Ribbon- and boardlike nanostructures of nickel hydroxide: synthesis, characterization, and electrochemical properties

We report the synthesis, characterization, and electrochemistry properties of ribbon- and boardlike nanostructures of nickel hydroxide, which crystallize in different phases. The ribbonlike nanostructures (nanoribbons) of nickel hydroxide were synthesized by treating amorphous alpha-Ni(OH)2 with high concentrations of nickel sulfate. These nanoribbons crystallized in a new phase had typical widths of 5-25 nm, thicknesses of 3-9 nm, and lengths of up to a few micrometers. After further treatment in alkali at 60 degrees C, the nanoribbons converted to boardlike nanostructures (nanoboards), which crystallized in the beta-phase with the average length-width-thickness ratio of 20:6:1. The crystal structures, Raman spectra, and electrochemical properties of these nanostructures of nickel hydroxide are described in this paper. For comparison, the amorphous alpha-Ni(OH)2 has also been investigated. Moreover, the intermediate product between the nanoribbons and the nanoboards displays a unique structure, which implied an interesting transformation process. The nanoribbons with the new phase show some unique features in Raman spectra, two new peaks located at 3534 and 3592 cm(-1) in the OH stretching region, indicating the new chemical environment of the hydroxyl groups. The nanoboards exhibit the highest specific capacity, which is close to the theoretical capacity of beta-Ni(OH)2. It suggests that the boardlike nanostructure is helpful in improving the electrochemical performance of nickel hydroxide. Because of their unique structures and properties, the nanoribbons and nanoboards of nickel hydroxide may give a new perspective for applications in the areas of catalysts and rechargeable batteries.