Rolf Ødegård

Transmission spectra of an electrochromic window based on polyaniline, tungsten oxide and a solid polymer electrolyte

Abstract An electrochromic window was fabricated by combining polyaniline and tungsten oxide with a solid polymer electrolyte binding the two electrochromic materials together. Polyaniline and tungsten oxide were deposited electrochemically on indium-tin-oxide glass plates. By applying a voltage between −1800 and +1600 mV, the transmission spectra for the electrochromic window show good light modulation in the 400–2700 nm wavelength region. For example, at 1000 nm the transmission changes from 0.76 to 0.22.Abstract An electrochromic window was fabricated by combining polyaniline and tungsten oxide with a solid polymer electrolyte binding the two electrochromic materials together. Polyaniline and tungsten oxide were deposited electrochemically on indium-tin-oxide glass plates. By applying a voltage between −1800 and +1600 mV, the transmission spectra for the electrochromic window show good light modulation in the 400–2700 nm wavelength region. For example, at 1000 nm the transmission changes from 0.76 to 0.22.

Dynamic light modulation in an electrochromic window consisting of polyaniline, tungsten oxide and a solid polymer electrolyte

Abstract The electrochemical and optical properties of an electrochromic window consisting of the two complementary electrochromic materials, polyaniline (PANI) and tungsten oxide (WO 3 ), have been investigated. Both PANI and WO 3 were electrochemically deposited on indium-tin oxide (ITO) glass substrates. Using the solid organic polymer electrolyte, poly(2-acrylamido-2-methyl-propane-sulfonic acid) (PAMPS), PANI and WO 3 were glued together. By applying a potential of ∼1.5V across the two external ITO contacts, we are able to modulate the light transmission, also in the near-infrared region (700–3000 nm), where about half of the solar energy lies, indicating that these ‘smart windows’ may significantly contribute to future energy savings in buildings. In order to study each of the electrochromic layers in the window, we have fabricated windows with holes in the electrochromic coatings, one window with a hole in the PANI film and another with a hole in WO 3 . This enables us to study the optical properties of PANI and WO 3 separately.

Transmission through an electrochromic window based on polyaniline, tungsten oxide and a solid polymer electrolyte

An electrochromic window was fabricated by combining polyaniline and tungsten oxide with a solid polymer electrolyte binding the two electrochromic materials together. Polyaniline and tungsten oxide were deposited electrochemically on indium-tin-oxide glass plates. By applying a voltage of ± 2 V, the transmission spectra for the electrochromic window show good light modulation in the 400–900 nm wavelength region, e.g. from 16% to 86% at 800 nm.

Reduction factor for polyaniline films on ITO from cyclic voltammetry and visible absorption spectra

Abstract The reduction factor as a function of applied potential for polyaniline films, deposited electrochemically on indium—tin oxide glass plates, has been determined from cyclic voltammetry and from visible absorption spectra, generally showing good agreement between the two methods.

Impedance analysis of the electrochemical doping of poly(3-methyl-thiophene) from aqueous nitrate solutions

Abstract Electrochemical impedance data for poly(3-methyl-thiophene) (P3MeT) films deposited on platinum electrodes were collected in aqueous solutions of KNO 3 and HNO 3 . The impedance results show that undoped P3MeT (0–400 mV vs. Ag/AgCl/3.5 M KCl) can be described as an electroactive electrode film into which ions are inserted upon oxidation. A space-charge layer develops in the polymer, probably at the polymer-solution interface. This space-charge layer can be adequately described as a diffuse double layer consisting of holes and counter-ions. At 600 mV a transitional behaviour is seen which can be described by a Randles equivalent circuit, and the response is similar to that of an ion-insertion electrode. This transition reflects the onset of doping, which is also seen as a break in the potential versus doping charge curve recorded by electrochemical voltage spectroscopy. Apparent diffusion coefficients are found to decrease from ca. 10 −7 cm 2 /s at 0 mV to ca. 10 −10 cm 2 /s at 600 mV. This decrease may be due to an enhancement of ionic transport by electrostatic coupling of the moving charged species (counter-ions and holes) below the insulator-metal transition. At 800 mV the thickness and electrolyte concentration dependences of the impedance spectra indicate that P3MeT is best described as a porous metal electrode. The experimentally determined values of capacitance per surface area are not consistent with typical metal/electrolyte double layers, unless unreasonably large surface-to-volume ratios are assumed for the porous electrode. Therefore it is suggested that the capacitance of the porous polymer electrode is due to doping (redox capacity). Replacing K + ions by protons had only a negligible effect on the electrochemical response of the film. Polarization at 1 V deactivates the film, and a new equivalent circuit is required to describe the degraded polymer. P3MeT is found to exhibit a doping-dependent wettability.

Electrochemical Response of Poly-(3-Methyl-Thiophene) to Various Anions in Aqueous Solutions

Abstract Electrochemically formed films of poly-(3-methyl-thiophene), (PMeT), on platinum electrodes have been characterized by cyclic voltammetry in aqueous solutions containing KNO3, KClO4, KCl and K2SO4. An observed enhanced anodic current response for CVs in nitrate and perchlorate solutions compared to the responses for the other solutions, is believed to be due to the oxidizing power of the nitrate and perchlorate ions. The demonstrated effect may suggest the possibility of applying PMeT as a sensor for oxidizing ions in aqueous solution.

Impedance analysis of the electrochemical doping of poly(3-methyl-thiophene) from aqueous solutions of KClO4, KCl and K2SO4

Abstract Impedance spectra of poly(3-methyl-thiophene) (P3MeT) films on Pt electrodes in aqueous solutions of 0.1 M KClO4, 0.1 M KCl and 0.1 M K2SO4 show that, in the undoped form, the polymer acts as an ion-insertion electrode. In the doped state, the behaviour in 0.1 M KClO4 is similar to that of porous metal electrodes with finite-length pores, although the low frequency capacitance is too high to be explained as an ordinary double-layer capacitance at the polymer-solution interface. This capacitance is therefore interpreted as a redox capacity connected to the doping of the polymer. In KClO4, the doping threshold found by stepwise coulometry is at least 250 mV lower than the transition to porous electrode behaviour seen in the impedance data. In 0.1 M KCl(aq) and 0.1 M K2SO4(aq) this doping threshold is ca. 200 mV higher than in 0.1 M KClO4, paralleling voltammetric data. In the KCl and K2SO4 solutions, the same equivalent circuit can be used both above and below the onset potential for doping. However, a Warburg element present in this circuit may be interpreted as due to diffusion below the metal-insulator transition and as capacitive charging of electrode pores of apparent infinite depth above this transition. The impedance data indicate that the pore structure of P3MeT varies with the contacting electrolyte.

The electrochemical response of polythiophenes in aqueous solutions

Abstract The electrochemical response of polythiophene, poly-3-methylthiophene and poly-3-octylthiophene in aqueous solutions of inorganic salts have been investigated by means of cyclic voltammetry. The experimental data show that these thiophenes are very sensitive to the anion employed in the electrolytic solution. Both doping and degradation processes are addressed.

Passivation of the aluminium cathode during deposition of aluminium from aluminium chloride-sodium chloride melts

The kinetics of aluminium deposition from NaCl-AlCl3 melts (cAlCl3 < 10 mol%) contained in alumina crucibles was studied by linear sweep voltammetry and potential step amperometry at temperatures around 820°C. At low concentrations (cAlCl3 < 0.4 mol%) the reduction of AlCl3 on liquid aluminium has been found to be diffusion controlled. At higher concentrations a passivation of the aluminium electrode was observed during the deposition reaction. The passivation appears to be caused by precipitation of alumina from supersaturated melt in the diffusion layer at the aluminium cathode.

On the kinetics of the cathodic deposition of aluminium on glassy carbon and tungsten electrodes from AlCl3 + NaCl + KCl melts

Abstract The kinetics of aluminium deposition from AlCl3 + NaCl + KCl melts were studied using several electrochemical relaxation techniques at 975 K. The deposition process was found to be controlled mainly by diffusion in the concentration range under study (cAlCl3 = 5 × 10−5-5 × 10−4 mol cm−3). The charge transfer reaction seems to be rather fast. No sign of a slow dissociation of a complex preceding the charge transfer was observed. Diffusion coefficients and rate constants have been obtained.