Abstract: An electrochemical fuel cell stack is provided for converting a fuel reactant stream and an oxidant stream to a reaction product, heat, and electrical energy. The fuel cell stack includes manifolding endplates with a plurality of unit cells therebetween, each unit cell incorporating a smooth conductive cooling layer, and anode and cathode layers incorporating gas distribution layers formed of a central, porous, sheet material and a peripheral gasket material. The cooling layer conducts heat from distant regions of the unit cell to longitudinal cooling passages which run through the length of the stack defining a serial path through turnaround grooves in the faceplate and endplate. There is further provided a method for introducing reactant gases to the gas distribution layers.