Thermogravimetric studies on nickel hydoxide electrode

Abstract

Thermogravimetric analysis (TGA) has been used as a quick and accurate method for determining the content of Ni(OH) 2 for nickel hydroxide electrodes (NOE) prepared by the chemical precipitation of nickel hydroxide on sintered nickel plaque. The analysis can be carried out in a reducing atmosphere (Ar+4%H 2) or in air, and, while the final products differ, results for the two methods should be mutually consistant. The chemical reactions expected (in air vs. in hydrogen) are shown below: ▪ From the weight loss of this reaction the loading of Ni(OH) 2 can be determined since the weight loss from the decomposition of pure Ni(OH) 2 is 19.4%. ▪ Again the Ni(OH) 2 loading can be calculated since the theoretical weight loss for the above reaction (i) is 36.7% (for pure Ni(OH) 2). Portions of a commercial NOE were cut and used for the TGA experiments in air and in hydrogen atmospheres. These TGA experiments gave consistent results for the nickel hydroxide concentration of our NOE. X-ray diffraction (XRD) studies indicated the active material was crystalline nickel hydroxide. After TGA in air to 500°C, XRD showed only NiO (plus the Ni from the plaque), while after TGA in H 2 to 500°C XRD showed only Ni peaks. In addition to these two chemical reactions, a weight loss of 1–3% was observed between 80–180°C corresponding to the loss of adsorbed H 2O. The molar ratio of adsorbed water to the calculated Ni(OH) 2 loading was about 0.1M H 2O per mole of Ni(OH) 2. This water was adsorbed and not structural based on the X-ray results discussed in this paper.