Evaluation of Electrolytes for Direct Oxidation Hydrocarbon/Air Fuel Cells.

Abstract : This program consisted of research studies on electrolytes for direct-oxidation hydrocarbon/air fuel cells, the objective being to find an electrolyte in which the rate of electrooxidation of propane is greater than that obtained using orthophosphoric acid at 140C as the electrolyte. Baseline data that were obtained at 104 and 140C with 95-97% orthophosphoric acid were in agreement with the results of other workers using this electrolyte. Experiments with trifluoromethanesulfonic acid showed it to be a promising electrolyte; however, the physical properties of its monohydrate (which is the actual form of the electrolyte) need to be investigated more thoroughly. Hexafluorosphosphoric acid was evaluated for possible use, but was rejected because it was not invariant, in that hydrogen fluoride was evolved rapidly during the tests. Hexafluorostibonic acid showed similar behavior, with evolution of fumes at temperatures of 85-90C, but at a much lower rate. Consideration was given to the possible use of bistrifluoromethylphosphinic acid as an electrolyte. A brief study was made of solid polymer electrolytes for the hydrocarbon fuel cell application. On the basis of these investigations, trifluoromethanesulfonic acid appears to be the most promising new electrolyte for direct oxidation hydrocarbon/air fuel cells.