Fuel cell system and heater/humidifier used therein

Degradation of membranes in fuel cells (10) due to dehydration by relatively dry incoming reactant gases is avoided through the use of a heater/humidifier (36) and/or (40) in the incoming reactant streams, (12,14). At least one of the humidifiers (36,40) is formed in a stack (66) having alternating flow passages (68,70) with the former receiving reactant gases and including fins (102) therein and the latter receiving hot coolant from the fuel cell (10). The fins (102) in the flow spaces (68) are provided with a hydrophilic coating to foster filmwise evaporation of water introduced through a nozzle (82). The humidifier (36) and/or (40) causes the reactant gas to attain a desired dewpoint before it is provided to the membranes of the fuel cell (10).