Sonochemically synthesized Ni(OH)2 and Co(OH)2 nanoparticles and their application in electrochromic electrodes

The present paper describes the behaviour of nanosized nickel and cobalt hydroxide, synthesized by a sonochemical method, deposited onto ITO transparent electrodes by using the electrostatic deposition layer-by-layer technique. Particles of about 5 nm diameter were obtained and characterized by High Resolution Transmission Electron Microscopy. The electrostatic self-assembly provide very thin electrochromic electrodes more homogeneous than those obtained by the ordinary electrodeposition method. The nanoparticulated material shows increased electrochromic efficiency of 80.3 cm2 C−1 and 130 cm2 C−1 (at 457 nm) for Ni(OH)2 and Co(OH)2, respectively. These values are greater than those reported for bulk electrodeposited films where the amount of active material is greater, indicating that nanometric size and defined geometry are relevant parameters for enhancing the chromogenic properties of both metal hydroxides.