A new cathodically coloring electrochromic material based on metallo-supramolecular polyelectrolyte containing Cu(I) metal ion (MEPE-Cu(I)) has been synthesized and studied. The electrochromic mechanism for MEPE series involves the redox reaction of Cu(I)/Cu(II) pair and metal-to-ligand charge transfer (MLCT). Both would drive MEPEs to change color upon the passage of a small reaction charge. The transmittance change (Delta T) of a MEPE-Cu(I) thin film at 580 nm reaches ca. 20.0% when switching the potential between 0.0 and +1.5 V (vs. Ag/Ag+). A fast response time of less than 1 s and a coloration efficiency value of 260 cm(2)/C at 580 nm are recorded. To fabricate MEPEs-based electrochromic device (ECD), polyaniline-carbon nanotube (PANI-CNT) was chosen to act as the ionic storage layer for MEPE-Cu(I). A liquid electrolyte containing 0.1 M tetrabutylammonium perchlorate (TBAP) in acetonitrile (ACN) with 1.0 mM HClO4 has been used in the ECD. By switching the potential between 0.0 and -1.5 V (PANI-CNT vs. MEPE-Cu(I)), the ECD behaves as a MEPE-Cu(I) thin film device with a similar Delta T value of about 20% at 580 nm, but with a faster response time of less than 0.5 s, presumably due to the presence of PANI-CNT. It remains 99% of the initial Delta T after 1500 cycles with good long-term stability. (C) 2013 Elsevier B.V. All rights reserved.