A Voltage-Modulation QCM: Application to Kinetic Studies on Electrode Processes

一种新的快速电化学石英晶体微天平(EQCM)应与工作电极电位的快速调制相结合，以便获得电极上过程的动力学。时间分辨率为100uM S。调制使该仪器在很大程度上不受仪器漂移的影响。由于要研究的过程是周期性的，累积和平均可以将频率读数的精度带入亚兆赫范围。应用可以来自电化学领域，在那里也将研究没有电子转移的过程。在后一种情况下，电势影响双电层中的电荷和电极附近的酸碱度。最初，将实施仪器改进。应进一步降低噪声，并将频域(随频率变化的正弦激励)和时间域(脉冲或阶跃激励)中的测量结果与其性能进行比较。将开发程序，可用于区分吸附/解吸、扩散双层粘弹性的变化以及主体粘弹性的变化。第一组要研究的现象是有机薄膜的电响应性。对于弱聚电解质，电响应性通常与pH诱导的溶胀和溶胀有关。膨胀和消胀的动力学往往是不同的。聚[2-(二甲氨基)-甲基丙烯酸乙酯](PDMAEMA)的表面连接链将是一个模型体系。此外，还将研究具有类似于pDMAEMA结构的聚合物的吸附和解吸。这些材料与电沉积涂料有关，在这里，吸附和解吸是可逆的。第二个应用将是将电子转移到溶液中的氧化还原活性分子。这些电重实验将补充循环伏安法。根据频移的时间导数，可以计算出表观传质速率，它可以直接与电流进行比较。应定量了解曲线形状(电流和表观传质)的差异。脉冲法(类似于方波伏安法)应允许分离对表观传质速率的不同贡献。这些实验应扩展到有机电合成的简单反应(即不可逆反应)。这项工作的长期前景是将电压调制应用于普通吸附过程，这可以利用吸附物对电压调制的响应来提高QCM获得的信息深度。

A new, fast electrochemical quartz crystal microbalance (EQCM) shall be coupled with fast modulation of the potential of the working electrode in order to access the kinetics of processes at the electrode. The time resolution is 100 µs. The modulation makes this instrument largely independent of instrumental drifts. Because the processes to be studied are periodic, accumulation and averaging can bring the precision of the frequency readings into the sub-mHz range. Applications can be from the field of electrochemistry, where processes without electron transfer will also be studied. In the latter case, the electric potential affects the charge in the electrical double layer and the pH near the electrode.Initially, instrumental improvements are to be implemented. Noise shall be further reduced and measurements in the frequency domain (sinusoidal excitation with variation of frequency) and the time domain (pulse or step excitation) shall be compared with respect to their performance. Procedures will be developed, that can be used to distinguish between adsorption/desorption, changes in the viscoelasticity of the diffuse double layer, and changes in the viscoelasticity of the bulk. A first set of phenomena to be studied is the electroresponsivity of thin organic films. For weak polyelectrolytes, electroresponsivity is often related to pH-induced swelling and deswelling. The kinetics of swelling and deswelling often are different. Surface-attached chains of poly[2(dimethylamino)ethyl methacrylate] (pDMAEMA) will be a model system. Furthermore, the adsorption and desorption of polymers with a constitution similar to pDMAEMA will be investigated. These materials are related to electrodeposition paints, where adsorption and desorption are reversible, here. A second application will be electron transfer to redox-active molecules in solution. These electrogravimetric experiments will complement cyclic voltammetry. From the time derivative of the frequency shift, an apparent mass transfer rate will be calculated, which can be directly compared to the electric current. The differences in the shape of the curves (current and apparent mass transfer) shall be understood quantitatively. Pulsed methods (analogous to square-wave voltammetry) shall allow to separate the different contributions to the apparent mass transfer rate. These experiments shall be extended to simple reactions from organic electrosynthesis (i.e., irreversible reactions).A long-term perspective of this work is the application of voltage modulation to ordinary adsorption processes, which can improve the depth of information obtained with the QCM, exploiting the adsorbate’s response to voltage modulation.