ELECTROCHEMICAL, SPECTROSCOPIC AND STRUCTURAL INVESTIGATIONS OF THE CD CD(II) SYSTEM IN ALKALINE MEDIA - I - CATION EFFECTS/

The composition and properties of the electrochemically formed passive layer on cadmium in alkaline solutions were shown to depend on the na ture of the electrolyte cation. In 1 M LiOH beta-Cd(OH)(2) was the onl y product formed, while in I M NaOH and KOH both beta-Cd(OH)(2) and ga mma-Cd(OH)(2) were detected. Ex situ FTIR spectroscopy and grazing ang le X-ray diffraction were used to characterise the anodic films formed and the results are interpreted in the concept of surface complexatio n. The reduction of synthetic samples of CdO, beta-Cd(OH)(2) and gamma -Cd(OH)(2), was investigated at a carbon paste electrode. The results show that the reduction of the pure substances is severely suppressed in carbon paste as compared with metallic cadmium. The impact of these results on battery performance is that for thick oxide layers without direct metal contact the reduction is severely retarded and sufficien t time and energy are needed to fully charge the cadmium electrode. It is concluded that the reduction process in the presence of cadmium me tal involves are-proportionation mechanism. (C) 1998 Elsevier Science S.A. All rights reserved.