Electrochemical cell, characterized in that it comprises: - a membrane electrode assembly including a proton exchange membrane and first and second electrodes fastened to opposite faces of said membrane; - a bipolar plate, comprising first and second conductive sheets (51, 52), and in which: - an inlet manifold and an outlet manifold of coolant, and an inlet manifold and an outlet manifold of a reactant are made through the first and second conductive sheets; - coolant flow channels are made between the conductive sheets (51, 52) and are in communication with the coolant inlet and outlet manifolds; - an outer face of the first conductive sheet comprising: - reactant flow channels in communication with the reactant inlet and outlet manifolds, covered by the first electrode of the membrane electrode assembly; - a first rib extending on the side of the reactant flow channels, a gasket extending at least partially on said first rib; - the bipolar plate comprising an intermediate zone extending between the first rib and said first electrode, and comprising: - a first band in which the first and second sheets have complementary shapes nested one in the other over the entire length of at least one coolant flow channel; - a second band positioned between the first band and the first rib, in which the first sheet comprises reliefs in contact with the membrane electrode assembly, and in which at least one coolant storage volume is made between the first and second sheets. - a membrane electrode assembly including a proton exchange membrane and first and second electrodes fastened to opposite faces of said membrane; - a bipolar plate, comprising first and second conductive sheets (51, 52), and in which: - an inlet manifold and an outlet manifold of coolant, and an inlet manifold and an outlet manifold of a reactant are made through the first and second conductive sheets; - coolant flow channels are made between the conductive sheets (51, 52) and are in communication with the coolant inlet and outlet manifolds; - an outer face of the first conductive sheet comprising: - reactant flow channels in communication with the reactant inlet and outlet manifolds, covered by the first electrode of the membrane electrode assembly; - a first rib extending on the side of the reactant flow channels, a gasket extending at least partially on said first rib; - the bipolar plate comprising an intermediate zone extending between the first rib and said first electrode, and comprising: - a first band in which the first and second sheets have complementary shapes nested one in the other over the entire length of at least one coolant flow channel; - a second band positioned between the first band and the first rib, in which the first sheet comprises reliefs in contact with the membrane electrode assembly, and in which at least one coolant storage volume is made between the first and second sheets. - an inlet manifold and an outlet manifold of coolant, and an inlet manifold and an outlet manifold of a reactant are made through the first and second conductive sheets; - coolant flow channels are made between the conductive sheets (51, 52) and are in communication with the coolant inlet and outlet manifolds; - an outer face of the first conductive sheet comprising: - reactant flow channels in communication with the reactant inlet and outlet manifolds, covered by the first electrode of the membrane electrode assembly; - a first rib extending on the side of the reactant flow channels, a gasket extending at least partially on said first rib; - reactant flow channels in communication with the reactant inlet and outlet manifolds, covered by the first electrode of the membrane electrode assembly; - a first rib extending on the side of the reactant flow channels, a gasket extending at least partially on said first rib; - the bipolar plate comprising an intermediate zone extending between the first rib and said first electrode, and comprising: - a first band in which the first and second sheets have complementary shapes nested one in the other over the entire length of at least one coolant flow channel; - a second band positioned between the first band and the first rib, in which the first sheet comprises reliefs in contact with the membrane electrode assembly, and in which at least one coolant storage volume is made between the first and second sheets. - a first band in which the first and second sheets have complementary shapes nested one in the other over the entire length of at least one coolant flow channel; - a second band positioned between the first band and the first rib, in which the first sheet comprises reliefs in contact with the membrane electrode assembly, and in which at least one coolant storage volume is made between the first and second sheets.