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Microbial electrosynthesis (MES) is an electrochemical reduction technology that converts carbon dioxide (CO2) efficiently into chemicals by electrically driving microorganisms attached to electrodes. However, due to the limited solubility of CO2 and hydrogen (H2), 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.

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 Mo2C (Mo2C/N-doped LS). Results revealed that the acetate production rate of MES with Mo2C/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 Mo2C/N-doped LS. Electrochemistry, scanning electron microscopy, and microbial community analyses showed that Mo2C/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.

Microbial electrosynthesis (MES) is an electrochemical reduction technique where microorganisms attached to electrodes are used as catalysts for CO2 reduction into chemicals. In situ grown molybden...

Microbial electrosynthesis (MES) is an emerging technology through which autotrophic microorganisms can directly uptake electrons or indirectly uptake electrons through H2 in the cathode for reducing CO2 to chemicals. In this study, the performance of MES with engineered Clostridium ljungdahlii was improved by electrochemically depositing a nickel phosphide (Ni–P) catalyst on the cathode. The acetate production rate of MES with 15 cycles was 0.17 g L–1 day–1, which was 1.7 times higher than that of MES without the catalyst. The corresponding butyrate production rate was remarkably enhanced at 0.1 g L–1 day–1, which was 2.5 times higher than that of MES without the catalyst. Electrochemical studies, scanning electron microscopy, and confocal scanning laser microscopy showed that Ni–P could accelerate the release of hydrogen and promote biofilm formation. These results also implied that more H2 evolution could provide more reducing power for butyrate production in the presence of Ni–P. This study attempted to provide effective strategies for the accumulation of C4 products in MES.

In this paper, a graphene/Fe2O3 (G/Fe2O3) modified anode was prepared through a simple one-step hydrothermal reduction method to improve the performance of microbial fuel cell (MFC). The power density of MFC with the G/Fe2O3 anode was 334 ± 4 mW/m2, which was 1.72 times and 2.59 times that of MFC with a graphene anode and an unmodified anode, respectively. Scanning electron microscopy and iron reduction rate experiment showed that G/Fe2O3 materials had good biocompatibility. Furthermore, microbial community analysis results indicated that the predominant populations on the anode biofilm belonged to Enterobacteriaceae, and the abundance of Desulfovibrio increased in the presence of the Fe2O3. Thus, the combination of graphene and Fe2O3 provided high electrical conductivity to facilitate extracellular electron transfer (EET) and improved biocompatibility to promote the cable bacteria formation and enhance electron transport efficiency over long distances. Therefore, G/Fe2O3 is an effective anode material for enhancing the performance of MFCs.

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. Electronic supplementary material The online version of this article (10.1186/s13068-019-1413-z) contains supplementary material, which is available to authorized users.

Microbial electrosynthesis (MES) is an electricity-driven technology for the microbial reduction of CO2 to organic commodities. However, the limited solubility of CO2 in a solution and the inefficient electron transfer make it impossible for microorganisms to obtain an efficient surface for catalytic interaction, thus resulting in the low efficiency of MES. To address this, we introduce a multifunctional perovskite-based cathode material Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3-δ-carbon felt (Pr0.5BSCF-CF), which provides a simultaneously significant increase in CO2 absorption and hydrogen production. As a result, the volumetric acetate production rate of MES obtained by Pr0.5BSCF-CF is 0.24 ± 0.01 g L-1 day-1, and it achieves a maximum acetate titer of 13.74 ± 0.20 g L-1 within 70 days. An adequate supply of CO2 and H2 also provides a sufficient amount of substrates and energy for the self-replication of the biocatalysts in the MES reactor. This effect not only increases the amount of biocatalysts but also optimizes the functions of the biocatalysts; the above benefits further improve the production efficiency of the MES system. This strategy demonstrates that the development of perovskite-based multifunctional cathodes with a simultaneous supplementation of substrates and electrons is a promising approach toward improving the MES efficiency.

Microbial electrosynthesis (MES) is a biocathode-driven process, producing high-value chemicals from CO2. 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 0.17gl-1d-1 has been achieved, 77% of the electrons consumed, were recovered and the final acetate concentration reached 7.1gl-1, within 40days. 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.

BACKGROUND Microbial electrosynthesis (MES) is a biocathode-driven process, producing high-value chemicals, from CO2. However, the low efficiency of the biocathode hinders the MES process efficiency significantly. RESULTS A novel 3D graphene–nickel foam (G-NF) cathode has been fabricated, by hydrothermal approach for the improvement of microbially-catalyzed reduction at the MES cathode. An increase of 1.8 times in the volumetric acetate production rate was obtained, compared with the untreated nickel foam. In MES with G-NF, a volumetric acetate production rate of 3.11 mmol L-1 day-1 has been achieved; 70% of the electrons consumed were recovered and the final acetate concentration reached 5.46 g L-1 within 28 days. CONCLUSION The hierarchical porous G-NF cathode improved bacterial colonization and the efficiency of mass, nutrients and protons transfer due to its 3D composition; the graphene coating considerably increased the effective surface area for microbial adhesion, as well as the electron transfer rate of biofilm in the MES. This study attempted to improve the efficiency of the biocathode, and provides a promising large electrode for large-scale MES devices. © 2017 Society of Chemical Industry

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.

It has been brought to our attention that in our article, explanations about cable bacteria are not rigorous. We apologize for these and note the specific reporting issues and errors below, with their corrections.

In this paper, we developed an environmental friendly, cost effective, simple and green approach to reduce graphene oxide (GO) by a sulfate-reducing bacterium Desulfovibrio desulfuricans. The D. desulfuricans reduces exfoliated GO to reduced graphene oxide (rGO) at 25 °C in an aqueous solution without any toxic and environmentally harmful reducing agents. The rGO was characterized with X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscope, X-ray Photoelectron Spectroscopy and Raman Spectroscopy. The analysis results showed that rGO had excellent properties and multi-layer graphene sheets structure. Furthermore, we demonstrated that D. desulfuricans, one of the primary bacteria responsible for the biocorrosion of various metals, might reduce GO to rGO on the surface of copper and prevented the corrosion of copper, which confirmed that electrophoretic deposition of GO on the surface of metals had great potential on the anti-biocorrosion applications.

Cobalt oxide/nanocarbon hybrid materials (graphene and carbon nanotube) are used as alternative cathode catalysts for oxygen reduction reaction in air-cathode microbial fuel cell (MFC) for the first time. Electrochemical results reveal that these hybrid materials exhibit high catalytic performance. In MFCs, the maximum power density of 469 ± 17 mW m−2 is achieved from the Co3O4/NCNT cathode, which is 5.3 times larger than that of the NCNT cathode. This value is competitive with those obtained using Pt/C (603 ± 23 mW m−2). Therefore, Co3O4/NCNT nanocomposite is an efficient and cost-effective cathode catalyst for practical MFC applications.

Low toxic and highly biocompatible graphene-based nanomaterials are in high demand within the biomedical fields. In this study, a highly biocompatible bacterially reduced graphene oxide (BRGO) was prepared by a “Generally Recognized As Safe” (GRAS) strain Bacillus subtilis 168 mediated with Vitamin K3 (VK3). The hypothesis of VK3 mediating electron transfer between succinate:quinine oxidoreductase, from B. subtilis 168, and graphene oxide (GO) was proposed. BRGO was characterized by Raman spectroscopy, XPS and XRD and showed excellent properties. Furthermore, BRGO illustrates greater biocompatibility, with less toxicity, than GO and chemically reduced graphene oxide (CRGO) by zebrafish toxicity assessment, which demonstrates its great potential in various biomedical applications.

For Cr(VI)-removal microbial fuel cell (MFC), a more efficient biocathode in MFCs is required to improve the Cr(VI) removal and electricity generation. RVC-CNT electrode was prepared through the electrophoretic deposition of carbon nanotube (CNT) on reticulated vitreous carbon (RVC). The power density of MFC with an RVC-CNT electrode increased to 132.1 ± 2.8 mW m −2 , and 80.9% removal of Cr(VI) was achieved within 48 h; compared to only 44.5% removal of Cr(VI) in unmodified RVC. Cyclic voltammetry, energy-dispersive spectrometry and X-ray photoelectron spectrometry showed that the RVC-CNT electrode enhanced the electrical conductivity and the electron transfer rate; and provided more reaction sites for Cr(VI) reduction. This approach provides process simplicity and a thickness control method for fabricating three-dimensional biocathodes to improve the performance of MFCs for Cr(VI) removal.

A multi-walled, carbon nanotube (MWNT)-modified graphite felt (GF) cathode was fabricated to improve the performance of sediment microbial fuel cells (SMFC). Three types of MWNT-modified GF cathodes were prepared by different electrophoretic deposition (EPD) times. Maximum power density of SMFC with MWNT-GF*** cathode at 60 min EPD was 215 ± 9.9 mW m(-2). This was 1.6 times that of SMFC with a bare GF cathode. Cyclic voltammetry and the amount of biomass showed that biomass density and electrochemical activity increased as the electrophoretic deposition time extended. Therefore the electrode possesses the highest catalytic behavior toward O2 reduction reaction. This simple process of carbon nanotube modification of a cathode by EPD can serve as an effective technique to improve the performance of SMFC.

One major limiting factor for sediment microbial fuel cells (SMFC) is the low oxygen reduction rate in the cathode. The use of the photosynthetic process of the algae is an effective strategy to increase the oxygen availability to the cathode. In this study, SMFCs were constructed by introducing the algae ( Chlorella vulgaris ) to the cathode, in order to generate oxygen in situ . Cyclic voltammetry and dissolved oxygen analysis confirmed that C. vulgaris in the cathode can increase the dissolved oxygen concentration and the oxygen reduction rate. We showed that power generation of SMFC with algae-assisted cathode was 21 mW m −2 and was further increased to 38 mW m −2 with additional carbon nanotube coating in the cathode, which was 2.4 fold higher than that of the SMFC with bare cathode. This relatively simple method increases the oxygen reduction rate at a low cost and can be applied to improve the performance of SMFCs.

SiO 2 : Sm 3+ nanotube arrays with excellent antireflective property at 1.06 μm were synthesized by a template-assisted sol–gel process. The molecular structure, morphology and optical properties of the fabricated SiO 2 :Sm 3+ nanotube arrays were investigated by a Fourier transform infrared spectroscope (FTIR), a Scanning electron microscope (SEM), and a spectro-fluorometer, respectively. The experimental results demonstrate that the SiO 2 :Sm 3+ nanotube arrays were formed via the AAO membrane during the sol–gel process. The remarkable antireflective characteristic of about 0.166% at 1.06 μm was attributed to the drastic decrease of effective refraction index which enhances the matching effect between air and substrate. As well as the absorption performance of Sm3+ at 1.06 μm which consumes the energies of incident light.

In this study, a simple method of biocathode fabrication in a Cr(VI)-reducing microbial fuel cell (MFC) is demonstrated. A self-assembling graphene was decorated onto the biocathode microbially, constructing a graphene/biofilm, in situ. The maximum power density of the MFC with a graphene biocathode is 5.7 times that of the MFC with a graphite felt biocathode. Cr(VI) reduction was also enhanced, resulting in 100% removal of Cr(VI) within 48 h, at 40 mg/L Cr(VI), compared with only 58.3% removal of Cr(VI) in the MFC with a graphite felt biocathode. Cyclic voltammogram analyses showed that the graphene biocathode had faster electron transfer kinetics than the graphite felt version. Energy dispersive spectrometer (EDS) and X-ray photoelectron spectra (XPS) analysis revealed a possible adsorption-reduction mechanism for Cr(VI) reduction via the graphene biocathode. This study attempts to improve the efficiency of the biocathode in the Cr(VI)-reducing MFC, and provides a useful candidate method for the treatment of Cr(VI) contaminated wastewater, under neutral conditions.

BACKGROUND: Sediment microbial fuel cells (SMFCs) could be used as power sources and one type of new technology for the removal of organic matters in sediments. Various types of materials have been used as electrodes. Nevertheless, there is still room to improve electrode materials and enhance their effect on the performance of SMFCs. In this work, performances of SMFCs with activated carbon fiber felt (ACFF) and with nitric acid-treated ACFF were compared with graphite felt (GF) materials. RESULTS: The maximum power density of the SMFC with ACFF electrode was the highest (33.5 ± 1.5 mW m−2). Nitric acid-treated GF electrode slightly increased the maximum power density of SMFC, while the nitric acid treated-ACFF resulted in significant decline in the maximum power density of SMFC. The maximum power density further increased to 74.5 ± 7.5 mW m−2 in SMFC using GF cathode and ACFF anode. CONCLUSIONS: ACFF as anode can enhance the transport of electrons from the oxidation of organic matter in the sediment, while the output power was found to reduce in SMFC with ACFF cathode. Further efforts are needed to study the formation conditions of the biocathode and new electrode modification technology. Copyright © 2012 Society of Chemical Industry

In this study, a modified microbial fuel cell (MFC) with a tubular photobioreactor (PHB) configuration as a cathode compartment was constructed by introducing Chlorella vulgaris to the cathode chamber used to generate oxygen in situ. Two types of cathode materials and light/dark cycles were used to test the effect on MFC with algae biocathode. Results showed that the use of algae is an effective approach because these organisms can act as efficient in situ oxygenators, thereby facilitating the cathodic reaction. Dissolved oxygen and voltage output displayed a clear light positive response and were drastically enhanced compared with the abiotic cathode. In particular, carbon paper-coated Pt used as a cathode electrode increased voltage output at a higher extent than carbon felt used as an electrode. The maximum power density of 24.4 mW/m(2) was obtained from the MFC with algae biocathode which utilized the carbon paper-coated Pt as the cathode electrode under intermittent illumination. This density was 2.8 times higher than that of the abiotic cathode. Continuous illumination shortened the algal lifetime. These results demonstrated that intermittent illumination and cathode material-coated catalyst are beneficial to a more efficient and prolonged operation of MFC with C. vulgaris biocathode.

Sediment microbial fuel cells (SMFCs) could be used as power sources and one type of new technology for the removal of organic matters in sediments. In order to improve electrode materials and enhance their effect on the performance, we deposited multi-walled carbon nanotube (MWNT) on stainless steel net (SSN). Electrophoretic deposition technique as a method with low cost, process simplicity, and thickness control was used for this electrode modification and produced this novel SSN-MWNT electrode. The performances of SMFCs with SSN-MWNT as electrode were investigated. The results showed that the maximum power density of SMFC with SSN-MWNT cathode was 31.6 mW m(-2), which was 3.2 times that of SMFC with an uncoated stainless steel cathode. However, no significant increase in the maximum power density of SMFC with SSN-MWNT anode was detected. Further electrochemical analysis showed that when SSN-MWNT was used as the cathode, the cathodic electrochemical activity and oxygen reduction rate were significantly improved. This study demonstrates that the electrophoretic deposition of carbon nanotubes on conductive substrate can be applied for improving the performance of SMFC.

In this work, sediment microbial fuel cell (SMFC) with granule activated carbon (GAC) cathode and stainless steel anode was constructed in laboratory tests and various factors on SMFC power output were investigated. The maximum power densities for the SMFC with GAC cathode was 3.5 mW m(-2), it was much higher than SMFC with round stainless steel cathode. Addition of cellulose reduced the output power from SMFC at the beginning of experiments, while the output power was found to increase after adding cellulose to sediments on day 90 of operation. On 160 day, maximum power density from the SMFC with adding 0.2% cellulose reached to 11.2 mW m(-2). In addition, the surface morphology of stainless steel anode on day 90 was analyzed by scanning electron microscope. It was found that the protection layer of the stainless steel as electrode in SMFCs was destroyed to some extent.