Hydrocarbons and aliphatic alcohols are difficult to electro-oxidize. Even at 190°C the oxidation of ethanol is incomplete ͑less than 40% CO 2 ͒. We report here, for the first time, on the complete electro-oxidation of two molecules having C-C bonds; ethylene glycol ͑EG͒ and dimethyl oxalate ͑DMO͒. 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.Fuel cells ͑FC͒ are electrochemical devices that convert, with high efficiency, the chemical energy of a fuel-oxidation reaction directly into electrical energy. Fuel cells employing organic fuels are extremely attractive as power sources for electric vehicles, and for both stationary and portable applications. A direct oxidation fuel cell ͑DOFC͒ is a device in which the organic fuel is fed directly into the fuel cell without any previous chemical modification. Inside the cell, the fuel is oxidized at the anode and oxygen is reduced to water at the cathode. Hence, DOFCs offer a considerable weight and volume advantage over indirect fuel cells, in which the fuel is reformed into hydrogen prior to use.Until now, methanol has been considered the ''best'' fuel. 1-9 It has a low cost and happens to be more efficiently oxidized, at certain conditions, than other alcohols and aqueous hydrocarbons. However, the use of methanol as a fuel presents several problems: methanol is toxic, highly flammable, has a low boiling point ͑65°C͒, and is highly prone to pass through the polymer-electrolyte membrane ͑high crossover͒. Fuel crossover lowers the operating potential of the oxygen electrode and results in the consumption of fuel and generation of heat without the production of useful electrical energy. Hence, it is obviously desirable to minimize the rate of fuel crossover. Hydrocarbons and aliphatic alcohols are difficult to electrooxidize completely, 10,11 the main products of aliphatic alcohols being aldehydes or ketones, CO 2 , and acids or esters. Even at 190°C, in a polymer-electrolyte membrane ͑PEM͒ FC, the oxidation of ethanol is incomplete, the main oxidation product ͑over 60%͒ is ethanal and not CO 2 ͑less than 40%͒. 11 There has been no report on the complete electro-oxidation of a molecule with a C-C bond, except for oxalic acid. 12 An appropriate fuel would be one that is oxidized completely...
