Homogeneous precipitation from solution by urea hydrolysis: a novel chemical route to the α-hydroxides of nickel and cobalt

Homogeneous precipitation from solution by hydrolysis of urea at elevated temperatures (T= 120 °C) yields novel ammonia-intercalated α-type hydroxide phases of the formula M(OH)x(NH3)0.4(H2O)y(NO3)2 –x where x= 2,y= 0.68 for M = Ni and x= 1.85, y= 0 for M = Co. These triple-layered hexagonal phases (a= 3.08 ± 0.01 Å, c= 21.7 ± 0.05 Å) are more crystalline than similar phases obtained by chemical precipitation or electrosynthesis. This method can be adapted as a convenient chemical route to the bulk synthesis of α-hydroxides.