Electrochromism in nickel oxide and tungsten oxide thin films: Ion intercalation from different electrolytes

Electrochromic (EC) NiOz and WOy thin films were prepared by sputtering and were used in a feasibility study aimed at investigating mixtures of these two oxides. The object was to identify a suitable electrolyte, compatible with both NiOz and WOy. To that end we carried out cyclic voltammetry (CV) in potassium hydroxide (KOH), propionic acid, and lithium perchlorate in propylene carbonate (Li-PC). WOy could be coloured in propionic acid and Li-PC, while NiOz could be coloured only in KOH. Both films showed best stability in Li-PC, which hence is well suited for further studies of mixed NiOz and WOy.