Electrochemical deposition of Ni-WO3 thin-film composites for electrochromic energy storage applications: Novel approach toward quantum-dot-sensitized solar cell-assisted Ni-WO3 electrochromic device

Abstract

A thin film of nickel-intermixed tungsten oxide (Ni-WO3) composite was assembled using a facile one-step electrochemical deposition method. Equal proportions of Ni(OH)2 and WO3 were used to obtain Ni-WO3 thin film and conducted a detail study on electrochromic energy storage properties. The composite film exhibited cathodic electrochromic behavior and displayed significantly improved performance compared to the Ni(OH)2 and WO3 thin films. Assembled Ni(OH)2 and WO3 in composite thin film formed a crosslinked and deagglomerated surface; therefore, both electrochemically active surface area and charge transfer kinetics were notably enhanced. Highest coloration efficiency (CE) of 68.5 cm2/C, optimum optical contrast (%ΔT) of 61, and fast coloration response of 3.9 s were recorded for thin film composite while the Ni(OH)2 and WO3 thin films possessed CE values of 41.1 and 46.6 cm2/C, and %ΔT values of 28 and 35, respectively. As an energy storage material, Ni-WO3 exhibited a maximum areal capacitance of 23.1 mF/cm2, at an applied current of 2 mA. Capacitive retention study showed an excellent retention of 76.5% even after 2000 charge/discharge cycles. Furthermore, electrochromic performances of Ni-WO3 were evaluated with a quantum-dot-sensitized solar cell, in which an applied potential of 1.15 V was sufficient for coloring the Ni-WO3 thin film.