Thermodynamic characterization of polyhydride complexes
- Univ. of Hawaii, Manoa, Honolulu, HI (United States)
The authors have investigated the interaction of hydrogen with solid IrXH{sub 2} (PPr{sup i}{sub 3}){sub 2}(H{sub 2}) (X=Cl, I). Gaseous hydrogen was found to react directly and reversibly with solid iridium chloro-complex, IrClH{sub 2}(PPr{sup i}{sub 3}){sub 2}(H{sub 2}) under mild conditions of pressure and temperature. Equilibrium absorption and desorption isotherms were obtained at fixed temperatures ranging from 273{degrees} K to 323{degrees} K over the pressure range from 0.1 to 11 atmospheres. The rates of hydrogen uptake and release were found to be very rapid. A Gaussian shaped thermal desorption spectrum showed that hydrogen desorption occurred over a wide range of temperatures from 200{degrees} K to 350{degrees} K. The TDS results and the absence of well defined plateaus in p-c isotherms indicated a disorder of the hydrogen arrangement in the iridium complex matrix. These observation were consistent with earlier findings from NMR and neutron diffraction measurements. The enthalpy ({Delta}H) and the entropy ({Delta}S) of hydrogen desorption, from a van`t Hoffs plot based on the hydrogen pressure at 50% of full loading of hydrogen at fixed temperatures, were {minus}4.9 {+-}0.3 kcaL/mole of H{sub 2} and 28.6{+-} cal/deg. mole of H{sub 2} respectively. Hydrogen desorption from IrIH{sub 2}(PPr{sup i}{sub 3}){sub 2}(H{sub 2}) was not observed at the above temperature and pressure ranges, indicating stronger hydrogen bond in iodo-complex compared to the chloro-complex.
- Research Organization:
- National Renewable Energy Lab., Golden, CO (United States)
- OSTI ID:
- 456749
- Report Number(s):
- NREL/CP--430-21968-Vol.2; CONF-9605195--Vol.2; ON: DE97001438
- Country of Publication:
- United States
- Language:
- English
Similar Records
Influence of halide ligands on the energetics of the reversible loss of hydrogen from the Iridium nonclassical polyhydride complexes IrXH[sub 2](H[sub 2])(PPr[sup i][sub 3])[sub 2] (X = Cl, Br, I)
VAPORIZATION OF IRIDIUM AND RHODIUM