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Microbial electrosynthesis (MES) is a promising technology through which carbon dioxide is converted into chemicals via bioelectrochemcal reaction. In this study, a natural loofah sponge (LS) was directly converted into a 3D macroporous carbon cathode through carbonization. The LS was codecorated with polydopamine and Mo 2 C (Mo 2 C/N-doped LS). Results revealed that the acetate production rate of MES with Mo 2 C/N-doped LS increased by 2.5 times compared with that of carbon felt. The maximum acetate concentration of 6.08 g L−1 and 64% of coulomb efficiency (CE) were obtained in MES with Mo 2 C/N-doped LS. Electrochemistry, scanning electron microscopy, and microbial community analyses showed that Mo 2 C/N-doped LS contributed to biofilm formation and improved the enrichment of electrochemically active bacteria. Thus, this study introduced a promising method for the fabrication of 3D cathodes with a high electrocatalytic activity from low-cost sustainable natural materials to improve MES efficiency. [Display omitted] • LS provided a high specific area for microbial attachment. • LS was widely available and could easily produce 3D electrodes for MES. • Mo 2 C/N-doped LS was beneficial to direct and indirect electron transfer rate. • The acetate production rate of Mo 2 C/N-doped LS increased by 2.5 times. • The maximum acetate concentration of 6.08 g L−1 and CE of 64% were obtained. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The acetate production rate with fluidized GAC was 2.8 times that of control. • Fluidized GAC provide a high electrode surface and a favorable mass transport. • Fluidized GAC likely promoted the enrichment of electrochemically active bacteria. • Fluidized GAC electrode is a promising strategy to improve MES efficiency. Abstract The electricity-driven bioreduction of carbon dioxide to multi-carbon organic compounds, particularly acetate, has been achieved in microbial electrosynthesis (MES). MES performance can be limited by the amount of cathode surface area available for biofilm formation and slow substrate mass transfer. Here, a fluidized three-dimensional electrode, containing granular activated carbon (GAC) particles, was constructed via MES. The volumetric acetate production rate increased by 2.8 times through MES with 16 g L−1 GAC (0.14 g L−1 d-1) compared with that of the control (no GAC), and the final acetate concentration reached 3.92 g L−1 within 24 days. Electrochemical, scanning electron microscopy, and microbial community analyses suggested that GAC might improve the performance of MES by accelerating direct and indirect (via H 2) electron transfer because GAC could provide a high electrode surface and a favorable mass transport. This study attempted to improve the efficiency of MES and presented promising opportunities for MES scale-up. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) is potentially useful for the biological conversion of carbon dioxide into value-added chemicals and biofuels. The study evaluated several limiting factors that affect MES performance. Among all these factors, the optimization of the applied cell voltage, electrode spacing, and trace elements in catholytes may significantly improve the MES performance. MES was operated under the optimal condition with an applied cell voltage of 3 V, an electrode spacing of 8 cm, 2× salt solution, and 8× trace element of catholyte for 100 days, and the maximum acetate concentration reached 7.8 g L−1. The microbial community analyses of the cathode chamber over time showed that Acetobacterium, Enterobacteriaceae, Arcobacter, Sulfurospirillum, and Thioclava were the predominant genera during the entire MES process. The abundance of Acetobacterium first increased and then decreased, which was consistent with that of acetate production. These results provided useful hints for replacing the potentiostatic control of the cathodes in the future construction and operation of MES. Such results might also contribute to the practical operation of MES in large-scale systems. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) is an electrochemical reduction technology that converts carbon dioxide (CO 2) efficiently into chemicals by electrically driving microorganisms attached to electrodes. However, due to the limited solubility of CO 2 and hydrogen (H 2), low mass transfer efficiency affects the performance of MES. In this study, fillers were introduced into the MES system and combined with a vertical or horizontal cathode. Through the barrier and shearing effect of fillers, it realized the reduction of bubbles volume, the increase of gas residence time and the optimization of mass transfer rate, thereby providing a sufficient substrate supply for the biocatalyst. The results showed that MES with horizontal cathode and 4 series of fillers generated the highest acetate production rate (0.18 gL−1 day−1), which was 1.6 times that of the control group. Furthermore, the acetate concentration reached 5.28 ± 0.2 g L−1 within 30 days. Scanning electron microscope and microbial community analyses showed that the filler was beneficial to the growth of biofilm on cathodes and fillers, and improved the enrichment of Acetobacterium. The presence of fillers significantly enhanced the performance of MES and demonstrated the potential as a new and simple strategy for the MES reactor improvement. [Display omitted] • Fillers provided the barrier and shearing effect for MES. • The placement of different electrodes further improved the shearing performance. • Fillers realized the reduction of bubbles volume, the increase of gas residence time. • Fillers provided a sufficient substrate supply for the biocatalyst. • The acetate production rate of 4 fillers-horizontal cathode increased by 1.6 times. [ABSTRACT FROM AUTHOR]

Background: Microbial electrosynthesis (MES) is a biocathode-driven process, in which electroautotrophic microorganisms can directly uptake electrons or indirectly via H2 from the cathode as energy sources and CO2 as only carbon source to produce chemicals. Results: This study demonstrates that a hydrogen evolution reaction (HER) catalyst can enhance MES performance. An active HER electrocatalyst molybdenum carbide (Mo2C)-modified electrode was constructed for MES. The volumetric acetate production rate of MES with 12 mg cm−2 Mo2C was 0.19 ± 0.02 g L−1 day−1, which was 2.1 times higher than that of the control. The final acetate concentration reached 5.72 ± 0.6 g L−1 within 30 days, and coulombic efficiencies of 64 ± 0.7% were yielded. Furthermore, electrochemical study, scanning electron microscopy, and microbial community analyses suggested that Mo2C can accelerate the release of hydrogen, promote the formation of biofilms and regulate the mixed microbial flora. Conclusion: Coupling a HER catalyst to a cathode of MES system is a promising strategy for improving MES efficiency. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) is a biocathode-driven process, producing high-value chemicals from CO 2 . Here, an in situ self-assembled graphene oxide (rGO)/biofilm was constructed, in MES, for high efficient acetate production. GO has been successfully reduced by electroautotrophic bacteria for the first time. An increase, of 1.5 times, in the volumetric acetate production rate, was obtained by self-assembling rGO/biofilm, as compared to the control group. In MES with rGO/biofilm, a volumetric acetate production rate of 0.17 g l −1 d −1 has been achieved, 77% of the electrons consumed, were recovered and the final acetate concentration reached 7.1 g l −1 , within 40 days. A three-dimensional rGO/biofilm was constructed enabling highly efficient electron transfer rates within biofilms, and between biofilm and electrode, demonstrating that the development of 3D electroactive biofilms, with higher extracellular electron transfer rates, is an effective approach to improving MES efficiency. [ABSTRACT FROM AUTHOR]