Redox mediators (RMs) play pivotal roles in enhancing the performance of electrochemical energy storage and conversion systems. Unlike the widely explored areas of electrode materials, electrolytes, separators, and electrolyte additives, RMs have received little attention. This review provides a comprehensive discussion toward understanding the effects of RMs on electrochemical systems, underlying redox mechanisms, and reaction kinetics both experimentally and theoretically. Our discussion focuses on the roles of RMs in various electrochemical systems such as lithium-ion batteries, Li–O₂ batteries, Li–S batteries, decoupling electrolysis, supercapacitors, and microbial fuel cells. Depending on the reaction regions where the RMs become active, we can classify them into bulk, solid–solid interfacial, solid–liquid interfacial, and cell-unit RMs. The prospect of developing RMs with effective charge transfer properties along with minimal side-effects is an exciting research direction. Moreover, the introduction of an efficient RM into an electrochemical system can fundamentally change its chemistry; in particular, the electrode reaction polarization can be considerably decreased. In this context, we discuss the key properties of RMs applied for various purposes, and the main issues are addressed.

中文翻译：

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氧化还原介体作为改变电化学反应的电荷剂

氧化还原介体（RM）在增强电化学能量存储和转换系统的性能方面起着关键作用。与电极材料，电解质，隔膜和电解质添加剂等广泛探索的领域不同，RM很少受到关注。这篇综述对理解RMs对电化学系统的影响，潜在的氧化还原机理以及实验和理论上的反应动力学进行了全面的讨论。我们的讨论重点是RM在各种电化学系统中的作用，例如锂离子电池，Li–O ₂电池，Li–S电池，去耦电解，超级电容器和微生物燃料电池。根据RM活化的反应区域，我们可以将其分为本体，固体-固体界面，固体-液体界面和细胞单位RM。开发具有有效电荷转移特性且副作用最小的RM的前景是令人兴奋的研究方向。而且，将有效的RM引入电化学系统可以从根本上改变其化学性质。特别地，可以显着降低电极反应极化。在这种情况下，我们讨论了用于各种目的的RM的关键属性，并解决了主要问题。