For renewable and sustainable bioenergy utilization with cost-effectiveness, electron-shuttles (ESs) (or redox mediators (RMs)) act as electrochemical "catalysts" to enhance rates of redox reactions, catalytically accelerating electron transport efficiency for abiotic and biotic electrochemical reactions. ESs are popularly used in cellular respiratory systems, metabolisms in organisms, and widely applied to support global lives. Apparently, they are applicable to increase power-generating capabilities for energy utilization and/or fuel storage (i.e., dye-sensitized solar cell, batteries, and microbial fuel cells (MFCs)). This first-attempt review specifically deciphers the chemical structure association with characteristics of ESs, and discloses redox-mediating potentials of polyphenolics-abundant ESs via MFC modules. Moreover, to effectively convert electron-shuttling capabilities from non-sustainable antioxidant activities, environmental conditions to induce electrochemical mediation apparently play critical roles of great significance for bioenergy stimulation. For example, pH levels would significantly affect electrochemical potentials to be exhibited (e.g., alkaline pHs are electrochemically favorable for expression of such electron-shuttling characteristics). Regarding chemical structure effect, chemicals with ortho- and para-dihydroxyl substituents-bearing aromatics own convertible characteristics of non-renewable antioxidants and electrochemically catalytic ESs; however, ES capabilities of meta-dihydroxyl substituents can be evidently repressed due to lack of resonance effect in the structure for intermediate radical(s) during redox reaction. Moreover, this review provides conclusive remarks to elucidate the promising feasibility to identify whether such characteristics are non-renewable antioxidants or reversible ESs from natural polyphenols via cyclic voltammetry and MFC evaluation. Evidently, considering sustainable development, such electrochemically convertible polyphenolic species in plant extracts can be reversibly expressed for bioenergy-stimulating capabilities in MFCs under electrochemically favorable conditions.

中文翻译：

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多酚化合物作为电子穿梭机用于可持续能源利用。

为了实现具有成本效益的可再生和可持续生物能源利用，电子穿梭（ES）（或氧化还原介体（RM））充当电化学“催化剂”来提高氧化还原反应的速率，催化加速非生物和生物电化学反应的电子传输效率。ES广泛应用于细胞呼吸系统、生物体新陈代谢，并广泛应用于支持全球生活。显然，它们适用于提高能源利用和/或燃料储存的发电能力（即染料敏化太阳能电池、电池和微生物燃料电池（MFC））。这项首次尝试的综述专门破译了与 ES 特性相关的化学结构，并揭示了富含多酚类的 ES 通过 MFC 模块的氧化还原介导潜力。此外，为了有效地将不可持续的抗氧化活性转化为电子穿梭能力，诱导电化学介导的环境条件显然对生物能刺激起着至关重要的作用。例如，pH水平将显着影响所表现出的电化学势（例如，碱性pH在电化学上有利于表达这种电子穿梭特性）。从化学结构效应来看，带有邻位和对位二羟基取代基的芳香族化合物具有不可再生抗氧化剂和电化学催化ESs可转换的特性；然而，由于氧化还原反应过程中中间自由基结构缺乏共振效应，间位二羟基取代基的ES能力明显受到抑制。此外，这篇综述提供了结论性的评论，阐明了通过循环伏安法和 MFC 评估来确定这些特性是否是不可再生的抗氧化剂或来自天然多酚的可逆 ES 的有希望的可行性。显然，考虑到可持续发展，植物提取物中的这种电化学可转化的多酚类物质可以在电化学有利的条件下可逆地表达MFC中的生物能刺激能力。