A planar fuel cell stack is provided. The planar fuel cell stack comprises an anode interconnect structure comprising a corrugated first internal manifold connected to a first anode flowfield; a cathode interconnect structure comprising a corrugated second internal manifold connected to a first cathode flowfield; and a thermally active, surface insulated metallic seal disposed between the corrugated parts of the anode and cathode interconnects, such that the thermally active metallic seal responds upon the application of heat to provide sealing between the anode interconnect structure and the cathode interconnect structure.