Abstract: In accordance with a preferred embodiment of this invention, the polarization or overvoltage of a carbon black-based air cathode is significantly reduced by adding from 1 to 5 percent, by weight based on the total carbon composition, of carbon derived from poly(vinylidene chloride) (hereinafter PVdC) to the carbon black, prior to the formation of the electrode. To accomplish this, the porous and particulate carbon black is initially blended with a solution of PVdC; the resulting blend is dried, and then dehydrochlorinated and baked at a temperature in the range of from 900.degree. C. to 1,100.degree. C. The electrocatalytic layer of the cathode is then prepared from this tailored carbon substrate.FIELD OF THE INVENTIONThis invention relates to a carbon-based substrate for electrodes used in fuel cells which operate at ambient temperatures and wherein the electrode separates a liquid electrolyte from a gaseous reactant.