Electrochemical properties of anisotropic nickel hydroxide structures synthesized from nickel ammine complexes

Abstract

Synthesis of c-axis grown β-Ni(OH)2was attempted by rapid hydrolysis and/or direct hydrothermal treatment of the mixed solution of NiCl2, HCl and NH3. The UVvis spectra revealed the addition of NH3into NiCl2solution shifted the peak position to shorter wavelength, indicating the formation of nickel ammine complex. Hydrolysis of the mixed solution containing nickel ammine complex gave β-Ni(OH)2particles. The amount of NH3in the mixed solution did not affect the crystallinity or morphology of the β-Ni(OH)2particle by the conventional rapid hydrolysis. Hydrothermal treatment of the hydrolyzed β- Ni(OH)2particles was changed the morphology from agglomerated particles to nanosheets-linked structure or hexagonal plates. However, any crystal growth or particular-axis growth was not recognized. Then, the direct hydrothermal treatment of the mixed solution was attempted. The direct treatment at certain amount of coexisting NH3gave small amount of the precipitates, and the precipitates showed distinctive XRD pattern of c-axis grown β-Ni(OH)2. The electrochemical property of the c-axis grown β- Ni(OH)2structures indicated that the diffusion control was the rate-determining step for the charge/discharge process.