MOF derived carbon embedded NiO for an alkaline Zn-NiO electrochromic battery

Abstract

In this era of intelligent automation, smart energy storage devices are highly sought after due to their capability to reveal their state of charge by a visual colour change. In principle, this is typically obtained by integrating electrochromic materials which demonstrate a change in optical band gap during redox reactions as electrodes in batteries/supercapacitors. Among various electrochromic materials, transition metal oxides have received significant interests because of their natural abundance, good cycling stability and high electrochemical response. In this work, metal organic framework (MOF) derived carbon embedded NiO (NiO@C) demonstrates very fast switching speeds of ~ 1.4 s for coloration and ~ 3.5 s for bleaching with high coloration efficiency of ~ 135.16 cm2/C. These aspects make MOF-derived NiO@C as a potential candidate to be integrated as a smart positive electrode in an alkaline zinc (Zn) battery to construct a rechargeable Zn-NiO electrochromic (EC) battery. The Zn-NiO EC battery delivers an average voltage of ~ 1.84 V and demonstrates a specific capacity of ~ 85.3 mAh/m2 at 0.1 mA/cm2 current density. It visually displays its energy storage level by changing its colour from dark brown (charged state) to colourless (discharged state), making it a potential candidate in smart windows and energy storage displays.