Effect of crystallinity on the electrochemical performance of nanometer Al-stabilized α-nickel hydroxide

Nanometer Al-stabilized alpha-Ni(OH)(2), synthesized by urea decomposition, was tested to have better crystallinity from Ni(NO3)(2)center dot 6H(2)O and Al(NO3)(3)center dot 9H(2)O (Sample A) than that from NiSO4 center dot 6H(2)O and Al-2(SO4)(3)center dot 18H(2)O (Sample B), and more agglomeration was found for the badly crystallized Sample B as shown by TEM. XPS spectra determined that the positively charged part for Sample A and B was [Ni0.78Al0.22(OH)(2)](0.22+) and [Ni0.95Al0.05(OH)(2)](0.05+), respectively. TG and DSC showed that the thermal processes of the two samples are different, where Sample B decomposed at a higher temperature. Cyclic voltammetry (CV) test showed that Sample A had better reversibility, and anodic oxidation peak of Sample B disappeared with the increase in scanning rate. Sample A had smaller electrochemical resistance as shown by electrochemical impedance spectroscopy (EIS), and electrode reaction of Sample A is mostly controlled by proton diffusion, while that of Sample B is a mixed controlled electrode process. Sample B also has poorer electrochemical discharge and cycle life performance. (C) 2007 Elsevier B.V. All rights reserved.