Carbon nanotube/polyaniline composite as anode material for microbial fuel cells

A carbon nanotube (CNT)/polyaniline (PANI) composite is evaluated as an anode material for high-power microbial fuel cells (MFCs). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) are employed to characterize the chemical composition and morphology of plain PANI and the CNT/PANI composite. The electrocatalytic behaviour of the composite anode is investigated by means of electrochemical impedance spectroscopy (EIS) and discharge experiments. The current generation profile and constant current discharge curves of anodes made from plain PANI, 1 wt.% and 20 wt.% CNT in CNT–PANI composites reveal that the performance of the composite anodes is superior. The 20 wt.% CNT composite anode has the highest electrochemical activity and its maximum power density is 42 mW m⁻² with Escherichia coli as the microbial catalyst. In comparison with the reported performance of different anodes used in E. coli-based MFCs, the CNT/PANI composite anode is excellent and is promising for MFC applications.     

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.     

An insight of bioelectricity production in mediator less microbial fuel cell using mesoporous Cobalt Ferrite anode

Microbial Fuel Cells (MFCs) are an alternative sustainable approach that utilizes the bacteria present in waste water as a bio-catalyst and produce electricity. Herein, Cobalt Ferrite (CF) is fabricated hydrothermally and deposited over graphite sheet to envision a cost-effective MFC anode. The intrinsic biocompatibility, together with mesoporous structure of CF greatly enhanced the microbial colonization. A comparative time dependent study of kinetic activity of CF/Graphite in domestic waste water and artificial waste water is reported. Electrochemical characterization (CV & EIS) indicated the process of active bio film formation on anode from day 1st to day 20th and then restricted bio film till day 30th. Improved extracellular electron transfer of exoelectrogens due to the variable valence state and high redox stability of CF, facilitated the MFC to deliver an excellent power density (1856 mW m⁻²) with the maximum anodic half–cell potential of 0.65 V in waste water. High capacitance (280%) and appropriate pore size (9.3 nm) of CF formed a capacitive bridge for an effective flow of electrons generated by the electro active bacteria. Therefore, use of noble metal free, low cost anodic material Cobalt Ferrite with long-term cell stability makes it a promising and sustainable power source for commercial application.     

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.     

Modified graphite electrode by polyaniline/tourmaline improves the performance of bio-cathode microbial fuel cell

Bio-cathode which uses microorganisms as catalyst can reduce MFC cost and sustain similar power output compared to noble metal catalyst. Thereby, looking for a cathode material which is high conductivity, good biocompatibility and even can stimulate and enhance activity of bio-catalyst is of great interest. In this paper, modified electrode by tourmaline and polyaniline (reactor 3) was used as cathode. The output power density was improved by 492.6% and 192.8% compared to reactor 1 (unmodified cathode) and reactor 2 (cathode modified only by polyaniline) (54 mW m⁻² for reactor 1, 138 mW m⁻² for reactor 2 and 266 mW m⁻² for reactor 3, respectively). When the external resistance was 800Ω, output voltages of reactor 1, 2 and 3 were kept at 0.20 ± 0.005 V, 0.26 ± 0.005 V and 0.37 ± 0.005 V, respectively. Cyclic voltammetry curves showed that reductive current of reactor 3 was higher than those of reactor 1 and 2, indicating that the cathode of reactor 3 had the strongest catalytic activity which was due to that tourmaline could help the interfacial electron transfer, and thereby facilitate the reduction of oxygen at the cathode. Results demonstrated that the tourmaline modified electrode could effectively improve the reduction reaction and enhance the performance of the whole MFC system.     

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.     

Innovative microbial fuel cell for electricity production from anaerobic reactors

A submersible microbial fuel cell (SMFC) was developed by immersing an anode electrode and a cathode chamber in an anaerobic reactor. Domestic wastewater was used as the medium and the inoculum in the experiments. The SMFC could successfully generate a stable voltage of 0.428 ± 0.003 V with a fixed 470 Ω resistor from acetate. From the polarization test, the maximum power density of 204 mW m⁻² was obtained at current density of 595 mA m⁻² (external resistance = 180 Ω). The power generation showed a saturation-type relationship as a function of wastewater strength, with a maximum power density (P_max) of 218 mW m⁻² and a saturation constant (K_s) of 244 mg L⁻¹. The main limitations for achieving higher electricity production in the SMFC were identified as the high internal resistance at the electrolyte and the inefficient electron transfer at the cathode electrode. As the current increased, a large portion of voltage drop was caused by the ohmic (electrolyte) resistance of the medium present between two electrodes, although the two electrodes were closely positioned (about 3 cm distance; internal resistance = 35 ± 2 Ω). The open circuit potential (0.393 V vs. a standard hydrogen electrode) of the cathode was much smaller than the theoretical value (0.804 V). Besides, the short circuit potential of the cathode electrode decreased during the power generation in the SMFC. These results demonstrate that the SMFC could successfully generate electricity from wastewater, and has a great potential for electricity production from existing anaerobic reactors or other anaerobic environments such as sediments. The advantage of the SMFC is that no special anaerobic chamber (anode chamber) is needed, as existing anaerobic reactors can be used, where the cathode chamber and anode electrode are immersed.     

Acclimatization of a microbial consortium into a stable biofilm to produce energy and 1,3-propanediol from glycerol in a microbial fuel cell

Glycerol, a by-product of biodiesel production, is a potential substrate for producing electricity and value-added products in bioelectrochemical systems. Here, we demonstrate a strategy to establish a highly specific energy-producing biofilm from glycerol in a microbial fuel cell (MFC). The MFC fed with 1 g L^?1 glycerol achieved maximum voltage, power density, and current of 0.4 V, 152 mW m^?2, and 19.0 mA m^?2, respectively, operating at a resistance of 1000 Ω. These values were much higher than the values previously described for the same glycerol concentration. High-throughput sequencing demonstrated that substituting acetate for glycerol diminished the anodic microbial diversity. In addition, glycerol shifted the microbial community composition from electroactive bacteria genera such as Delftia, Advenella, Thauera, Stenotrophomonas, and Dysgonomonas to bacteria with dual functions of electricity generation and 1,3-propanediol formation, including Citrobacter, Pseudomonas, and Klebsiella. Thus, establishing this biofilm opens the possibility of recovering energy and obtaining an added-value product from glycerol.     

Enhanced current production of the anode modified by microalgae derived nitrogen-rich biocarbon for microbial fuel cells

In this study, nitrogen-rich biocarbon derived from carbonized Chlorella pyrenoidosa (CCP) was proposed to enhance the current generation from the anode of microbial fuel cells (MFCs). The results revealed that the carbon cloth decorated by CCP (CCP-CC) achieved the highest bioelectrocatalytic current density of 13.44 ± 0.34 A m⁻² after the successful startup, which was 12% and 22% higher than those with carbon black (CB-CC) and the bare carbon cloth (CC), respectively. The results can be attributed to the advantages of CCP-CC over CB-CC and CC in terms of a higher active biomass content, a much smaller charge transfer resistance resulting from the facilitated direct electron transfer due to the presence of N-containing functional groups in CCP and the enhanced mediated electron transfer caused by the larger surface area of the CCP-CC anode for the flavin mediator adsorption.     

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.     

Simultaneous processes of electricity generation and ceftriaxone sodium degradation in an air-cathode single chamber microbial fuel cell

A single chamber microbial fuel cell (MFC) with an air-cathode is successfully demonstrated using glucose-ceftriaxone sodium mixtures or ceftriaxone sodium as fuel. Results show that the ceftriaxone sodium can be biodegraded and produce electricity simultaneously. Interestingly, these ceftriaxone sodium-glucose mixtures play an active role in production of electricity. The maximum power density is increased in comparison to 1000 mg L⁻¹ glucose (19 W m⁻³) by 495% for 50 mg L⁻¹ ceftriaxone sodium + 1000 mg L⁻¹ glucose (113 W m⁻³), while the maximum power density is 11 W m⁻³ using 50 mg L⁻¹ ceftriaxone sodium as the sole fuel. Moreover, ceftriaxone sodium biodegradation rate reaches 91% within 24 h using the MFC in comparison with 51% using the traditional anaerobic reactor. These results indicate that some toxic and bio-refractory organics such as antibiotic wastewater might be suitable resources for electricity generation using the MFC technology.     

Effect of an anode modified with nitrogenous compounds on the performance of a microbial fuel cell

Three kinds of nitrogenous compounds (ammonium peroxydisulfate, ethylenediamine, methylene blue) were applied to modify graphite felt anodes in microbial fuel cells. All of the performances were greatly improved by modifying the anode surface. The maximum power density of the microbial fuel cell with modified anode was 355, 545, and 510 mW/m², respectively, which was larger than the ungroomed control (283 mW/m²). The power density of microbial fuel cell with ethylenediamine-treated electrode was highest among the four microbial fuel cells. The increase of power density was correlated with the changes of N/C and O/C ratios on the anode according to the X-ray photoelectron spectrometry analysis.     

Fabrication of solid oxide fuel cell anode electrode by spray pyrolysis

Large triple phase boundaries (TPBs) and high gas diffusion capability are critical in enhancing the performance of a solid oxide fuel cell (SOFC). In this study, ultrasonic spray pyrolysis has been investigated to assess its capability in controlling the anode microstructure. Deposition of porous anode film of nickel and Ce_0.9Gd_0.1O_1.95 on a dense 8 mol.% yttria stabilized zirconia (YSZ) substrate was carried out. First, an ultrasonic atomization model was utilized to predict the deposited particle size. The model accurately estimated the deposited particle size based on the feed solution condition. Second, effects of various process parameters, which included the precursor solution feed rate, precursor solution concentration and deposition temperature, on the TPB formation and porosity were investigated. The deposition temperature and precursor solution concentration were the most critical parameters that influenced the morphology, porosity and particle size of the anode electrode. Ultrasonic spray pyrolysis achieved homogeneous distribution of constitutive elements within the deposited particles and demonstrated capability to control the particle size and porosity in the range of 2-17 μm and 21-52%, respectively.     

Decomposition characteristics of propionate when changing the electrode material,external resistance and reactor temperature of microbial fuel cells

Assuming a series-type microbial fuel cell (MFC) that sequentially consumes organic acid components, the effects of the electrode material, external resistance, and temperature of MFC on the decomposition characteristics of acetate and propionate were investigated. As to electrode materials, propionate decomposition required less time in carbon cloth (CC) than that in carbon felt (CF), and maximum power was produced higher in CC than that in CF as well as acetate substrate. When the external resistance of 1000 Ω was replaced with 100 Ω or 10 Ω, both the decomposition rate and maximum power in propionate were lower than those in acetate, respectively. The time required for acetate decomposition at the temperature of 30 °C and 37 °C was 14.8 and 19.4 h, while 25.3 and 17.2 h in propionate at 30 °C and 37 °C, respectively. The microbial community changed significantly between 30 °C and 37 °C of the temperature.     

Co-substrate strategy for improved power production and chlorophenol degradation in a microbial fuel cell

A co-substrate strategy has the potential to contribute toward minimizing the poisoning of refractories on the anode respiring bacteria (ARB), which is a necessity for microbial fuel cell (MFC) to recover energy from toxic wastewater. However, little is known about the underlying mechanisms. This study employed 4-chlorophenol (4-CP) as target refractory pollutant and acetate as co-substrate. The co-substrate could stimulate 4-CP sensitive extracellular electron transfer (EET) enzymes’ activity under 4-CP stress, such as succinate dehydrogenase (complex II) and cytochromes c OmcA and OmcB. For the microbial community, ARB were still abundant during 4-CP toxification; Azospirillum and Dechloromonas were enriched to conduct aromatic ring breakage and dechlorination. Thus, a 4.3-fold increased power generation was achieved, and the 4-CP and chemical oxygen demand (COD) removals increased by ∼42% and ∼53%, respectively. An easy-to-degrade substrate could improve power re-coverage from refractory wastewater by enhancing EET enzyme activity and optimizing the microbial community.     

An analysis of the performance of an anaerobic dual anode-chambered microbial fuel cell

The performance of a dual anode-chambered microbial fuel cell (MFC) inoculated with Shewanella oneidesis MR-1 was evaluated. This reactor was constructed by incorporating two anode chambers flanking a shared air cathode chamber in an electrically parallel, geometrically stacked arrangement. The device was shown to have the same maximum power density (approximately 24 W m⁻³, normalized by the anode volume) as a single anode-, single cathode-chambered MFC. The dual anode-chambered unit generated a maximum current of 3.66 mA (at 50 Ω), twice the value of 1.69 mA (at 100 Ω) for the single anode-chambered device at approximately the same volumetric current density. Increasing the Pt-coated cathode surface area by 100% (12 to 24 cm²) had no significant effect on the power generation of the dual anode-chambered MFC, indicating that the performance of the device was limited by the anode. The medium recirculation rate and substrate concentration in the anode were varied to determine their effect on the anode-limited power density. At the highest recirculation rate, 5 ml min⁻¹, the power density was about 25% higher than at the lowest recirculation rate, 1 ml min⁻¹. The dependence of the power density on the lactate concentration showed saturation kinetics with a half-saturation constant K_s on the order of 4.4 mM.     

High-capacity polyaniline-coated molybdenum oxide composite as an effective catalyst for enhancing the electrochemical performance of the microbial fuel cell

Microbial fuel cells (MFCs) are a promising technology, which can generate electrical energy by utilizing the organic compound as fuels through central metabolism system of exo-electrogenic bacteria. Anodes have been intensively explored for the development of high-performance MFCs as an alternative to conventional electrodes. Modified anodes were synthesized by the coating of molybdenum oxide (MoO₂) and polyaniline (PANI) composites on the carbon cloth (CC) surface. MoO₂/PANI electrocatalyst anodes have high capacitance and electrical conductivity, experimentally affirmed by cyclic voltammetry (CV)and charge-discharge analysis. The as-prepared modified anodes were found to efficiently enhance the performance of MFCs by facilitating the extracellular electron transfer from bacteria to the anode. MFCs with MoO₂/PANI (1:2 w/w) electrocatalyst anode delivered a maximum power density (PD) of 1101 mW/m², which was 7.8 times higher than unmodified CC anode. EIS results indicate that the composite MoO₂/PANI has also responsible for decreasing the interfacial charge transfer resistance which leads to the improvement in electron transfer between microbes and the modified anode. The results found in the present study will help in the design optimization of novel anode materials to deliver improved PD from MFCs.     

Power generation from furfural using the microbial fuel cell

Furfural is a typical inhibitor in the ethanol fermentation process using lignocellulosic hydrolysates as raw materials. In the literature, no report has shown that furfural can be utilized as the fuel to produce electricity in the microbial fuel cell (MFC), a device that uses microbes to convert organic compounds to generate electricity. In this study, we demonstrated that electricity was successfully generated using furfural as the sole fuel in both the ferricyanide-cathode MFC and the air-cathode MFC. In the ferricyanide-cathode MFC, the maximum power densities reached 45.4, 81.4, and 103 W m⁻³, respectively, when 1000 mg L⁻¹ glucose, a mixture of 200 mg L⁻¹ glucose and 5 mM furfural, and 6.68 mM furfural were used as the fuels in the anode solution. The corresponding Coulombic efficiencies (CE) were 4.0, 7.1, and 10.2% for the three treatments, respectively. For pure furfural as the fuel, the removal efficiency of furfural reached up to 95% within 12 h. In the air-cathode MFC using 6.68 mM furfural as the fuel, the maximum values of power density and CE were 361 mW m⁻² (18 W m⁻³) and 30.3%, respectively, and the COD removal was about 68% at the end of the experiment (about 30 h). Increase in furfural concentrations from 6.68 to 20 mM resulted in increase in the maximum power densities from 361 to 368 mW m⁻², and decrease in CEs from 30.3 to 20.6%. These results indicated that some toxic and biorefractory organics such as furfural might still be suitable resources for electricity generation using the MFC technology.     

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.     

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.