Brush Anode Research Articles

Preliminary evaluation of electricity recovery from palm oil mill effluent by anion exchange microbial fuel cell

This study assessed the viability of an anion-exchange microbial fuel cell (MFC) for extracting electricity from palm oil mill effluent (POME), a major pollutant in palm-oil producing regions due to increasing demand. The MFC incorporated a tubular membrane electrode assembly (MEA) with an air core, featuring a carbon-painted carbon-cloth cathode, an anion exchange membrane (AEM), and a nonwoven graphite fabric (NWGF) anode. An additional carbon brush (CB) anode was placed adjacent to the tubular MEA. The MFC operated under semi-batch conditions with POME replacement every 7 days. Results showed superior performance of the AEM, with the highest power density (Pmax) observed in POME-treated MFCs. Current and power density increased with CB addition; the best chemical oxygen demand (COD) removal efficiency reached 73 %, decreasing from 1249 to 332 mg/L with three CBs. The Pmax was 0.18 W/m−2(−|-) with 1000 mg/L COD and three CBs, dropping to 0.0031 W/m−2(−|-) without CB and at 410 mg/L COD. Anode resistance, calculated using organic matter supplementation, COD, and anode surface area, decreased with increased COD or surface area, improving electricity production. AEM and CB compatibility synergistically enhanced MFC performance, offering potential for POME wastewater treatment and energy recovery.

Anode biomass rather than soluble organic matter is fuel for electricity production in microbial fuel cell at longer hydraulic retention time

This study presents a novel method for independently calculating organic matter (OM) removal and electricity generation in a microbial fuel cell (MFC) treating sewage. This methodology used OM concentration as the exclusive variable for input, facilitating the prediction of electricity generation with variable Coulombic efficiency. The employed MFC, of tubular design, incorporates an air core surrounded by a carbon-based cathode, an anion exchange membrane, nonwoven graphite fabric, and encircled by twelve carbon brush anodes. This setup successfully reduced chemical oxygen demand (COD) from 180 to 50 mg L−1 and biological oxygen demand (BOD) from 84 to 15 mg L−1 within a 35 h hydraulic retention time (HRT). The resulting effluent BOD satisfies Japanese wastewater treatment standards. In the early HRT phase, the MFC exhibited rapid OM reduction, followed by a stabilization of OM concentration. Despite varying HRTs and the sustained OM levels at prolonged HRTs, the MFC consistently generated 0.29 ± 0.14 A m−2. This apparent contradiction prompted the consideration of additional OM sources from the anode biomass (Cb). Calculating electricity production based on OM concentration rather than OM degradation was achieved by assessing anode resistance (RAn) across different levels of OM supplementation, employing the Butler–Volmer equation. This approach, incorporating considerations for Cb and RAn, accurately reproduced MFC performance. It was observed that OM supplementation from Cb constituted 50% at 11 h HRT and escalated to 90% at 27 h HRT. Further analysis, including 16S rRNA gene-based microbial community profiling, indicated that higher cathode resistance (RCat) at 1.0 Ω m2, compared to a minimum RAn of 0.10 Ω m2, favored methanogenesis over electrogenesis on the carbon brushes. This finding underscores the importance of reducing RCat and minimizing electrode distance, coupled with enhancing the specific surface area of both electrodes, as crucial factors for the advancement of MFC technology.

Zinc-based metal organic framework on carbon fiber brush as a novel anode of yeast-based microbial fuel cell

A microbial fuel cell (MFC) is an eco-friendly device that uses living microorganisms' catalytic activity for energy harvesting. The power output of this device is still far from the targeted one. An improvement to the power can be accessed via the use of biocompatible high surface area anode materials. Metal-organic frameworks (MOFs) have a high surface area, crystalline, and can be prepared in different morphologies. MOF demonstrated excellent performance in various energy conversion/storage devices. For the first time, a standalone carbon fiber brush electrode modified with Zn-MOF is constructed via a simple hydrothermal approach. The prepared electrodes were investigated as the anode of yeast-based MFC. The MFC with Zn-MOF carbon fiber brush exhibited maximum current and power densities of 317 mA/m2 and 73.7 mW/m2, which are twofold those obtained using bare carbon brush anodes. The significant improvement in the MFC performance with modified carbon fiber brush would be related to the role of the Zn-MOF in facilitating the electron transfer between the anode and the yeast cells and thus promoting bio electrocatalytic activity as confirmed from the redox peaks that appeared during the cyclic voltammetry (CV) of the modified electrodes and supported by electrochemical impedance spectroscopy (EIS).

Bioelectricity production and bioremediation from sugarcane industry wastewater using microbial fuel cells with activated carbon cathodes

Clean energy and water are major challenges to meet for sustainable development. Microbial Fuel Cells or MFCs can treat wastewater with the treatment process becoming a method for capturing energy in the form of bioelectricity. In this work, biomass derived Activated Carbon was used as the MFC cathode with carbon yarn as the brush anode. Sugarcane processing plant wastewater was used to evaluate bioelectricity generation and contamination removal over multiple cycles. System performance was stable, this is attributed to absence of carboxylic acid functional group on cathode surface and the sufficiently developed bacteria biofilm on the anode. The reactors used were able to facilitate organic matter degradation continually. MFC reactors developed open circuit voltage of 870 ± 20 mV, and power density of 563 ± 30 mW/m2 with external resistors, having current density of 0.79 mA/m2. The chemical contamination of the wastewater was reduced from 1201 ± 60 mg/l to 240 ± 31 mg/l with average removal of 81%, with BOD removal efficiency of 86%. The utility of biomass derived Activated Carbon as a cathode material was evaluated with BET analysis, having a surface area of 230.131 m2/g for oxygen reduction. Surface feature includes distinct mesoporous structures for the growth of heterotrophs. Additionally, FTIR analysis of cathodes revealed the presence of heteroatoms on the carbon matrix which adds stability to its surface chemistry. This makes the cathode surface suitable for operation in real time conditions without corroding metal mesh collectors on which they are coated.

Reproducible polarization test methods and fair evaluation of polarization data by using interconversion factors in a single chamber cubic microbial fuel cell with a brush anode

MFC research has been conducted enormously in the last decade, and their electrochemical data has been accumulated enormously. Although reproducible measurement method and fair evaluation are essential elements in research, these elements are missing in MFC research. Herein, using single-chamber cubic MFCs, diverse polarization methods were conducted along with other electrochemical tests. 3-hour optimum resistance operation followed by 2-h open circuit time prevented power overshoots. In a faster polarization method, data reproducibility increased drastically, power and current were larger, and polarization resistance was smaller. In ERC-30 min, LSV-0.1, LSV-1, LSV-10 mV/s and, maximum power density was 1242, 1518, 2287 and 3417 mW/m2, and internal resistance 76, 63, 48 and 35 Ω, respectively. For fair evaluation of different polarization data, the interconversion factors were developed and applied. During the optimum resistance operation, average power and current densities were 994 mW/m2 and 3767 mA/m2, respectively. As similarly in the polarization tests, cathodic impedances (24.1 Ω) were 2.4 times larger than the anodic impedances (10.2 Ω). Charge transfer impedance (32.4 Ω) was the major component (>95%) in the electrodes and the whole cell (34.3 Ω). Ohmic impedance was detected only in the anode (0.2 Ω), and diffusion impedance was detected only in the cathodes (1.7 Ω). Cathodic capacitance (1.62 F) was 2.5 times larger than the anodic capacitance (0.64 F). Cyclic voltammogram cathodic capacitance (7.78 F) was 1.6 times larger than the anodic capacitance (4.76 F). Longer operation, lower internal resistance and higher anode performance increased coulombic and energy efficiencies. This study contains very important information on experimental accuracy and reproducibility, essential elements in research, and will greatly contribute to the firm foundation and the meaningful growth of the MFC research.

High current density with spatial distribution of Geobacter in anodic biofilm of the microbial electrolysis desalination and chemical-production cell with enlarged volumetric anode

The aim of this study was to establish the relationship between spatial distribution of Geobacter and electric intensity in the microbial electrolysis desalination and chemical-production cell (MEDCC) and to investigate the effect of enlarged volumetric anode on the performance of MEDCC. The MEDCC was constructed with nine carbon brush anodes (length × diameter = 11 cm × 3 cm) as enlarged volumetric anode, and operated by feeding with 1 g/L acetate as substrate and 35 g/L NaCl as artificial seawater under the applied voltages of 1.2–4.5 V. Spatial distribution of Geobacter in the anodic biofilm was determined according to the bacterial community analysis on 27 biofilm samples from the top, middle and bottom layers of anodes (i.e., with distance of 4.5, 10, and 15.5 cm to the cathode, respectively). Results showed that the enlarged volumetric anode significantly improved the performance of MEDCC. The maximum desalination rate and current density reached 338.5 ± 21.8 mg/L∙h and 55.7 ± 3.7 A/m2 in the MEDCC, respectively. The electric intensity values decreased with the distance from the anode to the cathode and formed an uneven distribution in the anode chamber. The samples in the top layer of anodes had the highest average 16S rRNA gene copy number of Geobacter of 1.55 × 107 copies/μL, which was 18 times higher than that in the bottom layer of anodes. A linear relation was established between the spatial distribution of Geobacter and electric intensity (R2 = 0.994–0.999). The electric intensity gradient created the uneven spatial distribution of Geobacter in the biofilms of volumetric anode. Results from this study could be useful to enrich Geobacter in the anodic biofilm thus to improve the performance of MEDCC.

Pilot scale microbial fuel cells using air cathodes for producing electricity while treating wastewater

Microbial fuel cells (MFCs) can generate electrical energy from the oxidation of the organic matter, but they must be demonstrated at large scales, treat real wastewaters, and show the required performance needed at a site to provide a path forward for this technology. Previous pilot-scale studies of MFC technology have relied on systems with aerated catholytes, which limited energy recovery due to the energy consumed by pumping air into the catholyte. In the present study, we developed, deployed, and tested an 850 L (1400 L total liquid volume) air-cathode MFC treating domestic-type wastewater at a centralized wastewater treatment facility. The wastewater was processed over a hydraulic retention time (HRT) of 12 h through a sequence of 17 brush anode modules (11 m2 total projected anode area) and 16 cathode modules, each constructed using two air-cathodes (0.6 m2 each, total cathode area of 20 m2) with the air side facing each other to allow passive air flow. The MFC effluent was further treated in a biofilter (BF) to decrease the organic matter content. The field test was conducted for over six months to fully characterize the electrochemical and wastewater treatment performance. Wastewater quality as well as electrical energy production were routinely monitored. The power produced over six months by the MFC averaged 0.46 ± 0.35 W (0.043 W m–2 normalized to the cross-sectional area of an anode) at a current of 1.54 ± 0.90 A with a coulombic efficiency of 9%. Approximately 49 ± 15 % of the chemical oxygen demand (COD) was removed in the MFC alone as well as a large amount of the biochemical oxygen demand (BOD5) (70%) and total suspended solid (TSS) (48%). In the combined MFC/BF process, up to 91 ± 6 % of the COD and 91 % of the BOD5 were removed as well as certain bacteria (E. coli, 98.9%; fecal coliforms, 99.1%). The average effluent concentration of nitrate was 1.6 ± 2.4 mg L–1, nitrite was 0.17 ± 0.24 mg L–1 and ammonia was 0.4 ± 1.0 mg L–1. The pilot scale reactor presented here is the largest air-cathode MFC ever tested, generating electrical power while treating wastewater.

Enhanced Microbial Electrochemical Systems Performance by Optimizing the “Anode-Collector” Collection Mode: From Enhancement Mechanism to Construction Strategy

The microbial electrochemical system (MES) provides a new idea for the recovery and utilization of energy contained in wastewater. Still, the inherent resistance of the commonly used carbon-based anode material of the system often leads to power loss during the electron collection process and reduces the system performance, especially in scale-up operations. Through experimental verification, we found that integrating a metal current collector into the anode and increasing its branches was an effective strategy to reduce power loss and enhance the system performance in the case of a limited area of a current collector. The system with five branches could obtain a higher maximum power density (1613.3 ± 155.5 mW/m2), 1.36 times that of system with one collector branch (1185.1 ± 29.1 mW/m2), and the corresponding power loss reduced by 86.7%. COMSOL software was used in MES to reveal the enhancement mechanism and provided effective “anode-collector” construction strategies. The simulation results indicated that at least three current collector branches should be integrated into the anode in scale-up MES to avoid excessive power loss. When using an optimized “anode-collector” combination to treat domestic wastewater, the system could quickly capture energy in sewage (≈20 h), and the effluent met the grade A standard of COD for municipal wastewater treatment plants in China (<50 mg/L). Moreover, this strategy only needed approximately $0.061 of cost per milliwatt of electricity generated, lower than the commonly used carbon brush anode ($0.08/mW). These results demonstrate that optimizing the “anode-collector” collection mode can effectively enhance energy harvesting and system performance with low cost and has promising potential for future practical applications.

Bioelectrochemical regulation accelerates biomethane production from waste activated sludge: Focusing on operational performance and microbial community

Bioelectrochemical regulation represents a newly emerging strategy to enhance anaerobic digestion (AD) of biowastes. Herein, a novel microbial electrolysis cell (MEC) system, equipped with a pair of carbon brush anode and hybrid Ti/RuO2-graphite felt cathode, was developed to explore the role of bioelectrochemical regulation in the proliferation/enrichment of functional microbes and methanation of waste activated sludge. The methane production was significantly improved by applying bioelectrochemical regulation. The maximum methane yield was 16.4 mL/L-reactor at the applied external voltage 1.2 V and solids retention time 15 d, 8.6-time higher than that of a single AD. Further analysis demonstrated that bioelectrochemical regulation selectively enriched electroactive fermentative partners and methanogens (especially Thermincola, Methanobacterium) in the MEC-AD system and built up a robust syntrophic interaction. This drove the decomposition of complex organics and concurrent bioelectroreduction of CO2 in biogas and subsequently enhanced methane generation. Besides, bioelectrochemical simulation attenuated N2O emissions and enhanced the dewaterability of digested sludge.

Comparison of different chemical treatments of brush and flat carbon electrodes to improve performance of microbial fuel cells

Anodes in microbial fuel cells (MFCs) can be chemically treated to improve performance but the impact of treatment on power generation has not been examined for different electrode base materials. Brush or flat anodes were chemically treated and then compared in identical two-chambered MFCs using the electrode potential slope (EPS) analysis to quantify the anode resistances. Flat carbon cloth anodes modified with carbon nanotubes (CNTs) produced 1.42 ± 0.06 W m−2, which was 3.2 times more power than the base material (0.44 ± 0.00 W m−2), but less than the 2.35 ± 0.1 W m−2 produced using plain graphite fiber brush anodes. An EPS analysis showed that there was a 90% decrease in the anode resistances of the CNT-treated carbon cloth and a 5% decrease of WO3 nanoparticle-treated brushes compared to unmodified controls. Certain chemical treatments can therefore improve performance of flat anodes, but plain brush anodes achieved the highest power densities.

3D modelling of bioelectrochemical systems with brush anodes under fed-batch and flow conditions

A 3D mathematical model of the different processes occurring in a bioelectrochemical system (BES) equipped with carbon fibres brush anodes has been implemented. The model combines equations of electrical charge conservation, with hydrodynamics, convection, diffusion and kinetics of the involved processes, such as biofilm formation, bioelectrochemical and electrochemical reactions. The model has been solved for different scenarios. A system with a single BES cell was simulated under fed-batch and flow conditions, as three cells hydraulically connected in-series have been also considered. Model parameters were derived from the literature or from experimental data obtained with replicate of a single-chamber BES under different conditions. The model solution provides space profiles of potential and current, concentration of substrate and protons and biofilm under transient conditions. Velocity profiles may also be calculated with simulations under flow conditions. The effects of operative conditions on the performance of the process, both for current generation and substrate removal, have been quantified. The model provides a versatile tool to design and optimise BES reactors with fibre brush anodes.

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.

Electrophoretic deposition of graphene oxide on carbon brush as bioanode for microbial fuel cell operated with real wastewater

Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm−2 to 381 mWm−2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements.

Electricity generation and storage in microbial fuel cells with porous polypyrrole-base composite modified carbon brush anodes

Microbial fuel cells (MFCs) equipped with three-dimensional (3D) electrodes are widely used in wastewater treatment. However, the power output and energy storage of MFCs with 3D anodes are still limited in application. Here, a biocompatible, capacitive, and adhesive polypyrrole, carboxymethyl cellulose, carbon nanotube/carbon brush (PPy-CMC-CNTs/CB) material was prepared, that was integrated into a composite to obtain a high-capacitance 3D anode. An SEM showed that the composite anode had a 3D-macroporous structure that had a large surface area, providing more places for the attachment and growth of microorganisms. The power density of the MFC with a PPy-CMC-CNTs/CB composite anode (2970 mW/m2) was 4.34 times greater than that of an MFC with a bare anode (683 mW/m2). In the tests with a charge for 15 min and discharge for 45 min, it was observed that the stored charge of the bioanode (333 mC/cm2) was 23.67 times higher than that of the bare anode (14.07 mC/cm2). High-throughput sequencing revealed that the modified composite anode had excellent biocompatibility and selective enrichment of electrogenic bacteria. This study provided a simple and environmentally-friendly modification to enable a PPy-CMC-CNTs/CB composite anode to promote energy storage and output performance of MFCs.

Effects of vertical and horizontal configurations of different numbers of brush anodes on performance and electrochemistry of microbial fuel cells

To maximize wastewater treatment and energy production by microbial fuel cells (MFCs), it is important to design the optimal anode arrangement. In this study, four brushes were tested horizontally or vertically to the cathode as the number of the anodes increased from one to four. In the horizontal configuration, adding the anodes greatly reduce electrode resistance and enhanced cell performance, showing four anodes (H4) was the best. In the vertical configuration, two anodes (V2) showed greatest performance and greatest decrease in anode resistance. Compared with one anode, maximum power increased by 59% in H4 and by 18% in V2; anode polarization resistance decreased by 95% in H4 and by 74% in V2; anode impedance decreased by 91% in H2 and by 73% in V2. Cathode resistance was relatively constant, showing adding anodes had negligible effect on it. Because diffusion resistance increases with increasing distance between an anode and a cathode, the vertical anodes should have different diffusion resistance and performances. In this study, adding more anodes vertically decreased cell performance in V3 and V4. However, in a cyclic voltammetry test, current production was substantially increased when the third and the fourth brush anodes were introduced in the both arrangements. Compared with one anode, current production increased by 200% in H4 and by 205% in V4. It shows that the external electrical input relieved diffusion resistance and increased current generation and that installing anodes away from the cathode is a good strategy to increase current production in a system with external power supply such as microbial electrolysis cell. Based on the results, we suggest the following strategy: i) install multiple anodes horizontally along the cathode; ii) install multiple anodes in the second row horizontally along the cathode; iii) install multiple anodes both horizontally and vertically if there is an external power supply.

Quantifying the factors limiting performance and rates in microbial fuel cells using the electrode potential slope analysis combined with electrical impedance spectroscopy

Improving power generation of microbial fuel cells (MFCs) requires better methods to quantify the impact of the solution chemistry on performance. While buffer concentration and conductivity have been indicated to impact performance of flat (carbon cloth) anodes, we were able for the first to time to quantitatively determine the impact of the phosphate buffer solution (PBS) concentration separate from conductivity on electrode resistances of commonly used brush anodes and activated carbon cathodes. Using the electrode potential slope (EPS) method, we showed that the anode resistance decreased by 64% (from 14.6 ± 0.1 mΩ m2 to 5.3 ± 0.1 mΩ m2) by increasing the PBS concentration from 50 to 200 mM. There was no appreciable change in the cathode resistance (17.0 ± 0.1 mΩ m2, 50 mM; 18.9 ± 0.2 mΩ m2, 200 mM) although overall performance increased due to a larger cathode experimental working potential (ECat,e0-50= 268.9 ± 0.9 mV, ECat,e0-200= 370 ± 1 mV). Adding phosphate buffer to low conductivity synthetic wastewater containing 0.25 g L−1 sodium acetate decreased the anode resistance by 52% (from 59.1 ± 0.2 mΩ m2 to 28.1 ± 0.1 mΩ m2), but increasing only conductivity by adding NaCl or acetate had little impact on electrode resistances. Using electrochemical impedance spectroscopy (EIS), we determined the reasons for these responses. The cathode was limited by oxygen reduction reaction (ORR) kinetics, while the brush anode was limited by mass transfer (proton diffusion), consistent with the impact of buffer concentration on performance. These results have important implications for operation of MFCs as increasing solution conductivity alone, for example, by adding seawater, will not be sufficient to improve anode performance.

High‐performance Microbial Fuel Cell Using Metal Ion Complexes as Electron Acceptors

Metal complex‐microbial fuel cells (MFCs) have been investigated in this work with intent manufacturing highly efficient MFC batteries. The performance of metal complex MFCs was evaluated by polarization and discharge experiments using a battery consisting of three MFC unit cells. The results indicated that the performance of the [Fe(III)(4,4′‐dimethyl‐2,2′‐bipyridyl)3]‐MFC was much better than the other MFC containing Cr(VI) or Fe(III) as an electron acceptor. At a discharging current of 3 mA (17.6 A/m3), the average discharging potential was found to be 0.927 V under a parallel‐connection, sustaining longer than 20 h with an open circuit voltage of 1.210 V. [Fe(III)(4,4′‐dimethyl‐2,2′‐bipyridyl)3]‐MFC showed much higher electrochemical parameters than Cr(VI)‐MFC and Fe(III)‐MFC. Highest maximum power of 34.87 Wm−3 could be obtained from the battery consisting of three MFCs in parallel‐connection, when each cell contains a carbon brush anode and a graphite plate. MFC battery containing a carbon brush anode and a carbon brush cathode showed better polarization and discharging performance. In particular, the maximum power of 45.45 Wm−3 was achieved. By installing the maximum amount of carbon brush anode and adjusting the amount of carbon brush cathode and the electron acceptors, the magnitude of current and the maximum power can be maximized.

Boosting the Energy Density of Flexible Asymmetric Supercapacitor with Three Dimensional Fe2O3 Composite Brush Anode

Flexible asymmetric supercapacitor is fabricated with three dimensional(3D) Fe2O3/Ni(OH)2 composite brush anode and Ni(OH)2/MoO2 honeycomb cathode. Particularly for 3D composite brush anode, a layer of thin Fe2O3 film is firmly adhered on a 3D Ni brush current collector with the assist of Ni(OH)2, functioning as both adherence layer and pseudocapacitive active material. The unique 3D Ni brush current collector possesses large surface area and stretching architecture, which facilitate to achieve the composite anode with high gravimetric capacitance of 2158 F/g. In terms of cathode, Ni(OH)2 and MoO2 have a synergistic effect to improve the specific capacitance, and the resulting Ni(OH)2/MoO2 honeycomb cathode shows a very high gravimetric capacitance up to 3264 F/g. The asymmetric supercapacitor(ASC) has balanced cathode and anode, and exhibits an ultrahigh gravimetric capacitance of 1427 F/g and an energy density of 476 Wh/kg. The energy density of ASC is 3–4 times higher than those of other reported aqueous electrolyte-based supercapacitors and even comparable to that of commercial lithium ion batteries. The device also shows marginal capacitance degradation after 1000 cycles’ bending test, demonstrating its potency in the application of flexible energy storage devices.

Performance Assessment of Multi-Electrodes Reactors for Scaling-up Microbial Fuel Cells

The microbial fuel cells (MFCs) represent an emerging technology for converting directly organic waste into electricity. In recent years, the application of MFCs to the energy recovery from wastes has been widely explored. The main aspect that limits the development and implementation of this technology on a larger-scale is the possibility of realizing its scaling-up. In order to overcome this critical factor, it is useful to analyze novel MFCs configurations based on compact reactors with multiple electrodes.In this paper, single chamber MFCs provided with multiple fiber brush anodes and a single air-cathode were designed and realized by using a 3D printer. The reactors had a cubic shape, with a cylindrical chamber of 350 mL in volume. The mineral medium added with sodium acetate (0.25 M), as sole source of carbon and energy to sustain exoelectrogenic bacteria metabolism, were used. Anodes biofilms were prepared from a mix of compost and sodium acetate dissolved in phosphate buffer solution (0.2M), in a 1:3 ratio. The performances of two MFCs provided with two and three anodes were assessed in terms of voltage, current density and power density. These performances were compared to those of a smaller cubic MFC (30mL).

Agri‐food waste valorisation

Agri‐food waste valorisation