A simple chemical method for deposition of electrochromic potassium manganese oxide hydrate thin films

A new chemical method for fast deposition of electrochromically active thin films of birnessite-type potassium manganese oxide (K0.27MnO2·xH2O) has been developed. The chemical deposition has been performed at room temperature by a reaction of aqueous solutions of potassium permanganate and manganese(II) chloride. The prepared thin films have thickness from 50 to 250 nm depending on the number of the deposition cycles. The composition and the structure of the K-birnessite films are studied by XRD, IR spectroscopy and TG/DTA analyses. Electrochemical studies using four different electrolytes such as aqueous K2SO4, Li2SO4, KNO3, and LiClO4 in PC have been performed. The electrochromic activity has been explored by cyclic voltammetry and VIS spectrometry. The best electrochromic properties are obtained using aqueous KNO3, where the difference in the transmittance at 400 nm between the bleached and colored state is 40% for both as-deposited and annealed films. The obtained data allow the prepared K-birnessite thin films in aqueous KNO3 electrolyte to be proposed as a promising system for electrochromic applications.