A Mathematical Model for Predicting Nonuniform Electrochemical Impregnation of Nickel Hydroxide

Abstract

This paper presents a mathematical model for the electrochemical impregnation of nickel hydroxide in the type of porous nickel plaque used commonly in the positive electrode of Ni/Cd and normalNi/H2 cells. The model includes the transport of Ni2+,NO3−,OH− , and H+ ions the electrochemical reduction of NO3− , and the homogenous acid/base and precipitation reactions. The effect of plaque thickness, plaque tortuosity, and applied current density on the time‐dependent porosity distribution and on the uniformity of normalNifalse(OH)2 loading are discussed. Predictions for both constant‐current and constant‐potential operating conditions are presented. It is shown that a change in tortuosity from 1.6 to 3.0 can yield a 27% decrease in uniformity at 30 mA/cm2 for a 0.075 cm thick plaque at 1.6 g/cm3 of void loading. It is also shown that when the current density is changed from 30 to 40 mA/cm2, the uniformity decreased by 20% for a plaque of the same thickness with a tortuosity of 1.6 at the same loading. The model could be used to develop quality‐control tools to insure a uniformly loaded plaque during electrochemical impregnation.

Fabrication of Ni-Plaque-Based Manganese Dioxide Electrodes for Electrochemical Supercapacitors

“…Ni hydroxide is used as a positive electrode material for a number of alkaline secondary cells such as Ni/Cd, Ni/Fe, Ni/Zn, and Ni/MH cells [5]. Due to the small pore size of Ni plaques, the impregnation of the plaques with Ni hydroxide was achieved by in-situ chemical or electrochemical synthesis in pores using Ni nitrate solutions [5][6][7]. Chemical impregnation is based on multiple dipping of the plaques in the Ni nitrate solutions and treatment in basic solutions.…”