Electrochromic-Supercapacitor Based on MOF Derived Hierarchical-Porous NiO Film
Nickel oxide (NiO) is a promising candidate for future electrochromic-supercapacitors due to its pronounced electrical properties and low cost. Unfortunately, the weak interaction between NiO film and conductive substrate results in poor cycle stability. In addition, the long color-switching time and low capacitance by the small lattice spacing in dense NiO impede its practical applications seriously. Herein, a hierarchical porous NiO film/ITO glass bifunctional electrode has been prepared via the solvothermal and subsequent calcination process of MOF-74 growing in-situ on ITO, which shows outstanding cycle reversibility, excellent capacitance, high coloration efficiency and short color-switching time. Because of the strong binding force between NiO film and substrate, and large surface areas with a hierarchical porous structure which are beneficial to the ion transport, the NiO film demonstrates perfect capacitive and electrochromic properties. As a bifunctional electrode, the NiO film shows the specific capacitance of 2.08 F cm-2 at 1 mA cm-2, large optical modulation of 41.08% and more than 90% of optical modulation retention after 10000 cycles. Furthermore, we assembled a bifunctional device whose energy condition can be roughly estimated according to the color state of the device. This finding can provide us with a new application of MOFs in the dual device of electrochromic-supercapacitor.