Solid amorphous cobalt oxysulfide “CoSOH” obtained by basic aqueous precipitation absorbs gaseous
hydrogen up to a limit close to the H2/Co molar ratio of 0.5. To understand the nature of this phenomenon,
the cobalt compound was characterized before and after hydrogen absorption (XRD, IR, TEM, XPS,
inelastic neutrons scattering, and extended X-ray absorption fine structure spectroscopy). The initial
oxysulfide is an amorphous solid containing hydroxide groups and sulfide moieties. Considerable amounts
of hydrogen (as high as 0.3 mol of H2/Co atom) can be absorbed by this solid without any apparent
changes of its structure and morphology, due to the reductive opening of S−S bridges leading to the
formation of −SH groups. At higher levels of hydrogen consumption (0.3−0.5 mol of H2/Co atom),
formation of crystalline Co9S8 compound was observed. Isotopic exchange and volumetric experiments
demonstrated that the absorption of hydrogen is a slow and irreversible first-order solid−gas reaction.
Sorption G 6000Amorphous Cobalt Oxysulfide as a Hydrogen Trap. -Solid amorphous cobalt oxysulfide "CoSOH" is prepared at room temperature by basic precipitation of aqueous Co(NO3)2 with aqueous Na2S. The samples are characterized before and after hydrogen absorption by XRD, IR, TEM, XPS, inelastic neutron scattering, and EXAFS. The material absorbs gaseous H2 up to a limit close to the H2/Co molar ratio of 0.5. At intermediate absorption levels, S-S bridge opening by molecular hydrogen assembly presumably occurs. At final stages, crystalline Co 9 S 8 forms. -(LOUSSOT, C.; AFANASIEV*, P.; VRINAT, M.; JOBIC, H.; LEVERD, P. C.; Chem. Mater. 18 (2006) 24, 5659-5668; Inst. Rech. Catal., CNRS, Univ. Claude Bernard Lyon, F-69626 Villeurbanne, Fr.; Eng.) -W. Pewestorf 08-014
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