Activated microporous-mesoporous carbon derived from chestnut shell as a sustainable anode material for high performance microbial fuel cells

Efficient anode material derived from nutshells for bio-energy production in microbial fuel cell

Biochar is a carbonaceous solid that is prepared through thermo-chemical decomposition of biomass under an inert atmosphere. The present study compares the performance of biochar prepared from Peanut shell, coconut shell and walnut shell in dual chamber microbial fuel cell. The physicochemical and electrochemical analysis of biochar reveals that prepared biochar is macroporous, amorphous, biocompatible, and electrochemically conductive. Polarization studies show that Peanut shell biochar (PSB) exhibited a maximum power density of 165 mW/m2 followed by Coconut shell biochar (CSB) Activated Charcoal (AC) and Walnut shell biochar (WSB). Enhanced power density of PSB was attributed to its surface area and suitable pore size distribution which proved conducive for biofilm formation. Furthermore, the high electrical capacitance of PSB improved the electron transfer between microbes and anode.

Study of the influence of nanoscale porosity on the microbial electroactivity between expanded graphite electrodes and Geobacter sulfurreducens biofilms

Expanded graphite (EG) electrodes gather several advantages for their utilization in microbial electrochemical technologies (MET). Unfortunately, the low microbial electroactivity makes them non-practical for implementing them as electrodes. The objective of this work is to explore the enhancement of microbial electroactivity of expanded graphite (commercial PV15) through the generation of nanopores by CO2 treatment. The changes in properties were thoroughly analysed by TG, XRD, Raman, XPS, gas adsorption, SEM and AFM, as well as microbial electroactivity in the presence of Geobacter sulfurreducens. Nanopores remarkably enhance the microbially derived electrical current (60-fold increase). Given the inaccessibility of micron-sized bacteria to these nanopores, it is suggested that the electric charge exchanged by electroactive microorganisms might be greatly affected by the capability of the electrode to compensate these charges through ion adsorption. The increased microbial current density produced on activated PV15 opens the possibility of using such materials as promising electrodes in MET.

Microporous nitrogen-rich biomass derived anode catalyst in clay membrane MFC for kitchen wastewater treatment

Microbial fuel cells (MFC) have emerged as a sustainable wastewater treatment technique that offers simultaneous energy generation; however, the high cost of electrodes and their reduced catalytic activity have hindered their widespread adoption. To overcome this, an activated carbon synthesised from Areca nut husk was coated on different anodes viz. Carbon cloth and Stainless Steel (SS) mesh. Activated carbon was found to be highly porous with a carbon content of 85.39%, and a surface area of 767.98 m2/g, and was found to be amorphous with a high degree of graphitic structure. The electrical conductivities of the catalyst-coated SS mesh and carbon cloth were comparable, and the performance of the MFC was studied using both electrodes as anodes. A batch MFC with modified SS mesh as anode exhibited the highest power density of 155.35 mW/m3 in synthetic wastewater and 101.68 mW/m3 in kitchen wastewater, with COD removal efficiencies of 95.32% and 95.24%, respectively. In a continuous mode, the MFC delivered a maximum current density and power of 52.38 mA/m2 and 21.60 mW, respectively, with a maximum COD removal efficiency of 80.70% for an HRT of 20 hrs. These findings underscore the viability of using biomass-derived activated carbon as an anode catalyst in both batch and continuous modes of MFC.

Synergistic advancements in sewage-driven microbial fuel cells: novel carbon nanotube cathodes and biomass-derived anodes for efficient renewable energy generation and wastewater treatment

Microbial fuel cells (MFCs) offer a dual solution of generating electrical energy from organic pollutants-laden wastewater while treating it. This study focuses on enhancing MFC performance through innovative electrode design. Three-dimensional (3D) anodes, created from corncobs and mango seeds via controlled graphitization, achieved remarkable power densities. The newly developed electrode configurations were evaluated within sewage wastewater-driven MFCs without the introduction of external microorganisms or prior treatment of the wastewater. At 1,000°C and 1,100°C graphitization temperatures, corncob and mango seed anodes produced 1,963 and 2,171 mW/m2, respectively, nearly 20 times higher than conventional carbon cloth and paper anodes. An advanced cathode composed of an activated carbon-carbon nanotube composite was introduced, rivaling expensive platinum-based cathodes. By optimizing the thermal treatment temperature and carbon nanotube content of the proposed cathode, comparable or superior performance to standard Pt/C commercial cathodes was achieved. Specifically, MFCs assembled with corncob anode with the proposed and standard Pt/C cathodes reached power densities of 1,963.1 and 2,178.6 mW/m2, respectively. Similarly, when utilizing graphitized mango seeds at 1,100°C, power densities of 2,171 and 2,151 mW/m2 were achieved for the new and standard cathodes, respectively. Furthermore, in continuous operation with a flow rate of 2 L/h, impressive chemical oxygen demand (COD) removal rates of 77% and 85% were achieved with corncob and mango seed anodes, respectively. This work highlights the significance of electrode design for enhancing MFC efficiency in electricity generation and wastewater treatment.

The restricted mass transfer inside the anode pore channel affects the electroactive biofilms formation, community composition and the power production in microbial electrochemical systems

Porous anodes improve system performance in microbial electrochemical systems by increasing the specific surface area for electroactive bacteria. In this study, multilayer anodes with different pore diameters were constructed to assess the impact of pore size and depth on anode performance. This layered structure makes detecting electroactive biofilms more accessible layer by layer, which is the first study to examine electroactive biofilms' molecular biology and electrochemical properties at different depths in pores with varied pore sizes. The millimeter-scale pores inside the bioanode have a limited effect in increasing power. The larger the pore diameter, the higher the maximum power density (Pmax) obtained. The Pmax of anodes with 4 mm pore (1.91 ± 0.15 W m-2) was 1.4 times higher than that of the non-perforated (1.37 ± 0.07 W m-2) and 0.5 mm pore anodes (1.39 ± 0.04 W m-2). Electricigens can colonize into pore channels for at least 10 mm with a pore diameter ≥3 mm and current densities >0.05 A m-2. However, in the pores channel with 0.5 mm diameter, electricigens can only colonize to a depth of 2 mm. The biofilm thickness, electricity output, metabolic activity, and biocommunity changed with pore depth and were restricted by the limited mass transfer. The Geobacter sp. was the dominant species in inter-pore biofilms, with 43.8 %-78.6 % in abundance and decreased in quantity as pore depth increased. The inter-pore biofilms on the outer layer contributed a current density of 0.17 ± 0.003 A m-2, while that of the inner layer was only 0.02 ± 0.01 A m-2. Further studies found that the pore edge mass transfer effect can contribute up to 75 % of the current. The mass transfer process at the pore edge region could be a multidirectional mass transfer rather than a pore channel mass transfer.

Optimal aeration area of cathode electrode in the batch type of microbial fuel cells with non-woven interface

Microbial fuel cells (MFCs) are based on the biochemical reaction of microorganisms to decompose organic wastewater for converting chemical energy into power energy. MFCs are considered an environmentally friendly technology that is gaining popularity due to their simultaneous digestion and energy production abilities. To enhance its real application in wastewater treatment, this study proposes to use a non-woven material for replacing the usage of expensive membranes in MFCs. In addition, the study aims to consider a series of different aeration areas of cathode electrodes for finding an optional design. Results have shown that the adoption of non-woven with 0.45 μm can effectively prohibit the diffusion of oxygen into the anode chamber. Moreover, the non-woven material played an important role as an interface between the anode and cathode, enhancing the MFC performance. The usage of suitable non-woven material can replace the role of the membrane when applied in real wastewater applications. The results have shown that the case study where a combination of a 50% aeration area of the cathode electrodes with 25% exposure of the cathode plate in the air yielded relatively better aeration in terms of a higher current density of 250 mA/m², higher power density of 220 mW/m², and higher open voltage circuit of 0.4 V, compared to other case studies considered. These results indicate the optimal aeration configuration for MFCs applied in commercial wastewater treatment in the future.

Cattail-Grass-Derived Porous Carbon as High-Capacity Anode Material for Li-Ion Batteries

Cattail-grass-derived porous carbon as high-capacity anode materials were prepared via high-temperature carbonization and activation with KOH. The samples exhibited different structures and morphologies with increasing treatment time. It was found that the cattail grass with activation treatment-1 (CGA-1) sample obtained at 800 °C for 1 h presented excellent electrochemical performance. As an anode material for lithium-ion batteries, CGA-1 showed a high charge-discharge capacity of 814.7 mAh g-1 at the current density of 0.1 A g-1 after 400 cycles, which suggests that it has a great potential for energy storage.

Comparative review on microbial electrochemical technologies for resource recovery from wastewater towards circular economy and carbon neutrality

Newly arising concepts such as the circular economy and carbon neutrality motivate resource recovery from wastewater. This paper reviews and discusses state-of-the-art microbial electrochemical technologies (METs), specifically microbial fuel cells (MFCs), microbial electrolysis cells (MECs) and microbial recycling cells (MRCs), which enable energy generation and nutrient recovery from wastewater. Mechanisms, key factors, applications, and limitations are compared and discussed. METs are effective in energy conversion, demonstrating advantages, drawbacks and future potential as specific scenarios. MECs and MRCs exhibited greater potential for simultaneous nutrient recovery, and MRCs offer the best scaling-up potential and efficient mineral recovery. Research on METs should be more concerned with lifespan of materials, secondary pollutants reduction and scaled-up benchmark systems. More up-scaled application cases are expected for cost structures comparison and life cycle assessment of METs. This review could direct the follow-up research, development and successful implementation of METs for resource recovery from wastewater.

Lignocellulose reconstituted shape-controllable self-supporting carbonaceous capacitance-anodes with high electron transfer rates for high-performance microbial electrochemical system

Natural biomass is a promising candidate for manufacturing an efficient anode in the microbial electrochemical system (MES) for its abundance and low cost. However, the structure and performance of the electrode highly depend on the biomass species. A simple and sustainable method for creating a self-supporting electrode is proposed by freeze-drying and carbonizing a blend of cellulose, lignin, and hemicellulose. This strategy leads to a cork-like structure and improved mechanical strength of the lignocellulose carbon. A power density of 4780 ± 260 mW m^-2 (CLX-800) was achieved, which was the highest record for unmodified lignocellulose-based anodes in the microbial fuel cells. The morphological as lamellar multilayer and rich in hydrophilic functional groups could facilitate the formation of thick electroactive biofilms and enrich Geobacter with the highest abundance of 92.3%. The CLX material is expected to be the ideal electrode for high performance and functionally controllability.

Three-Dimensional Carbon Monolith Coated by Nano-TiO2 for Anode Enhancement in Microbial Fuel Cells

A three-dimensional (3D) anode is essential for high-performance microbial fuel cells (MFCs). In this study, 3D porous carbon monoliths from a wax gourd (WGCM) were obtained by freeze-drying and carbonization. Nano-TiO2 was further coated onto the surface of WGCM to obtain a nano-TiO2/WGCM anode. The WGCM anode enhanced the maximum power density of MFCs by 167.9% compared with the carbon felt anode, while nano-TiO2/WGCM anode additionally increased the value by 45.8% to achieve 1396.2 mW/m2. WGCM enhancement was due to the 3D porous structure, the good conductivity and the surface hydrophilicity, which enhanced electroactive biofilm formation and anodic electron transfer. In addition, nano-TiO2 modification enhanced the enrichment of Acinetobacter, an electricigen, by 31.0% on the anode to further improve the power production. The results demonstrated that the nano-TiO2/WGCM was an effective anode for power enhancement in MFCs.

A three-dimensional phenolic-based carbon anode for microbial electrochemical system with customized macroscopic pore structure to promote interior bacteria colonization

Microbial electrochemical system (MES) is an emerging wastewater treatment technology that compensates the energy demands of containments removal by in situ converting the chemical energy of organic pollutants. As the structure for exoelectrogens and the reaction site of extracellular electron transfer (EET), the anode is essential for MES. The future commercial application of MES requires efficiency and large-scale fabrication available anode. In this study, a 3D anode with millimeter-scale pores (3D-MPA) was successfully constructed by sacrificial template method, with low-cost phenolic resin as carbon precursor and polymethyl methacrylate (PMMA) pellets as template. With customized and ordered pore of 1 mm, the 3D-MPAs allowed the microorganisms to colonize inside, improving anodic space utilization efficiency. Different carbonization temperature in tested range from 700 °C to 1000 °C regulated the micrometer-scale convex structures and surface roughness of 3D-MPAs, causing electrochemical performance changes. The 3D-MPA-900 obtained the largest electroactive surface area (102 ± 4.1 cm²) and smallest ohmic resistance (1.8 ± 0.09 Ω). Equipped with MES, 3D-MPA-900 reached the highest power density and current density (2590 ± 25 mW m^-2 and 5.20 ± 0.07 A m^-2). Among tested 3D-MPA, the excellent performance of 3D-MPA-900 might be attributed by its convex structures with suitable size and surface coverage. The surface roughness of 3D-MPA-900 enhanced the microorganism adherence, which then promoted EET on anode surface. Generally, phenolic-based 3D-MPA made of sacrificial-template method had controllable porous structure, large-scale fabrication availability, high chemical stability and excellent mechanical property, which could be promising for the commercial application of MES.

Applications of Nanomaterials in Microbial Fuel Cells: A Review

Microbial fuel cells (MFCs) are an environmentally friendly technology and a source of renewable energy. It is used to generate electrical energy from organic waste using bacteria, which is an effective technology in wastewater treatment. The anode and the cathode electrodes and proton exchange membranes (PEM) are important components affecting the performance and operation of MFC. Conventional materials used in the manufacture of electrodes and membranes are insufficient to improve the efficiency of MFC. The use of nanomaterials in the manufacture of the anode had a prominent effect in improving the performance in terms of increasing the surface area, increasing the transfer of electrons from the anode to the cathode, biocompatibility, and biofilm formation and improving the oxidation reactions of organic waste using bacteria. The use of nanomaterials in the manufacture of the cathode also showed the improvement of cathode reactions or oxygen reduction reactions (ORR). The PEM has a prominent role in separating the anode and the cathode in the MFC, transferring protons from the anode chamber to the cathode chamber while preventing the transfer of oxygen. Nanomaterials have been used in the manufacture of membrane components, which led to improving the chemical and physical properties of the membranes and increasing the transfer rates of protons, thus improving the performance and efficiency of MFC in generating electrical energy and improving wastewater treatment.

Nutrient limitation regulates the properties of extracellular electron transfer and hydraulic shear resistance of electroactive biofilm

Understanding the roles of nutrient restriction in extracellular electron transfer (EET) and stability of mixed electroactive biofilm is essential in pollutant degradation and bioenergy production. However, the relevant studies are still limited so far. Herein, the effect of nutrient restriction on the EET pathways and stability of mixed electroactive biofilm was explored. It was found that the electroactive Pseudomonas and Geobacter genera were selectively enriched in the biofilms cultured under total nutrient and P-constrained conditions, and two EET pathways including direct and indirect were found, while Rhodopseudomonas genus was enriched in the N-constrained biofilm, which only had the direct EET pathway. Moreover, multiple analyses including 2D confocal Raman spectra revealed that P-constrained biofilm was rich in extracellular polymeric substances (EPS) especially for polysaccharide, presented a dense and uniform layered distribution, and had better stability than N-constrained biofilm with lower EPS and biofilm with heterostructures cultured under total nutrient conditions.

Biomass-Derived Carbon Anode for High-Performance Microbial Fuel Cells

: Although microbial fuel cells (MFCs) have been developed over the past decade, they still have a low power production bottleneck for practical engineering due to the ineffective interfacial bioelectrochemical reaction between exoelectrogens and anode surfaces using traditional carbonaceous materials. Constructing anodes from biomass is an effective strategy to tackle the current challenges and improve the efficiency of MFCs. The advantage features of these materials come from the well-decorated aspect with an enriched functional group, the turbostratic nature, and porous structure, which is important to promote the electrocatalytic behavior of anodes in MFCs. In this review article, the three designs of biomass-derived carbon anodes based on their final products (i.e., biomass-derived nanocomposite carbons for anode surface modification, biomass-derived free-standing three-dimensional carbon anodes, and biomass-derived carbons for hybrid structured anodes) are highlighted. Next, the most frequently obtained carbon anode morphologies, characterizations, and the carbonization processes of biomass-derived MFC anodes were systematically reviewed. To conclude, the drawbacks and prospects for biomass-derived carbon anodes are suggested.

Review on Material and Design of Anode for Microbial Fuel Cell

Microbial Fuel Cell (MFC) is a bio-electrochemical system that generates electricity by anaerobic oxidation of substrates. An anode is the most critical component because the primary conversion of wastewater into electrons and protons takes place on the surface of the anode, where a biofilm is formed. This paper describes the essential properties of the anode and classifies its types according to the material used to make it. Anode material is responsible for the flow of electrons generated by the microorganism; hence biocompatibility and conductivity can considered to be the two most important properties. In this paper, the various modification strategies to improve the performance of anodes of MFC are explained through the review of researchers’ published work in this field. The shape and size of the anode turned out to be very significant as the microbial growth depends on the available surface area. The attachment of biofilm on the surface of an anode largely depends on the interfacial surface chemistry. Methods for improving MFC performance by altering the anode material, architecture, biocompatibility, and longevity are discussed with a future perspective giving special importance to the cost.

Nano-Biochar as a Sustainable Catalyst for Anaerobic Digestion: A Synergetic Closed-Loop Approach

Nowadays, the valorization of organic wastes using various carbon-capturing technologies is a prime research area. The anaerobic digestion (AD) technology is gaining much consideration in this regard that simultaneously deals with waste valorization and bioenergy production sustainably. Biochar, a well-recognized carbonaceous pyrogenic material and possessing a broad range of inherent physical and chemical properties, has diverse applications in the fields of agriculture, health-care, sensing, catalysis, carbon capture, the environment and energy. The nano-biochar-amended anaerobic digestion approach has intensively been explored for the past few years. However, an inclusive study of multi-functional roles of biochar and the mechanism involved for enhancing the biogas production via the AD process still need to be evaluated. The present review inspects the significant role of biochar addition and the kinetics involved, further focusing on the limitations, perspectives, and challenges of the technology. Additionally, the techno-economic analysis and life-cycle assessment of biochar-aided AD process for the closed-loop integration of biochar and AD and possible improvement practices are discussed.

Sludge Derived Carbon Modified Anode in Microbial Fuel Cell for Performance Improvement and Microbial Community Dynamics

The conversion of activated sludge into high value-added materials, such as sludge carbon (SC), has attracted increasing attention because of its potential for various applications. In this study, the effect of SC carbonized at temperatures of 600, 800, 1000, and 1200 °C on the anode performance of microbial fuel cells and its mechanism are discussed. A pyrolysis temperature of 1000 °C for the loaded electrode (SC1000/CC) generated a maximum areal power density of 2.165 ± 0.021 W·m⁻² and a current density of 5.985 ± 0.015 A·m⁻², which is 3.017- and 2.992-fold that of the CC anode. The addition of SC improves microbial activity, optimizes microbial community structure, promotes the expression of c-type cytochromes, and is conducive to the formation of electroactive biofilms. This study not only describes a technique for the preparation of high-performance and low-cost anodes, but also sheds some light on the rational utilization of waste resources such as aerobic activated sludge.

Denitrification performance and microbial community of bioreactor packed with PHBV/PLA/rice hulls composite

In this study, a novel biodegradable PHBV/PLA/rice hulls (PPRH) composite was applied and tested as biofilm attachment carrier and carbon source in two bioreactors for biological denitrification process. The denitrification performance, effect of operational conditions and microbial community structure of PPRH biofilm were evaluated. The batch experiment results showed that PPRH-packed bioreactor could completely remove 50 mg L^-1 of NO₃^--N at natural pH (ca. 7.5) and room temperature. The continuous flow experiments indicated that high NO₃^--N removal efficiency (77%-99%) was achieved with low nitrite (<0.48 mg L^-1) and ammonia (<0.81 mg L^-1) accumulation, when influent NO₃^--N concentration was 30 mg L^-1 and hydraulic retention time was 2-6 h. Furthermore, the microbial community analysis indicated that bacteria belonging to genus Diaphorobacter in phylum Proteobacteria were the most dominant and major denitrifiers in denitrification. In summary, PPRH composite was a promising carbon source for biological nitrate removal from water and wastewater.

Trends in renewable energy production employing biomass-based biochar

Tremendous population growth and industrialization have increased energy consumption unprecedentedly. The depletion of fossil-based energy supplies necessitates the exploration of solar, geothermal, wind, hydrogen, biodiesel, etc. as a clean and renewable energy source. Most of these energy sources are intermittent, while bioelectricity, biodiesel, and biohydrogen can be produced using abundantly available organic wastes regularly. The production of various energy resources requires materials that are costly and affect the applicability at a large scale. Biomass-derived materials (biochar) are getting attention in the field of bioenergy due to their simple method of synthesis, high surface area, porosity, and availability of functional groups for easy modification. Biochar synthesis using various techniques is discussed and their use as an electrode (anodic/cathodic) in a microbial fuel cell (MFC), catalysts in transesterification, and anaerobic digestion for energy production are reviewed. Renewable energy production using biochar would be a sustainable approach to create an energy secure world.

Carbon-Based Composites as Anodes for Microbial Fuel Cells: Recent Advances and Challenges

Owing to the low price, chemical stability and good conductivity, carbon-based materials have been extensively applied as the anode in microbial fuel cells (MFCs). In this review, apart from the charge storage mechanism and anode requirements, the major work focuses on five categories of carbon-based anode materials (traditional carbon, porous carbon, nano-carbon, metal/carbon composite and polymer/carbon composite). The relationship is demonstrated in depth between the physicochemical properties of the anode surface/interface/bulk (porosity, surface area, hydrophilicity, partical size, charge, roughness, etc.) and the bioelectrochemical performances (electron transfer, electrolyte diffusion, capacitance, toxicity, start-up time, current, power density, voltage, etc.). An outlook for future work is also proposed.

Bioanodes containing catalysts from onion waste and Bacillus subtilis for energy generation from pharmaceutical wastewater in a microbial fuel cell

Performance of the FAOW8 + B. subtilis bioanode in an MFC (a 14-day test) using pharmaceutical wastewater (pH = 9.2) as a substrate.

Chestnut-Derived Activated Carbon as a Prospective Material for Energy Storage

In this work, we present the preparation and characterization of biomass-derived activated carbon (AC) in view of its application as electrode material for electrochemical capacitors. Porous carbons are prepared by pyrolysis of chestnut seeds and subsequent activation of the obtained biochar. We investigate here two activation methods, namely, physical by CO2 and chemical using KOH. Morphology, structure and specific surface area (SSA) of synthesized activated carbons are investigated by Brunauer-Emmett-Teller (BET) technique and scanning electron microscopy (SEM). Electrochemical studies show a clear dependence between the activation method (influencing porosity and SSA of AC) and electric capacitance values as well as rate capability of investigated electrodes. It is shown that well-developed porosity and high surface area, achieved by the chemical activation process, result in outstanding electrochemical performance of the chestnut-derived porous carbons.

Improved bio-electricity production in bio-electrochemical reactor for wastewater treatment using biomass carbon derived from sludge supported carbon felt anode

Microbial fuel cell (MFC), a promising bio-electrochemical reactor could decompose organics in wastewater by redox processes of electro-active microorganism in anode and produce bio-energy, and the total MFC performance could mainly rely on electrochemical performance anode. Here, biomass carbon derived from municipal sludge was employed as low-cost and high-performance bio-anode for enhancing bioelectricity generation and wastewater treatment in MFC simultaneously. The electrochemical tests demonstrated that the large electrochemical active surface area, strong conductivity, and good biocompatibility in sludge carbon (SC) electrode resulted in higher power density (615.2 mW m^-2) and lower power loss (5.4%) than those of none carbon (NC) electrode in long term operation. After 30-cycle of continuous running, the low loss of chemical oxygen demand (COD) removal was achieved up to 5.2%, which was smaller than that of NC electrode (14.1%), indicating that the MFC with SC anode could effectively treat wastewater and keep stable redox processes in anode electrode. After the formation of biofilm, the charge transfer resistance of SC electrode (16.38 Ω) was 72.4% lower than that of NC electrode (59.35 Ω). High-throughput analysis of biofilm exhibit Proteobacteria was the dominant electro-active bacteria, and the modification of SC could slightly change the bacterial community. Therefore, resource utilization of natural wastes provided the novel concept of anode catalyst fabrication for MFC in enhancing electron transfer, power output and wastewater decomposition.

Application of advanced anodes in microbial fuel cells for power generation: A review

Microbial fuel cells (MFCs) the most extensively described bioelectrochemical systems (BES), have been made remarkable progress in the past few decades. Although the energy and environment benefits of MFCs have been recognized in bioconversion process, there are still several challenges for practical applications on large-scale, particularly for relatively low power output by high ohmic resistance and long period of start-up time. Anodes serving as an attachment carrier of microorganisms plays a vital role on bioelectricity production and extracellular electron transfer (EET) between the electroactive bacteria (EAB) and solid electrode surface in MFCs. Therefore, there has been a surge of interest in developing advanced anodes to enhance electrode electrical properties of MFCs. In this review, different properties of advanced materials for decorating anode have been comprehensively elucidated regarding to the principle of well-designed electrode, power output and electrochemical properties. In particular, the mechanism of these materials to enhance bioelectricity generation and the synergistic action between the EAB and solid electrode were clarified in detail. Furthermore, development of next generation anode materials and the potential modification methods were also prospected.

Microbial Fuel Cell stack performance enhancement through carbon veil anode modification with activated carbon powder

The chemical energy contained in urine can be efficiently extracted into direct electricity by Microbial Fuel Cell stacks to reach usable power levels for practical implementation and a decentralised power source in remote locations. Herein, a novel type of the anode electrode was developed using powdered activated carbon (PAC) applied onto the carbon fibre scaffold in the ceramic MFC stack to achieve superior electrochemical performance during 500 days of operation. The stack equipped with modified anodes (MF-CV) produced up to 37.9 mW (21.1 W m-3) in comparison to the control (CV) that reached 21.4 mW (11.9 W m-3) showing 77% increase in power production. The novel combination of highly porous activated carbon particles applied onto the conductive network of carbon fibres promoted simultaneously electrocatalytic activity and increased surface area, resulting in excellent power output from the MFC stack as well as higher treatment rate. Considering the low cost and simplicity of the material preparation, as well as the outstanding electrochemical activity during long term operation, the resulting modification provides a promising anode electrocatalyst for high-performance MFC stacks to enhance urine and waste treatment for the purpose of future scale-up and technology implementation as an applied off-grid energy source.

Spraying carbon powder derived from mango wood biomass as high-performance anode in bio-electrochemical system

Microbial fuel cell is a green and sustainable bio-electrochemical system that can harvest bioelectricity from organic matter conversion by bacteria in wastewater, but weak electrochemical activity and poor biocompatibility between electro-active bacteria and anode limit its scale-up application. In the present, the biomass carbon derived from mango wood was prepared via one-step carbonization method for anode materials in microbial fuel cell. A desirable anode C/1050 with large electrochemical active surface area (75.3 cm²), low electron transfer resistance (4.36 Ω), and benign biocompatibility were developed, achieving power density up to 589.8 mW·m^-2. This study provides a low-cost and high-performance biomass carbon used as anode material in microbial fuel cell for practical application.

Silver grass-derived activated carbon with coexisting micro-, meso- and macropores as excellent bioanodes for microbial colonization and power generation in sustainable microbial fuel cells

In this study, highly biocompatible three-dimensional hierarchically porous activated carbon from the low-cost silver grass (Miscanthus sacchariflorus) has been fabricated through a facile carbonization approach and tested it as bioanode in microbial fuel cell (MFC) using Escherichia coli as biocatalyst. This silver grass-derived activated carbon (SGAC) exhibited an unprecedented specific surface area of 3027 m² g^-1 with the coexistence of several micro-, meso-, and macropores. The synergistic effect from pore structure (macropores - hosting E. coli to form biofilm and facilitates internal mass transfer; mesopores - favors fast electron transfer; and micropores - promotes nutrient transport to the biofilm) with very high surface area facilitates excellent extracellular electron transfer (EET) between the anode and biofilm which resulted in higher power output of 963 mW cm^-2. Based on superior biocompatibility, low cost, environment-friendliness, and facile fabrication, the proposed SGAC bioanode could have a great potential for high-performance and cost-effective sustainable MFCs.

Three-dimensional high performance free-standing anode by one-step carbonization of pinecone in microbial fuel cells

In this paper, the free-standing macroporous carbon anode is prepared by one-step carbonization of pinecone without any further modification. The obtained anode is N, P-codoped porous carbon material, which is beneficial for electrochemical active bacterial adhesion and the fast start-up of cells. Both of the output voltage and long-term operation stability of the obtained anode are higher than that of carbon felt. The charge transfer resistance after biofilm formation is only 1.4 Ω, being 85.1% lower than that of carbon felt anode. 16S rRNA gene sequence analysis shows that Geobacter soli is the main electricigen and its ratio at the obtained anode is much higher than that at carbon felt (77.4% vs 34.0%). The N, P-codoped carbon as the three-dimensional free-standing anode has excellent electrochemical properties and is low cost and easy preparation. Most importantly, it enhances extracellular electron transfer, thus has potential application in microbial fuel cells.

Microbial recycling cells (MRCs): A new platform of microbial electrochemical technologies based on biocompatible materials, aimed at cycling carbon and nutrients in agro-food systems

This article reviews the mechanisms that drive nutrients and carbon sequestration from wastewaters by microbial electrochemical technologies (METs). In this framework, a new generation of METs is also presented (to be called microbial recycling cells, MRCs), based on 100%-recyclable materials (biomass-derived char coal, clay, terracotta, paper, ligno-cellulosic plant materials, etc.), which can act as bio-electrodes, separators and structural frames. In traditional METs architectures (based on technological materials such as carbon cloths, plastic panels, membranes, binders), inorganic salts precipitation and adsorption, as well as biofouling due to organic-matter deposition, are considered as main drawbacks that clog and hinder the systems over relatively short periods. In MRCs, these mechanisms should be maximized, instead of being avoided. In this perspective, both inorganic and organic forms of the main nutrients are sequestered from wastewater and deposited on METs modules. Once the systems become saturated, they can entirely be recycled as agricultural soil conditioners or as base for organic-mineral fertilizers.