Lamella self-assembled Cu-doped NiO nanosheet arrays for dual-function devices with balanced electrochromic and energy storage performance

In this study, a novel bifunctional lamella self-assembled nanosheet arrays of Cu-doped NiO electrode was hydrothermally synthesized to improve and balance its electrochromic-energy storage performance. When Cu doping amount was 1%, the as-prepared nanostructured electrode exhibited both excellent electrochromic properties including large optical modulation (77.1% at 550 nm) and long stability (98.3% retention of maximum optical modulation after 4000 cycles), and good capacitive properties, especially high area specific capacitance (94.7 mF/cm 2 at 0.2 mA/cm 2 ) as well as excellent capacitance stability (100% at 50 mV/s for 2000 cycles; 80.6% retention at 0.8 mA/cm 2 for 5000 cycles). These excellent properties may benefit from the large active specific surface area and low charge transport resistance. Meanwhile, the self-assembled structure and cross-linked nanosheets optimize the structural stability of the film. Notably, an electrochromic-energy storage device (EESD) was constructed and demonstrated excellent electrochromic-energy storage performance. In charging process, two integrated EESDs in series turned into dark brown and an LED was lit up. While, in discharging process, the EESD gradually became colorless and the LED went out. This study may point out the direction for developing new visualized energy storage devices.