Effect of Water Vapor on Hydrogen Isotopes Separation by Polymer Electrolyte Fuel Cell

Abstract

IntroductionHydrogen isotopes are protium (H), deuterium (D) and tritium (T). D and T are important materials not only for fission and fusion reactors, but also for semiconductors since the strong hydrogen termination improves the durability. Various techniques for hydrogen isotope separation have been known for long time, but they have some drawbacks such as low separation efficiency and poor energy consumption. Therefore, new separation and purification methods are required.In polymer electrolyte fuel cell (PEFC), wettability is optimized well and small amount of Pt catalyst is used. The configuration is also key issue for the conventional method of water-hydrogen chemical exchange. Therefore, we investigated the effect of water in hydrogen isotope separation by PEFC [1].ExperimentalA mixture hydrogen gas of H2 and D2 was supplied to the PFEC. The separation factor for dry and wet gas flow was measured, respectively. Hydrogen gas and water vapor from PEFC were analyzed by quadrupole mass spectrometry (Q-mass) and Fourier infrared spectrometer (FTIR), respectively. The separation factor and mass balance were calculated.Results and discussionWhen no electricity was generated, FTIR results showed that D was enriched in water vapor. This is explained by a gas-phase chemical exchange reaction occurring on a platinum catalyst. When the PEFC was operated, the electrochemical reaction promoted the D separation. A large amount of D (about 45%) was transferred to water vapor during power generation. The separation factor was approximately 1.7, while it was approximately 1.3 for no generation. The present results suggested that gas-phase chemical exchange and the cell reaction had a synergistic effect on D separation.