Electrochemistry on Polymer Thin Films and Their Applications:Ion Transport, Electron Transfer and Electro-Optical Devices
Date Issued
2010
Date
2010
Author(s)
Hsu, Chih-Yu
Abstract
In this dissertation, the main purpose is to investigate the electrochemical behaviors and electro-optical applications of two different polymer thin films, poly(butyl viologen) (PBV) and poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et2).
In the first part (Chapters 3 and 4), the ion transport phenomena of PBV film is studied by scanning electrochemical microscopy (SECM) and electrochemical quartz crystal microbalance (EQCM) analysis. The ion exchange behavior between Fe(CN)64- and Cl- at the interface of PBV film/electrolyte can be probed using a SECM. The ion flux during the redox reaction of PBV can be calculated after obtaining the EQCM data. It is thus realized that the release of Fe(CN)64- begins at ca. -0.43 V (vs. Ag/AgCl) and reaches a maximum flux at ca. -0.55 V during the reduction of a PBV film. The ion exchange mechanism can also be proposed. As for the ion flux of Cl- within the PBV film, the average numbers of accompanying water are calculated to be about 24.8 per Cl-. The instantaneous water to anion molar ratios at any potential can also be obtained. Based on this investigation, the mechanism of the redox behavior of any chemically modified electrodes can be realized.
In the second part (Chapters 5 and 6), the electron transfer characteristics of PProDOT-Et2 is analyzed by electrochemical impedance spectroscopy (EIS) and rotating disk electrode (RDE) technique. In the presence of redox couple, the electron transfer at the PProDOT-Et2 thin film shows a standard heterogeneous rate constant (k0) that depends on the kind of redox couples and their concentration ratios. The k0 value for I-/I3- is 1.3×10-3 cm s-1, which is higher than that for Br-/Br3- of 2.8×10-4 cm s-1. Due to the electrochromic nature, the PProDOT-Et2 films are darkened in the environment of redox couples. The k0 values under different redox couples result in different darkened rates. In order to achieve better optical attenuation, Br-/Br3- is selected for further investigation by adding Br2 into the redox electrolyte. By changing the concentration ratio of Br-/Br3- in the redox electrolyte solution, it is realized that once the forward and backward electron transfer rate reaches balance, PProDOT-Et2 film can fully exhibit its electrochromic property. As for the capacitance performance of PProDOT-Et2 thin film, it is affected by the electron transfer of the polymer. The heterogeneous electron transfer rate constant (ks) of PProDOT-Et2 film is 0.49 s-1 and the specific capacitance achieved ca. 6.5 F cm-2. Based on this, a novel photo-supercapacitor (PSC) was fabricated to store solar energy in-situ with a specific capacitance of 0.48 F cm-2, a photocharge voltage of 0.75 V and an energy storage efficiency of 0.6%.
In the last part (Chapters 7 and 8), the electro-optical applications of PBV and PProDOT-Et2 are incorporated into an electrochromic device (ECD) and a photoelectrochromic device (PECD), respectively. The new ECD is fabricated with PBV and Prussian blue and has a good optical contrast. The coloration efficiency of this device exhibits ca. 105 cm2/C and the transmittance is changed from 68% to 4% at 550 nm. As for the PECD using the PProDOT-Et2 electrochromic film and the FL dye1-TiO2 photoactive layer, Br-/Br3- redox electrolyte is selected and optimized to obtain a self-powered PECD exhibiting exceptional optical attenuation of fast switching rate and stability under light illumination. The PECD exhibited a transmittance change of 32.0% under 620 nm initially and shows only 5.3% decay after a consecutive 100 cycles with a fast switching time less than 10 s. Simple design equations are also proposed to explain the optimization process and better understand the key elements in the PECDs.
Subjects
capacitance
electron transfer
electrochromism
ion transport
polymer thin film
photoelectrochromic device
redox couple
Type
thesis
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