Renault Christophe, Nicole Lionel, Sanchez Clément, Costentin Cyrille, Balland Véronique, Limoges Benoît
Laboratoire d'Electrochimie Moléculaire, UMR 7591 CNRS, Université Paris Diderot, Sorbonne Paris Cité, 15 rue Jean-Antoine de Baïf, F-75205 Paris Cedex 13, France.
Phys Chem Chem Phys. 2015 Apr 28;17(16):10592-607. doi: 10.1039/c5cp00023h.
In this work, we demonstrate that chronoabsorptometry and more specifically cyclic voltabsorptometry are particularly well suited techniques for acquiring a comprehensive understanding of the dynamics of electron transfer/charge transport within a transparent mesoporous semiconductive metal oxide film loaded with a redox-active dye. This is illustrated with the quantitative analysis of the spectroelectrochemical responses of two distinct heme-based redox probes adsorbed in highly-ordered mesoporous TiO2 thin films (prepared from evaporation-induced self-assembly, EISA). On the basis of a finite linear diffusion-reaction model as well as the establishment of the analytical expressions governing the limiting cases, it was possible to quantitatively analyse, predict and interpret the unusual voltabsorptometric responses of the adsorbed redox species as a function of the potential applied to the semiconductive film (i.e., as a function of the transition from an insulating to a conductive state or vice versa). In particular, we were able to accurately determine the interfacial charge transfer rates between the adsorbed redox species and the porous semiconductor. Another important and unexpected finding, inferred from the voltabsorptograms, is an interfacial electron transfer process predominantly governed by the extended conduction band states of the EISA TiO2 film and not by the localized traps in the bandgap. This is a significant result that contrasts those previously observed for dye-sensitized solar cells formed of randomly sintered TiO2 nanoparticles, a behaviour that was ascribed to a particularly low density of localized surface states in EISA TiO2. The present methodology also provides a unique and straightforward access to an activation-driving force relationship according to the Marcus theory, thus opening new opportunities not only to investigate the driving-force effects on electron recombination dynamics in dye-sensitized solar cells but also to study the electron transfer/transport mechanisms in heterogeneous photoelectrocatalytic systems combining nanostructured semiconductor electrodes and heterogeneous redox-active catalysts.
在本研究中，我们证明了计时吸收法，更具体地说是循环伏安吸收法，是特别适合用于全面理解负载氧化还原活性染料的透明介孔半导体金属氧化物薄膜内电子转移/电荷传输动力学的技术。这通过对吸附在高度有序介孔TiO₂薄膜（由蒸发诱导自组装法，即EISA制备）中的两种不同的基于血红素的氧化还原探针的光谱电化学响应进行定量分析得以说明。基于有限线性扩散 - 反应模型以及对极限情况的解析表达式的建立，能够定量分析、预测和解释吸附的氧化还原物种的异常伏安吸收响应与施加到半导体薄膜上的电位的函数关系（即，作为从绝缘态到导电态转变或反之的函数）。特别地，我们能够准确确定吸附的氧化还原物种与多孔半导体之间的界面电荷转移速率。从伏安吸收图推断出的另一个重要且意外的发现是，界面电子转移过程主要由EISA TiO₂薄膜的扩展导带态而非带隙中的局域陷阱控制。这是一个显著的结果，与先前在由随机烧结的TiO₂纳米颗粒形成的染料敏化太阳能电池中观察到的情况形成对比，该行为归因于EISA TiO₂中特别低的局域表面态密度。本方法还根据马库斯理论提供了一种独特且直接的获取活化 - 驱动力关系的途径，从而不仅为研究染料敏化太阳能电池中驱动力对电子复合动力学的影响开辟了新机会，也为研究结合纳米结构半导体电极和非均相氧化还原活性催化剂的异质光催化系统中的电子转移/传输机制开辟了新机会。
