Evolution of cobalt hydroxide from 2D microplatelets to a 3D hierarchical structure mediated by precursor concentration

Abstract

We presented a facile and surfactant free approach to prepare 3-dimensional (3D) hierarchical Co(OH)2 with enhanced specific capacitance. The hierarchical Co(OH)2 was synthesized by a simple reaction of cobalt nitrate and ammonia solution with an appropriate concentration of the precursor. The effects of cobalt nitrate concentration on the crystal morphology were studied. When the concentration of cobalt nitrate was as low as 0.05 mol L−1, 2-dimensional (2D) hexagonally shaped (001) Co(OH)2 microplatelets were formed. As the concentration of the cobalt precursor was increased to 0.1 mol L−1, 3D hierarchical Co(OH)2 structures with nano-sized nanorods vertically assembled on the hexagonal microplatelets formed. Electrochemical tests showed that the hierarchical Co(OH)2 had a much higher specific capacitance than that of the Co(OH)2 microplatelets. This was mainly due to the increased number of pores in the hierarchical Co(OH)2 structure.