1D/2D Co3O4/NiO composite film for high electrochromic performance

Abstract

As an electrochromic material, Co3O4 has limited applications due to its low optical modulation range and short cycle life. In order to improve the electrochromic properties, a 1D/2D Co3O4/NiO composite film was prepared by simple two-step hydrothermal process and discontinuous annealing. The electrochromic properties of the composite structure are significantly improved compared with the nanostructures using two oxides alone. The effect of film structure on electrochromic properties was studied in detail. The results show that the 1D/2D Co3O4/NiO composite film have remarkable optical modulation (16–73% in the 350–800 nm range) and high Li+ diffusion rate (5.15 × 10−12 cm2/s). The improvement of electrochromic properties is mainly due to the porous structure, which increase the two active materials to leak fully in the electrolyte, thus enhancing the diffusion of ions and electrons. NiO nanosheets grow well and distribute uniformly on the surface of Co3O4 nanowires, allowing the two parts to fully contact the electrolyte. Cyclic voltammetry (CV) analysis shows that the peak current of the composite film is much higher than that of the single film, indicating that the nanoarray has high electrochemical reactivity. Results of electrochemical impedance spectroscopy show that the composite film has the lower charge transfer resistance and ion diffusion resistance, which are conducive to rate capacity. This work provides a strategy for improving the electrochromic properties of cobaltosic oxide.