Electrochromic properties of nanoporous α and β nickel hydroxide thin films obtained by chemical bath deposition

Nickel hydroxide nanoporous electrochromic thin films were obtained by chemical bath deposition method using nickel nitrate in two different formulations. In one case, ammonium hydroxide controlled the precipitation of the β-Ni(OH)₂ phase through the formation of coordination compounds. In the second case, the decomposition of urea yielded the α-Ni(OH)₂ phase. After thermal annealing in air in between 250 and 300 °C, the electrochromic behavior of the films was examined by cyclic voltammetry and single wavelength transmittance. The optical contrast and structural transformations between colored and bleached states of the samples were studied by exsitu optical transmittance, X-ray diffraction, as well as Raman and infrared reflectance spectroscopies. The α-Ni(OH)₂ films showed higher optical contrast and reversibility, properties associated with their porous morphology which is revealed by scanning electron microscopy studies.