Optimization of the preparation conditions of sol-gel derived Ni-Co oxide films

In this work. sol-gel (SG) oxide films were formed by dip-coating Pt substr ates from Ni, Co, and mixed Ni-Co sols. After withdrawing the substrate at a constant rate. the films were dried between 100 and 300 degrees C for var ious periods of time (15 min to 1 h). Based primarily on the cyclic voltamm etric behavior of the SC-formed Ni-Co films after drying at high temperatur es. it is suggested that both the Ni and Co sites undergo redox reactions i n I M NaOH solutions. This also explains the high charge efficiency and cha rge density of SC-derived, Go-containing Ni oxide films. Careful optimizati on 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 dryin g at 250 degrees C for 1 h yields films which display the highest charge de nsity, the most rapid redox kinetics, and good stability to prolonged poten tial 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 supe rior ro those for Ni:Co oxide films of comparable charges. but formed in ot her ways. Diminished reaction rates resulted when higher film drying temper atures were used (denser films) and when thicker, multilayered films were f ormed. (C) 2000 The Electrochemical Society. S0013-4651(00)03-130-X. All ri ghts reserved.