Electrochromic properties of nickel oxide and mixed Co/Ni oxide films prepared via sol–gel route

The Ni oxide and mixed Co/Ni oxide films were prepared by sol–gel dip coating method at optimum conditions. The XRD analysis reveals the pure and Co mixed nickel oxide films to be in amorphous state. The field emission SEM images reveal nanopore like structure for Ni oxide film and well defined grains with pores for Ni oxide films containing 5 wt.% of Co. Electrochromic properties have been studied using cyclic voltammetric (CV) and in situ spectro-electrochemical techniques. The pure and cobalt mixed (5 wt.%) Ni oxide films exhibit anodic/cathodic diffusion coefficient of 4.93 ± 0.14/3.74 ± 0.10 × 10−10 cm2/s and 10.00 ± 0.24/7.60 ± 0.20 × 10−10 cm2/s respectively after 300 cycles. The cobalt mixed (5 wt.%) Ni oxide films exhibit the bleached/coloured state transmission of 90.42/7.21% with a photopic constrast ratio of 12.54 and the colouration and bleaching time were 5.9 and 2.4 s respectively. The addition of cobalt beyond 5% leads to poor transparency and inhibited electrochromic switching character.