Polyaniline/reduced graphene oxide-modified carbon fiber brush anode for high-performance microbial fuel cells

Polyaniline (PANI)/reduced graphene oxide (rGO) were synthesized by in-situ polymerization and were decorated on mesophase pitch-based carbon fiber brush (Pitch-CB) anode to promote microbial fuel cells (MFCs) power production. Mesophase pitch-based carbon fiber brush (Pitch-CB) becomes one of the most important research objects in MFCs. The mesophase pitch-based carbon fiber (CF) has excellent conductivity (about 2.0 μΩ m) compared with PAN-based CF (about 30 μΩ m). But the high conductive CF's surfaces have strong inert, and they are relatively smooth, which make it difficult to be adhered and enriched by microbes. By applying the PANI/rGO composite anode, the maximum power density (MPD) was increased to 862 mW m^?2, which was approximately 1.21 times higher than that of the Pitch-CB. The PANI can improve the surface roughness and surface potential of CFs, thus enhancing the adhesion of microbes and electrogenic performance of MFC. After the rGO was doped, the electrogenic performance of MFC was further improved. This study introduces a promising modifying method for the fabrication of high-performance anodes from simple, environment-friendly materials.     

Electrodeposition of graphene by cyclic voltammetry on nickel electrodes for microbial fuel cells applications

Ni electrode was modified with graphene by the electrodeposition (ED) method to prepare an anode (anode‐ED) for microbial fuel cell (MFC). Electrochemical and morphological characterizations of anode‐ED along with the effects of anode modification on the MFC performance were investigated. The graphene modification based on cyclic voltammetric electrodeposition resulted in the decrease of charge transfer resistance (R_ct) and improved extracellular electron transfer efficiency of anode. The maximum power density obtained from the MFC equipped with anode‐ED was 25.83 and 17.86 times larger than those of MFCs equipped with bare Ni anode and anode modified with graphene by traditional hydrothermal treatment method (anode‐HT), respectively. The electrochemical impedance spectroscopy (EIS) analysis results indicated that the R_ct of anode decreased significantly after inoculation during the MFC operation. The improvement in power density was attributed to the decreasing R_ct and the biocompatibility of graphene modified on anode‐ED surface. This study presented an effective electrodeposition method to make graphene‐modified anodes, which could improve the MFC performance.     

Facile microwave-assisted synthesized reduced graphene oxide/tin oxide nanocomposite and using as anode material of microbial fuel cell to improve power generation

A new nanocomposite material was fabricated by a facile and reliable method for microbial fuel cell (MFC) anode. Tin oxide (SnO₂) nanoparticles were anchored on the surface of reduced graphene oxide (RGO/SnO₂) in two steps. The hydrothermal method was used for the modification of GO and then microwave-assisted method was used for coating of SnO₂ on the modified GO. Nanohybrids of RGO/SnO₂ achieved a maximum power density of 1624 mW m⁻², when used as the MFC anode. The obtained power density was 2.8 and 4.8 times larger than that of RGO coated and bare anodes, respectively. The electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics were also studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The high conductivity and large specific surface of the nanocomposite were greatly improved the bacterial biofilm formation and increased the electron transfer. The results demonstrate that the RGO/SnO₂ nanocomposite was advantageous material for the modification of anode and enhanced electricity generation of MFC.     

Effect of surface modification of anode with surfactant on the performance of microbial fuel cell

Surface modification of anode using surfactant has great influence on the electrical performance of a microbial fuel cell (MFC). In this study, the effect of surface‐modified exfoliated graphite used for anode fabrication on a cube‐type MFC batch reactor was examined. The surface exfoliated graphite was modified with 5‐mM anionic surfactant, sodium dodecyl sulfate. Anaerobic sludge used as inoculum containing 70% (v/v) of artificial wastewater and 30% (v/v) of seed sludge in an anode chamber and air cathode was used in cathode side. Anode modification was explored as an approach to enhance the start‐up and improve the performance of the reactor. Scanning electron microscopy was used to evaluate the morphology and activity of electrochemically active bacteria. In the study, the start‐up time of MFC required to approach stable voltage was substantially reduced, and the maximum stable voltage was higher than the control. In addition, the activation resistance of the MFC was considerably reduced, and the maximum power density (1640 mW/m²) was 20% higher than control. However, when the surface of exfoliated graphite was modified with over 10‐mM anionic surfactant, some negative effects on start‐up time, activation resistance and maximum power density were observed. This modification also enhanced the bacterial attachment and biofilm formation on the modified anode surface. The result suggested that surface modification anode with surfactant is effective for electrical responses achieved in the MFC. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance improvement of air-cathode single-chamber microbial fuel cell using a mesoporous carbon modified anode

A novel mesoporous carbon (MC) modified carbon paper has been constructed using layer-by-layer self-assembly method and is used as anode in an air-cathode single-chamber microbial fuel cell (MFC) for performance improvement. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we have demonstrated that the MC modified electrode exhibits a more favorable and stable electrochemical behavior, such as increased active surface area and enhanced electron-transfer rate, than that of the bare carbon paper. The MFC equipped with MC modified carbon paper anode achieves considerably better performance than the one equipped with bare carbon paper anode: the maximum power density is 81% higher and the startup time is 68% shorter. CV and EIS analysis confirm that the MC layer coated on the carbon paper promotes the electrochemical activity of the anodic biofilm and decreases the charge transfer resistance from 300 to 99 Ω. In addition, the anode and cathode polarization curves reveal negligible difference in cathode potentials but significant difference in anode potentials, indicating that the MC modified anode other than the cathode was responsible for the performance improvement of MFC. In this paper, we have demonstrated the utilization of MC modified carbon paper to enhance the performance of MFC.     

Facile preparation of binder-free NiO/MnO2-carbon felt anode to enhance electricity generation and dye wastewater degradation performances of microbial fuel cell

Binder-free NiO/MnO₂-carbon felt electrode is prepared with a facile two-step hydrothermal method. The NiO self-grown on the carbon felt is used as the skeleton structure to support the in-situ growth of MnO₂. Both the core and shell materials are excellent pseudocapacitance materials. The compositing of such pseudocapacitance metal oxides can produce synergistic effects, so that the modified electrode has a high capacitance. NiO/MnO₂-carbon felt electrode also possesses a high specific surface area, super hydrophilicity and good biocompatibility, which are conducive to the enrichment of typical exoelectrogen Geobacter. As the anode, NiO/MnO₂-carbon felt electrode can effectively improve the electricity generation and methyl orange (MO) wastewater degradation performances of microbial fuel cell (MFC). The highest output voltage and the maximum power density of MFC with NiO/MnO₂-carbon felt anode are respectively 652 mV and 628 mW m^?2, which are much higher than those of MFC with MnO₂-carbon felt anode (613 mV, 544 mW m^?2), NiO-carbon felt anode (504 mV, 197 mW m^?2) and unmodified carbon felt anode (423 mV, 162 mW m^?2). The decolourization efficiency and the chemical oxygen demand (COD) removal rate of MO for MFC with NiO/MnO₂-carbon felt anode are respectively 92.5% and 58.2% at 48 h.     

Improved performance of a tubular microbial fuel cell with a composite anode of graphite fiber brush and graphite granules

In this study, a composite electrode combined of a graphite fiber brush and carbon granules (MFC-GFB/GG) was adopted as the anode of a tubular microbial fuel cell (MFC). Compared with an MFC with graphite granules (MFC-GG) and an MFC with a graphite fiber brush (MFC-GFB), MFC-GFB/GG showed a longer lag time during the start-up process, while it reached the highest operating voltage at 50 Ω. Furthermore, during the stable operation, the MFC-GFB/GG achieved the highest power density of 66.9 ± 1.6 W m⁻³, which was about 5.3 and 1.2 times as that of MFC-GG and MFC-GFB, respectively. The highest performance of the MFC-GFB/GG can be attributed to the highest active biomass content on the electrode and the smallest internal resistance of the MFC. The optimum COD concentration was found to be 500 mg COD L⁻¹ for MFC-GFB/GG.     

A graphene modified anode to improve the performance of microbial fuel cells

Graphene with a Brunauer-Emmett-Teller (BET) specific surface area of 264 m² g⁻¹ has been used as anodic catalyst of microbial fuel cells (MFCs) based on Escherichia coli (ATCC 25922). The electrochemical activities of plain stainless steel mesh (SSM), polytetra?uoroethylene (PTFE) modified SSM (PMS) and graphene modified SSM (GMS) have been investigated by cyclic voltammetry (CV), discharge experiment and polarization curve measurement. The GMS shows better electrochemical performance than those of SSM and PMS. The MFC equipped with GMS anode delivers a maximum power density of 2668 mW m⁻², which is 18 times larger than that obtained from the MFC with the SSM anode and is 17 times larger than that obtained from the MFC with the PMS anode. Scanning electron microscopy (SEM) results indicate that the increase in power generation could be attributed to the high surface area of anode and an increase in the number of bacteria attached to anode.     

Enhancing sustainable bioelectricity generation using facile synthesis of nanostructures of bimetallic Co–Ni at the combined support of halloysite nanotubes and reduced graphene oxide as novel oxygen reduction reaction electrocatalyst in single-chambered microbial fuel cells

The present study aims to utilize the high surface area of the nanotube structure of halloysite (HNTs), an aluminosilicate clay, and conductivity of reduced graphene oxide (rGO) as support material for the deposition of nickel (Ni) and cobalt (Co) nanoparticles. With that aim, a novel bimetallic cathode electrocatalyst, Co–Ni @ HNTs-rGO (Catalyst H₃), is developed. This catalyst is characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Transmission Electron Microscopy (TEM). Catalyst H₃ demonstrates outstanding oxygen reduction reaction (ORR) activity, electrochemical stability, electrocatalytic performance, and lowest resistance in comparison to the other developed catalysts and conventional Pt/C. Catalyst H₃ is used in single-chambered MFCs (microbial fuel cells), where the anode is filled with molasses-laden wastewater. The attained maximum power density in MFC (catalyst H₃) is 455 ± 9 mW/m², which is higher than other catalysts. All the results indicate towards its potential use in MFC application.     

Improving microbial electrolysis stability using flow-through brush electrodes and monitoring anode potentials relative to thermodynamic minima

Graphite fiber brush electrodes are commonly used in microbial electrolysis cells (MECs) for simultaneous wastewater treatment and electrochemical hydrogen production. Previous brush anode designs for continuous flow systems were configured to have flow over an array of brush electrodes. Here we compared the performance of two systems, one with flow through a single smaller or larger brush anode to an MEC with multiple brushes. The single brush MECs had only a single large brush that had a diameter larger than the chamber height, so that the brush fibers were compressed to nearly (4.5 cm diameter) or completely (5.5 cm diameter) fill the 1.3 cm high anode chamber. To evaluate the time needed for acclimation of the anode potentials were continuously monitored for 138 d (4.5 cm brush) or 143 d (5.5 cm brush). The best performance was obtained using the 5.5 cm brush fibers with a volumetric current density of 554 ± 26 A/m³, compared to <400 A/m³ when using the smaller 4.5 cm brush or the multiple brush reactor. Full acclimation was shown by a consistent and low anode potential, for example by ?248 ± 8 mV (vs. a standard hydrogen electrode) for the 5.5 cm brush, which was only 31 ± 8 mV above the minimum estimated for acetate oxidation under standard biological conditions. These results show that brush compression into a smaller chamber can enhance MEC performance and produce anode potentials close the thermodynamic minima.     

Increasing power generation of microbial fuel cells with a nano-CeO2 modified anode

Nano-CeO₂ was used to modify the carbon felt anode in microbial fuel cell (MFC). The MFC with the modified anode obtained the higher closed circuit voltage resulting from the lower anode potential, the higher maximum power density (2.94 W m^?2), and the lower internal resistance (77.1 Ω). Cyclic voltammetry (CV) results implied that the bioelectrochemical activity of exoelectrogens was promoted by nano-CeO₂. Electrochemical impedance spectroscopy (EIS) results revealed that the anodic charge transfer resistance of the MFC decreased with modified anode. This study demonstrates that the nano-CeO₂ can be an effective anodic catalyst for enhancing the power generation of MFC.     

Graphite nanopowder functionalized 3-D acrylamide polymeric anode for enhanced performance of microbial fuel cell

3-D highly conductive polyvinyl formaldehyde sponges functionalized with acrylamide are fabricated using polyvinyl alcohol with varying concentrations of graphite nanopowder. The properties of the fabricated anodes are analyzed and its application in microbial fuel cells is evaluated. A comparative study with Graphite felt is also performed to evaluate its commercial viability. The presence of Hydroxyl and Amine functional groups enhanced the hydrophilic and biocompatible nature of the synthesized anodes. The phylogenetic analysis substantiated the biocompatible nature and mercury porosimetry showed macroporous nature of the fabricated anode. The highest power density of ~8 W/m² is recorded for C10 establishing solid biofilm formation. A ~94% COD removal revealed the versatility of the anode for MFC based wastewater treatment. The MFC performance was twice than that of control and was also highest among the most reported modified 3-D anodes. The durability study displayed the commercial opportunity of the anode for real-time MFC operation.     

The fabrication of silane modified graphene oxide supported Ni–Co bimetallic electrocatalysts: A catalytic system for superior oxygen reduction in microbial fuel cells

Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate clean energy from organic pollutants in wastewater. However, the poor cathode performance and the use of the expensive rare metal platinum as a catalyst limit their application and scalability. In this study, we have synthesised a Ni–Co/GO nanocomposite and applied it as a potential cathode catalyst to single-chamber MFCs. To improve the performance of a Ni–Co-based hybrid nanocomposite, the support of graphene oxide (GO) is covalently modified with γ-amino propyl tri-ethoxy silane (APTES) through a silane modification reaction. The physical and chemical properties of the synthesised materials are characterised with Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) techniques. A microscopic study has shown that metal nanoparticles are distributed uniformly on the MGO matrix. The electrocatalytic activity of the synthesised hybrid nanocatalysts is analysed for oxygen reduction reaction (ORR). A cyclic voltammetry experiment has shown that the Ni–Co/MGO catalyst exhibits a higher reduction peak current value and a higher positive onset potential than the Ni–Co/GO catalyst and Pt/C catalyst, indicating an enhanced ORR activity of the Ni–Co/MGO catalyst. Ni–Co/MGO also exhibits the highest initial current of 0.116 mA in the chronoamperometry test, which decreases to 0.049 mA after 16000 s. The electrochemical results demonstrate that the synthesised Ni–Co/MGO catalyst has a higher electrocatalytic activity and higher stability than the state-of-the-art Pt/C catalyst. More importantly, a MFC with Ni–Co/MGO as a cathode catalyst shows the maximum power density of 1003.18 mWm⁻², which is much higher than in the case of the Ni–Co/GO catalyst (889.6 mWm⁻²) and approximately 2.1 times higher than that of the state-of-the-art Pt/C (483.48 mWm⁻²). Consequently, the Ni–Co/MGO nanocomposite also shows the highest open circuit voltage of 0.857 V among the other studied catalysts. Moreover, the Ni–Co/MGO catalyst has a lower biofouling level than a commercial 10 wt% Pt/C catalyst, which shows that the synthesised cathode catalyst is superior in terms of stability, overall performance and usage. These results suggest that the newly developed Ni–Co/MGO catalyst can be applied as a potential substitute for the Pt/C cathode catalyst for the practical application of MFCs.     

Cellulose – Carrageenan coated carbon felt as potential anode structure for yeast microbial fuel cell

Anode material is an important part of Microbial Fuel Cells (MFCs). Carrageenan and cellulose are strong candidates for modifying anode due to their many advantages, especially their biocompatibility. Cellulose microfibrils and microcrystalline were trapped on the surface of carbon felt (CF) using carrageenan (KC). The MFC adopted with CF/[KC/CMF] as anodes structures produced a power density of 70.98 mW?m^?2, higher than MFC that used plain CF. The presence of KC changed the CF properties from hydrophobic to hydrophilic. This can be seen from the weight of biofilms formed in CF/KC, CF/[KC/CMC], and CF/[KC/CMF] being 60, 80, and 90 mg, respectively, higher than plain CF (60 mg). Carrageenan was also successful in entrapping cellulose. Cellulose donated hydrogen ions to form oxycellulose, which has a carboxyl group, wherein can increase Direct Electron Transfer (DET) between yeast and the anode. CF/[KC/CMF] anode structure showed excellent performance and has the potential to be developed in the future.     

Enhanced performances of microbial fuel cells using surface-modified carbon cloth anodes: A comparative study

In this study, performances of two-chamber microbial fuel cells (MFCs) with surface-modified carbon cloth anodes by four methods are compared including soaking in aqueous ammonia (CC-A), electrolysis in phosphate buffer (CC-P), electrolysis in nitric acid (CC-N) and electrolysis in nitric acid followed by soaking in aqueous ammonia (CC-NA). It is found that performances of all these modified anodes are better than that of the bare one. The MFC with the anode modified by CC-NA yield the maximum power density of 3.20 ± 0.05 W m⁻², which is 58%, 36%, 35% and 28% higher than those of the MFC with untreated anode (CC-C, 2.01 ± 0.02 W m⁻²), and treated by the CC-A (2.35 ± 0.15), CC-N (2.38 ± 0.02 W m⁻²) and CC-P (2.50 ± 0.08 W m⁻²) methods, respectively. The active biomass and EIS analysis for the anodes indicated that the highest power output of the CC-NA MFC may primarily attributed to the enhanced electron transfer resulting from the existence of quinoid groups on the CC-NA surface, rather than the biomass effect. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopic analyses of the CC-NA anode further demonstrate that the formation of quinoid groups contributes to the improvement in the MFC performance by accelerating the electron transfer between electrochemically active bacteria (EAB) and the anode surface.     

In-situ modified titanium suboxides with polyaniline/graphene as anode to enhance biovoltage production of microbial fuel cell

Microbial fuel cell (MFC) has been the focus of much investigation in the search for harvesting electricity from various organic matters. The electrode material plays a key role in boosting MFC performance. Most studies, however, in the field of MFC electrode material has only focused on carbonaceous materials. The finding indicates that titanium suboxides (Ti₄O₇, TS) can provide a new alternative for achieving better performance. Polyaniline (PANI) together with graphene is chosen to in-situ modify TS (TSGP). The MFC reactor with TSGP anode achieves the highest voltage with 980 mV, and produces a peak power density of 2073 mW/m², which is 2.9 and 12.7 times those with the carbon cloth control. The rather intriguing result could be due to the fact that TSGP has the high conductivity and large electrochemical active surface area, greatly improving the charge transfer efficiency and the bacterial biofilm loading. This study has gone some way towards exploring the conducting ceramics materials in MFC.     

Transition metal nanoparticles doped carbon paper as a cost-effective anode in a microbial fuel cell powered by pure and mixed biocatalyst cultures

The poor wettability and high cost of the carbonaceous electrodes materials prohibited the practical applications of microbial fuel cells (MFCs) on large scale. Here, a novel nanoparticles of metal sheathed with metal oxide is electrodeposited on carbon paper (CP) to introduce as high-performance anodes of microbial fuel cell (MFC). This thin layer of metal/metal oxide significantly enhance the microbial adhesion, the wettability of the anode surface and decrease the electron transfer resistance. The investigation of the modified CP anodes in an air-cathode MFCs fed by various biocatalyst cultures shows a significant improving in the MFC performance. Where, the generated power and current density was 140% and 210% higher as compared to the pristine CP. Mixed culture of exoelectrogenic microorganism in wastewater exhibited good performance and generated higher power and current density compared to yeast as pure culture. The excellent capacitance with a distinctive nanostructure morphology of the modified-CP open an avenues for practical applications of MFCs.     

A dual photoelectrode-based double-chambered microbial fuel cell applied for simultaneous COD and Cr (VI) reduction in wastewater

Cerium oxide (CeO₂) and cuprous oxide (Cu₂O) were used for the first time as photoanode and photocathode, respectively, in a microbial fuel cell (MFC) for simultaneous reduction of chemical oxygen demand (COD) and Cr(VI) in wastewater. The photoelectrodes, viz. Photoanode and photocathode were separately prepared by impregnating activated carbon fiber (ACF) with the respective metal oxide nanoparticles, followed by growing carbon nanofibers (CNFs) on the ACF substrate using catalytic chemical vapor deposition. The MFC, operated under visible light irradiation, showed reduction in COD and Cr(VI) by approximately 94 and 97%, respectively. The MFC also generated high bioelectricity with a current density of ~6918 mA/m² and a power density of ~1107 mW/m². The enhanced performance of the MFC developed in this study was attributed to the combined effects of the metal oxide photocatalysts, the graphitic CNFs, and the microporous ACF substrate. The MFC based on the inexpensive transition metal oxides-based photoelectrodes developed in this study has a potential to be used at a large scale for treating the industrial aqueous effluents co-contaminated with organics and toxic Cr(VI).     

Enhancing performance of microbial fuel cells by using novel double-layer-capacitor-materials modified anodes

Super-capacitor (SC) activated-carbon (AC) carbon-nanotubes (CNTs) (SC-AC-CNTs) is a kind of AC-based composite material and it combines the advantages of carbon nanotubes and activated carbon, including a series of peculiar properties such as low charge transmission resistance, super large specific area and excellent power characteristic. In this study, SC-AC-CNTs are first used to modify the carbon cloth (CC) anodes of microbial fuel cells (MFCs) and compared with that of SC-AC and CC. The measurements show that the specific surface area is increased from 219.519 m² g^?1 to 283.643 m² g^?1 after modification. The new anode is assembled in a urine-powered MFC (UMFC) to test its effectiveness. It is found that the amount of microorganisms attached on the new anode is much larger than that on the blank anode in UMFC. The maximum power densities of the UMFC assembled with SC-AC-CNTs and SC-AC modified anodes are 899.52 mW m^?2 and 555.10 mW m^?2, which are 2.9 and 1.8 times of that of the blank UMFC, respectively. The tests also shows that the UMFC with SC-AC-CNTs-modified anode creates a much longer duration of 105 h at high-voltage plateau in a single cycle that is about 2–3 times of the other two groups. These findings demonstrate that these two double layer capacitor materials can effectively boost overall MFC performance.     

Effect of hydrogen producing mixed culture on performance of microbial fuel cells

This study examined the influence of H₂-producing mixed cultures on improving power generation using air-cathode microbial fuel cells (MFCs) inoculated with heat-treated anaerobic sludge. The MFCs installed with graphite brush anode generated higher power than the MFCs with carbon cloth anode, regardless heat treatment of anaerobic sludge. When the graphite brush anode-MFCs were inoculated selectively with H₂-producing bacteria by heat treatment, power production was not improved (about 490 mW/m²) in batch mode operation, but for slightly increased in carbon cloth anode-MFCs (from 0.16 to 2.0 mW/m²). Although H⁺/H₂ produced from H₂-producing bacteria can contribute to the performance of MFCs, suspended biomass did not affect the power density or potential, but the Coulombic efficiency (CE) increased. A batch test shows that propionate and acetate were used effectively for electricity generation, whereas butyrate made a minor contribution. H₂-producing mixed cultures do not affect the improvement in power generation and seed sludge, regardless of the pretreatment, can be used directly for the MFC performance.