Abstract: Apparatus for on demand production of hydrogen by electrolysis of water including an elongated, tubular housing with a first open end and second open end, wherein the first end is closed with a first lid and the second end is closed with a second lid; a solid rod anode is arranged centrally within said tubular housing and a electrical connector of the rod anode reaches through the first lid; a plurality of tube shaped cathodes is arranged concentrically with respect to the central anode, wherein the tube shaped cathodes are arranged at a certain pitch within the tubular housing and a connector element is provided within the tubular housing for electrically connecting the tube shaped cathodes, wherein at least one connector which is attached to the connector element reaches through the first lid; at least one neutral conductive tube is placed between two consecutive tube shaped cathodes; and at least one neutral conductive tube is placed between the rod anode and the first tube shaped cathode surrounding the r