Types of Fuel Cells Literature Review:
Fuel cells are basically electrochemical cells that produce electrical energy from the chemical energy of the fuel. These are highly efficient because in this process we don’t need to produce heat or mechanical work as intermediate steps to generate electrical energy. Since there is no burning in the fuel cells, so there is less production of pollutants.
Fuel cell usually comprises on fuel cell kits and stacks. In fuel cell kit, the chemical reaction occurs which produce charges on electrodes, while stacks are used to regulate the flow of charges or electric current from cell kit (Appleby, 1988, Larminie et al., 2003).
In 1839 William Grove demonstrated the basic operation of fuel cell, he electrolyzed water into hydrogen and oxygen by using platinum electrode in the presence of dilute acid as electrolyte, and then he replaced the power supply with ammeter. Electrolysis process is reversed and it produced water and electric current. Choice of electrolyte depend upon operating temperature conditions. Aqueous electrolyte can be used under 200 oC, high temperature can resulted into more vapours and more degradation (Appleby, 1988, O’Hayre et al., 2006).
Types of Fuel Cells
Fuel cells are classified in 5 types on the basis of electrolyte used in fuel cell kit.
- Polymer Electrolyte fuel cell
- Alkaline fuel cell
- Phosphoric acid fuel cell
- Molten carbonate fuel cell
- Solid oxide fuel cell
Polymer Electrolyte Fuel cell:
Membrane is used in this cell for transfer of ion, this ion exchange membrane is usually made from fluorinated sulfonic acid polymer because it is an excellent proton conductor. As there liquid is only water so there is less chances of corrosion in it. This electrolyte perform under the wet condition of membrane and this type of fuel cell can be used when the temperature is below than 80 oC. If the temperature is increased from 80 oC, it will dehydrate the membrane which will decrease the efficiency of the cell (Borup et al., 2007, Amphlett et al., 1995).
Due to solid electrolyte it is easy to handle and it gives high resistance to gas crossover. Polymer electrolyte fuel cells are capable of high current duties that’s why it used in large variety of applications, especially in fuel cell powered vehicles. The cell is quite sensitive to a little amount of carbon monoxide, sulfur and ammonia, even a little traces can poisoned to the cell (Borup et al., 2007, Steele and Heinzel, 2001).
Alkaline Fuel Cell:
The first alkaline fuel cell was developed in early 1960 and the same type of cell is used in Apollo mission to empower the space vehicle. The electrolyte of this cell is consist of concentrated potassium hydroxide, for high operating temperature like 350 oC the concentration of KOH is increased to 80 percent by weight and when the operating temperature is lowered (120 oC), dilute KOH (50 % by weight) is used to maintain the efficiency of the cell (Coutanceau et al., 2006).
Since the drawback of this type of cell also same like in polymer electrolyte fuel cell, a little concentration of CO and CO2 can poison the cell, so ambient air is treated before it allows to enter in the cell, which makes it costly (Lee et al., 1997, Saari and Lampinen, 1990, McLean et al., 2002).
Phosphoric Acid Fuel Cell:
Phosphoric acid termed as PAFC, high concentrated phosphoric (100%) used as the electrolyte in this cell, due to concentrated electrolyte this cell can be used at relatively high-temperature ranges from 150 oC to 220 oC. At lower temperature phosphoric acid become a poor conductor, and the chances of carbon monoxide poisoning increased on Pt electrolyte, but still lower than other type of fuel cells (Stonehart, 1984, Bagotsky, 2012). Oxygen reduction is slower on cathode so, Pt catalyst used in this cell to increase the reduction rate. Extensive fuel processing and the expensive material is used to avoid corrosion make it more costly than another type of cells (Steele and Heinzel, 2001).
Molten Carbonate Fuel Cell:
A molten carbonate fuel cell is typically made for high operating temperature, it operate at 600 oC to 700 oC. Different combination alkali and carbonate are used as the electrolyte in the ceramic matrix of lithium aluminum oxide. Nickel anode and nickel oxide cathode are used to promote the rate of reaction at high temperature. Several types of hydrocarbons can be used as fuel. MCFCs slower in start-up and bigger in size, are used in that kind of application where start-up time is not an issue, they are usually used in marine and stationary applications (Dicks, 2004, Kaun and Smith, 1987).
High operating temperature and less expensive electrolyte make it more economical than other type fuel cell.
Solid Oxide Fuel Cell:
Solid and nonporous metal oxide with ZrO2 stabilizer is used as an electrolyte in this type of cell. Cupper zirconium can be used as the anode with LaMnO3 cathode (Bagger et al., 1997). At in early stages it operates only at high temperature like 1000 oC, but later on, with little modification of electrolyte (thin layer electrolyte) this can be used for lower temperature as 650 oC. In the last decade, a lot work done on the Solid oxide fuel cell to decrease down its operating temperature so it can be used as the power source in vehicles. Due to the solid electrolyte, it can be shaped into tubular and planner shape which are easy to handle.
The only drawback of this cell is its high operating temperature, it will be costly practice to achieve high temperature and then maintain it, high temperature also causes thermal expansion (Singhal, 2007, Ormerod, 2003).
- AMPHLETT, J. C., BAUMERT, R., MANN, R. F., PEPPLEY, B. A., ROBERGE, P. R. & HARRIS, T. J. 1995. Performance modeling of the Ballard Mark IV solid polymer electrolyte fuel cell I. Mechanistic model development. Journal of the Electrochemical Society, 142, 1-8.
- APPLEBY, A. J. 1988. Fuel cell handbook.
- BAGGER, C., KINDL, B. & MOGENSEN, M. 1997. Solid oxide fuel cell. Google Patents.
- BAGOTSKY, V. S. 2012. Phosphoric Acid Fuel Cells. Fuel Cells: Problems and Solutions, Second Edition, 99-106.
- BORUP, R., MEYERS, J., PIVOVAR, B., KIM, Y. S., MUKUNDAN, R., GARLAND, N., MYERS, D., WILSON, M., GARZON, F. & WOOD, D. 2007. Scientific aspects of polymer electrolyte fuel cell durability and degradation. Chemical reviews, 107, 3904-3951.
- COUTANCEAU, C., DEMARCONNAY, L., LAMY, C. & LÉGER, J.-M. 2006. Development of electrocatalysts for solid alkaline fuel cell (SAFC). Journal of Power Sources, 156, 14-19.
- DICKS, A. L. 2004. Molten carbonate fuel cells. Current Opinion in Solid State and Materials Science, 8, 379-383.
- KAUN, T. D. & SMITH, J. L. 1987. Molten carbonate fuel cell. Google Patents.
- LARMINIE, J., DICKS, A. & MCDONALD, M. S. 2003. Fuel cell systems explained, Wiley New York.
- LEE, J. Y., LEE, H. H., LEE, J. H. & KIM, D. M. 1997. Alkaline fuel cell. Google Patents.
- MCLEAN, G., NIET, T., PRINCE-RICHARD, S. & DJILALI, N. 2002. An assessment of alkaline fuel cell technology. International Journal of Hydrogen Energy, 27, 507-526.
- O’HAYRE, R. P., CHA, S.-W., COLELLA, W. & PRINZ, F. B. 2006. Fuel cell fundamentals, John Wiley & Sons New York.
- ORMEROD, R. M. 2003. Solid oxide fuel cells. Chemical Society Reviews, 32, 17-28.
- SAARI, K. & LAMPINEN, M. 1990. Alkaline fuel cell. NASA STI/Recon Technical Report N, 92, 16204.
- SINGHAL, S. C. 2007. Solid oxide fuel cells. The Electrochemical Society Interface, 16, 41.
- STEELE, B. C. & HEINZEL, A. 2001. Materials for fuel-cell technologies. Nature, 414, 345-352.
- STONEHART, P. 1984. Carbon substrates for phosphoric acid fuel cell cathodes. Carbon, 22, 423-431.