Design and synthesis of 2D rGO/NiO heterostructure composites for high-performance electrochromic energy storage

Two-dimensional (2D) transition metal oxide composited with graphene has attracted worldwide attention in the energy storage and conversation field. Here, a 2D rGO/NiO heterostructure film on ITO glass was designed and applied to electrochromic energy storage. The 2D heterostructure increases the interlayer spacing of the NiO-based films and the electrochemically active surface area, reduces the charge transfer resistance and band gap, and then realizes fast ion diffusion and electron transport, thus improving the electrochromic and supercapacitor performance of the NiO film. The film exhibits outstanding areal capacitance (269 mF cm−2 at current density of 0.5 mA cm−2), excellent cyclic stability (capacitance retention almost 100% after 1000 cycles at current density of 1.5 mA cm−2) and superior electrochromic performance (high optical contrast of 53% at 630 nm, fast response time of 3.4 s for coloration and 5.3 s for bleaching). Furthermore, integrated the 2D heterostructure rGO/NiO film into a smart electrochromic-supercapacitor device, two devices could light up an electronic watch for about 2 h, at the same time, the color of the device changes in the process of electric output.