Proton Exchange Membrane Fuel cell

1. Proton Exchange Membrane Fuel cell

2. History • Invented in early 1960’s at General electric • First used by NASA to provide power for gemini space project

3. Operation • In PEMFC, the electrolyte used is a thin polymer membrane (such as poly[perfluorosulphonic] acid, which are permeable to protons but does not conduct electrons • Hydrogen flows into the fuel cell onto the anode and is split into hydrogen ions and electrons

4. Cont.. • Hydrogen ions permeate across the electrolyte to the cathode • Electrons flow through an external circuit and provide power • Oxygen is supplied to the cathode and this combines with electrons and hydrogen ions to produce water • PEMFC operate at a temperature of around 80°C

5. Cont..

6. Cont.. • Electrolyte is sandwiched between two field flow plates to create a fuel cell • Each cell produces around 0.7 volts, about enough power to run a light bulb • To generate high voltage, a number of individual cells are combined in series

7. Advantages • Operate at low temperatures which allows them to start up rapidly from cold • High power density which makes them really compact and lightweight • PEMFC work at high efficiencies, producing around 40-50 percent of the maximum voltage, and can vary their output quickly to meet shifts in power demand

8. Disadvantages • Needs pure hydrogen to operate as they are very susceptible to poisoning by carbon monoxide and other impurities

9. Current research • At present, demonstration units capable of producing 50kw are in operation and units producing 200kw are under development • Still number of barriers need to be overcome • The main issue is that the cost of membrane and catalysts are expensive but the ongoing research and development is constantly reducing the cost.

10. Applications • In 1995,Ballard systems tested PEM cells in buses in Chicago and later in experimental vehicles made by Daimler Chrysler • In 2000,AeroVironments selected PEM technology to provide night time power for its solar powered Helios long duration aircraft

11. Q&A 1.What is the operating temperature for PEMFC? • 1000°C • 500°C • 250°C • 80°C

12. Cont.. 2.What is the electrolyte used in PEMFC? • Lithium sodium carbonate salts • Liquid phosphoric acid • Potassium hydroxide • Perfluorosulphonic acid

13. Cont.. 3.What is the amount of voltage produced by each cell in PEMFC? • 10 V • 20 V • 5.5 V • 0.7 V

14. Cont.. 4.Which of the following matches the needs and characteristics of PEMFC? • Pure hydrogen • Feedstocks free from carbon-dioxide • Membrane materials and catalysts are inexpensive • Capable of producing output equivalent to 50kw

15. Cont.. 5.Which of the following are susceptible to CO? • PEM fuel cell • Alkaline fuel cell • Solid oxide fuel cell • Molten carbonate fuel cell

16. Storage medium for Hydrogen

17. Storage methods • Hydrogen can be stored as compressed gas or as a cooled liquid • Despite these methods storing hydrogen to power a car requires a large tank

18. Obstacle • With the current technology, the compressed hydrogen tank size required to contain 6.8 kg hydrogen for a 1500 kg vehicle with a driving range of 560km is 340 litres. • A typical gasoline tank for such a vehicle is 70 litres

19. Current trend • Currently the hydrogen is injected directly into the cell • There is a tank which holds methanol • Methanol and water vaporize forming hydrogen