Hydrogen Storage in Semiclathrate Hydrates of Tetrabutyl Ammonium Chloride and Tetrabutyl Phosphonium Bromide

Original calorimetric and phase equilibrium properties for hydrogen + tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBACl), or tetrabutylphosphonium bromide (TBPB) semiclathrate hydrates were measured using differential scanning calorimetry under pressure. The dissociation temperatures of H 2 + TBACl and H 2 + TBPB semiclathrate hydrates are very close to the ambient temperature at low pressures around 15.0 MPa. H 2 + TBACl and H 2 + TBPB systems therefore exhibit better and comparable stability than the H 2 + TBAB system at equivalent pressure, respectively. The amount of hydrogen stored in H 2 + TBACl and H 2 + TBPB semiclathrate hydrates was estimated in terms of the H 2 -to-water mole ratio ( n H 2 / n H 2 O ) calculated from disssociation enthalpies and ( p, T ) equilibrium data. In terms of mass fraction deduced from the ratio ( n H 2 / n H 2 O ), H 2 + TBACl and H 2 + TBPB semiclathrate hydrates can store 0.12 % and 0.14 % of hydrogen, respectively. Moreover, the quantity of hydrogen stored in these two semiclathrate hydrates is significantly higher than that stored in the H 2 + TBAB system.