Department of Chemistry, University of Warwick, CoventryCV4 7AL, U.K.
Centre for Diamond Science and Technology, University of Warwick, CoventryCV4 7AL, U.K.
Anal Chem. 2022 Sep 20;94(37):12673-12682. doi: 10.1021/acs.analchem.2c01976. Epub 2022 Sep 7.
The voltammetric response of electrodes coated with a redox-active monolayer is computed by finite element simulations based on a generalized model that couples the Butler-Volmer, Nernst-Planck, and Poisson equations. This model represents the most complete treatment of the voltammetric response of a redox film to date and is made accessible to the experimentalist via the use of finite element modeling and a COMSOL-generated report. The model yields a full description of the electric potential and charge distributions across the monolayer and bulk solution, including the potential distribution associated with ohmic resistance. In this way, it is possible to properly account for electrostatic effects at the molecular film/electrolyte interface, which are present due to the changing charge states of the redox head groups as they undergo electron transfer, under both equilibrium and nonequilibrium conditions. Specifically, our numerical simulations significantly extend previous theoretical predictions by including the effects of finite electron-transfer rates () and electrolyte conductivity. Distortion of the voltammetric wave due to ohmic potential drop is shown to be a function of electrolyte concentration and scan rate, in agreement with experimental observations. The commonly used Laviron analysis for the determination of fails to account for ohmic drop effects, which may be non-negligible at high scan rates. This model provides a more accurate alternative for determination at all scan rates. The electric potential and charge distributions across an electrochemically inactive monolayer and electrolyte solution are also simulated as a function of applied potential and are found to agree with the Gouy-Chapman-Stern theory.
基于一种将 Butler-Volmer、Nernst-Planck 和 Poisson 方程耦合的广义模型，通过有限元模拟计算了涂覆有氧化还原活性单层的电极的伏安响应。该模型代表了迄今为止对氧化还原膜的伏安响应的最完整处理，并且通过使用有限元建模和 COMSOL 生成的报告使实验人员可以使用。该模型提供了对整个单层和本体溶液的电势和电荷分布的完整描述，包括与欧姆电阻相关的电势分布。通过这种方式，可以正确考虑分子膜/电解质界面处的静电效应，这些效应是由于氧化还原头基在经历电子转移时的电荷状态变化而存在的，无论是在平衡还是非平衡条件下。具体来说，我们的数值模拟通过包括有限的电子转移速率（）和电解质电导率的影响，显著扩展了先前的理论预测。由于欧姆电势降引起的伏安波的变形被证明是电解质浓度和扫描速率的函数，与实验观察结果一致。通常用于确定的 Laviron 分析未能考虑到欧姆降效应，在高扫描速率下，欧姆降效应可能不可忽略。该模型为在所有扫描速率下进行提供了更准确的替代方法。作为施加电势的函数，还模拟了电化学惰性单层和电解质溶液的电势和电荷分布，并且发现与 Gouy-Chapman-Stern 理论一致。
