Gamero-Quijano Alonso, Molina-Osorio Andrés F, Peljo Pekka, Scanlon Micheál D
The Bernal Institute and Department of Chemical Sciences, School of Natural Sciences, University of Limerick (UL), Limerick V94 T9PX, Ireland.
Phys Chem Chem Phys. 2019 May 15;21(19):9627-9640. doi: 10.1039/c9cp00774a.
Closed bipolar electrochemistry in a 4-electrode configuration is a highly versatile, but under-utilized, technique with major potential to emerge as a powerful methodology impacting areas as diverse as spectro-electroanalysis, energy storage, electrocatalysis and electrodeposition. In this perspective, we provide the thermodynamic framework for understanding all such future applications of closed bipolar electrochemistry in a 4-electrode configuration. We distinguish the differences between open and closed bipolar electrochemical cells. In particular, the use of the 4-electrode configuration in both open and closed bipolar electrochemical cells with immiscible aqueous-organic solutions is outlined. A comprehensive overview of the influence of external bias on the thermodynamics underpinning electron transfer from an organic redox couple to an aqueous redox couple, or vice versa, by electrons flowing along a conducting bipolar electrode serving as an electronic bridge is provided. Fermi level equilibration between redox species at opposite poles of a bipolar electrode under external bias is discussed. The concept of the Line of Zero Overpotential (LZO) on the bipolar electrode at steady-state conditions under an external bias is introduced. The influence of a series of experimental variables (redox potential of each redox couple, rate constant of electron transfer at each pole, an excess bulk concentration of one redox couple over the other, and areas of the poles of the bipolar electrode in contact with each electrolyte solution) on the final position of the LZO on the bipolar electrode is highlighted. A cyclic voltammogram obtained using a closed bipolar electrochemical cell in a 4-electrode configuration with immiscible aqueous-organic electrolyte solutions is explained using the thermodynamic theory detailed throughout the perspective. The theory presented herein is equally applicable to a closed bipolar electrochemical cell in a 4-electrode configuration with aqueous electrolyte solutions, each containing redox active species, in both compartments connected by a bipolar electrode.
四电极配置的封闭式双极电化学是一种用途广泛但未得到充分利用的技术，具有巨大潜力，有望成为一种强大的方法，影响光谱电化学分析、能量存储、电催化和电沉积等多个领域。从这个角度出发，我们提供了一个热力学框架，用于理解四电极配置的封闭式双极电化学在所有此类未来应用中的情况。我们区分了开放式和封闭式双极电化学电池之间的差异。特别概述了在开放式和封闭式双极电化学电池中使用四电极配置以及不混溶的水 - 有机溶液的情况。全面综述了外部偏压对热力学的影响，这种影响是通过电子沿着用作电子桥的导电双极电极流动，从而实现从有机氧化还原对到水相氧化还原对的电子转移，反之亦然。讨论了外部偏压下双极电极相反两极的氧化还原物种之间的费米能级平衡。引入了外部偏压下稳态条件下双极电极上零过电位线（LZO）的概念。强调了一系列实验变量（每个氧化还原对的氧化还原电位、每个电极上电子转移的速率常数、一种氧化还原对相对于另一种氧化还原对的过量本体浓度以及双极电极与每种电解质溶液接触的电极面积）对双极电极上LZO最终位置的影响。使用具有不混溶的水 - 有机电解质溶液的四电极配置的封闭式双极电化学电池获得的循环伏安图，通过本视角详细阐述的热力学理论进行了解释。本文提出的理论同样适用于四电极配置的封闭式双极电化学电池，该电池在两个隔室中均含有含氧化还原活性物种的水性电解质溶液，并通过双极电极连接。
