Trifunctional NiO–Ag–NiO electrodes for ITO-free electrochromic supercapacitors

Abstract

Transparent, conductive, and ITO-free NiO/Ag/NiO (NAN) electrodes, which combined excellent electrochromism and supercapacitance, were successfully fabricated by an easy one-step electron-beam deposition method at room temperature. This NAN film shows a satisfactory average transmittance over 70% in the visible region and extraordinarily low square resistance of only 8.0 Ω □⁻¹. Large optical modulation (24.3% at 550 nm), fast response time (τ_c = 4.3 s, τ_b = 4.0 s) and extremely high coloration efficiency (76.6 cm² C⁻¹) are achieved at an EC layer thickness of just 35 nm. Moreover, high specific capacitance (364.0 F g⁻¹ at 2 A g⁻¹), good rate capability, and great long-term cycling stability demonstrated an excellent electrochemical energy storage performance of the NAN film, which can even compete with nanostructured NiO films. Electrochemical kinetics analysis indicates that the essential reasons of such superior comprehensive performances lie in high conductivity, fast charge-transfer, and ion-diffusion dynamics, as well as good contact between Ag and NiO layers.