Homogeneous Precipitation of Layer Double Hydroxides

• Published in: Key engineering materials 2004-01, Vol.264-268, p.41-44
• Main Authors: Akinc, Mufit, Maviş, Bora
• Format: Article
• Language: English
• ISSN: 1013-9826; 1662-9795; 1662-9795
• DOI: 10.4028/www.scientific.net/KEM.264-268.41

Structure of nickel precipitate from decomposition of urea was found to be *a-Ni(OH)2. FTIR analysis revealed the intercalation of cyanate (OCN-), which is an intermediate product of urea decomposition. This observation implied that the assumption of single step decomposition of urea to carbon dioxide and ammonia was over simplified. For quantitative analysis on the effects of critical system parameters like initial pH and metal ion concentration, a detailed analysis of the possible reactions in urea system was carried out. Numerical solutions to reaction pathways predicted significant accumulation of the intermediate cyanate in the time-temperature range investigated. Further elaboration was possible by considering the effects of hydrolysis products of Ni2+ and Ni-amine, Ni-cyanate, and Ni-carbonate complexes in the numerical simulations. Chemical analysis of the precipitate showed a decrease in nitrogen content with increasing reaction times. This was consistent with the predicted decrease in concentration of Ni-cyanate complexes with time. At extended digestion times, formation of Ni-amine complexes limits the complete recovery of the Ni2+. From the two phases of Ni(OH)2, *a-phase, with its larger interlayer spacing, offers enhanced electrochemical properties but it transform into thermodynamically stable *b-phase. Stabilizing *a-phase with Co2+ substitution which oxidizes irreversibly to Co3+ with electrochemical cycling along with forming layer double hydroxides (LDH's: [M2+1-xM3+x(OH)2]x+[An-x/n]x-mH2O) were studied. Various compositions of LDH's containing Ni2+/Co2+ and A13+ ions were produced by urea and tested with chronopotentiometry to assess their potential utility as rechargeable electrode materials.