Coprecipitation Synthesis of NixMn1-x(OH)2 Mixed Hydroxides

Four separate coprecipitation routes were applied to the preparation or NixMn1-x(OH)(2) mixed hydroxides with x = 1, 5/6, 2/3, 1/2, 1/3, and 0, beginning with divalent nitrates. The structure and morphology of the samples were studied by X-ray diffraction and scanning electron microscopy techniques. Intentionally bubbled air during coprecipitation was found to create layered double hydroxide (LDH) phases for x = 5/6, coexisting LDH and Mn3O4 phases for 5/6 > x > 0, and Mn3O4 for x = 0. On the basis of the structures observed, these trends could be attributed to the relative ease of oxidation of Mn2+ to Mn3+. Pure hydroxides, with the expected Ni(OH)(2) structure, were prepared for all x when air was excluded from the coprecipitation reaction. Spherical and dense particles could be prepared for all compositions attempted when ammonia was added during coprecipitation under anaerobic conditions.