Solid-state nanocomposite electrochromic pseudocapacitors

We report on an electrochromic phenomenon in transition metal oxide materials induced by a novel mechanism involving charge/discharge of a solid-state electrochemical pseudocapacitor. Thin film nanocomposites of polycrystalline nickel oxide nanoparticles embedded in an amorphous tantalum oxide electrolyte matrix have been fabricated by reactive radio-frequency magnetron sputtering from a composite Ni/Ta metal target followed by a 400 degrees C oxygen anneal. Polycrystalline NiO nanoparticles within the composite play a role as an active electrochemical component while a surrounding amorphous Ta2O5 matrix acts as a proton electrolyte. This unique nanocomposite material construction exhibits a substantial electrochromic optical modulation. (C) 2005 The Electrochemical Society.