Solvent-Free Electrolytes with Aqueous Solution-Like Conductivities

Aqueous solutions are generally assumed to be superior electrolytic conductors because of the unique dielectric and fluid properties of water. We show that their conductivities can be matched by liquid electrolytes that contain no solvent. These are proton transfer salts that are liquid at ambient temperature. The high conductivities are due to the high fluidity and ionicity rather than some sort of Grotthus mechanism, although in certain cases a mobile proton population may make a non-negligible contribution. The highest conductivities have been obtained when both cations and anions contain protons. At 25°C, values of >150 millisiemens per centimeter (mS cm^-1) appear possible; at 100°C, 470 mS cm^-1 has been measured. Because of the combination of high ionicity and proton exchange kinetics with low vapor pressure, the systems we describe also make excellent fuel cell electrolytes.