Martínez-García Antonio J, Hernández-Tovar José V, López-Tenés Manuela, González Joaquín
Departamento de Química Física, Facultad de Química, Regional Campus of International Excellence "Campus Mare Nostrum", Universidad de Murcia, 30100 Murcia, Spain.
ACS Electrochem. 2025 Apr 11;1(7):1110-1124. doi: 10.1021/acselectrochem.4c00241. eCollection 2025 Jul 3.
Molecular electrocatalytic processes in confined environments are becoming relevant processes with many applications in electrosynthesis, electroanalysis, and electrical energy generation and conversion. Nevertheless, the analysis of catalytic responses is mostly carried out with theoretical frameworks developed for semi-infinite linear diffusion conditions, which are not applicable for the adequate understanding of electrochemical processes in confined spaces. To fill the existing gap in the comprehension of these complex reactions, the analysis of a molecular catalytic process under finite diffusive conditions for cyclic staircase voltammetry (CSCV) and cyclic voltammetry (CV) techniques is presented in this work. The proposed model considers a finite diffusive field of thickness under two configurations: bounded diffusion, where no mass renovation is allowed, and unbounded diffusion, where there is effective mass replenishment at . Expressions for the current-potential responses under different particular cases have been obtained, leading to a kinetic zone diagram for limiting cases in terms of two key variables related to the thickness of the solution region and the catalytic rate constant. From the general expression of the current, it is observed that the electrochemical response of molecular electrocatalytic processes taking place in confined spaces is strongly dependent on the mass transport conditions. Thus, under bounded diffusion, a decrease of the catalytic current with is observed, which is more pronounced when the diffusive field is narrower. On the other hand, unbounded conditions give rise to an enhancement of the catalytic current and, eventually, to the loss of the kinetic sensitivity of the response for small enough values of . An experimental application of the theoretical results is performed for the conversion of isopropyl alcohol (IPA) to acetone mediated by the oxidation of 4-methoxy-2,2,6,6-tetra-methyl-1-piperi-dinyl-oxy (4-methoxy-TEMPO radical) at a glassy carbon electrode for both bound and unbounded configurations. The catalytic rate constant for this process has been obtained from the equations for the current, indicating that the accuracy of the result is strongly dependent on the correct understanding of the mass transport influences at play.
受限环境中的分子电催化过程正成为在电合成、电分析以及电能产生与转换等诸多领域具有广泛应用的重要过程。然而，催化响应的分析大多是基于为半无限线性扩散条件所开发的理论框架进行的，这些框架并不适用于充分理解受限空间中的电化学过程。为填补对这些复杂反应理解上的现有空白，本文对循环阶梯伏安法（CSCV）和循环伏安法（CV）技术在有限扩散条件下的分子催化过程进行了分析。所提出的模型考虑了厚度为 的有限扩散场的两种配置：有界扩散，即不允许质量更新；无界扩散，即在 处有有效的质量补充。已获得不同特定情况下电流 - 电势响应的表达式，从而得出了一个动力学区域图，该图依据与溶液区域厚度和催化速率常数相关的两个关键变量给出了极限情况。从电流的一般表达式可以看出，受限空间中发生的分子电催化过程的电化学响应强烈依赖于传质条件。因此，在有界扩散下，观察到催化电流随 减小，当扩散场更窄时这种减小更为明显。另一方面，无界条件会导致催化电流增强，最终对于足够小的 值，响应的动力学灵敏度丧失。在玻碳电极上针对有界和无界配置，对由4 - 甲氧基 - 2,2,6,6 - 四甲基 - 1 - 哌啶氧基（4 - 甲氧基 - TEMPO自由基）氧化介导的异丙醇（IPA）转化为丙酮进行了理论结果的实验应用。该过程的催化速率常数已从电流方程中获得，这表明结果的准确性强烈依赖于对所起传质影响的正确理解。
