New fuels as alternatives to methanol for direct oxidation fuel cells

Hydrocarbons and aliphatic alcohols are difficult to electro-oxidize. Even at 190 degreesC the oxidation of ethanol is incomplete (less than 40% CO2). We report here, for the first time, on the complete electro-oxidation of two molecules having C-C bonds; ethylene glycol (EG) and dimethyl oxalate (DMO). Both are less prone to pass through the membrane, and, as a result, have up to 94-95% fuel utilization, 9-10% higher than that of methanol. EG is well known in the automobile industry and, in contrast to methanol, its distribution infrastructure already exists, making it a promising candidate for practical electric vehicles. DMO is a solid that has limited solubility in water, thus it may be added directly to the anode compartment with no need of a separate fuel tank and monitoring and feeding systems. It is projected that a flat dimethyl oxalate fuel cell will deliver up to 600 Wh/kg, five to ten times the specific energy of the lithium-ion battery in small portable devices. However, methanol does have some advantages over EG and DMO, its theoretical capacity is 20 to 40% higher and so far it has higher energy conversion efficiency. (C) 2001 The Electrochemical Society.