Electrochemical studies of cobalt hydroxide-an additive for nickel electrodes

Elumalai, P and Vasan, HN and Munichandraiah, N (2001) Electrochemical studies of cobalt hydroxide-an additive for nickel electrodes. In: Journal of Power Sources, 93 (1-2). pp. 201-208.

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Abstract

The electrochemical behavior of chemically precipitated cobalt hydroxide is studied by cyclic voltammetry and galvanostatic charge/discharge cycling. When cycled in the potential range between the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the electrode undergoes two pairs of reactions. The pair of current peaks close to the OER is attributed to quasi-reversible oxidation of $Co(OH)_2$ to CoOOH, whereas the pair of current peaks close to the HER is due to quasi-reversible reduction of $Co(OH)_2$ to Co. The peak current values of both reactions do not show dependence on alkali concentration. Possible mechanisms are proposed for the reactions, in which the diffusion of dissolved $Co(OH)_2$ prior to the electron-transfer step is considered to be the rate-determining step. Considering the fact that the $Co(OH)_2/CoOOH$ and $Co(OH)_2/Co$ reactions are separated by a potential difference of about 1.2 V, a galvanic cell is constructed by using two $Co(OH)_2$ electrodes in 6 M KOH. On charging, the positive electrode attained a stable potential of about 0.4 V versus Hg/HgO, $OH^−$ and the negative electrode attained a stable potential of about −0.8 V versus Hg/HgO, $OH^−$, thus resulting in an open circuit cell voltage of about 1.2 V. By discharging the cell, a capacity of $15 mA h g^{−1}$ of $Co(OH)_2$ is obtained over about 15 charge/discharge cycles. The charged electrodes are analyzed by powder XRD and IR spectroscopy and the presence of Co and CoOOH in the negative and positive electrodes, respectively, is confirmed. Although the cell is not commercially viable, the concept of a "double hydroxide" is demonstrated akin to the "double sulfate" principle of lead-acid batteries. It is expected that $Ni(OH)_2$, which is isostructural to $Co(OH)_2$, may also show a similar behavior.

Item Type:	Journal Article
Publication:	Journal of Power Sources
Publisher:	Elsevier
Additional Information:	Copyright of this article belongs to Elsevier.
Keywords:	Cobalt hydroxide; yclic voltammetry;Reaction mechanism;Oxidation to CoOOH;Reduction to Co;Galvanic cell;Double hydroxide principle
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	11 Jan 2007
Last Modified:	19 Sep 2010 04:28
URI:	http://eprints.iisc.ac.in/id/eprint/7450

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