Abstract
The extracellular electron transfer (EET) that connects the intracellular metabolism of electroactive microorganisms to external electron donors/acceptors, is the foundation to develop diverse microbial electrochemical technologies. For a particular microbial electrochemical device, the surface chemical property of an employed electrode material plays a crucial role in the EET process owing to the direct and intimate biotic-abiotic interaction. The functional modification of an electrode surface with redox mediators has been proposed as an effectual approach to promote EET, but the underlying mechanism remains unclear. In this work, we investigated the enhancement of electrochemically polymerized riboflavin interface on the bidirectional EET of Shewanella putrefaciens CN32 for boosting bioelectrocatalytic ability. An optimal polyriboflavin functionalized carbon cloth electrode achieved about 4.3-fold output power density (∼707 mW/m2) in microbial fuel cells and 3.7-fold cathodic current density (∼0.78 A/m2) for fumarate reduction in three-electrode cells compared to the control, showing great increases in both outward and inward EET rates. Likewise, the improvement was observed for polyriboflavin-functionalized graphene electrodes. Through comparison between wild-type strain and outer-membrane cytochrome (MtrC/UndA) mutant, the significant improvements were suggested to be attributed to the fast interfacial electron exchange between the polyriboflavin interface with flexible electrochemical activity and good biocompatibility and the outer-membrane cytochromes of the Shewanella strain. This work not only provides an effective approach to boost microbial electrocatalysis for energy conversion, but also offers a new demonstration of broadening the applications of riboflavin-functionalized interface since the widespread contribution of riboflavin in various microbial EET pathways together with the facile electropolymerization approach.
Highlights
Microbial electrochemical systems (MESs) have become an intensive focus of fundamental and applied research owing to their potential to achieve sustainable value-added resources from organic or inorganic wastes (Logan and Rabaey, 2012; Zou and He, 2018; Zou et al, 2018), providing a promising solution for the Shewanella Bidirectional electron transfer (EET) on Polyriboflavin Interface increasingly serious risks of energy shortage and environmental degradation
More detailed mechanisms of electrochemical polymerization of riboflavin can be found in previous reports (Radzevic et al, 2016; Celiesiute et al, 2017), and a possible bonding mode between molecules in the polyriboflavin is shown in Supplementary Figure S2
The Fourier transform infrared (FTIR) and Raman spectra of the prepared PRF@carbon cloth (CC)-30, bare CC and pure riboflavin are compared in Supplementary Figure S3
Summary
Microbial electrochemical systems (MESs) have become an intensive focus of fundamental and applied research owing to their potential to achieve sustainable value-added resources (bioelectricity, biofuels and chemical commodities) from organic or inorganic wastes (Logan and Rabaey, 2012; Zou and He, 2018; Zou et al, 2018), providing a promising solution for the Shewanella Bidirectional EET on Polyriboflavin Interface increasingly serious risks of energy shortage and environmental degradation. By virtue of advances in design of device configurations, engineering of electrode materials, transformation of biocatalysts and optimization of operating conditions, the MES performances have achieved great improvement in recent years (Logan et al, 2015; Santoro et al, 2017; Saratale et al, 2017; Katuri et al, 2018), but they are still unable to meet the requirements of realworld applications. More efforts are perseveringly needed to be directed to enhance microbial EET rates for boosting MES development and future applications
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