Ammonia controlled synthesis of NiO nanosheet arrays for high-performance electrochromic-supercapacitors

Abstract

To optimize the synthesis process and improve the electrochromic and energy storage performance of NiO, in this paper, an ammonia hydrothermal method is used to prepare NiO nanosheet array electrodes with dual-functions of electrochromic and energy storage. When the concentration of ammonia reaches pH = 11.5, the prepared electrode exhibits optimal optical modulation capability (79.2 % at 620 nm). Additionally, this electrode also provides a large area specific capacitance (69.5 mF/cm² at 0.2 mA/cm²), good rate capability (maintaining 46.7 mF/cm² at 1.0 mA/cm²), and excellent capacitive stability (retaining 96 % of the initial capacitance after 5000 cycles). These excellent performances are mainly attributed to the hierarchical assembled nanosheets structure, which has a large active surface area and short ion transport paths. Furthermore, the uniform and interlinked self-assembled structure, as well as the preset seed layer significantly enhance the film's structural stability and the adhesion to the substrate. Notably, we also construct electrochromic-supercapacitors (ECSCs). During the charging process, two series-connected ECSCs turn dark brown and light up an LED lamp, while during the discharging process, the ECSCs gradually becomes colorless, and the LED lamp goes out. This study provides directions for the preparation of novel dual-functional visual energy storage materials and boosts the development of dual-functional electrochromic-energy storage devices.