Deuterium Enrichment by PEM Water Electrolysis with Electrolyte Circulation

Abstract

Nuclear fusion is attracting attention as a new energy supply method. Nuclear fusion requires high purity deuterium (D) as fuel, but it is difficult to separate and enrich the isotopes because they have very similar chemical properties. In polymer electrolyte membrane water electrolysis (PEMWE), protium (H) is easily generated as hydrogen gas at the cathode electrode, while D can be concentrated in the electrolyte [1]. In this study for pursing high D enrichment process, the electrolyte circulation was employed and the relationship between the consumption ratio and D concentration was investigated.The initial D concentrations in the electrolyte were 10, 30, and 50 at%. The electrolyte was supplied to the cathode. IrO2 was used as the anode catalyst and Pt/C as the cathode one. Experiments were conducted at atmospheric pressure and room temperature. The electrolysis was conducted at constant current. Hydrogen gas produced by electrolysis was analyzed by a quadrupole mass spectrometer (Q-Mass) to determine the ratio of H2, HD, and D2. The drain from the cathode was returned to the electrolyte reservoir. The electrolyte was analyzed by Fourier transform infrared spectrophotometer (FT-IR) to determine the ratio of H2O, HDO, and D2O.The D concentrations, CD , in the solution relative to the consumption ratio of the electrolyte, R, were shown in Fig. 1. The experimental results showed that CD increased exponentially with R, confirming D enrichment in the electrolyte. Figure 2 shows the variation of the separation factor, α, in the gases as a function of R. α is the [H]/[D] ratio in the evolved gas divided by the [H]/[D] ratio in the liquid. H was concentrated in the gas. While about 90% of the electrolyte was consumed, α remained constant value (α ≈ 4), but as the electrolyte was further consumed, α dropped to about 3.