ELECTROCHEMICAL IMPREGNATION OF NICKEL-HYDROXIDE - FLOW-THROUGH VS STAGNANT ELECTRODES

The electrochemical impregnation of nickel hydroxide in porous electrodes has been investigated both experimentally and theoretically. The loading level and plaque expansion were the most important parameters to be considered. The effects of flow, counterelectrode placement, and pH have been identified. A novel flow-through electrochemical impregnation is proposed in which the electrolyte is forced through the porous nickel plaque. The thickening of the plaque can be reduced while maintaining high loading capacity. A mathematical model for flow-through electrochemical impregnation is presented which describes the transport of the nitrate, nickel, and hydroxyl ions and the consecutive heterogeneous electrochemical reduction of nitrate and the homogeneous precipitation reaction of nickel hydroxide. The distributions of rate of precipitation and active material within the porous electrodes are obtained. Deviation of loading curve from Faraday’s law, in the case of stagnant electrodes, is believed to be the dissolution of surface-deposited Ni(OH)2; while the main loss in loading, in the case of flow-through electrodes, is attributed to the hydrodynamic washout. © 1990, The Electrochemical Society, Inc. All rights reserved.