Improved cyclability by tungsten addition in electrochromic NiO thin films

Aiming at improving the electrochromic properties of NiO thin films, well-known as anodic counter electrodes, the effect of tungsten addition was investigated. Ni–W–O thin films were deposited by pulsed laser deposition in optimized conditions, namely a 10−1 mbar oxygen pressure and a room temperature substrate. The presence of W led to a progressive film amorphization. An increase in cyclability for Ni–W–O (5%t WO3) electrode, cycled in KOH 1 M electrolyte, was associated with a limited dissolution of the oxidized phases with tungsten addition. HRTEM investigations of cycled films revealed that the stabilization is correlated to the existence of an α(II) hydroxide phase.