Abstract
It has been shown that the a.c. impedance of a sintered plate cadmium electrode can be related to that for a planar cadmium electrode by considering the penetration of the a.c. signal down the pores of the sinter matrix. Evenly and poorly-impregnated electrodes were studied and complex impedance plane plots obtained for regions corresponding to double layer charging, active dissolution and passivation. At high frequencies when porous behaviour was observed, the results displayed a close agreement with those predicted by the simple a.c. theory developed for a porous electrode with semi-infinite pores. Discrepancies could be attributed to the presence of uncharged Cd(OH) 2 or Cd(OH) 2 precipitate formed during discharge. The effect of charge-discharge cycling was investigated and the resulting impedance spectra interpreted in terms of changes in the wetted areas of cadmium, redistribution of active material and the progressive build up of Cd(OH) 2 within the sinter pores.
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