Hydrogen sorption capacity as a tunable parameter in aprotic ionic liquids

The process of hydrogen sorption from a mixture of the organic acid – methanesulfonic acid (MS) and the aprotic ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate (EMIm-MS) was studied using a palladium limited volume electrode (Pd-LVE). Cyclic voltammetry, chronoamperometry and chronopotentiometry were used to characterize the hydrogen sorption properties of Pd in non-aqueous media. The influence of MS acid concentration on the aximum hydrogen capacity of the Pd-LVE was examined. The studies revealed that ca. 0.43 M MS in EMIm-MS is the optimal concentration, yielding the highest value for the hydrogen absorption capacity. Hydrogen absorption sotherms (HAIs) at a slightly higher MS acid concentration (0.5 M) were determined for the Pd electrode before and after a hydrogen pretreatment procedure (HPP). The HPP enables reproducible results to be obtained and increases the reversibility of the hydrogen electrosorption process. The maximum hydrogen capacity (H/Pd) in EMIm-MS with 0.5 M MS is ca. 0.74. This is higher than the value obtained in protic ionic liquids (ca. 0.7) and comparable with results obtained in aqueous acid or base electrolytes.