The present invention is directed to a fuel cell dielectric coolant and evaporative cooling process using same. The coolant comprises an emulsion that defines a polar internal phase and a hydrocarbon external phase. The polar internal phase comprises an azeotropic mixture that includes one or more polar compounds selected from water, alcohol, or combinations thereof. The fuel cell is configured to react fuel with oxygen to generate an electric current and at least one reaction product, and comprises an electrochemical catalytic reaction cell configured to include a fuel flowpath, an oxygen flowpath, and a coolant flowpath fluidly decoupled from the fuel and oxygen flowpaths, and which defines a coolant isolation manifold including the fluid dielectric coolant described above. The method of cooling a fuel cell comprises, inter alia, evaporating the polar internal phase of the fluid dielectric coolant emulsion in the coolant isolation manifold.