Electrochromism of heat-treated anodic iridium oxide films in acidic, neutral, and alkaline solutions

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Abstract
We show that coloration and bleaching times of anodic iridium oxide films (AIROF’s) are insensitive to pH. Similar kinetics are observed for aqueous solutions of 0.5M H2SO4, 4M LiNO3, or 0.5M NaOH, and for a solution of 3M LiNO3 in methanol. This suggests that long‐term stability may be achieved without degrading response time. It also shows that the mechanism for electrochromism in AIROF’s is fundamentally different from the ion‐electron double‐injection operative in the tungsten bronzes and recently proposed for AIROF’s. In fact it appears to be sufficient that current flow across the AIROF solution interface be carried solely by electrons. We also show that AIROF’s have markedly improved bleaching kinetics, reproducibility, and stability following heat treatment.