1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 DOI: 10.1002/elan.201700535 A Novel Blue to Transparent Polymer for Electrochromic Supercapacitor Electrodes R. Yuksel,* [a] A. Ekber, [b] J. Turan, [b] E. Alpugan, [c] S. O. Hacioglu, [d] L. Toppare, [b, d, e] A. Cirpan, [a, b, d, e] G. Gunbas,* [b, d, e] and H. E. Unalan [a, c, e] Abstract: Electrochromic supercapacitors may alert the user on the remaining capacity of the devices. The color change indicating the remaining capacity can be simply and rapidly recognized by the human eye or by optical instruments. A rapid indication of charged state may extend device service life and prevent overcharging, which would otherwise result in electrode aging and decomposi- tion. In this study, a blue to the transmissive electro- chromic polymer, poly(4,7-bis(2,3-dihydrothieno[3, 4-B] [1, 4]dioxin-5-YI)-2-(2-octyldodecyl)-2H-benzo[D][1, 2,3] triazole) (P1C), was used in nanocomposite form with transparent silver nanowire (Ag NW) network current collectors for the fabrication of electrochromic super- capacitor electrodes. Highly conductive and transparent Ag NW networks have an important role in the realiza- tion of electrochromic supercapacitors using P1C. Fabri- cated Ag NW/P1C nanocomposite electrodes had a specific capacitance of 65.0 F g 1 at a current density of 0.1 A g 1 . Nanocomposite electrode showed excellent stability (capacity retention of > 98 %) after 11000 cycles associated with a resistance decrease associated with charge transfer. Keywords: silver nanowires · conducting polymers · supercapacitors · energy storage. 1 Introduction Supercapacitors are used as electrochemical energy stor- age devices in many systems from electric cars to renew- able energy systems due to their long cycle life and high power densities [1–4]. Supercapacitors are getting more and more prominent and even started to be used in daily gadgets. Fabrication with new form factors will certainly accelerate their widespread use in portable consumer electronics [5,6]. Fabrication of vivid power sources, in particular supercapacitors, may be an important step for the extensive utilization of smart electronic technologies [7]. Integration of unique properties (i. e. user communica- tion, environmental sensing, color change, flexibility etc.) to energy storage devices brings them one step closer to smart electronics. While the basic function of the super- capacitors is electrochemical energy storage, the growing demands on the multifunctional supercapacitor devices led to discovery and implementation of new functional- ities. Some of the most desirable functionalities may be listed as flexibility, biocompatibility, stretchability, print- ability and interaction with the user [7, 8]. Electrochromism is the reversible color change of organic or inorganic materials during oxidation/reduction reactions or ion intercalation. Integration of electro- chromism into supercapacitors is a major step for the multifunctional energy storage devices. Electrochromic supercapacitors have dual properties of simultaneous color change and electrochemical energy storage. The instant capacity of the supercapacitor devices with active electrochromic materials can be simply recognized by humans because the human eye is incredibly perceptive to color changes. Implementation of electrochromism to supercapacitors may also extend the lifetime of the devices through the prevention of overcharging (electro- lyte decomposition, polymer degradation). Various exam- ples of electrochromic supercapacitors are demonstrated in the literature. Conducting polymers (CPs) and transi- tional metal oxides are the commonly utilized materials in electrochromic supercapacitors. Vanadium oxide (V 2 O 5 ) [9], tungsten oxide (W 18 O 49 and WO 3 ) [10–12] and nickel oxide (NiO) [13] are the mostly investigated electro- chromic metal oxides; however, they have slow color shifting properties. Another electrochromic material group is CPs and polyaniline (PANI) is the most widely investigated CP [14,15]. PANI has a light green color at the reduced state, while it has a blue color in the oxidized state. However, its electrochromic properties such as coloration efficiency and the color shifting are quite [a] R. Yuksel, A. Cirpan, H. E. Unalan Department of Micro & Nanotechnology, Middle East Tech- nical University (METU), Ankara 06800, Turkey E-mail: reyuksel@gmail.com [b]A. Ekber, J. Turan, L. Toppare, A. Cirpan, G. Gunbas Department of Polymer Science & Technology, METU, Ankara 06800, Turkey E-mail: ggunbas@metu.edu.tr [c] E. Alpugan, H. E. Unalan Department of Metallurgical and Materials Engineering, METU, Ankara 06800, Turkey [d] S.O. Hacioglu, L. Toppare, A. Cirpan, G. Gunbas Department of Chemistry, METU, Ankara 06800, Turkey [e] L. Toppare, A. Cirpan, G. Gunbas, H.E. Unalan The Center for Solar Energy Research and Application, METU, Ankara 06800, Turkey Full Paper www.electroanalysis.wiley-vch.de  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2017, 29, 1 – 9 1 These are not the final page numbers! ÞÞ