The invention relates to an electrolysis cell of the single-element type design for chlor-alkali electrolysis plants, comprising an anode compartment and a cathode compartment, each of the two compartments containing an electrode connected to the rear wall of the respective compartment by means of parallel bars. The electrodes are thus subdivided into several sections. In accordance with the invention, at least one of two electrodes is provided with a curved shape in each section, this curved section protruding towards the opposite electrode and pressing a membrane area against the opposite electrode. According to a preferred embodiment, the curved shape of the various electrode sections is obtained by means of springs.