Abstract
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.
Highlights
In this review, we aim to clarify some of the mysteries of the electron shuttles (ESs) used in sustainable bioenergy applications
*Correspondence: boryannchen@yahoo.com.tw; bychen@niu.edu.tw 1 Department of Chemical and Materials Engineering, National I-Lan University, I‐Lan 26047, Taiwan Full list of author information is available at the end of the article. One example of this technology is the exploitation of the bioelectrochemical potential of electroactive microorganisms. Bioelectrochemical devices, such as microbial fuel cells (MFCs), can use synergistic/cooperative consortia of microbes as biocatalysts, and the electric current produced by the oxidation of organic compounds can be used for simultaneous bioelectricity generation and wastewater treatment [1,2,3,4,5]
Firuzi et al [37] revealed that redox peaks on cyclic voltammetry (CV) profiles of taxifolin, rutin, catechin, baicalein, quercetin, fisetin, and myricetin with redox peaks corresponding to the ortho-dihydroxy groups on the B rings appearing at ca. 300–460 mV in the CV profile. These results suggest that 3′,4′-dihydroxy groups on the B ring result in reversible redox behavior
Summary
We aim to clarify some of the mysteries of the electron shuttles (ESs) used in sustainable bioenergy applications (e.g., electro-fermentation and electrochemical biorefining). The creation of innovative, practical “green” sustainable bioenergy applications is inevitably required. One example of this technology is the exploitation of the bioelectrochemical potential of electroactive microorganisms. Bioelectrochemical devices, such as microbial fuel cells (MFCs), can use synergistic/cooperative consortia of microbes as biocatalysts, and the electric current produced by the oxidation of organic compounds can be used for simultaneous bioelectricity generation and wastewater treatment [1,2,3,4,5]. MFCs are a promising platform to explore the electrochemical potential of bioresources for bioenergy and biorefinery uses.
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