A Stable High-Valency Nickel Oxide

Abstract

A high-valency amorphous nickel oxide prepared by the hypochlorite oxidation of nickel nitrate exhibited a mixture of oxidation states characterized by a mean nickel valency of approximately 3.5. The high-valency amorphous oxide was stable in strongly alkaline solutions, but it decomposed rapidly below pH 9. The oxide discharged efficiently when used as a cathode in an alkaline primary cell.The existence of high-valency amorphous nickel oxides is well established (1), but there has been some discussion regarding the nature of the excess nickel valency in such oxides. The high valency has been attributed to the presence of a tetravalent nickel ion (2) and to superficial oxygen (3). The recent magnetic studies of Labat (4) provide convincing evidence for the existence of a tetravalent nickel.Data in the literature (5, 6) indicate that highvalency nickel oxides decompose readily, but recent work of Tuomi (7) shows that it is not necessarily so. The data given by Tuomi imply a reasonable stability of tetravalent nickel prepared electrochemically under suitable conditions. We were interested in exploring the use of a highvalency amorphous nickel oxide as a cathode material for primary cells, but before such use could be considered, it would be necessary to establish whether the high valence state could be stabilized and whether it could be exploited faradaically. Both of these questions can be answered affirmatively, and we report here the work which led to these conclusions. Experimental TechniquesA laboratory evaluation was conducted of the various methods for preparing high-valency nickel oxide. First among them was the anodic oxidation of mixtures of divalent nickel hydroxide and carbon with a CMC binder in concentrated base at room temperature on a nickel screen. The electrochemical method was unsatisfactory because of the poor adhesion of the oxide to the conductor and because of analytical complications due to the oxides of carbon and the presence of nickel. These considerations notwithstanding, Tuomi (7) obtained satisfactory results with the electrochemical method. Among the chemical methods, the hypochlorite oxidation was found to be most convenient and we used it. It is interesting to note that, although this method has been known for many years (8), it apparently was not recognized that it could yield a stable high-valency oxide.Preparative procedures.--All the reagents, except the technical grade hypochlorite, were analytical grade chemicals, and the specific preparative conditions were varied as shown in Table I. The sequence of the operations was the same in all cases. The solution of nickel nitrate was added dropwise to the solution of the alkaline hypochlorite during approximately Yz hr. When the nickel oxide precipitate had settled the supernatant liquid was removed by siphoning, and the precipitate was washed twice with fresh base. The oxide was stored under base in a polyethylene container at 25.0~No interferences would be expected by the nitrate shuttle discussed by Casey et aL (9), since no reduc...

Electrochemical and Spectroscopic Evidence on the Participation of Quadrivalent Nickel in the Nickel Hydroxide Redox Reaction

“…The valence of nickel achieved in the oxidation of nickel hydroxide electrodes is a matter of practical interest because oxidation beyond the trivalent state would make it possible, in principle, to exceed the theoretical capacity for the ohe-electron charge storage reaction and significantly increase the specific energy of nickel battery e]ectrodes. While the charged state of nickel hydroxide is customarily considered to be a triva]ent nickel oxyhydroxide, designated NiOOH, there has been persistent electrochemical evidence that nickel hydroxide can be oxidized above the trivalent state (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). For example, it is now widely realized that -~-NiOOH may contain some quadrivalent nickel (3).…”