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Inefficient extracellular electron transfer within bioanode leads to low current production by microbial fuel cell (MFC). In this study, magnetite was sprinkled in electroactive biofilm with the aid of magnet field. Magnetite located inside biofilm (interior-doped biofilm) facilitated the electron delivery of electroactive bacteria far away from electrode surface. Electron transfer efficiency was improved by 12% and 37% compared with that of biofilms with magnetite located at the interface of biofilm/electrode (surface-doped biofilm) and that without any magnetite (control biofilm) respectively. The output power density of MFC with interior-doped biofilm (764 ± 32 mW m −2 ) was greatly increased compared with that of MFCs with surface-doped biofilm (604 ± 22 mW m −2 ) and control biofilm (475 ± 12 mW m −2 ). SEM images showed that magnetite evenly distributed inside the interior-doped biofilm and penetrated the electroactive biofilm, which would facilitate extracellular electron transfer across electroactive biofilms and thus improving the bioelectricity production. [ABSTRACT FROM AUTHOR]

A novel anode was developed by coating reduced graphene oxide (rGO) and manganese oxide (MnO 2 ) composite on the carbon felt (CF) surface. With a large surface area and excellent electrical conductivity, this binder-free anode was found to effectively enhance the enrichment and growth of electrochemically active bacteria and facilitate the extracellular electron transfer from the bacteria to the anode. A microbial fuel cell (MFC) equipped with the rGO/MnO 2 /CF anode delivered a maximum power density of 2065 mW m −2 , 154% higher than that with a bare CF anode. The internal resistance of the MFC with this novel anode was 79 Ω, 66% lower than the regular one's (234 Ω). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses affirmed that the rGO/MnO 2 composite significantly increased the anodic reaction rates and facilitated the electron transfer from the bacteria to the anode. The findings from this study suggest that the rGO/MnO 2 /CF anode, fabricated via a simple dip-coating and electro-deposition process, could be a promising anode material for high-performance MFC applications. [ABSTRACT FROM AUTHOR]

Abstract Electron transfer efficiency in electroactive biofilm is the limiting factor for bioelectricity output of bioelectrochemical system. Here, carbon felt (CF) is coated with manganese dioxide (MnO 2) which acts as electron mediator in electroactive biofilm. A wrapping layer of conducting Poly 3,4-ethylenedioxythiophene is developed to protect the MnO 2 and enhance electron transfer efficiency of MnO 2 mediator. The hybrid bioanode (PEDOT/MnO 2 /CF bioanode) delivered the highest electron transfer efficiency (6.3 × 10−9 mol cm−2 s−1/2) and the highest capacitance of 4.78 F, much higher than bare CF bioanode (1.50 ± 0.04 × 10−9 mol cm−2 s−1/2 and 0.42 F). As a result, microbial fuel cells could produce a maximum power density of 1534 ± 13 mW m−2, approximately 57.7% higher than that with the bare carbon felt anode (972 ± 21 mW m−2). Possible mechanisms are proposed to help understanding the different function of the PEDOT and MnO 2 on the anodic layer. This study introduces an effective method for the fabrication of high performance anode. Graphical abstract Unlabelled Image Highlights • A MnO 2 layer acts as electron mediator in electrochemical biofilm. • The wrapping layer of PEDOT helps to enhance electron transfer efficiency. • Electron transfer efficiency improved by ~4 times. • PEDOT/MnO 2 /CF anode increases the maximum power density by 143%. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) has been proposed as a sustainable platform to simultaneously achieve wastewater treatment, renewable energy generation and chemicals production. Currently, the CO 2 valorization via MES is restricted by the low production rate, while that via electrochemical reduction is limited by the production of C1 products with high efficiency and selectivity. The electrocatalyst-assisted MES could potentially solve these bottlenecks of both MES and electrochemical reduction technology by increasing the production rate and expanding the product range. Here, four types of metals were evaluated for mixed culture-based, electrocatalyst-assisted MES with the fabrication of electrical-biological hybrid cathodes. Cathodes based on In, Zn, Ti and Cu showed high parallelism at 30 A/m2. However, no parallelism was observed at 50 A/m2, and only Zn experienced a further increase of the maximum acetic acid production rate (1.23 ± 0.02 g/L/d, 313 ± 5 g/m2/d) and titer (9.2 ± 0.1 g/L), with the highest value of the production rate normalized to the project area of the fiber cathodes. Other volatile fatty acids and ethanol were below 0.5 g/L. Moreover, it was the sharp H 2 generation, which mainly caused the fluctuation of coulombic efficiency. The application of such Zn-based electrical-biological hybrid system shall provide a more efficient route for CO 2 valorization. Image 1 • Electrocatalysts (In, Zn, Ti, Cu) were evaluated for electrocatalyst-assisted MES. • Zn based electrical-biological hybrid cathode can be steadily operated at 50 A/m2. • It has the highest record of fiber cathodes (1.23 ± 0.02 g/L/d, 313 ± 5 g/m2/d). • Sharp H 2 generation mainly caused the catholyte alkalization and CE fluctuation. [ABSTRACT FROM AUTHOR]