hydroxide at much lower temperature of 120 degrees. These cells have better cathode performance than acidic fuel cells.
3. Phosphoric acid fuel cell
These cells are one the simplest fuel cells made. They are a little heavy and bigger than polymer electrolyte cells. They have the advantage of high electrolyte stability. The working temperature of such cells is about 150 to 220 degrees Celsius.
4. Molten carbonate fuel cell
In these cells, carbonates of alkaline metals like lithium, sodium and potassium are used as electrolytes. Since electrolytes are used in liquid manner, the stability and life time of the cell will reduce. The working temperature of these cells is above the melting point of carbonates about 600 to 700 degrees Celsius.
5. Polymer electrolyte fuel cell (proton exchange membrane)
Working at 80 degrees Celsius with efficiency of 50 percent, they are one of the most favorable cells ever made. In these cells, an ion exchange membrane is used as electrolyte. The advantage of these cells is the use of solid electrolyte that is very stable. Also, the only liquid used in the cell is water which reduces the corrosion significantly.
by N. Ghodrati – Persian Gulf university of Iran
Director: Dr. M. Mofarahi
Translated by: P. Jowkar
Editor: M. A. Makarem