Addition of Multi‐walled Carbon Nanotubes to Fe‐ and Ru‐Metallopolymer Electrodes Enhances Response Time and Cycling Stability in Electrochromic Cells

Abstract

AbstractMetallopolymers (MEPEs) show a strong absorption band attributed to a metal‐to‐ligand charge transfer (MLCT) transition. Fe‐MEPE and Ru‐MEPE thin films switch reversibly from blue‐purple (λmax=584 nm, Fe2+) to colorless (Fe3+) or orange (λmax=518 nm, Ru2+) to pale green (Ru3+). The addition of multi‐walled carbon nanotubes (MWCNTs) enhances the electrochromic (EC) properties of Fe‐ and Ru‐MEPE electrodes in several ways: (1) faster response for bleaching/coloring; (2) enhanced Coulombic efficiency; and (3) improved cycling stability, particularly for Ru‐MEPE. Moreover, the charge density of the thin film electrodes can be increased upon the addition of the MWCNTs. This performance improvement is demonstrated in electrochromic devices (ECDs) with titanium‐doped vanadium oxide (TiVOx) as the optically‐passive ion storage layer. The visible light transmittance τv values of the ECDs are improved by the addition of the MWCNTs from 20 %/56 % to 17 %/56 % and from 31 %/47 % and 34 %/55 % in the dark/bright state, for Fe‐MEPE and Ru‐MEPE, respectively. Thus, the addition of MWCNTs to Fe‐ or Ru‐MEPE is a very promising route for future fast‐switching EC applications, e. g., displays, sunroofs, and rear‐view mirrors.