Electrochemical studies of spherical nickel hydroxide Ni(OH)(2) with high density were carried out by using a microelectrode technique. A carbon fiber microelectrode was contacted with a single particle of nickel hydroxide in 5 M KOH aqueous solution. In this way, cyclic voltammetry and galvanostatic charge/discharge experiments were carried out. The Ni(OH)(2); NiOOH redox reaction, oxygen evolution reaction and charge/discharge capacity were examined without any dilution with a binder and a conductive additive. Data were compared with those of the composite electrode consisting of the nickel hydroxide particle and a polymer binder, which is the practical form in the Ni-MH batteries. The potential-step technique was also performed to evaluate the apparent chemical diffusion coefficient of the proton (D-app) in the nickel hydroxide. Since the nickel hydroxide particle was a dense, conductive sphere, the spherical diffusion model was employed for the analysis. The D-app was found to be around 10(-9) cm(2) s(-1). (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.