In the last years, borohydrides have been extensively studied as possible candidates for hydrogen storage. Due to its high gravimetric and volumetric hydrogen capacity coupled with a calculated decomposition enthalpy in the range 30-40 kJ/mol H2, calcium borohydride represents an ideal candidate for storing hydrogen. Unfortunely, during to the formation of stable products during desorption, the pristine compound does not show a significant reversibility. A maximum reversibility of about 60 % was reported as possible only after addition of selected halogenated additives. It was shown that the complete formation of Ca(BH4)2 and MgH2 is possible by hydrogenation of the system CaH2 + MgB2. This system has still a high hydrogen gravimetric capacity, however the reversible hydrogenation of the system is still hindered by the formation of stable side products. In this work, the effect of a partial replacement of CaH2 by CaF2 on the sorption properties of the CaH2 + MgB2 system is studied. It was observed that already during the mixing of the reactants, the formation of a non stoichiometric CaH2-CaF2 solid solution takes place. The formation of this new phase affect sensibly the sorption reactions of the CaH2 + MgB2 system.
Effect of a partial replacement of CaH2 by CaF2 in the mixed system CaH2 + MgB2
MILANESE, CHIARA;
2012-01-01
Abstract
In the last years, borohydrides have been extensively studied as possible candidates for hydrogen storage. Due to its high gravimetric and volumetric hydrogen capacity coupled with a calculated decomposition enthalpy in the range 30-40 kJ/mol H2, calcium borohydride represents an ideal candidate for storing hydrogen. Unfortunely, during to the formation of stable products during desorption, the pristine compound does not show a significant reversibility. A maximum reversibility of about 60 % was reported as possible only after addition of selected halogenated additives. It was shown that the complete formation of Ca(BH4)2 and MgH2 is possible by hydrogenation of the system CaH2 + MgB2. This system has still a high hydrogen gravimetric capacity, however the reversible hydrogenation of the system is still hindered by the formation of stable side products. In this work, the effect of a partial replacement of CaH2 by CaF2 on the sorption properties of the CaH2 + MgB2 system is studied. It was observed that already during the mixing of the reactants, the formation of a non stoichiometric CaH2-CaF2 solid solution takes place. The formation of this new phase affect sensibly the sorption reactions of the CaH2 + MgB2 system.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
