An electrolysis unit having a plurality of membrane electrolytic cells connected in series suitable for use in a service station for supplying a motor vehicle with hydrogen as fuel. Each of the membrane electrolytic cells has a membrane provided on both sides with an appertaining contacting disk, especially a support mat made up of a large number of metal wires laid over each other and pressed together. In a service station, a gas cleaning unit is installed on the inlet side upstream from such an electrolysis unit.