Anodic iridium oxide films: A new electrochromic

We review the preparation and properties of a new electrochromic material, an anodically grown iridium oxide film (AIROF), and describe three new developments: 1) a heat treatment which improves response times and greatly improves stability; 2) the observation that the maximum coloration and the speed of response are independent of pH, i.e., essentially the same for acidic, neutral, or alkaline electrolytes, and 3) the development of a transmission device in which the AIROF is grown on a semitransparent conducting substrate. We have also observed a new electrochromism isotherm in AIROF's, and shown that there are two distinct electrochromic processes with different isotherms. Since the two distinct processes cannot both be simple proton injection, our results show clearly that other processes can accomplish coloration in AIROF's. Moreover, both isotherms are dominated by internal entropy changes of noninteracting particles. Such isotherms are qualitatively different from that of the proton-injection process in WO
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electrochromics.