Color-switchable electrochromic Co(OH)2/Ni(OH)2 nanofilms with ultrafast kinetics for multifunctional smart windows

Electrochromic devices have received great attention due to the steep growth of smart window markets and demands from various emerging fields. Recently, elaborately designed materials not only enhanced coloring/bleaching performances but also provided additional functionality, energy storage, since electrochromism relies on capture and release of ions. Meanwhile, given that electrochromic devices are mostly targeted for large-scale applications such as smart windows, there are still significant needs for further advances, especially in terms of reliability and simplicity of materials and their manufacturing processes. In this study, double-layer hydroxide films are reported as energy-storable electrochromic materials with ultrafast transition kinetics. Core/shell-like Co(OH)2/Ni(OH)2 films produced within a minute of electrodepositions have capabilities for multiple color changes and show extremely fast optical responses that are comparable to state-of-the-arts. In addition, the electrodeposited hydroxide films manifest high capacitance and rate capabilities when applied as capacitors, with electrochromic kinetics an order of magnitude higher than those with similar level of capacities for energy storage.