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Structural Study of Poly-Molybdate Ions in Acid Mo-Ni Aqueous Solutions

1997; De Gruyter; Volume: 52; Issue: 12 Linguagem: Inglês

10.1515/zna-1997-1204

1865-7109

Kōzō Shinoda, Eiichiro Matsubara, Masatoshi Saito, Yoshio Waseda, Tetsuji Hirato, Yasuhiro Awakura,

Electrocatalysts for Energy Conversion

The atomic structure of poly-molybdate ions formed in acid Ni-Mo aqueous solutions has been determined by applying anomalous X-ray scattering (AXS) and EXAFS methods. In a solution containing only molybdenum ions, we found only a poly-molybdate ion consisting of seven edgesharing MoO 6 octahedra. In a solution containing both Mo and Ni ions, there exists another polymolybdate ion consisting of 6 edge-sharing MoO 6 surrounding an Ni ion. The total coordination number of Mo and Ni ions around a molybdenum ion is reduced by half when introducing citric ions into the Ni and Mo solution. This indicates that the large poly-molybdate ion is decomposed to smaller molybdate ions when forming citric complexes. Since molybdenum-nickel alloys can not be electrodeposited from solutions without citric ions, we propose a view that the structural change of the poly-molybdate ions in the solutions is closely related with the mechanism of induced codeposition of molybdenum and nickel alloy. The results of small-angle X-ray scattering (SAXS) measurements also support this conclusion.