Scalability of biomass-derived graphene derivative materials as viable anode electrode for a commercialized microbial fuel cell: A systematic review

Microbial fuel cell(MFC) is an advanced bioelectrochemical technique that can utilize biomass materials in the process of simultaneously generating electricity and biodegrading or bio transforming toxic pollutants from wastewater. The overall performance of the system is largely dependent on the efficiency of the anode electrode to enhance electron transportation. Furthermore, the anode electrode has a significant impact on the overall cost of MFC setup. Hence, the need to explore research focused towards developing cost-effective material as anode in MFC. This material must also have favourable properties for electron transportation. Graphene oxide(GO) derivatives and its modification with nanomaterials have been identified as a viable anode material. Herein, we discussed an economically effective strategy for the synthesis of graphene derivatives from waste biomass materials and its subsequent fabrication into anode electrode for MFC applications. This review article offers a promising approach towards replacing commercial graphene materials with biomass-derived graphene derivatives in a view to achieve a sustainable and commercialized MFC.

Bimetallic catalysts as electrocatalytic cathode materials for the oxygen reduction reaction in microbial fuel cell:A review

Microbial fuel cell(MFC) is one synchronous power generation device for wastewater treatment that takes into account environmental and energy issues, exhibiting promising potential. Sluggish oxygen reduction reaction(ORR) kinetics on the cathode remains by far the most critical bottleneck hindering the practical application of MFC. An ideal cathode catalyst should possess excellent ORR activity, stability, and costeffectiveness, experiments have demonstrated that bimetallic catalysts are one of the most promising ORR catalysts currently. Based on this, this review mainly analyzes the reaction mechanism(ORR mechanisms, synergistic effects), advantages(combined with characterization technologies), and typical synthesis methods of bimetallic catalysts, focusing on the application effects of early Pt-M(M = Fe, Co, and Ni) alloys to bifunctional catalysts in MFC, pointing out that the main existing challenges remain economic analysis, long-term durability and large-scale application, and looking forward to this. At last, the research trend of bimetallic catalysts suitable for MFC is evaluated, and it is considered that the development and research of metal-organic framework(MOF)-based bimetallic catalysts are still worth focusing on in the future, intending to provide a reference for MFC to achieve energy-efficient wastewater treatment.

The growth of biopolymers and natural earthen sources as membrane/separator materials for microbial fuel cells:A comprehensive review

Microbial fuel cell(MFC)technology has emerged as an effective solution for energy insecurity and bioremediation.However,identifying suitable components(particularly separators or membranes)with the required properties,such as low cost and high performance,remains challenging and restricts practical application.Commercial membranes,such as Nafion,exhibit excellent performance in MFC.However,these membranes have high production costs,which considerably increase the overall MFC unit cell cost.Among the numerous types,the separators or membranes developed from biopolymers and naturally occurring earthen sources have proven to be a novel and efficient concept due to their natural abundance,cost-effectiveness(approximately$20 m^(-2),$5 m^(-2),and$1 kg-1for biopolymers,ceramics,and earthensources,respectively),structural properties,proton transportation,manufacturing and modification ease,and environmental friendliness.In this review,we emphasize cost-effective renewable green materials(biopolymers,bio-derived materials,and naturally occurring soil,clay,ceramics or minerals)for MFC applications for the first time.Biopolymers with good thermal,mechanical,and water retention properties,sustainability,and environmental friendliness,such as cellulose and chitosan,are typically preferred.Furthermore,the modification or introduction of various functional groups in biopolymers to enhance their functional properties and scale MFC power density is explored.Subsequently,separator/membrane development using various bio-sources(such as coconut shells,banana peels,chicken feathers,and tea waste ash)is described.Additionally,naturally occurring sources such as clay,montmorillonite,and soils(including red,black,rice-husk,and Kalporgan soil)for MFC were reviewed.In conclusion,the existing gap in MFC technology was filled by providing recommendations for future aspects based on the barriers in cost,environment,and characteristics.

Influence of Cathode Modification by Chitosan and Fe^(3+)on the Electrochemical Performance of Marine Sediment Microbial Fuel Cell

The electrochemical performances of cathode play a key role in the marine sediment microbial fuel cells(MSMFCs)as a long lasting power source to drive instruments,especially when the dissolved oxygen concentration is very low in seawater.A CTS-Fe^(3+)modified cathode is prepared here by grafting chitosan(CTS)on a carbon fiber surface and then chelating Fe^(3+)through the coordination process.The electrochemical performance in seawater and the output power of the assembled MSMFCs are both studied.The results show that the exchange current densities of CTS and the CTS-Fe^(3+)group are 5.5 and 6.2 times higher than that of the blank group,respectively.The potential of the CTS-Fe^(3+)modified cathode increases by 138 mV.The output power of the fuel cell(613.0 mW m^(-2))assembled with CTS-Fe^(3+)is 54 times larger than that of the blank group(11.4 mW m^(-2))and the current output corresponding with the maximum power output also increases by 56 times.Due to the valence conversion between Fe^(3+)and Fe^(2+)on the modified cathode,the kinetic activity of the dissolved oxygen reduction is accelerated and the depolarization capability of the cathode is enhanced,resulting higher cell power.On the basis of this study,the new cathode materials will be encouraged to design with the complex of iron ion in natural seawater as the catalysis for oxygen reduction to improve the cell power in deep sea.

Three-Dimensional N-Doped Carbon Nanotube/Graphene Composite Aerogel Anode to Develop High-Power Microbial Fuel Cell

Optimizing the structure of electrode materials is one of the most effective strategies for designing high-power microbial fuel cells(MFCs).However,electrode materials currently suffer from a series of shortcomings that limit the output of MFCs,such as high intrinsic resistance,poor electrolyte wettability,and low microbial load capacity.Here,a three-dimensional(3D)nitrogen-doped multiwalled carbon nanotube/graphene(N-MWCNT/GA)composite aerogel is synthesized as the anode for MFCs.Comparing nitrogen-doped GA,MWCNT/GA,and N-MWCNT/GA,the macroporous hydrophilic N-MWCNT/GA electrode with an average pore size of 4.24μm enables high-density loading of the microbes and facilitates extracellular electron transfer with low intrinsic resistance.Consequently,the hydrophilic surface of N-MWCNT can generate high charge mobility,enabling a high-power output performance of the MFC.In consequence,the MFC system based on N-MWCNT/GA anode exhibits a peak power density and output voltage of 2977.8 mW m^(−2)and 0.654 V,which are 1.83 times and 16.3%higher than those obtained with MWCNT/GA,respectively.These results demonstrate that 3D N-MWCNT/GA anodes can be developed for high-power MFCs in different environments by optimizing their chemical and microstructures.

Recovery of copper from copper slag using a microbial fuel cell and characterization of its electrogenesis

The microbial fuel cell, which can convert the chemical energy of organic matter into electricity via the catalytic action of microorganisms, is a novel environmentally friendly technology for wastewater treatment and energy generation. The electrical energy generated by the microbial fuel cell can be used as an alternative to a traditional external power source required to extract copper via electrolytic treatment. A dual-chamber microbial fuel cell(DMFC) for the treatment of copper slag sulfuric acid leach liquor was constructed. The electrogenesis performance of the DMFC and its ability to extract copper from the copper slag leachate were investigated. The results demonstrated that the maximum voltage was 540 mV when the DMFC achieved steady-state operation. The removal rate of copper ions was greater than 80.0%, and the maximum value was 92.1%. Moreover, X-ray diffraction and scanning electron microscopy were used to characterize the cathodal products. The results showed that the product deposited onto the cathode was copper and that its morphology was similar to that of the electrolytic copper powder. The DMFC can generate electricity and recover copper from copper slag simultaneously.

Melamine modified carbon felts anode with enhanced electrogenesis capacity toward microbial fuel cells

Surface electropositivity and low internal resistance are important factors to improve the anode performance in microbial fuel cells (MFCs). Nitrogen doping is an effective way for the modification of traditional carbon materials. In this work, heat treatment and melamine were used to modify carbon felts to enhance electrogenesis capacity of MFCs. The modified carbon felts were characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscopy (AFM) and malvern zeta potentiometer. Results show that the maximum power densities under heat treatment increase from 276.1 to 423.4 mW/m(2) (700 degrees C) and 461.5 mW/m(2) (1200 degrees C) and further increase to 472.5 mW/m(2) (700 degrees C) and 515.4 mW/m(2) (1200 degrees C) with the co-carbonization modification of melamine. The heat treatment reduces the material resistivity, improves the zeta potential which is beneficial to microbial adsorption and electron transfer. The addition of melamine leads to the higher content of surface pyridinic and quaternary nitrogen and higher zeta potential. It is related to higher MFCs performance. Generally, the melamine modification at high temperature increases the feasibility of carbon felt as MFCs's anode materials. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Nitrogen and Sulfur Co-doped Porous Carbon Derived from ZIF-8 as Oxygen Reduction Reaction Catalyst for Microbial Fuel Cells

Nitrogen and sulfur co-doped porous nanocarbon (ZIF-C-N-S) catalyst was successfully synthesized derived from ZIF-8 and thiourea precursors.The electrochemical measurements indicate that the as-obtained ZIF-C-N-S catalyst exhibits higher electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline electrolyte and superior durability-longer than commercial Pt/C catalyst.The enhancment of electrocatalytic activity mainly be come from the open pore structure,large specific surface area as well as the synergistic effect resulted from the co-doping of N and S atoms.In addition,the ZIF-C-N-S catalyst is also used as the air cathode catalyst in the microbial fuel cell (MFC) device.The maximum power density and stable output voltage of ZIF-C-N-S based MFC are 1315 mW/m2 and 0.48 V,respectively,which is better than that of Pt/C based MFC.

Sustainable biochar as an electrocatalysts for the oxygen reduction reaction in microbial fuel cells

Microbial fuel cells(MFCs)have gained remarkable attention as a novel wastewater treatment that simultaneously generates electricity.The low activity of the oxygen reduction reaction(ORR)remains one of the most critical bottlenecks limiting the development of MFCs.To date,although research on biochar as an electrocatalyst in MFCs has made tremendous progress,further improvements are needed to make it economically practical.Recently,biochars have been considered to be ORR electrocatalysts with developmental potential.In this review,the ORR mechanism and the essential requirements of ORR catalysts in MFC applications are introduced.Moreover,the focus is to highlight the material selection,properties,and preparation of biochar electrocatalysts,as well as the evaluation and measurement of biochar electrodes.Additionally,in order to provide comprehensive information on the specific applications of biochars in the field of MFCs,their applications as electrocatalysts,are then discussed in detail,including the uses of nitrogen-doped biochar and other heteroatom-doped biochars as electrocatalysts,poisoning tests for biochar catalysts,and the cost estimation of biochar catalysts.Finally,profound insights into the current challenges and clear directions for future perspectives and research are concluded.

A system combining microbial fuel cell with photobioreactor for continuous domestic wastewater treatment and bioelectricity generation

A coupled system consisting of an upflow membrane-less microbial fuel cell (upflow ML-MFC) and a photobioreactor was developed, and its effectiveness for continuous wastewater treatment and electricity production was evaluated. Wastewater was fed to the upflow ML-MFC to remove chemical oxygen demand (COD), phosphorus and nitrogen with simultaneous electricity generation. The effluent from the cathode compartment of the upflow ML-MFC was then continuously fed to an external photobioreactor for removing the remaining phosphorus and nitrogen using microalgae. Alone, the upflow ML-MFC produces a maximum power density of 481 mW/m 3 , and obtains 77.9% COD, 23.5% total phosphorus (TP) and 97.6% NH4+-N removals. When combined with the photobioreactor, the system achieves 99.3% TP and 99.0% NH4+-N total removal. These results show both the effectiveness and the potential application of the coupled system to continuously treat domestic wastewater and simultaneously generate electricity and biomass.

Electricity Generation Using Membrane-less Microbial Fuel Cell during Wastewater Treatment

upflow 模式膜更少微生物引起的燃料房间(ML-MFC ) 为废水处理被设计。小粒的石墨电极，在尺寸灵活，在 ML-MFC 被采用。当 biocatalyst 和人工的废水作为底层被测试，在厌氧的激活的污泥在场的微生物被使用。在电气化学地活跃的微生物丰富阶段期间， 536 mW 路 m 的稳定的力量产量 ? 3 被在批模式跑的 ML-MFC 与阳极体积的参考产生。在 ML-MFC 从批模式被改变到通常连续的模式以后，电压产量从 203 mV 减少了到大约 190 mV，显示那 planktonic 在 ML-MFC 的电气化学地活跃的细菌的紧张可以与自河一起被移走。周期的 voltammograms 证明依附的微生物比 planktonic 微生物拥有了更高的 bioelectrochemical 活动。到阴极的强迫的通风显然有益于电产生。更高的喂率和更长的电极距离两个都增加了电产生。coulombic 收益在整个学习是不超过 20% ，它是比有膜的 MFC 的低的。从阴极传播到阳极的溶解的氧可以消费底层的部分，这被建议。

Characterization of Fe/N-doped graphene as air-cathode catalyst in microbial fuel cells

This work proposed a simple and efficient approach for synthesis of durable and efficient non-precious metal oxygen reduction reaction（ORR） electro-catalysts in MFCs. The rod-like carbon nanotubes（CNTs）were formed on the Fe–N/SLG sheets after a carbonization process. The maximum power density of1210 ± 23 m W·mobtained with Fe–N/SLG catalyst in an MFC was 10.7% higher than that of Pt/C catalyst(1080 ± 20 mW ·m) under the same condition. The results of RDE test show that the ORR electron transfer number of Fe–N/SLG was 3.91 ± 0.02, which suggested that ORR catalysis proceeds through a four-electron pathway. The whole time of the synthesis of electro-catalysts is about 10 h, making the research take a solid step in the MFC expansion due to its low-cost, high efficiency and favorable electrochemical performance. Besides, we compared the electrochemical properties of catalysts using SLG, high conductivity graphene（HCG, a kind of multilayer graphene） and high activity graphene（HAG, a kind of GO） under the same conditions, providing a solution for optimal selection of cathode catalyst in MFCs.The morphology, crystalline structure, elemental composition and ORR activity of these three kinds of Fe–N/C catalysts were characterized. Their ORR activities were compared with commercial Pt/C catalyst.It demonstrates that this kind of Fe–N/SLG can be a type of promising highly efficient catalyst and could enhance ORR performance of MFCs.

Simultaneous Denitrification and Carbon Removal in Microbial Fuel Cells

In this article,microbial fuel cell( MFC) was used for simultaneous denitrification and carbon removal to ascertain their electricity generation performance. The results showed that strengthening domestication and enrichment of electrogenic bacteria had the best start-up effect. An increase in volumetric loading reduced the rate of pollutant removal but promoted the output voltage. The changes of working conditions such as influent concentration,sludge concentration and temperature had a great influence on the electricity generation performance of MFC,and their optimum values were 500 mg/L,2 000 mg/L and 35℃,respectively.

A Comprehensive Review on Oxygen Reduction Reaction in Microbial Fuel Cells

The focus of microbial fuel cell research in recent years has been on the development of materials,microbes,and transfer of charges in the system,resulting in a substantial improvement in current density and improved power generation.The cathode is generally recognized as the limiting factor due to its high-distance proton transfer,slow oxygen reduction reaction(ORR),and expensive materials.The heterogeneous reaction determines power gen-eration in MFC.This comprehensive review describes-recent advancements in the development of cathode mate-rials and catalysts associated with ORR.The recent studies indicated the utilization of different metal oxides,the ferrite-based catalyst to overcome this bottleneck.These studies conclude that some cathode materials,in parti-cular,graphene-based conductive polymer composites with non-precious metal catalysts provide substantial ben-efits for sustainable development in the field of MFCs.Furthermore,it also highlights the potentiality to replace the conventional platinum air cathode for the large-scale production of the next generation of MFCs.It was evi-dent from the experiments that cathode catalyst needs to be blended with conductive carbon materials to make cathode conductive and efficient for ORR.This review discusses various antifouling strategies for cathode biofoul-ing and its effect on the MFC performance.Moreover,it also depicts cost estimations of various catalysts essential for further scale-up of MFC technology.

Microbial Fuel Cells for Nitrate Removal in Ground Water

The increasing nitrate concentration in groundwater has become a serious concern all over the world. In this study, the double chamber microbial fuel cell (MFC) and single chamber MFC systems were proposed for simultaneous removal of chemical oxygen demand (COD) and nitrate (NO3- - N). Transforming the various variables (cathod materials, external resistance and initial concentrations of NO3- - N) of double chamber MFC to determine the optimal operating parameters. Observing the treatment effect of single chamber MFC when adding an external resistance. The results showed: in the case of connecting external circuit, the double chamber MFC could reach the best degradation effect of NO3- - N and COD when cathode and anode materials are made of stainless steel velvet, the external resistance of 100 Ω and the initial concentrations of NO3- - N of around 250 mg/L. The best degradation rate of NO3- - N and COD reached 66.88% and 82.85% respectively. Adding an external solar power to single chamber could enhance the treatment effect;specifically, NO3- - N and COD removal rate reached 65.06% and 70.42% respectively, 6.14% and 9.73% higher than without external power.

Carbon material-based anodes in the microbial fuel cells

For the performance improvement of microbial fuel cells(MFCs),the anode becomes a breakthrough point due to its influence on bacterial attachment and extracellular electron transfer(EET).On other level,carbon materials possess the following features:low cost,rich natural abundance,good thermal and chemical stability,as well as tunable surface properties and spatial structure.Therefore,the development of carbon materials and carbon-based composites has flourished in the anode of MFCs during the past years.In this review,the major carbon materials used to decorate MFC anodes have been systematically summarized,based on the differences in composition and structure.Moreover,we have also outlined the carbon material-based hybrid biofilms and carbon material-modified exoelectrogens in MFCs,along with the discussion of known strategies and mechanisms to enhance the bacteria-hosting capabilities of carbon material-based anodes,EET efficiencies,and MFC performances.Finally,the main challenges coupled with some exploratory proposals are also expounded for providing some guidance on the future development of carbon material-based anodes in MFCs.

Utilization of Nanomaterials as Anode Modifiers for Improving Microbial Fuel Cells Performance

Microbial fuel cells(MFCs)are an attractive innovation at the nexus of energy and water security for the future.MFC utilizes electrochemically active microorganisms to oxidize biodegradable substrates and generate bioelectricity in a single step.The material of the anode plays a vital role in increasing the MFC’s power output.The anode in MFC can be upgraded using nanomaterials providing benefits of exceptional physicochemical properties.The nanomaterials in anode gives a high surface area,improved electron transfer promotes electroactive biofilm.Enhanced power output in terms of Direct current(DC)can be obtained as the consequence of improved microbe-electrode interaction.However,several limitations like complex synthesis and degeneration of property do exist in the development of nanomaterial-based anode.The present review discusses different renewable nanomaterial applied in the anode to recover bioelectricity in MFC.Carbon nanomaterials have emerged in the past decade as promising materials for anode construction.Composite materials have also demonstrated the capacity to become potential anode materials of choice.Application of a few transition metal oxides have been explored for efficient extracellular electron transport(EET)from microbes to the anode.

Parameters Influencing Power Generation in Eco-friendly Microbial Fuel Cells

Pulp and papermaking industries generate high volumes of carbohydrate-rich effluents. Microbial fuel cell(MFC) technology is based on organic materials' consumption and efficient power production. Using a classical two-chamber lab-scale MFC design with an external resistance of2000 W, we investigated the effects of anode chamber biofilm adaptation(ACBA) and cathode chamber redox solutions(CCRS) on the operation efficiency of MFC when treating wastewater. In ACBA studies, biofilm growth activation showed an increase in the power density to 20.48, 35.18, and36.98 mW/m^2 when the acetate feeding concentrations were 3, 6, and 12 g/L,respectively. Improvement by biofilm adhesion on granular activated carbon(GAC) was examined by scanning electron microscopy(SEM). The obtained power density increased to 25.47, 33.42, and 40.39 mW/m^2 when the GAC particles concentrations were 0, 50, and 100 g/L, respectively. The generated power densities were 51.26 and 40.39 mW/m^2 as well as the obtained voltages were 0.41 and 0.72 V when the electrode area increased from 16 to 64 cm^2,respectively. Using the MFC optimized parameters, CCRS studies carried out using five different cathodic redox solutions. The results revealed that the use of manganese dioxide dissolved in hydrochloric acid generated the maximum power density of 112.6 mW/m^2, current density of 0.094 A/m^2, and voltage of1.20 V with a successful organic removal efficiency of 86.0% after 264 h of operation.

Electrochemical Properties of Electrodes with Different Shapes and Diffusion Kinetic Analysis of Microbial Fuel Cells on Ocean Floor

Microbial fuel cell(MFC) on the ocean floor is a kind of novel energy-harvesting device that can be developed to drive small instruments to work continuously.The shape of electrode has a great effect on the performance of the MFC.In this paper,several shapes of electrode and cell structure were designed,and their performance in MFC were compared in pairs:Mesh(cell-1) vs.flat plate(cell-2),branch(cell-3) vs.cylinder(cell-4),and forest(cell-5) vs.disk(cell-6) FC.Our results showed that the maximum power densities were 16.50,14.20,19.30,15.00,14.64,and 9.95 mWm-2 for cell-1,2,3,4,5 and 6 respectively.And the corre-sponding diffusion-limited currents were 7.16,2.80,18.86,10.50,18.00,and 6.900 mA.The mesh and branch anodes showed higher power densities and much higher diffusion-limited currents than the flat plate and the cylinder anodes respectively due to the low diffusion hindrance with the former anodes.The forest cathode improved by 47% of the power density and by 161% of diffusion-limited current than the disk cathode due to the former's extended solid/liquid/gas three-phase boundary.These results indicated that the shape of electrode is a major parameter that determining the diffusion-limited current of an MFC,and the differences in the elec-trode shape lead to the differences in cell performance.These results would be useful for MFC structure design in practical applica-tions.

Effect of bamboo charcoal filler on the performance of microbial fuel cell

微生物燃料电池（MFC）的阳极对提高MFC产电性能有至关重要的影响.利用竹炭比表面积大、吸附能力强等特性,将其作为“三合一”膜电极MFC的阳极填充材料,通过增大阳极比表面积来提高其产电能力.实验结果表明,加入竹炭至阳极室后,MFC最高输出电压（外接电阻1 000Ω时）由0.280V增大到0.387V,提高了38.2％,并且输出电压更加稳定;而最大功率密度也由原来的0.22 W/m3增大到1.42 W/m3,同时内阻降低了80.85％（由235 Ω降为45 Ω）;库仑效率由15.0％增大到25.6％.说明MF℃阳极室填充竹炭可以显著促进MFC的产电性能.