A Study of the Influence of Polyvinyl Pyrrolidone Concentration in the Deposition Electrolyte on the Properties of Electrochromic Ni(OH)2 Films

Electrochromic devices are actuation elements of smart windows and allow saving the energy needed to cool the premises. Electrochemical deposition can significantly reduce the cost of electrochromic deposition.This paper discusses an electrochemical method of deposition based on nickel hydroxide from an electrolyte containing nickel nitrate and polyvinylpyrralidone (PVP). The electrochromic films were obtained in a galvanostatic mode at different PVP concentrations.As a result of the studies, it has been shown that the presence of PVP in the deposition electrolyte significantly affects the properties of the resulting electrochromic films. Moreover, the properties of the resulting films strongly depend on the used PVP concentration. Thus, at low concentrations, the addition of PVP causes an improvement in electrochromic and electrochemical characteristics, including stability in the properties of films. While at high concentrations of PVP, the electrochemical and electrochromic characteristics deteriorate significantly up to their almost complete disappearance. The paper proposes a possible mechanism that explains the improvement in the characteristics of the films obtained from the solutions with low PVP concentrations. This mechanism consists in improving the wettability of the substrate, increasing the contact area of the deposit with the substrate and, as a consequence, improving the adhesion and a decrease in the contact resistance at the conductive oxide – Ni(OH)2 film boundary.Also, the work has found the range of optimal PVP concentrations for an electrolyte containing 0.1 М Ni(NO3)2, which is 0.5–2