Regulation of carbon content in MOF-derived hierarchical-porous NiO@C films for high-performance electrochromism

Nickel oxide (NiO) is a promising candidate in practical electrochromic (EC) applications owing to its low cost and neutral colored state. However, the co-influence of low electrical conductivity and small lattice spacing leads to the slow switching speed and poor coloration efficiency of NiO-based EC electrodes. In this study, novel hierarchical-porous NiO@C thin film electrodes are fabricated through two-step pyrolysis of Ni-MOF on FTO glass, and the electrochemical and electrochromic performance of the electrodes can be improved by the regulation of the carbon residues. As a result, the desired NiO@C EC electrodes with both good ion diffusion and electrical conductivity are achieved. The film electrode shows a fast switching speed (0.46 s for coloring/0.25 s for bleaching), high coloration efficiency (113.5 cm(2) C-1) and ultra-stable EC cycles (90.1% after 20000 cycles). Additionally, EC eyewear devices and digital displays are assembled to illustrate the feasibility of the material in wearable devices and smart electronics.