Browsing by Subject "Electrochromism"

Now showing 1 - 4 of 4

Open Access
Electrochromic properties of nanostructured tungsten trioxide (hydrate) films and their applications in a complementary electrochromic device
(Elsevier, 2011-12-26) Jiao, Z.; Wang, J.; Ke, L.; Liu, X.; Demir, Hilmi Volkan; Yang, M. F.; Sun, X. W.
Orthorhombic hydrated tungsten trioxide (3WO(3)center dot H2O) films consisted of nanosticks and nanoparticles were prepared on fluorine doped tin oxide (FTO)-coated substrate by a facile and template-free hydrothermal method using ammonium acetate (CH3COONH4) as the capping agent. Irregular nanobrick films were obtained without capping agent. Due to the highly rough surface, the nanostick/nanoparticle film depicts faster ion intercalation/deintercalation kinetics and a greater coloration efficiency (45.5 cm(2)/C) than the nanobrick film. A complementary electrochromic device based on the nanostick/nanoparticle 3WO(3)-H2O film and Prussian blue (PB) was assembled. As a result, the complementary device shows a higher optical modulation (54% at 754 nm), a larger coloration efficiency (151.9 cm(2)/C) and faster switching responses with a bleaching time of 5.7 s and a coloring time of 1.3 s than a single 3WO(3).H2O layer device, making it attractive for a practical application.
Open Access
Investigation of electrochromism process through ultrafast broadband spectroelectrochemistry
(2021-01) Zakaria, Musah
Electrochromism is the reversible change in color of an electroactive material due to a redox reaction induced by the application of voltage. Electrochromic materials have gained much research attention since the discovery of organic conducting polymers in the late 1970s, with high prospects for diverse applications. Color change in electrochromic materials involves two processes. First, a redox reaction that leads to the oxidation or the reduction of the EC material. Then the intercalation of counter-ions into the material for charge balancing. For instance, to effect a color change in a neutral conducting polymer through oxidation, first, an oxidizing potential is applied and the polymer loses electrons in a heterogeneous electron transfer leading to a net positive charge creation. To achieve further oxidation, electroneutrality is partially restored by anions that diffuse from the bulk solution into the polymer. Since the diffusion rate of counter-ions is much slower than electron transfer, it is widely assumed that the oxidation process is rate-limited by ion transport. The main aim of this work is to put this assumption to test. Relying on the fact that heterogeneous electron transfer is much faster than ionic charge transfer, experiments at very short time scales down to a few microseconds are performed. Under such experimental conditions, counter-ions do not have enough time to move into the electrochromic material and any sign of electrochromism is due to electron transfer. Through Ultrafast Cyclic Voltammetry with online iR compensation, sweep rates in the order of kV/s to MV/s are reached. We used thin films of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) used as the electrochromic material in this work. In monitoring the color change of the polymer film, we employ in situ UV-visible spectroscopy. To keep up with the rapid conversion of the polymer between its redox forms, we collect spectra in aggregate mode where several spectra are averaged into a single spectrum. By using a principal component analysis algorithm, the compound spectra are decomposed and we calculate the time that the polymer spends in each of its redox forms during the Ultrafast Cyclic Voltammetry experiments.
Open Access
Optical and electronic properties of fluorene-based copolymers and their sensory applications
(John Wiley & Sons, Inc., 2013) Ibrahimova, V.; Kocak, M. E.; Önal, A. M.; Tuncel, D.
A series of novel, fluorene-based conjugated copolymers, poly[(9,9-bis{propenyl}-9H-fluorene)-co-(9,9-dihexyl9H-fluorene)] (P1), poly[(9,9-bis{carboxymethylsulfonyl-propyl}- fluorenyl-2,7-diyl)-co-(9,9-dihexyl-9H-fluorene)] (P2) and poly[(9,9- dihexylfluorene)-co-alt-(9,9-bis-(6-azidohexyl)fluorene)] (P3), are synthesized by Suzuki coupling reactions and their electrochemical properties, in the form of films, are investigated using cyclic voltammetry. The results reveal that the polymer films exhibit electrochromic properties with a pseudo-reversible redox behavior; transparent in the neutral state and dark violet in the oxidized state. Among the three polymers, P2 possesses the shortest response time and the highest coloration efficiency value. These polymers emit blue light with a band gap value of around 2.9 eV and have high fluorescent quantum yields. Their metal ion sensory abilities are also investigated by titrating them with a number of different transition metal ions; all of these polymers exhibit a higher selectivity toward Fe3þ ions than the other ions tested with Stern–Volmer constants of 4.41 106 M1 , 3.28 107 M1 , 1.25 106 M1 , and 6.56 106 M1 for P1, P2, water soluble version of P2 (P2S) and P3, respectively.
Open Access
Reversible electrical reduction and oxidation of graphene oxide
(American Chemical Society, 2011) Ekiz, O. O.; Ürel, M.; Güner, H.; Mizrak, A. K.; Dâna, A.
We demonstrate that graphene oxide can be reversibly reduced and oxidized using electrical stimulus. Controlled reduction and oxidation in two-terminal devices containing multilayer graphene oxide films are shown to result in switching between partially reduced graphene oxide and graphene, a process which modifies the electronic and optical properties. High-resolution tunneling current and electrostatic force imaging reveal that graphene oxide islands are formed on multilayer graphene, turning graphene into a self-assembled heterostructure random nanomesh. Charge storage and resistive switching behavior is observed in two-terminal devices made of multilayer graphene oxide films, correlated with electrochromic effects. Tip-induced reduction and oxidation are also demonstrated. Results are discussed in terms of thermodynamics of oxidation and reduction reactions. © 2011 American Chemical Society.