Electricity Generation In Microbial Fuel Cells Research Articles

Bioelectricity Generation from Microbial Fuel Cell utilizing Sewage Wastewater and Cow Urine from Dutse Metropolis Jigawa State

Microbial fuel cells (MFCs) are technologies that directly transform chemical energy into electrical energy by oxidizing organic matter using bacteria as biocatalysts. MFCs offer a potential technology for converting wastewater into useful energy source and at the same time serve as wastewater treatment facilities. This makes it superior to other wastewater treatment methods. This study focused on the utilization of MFCs to generate bioelectricity from sewage wastewater using cow urine as inoculum and identify the bacteria colonizing the anode electrode. The experiment were conducted using two-chambered MFC constructed using locally sourced materials. Wastewater was characterized using standard methods. The characteristics of the sewage wastewater are: 680 mg/L Chemical oxygen Demand (COD), 457 mg/L Biochemical oxygen Demand (BOD) and pH of 7.4. The maximum voltage, power and current density obtained were 196 mV, 18.26 mW/m2 and 97 mA/m2 respectively. The MFC shows a reduction in COD value by 82 % (680mg/L initial and 120 mg/L final).The identification of the anodic biofilms showed the presence of Bacillus spp and klebsiella spp based on their microscopic and biochemical characterization. The results of this study can contribute to improve understanding and optimizing electricity generation in MFC, Further study would be conducted in order to identify the microorganisms at molecular level.

Influence of environmental factors on electricity generation performance of electricity‐producing bacteria from oily sludge microbial fuel cells

AbstractElectricity‐generating bacteria are used as the biocatalysts of microbial fuel cells (MFCs). The power‐generating properties of electricity‐generating bacteria play an important role in organic matter degradation and electricity generation of MFCs. However, there are few electricity‐producing bacteria isolated from the anode biofilm of microbial fuel cells containing oily sludge. More importantly, the adaptability of nitrogen‐to‐phosphorus ratio, temperature and pH of the electricity‐generating bacteria were adjusted by controlled variable method. The results of this study showed that the isolated electricity‐producing bacteria (Citrobacter freundii) with a rod‐shaped cell, wrinkled surface, about 0.5–1.0 μm in length. The optimal nitrogen‐to‐phosphorus ratio, temperature and pH of MFCs are 5.67:1, 25°C, and pH = 7.5, Its maximum voltage and power density was up to 143.01 mV and 65 mW·m−3, respectively. Furthermore, the growth rate of the electricity‐producing bacteria is the highest. This lays the foundation for inoculating electricity‐generating bacteria into oily sludge MFCs to improve the oil removal and power generation performance.

Efficient bioelectricity generation and carbazole biodegradation using an electrochemically active bacterium Sphingobium yanoikuyae XLDN2-5

Carbazole and its derivatives are polycyclic aromatic heterocycles with unusual toxicity and mutagenicity. However, disposal of these polycyclic aromatic heterocycles remains a significant challenge. This study focused on efficient resource recovery from carbazole using an obligate aerobe, Sphingobium yanoikuyae XLDN2-5, in microbial fuel cells (MFCs). S. yanoikuyae XLDN2-5 successfully achieved carbazole degradation and simultaneously electricity generation in MFCs with a maximum power density of 496.8 mW m−2 and carbazole degradation rate of 100%. It is the first time that S. yanoikuyae XLDN2-5 was discovered as an electrochemically active bacterium with high extracellular electron transfer (EET) capability. Redox mediator analysis indicated that no self-produced redox mediators were found for S. yanoikuyae XLDN2-5 under analysis conditions, and the exogenous redox mediators used in this study did not promote its EET. The nanowires produced by S. yanoikuyae XLDN2-5 cells were found in the biofilm by morphology characterization and the growth process of the nanowires was consistent with the discharge process of the MFC. Conductivity determination further verified that the nanowires produced by S. yanoikuyae XLDN2-5 cells were electrically conductive. Based on these results, it is speculated that S. yanoikuyae XLDN2-5 may mainly utilize conductive nanowires produced by itself rather than redox mediators to meet the requirements of normal energy metabolism when it grows in the low dissolved oxygen zone of the anodic biofilm. These novel findings on the EET mechanism of S. yanoikuyae XLDN2-5 lay a foundation for further exploration of polycyclic aromatic heterocyclic pollutants treatment in electrochemical devices, which may create new biotechnology processes for these pollutants control.

In-situ growth of N@MoO2 microflowers on carbon cloth for high-performance anodes in microbial fuel cells

Anode is a crucial component enabling microbial fuel cells (MFCs) to achieve efficient and durable power generation; however, the preparation of high-performance and up-scaling anodes via facile methods remains a practical challenge. In this study, a nitrogen-doped carbon cloth grafted with molybdenum dioxide microspheres (N @ MoO2/CC) was fabricated using a facile two-step method: in situ polymerization and high-temperature carburization. N @ MoO2/CC exhibited excellent bioelectricity harvesting capacity owing to its dual function of promoting bacterial colonization while enriching electroactive bacteria. The synergy of N-doping and MoO2-grafting enabled the development of a biocompatible interface for bacterial adhesion, resulting in a high bacterial loading capacity. Furthermore, N-doping and MoO2-grafting modifications facilitated the enrichment of Geobacter, thereby enhancing the electrocatalytic activity of the electrode. MFC equipped with N @ MoO2/CC achieved a maximum power density of 3.01 ± 0.23 W·m−2, i.e., 1.43 times the power density achieved using a pristine carbon cloth (2.10 ± 0.04 W·m−2). Additionally, the physical and electrochemical characterizations confirmed that the as-prepared N @ MoO2/CC exhibited excellent operational stability. In summary, N @ MoO2/CC could significantly enhance bacterial colonization, enable electroactive bacteria to flourish, and boost charge transfer efficiency at the microbe–electrode interface, thus improving the electricity generation in MFCs.

Sulfate/sulfide removal from wastewater by lab-scale microbial fuel cell

Sulfate/sulfide-containing wastewater is a widespread environmental contaminant resulting from human activities. These pollutants have negative impact on natural ecosystems and human beings. Biological sulfate/sulfide removal can be achieved by reducing sulfate to sulfide with sulfate-reducing bacteria and then oxidizing sulfide to elemental sulfur (So) with sulfide oxidizing bacteria. In sulfate/sulfide contaminant wastewater lacking electron acceptor for sulfide oxidization, excess sulfide will be produced and accumulated in the treatment system. Therefore, microbial fuel cells (MFCs) have been shown to be a promising technique for the removal of sulfate/sulfide pollutants in wastewater. In this study, a lab-scale MFCs has been developed based on the activity of sulfate-reducing bacterium Desulfovibrio. sp. The results showed that sulfate and sulfide removal efficiencies of 74 - 82% (78 ± 2,5%) and 80.8 - 89.1% (~85,6 ± 3,1%) were achieved, respectively, from the 5th day to the 14th day of operation. The voltage of 0.02V and power density of 7.2 to 7.8 mW/m2 was obtained. In this study, sulfide oxidizing-based MFC integrated with sulfate-reducing bioreactor, representing the feasibility of simultaneous sulfate/sulfide pollutants removal and electricity generation in MFCs. This provides a promising treatment system to scale up for its actual applications in sulfate/sulfide removal.

Optimization of operational factors using statistical design and analysis of nanofiller incorporated polymer electrolyte membrane towards performance enhancement of microbial fuel cell

Response Surface Methodology (RSM) coupled with Box–Behnken (BB) design is adopted to optimize Microbial Fuel Cell (MFC) performance statistically as a function of three selected operational factors such as filler concentration, membrane thickness and anode surface area. Various concentrations (2%, 4%, 6% and 8%) of Sulphonated Zinc Oxide Nano Rods (SZnO NR) with Sulphonated Polystyrene Ethylene Butylene Polystyrene (SPSEBS) are used as Proton Exchange Membranes (PEM) in a fabricated tubular MFC with a holding volume of 300 mL. The prepared nanocomposite membranes are analyzed for their water uptake, ion exchange capacity (IEC), oxygen crossover and proton conductivity to confirm the membrane suitability for MFC operation. The results indicate that SPSEBS + 6% SZnO NR possesses highest proton conductivity of 1.49 × 10-2 S/cm compared to other nanocomposite membranes and is thus selected for statistical analysis. Statistical analysis shows that STAT 15 with filler concentration of 6.5%, membrane thickness of 120 µm and anode surface area of 19.7 cm2 exhibits the highest maximum power density of 147 mW/m2. The results suggest a novel nanocomposite membrane that could be a suitable PEM and also gives a regression equation for optimizing factors which enhances electricity generation in MFC.

Microbial community dynamics and electricity generation in MFCs inoculated with POME sludges and pure electrogenic culture

Palm Oil Mill Effluent (POME) requires treatment before disposal due to its high organic matter content. In this study, the electrical performance and wastewater treatment efficiency were evaluated for Microbial Fuel Cells (MFC) treating unsterile POME with chemical oxygen demand (COD) from 200 to 10 000 mg/L. Since the inoculum type is a key factor in MFC performance, three types of sludge (methanogenic sludge (MS), facultative sludge (FS), and dry sludge (DS), obtained from the current POME treatment ponds were evaluated as inoculum. Dry sludge (DS) developed a maximum power output of 3.30 W/m3 by oxidizing 71% out of the COD provided by POME (1000 mg/L). Also, raw POME microbiota contributed to an enrichment of the community in DS inoculum along with the operation, in which Geobacter was the predominant genus reaching a current generation of 247 mA/m2 and a power density of 2.36 W/m3. Conversely, pure electrogenic (Shewanella sp.) inoculation led to a diversification process, resulting in a lower current generation of 52 mA/m2 and a power density of 0.10 W/m3. Consequently, microbial community dynamics revealed that MFC inoculation tends to a microbial equilibrium wherein generation of high current density was achieved by gradual microbial enrichment rather than external electrogenic invasion.

Three-dimensional graphitic mesoporous carbon-doped carbon felt bioanodes enables high electric current production in microbial fuel cells

Microbial fuel cells (MFCs) represent a new approach that can simultaneously enhance the treatment of waste streams and generate electricity. Although MFCs represent a promising technology for renewable energy production, they have not been successfully scaled-up mainly due to the relatively-low electricity generation and high cost associated with MFCs operation. Here, we investigated whether graphitic mesoporous carbon (GMC) decoration of carbon felt would improve the conductivity and biocompatibility of carbon felt anodes, leading to higher biomass attachment and electricity generation in MFCs fed with an organic substrate. To test this hypothesis, we applied 3 different GMC loading (i.e., 2, 5, and 10 mg/cm2 of anode surface area) in MFCs compared to control MFCs (with pristine carbon felt electrodes). We observed that the internal resistances of modified anodes with GMC were 1.2–2.3-order of magnitude less than pristine carbon felt anode, leading to maximum power densities of 70.3, 33.3, and 9.8 mW/m2 for 10, 5, and 2 mg/cm2-doped anode, respectively compared to only 3.8 mW/m2 for the untreated carbon felt. High-throughput sequencing revealed that increasing the GMC loading rate was associated with enriching more robust anode-respiring bacteria (ARB) biofilm community. These results demonstrate that 3-D GMC-doped carbon felt anodes could be a potential alternative to other expensive metal-based electrodes for achieving high electric current densities in MFCs fed with organic substrates, such as wastewater. Most importantly, high electron transfer capability, strong chemical stability, low cost, and excellent mechanical strength of 3-D GMC-doped carbon felt open up new opportunities for scaling-up of MFCs using cheap and high-performance anodes.

The inhibiting effect of oxygen diffusion on the electricity generation of three-chamber microbial fuel cells

Microbial fuel cell (MFC) as an emerging biotechnology is applied to generate electricity from the degradation of organic matter. This work explores the performance of the three-chamber MFCs in regard to oxygen diffusion with air aeration or radial oxygen swap (stream reaeration) cathodes during considerably prolonged operation (206 days). Results show that the oxygen diffusing from cathode chamber to anode chamber can accelerate the degradation of organic matter in anode chamber to some extent, and weaken the electricity generation of MFC. The electrogenesis for the radial oxygen swap cathode MFC (OSCMFC) is superior to air aeration cathode MFC (AACMFC), with the maximum voltage and power density of 0.855 V and 3.954 W m−3, respectively. Compared with radial oxygen swap, air aeration causes more oxygen diffusion from cathode to anode chamber, which facilitates the growth of facultative anaerobes to accelerate the hydrolysis and acidification of the substrate and inhibits the activities of electricigens, resulting in the redox reaction of the oxygen and electrons in micro scales. The inhibiting effect of oxygen diffusion on electrogenic bacteria results in that a fraction of hydrolyzed organic matters is not converted into electricity, but rather to be devoured by non-electrogenic bacteria for the self-metabolic consumption and reproduction.

Adding Zero-Valent Iron to Enhance Electricity Generation during MFC Start-Up.

The low power generation efficiency of microbial fuel cells (MFCs) is always a barrier to further development. An attempt to enhance the start-up and electricity generation of MFCs was investigated by adding different doses of zero-valent iron into anaerobic anode chambers in this study. The results showed that the voltage (289.6 mV) of A2 with 0.5 g of zero-valent iron added was higher than the reference reactor (197.1 mV) without dosing zero-valent iron (A4). The maximum power density of 27.3 mW/m2 was obtained in A2. CV analysis demonstrated that A2 possessed a higher oxidation–reduction potential, hence showing a stronger oxidizing property. Meanwhile, electrochemical impedance analysis (EIS) also manifested that values of RCT of carbon felts with zero-valent iron supplemented (0.01–0.03 Ω) were generally lower. What is more, SEM images further proved and illustrated that A2 had compact and dense meshes with a hierarchical structure rather than a relatively looser biofilm in the other reactors. High-throughput sequencing analysis also indicated that zero-valent iron increased the abundance of some functional microbial communities, such as Acinetobacter, Ignavibacteriales, Shewanella, etc.

Electricity production of microbial fuel cells by degrading cellulose coupling with Cr(VI) removal

A facultative exoelectrogen strain Lsc-8 belonging to the Cellulomonas genus with the ability to degrade carboxymethyl cellulose (CMC) coupled with the reduction of Cr(VI), was successfully isolated from rumen content. The maximum output power density of the microbial fuel cells (MFCs) inoculated strain Lsc-8 was 9.56 ± 0.37 mW·m-2 with CMC as the sole carbon source. From the biomass analysis it can be seen that the electricity generation of the MFCs was primarily attributed to the planktonic cells of strain Lsc-8 rather than the biofilm attached on the electrode, which was different from Geobacter sulfurreducens. Especially, during electricity generation of the MFCs using CMC as carbon source in the anode chamber, the Cr(VI) reduction were simultaneously realized. And it is also found that the Cr(VI) reduction ratio by strain Lsc-8 is directly related to the initial Cr(VI) concentration, and it increased with the increase of initial Cr(VI) concentration at first, then started to decrease when the Cr(VI) concentration was above 21 mg ·L-1. Meanwhile, the highest output power density of 3.47 ± 0.28 mW·m-2 was observed coupling with 95.22 ± 2.72 % of Cr(VI) reduction. These data suggested that the strain Lsc-8 could reduce high toxicity Cr(VI) to low toxicity Cr(III) coupled with electricity generation in MFCs with CMC as the carbon source. Our results also suggested that this study will provide a possibility to simultaneously degrade Cr(VI) and generate electricity by using cellulose as the carbon source via MFCs.

Osmotic Pressure Compensated Solute Ectoine Improves Salt Tolerance of Microbial Cells in Microbial Fuel Cells

AbstractIn the technology of microbial fuel cells (MFCs) for simultaneous electricity production and wastewater purification, the electricity production of MFCs decreases when the salt concentration in the wastewater is high. Increasing the electricity production of MFCs under high salt conditions is a great challenge. This paper studies the reasons for the decline of electricity production of MFCs under high salt conditions and develops ways to increase the electricity generation. The results show that high salt inhibits the growth of electrogenic microorganisms on the anode of MFCs, thereby reducing the electricity production. Addition of ectoine, an osmotic pressure compensated solute, can increase the salt tolerance of electrogenic microorganisms, thereby increasing the electricity generation of MFCs. With the addition of 1 mmol L−1 ectoine to the substrate, the average voltage output of the MFCs based on mixed microbial flora anode was increased by 60.4% (±3.9%). Under this condition, microbial diversity analysis showed that the dominant growth and electricity production genus Acinetobacter accounted for 38.9% in the microbial community of anode biofilm.

Performance of Single Chamber Microbial Fuel Cell (SCMFC) for biological treatment of tofu wastewater

The wastewater of tofu industries consists of organic compounds and in turn, may affect the environment; therefore, a proper wastewater treatment system is needed. Based on its characteristics, biological treatment is a good method to treat tofu wastewater. One of the biological treatment methods that can be used is Microbial Fuel Cell (MFC), which can reduce the pollutant and at the same time generating low-power electricity. This system utilizes microorganisms as a biocatalyst to degrade organic compounds in the wastewater. This study aimed to examine the performance of Single Chamber MFC (SCMFC) to decrease biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) of the tofu wastewater, as well as to generate electricity. Tofu wastewater was sterilized then filled into the reactor. Microbes that either have been acclimatized or not acclimatized were then added. Bacteria that were used were one of the three consortiums of native microbes of tofu wastewater, namely Escherichia coli, Saccharomycopsis fibuligera, and mixed culture of E. coli and S. fibuligera. Carbon (C) was used as both anode and cathode. We found that the acclimatized mixed culture of E. coli and S. fibuligera showed high BOD5, COD removal after 48 hours at 76.57 and 77.22 %, respectively. It also generated 5.49 mA of current, 757 mV of voltage, and the electrical energy produced was 9.216 x10− 5 kWh. The results suggest that using mixed microorganisms is one of the strategies to improve the electricity generation of MFC. The scale-up of the volume, selection of microorganism cultures, and immobilization could be other strategies for further studies.

Overexpression of c‐type cytochrome, CymA in Shewanella oneidensis MR‐1 for enhanced bioelectricity generation and cell growth in a microbial fuel cell

AbstractBACKGROUNDThe c‐type cytochrome of the CymA of Shewanella oneidensis MR‐1 is essential for the anaerobic respiration of Shewanella sp. and transfers electrons from the inner membrane to various terminal electron acceptors, such as soluble redox shuttles and insoluble metal oxides. CymA is believed to be a passage to the outer membrane for dissipating the respiratory electron to the carbon electrode in a microbial fuel cell (MFC) with simultaneous electricity generation. While the deletion and heterologous expression of cymA in Escherichia coli have been studied, there are no reports of the overexpression and its effects on the corresponding bioelectrochemical performance in a MFC.RESULTSThe cymA gene was overexpressed in Shewanella oneidensis MR‐1, and its upregulation was examined under aerobic, anaerobic, and MFC operating conditions by a reverse transcription‐polymerase chain reaction (RT‐PCR). Overexpression of the CymA protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE). The MFCs inoculated with the engineered strains of MR‐1 achieved a higher maximum power of 0.13 mW and specific growth rate of 0.087 h−1 than those of the wild type MR‐1 (0.11 mW and 0.043 h−1, respectively). The higher electrochemical activity of the mutant strains demonstrated by cyclic voltammetry and linear sweep voltammetry, indicates that more respiratory electrons can be transferred to the electrodes through overexpression of the cymA gene of MR‐1 in a MFC.CONCLUSIONOverexpression of CymA improves the bioelectrochemical performance of MFCs. This suggests that metabolic engineering of a membrane‐associated redox protein, such as CymA, can further improve electricity generation of MFCs and produce an electrochemically enhanced bioprocess. © 2018 Society of Chemical Industry

Anode modification by biogenic gold nanoparticles for the improved performance of microbial fuel cells and microbial community shift

In this study, carbon cloth anodes were modified using biogenic gold nanoparticles (BioAu) and nanohybrids of multi-walled carbon nanotubes blended with BioAu (BioAu/MWCNT) to improve the performance of microbial fuel cells (MFCs). The results demonstrated that BioAu modification significantly enhanced the electricity generation of MFCs. In particular, BioAu/MWCNT nanohybrids as the modifier displayed a better performance. The MFC with the BioAu/MWCNT electrode had the shortest start-up time (6.74 d) and highest power density (178.34 ± 4.79 mW/m2), which were 141.69% shorter and 56.11% higher compared with those of the unmodified control, respectively. These improvements were attributed to the excellent electrocatalytic activity and strong affinity towards exoelectrogens of the BioAu/MWCNT nanohybrids on the electrode. High throughput sequencing analysis indicated that the relative abundance of electroactive bacteria in the biofilm community, mostly from the classes of Gammaproteobacteria and Negativicutes, increased after anode modification.

Microbial fuel cells equipped with an iron-plated carbon-felt anode and Shewanella oneidensis MR-1 with corn steep liquor as a fuel

A single chamber type microbial fuel cell (MFC) with 100mL of chamber volume and 50cm2 of air-cathode was developed in this study wherein a developed iron-plated carbon-felt anode and Shewanella oneidensis MR-1 were used. The performance of the iron-plated carbon-felt anode and the possibility of corn steep liquor (CSL) as a fuel, which was the byproduct of corn wet milling and contained lactic acid, was investigated here. MFCs equipped with iron-plated or non-plated carbon-felt anodes exhibited maximum current densities of 443 or 302mA/m2 using 10g/L of reagent-grade lactic acid, respectively. In addition, using centrifuged CSL without insoluble ingredients or non-centrifuged CSL as a fuel, the maximum current densities of the MFCs with iron-plated carbon-felt anode were 321 or 158mA/m2, respectively. This report demonstrated the effect of iron-plated carbon-felt anode for electricity generation of MFC using S.oneidensis MR-1 and the performance of CSL as a fuel.

Development of platinum supported on single-walled carbon nanotubes by deposition-precipitation for microbial fuel cells.

Microbial fuel cells (MFCs) are an ecologically friendly technology that can recover electricity and simultaneously treat wastewater. Among all the influential factors, cathode material and catalyst play a crucial role in electricity production and oxygen reduction. In this study, Pt nanocatalysts deposited on single-walled carbon nanotubes (Pt/SWCNTs) were synthesized by the deposition-precipitation (DP) method under optimal conditions. The results show that DP might be a promising method for the preparation of Pt/SWCNTs due to its simple, cost-effective and time-saving procedure, in addition to being highly efficient at creating small Pt particles (0.9 nm) that were very uniformly distributed. The synthesized Pt/SWCNTs suspension was spray-coated on to carbon cloth and then used as a cathode for MFCs. The electricity generation of MFCs equipped with a Pt/SWCNTs cathode was evaluated in terms of open circuit voltage (0.6954 V), internal resistance (63.3 Ω•m2) and maximum power density (2,022 mW/m2). The chemical oxygen demand removal, biological oxygen demand removal, total dissolved solids removal, total suspended solids removal and silver recovery was satisfactory at 84.5%, 74.0%, 45.7%, 60.0% and 99.0%, respectively. Therefore, Pt/SWCNTs from the DP method was identified as a potential candidate to replace commercial Pt-carbon cloth for MFC cathodes.

Pre-treatment of anodic inoculum with nitroethane to improve performance of a microbial fuel cell.

Methanogenic substrate loss is reported to be a major bottleneck in microbial fuel cell (MFC), which significantly reduces the power production capacity and coulombic efficiency (CE) of this system. Nitroethane is found to be a potent inhibitor of hydrogenotrophic methanogens in rumen fermentation process. Influence of nitroethane pre-treated sewage sludge inoculum on suppressing the methanogenic activity and enhancing the electrogenesis in MFC was evaluated. MFC inoculated with nitroethane pre-treated anodic inoculum demonstrated a maximum operating voltage of 541 mV, with CE and maximum volumetric power density of 39.85% and 20.5 W/m3, respectively. Linear sweep voltammetry indicated a higher electron discharge on the anode surface due to enhancement of electrogenic activity while suppressing methanogenic activity. A 63% reduction in specific methanogenic activity was observed in anaerobic sludge pre-treated with nitroethane, emphasizing the significance of this pre-treatment for suppressing methanogenesis and its utility for enhancing electricity generation in MFC.

Molybdenum anode: a novel electrode for enhanced power generation in microbial fuel cells, identified via extensive screening of metal electrodes

BackgroundMetals are considered a suitable anode material for microbial fuel cells (MFCs) because of their high electrical conductivity. However, only a few types of metals have been used as anodes, and an extensive screening of metals has not yet been conducted. In this study, to develop a new metal anode for increased electricity generation in MFCs, 14 different metals (Al, Ti, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Ag, In, Sn, Ta, and W) and 31 of their oxidized forms were comprehensively tested. Oxidized-metal anodes were prepared using flame oxidation, heat treatment, and electrochemical oxidation. The selected anodes were further evaluated in detail using air–cathode single-chambered MFCs.ResultsThe untreated Mo and electrochemically oxidized Mo anodes showed high averages of maximum power densities in the screening test, followed by flame-oxidized (FO) W, FO-Fe, FO-Mo, and Sn-based anodes. The untreated Mo and FO-W anodes were selected for further evaluation. X-ray analyses revealed that the surface of the Mo anode was naturally oxidized in the presence of air, forming a layer of MoO3, a known oxidation catalyst. A high maximum power density (1296 mW/m2) was achieved using the Mo anode in the MFCs, which was superior to that obtained using the FO-W anode (1036 mW/m2). The Mo anode, but not the FO-W anode, continued to produce current without detectable corrosion until the end of operation (350 days). Geobacter was abundant in both biofilms on the Mo and FO-W anodes, as analyzed by high-throughput sequencing of the 16S rRNA gene.ConclusionsThe screening test revealed that Mo, W, Fe, and Sn are useful MFC anode materials. The detailed analyses demonstrated that the Mo anode is a high-performance electrode with structural simplicity and long-term stability in MFCs. The anode can be easily prepared by merely shaping Mo materials to the desired forms. These properties would enable the large-scale preparation of the anode, required for practical MFC applications. This study also implies the potential involvement of Geobacter in the Mo and W cycles on Earth.

Microbial fuel cell assisted band gap narrowed TiO2 for visible light-induced photocatalytic activities and power generation

This paper reports a simple, biogenic and green approach to obtain narrow band gap and visible light-active TiO2 nanoparticles. Commercial white TiO2 (w-TiO2) was treated in the cathode chamber of a Microbial Fuel Cell (MFC), which produced modified light gray TiO2 (g-TiO2) nanoparticles. The DRS, PL, XRD, EPR, HR-TEM, and XPS were performed to understand the band gap decline of g-TiO2. The optical study revealed a significant decrease in the band gap of the g-TiO2 (Eg = 2.80 eV) compared to the w-TiO2 (Eg = 3.10 eV). The XPS revealed variations in the surface states, composition, Ti4+ to Ti3+ ratio, and oxygen vacancies in the g-TiO2. The Ti3+ and oxygen vacancy-induced enhanced visible light photocatalytic activity of g-TiO2 was confirmed by degrading different model dyes. The enhanced photoelectrochemical response under visible light irradiation further supported the improved performance of the g-TiO2 owing to a decrease in the electron transfer resistance and an increase in charge transfer rate. During the TiO2 treatment process, electricity generation in MFC was also observed, which was ~0.3979 V corresponding to a power density of 70.39 mW/m2. This study confirms narrow band gap TiO2 can be easily obtained and used effectively as photocatalysts and photoelectrode material.