Porous thin films of It oxide were prepared by reactive dc magnetron sputtering onto unheated substrates. The crystallite size was similar to 5 nm, and a small amount of unoxidized Ir was present. The electrochromic performance was studied by optical transmittance measurements and cyclic voltammetry applied to films in aqueous and non-aqueous electrolytes, specifically being 1 M propionic acid, 1 M potassium hydroxide (KOH), and 1 M lithium perchlorate in propylene carbonate (Li-PC). Cyclic voltammetry measurements indicated that the films had a fractal surface structure. Good electrochromism, with mid-luminous transmittance modulation between similar to 55 and similar to 90% in similar to 100-nm-thick films, was documented in all of the electrolytes. (C) 2013 Elsevier B.V. All rights reserved.