THE ELECTROCHEMICAL IMPEDANCE OF POROUS NICKEL ELECTRODES IN ALKALINE MEDIA .1. EXPERIMENTAL STUDIES

Electrochemical impedance and capacity data for porous nickel electrodes in 31% KOH at ambient temperature (20 +/- 2-degrees-C) were obtained as a function of cycle number. The isopotential impedance magnitude at any given frequency, \Z\, decreased and the capacity of two types of sintered porous nickel electrodes increased during the first few hundred cycles, before becoming constant. The electrodes were cycled for about 1400 cycles under two different cycling regimes simulating low earth orbit operation and stress charging/discharging. Electrochemical impedance data were also obtained for a planar nickel electrode in 31% KOH as a function of applied dc potential to provide fundamental data for simulating the Ni(OH)2 and NiOOH phases within the pores. These data are used in Part II of this series to model porous nickel electrodes in terms of nonuniform transmission lines.