Deuterium Isotope Separation By Polymer Electrolyte Fuel Cell with Gas Circulation System

Abstract

IntroductionHydrogen isotopes such as deuterium (D) and tritium (T) are in increasing demand in the fields of materials, energy, and medicine. A international fusion reactor in France will be equipped with water electrolysis for T separation. New methods are required, since the conventional processes perform low separation and consume large amount of energy. We have been studying D separation by polymer electrolyte fuel cell (PEFC) [1-3]. Here, the relationship between the gas consumption rate and separation efficiency is investigated. Therefore, the present PEFC can recirculate the unreacted hydrogen gas discharged from the anode, which proceeds high gas utilization. In our poster presentation, we will show the separation factor, D concentration and production volume depending on the gas circulation ratio.ExperimentalA JARI cell (electrode area: 25 cm2) was used for PEFC, and platinum was used as catalyst for both electrodes. For the anode, protium (H) concentration was set to 90 at% as a mixed gas. Oxygen gas was supplied to the cathode. Power generation was performed at room temperature, and a constant output current was obtained using a variable resistor. The H concentration in the anode gas was analyzed with a quadrupole mass spectrometer, and the gas volume discharged from the PEFC circulation system was calculated.Results and discussionThe ratio of the hydrogen gas circulation rate to the supply rate is defined as λ. The relationship with the H concentration is shown (Fig. 1). The H concentration was enriched during PEFC operation, while D was condensed in produced water. The gas circulation improved the separation efficiency because the outlet gas was repeatedly processed in PEFC. Figure 2 shows the relationship between λ and the volume rate of exhaust gas from anode. As λ increased, the gas rate decreased linearly from 8 mL min-1 to 2 mL min-1. That is, the circulation system let the gas residential time in PEFC be longer. When the gas was circulated more, the gas could react for long time. This was attributed to the high H concentration seen in Fig. 1. The present results demonstrated the importance of circulation parameter, λ, for the enrichment production.