高分子薄膜之電化學及其應用：離子進出、電子傳遞與光電元件

Electrochemistry on Polymer Thin Films and Their Applications:Ion Transport, Electron Transfer and Electro-Optical Devices

徐志宇(Chih-Yu Hsu)

指導教授 ： 何國川

國立臺灣大學/工學院/化學工程學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.00206

摘要

本論文主要探討兩種高分子薄膜材料，聚紫精(PBV)及PProDOT-Et2之電化學特性與光電方面之應用。
在第一部份(第三章與第四章)針對聚紫精於電化學反應時之離子進出現象透過掃瞄式電化學顯微儀(SECM)與電化學石英震盪微天平(EQCM)進行分析。透過SECM可以探討於聚紫精薄膜/電解液介面之Fe(CN)64-離子與氯離子之離子交換狀況。而透過EQCM的量測則可以計算出聚紫精薄膜於氧化還原反應時之離子進出通量。因此可以得知Fe(CN)64-離子約在-0.43 V (vs. Ag/AgCl) 之操作電壓下會離開聚紫精薄膜，而其通量則會在-0.55 V左右達到最大值，也可以因此而提出離子交換之反應機制。另一方面，氯離子之進出通量則可計算出每個氯離子會平均攜帶約24.8個水分子同時進出。而在每個電位之下的水分子對離子之比例也可以求得。根據以上探討，可以決定任何化學修飾電極之氧化還原機制。
第二部份(第五章與第六章)針對PProDOT-Et2之電子傳遞特性透過電化學組抗分析與旋轉電極進行探討。當PProDOT-Et2薄膜於具有氧化還原對之電解液中，兩者之間所發生的電子轉移現象受到不同氧化還原對以及濃度比例而影響其速率常數(k0)。對於碘離子，該速率常數為1.3×10-3 cm s-1較高於溴離子之2.8×10-4 cm s-1。而由於PProDOT-Et2本身具備之電致色變性質，因此會在接觸氧化還原對之後使薄膜因為反應而著色，而不同氧化還原對之電子轉移速率常數便會造成不同的著色速度。為了達到較佳之光學調幅，在本研究中選用了Br-/Br3-氧化還原對，並進一步探討添加Br2之後之影響。經過調整Br-/Br3-氧化還原對的濃度比例後，可以瞭解當正逆反應速率平衡時，PProDOT-Et2薄膜可以不受到氧化還原對之電子轉移影響，而完整表現出其原有之電致色變性質。另一方面，有關於PProDOT-Et2高分子之電容表現，我們發現該性質與高分子膜之電子傳遞特性具相關性。PProDOT-Et2的電子傳遞的速率常數(ks)可以求得為0.49 s-1，而該薄膜於一定析鍍電量時則可以達到6.5 F cm-2之特徵電容值。根據此結果，我們開發出一全新的光超級電容元件用以同步於光能轉電能之後將電能儲存，該光超級電容可以達到特徵電
容值為0.48 F cm-2，光充電電壓為0.75 V，以及能量儲存效率為0.6%。
在本論文之最後一部份(第七章與第八章)，針對聚紫精與PProDOT-Et2之光電應用進行開發，於電致色變元件與光電致色變元件。此全新之電致色變元件由聚紫精與普魯士藍所組成，並達到高對比之效果。該元件在波長為550 nm之下之著色效率達到約105 cm2/C，並具有68%至4%之穿透度變化。在光電致色變元件方面，則利用PProDOT-Et2電致色變薄膜與FL dye1-二氧化鈦之光電極所組成，並選用以及最適化具有Br-/Br3- 氧化還原對之電解液配方，使得該元件可以在陽光之照射下達到無須外加電能、優異的光學調幅、高反應速度以及良好的穩定性。該光電致色變元件在波長620 nm下具有32.0%的穿透度變化，並在經過100圈連續操作測試後僅衰退了5.3%，其每圈之反應時間皆少於10秒。我們亦針對此光電致色變元件系統提出初步的設計方程式，藉以瞭解未來最適化的條件與瞭解關鍵的元素。

關鍵字

電容值 ； 電子傳遞 ； 電致色變 ； 離子進出 ； 高分子薄膜 ； 光電致色變元件 ； 氧化還原對

並列摘要

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.

並列關鍵字

capacitance ； electron transfer ； electrochromism ； ion transport ； polymer thin film ； photoelectrochromic device ； redox couple

參考文獻

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