Optimization of the Preparation Conditions of Sol‐Gel Derived Ni‐Co Oxide Films

Abstract

In this work, sol‐gel (SG) oxide films were formed by dip‐coating Pt substrates from Ni, Co, and mixed Ni‐Co sols. After withdrawing the substrate at a constant rate, the films were dried between 100 and 400°C for various periods of time (15 min to 1 h). Based primarily on the cyclic voltammetric behavior of the SG‐formed Ni‐Co films after drying at high temperatures, it is suggested that both the Ni and Co sites undergo redox reactions in 1 M NaOH solutions. This also explains the high charge efficiency and charge density of SG‐derived, Co‐containing Ni oxide films. Careful optimization of the experimental variables in the SG film preparation route indicated that the use of 50:50 Ni‐Co sols, a withdrawal rate of 6 cm/min, and drying at 250°C for 1 h yields films which display the highest charge density, the most rapid redox kinetics, and good stability to prolonged potential cycling. In addition, the charge capacity of the optimized 50:50 Ni‐Co SG oxide films can be increased further by the deposition of multilayers. The redox kinetics of the optimized coatings in 1 M NaOH solution were superior to those for Ni‐Co oxide films of comparable charges, but formed in other ways. Diminished reaction rates resulted when higher film drying temperatures were used (denser films) and when thicker, multilayered films were formed. © 2000 The Electrochemical Society. All rights reserved.