Review Lecture - The development and practical application of fuel cells

Abstract

First, a definition is given of what a fuel cell is, and a description is given of the principle of operation; this is followed by a brief account of the early history of the hydrogen fuel cell. Next, the alkaline fuel cell is considered in some detail, first with respect to choice of electrolyte and working temperature, then choice of materials and finally electrode design; it is shown that the trend now is towards operating temperatures somewhat below 100°C; as regards catalysts for hydrogen, platinum or palladium are still widely used for space and submarine applications where cost is of minor significance, though considerable progress is being made with Raney alloys of nickel with iron, molybdenum or titanium. Catalysts for the oxygen electrode include silver and certain spinels; mention is also made of work on strontium-doped lanthanum cobaltite, which appears to show great promise at temperatures rather above 100°C. As regards electrode design, the trend is now towards the use of a catalyst mixed with a hydrophobic material such as polytetrafluoroethylene, the object being to increase the area of 3-phase interface between gas, electrolyte and electrode. A description is given of the hydrogen-oxygen fuel cell system used in the Apollo space flights, and the results obtained. A short account is given of the extra difficulties encountered when air is used as oxidant in alkaline systems, in place of pure oxygen. The development of acid fuel cells has been rapid in recent years, and the use of carbon or graphite as a structural material and as an electrical conductor has led to a great reduction in cost, with an electrolyte of either phosphoric or sulphuric acid. Mention is also made of recent developments with acidic ion-exchange membranes as electrolyte, and a brief descrip­tion is given of the early design used in the Gemini space flights. Although platinum-based catalysts are still widely used in the United States, research work in Germany has led to the use of cheaper materials such as tungsten carbide and graphited charcoal in sulphuric acid cells. As regards terrestrial applications for fuel cells, a number of units using pure hydrogen and oxygen have been developed for underwater use; but much the biggest effort is now being directed to the production of units incorporating a steam reformer, fuel cells and inverter, and which will consume a gaseous, or liquid, hydrocarbon fuel, and air as oxidant; they will deliver alternating current, and will be for stationary applications. Finally, a section is devoted to energy storage and synthetic fuels; emphasis is placed on the possibility that hydrogen, obtained from nuclear energy and water by one of two different routes, may eventually become a widely available fuel, thus improving the prospects for hydrogen-air fuel cells. It is even suggested that liquid hydrogen may eventually come into use as a fuel for road and rail traction, though this may not come about until liquid hydro­carbon fuels become scarce and expensive. Finally, a proposal is made that work should be initiated on an improved form of electrolyser, using all the experience which has now been accumulated in the design of fuel cells.