Increased power from a two-chamber microbial fuel cell with a low-pH air-cathode compartment

Pt-supported air-cathodes still need improvement if their application in MFC technology is to be sustainable. In this context, the efficiency of an air-cathode was studied with respect to the pH of the solution it was exposed to. Voltammetry showed that oxygen reduction was no longer limited by H⁺ availability for pH lower than 3.0. A new MFC was designed with a catholyte compartment setup between the anode compartment and the air-cathode. With a catholyte compartment at pH 1.0, the MFC provided up to 5 W/m², i.e., 2.5-fold the power density obtained with the same anode and cathode in a single-chamber MFC working at pH 7.5. Current density exceeded 20 A/m². The benefit of low-pH in the catholyte chamber largely counterbalanced the mass transfer hindrance due the membrane that separated the two compartments. The MFC kept 66% its performance during nine days of continuous operation.     

Electricity production of a microbial fuel cell stack integrated into a sink drain pipe

In this study, five two-chambered microbial fuel cells (MFCs) were hydraulically connected in series to constitute a MFC stack, which was integrated into a sink drain pipe for kitchen wastewater treatment. Performances of the MFC stack operating with artificial and real wastewater were studied. Considering the practical application, the voltage response to different flow rates and temperatures of the substrate was also investigated. It was found that the MFC stack could achieve a reasonable performance, with an average open circuit voltage of 3.44 ± 0.02 V, a peak power of 45.74 ± 1.39 mW (i.e. 809.27 mW/m²) and a coulombic efficiency of 78.2 ± 3.6 %. The MFC performance was disturbed by the flushing process, but could recover after a few minutes. The results also suggest that the MFC stack can operate after flushing by the substrate at 50 °C, above which irreversible performance deterioration was observed. The proposed MFC stack is expected to serve as a potential power source for lighting and low-power devices, especially in off-grid rural areas.     

Effect of electrolyte pH on the rate of the anodic and cathodic reactions in an air-cathode microbial fuel cell

The measurement of electricity generation from an air-cathode microbial fuel cell (MFC) with a mixed bacteria culture at different pH showed that this MFC could tolerate an initial (feed solution) pH as high as 10. The optimal initial pH was between 8 and 10 with higher current generation compared to lower or higher pH. The bacterial metabolism exhibited a buffer effect and changed the electrolyte pH. The impedance spectra of the anode and cathode of the MFC at the open-circuit potential (OCP) revealed that the anodic microbial process preferred a neutral pH and microbial activities decreased at higher or lower pH; while the cathodic reaction was improved with increasing pH.     

Enhanced Performance of a Microbial Fuel Cell with a Capacitive Bioanode and Removal of Cr (VI) Using the Intermittent Operation

This study investigated a system which simultaneously produced electricity and stored energy in the MFC integrated MnO₂-modified capacitive bioanode. Compared to the noncapacitive anode, the maximum power density of MFC with MnO₂-modified bioanode reached 16.47 W m^?3, which was 3.5 times higher than that of the bare anode (4.71 W m^?3). During the charging-discharging experiment, the MFC with a capacitance bioanode has a higher average peak current density of 5.06 mA cm^?2 and 36 times larger than that with the bare bioanode. With the capacitive electrode, it is possible to let the MFC at the same time for production and storage of renewable electricity. Then two different operations (intermittent operation and continuous operation) of the MFC with a capacitive bioanode were studied to degrade Cr (VI) in cathode chamber. Results showed that the Cr (VI) removal rates of intermittent operation are much higher than that of continuous operation under the same time in the closed circuit state. This is due to the good ability of storing and releasing electron of the biological capacitor with MnO₂ modified material. And this study showed that MFC with a capacitive bioanode is better adapted to treat heavy metal pollutants by intermittent mode.     

Construction and Operation of Microbial Fuel Cell with Chlorella vulgaris Biocathode for Electricity Generation

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/m² 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.     

Nanoporous gold electrode prepared from gold compact disk as the anode for the microbial fuel cell

The electrodes (anode and cathode) have an important role in the efficiency of a microbial fuel cell (MFC), as they can determine the rate of charge transfer in an electrochemical process. In this study, nanoporous gold electrode, prepared from commercially available gold-made compact disk, is utilized as the anode in a two-chamber MFC. The performance of nanoporous gold electrode in the MFC is compared with that of gold film, carbon felt and acid-heat-treated carbon felt electrodes which are usually employed as the anode in the MFCs. Electrochemical surface area of nanoporous gold electrode exhibits a 7.96-fold increase rather than gold film electrode. Scanning electron microscopy analysis also indicates the homogeneous biofilm is formed on the surface of nanoporous gold electrode, while the biofilm formed at the surface of acid-heat-treated carbon felt electrode shows rough structure. Electrochemical studies show although modifications applied on carbon felt electrodes improve its performance, nanoporous gold electrode, due to its structure and better electrochemical properties, acts more efficiently as the MFC’s anode. The maximum power density produced by nanoporous gold anode is 4.71 mW m^?2 at current density of 16.00 mA m^?2, while this value for acid-heat-treated carbon felt anode is 3.551 mW m^?2 at current density of 9.58 mA m^?2.     

Thickness difference induced pore structure variations in cellulosic separators for lithium-ion batteries

The pore structure of the separator is crucial to the performance of a lithium-battery as it affects the cell resistance. Herein, a straightforward approach to vary the pore structure of Cladophora cellulose (CC) separators is presented. It is demonstrated that the pore size and porosity of the CC separator can be increased merely by decreasing the thickness of the CC separator by using less CC in the manufacturing of the separator. As the pore size and porosity of the CC separator are increased, the mass transport through the separator is increased which decreases the electrolyte resistance in the pores of the separator. This enhances the battery performance, particularly at higher cycling rates, as is demonstrated for LiFePO₄/Li half-cells. A specific capacity of around 100 mAh g^?1 was hence obtained at a cycling rate of 2 C with a 10 µm thick CC separator while specific capacities of 40 and close to 0 mAh g^?1 were obtained for separators with thicknesses of 20 and 40 µm, respectively. As the results also showed that a higher ionic conductivity was obtained for the 10 µm thick CC separator than for the 20 and 40 µm thick CC separators, it is clear that the different pore structure of the separators was an important factor affecting the battery performance in addition to the separator thickness. The present straightforward, yet efficient, strategy for altering the pore structure hence holds significant promise for the manufacturing of separators with improved performance, as well as for fundamental studies of the influence of the properties of the separator on the performance of lithium-ion cells.     

Optimization of Bioelectricity Generation in Fed-Batch Microbial Fuel Cell: Effect of Electrode Material,Initial Substrate Concentration,and Cycle Time

Effective wastewater treatment and electricity generation using dual-chamber microbial fuel cell (MFC) will require a better understanding of how operational parameters affect system performance. Therefore, the main aim of this study is to investigate the bioelectricity production in a dual-chambered MFC-operated batch mode under different operational conditions. Initially, platinum (Pt) and mixed metal oxide titanium (Ti-TiO₂) electrodes were used to investigate the influence of the electrode materials on the power generation at initial dissolved organic carbon (DOC) concentration of 400 mg/L and cycle time of 15 days. MFC equipped with Ti-TiO₂ electrode performed better and was used to examine the effect of influent DOC concentration and cycle time on MFC performance. Increasing influent DOC concentration resulted in improving electricity generation, corresponding to a 1.65-fold increase in power density. However, decrease in cycle time from 15 to 5 days adversely affected reactor performance. Maximum DOC removal was 90?±?3 %, which was produced at 15-day cycle time with an initial DOC of 3,600 mg/L, corresponding to maximum power generation of about 7,205 mW/m².     

Poly(vinyl alcohol) separators improve the coulombic efficiency of activated carbon cathodes in microbial fuel cells

High-performance microbial fuel cell (MFC) air cathodes were constructed using a combination of inexpensive materials for the oxygen reduction cathode catalyst and the electrode separator. A poly(vinyl alcohol) (PVA)-based electrode separator enabled high coulombic efficiencies (CEs) in MFCs with activated carbon (AC) cathodes without significantly decreasing power output. MFCs with AC cathodes and PVA separators had CEs (43%–89%) about twice those of AC cathodes lacking a separator (17%–55%) or cathodes made with platinum supported on carbon catalyst (Pt/C) and carbon cloth (CE of 20%–50%). Similar maximum power densities were observed for AC-cathode MFCs with (840 ± 42 mW/m²) or without (860 ± 10 mW/m²) the PVA separator after 18 cycles (36 days). Compared to MFCs with Pt-based cathodes, the cost of the AC-based cathodes with PVA separators was substantially reduced. These results demonstrated that AC-based cathodes with PVA separators are an inexpensive alternative to expensive Pt-based cathodes for construction of larger-scale MFC reactors.     

Municipal Solid Waste Landfill Leachate Treatment and Electricity Production Using Microbial Fuel Cells

Microbial fuel cells were designed and operated to treat landfill leachate while simultaneously producing electricity. Two designs were tested in batch cycles using landfill leachate as a substrate without inoculation (908 to 3,200 mg/L chemical oxygen demand (COD)): Circle (934 mL) and large-scale microbial fuel cells (MFC) (18.3 L). A total of seven cycles were completed for the Circle MFC and two cycles for the larger-scale MFC. Maximum power densities of 24 to 31 mW/m² (653 to 824 mW/m³) were achieved using the Circle MFC, and a maximum voltage of 635 mV was produced using the larger-scale MFC. In the Circle MFC, COD, biological oxygen demand (BOD), total organic carbon (TOC), and ammonia were removed at an average of 16%, 62%, 23%, and 20%, respectively. The larger-scale MFC achieved an average of 74% BOD removal, 27% TOC removal, and 25% ammonia reduction while operating over 52 days. Analysis of the microbial characteristics of the leachate indicates that there might be both supportive and inhibiting bacteria in landfill leachate for operation of an MFC. Issues related to scale-up and heterogeneity of a mixed substrate remain.     

Enhanced performance of lithium polymer batteries using a V2O5–PEG composite cathode

A new concept is proposed to realize solid-state high-performance lithium polymer batteries in which two different polymers are used as ionically conductive matrices in the cathode and in the separator. A solid, low molecular weight poly(ethylene glycol) was used in the cathode while a blend with a higher molecular weight poly(ethylene oxide) (PEO) was used in the separator. The enhanced transport properties in the cathodic compartment allow us to discharge the battery (190 mAh g⁻¹) at a moderate temperature (65°C) in a reasonable time (about 3.3 h). Batteries cycled at 100°C showed enhanced performance with respect to PEO-based batteries. At a power density of about 416 W kg⁻¹, energy density as high as 460 Wh kg⁻¹, based on the weight of the active material, was achieved in about 1 h of discharge. The work was developed within the ALPE (Advanced Lithium Polymer Electric Vehicle Battery) project, an Italian integrated project devoted to the realization of lithium polymer batteries for electric vehicle applications, in collaboration with the Osaka National Research Institute.     

Influence of solvent type on porosity structure and properties of polymer separator for the Li-ion batteries

Polyethylene-supported polymethyl methacrylate/poly(vinylidene fluoride-co-hexafluoropropylene) separator for gel polymer lithium-ion battery use was prepared with a mixed solvent of n-butanol and acetone. The prepared separator was characterized with scanning electron spectroscopy and X-ray diffraction, and its performance was investigated by electrochemical impedance spectroscopy and battery charge/discharge test. Compared to the separator prepared with acetone, the separator prepared with the mixed solvent shows an enhanced porosity (from 42 to 49 %) and electrolyte uptake (from 104 to 125 %). The ionic conductivity of the corresponding gel polymer electrolyte is improved from 2.81 to 3.39 mS cm^?1, the discharge capacity retention of the LiCoO₂/artificial graphite battery is increased from 95 to 98 % after 100 cycles at 0.5 C, and the discharge capacity of the battery at 1 C increases by 4 %.     

An enhanced poly(vinylidene fluoride) matrix separator with high density polyethylene for good performance lithium ion batteries

A sponge-like poly(vinylidene fluoride)/high density polyethylene (PVDF/HDPE) separator exhibiting high ionic conductivity and transference number of Li⁺ ion for lithium ion battery has been prepared by non-solvent induced phase separation (NIPS) method. HDPE fillers with size smaller than 250 nm are prepared with moderated reverse phase emulsion. The ion conductivity of PVDF/HDPE separator saturated with 1.0 M LiPF₆–ethylene carbonate (EC)/dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) (1:1:1, v/v/v) can be up to 2.54 mS cm^?1 at 25 °C, which is higher than that of pristine PVDF separator (1.85 mS cm^?1). The transference number of lithium ion with PVDF/HDPE separator is 0.495, better than that with commercial PP separator (0.33) and pristine PVDF separator (0.27). What is more, LiCoO₂/Li cells assembled with PVDF/HDPE separator show good C-rate and cycling performance which indicates great potential in serving as a good candidate of polymer separator for lithium ion batteries application.     

Flexible,high-wettability and thermostable separator based on fluorinated polyimide for lithium-ion battery

To meet the booming demands for lithium-ion battery (LIB), it is practically significant to promote its electrochemical performance and safety. In our work, a novel kind of flexible membrane as separator for LIB is prepared via phase inversion method with soluble polyimide (SPI) containing trifluoromethyl substituent, which is synthesized from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 4,4′-oxydiphthalic anhydride (ODPA). The SPI separator shows 5% weight loss temperature (T_d5%) of 535 °C and maintains intrinsic dimension even after heating at 200 °C. The SPI membrane depicts a sponge-like structure with abundant interconnected pores and delivers a dominant porosity (67%). The SPI membrane displays desired electrolyte wettability, validated by contact angle tests (16.2° and 46.8° for SPI membrane and PE separator, respectively) and electrolyte uptake tests (420 and 132% for SPI membrane and PE separator, respectively). The LIB with SPI membrane as separator exhibits nice ionic conductivity (0.92 mS cm^?1) than that with PE separator (0.30 mS cm^?1), and therefore affords better electrochemical performance, such as cycling stability and rate capability.     

Effect of Temperature on the Catalytic Ability of Electrochemically Active Biofilm as Anode Catalyst in Microbial Fuel Cells

In this study we report the effect of temperature on the catalytic ability of an electrochemically active biofilm based on mixed‐culture to oxidize acetate and found the optimum temperature showing maximal catalytic activity and power output. Electrochemical characterization of biofilm and power output and internal resistance of microbial fuel cell (MFC) have been investigated at different temperatures. When temperature increased from 30 to 45 °C the catalytic ability of biofilms to oxidize acetate increased following the Arrhenius law with apparent activation energy of 44.85 kJ/mol. At temperatures higher than 48 °C, however, the bioelectrocatalytic current decreased. At 53 °C the bacterial metabolism was in inactivation. The optimum working temperature of the biofilm was 45 °C, producing current of 1339 µA cm^?2. This current was almost three times higher than 527 µA cm^?2 at 30 °C. The MFC performance at different temperatures showed consistent temperature dependence to that of a semi‐batch cell, which implies that anode catalytic ability in MFC is the main limit factor for increasing power output. A maximum power output of 1065 mW m^?2 was also observed at 45 °C and it was 1.5 times higher than 764 mW m^?2 at 30 °C. The increased MFC performance from 30 °C to 45 °C is lower in comparison with about three times higher increase in semi‐batch cells. This could be due to other factors such as proton migration rate in membrane of MFC, which can be seen from that the internal resistance value of 121.5 Ω in the MFC at 45 °C was only slightly lower than 177.6 Ω at 30 °C. Also, some other factors such as cell configuration which would limit the power output and can be further optimized. This work contributes to the study of influence from temperature on anodic electrochemically active biofilm activity and their subsequent influence on MFC performance and reports the optimal temperature for biofilm activity based on mixed‐culture.     

Biotic Cathode of Graphite Fibre Brush for Improved Application in Microbial Fuel Cells

The biocathode in a microbial fuel cell (MFC) system is a promising and a cheap alternative method to improve cathode reaction performance. This study aims to identify the effect of the electrode combination between non-chemical modified stainless steel (SS) and graphite fibre brush (GFB) for constructing bio-electrodes in an MFC. In this study, the MFC had two chambers, separated by a cation exchange membrane, and underwent a total of four different treatments with different electrode arrangements (anodeǁcathode)—SSǁSS (control), GFBǁSS, GFBǁGFB and SSǁGFB. Both electrodes were heat-treated to improve surface oxidation. On the 20th day of the operation, the GFBǁGFB arrangement generated the highest power density, up to 3.03 W/m³ (177 A/m³), followed by the SSǁGFB (0.0106 W/m³, 0.412 A/m³), the GFBǁSS (0.0283 W/m³, 17.1 A/m³), and the SSǁSS arrangements (0.0069 W/m⁻³, 1.64 A/m³). The GFBǁGFB had the lowest internal resistance (0.2 kΩ), corresponding to the highest power output. The other electrode arrangements, SSǁGFB, GFBǁSS, and SSǁSS, showed very high internal resistance (82 kΩ, 2.1 kΩ and 18 kΩ, respectively) due to the low proton and electron movement activity in the MFC systems. The results show that GFB materials can be used as anode and cathode in a fully biotic MFC system.     

Ammonia treatment of carbon cloth anodes to enhance power generation of microbial fuel cells

Changes in microbial fuel cell (MFC) architecture, materials, and solution chemistry can be used to increase power generation by microbial fuel cells (MFCs). It is shown here that using a phosphate buffer to increase solution conductivity, and ammonia gas treatment of a carbon cloth anode substantially increased the surface charge of the electrode (from 0.38 to 3.99 meq m⁻²), and improved MFC performance. Power increased to 1640 mW m⁻² (96 W m⁻³) using a phosphate buffer, and further to 1970 mW m⁻² (115 W m⁻³) using an ammonia-treated electrode. The combined effects of these two treatments boosted power production by 48% compared to previous results using this air-cathode MFC. In addition, the start up time of an MFC was reduced by 50%.     

Substrate cross-conduction effect on the performance of serially connected microbial fuel cell stack

This study presented a new design of scalable, air-cathode microbial fuel cell (MFC) stack that shared a common fuel feed passage. As two individual cells were electrically connected in series by metal wires and hydraulically joined by conductive substrate flow, the performance degradation phenomenon was observed. The open circuit voltage (OCV) and low current behavior of stacked MFC were lower than should be expected. This energy loss was proposed to be a consequence of parasitic current flow due to the substrate cross-conduction effect and can be likely minimized through controlling the distance between the anode electrodes or/and the cross-sectional area of substrate flow. The unique and simple water distribution system of the tubular MFC stack would contribute to the further scale-up and implementation of MFC technologies, especially for wastewater treatment.     

Electrochemically Prepared Manganese Oxide as a Cathode Material for a Microbial Fuel Cell

This work describes the construction of a mediatorless microbial fuel cell (MFC) using the microorganism Acetobacter aceti as the biocatalyst in the anode compartment with glucose as a fuel. The periplasmic membrane bound pyrroloquinoline quinone (PQQ) containing enzymes of these genera provide fast and highly efficient oxidation of a wide variety of substrates and helps in the direct routing of electrons to the anode. We describe our preliminary findings with regard to the use of electrochemically deposited manganese oxide films on carbon substrates as cathode materials in MFCs. Manganese oxide was electrochemically deposited on carbon paper in the presence and in the absence of the surfactant, sodium lauryl sulfate (SLS). Electrochemical characterizations of the electrodeposited films are carried out by cyclic voltammetry and impedance spectroscopy. Structural characterization of the film is carried out by XRD, XPS, and SEM. The XPS studies reveal that the presence of Mn⁴⁺ (as MnO₂) in the absence of SLS and Mn^3+/2+ (as Mn₃O₄or Mn₂O₃ or MnOOH) ion in the presence of SLS. The power output obtained from MnO₂ cathode was 666 ± 9 mW m^?3 and it is the highest value reported for MFCs with cubical configuration with the same cathode.     

Novel aqueous spongy foams made of three-dimensionally dispersed wood-fiber: entrapment and stabilization with NFC/MFC within capillary foams

This article describes the preparation of novel aqueous spongy foams that are composed of three-dimensionally distributed wood-fiber networks stabilized with nanofibrillate cellulose (NFC) and/or microfibrillated cellulose (MFC). The free standing aqueous spongy foams were prepared with the entrapment of NFC and/or MFC—stabilized air-in-water (A/W) capillary foams using “gel trapping technique”. The stability of spongy foams could be controlled by manipulating the volume fraction of NFC and/or MFC and a secondary liquid immiscible with the continuous phase of the NFC and/or MFC suspension. Possible morphology and mechanical distribution of NFC and/or MFC within spongy foams were verified with optical microscope, SEM, and functional load-bearing method. Owing to three-dimensionally dispersed wood-fiber structure, ultra-lightweight (0.01–0.06 g/cm³), high porosity (>90%), and microporous (10–80 μm), the NFC and/or MFC reinforced spongy foams, improved compressional strength-vertical direction obviously, from 0.0 to more than 13.78 kPa.