Effect of precipitating agents on the physicochemical and electrolytic characteristics of nickel hydroxide

Nickel hydroxide samples were prepared from nickel sulphate solution using three different precipitating agents, namely urea, sodium hydroxide and ammonia under identical preparation conditions. Depending on the nature of precipitating agent, Ni content of the precipitates varied between 44.5% and 53.6%. From the XRD patterns, it was observed that urea produces poorly crystalline nickel hydroxide with only a few broad peaks corresponding to alpha-form, The presence of this phase was confirmed from the FTIR spectrum. beta-Nickel hydroxide was obtained using sodium hydroxide or ammonia as the precipitating agent. The initial discharge potentials of 420, 436 and 441 mV with discharge capacities of 415, 374 and 335 mA h/g of nickel were obtained from the products obtained using urea, sodium hydroxide and ammonia, respectively, The study showed that the product obtained by using urea is of best quality with respect to its electrolytic property. However, this product was lowest in percentage of nickel (44.5%) and exhibited maximum weight loss (37.9%) at 800 degreesC, which is found to be due to a combination of water of hydration and intercalation of anions. The study on the effect of precipitation parameters such as initial nickel salt concentration and ageing time (urea as the precipitating agent) showed that the discharge capacity decreases with the increase in initial nickel concentration or on ageing the samples at ambient temperature. The nickel content during these variations was similar to 42%. (C) 2003 Elsevier Science B.V All rights reserved.