Interlaced NiCoO2 nanoparticle/nanosheet films for electrochromic energy storage devices with wide-band optical modulation and robust stability

Abstract

Electrochromic smart windows offer an energy-saving route and a comfortable indoor environment for buildings due to their dynamic modulation of solar radiation. However, it is still challenging to facilely fabricate electrochromic films with large optical modulation in a wide wavelength band, neutral coloration, and long-term cycling stability. Herein, a type of in situ grown NiCoO₂ bimetallic oxide film on fluorine-doped tin oxide (FTO) substrates with an interlaced nanoparticle/nanosheet structure is developed for electrochromism using a facile one-step solvothermal strategy. Owing to its unique structure, the NiCoO₂ film delivers a neutral transparent-to-brown tinting, wide-band modulation (54.67% at 550 nm, 34.8% at 900 nm) in the visible-near-infrared region, with fast switching speed (9/8.2 s), and high coloration efficiency (44.5 cm² C⁻¹ at 550 nm). Moreover, the solvothermal growth approach enables good bonding of the NiCoO₂ to the substrates, exhibiting excellent cycling stability of 2500 cycles. Additionally, a model of the smart window with the dual functions of electrochromism and energy storage was assembled using a NiCoO₂ film (electrochromic layer) and a reduced graphene oxide (rGO) film (ion storage layer), realizing the visualization of the stored energy level through the color change. It is believed that this work would provide fundamental insights for the exploration of high-performance electrochemical materials and devices.