Thermal Decomposition of Chemical Hydrides

• Autorzy: Grochala W.
• Języki publikacji: EN
• Wydawca: Polskie Towarzystwo Chemiczne
• Czasopismo: Polish Journal of Chemistry
• Rocznik: 2005
• Tom: Vol. 79 / nr 6
• Strony: 1087--1092
• Opis fizyczny: Bibliogr. 14 poz., rys.

Twórcy

autor

Grochala W.

• Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland Fax: [phone]; Tel: [phone] ext. 276,

Bibliografia

• 1.Prof. Wrona wrote in his letter to me (dated 3 Jul 2003): “Problem of the thermal decomposition temperature is interesting, and perhaps it (Tdec) could be formalized one day, similarly to the melting or boiling temperature”. Author is now happy that the first small step was done towards achieving this goal.
• 2.Schlapbach L. and Zuttel A., Nature, 414, 353 (2001).
• 3.Carrette L., Friedrich K.A. and Stimming U., Fuel Cells, 1, 5 (2001).
• 4.Grochala W. and Edwards P.P., Chem. Rev., 104, 1283 (2004).
• 5.Importantly, the validity of the presented relationship is additionally supported by the failure to experimentally generate the stoichiometric trihydrides of In, Tl, Bi, Sc, Ti, V, Yb and Eu, the tetrahydrides of Pb, Ti, Zr, Hf, Ce, Th, and U, and the pentahydrides of P, As, Sb and Bi. In all cases the corresponding metal cations are highly oxidizing towards H-1.
• 6.Zn(BHf)2 is an efficient but irreversible hydrogen store (Grochala W., Edwards P.P., Harris R., Chang I.T.H., British Patent Application).
• 7.Ligands should not contain unsaturated bonds, as they are meant to be embedded in the strongly reducing hydrogen store. They should also be built of as light elements as possible, so that not to decrease the effective hydrogen storage capacity of the reservoir.
• 8.Unfortunately, due to large entropy effects connected with H2 evolution, relatively large negative enthalpy of hydride formation is requested so that the store is thermodynamically stable.
• 9.The most thermally stable among the binary hydrides; it starts decomposing at 720°C, above its melting temperature, Tmc), = 680°C (Ref. 9). Some data indicate even Tdec as high as 950°C.
• 10. The interesting Ga}+/Ga1+ redox pair appears in electrochemistry for some compounds of Ga. For other species, this is mainly the M27M° pair, which is thought to be involved in catalytic process. In principle, two concerted le~ processes (e.g. Ni2‘/Ni1+, Cr37Cr* etc.) can also be used for H2 activation.
• 11. Indeed, indications of enhanced reversibility and lowering of the T
• 12.Si02 turns out to catalyze H2 evolution from LiBH4: Zuttel A., Wenger P., Rentsch S., Sudan R, Ma P. and Emmenegger C.,. J. Power Sources, 118,1 (2003). Chemical identity of a catalyst is as yet uknown.
• 13.Tdcc is formally defined as the temperature at which H2 pressure above the solid hydride equals to 1 Here we show the “practical” values of Tdcc, obtained from thermogravimetric analysis, and not fror H2 pressure-composition isotherms.
• 14.The computational aspects of the chemical tuning of the thermal decomposition temperature of ganic hydrides will be discussed elsewhere: Grochala W. and Edwards P.P., J. Alloys Comp., (in press)