On the Oxidation-Reduction Mechanism of the Cadmium Metal-Cadmium Hydroxide Electrode

Abstract

Electrochemical oxidation‐reduction processes of the normalCd/normalCdfalse(OH)2 electrode in concentrated alkaline solutions were investigated by using a rotating ring‐disk electrode as well as a stationary electrode. Results support the mechanism that the anodic oxidation of Cd to normalCdfalse(OH)2 in the active potential range proceeds entirely through the dissolution‐precipitation sequence, while the cathodic reduction of normalCdfalse(OH)2 takes place both through the solution phase and by a direct solid‐state mechanism. * Electrochemical Society Active Member.

Charge Acceptance of the Cadmium-Cadmium Hydroxide Electrode at Low Temperatures

“…In the potential range of interest, these reactions may be represented by the following simple equations (5,6) Discharge:…”

Reactivity of Scratched Cadmium Electrodes in Alkaline Solutions

“…The electrochemical reactions of Te, Sb, As, Co, and Ni have been recently reviewed (15,16). The reactions pertinent to the lead-acid battery operational potential range taken from the aforementibned references are shown in Fig.…”

“…This is not in agreement with the dissolution-precipitation model (14-16) in which metal ions enter solution and are then precipitated to form the film. While there is general agreement that the steady-state film consists primarily of Cd(OH)2 (2), in both the ~ and -y structures (17, 18), the formation of CdO, either anhydrous or hydrated, cannot be ruled out (16,17). Indeed, it is claimed that a thin amorphotis film of CdO may well exist (17) and that this film provides the passivity of the Cd electrode (16).…”

“…While there is general agreement that the steady-state film consists primarily of Cd(OH)2 (2), in both the ~ and -y structures (17,18), the formation of CdO, either anhydrous or hydrated, cannot be ruled out (16,17). Indeed, it is claimed that a thin amorphotis film of CdO may well exist (17) and that this film provides the passivity of the Cd electrode (16). The dissolved ion in alkaline solutions has been identified as Cd(OH)~ 2- (11,12) or Cd(OH)~-(t5).…”

“…Thus, measurements of dissolved ion concentra- 9 Electrochemical Society Active Member. tions in ring disk electrode studies (12,16) probably detect dissolution of the films, Milner and Thomas (19) have, however, mentioned that other dissolved ions such as Cd '~+ and CdOH § may be involved as intermediates in the dissolution reaction. Detailed summaries and ~ discussions of these investigations have been provided in the two reviews of the behavior of the Cd electrode (1, 2).…”