Electro chemical reactions always consist of two half reactions taking place in anode and cathode electrodes. In polymer electrolyte membrane fuel cells or PEFCs, hydrogen ions produced in anode electrode travel through the ion conductive membrane and reach to the cathode electrode and the released electrons in anode, will go to cathode through an external circuit. These electrons and hydrogen ions react with oxygen producing heat and water in cathode.
In today’s world, one of the most important problems of humanity is the energy. Due to irregular use of fossil fuels, the environment is getting polluted more and more. Therefore, it’s crucial to replace the fossil fuels with modern clean energies. Fuel cells are one of the most promising technologies that can be used with any electrical system. Polymer electrolyte membrane or proton exchange membrane (PEM) fuel cells are currently one of the most efficient systems designed to convert chemical energy of hydrogen and oxygen to electricity directly. These systems can be used anywhere from cars to power plants.
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- .