Production of hydrogen from the Na/NaH-process

Abstract

The metal/metal hydride processes are used to produce hydrogen from water through the direct employment of high-temperature heat. Compared to purely electrolytic hydrogen generation processes they are characterized by considerably higher overall efficiencies. In order to demonstrate the process and develop the hydrogen-permeable membrane cathode required in the procedure a laboratory cycle was constructed using sodium as the depolarizer. Loading tests through an α-iron membrane at hydrogen admission pressures of 100–1000 mbar and a membrane temperature in the range between 250 and 300°C show that hydrogen permeation was not kinetically inhibited through the presence of sodium on the rear side of the membrane. Measurements of the permeation rates using a double-layer membrane of vanadium and palladium/silver foil at a membrane temperature of 288°C and hydrogen admission pressures of between 10 and 130 mbar show that the membrane is suitable for electrolysis tests. We should like to present here the design for the molten-hydroxide electrolysis cell necessary for a complete demonstration of the process.