Application of Alkali Metal-Doped Carbons for Hydrogen Recovery and Isotope Separation

Hydrogen-sorption isotherms of alkali metal-doped carbons at 77 K were determined for promoting application of these materials as hydrogen-recovery and isotope-separation agent. The hydrogen-sorption behavior of rubidium-doped Grafoil, with composition of RbC₂₄, showed high sorption ability against hydrogen at low pressure. Taking into account the fact that sorption–desorption was fast and reversible, and the equilibrium pressure at half coverage was very low, i.e., 40 Pa, RbC₂₄ prepared from Grafoil is promising as a recovery agent for hydrogen gas at low pressure. The hydrogen (H₂)/deuterium(D₂)-sorption isotherms of potassium-doped carbons with composition of KC₁₀, prepared from multi wall carbon nanotube (MWCNT) and carbons derived from petroleum cokes with heat-treatment temperatures of 1000 and 1500 °C, were also determined. Isotope separation coefficient was estimated from those isotherms. A very large isotope effect was found for KC₁₀ prepared from MWCNT, comparable to those prepared from carbons with heat-treatment temperatures of 1000 or 1500 °C. However, a severe problem was found for KC₁₀ (MWCNT) that repetition of the sorption–desorption cycles resulted in the decrease of the sorbed amount of H₂ and D₂.