A study of multilayered electrochromic platings based on nickel and cobalt hydroxides

Abstract

The multilayered electrochromic films based on Ni(OH) 2 and Co(OH) 2 have been prepared using sequential cathodic template deposition for solutions containing polyvinyl alcohol, nickel nitrate and cobalt nitrate at a current density of 0.625 mA/cm 2 . The prepared films have demonstrated electrochemical activity and high electrochromic properties – coloration degree 25–80 %, high reversibility during cycling. The prepared films had a large number of structural defects and, possibly, large amounts of structural water, determined from them being X-ray amorphous. All the films had demonstrated similar electrochemical characteristics, except for the film composed of three layers of Ni(OH) 2 , Co(OH) 2 and Ni(OH) 2 . The best electrochromic characteristics had been demonstrated by the film prepared by consecutive deposition from solutions with polyvinyl alcohol containing nickel nitrate and cobalt nitrate for 2 and 78 minutes, respectively: coloration degree of 80 %, rectangular shape of the coloration-bleaching curve. A simple mechanism has been proposed, which describes better electrochromic characteristics of this film. It consists in the oxidation of cobalt hydroxide to CoOOH, which can act as an electrically conductive bridge between the substrate and the Ni(OH) 2 layer