| 摘要: | 本研究以電化學阻抗譜(Electrochemical Impedance Spectroscopy)分析光化學於光反應與暗反應之行為，藉由擬合(fitting)以及電路圖了解光電化學反應系統，
以mott-schottky 方程式協助理解光陽極之各項參數。
材料以CIS、CZIS系列與BiVO4為主，分為暗反應與光反應兩種電化學機制，對於暗反應使用Randles cirsuit等效電路模型；對於光反應，經過fitting比較後選用以表面態傳輸電荷為主的等效電路模型。
由暗反應不同偏壓之測量，透過Mott-Schottky方程式繪製Mott-Schottky plot，藉此計算斜率與截距，進而推得實驗材料之平帶電位與載子濃度，配合霍爾測量交叉確認其值。
透過光暗反應之等效電路元件數值，Rct,trap(表面態電荷傳輸界面阻抗)相較於暗反應，其值大幅下降，Rtrapping(表面態再結合阻抗)，確認實驗材料於光照下，電子與電洞的再結合率很低，且Rct的下降反映了電洞更易與電解液接觸且進行電荷傳遞、產生氧氣。
電荷傳輸阻抗、表面態電容變化曲線圖配合Mott-Schottky plot之平帶電位，表明當偏壓在平帶電位附近時，表面態有大量電荷累積而電容達到最大值，電荷不易擺脫電場束縛進行傳遞，表面態電荷轉移阻抗也達到最高；而加大偏壓後，電洞較易於抵達電解液而與界面上之陰離子結合且產氧，因此電荷累積情形下降，表面態電容與電荷轉移阻抗也對應下降。
;In this study, we analyzed the photochemical behavior of light and dark reaction on Electrochemical Impedance Spectroscopy, by fitting (fitting) and circuit diagram to understand photoelectric chemical reaction system.
The mott-schottky equation was used to understand the parameters of photoanode.The materials are mainly CIS, CZIS series and BiVO4, which are divided into two electrochemical mechanisms: dark reaction and light reaction. Randles cirsuit equivalent circuit model is used for dark reaction.
For the light reaction, an equivalent circuit model dominated by surface state transfer charge is selected after the comparison of fitting.
Mott-schottky plot was plotted by using Mott-schottky equation to calculate slope and intercept, and then the horizontal band potential and carrier concentration of the experimental materials were obtained, and the values were cross-confirmed by hall measurement.
By Observing equivalent circuit element of light and dark reation, Rct,trap (surface charge transfer impedance interface) value has fallen dramatically which compared with dark reaction.
Confirmed that the recombination rate of electrons and holes is very low under illumination. The trop of Rct reflects the holes are more likely to be in contact with the electrolyte, and transfers charge, then produces oxygen.
The curve of charge transfer impedance and surface state capacitance change, combined with the flat band potential of mott-schottky plot, indicated that when the bias voltage was near the flat band potential, the surface state had a large amount of charge accumulation and the capacitance reached the maximum value, the charge was not easy to be transferred from the electric field, and the surface state charge transfer impedance also reached the highest level.
However, when the bias voltage is increased, the hole is easier to reach the electrolyte and combine with the anions on the interface to produce oxygen, so the charge accumulation situation decreases, and the surface state capacitance and charge transfer impedance also decrease correspondingly. |
