Well-defined K2Zn3[Fe(CN)6]2-nanoparticles (NPs) synthesized with a micromixer showed robust redox reaction cyclability. Crystal structure analysis revealed that the robustness results from the maintenance of the original rhombohedral crystal structure in the oxidation state. The blue/colourless electrochromic device with the K2Zn3[Fe(CN)6]2-NPs and Prussian blue NPs showed recyclability over 1 million redox reactions.
![Graphical abstract: One million cyclable blue/colourless electrochromic device using K2Zn3[Fe(CN)6]2 nanoparticles synthesized with a micromixer](http://hg.y866.cn/compound/lib/scimg/usr/1/C9RA09496B.jpg)
