In 1839 the English physicist William Grove made a remarkable discovery. He had electrolyzed dilute sulphuric acid between two platinum electrodes with the well-known result: The water was split, and hydrogen bubbled up at the negative electrode and oxygen bubbled up at the positive electrode. When Grove disconnected his current supply, he discovered that the small amounts of oxygen and hydrogen left on the electrodes could actually produce a weak electrical current. He had discovered the principle of the fuel cell. In the following years he developed a so-called gas battery based on this principle. However, it would take many years before fuel cells had any practical applications.
William Grove's 'gas battery', the first fuel cell
The first major breakthrough in fuel cell research came in the 1890s when the British chemist Ludwig Mond (born in Germany) and his assistant Carl Langer introduced porous electrodes. The porous electrodes allow air and fuel gas to enter and react in a much greater region than solid electrodes do. In 1895 the American engineer and chemist William W. Jacques succeeded in making a large fuel cell system capable of delivering a sizable amount of energy. Jacques connected 100 fuel cells, each consisting of an iron electrode and a coal electrode immersed in molten potassium hydroxide at 450 °C. Atmospheric air was blown down around the iron electrode while the fuel consisted of the coal anode which oxidized to carbonate. The fuel cell system had an electrical power of 1.5 kilowatt – enough to light up 25 ordinary light bulbs. But not for long; the carbonate was deposited around the coal anode and blocked the cell.
Low temperature fuel cells
A new era started with the British engineer Francis Thomas Bacon. In 1933 he began the development of alkaline fuel cells (AFC). They contained potassium hydroxide in aqueous solution at 200 °C. The electrodes consisted of porous nickel, and they were fed hydrogen and oxygen at a pressure of 45 atmospheres. However, fuel cell development is a long-term endeavour. Only in 1959 Bacon had a 5 kilowatt demonstration unit ready. In the 1960s the aircraft engine manufacturer Pratt & Whitney licensed Bacon's patents and obtained a contract with NASA to use the fuel cells on the Apollo spacecraft.
The main problem for AFC is that it does not tolerate CO2. Both hydrogen and oxygen must be cleaned which adds considerably to the system costs. In the 1960s and 1970s development of CO2 tolerant cells began. One type, PEMFC, has a proton conducting ion exchange membrane as electrolyte. In another type, PAFC, the electrolyte is phosphoric acid at 150-200 °C. PAFC was the object of a large scale development program in the 1970s and is commercially available today.
High temperature fuel cells
The high temperature fuel cells MCFC og SOFC both have their origin in research carried out by the Swiss chemist E. Baur in the 1920s and 1930s. In contrast to the low temperature cells they can utilize both natural gas and coal gas by internal reforming, or, depending on the type of electrode, by a more direct reaction. This means that both types have a significantly higher efficiency than the low temperature fuel cells. It is only after 1980 that MCFC and SOFC development have taken off, and today both types have been demonstrated in prototype systems larger than 100 kilowatt. |