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

Four separate coprecipitation routes were applied to the preparation of Ni x Mn 1− 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 Mn 3 O 4 phases for 5/6 > x > 0, and Mn 3 O 4 for x = 0. On the basis of the structures observed, these trends could be attributed to the relative ease of oxidation of Mn 2+ to Mn 3+ . 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.