Hierarchical crystalline/defective NiO nanoarrays with (111) crystal orientation for effective electrochromic energy storage

Developing high performance electrochromic materials with energy storage function is essential for next generation smart display devices. Here, a double-layer NiO film (NiO-dl) was prepared by compositing the defective NiO (d-NiO) with the crystalline NiO (c-NiO), with a unique prismatic nanosheet array structure. The synergistic effect as well as the large active area with defect sites and valence modulation brought about by the (111) crystal plane-oriented growth of the sputtering process can promote the intercalation and extraction of OH⁻ and Li⁺, which greatly enhances the electrochemical properties. Specifically, the NiO-dl film achieves a prominent optical modulation covering visible region (89.5 % in KOH and 64.8 % in Li⁺ electrolyte at 550 nm) and near-infrared region (54.5 % in KOH and 37.2 % in Li⁺ electrolyte at 1000 nm), a high transparent bleached state (92.7 %), a superior coloring efficiency (44.7 cm² C⁻¹) and robust stability (95.1 % retention after 1000 cycles). A high area capacitance of 99.5 mF cm⁻² at 0.14 mA cm⁻² with the promising cycling performance exhibits the supercapacitor characteristics. The comprehensive evaluation of the NiO-dl film demonstrated its exploitative potential application in electrochromic energy storage fields.