A fuel cell stack configured to alleviate pressure and decrease the flow rate of at least one of a fuel and an oxidant is disclosed. The fuel cell stack includes a membrane-electrode assembly, an anode separator, a cathode separator and a filing member. The membrane-electrode assembly may include an electrolyte membrane, an anode formed on a first surface of the electrolyte membrane, and a cathode formed on a second surface of the electrolyte membrane. The anode separator may include a fuel channel, a fuel inlet manifold in fluid communication with the fuel channel, and a fuel outlet manifold in fluid communication with the fuel channel. The cathode separator may include an oxidant channel, an oxidant inlet manifold in fluid communication with the oxidant channel, and an oxidant outlet manifold in fluid communication with the oxidant channel. The filling member may be positioned within at least one of the fuel inlet manifold and the oxidant inlet manifold.