Fuel Cell Panel Discussion E C O N O M I C FEASIBILITY of fuel cells as sources of power depends partly on the nature of fuels employed. A number of audience questions were related to the role that certain industries such as petroleum, large chemical, or coal would play in furnishing such fuels. Coal, considering its ready availability in this country, will remain a major fuel source for many years. Integrating a coal gasification unit with a fuel cell station has been one ultimate objective in high temperature fuel cell research. I n such a process the coal would be gasified with steam to produce water gas which would subsequently be oxidized in fuel cells to produce electrical energy. T o obtain favorable over-all efficiencies, it is essential that the fuel cells be operated a t temperatures higher than the coal gasification process so that the heat developed by the cells would be available for the endothermic gasification reactions. If the coal gasification and fuel cell operations were conducted separately, the over-all efficiency would be little better than that achieved by the best steam cycles available today. At present the major limitation to such a n integrated process is the lack of a n efficient, long life, high temperature fuel cell. Saturated hydrocarbon fuels such as kerosine or propane, can be used effectively in high temperature fuel cells, but again more research and development is required before a n efficient hydrocarbon-fuel cell system is ready for commercial purposes. The objective with the direct use of hydrocarbon fuels is to operate a t the lowest temperature that allows reasonable current densities without excessive carbon deposition. Unsaturated hydrocarbons a r e readily oxidized even in ambient temperature cells. Fuel storage might pose a problem in certain types of traction devices and other mobile or small scale applications for those cells operating on gaseous fuels that are not readily liquefied. Methanol and other simple oxygenated organic compounds might find use as a fuel in such cases. Methanol vapor can be oxidized readily in fuel gas cells, both those operating on molten salt electrolytes and those operating a t ambient temperature, and liquid methanol can be used in low temperature "direct feed" cells. Depending on the projected applications, inexpensive organic chemicals that are easily oxidized might well find extensive use as fuels.
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Cel1:Construction and Operation
As would be expected, the majority of questions from the floor concerned principles of operation and construction of the various types of cells. Many of these questions clearly demonstrated the great need for extensive fundamental research on fuel cells and allied problems. Present high temperature fuel cells employ molten salt electrolytes, usually contained in a porous matrix. There would be several advantages to the use of solid electrolytes if suitable materials could be found. Three major difficulties are encountered with solid electrolytes investigated to date: T h e conductivities are generally much less than for molten salts and consequently the IR drop across the cell is excessive; it is difficult to keep the solid electrolyte in an equilibrium state; and many of the solid electrolytes become highly semiconducting a t higher temperatures which short circuits the cell. T h e immediate prospect of finding a suitable solid electrolyte does not appear promising. One important variable in electrode design is porosity. In low temperature
Following the papers presented during the symposium on fuel cells, held by the Division of Gas and Fuel Chemistry, a panel discussion was held, based on questions from the floor. This report summarizes some of the major points raised during the discussion. Although representing opinions expressed by individual panel members, this summary does not necessarily reflect the unanimous views of all the members. The panel members were F. T. Bacon, National Research Corp., London, England 0. H. J. Broers, Central Technical Institute, The Hague, Netherlands H. H. Chambers, Sondes Place Research Instifute, Dorking, Surrey, England K. Kordesch, National Carbon Co., Cleveland, Ohio H. A. Liebhafsky, General Electric Co., Schenectady, N. Y. G. J. Young, Alfred University, Alfred, N. Y.
INDUSTRIAL AND ENGINEERING CHEMISTRY
cells a proper ratio between the larger pores, which serve as the means of transport for the reactants (and products), and the fine pores a t the gaselectrolyte interface, where the major portion of the reaction occurs, is necessary for optimum current densities. The upper limit on the permissible electrode surface area (primarily microporosity) thus is determined by the effectiveness of the macroporosity in allowing diffusion of the product and reactant gases. Excessively large macropores a t the gas-electrolyte interface are undesirable since flooding of the electrode occurs. In high temperature cells which employ porous metal electrodes, porosity and surface area of the electrodes are restricted due to sintering of the metal either in fabrication or during operation. T h e proper selection of electrode catalysts is another important factor in obtaining optimum power characteristics with low temperature fuel cells. A large variety of organic compounds can be electrochemically oxidized with appropriate catalysts. I n cells operating a t higher temperatures, the role o f the catalyst becomes less important.
Future Prospects The extent to which fuel cells are employed in various power applications within the next few years depends on the amount of research and development work expended. If a sizable fraction of the investment that has gone into atomic energy development were put into fuel cells, the prospects for wide application would be fairly good. Small mobile power sources will probably be available in the near future. Fuel cells to power certain types of traction devices appear feasible. T h e combination of a fuel cell and a direct current motor is particularly attractive from the point of view of the high torque developed a t low speeds. I n Germany battery driven rail cars are competitive with Diesel electrics. Fuel cells seem to offer several advantages over conventional batteries in this area and might in time find applications such as for locomotives, large earth moving equipment, and small ships operating over short distances. T h e prospects for the use of fuel cells in large central power stations are unknown a t present. T h e answer to this question as well as many others must await further development. Division of Gas and Fuel Chemistry, Symposium on Fuel Cells, 136th Meeting, ACS, .4tlantic City, N. J., September 13-18, 1959.
G. J. YOUNG Alfred University, Alfred, N. Y.
