Ni(OH)2@Co(OH)2 hollow nanohexagons: Controllable synthesis, facet-selected competitive growth and capacitance property

Abstract

Hollow nanohexagons with a core–shell structure have been synthesized from a mixture of Ni and Co hydroxide by a mild wet chemical approach. Ni(OH)2@Co(OH)2 nanohexagons with controllable sizes of about 200nm, morphology and structure are obtained. Comprehensive microstructure analysis reveals that the Ni(OH)2 and Co(OH)2 components are single-crystalline. The surfaces of the nanohexagons are smooth and their inner facets can be controlled to be parallel to the outer facets or rotated by 30°. A growth mechanism depending on the N2H4·H2O content and reaction temperature has been proposed to explain the different structures. The parallel inner facets tend to form with higher amounts of N2H4·H2O while the rotated ones tend to form at higher temperature. The specific capacitance of the hollow nanohexagon is about 369F/g, which can be remained as high as 96.4% after 2500 cycles at current density of 1A/g.