NOVELTY - A fuel cell system includes an alcohol supply tank (52) containing a source of low molecular weight alcohol, preferably methanol or ethanol, for controllably supplying to the water circulating loop, upon shut-down of the fuel cell, an alcohol needed to prevent the water from freezing at a predetermined temperature.    USE - For use in vehicles.    ADVANTAGE - Alcohol introduced into the fuel cell system protects the fuel cell against freezing especially in sub-freezing environments.    DETAILED DESCRIPTION - A fuel cell system comprises stack of fuel cells comprising a proton exchange membrane (8), cathode catalyst (20), anode catalyst (12) disposed on opposing sides of the membrane, and coolant water flow fields adjacent to one of the anode and cathode sides of each membrane; blower (30) for supplying a controlled flow of oxidant to the cathode (18) through the cathode reactant flow field so that the alcohol diffusing from the water circulating loop to the cathode catalyst is oxidized, producing heat which warms the fuel cell; a coolant water circulating loop including a pump (38); and an alcohol supply tank (52) containing a source of low molecular weight alcohol for controllably supplying to the water circulating loop, upon shut-down of the fuel cell, an alcohol needed to prevent the water from freezing at a predetermined temperature, preferably -40 degrees C. An INDEPENDENT CLAIM is also included for a method of operating the fuel cell system comprising:    (a) upon shut-down of the fuel cell, introducing a low molecular weight alcohol into the coolant water circulating loop; and    (b) at the beginning of the start-up sequence, introducing a limited flow of oxidant into the cathode reactant flow field to combust the alcohol and generate a heat which raises the fuel cell temperature.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram a fuel cell system.    proton exchange membrane (8)    anode catalyst (12)    cathode (18)    cathode catalyst (20)    pump (38)    heat exchanger (40)    alcohol supply tank (52)