M.F. Ahmed

Cyclic voltammetric studies of nickel hydroxide and cobalt hydroxide thin films in alkali and alkaline earth metal hydroxides

Cyclic voltammetric studies of thin films of electrosynthesized (ES)-Ni(OH)2 and Co(OH)2 in different alkaline electrolytes suggest that the mechanism of oxidation is different from the mechanism of reduction. While the metal ion (alkali or alkaline earth metal) intercalation-deintercalation from the electrolyte into the film provides the driving force, the reduction reaction takes place heterogeneously independent of the electrolyte concentration, whereas oxidation takes place homogeneously across a nebulously defined electrode-electrolyte interphase. ES-Ni(OH)2 permits facile intercalationdeintercalation of alkali metal ions Li+, Na+ and K+, irrespective of their ionic size, while the reactions of ES-Co(OH)2 are sensitive to ionic size, requiring larger potentials in KOH compared to LiOH. In the alkaline earth metal hydroxides, both Ni(OH)2 and Co(OH)2 films show greater reversible characteristics in the order Ba(OH)2 > Sr(OH)2 > Ca(OH)2. This may be trivially related to the order of the solubilities of the three hydroxides.

Cyclic voltammetric studies of pure and doped films of cobalt hydroxide in 1 M KOH

Abstract Cyclic voltammetric studies of electrosynthetically prepared pure and doped thin films of cobalt hydroxide (on a platinum foil substrate) in 1 M KOH show that Co(OH) 2 undergoes a quasi-reversible redox reaction between a nearly quadrivalent black oxidic phase and a trivalent brown bronze-like phase. The coulombic efficiency is 60%. A common scheme is proposed for the electrode reactions of oxide electrodes in alkaline media, namely: M II (OH) 2 ⇋HM III O 2 ⇋M IV O 2 , where M = Mn, Co, Ni. The three metals execute different steps in this two-electron redox reaction, either reversibly or quasireversibly. Based on this scheme, new compounds are suggested as possible electrode materials for secondary storage battery systems. The effect of eight, different, dopant metal ions on the redox reactions of Co(OH) 2 is investigated. Only La 3+ ions are found to influence favourably the performance of Co(OH) 2 as an electrode material.

Cyclic voltammetric studies of electrodeposited solid solution and composite oxide/hydroxide electrodes in 1 M KOH: the Co(OH)2-Ni(OH)2-MnO2 system

Abstract Solid solutions of the type Ni1-xCox(OH)2 (x = 0.1 to 0.9) obtained by cathodic deposition from a mixed nitrate bath show a redox behaviour that is completely different to that of the pure components. The solid obtained from a bath containing a Ni/Co ratio of 40/60 exhibits the lowest Erev and the smallest difference between the anodic and cathodic peak potentials (0.03 V). This is indicative of the high reversibility achieved at this composition. A layer-by-layer deposited composite electrode Pt/Ni(OH)2/MnO2 shows the migration of the active nickel oxide species from the inner layer to the surface and a marked lowering in the Erev of the nickel hydroxide reaction. By contrast, the cobalt counterpart of this electrode does not show any of these interesting features. The Pt/MnO2/Ni(OH)2 electrode does not hold much promise as it exhibits a markedly reduced reversibility of the nickel hydroxide reaction. In the cobalt counterpart Pt/MnO2/Co(OH)2, MnO2 profoundly affects the reactions of cobalt hydroxide: first anodic reaction is suppressed and the second anodic reaction is less reversible. These observations suggest that there is a common chemical reaction mechanism for all oxide electrodes in alkaline media.

Electro-oxidative polymerization of m-chlorophenol and m-bromophenol

The various products formed by the electrooxidation of m-chlorophenol and m-bromophenol are analyzed by IR spectroscopy. An interesting and important by-product was found

Cyclic voltammetry studies of electrodeposited thin films of bismuth in 1 M KOH

Abstract Cyclic voltammetry studies of electrodeposited thin films of bismuth (Pt substrate) indicate the possible generation of higher oxidation states of Bi (greater than 3 +) in 1 M KOH, which then undergo chemical reduction to a Bi 3+ phase. However, the higher oxides are not observed on splat-cooled Bi foil electrodes, suggesting that they can only form in a hydrous oxide—electrolyte gel-like interphase, produced by electrodeposited Bi films, which are known to have a high roughness factor.

Relationship between permselectivity and the acidity of polyphenols pertaining to the pH response of Pt/polyphenol electrode

Abstract The permselectivity of Pt/polyphenols has been investigated. The selective permeability is found to be different for various polyphenols. Relationships of the diffusion rates, the limiting currents for the reduction of H+ ions and the pKa values of the polyphenols have been established. Electron-withdrawing substituents increase the diffusion rate of the H+ ions with increasing acidity of the polyphenol; whereas electron-donating groups bring out the reverse effect. Poly(p-cyanophenol) and poly(2,6-dichlorophenol) are found to be better candidates to modify a Pt electrode for application as pH sensor than existing polyphenol and poly(2,6-dimethylphenol) films.

Poly(benzimidazole) and substituted poly(benzimidazoles) : Novel, electroactive, and conducting polymers possessing high catalytic and coordination properties

Benzimidazoles and substituted benzimidazoles were electropolymerized on a Pt electrode using acetonitrile containing 0.1 MNaClO4. The polymers are electroactive and conducting. They have a high electrocatalytic effect on the reduction of H+, O2, and CO2 and exhibit high coordination ability. The properties of the polymers depend on the extent of conjugation in the monomer.