Decoupling of transport, charge storage, and interfacial charge transfer in the nanocrystalline TiO2/electrolyte system by impedance methods
Decoupling of transport, charge storage, and interfacial charge transfer in the nanocrystalline TiO2/electrolyte system by impedance methods
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DOI：
10.1021/jp0119429
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发表时间：
2002-01-17
影响因子：
3.3
通讯作者：
Salvador, P
中科院分区：
文献类型：
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作者：
Fabregat-Santiago, F;Garcia-Belmonte, G;Salvador, P
用电化学阻抗技术研究了几种纳米多孔二氧化钛薄膜中暗电子输运和复合过程随外加电势的变化。应用传输线模型识别、分离和解释了接触和整体特性，该传输线模型识别了以下元素：(I)衬底的暴露表面和电解液之间的界面的电容，(Ii)电子传输电阻，(Iii)分布在二氧化钛/电解液界面中的电荷传输电阻，以及(Iv)与充电多孔基质有关的分布电容元件。该模型较好地描述了二氧化钛相在不同电导率条件下的光谱。电子电导率已被确定为外加电势的函数，并与所研究的不同样品的电导率一致。用于多孔电极的经典的传输和界面电荷转移的电化学框架不能完全解释所获得的参数。根据以下特征，提出了一个更完整的框架来解释该系统：(I)大量电子陷阱的存在，导致陷阱限制的迁移率和指数增加的电容，以及(Ii)在外极化电势下的带边移动。
Processes in the dark of electron transport and recombination in several nanoporous titanium dioxide Films have been studied as a function of the applied potential, using the electrochemical impedance technique. Contact and bulk characteristics have been identified, decoupled, and interpreted, applying a transmission line model that identifies the following elements: (i) the capacitance of the interface between the exposed surface of the substrate and the electrolyte, (ii) the electron transport resistance, (iii) the charge-transfer resistance distributed in the TiO2/electrolyte interface, and (iv) a distributed capacitive element related to charging the porous matrix. The model provides a satisfactory description of the spectra in widely different conditions of conductivity of the TiO2 phase. The electron conductivity has been determined as a function of applied potential and coincides for the different samples under study. Classical electrochemical frameworks of transport and interfacial charge transfer used in porous electrodes do not explain the obtained parameters completely. A more complete framework is suggested to explain the system on the basis of the following characteristic features: (i) existence of a large density of electron traps, giving rise both to a trap-limited mobility and to an exponentially increasing capacitance, and (ii) band-edge shifts under external polarization potential.