Electrochemical and electrochromic characteristics of Ta2O5–ZnO composite films

Ta2O5–ZnO composite films with different molar ratios of Ta/Zn have been deposited on indium tin oxide (ITO) coated glass and stainless-steel substrates by pulsed reactive ablation in an O2 ambient. Films were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical and electrochromic behaviors of Ta2O5–ZnO composite film electrodes were investigated by cyclic voltammetry, galvanostatic cycling, potential stepping and in situ optical transmittance measurements. Results show that the composite film with the presence of ZnO within Ta2O5 can significantly improve electrochemical and electrochromic properties. The composite Ta2O5–ZnO film with Ta/Zn molar ratio of 2.5 exhibits an initial reversible capacity of 600 mA h/g and retains good cyclability at 10 μA cm−2 in the voltage range 0.01 to 3.0 V, and its excellent electrochromic efficiency is estimated to be 47 cm2/C at 650 nm, which are superior to those of pure Ta2O5 or ZnO. The formation of ZnTa2O6 may be responsible for the improvement effect.