Proton transfer salts: A new class of solvent-free, involatile, fuel cell electrolytes

Many problems with fuel cells, such as electrolyte water management and cost, would be alleviated if an inexpensive high temperature electrolyte permeable only to protons could be found. One class of materials that has not been systematically investigated as fuel cell electrolytes are proton transfer salts. These are made by neutralizing an acid with an equimolar amount of base to yield a salt, which contains proton. This allows for great flexibility in tailoring electrolyte properties. When the energy difference for the proton residing on the donor versus the acceptor corresponds to a free energy gap of 0.8-1.0 eV, the resulting proton transfer salts are not volatile, need no solvent to conduct proton and can be used in fuel cells operating at temperatures above 100°C. One proton transfer salt electrolyte, liquid ethyl ammonium nitrate (EAN), replaced aqueous concentrated H3PO4electrolyte in a fuel cell, and the result was a higher open circuit voltage and relatively smaller polarization. These liquid proton transfer salt electrolytes may be useful themselves, however we consider them as models to membrane electrolytes. New work is focused on making membranes based on the use of the proton transfer salt concept based on results obtained with liquids.