Boosting current generation in microbial fuel cells by an order of magnitude by coating an ionic liquid polymer on carbon anodes

Enhanced electroactive bacteria enrichment and facilitated extracellular electron transfer in microbial fuel cells via polydopamine coated graphene aerogel anode

The structure and surface physicochemical properties of anode play a crucial role in microbial fuel cells (MFCs). To enhance the enrichment of exoelectrogen and facilitate extracellular electron transfer (EET), a three-dimensional macroporous graphene aerogel with polydopamine coating was successfully introduced to modify carbon brush (PGA/CB). The three-dimensional graphene aerogel (GA) with micrometer pores improved the space utilization efficiency of microorganisms. Polydopamine (PDA) coating enhanced the physicochemical properties of the electrode surface by introducing abundant functional groups and nitrogen-containing active sites. MFCs equipped with PGA/CB anodes (PGA/CB-MFCs) demonstrated superior power generation compared to GA/CB-MFCs and CB-MFCs (MFCs with GA/CB and CB anodes respectively), including a 23.0 % and 30.1 % reduction in start-up time, and an increase in maximum power density by 2.43 and 1.24 times respectively. The higher bioelectrochemical activity exhibited by the biofilm of PGA/CB anode and the promoted riboflavin secretion by PGA modification imply the enhanced EET efficiency. 16S rRNA high-throughput sequence analysis of the biofilms revealed successful enrichment of Geobacter on PGA/CB anodes. These findings not only validate the positive impact of the synergistic effects between GA and PDA in promoting EET and improving MFC performance but also provide valuable insights for electrode design in other bioelectrochemical systems.

Imidazolium-based ionic liquids support biosimilar flavin electron transfer

Understanding electron transport with electroactive microbes is key to engineering effective and scalable bio-electrochemical technologies. Much of this electron transfer occurs through small-molecule flavin mediators that perform one-electron transfers in abiotic systems but concerted two-electron transfer in biological systems, rendering abiotic systems less efficient. To boost efficiency, the principles guiding flavin electron transfer must be elucidated, necessitating a tunable system. Ionic liquids (ILs) offer such a platform due to their chemical diversity. In particular, imidazolium-containing ILs that resemble the amino acid histidine are bio-similar electrolytes that enable the study of flavin electron transfer. Using the model IL 1-ethyl-3-methylimidazolium ([Emim][BF4]), we observe concerted two-electron transfer between flavin mononucleotide and an unmodified glassy carbon electrode surface, while a one-electron transfer occurs in standard inorganic electrolytes. This work demonstrates the power of ILs to enable the mechanistic study of biological electron transfer, providing critical guidelines for improving electrochemical technologies based on these biological properties.

A comprehensive review of microbial fuel cells considering materials, methods, structures, and microorganisms

Microbial fuel cells (MFCs) are promising for generating renewable energy from organic matter and efficient wastewater treatment. Ensuring their practical viability requires meticulous optimization and precise design. Among the critical components of MFCs, the membrane separator plays a pivotal role in segregating the anode and cathode chambers. Recent investigations have shed light on the potential benefits of membrane-less MFCs in enhancing power generation. However, it is crucial to recognize that such configurations can adversely impact the electrocatalytic activity of anode microorganisms due to increased substrate and oxygen penetration, leading to decreased coulombic efficiency. Therefore, when selecting a membrane for MFCs, it is essential to consider key factors such as internal resistance, substrate loss, biofouling, and oxygen diffusion. Addressing these considerations carefully allows researchers to advance the performance and efficiency of MFCs, facilitating their practical application in sustainable energy production and wastewater treatment. Accelerated substrate penetration could also lead to cathode clogging and bacterial inactivation, reducing the MFC's efficiency. Overall, the design and optimization of MFCs, including the selection and use of membranes, are vital for their practical application in renewable energy generation and wastewater treatment. Further research is necessary to overcome the challenges of MFCs without a membrane and to develop improved membrane materials for MFCs. This review article aims to compile comprehensive information about all constituents of the microbial fuel cell, providing practical insights for researchers examining various variables in microbial fuel cell research.

Putting the electro-bugs to work: A systematic review of 22 years of advances in bio-electrochemical systems and the parameters governing their performance

Wastewater treatment using bioelectrochemical systems (BESs) can be considered as a technology finding application in versatile areas such as for renewable energy production and simultaneous reducing environmental problems, biosensors, and bioelectrosynthesis. This review paper reports and critically discusses the challenges, and advances in bio-electrochemical studies in the 21st century. To sum and critically analyze the strides of the last 20+ years on the topic, this study first provides a comprehensive analysis on the structure, performance, and application of BESs, which include Microbial Fuel Cells (MFCs), Microbial Electrolysis Cells (MECs) and Microbial Desalination Cells (MDCs). We focus on the effect of various parameters, such as electroactive microbial community structure, electrode material, configuration of bioreactors, anode unit volume, membrane type, initial COD, co-substrates and the nature of the input wastewater in treatment process and the amount of energy and fuel production, with the purpose of showcasing the modes of operation as a guide for future studies. The results of this review show that the BES have great potential in reducing environmental pollution, purifying saltwater, and producing energy and fuel. At a larger scale, it aspires to facilitate the path of achieving sustainable development and practical application of BES in real-world scenarios.

Enhancing extracellular electron transfer through selective enrichment of Geobacter with Fe@CN-modified carbon-based anode in microbial fuel cells

Microbial fuel cells (MFCs) have been demonstrated as a renewable energy strategy to efficiently recover chemical energy stored in wastewater into clean electricity, yet the limited power density limits their practical application. Here, Fe-doped carbon and nitrogen (Fe@CN) nanoparticles were synthesized by a direct pyrolysis process, which was further decorated to fabricate Fe@CN carbon paper anode. The modified Fe@CN anode with a higher electrochemically active surface area was not only benefit for the adhesion of electrochemically active microorganisms (EAMs) and extracellular electron transfer (EET) between the anode and EAMs but also selectively enriched Geobacter, a typical EAMs species. Accordingly, the MFCs with Fe@CN anode successfully achieved a highest voltage output of 792.76 mV and a prolonged stable voltage output of 300 h based on the mixed culture feeding with acetate. Most importantly, the electroactive biofilms on Fe@CN anode achieved more content ratio of proteins to polysaccharides (1.40) in extracellular polymeric substances for the balance between EET and cell protection under a harsh environment. This work demonstrated the feasibility of development on anode catalysts for the elaboration of the catalytic principle about interface modification, which may contribute to the practical application of MFC in energy generation and wastewater treatment.

Enhanced electricity generation and storage by nitrogen-doped hierarchically porous carbon modification of the capacitive bioanode in microbial fuel cells

Microbial fuel cells (MFCs) can potentially be utilized for power generation, but their low power density and low energy storage capabilities remain major bottlenecks for their large-scale development. In this research, a simplistic nitrogen-doped hierarchically porous carbon material (HPC-A) was developed through a one-step carbonization and activation process and was successfully hot-pressed on the carbon cloth (CC) substrate. This process fabricates capacitive bioanodes (HPC-A-CC) that can enhance electricity generation and storage in MFCs. The as-prepared HPC-A-CC anode delivered a power density of 2043.6 mW·m^-2 and a cumulative total charge (Q_m) of 426.4 ± 13.4C·m^-2 at each cycle, which was 2.1 and 34.8 times higher than that of the plain CC anode, respectively. This was a result of the hierarchical and interconnected porous structure, improved hydrophilic surface, and increased number of active centers which host the bacteria for enhanced electron transfer. Electrochemical measurements indicated the superior electrochemical activity and capacitive behavior of the HPC-A-CC anode. Furthermore, biofilm analysis revealed that the HPC-A-CC biofilm exhibited higher cell viability and a more uniform spatial distribution. These findings not only demonstrate the potential of HPC-A-CC for power enhancement in MFCs but also provide a feasible solution to the problem of power generation and demand mismatch in MFC applications.

Polydopamine/polypyrrole-modified graphite felt enhances biocompatibility for electroactive bacteria and power density of microbial fuel cell

The interactions between the microbes and the surface of an anode play an important role in capturing the respiratory electrons from bacteria in a microbial fuel cell (MFC). The chemical and electrochemical characteristics of the carbon material affect biofilm growth and direct electron transfer in MFCs. This study examined the electrodeposition of polydopamine (PDA) and polypyrrole (PPY) on graphite felt electrode (GF). The MFC with the modified PDA/PPY-GF reached 920 mW/m², which was 1.5, 1.17, and 1.18 times higher than those of the GF, PDA-GF, and PPY-GF, respectively. PDA has superior hydrophilicity and adhesive force biofilm formation, while PPY provides electrochemically active sites for microbial electron transfer. Raman spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area measurements, and contact angle analysis revealed the enhanced physicochemical properties of the carbon electrode. These results show that co-doped PDA/PPY provides a strategy for electroactive biofilm development and improves the bioelectrochemical performance in realistic MFC reactors.

Effective salt removal from domestic reverse osmosis reject water in a microbial desalination cell

Microbial desalination cells (MDC) are evaluated as an environmentally friendly approach for purifying saline water by using power generated by the decomposition of organic materials in the wastewater. The present study is to evaluate the ferrocyanide-redox and biocathode approach in treating simulated saline water and subsequently recovering bio-electricity using actual domestic reverse osmosis reject water. For the desalination of simulated saline water and domestic reverse osmosis reject water, a three-chamber microbial desalination cell with graphite electrodes and anion and cation exchange membranes was constructed. When treating simulated saline water, the biocathode technique achieved a 5% improvement in salt removal and a 4.9% increase in current and power density when compared to the ferrocyanide-redox approach. When biocathode MDC was used to treat domestic reverse osmosis reject water, a maximum current and power density of 3.81 μA/cm² and 0.337 μW/cm², respectively, were recorded, as well as COD removal of 83.9% at the desalination chamber and ions reduction for Na, K, and Ca of up to 79%, 76.5%, and 72%, respectively, in a batch operation for 31 days with a stable pH (≈ 7). Thus, the study revealed a microbial desalination cell capable of recovering bioenergy and reducing salt from domestic reverse osmosis reject water with a consistent pH range.

Economic affordable carbonized phenolic foam anode with controlled structure for microbial fuel cells

In microbial fuel cells (MFCs), the anode electrode is a core structure as the catalytic area of exoelectrogens. The anode material for large-scale MFCs needs excellent bioelectrochemical performance and low fabrication costs. Herein, carbonized phenolic foam with controllable porous structures was developed as the bio-capacitor of MFCs. The proportion of sodium dodecylbenzene sulfonate (SDBS), which improved mixing and dissolution between the resin liquid and the foaming agent, was adjusted to form open pores on the foam film and skeletons, which promoted both the capacitance and biocompatibility of the anode. Within SDBS proportion from 0 to 1.2 wt%, the anode SPF-9 (0.9 wt%) obtained the best capacitance (37 ± 0.13 F g^-1), electrochemical active surface area (87 ± 0.38 cm²) and hydrophilia (contact angle 79 ± 0.2°). The MFCs with SPF-9 obtained the highest power density of 3980 ± 178 mW m^-2, while those of carbon-cloth anodes were 1600 ± 28 mW m^-2. The biofilm of SPF-9 also demonstrated higher activity and obtained larger abundance of exoelectrogens (68 ± 0.38%). The increased capacitance and biocompatibility mainly resulted in the good performance of SPF-9. The carbonized phenolic foam anode material was worth considering for the future application of MFCs due to its superior electrochemical performance and large-quantity fabrication capability.

Effect of β-cyclodextrin/polydopamine composite modified anode on the performance of microbial fuel cell

The relatively weak microbial adhesion is a bottleneck in improving the power generation performance of microbial fuel cell (MFC). Anode modification is a simple and effective method to solve this problem. A new type of β-cyclodextrin/polydopamine modified carbon felt anode was prepared, and the effects of β-cyclodextrin/polydopamine modified anode on the main performance indexes such as power density and chemical oxygen demand (COD) removal rate of MFC were evaluated. The maximum power density and the output electric energy during the test period of MFC using the modified anode were 102 mW/m² and 84.96 J, which were 364% and 295.3% higher than those of MFC with conventional carbon felt anode, respectively; and the COD removal rate was 124.4% higher than that of MFC with unmodified anode. Modifying the anode with β-cyclodextrin-polyacyclic composite materials is an effective method to improve the overall performance of MFC.

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.

Effect of the tetracycline antibiotics on performance and microbial community of microbial fuel cell

The adverse effect of tetracycline antibiotics on microbial activity is one of the serious risks for the biologic wastewater treatment process. The microbial fuel cells (MFCs) are a promising technology for wastewater treatment and renewable power generation process. For this reason, the investigation of the inhibition effect of the tetracyclines on the MFCs is essential for reducing damage on the environment. This paper focused on the performance of MFCs under different antibiotic concentrations at the range of 0.25-50 mg/L. The power generation performance, microbial community and biofilm characteristics (morphology, resistance and viability) of MFCs were investigated in detail. The results indicated that the increase in the antibiotic concentration significantly affected the MFC performance and microbial community. A modified non-competitive inhibition model was used to predict the inhibition effect of tetracycline antibiotics on the MFCs.

Impact of cathodic electron acceptor on microbial fuel cell internal resistance

Ferricyanide is often used in microbial fuel cells (MFCs) to avoid oxygen intrusion that occurs with air cathodes. However, MFC internal resistances using ferricyanide can be larger than those with air cathodes even though ferricyanide results in higher power densities. Using a graphite fiber brush cathode and a ferricyanide catholyte (FC-B) the internal resistance was 62 ± 4 mΩ m², with 84 ± 8 mΩ m² obtained using ferricyanide and a flat carbon paper cathode (FC-F) and only 51 ± 1 mΩ m² using a 70% porosity air cathode (A-70). The FC-B MFCs produced the highest maximum power density of all configurations examined: 2.46 ± 0.26 W/m², compared to 1.33 ± 0.14 W/m² for the A-70 MFCs. The electrode potential slope (EPS) analysis method showed that electrode resistances were similar for ferricyanide and air-cathode MFCs, and that higher power was due to the larger experimental working potential (500 ± 12 mV) of ferricyanide compared to the air cathode (233 ± 5 mV).

Oily wastewater treatment by a continuous flow microbial fuel cell and packages of cells with serial and parallel flow connections

This study reports the results of the application of microbial fuel cells (MFC) in refinery wastewater (RW) treatment. In this research, the effect of hydraulic retention time (HRT), and scale-up on the performance of a novel expandable modular design of single-chamber MFC (SCMFC) has been investigated. In the first part of the paper, the effect of HRT on chemical oxygen demand (COD) removal and electricity generation was examined. The generated steady open-circuit voltage (OCV) was 785 mV at HRT 90 h, and the provided maximum power density (PD) was 113 mW/m² at HRT 15 h. At HRT of 45 h, COD removal increased up to 87% via an increase in the HRT. In the second part, the scale-up of SCMFC was investigated by serial (SFC) or parallel (PFC) connecting the outlets and inlets of fluid flows. The average produced OCV was 760 mV in PFC mode, and average produced PD in PFC and SFC modes were 97 and 75.6 mW/m², respectively. COD removal in SFC and PFC modes were reported to be 89 and 42%, respectively. Compared to PFC mode, SFC mode was more efficient in terms of COD removal and coulombic efficiency. However, it produced lower PD compared to PFC mode. It is possible to control the quality and capacity of wastewater treatment by using combining the SFC and PFC mode connections in packages of MFCs.

Progress and Prospects of Bioelectrochemical Systems: Electron Transfer and Its Applications in the Microbial Metabolism

Bioelectrochemical systems are revolutionary new bioengineering technologies which integrate microorganisms or enzymes with the electrochemical method to improve the reducing or oxidizing metabolism. Generally, the bioelectrochemical systems show the processes referring to electrical power generation or achieving the reducing reaction with a certain potential poised by means of electron transfer between the electron acceptor and electron donor. Researchers have focused on the selection and optimization of the electrode materials, design of electrochemical device, and screening of electrochemically active or inactive model microorganisms. Notably, all these means and studies are related to electron transfer: efflux and consumption. Thus, here we introduce the basic concepts of bioelectrochemical systems, and elaborate on the extracellular and intracellular electron transfer, and the hypothetical electron transfer mechanism. Also, intracellular energy generation and coenzyme metabolism along with electron transfer are analyzed. Finally, the applications of bioelectrochemical systems and the prospect of microbial electrochemical technologies are discussed.

Significant enhancement of electron transfer from Shewanella oneidensis using a porous N-doped carbon cloth in a bioelectrochemical system

Modifying the surface of an anode can improve electron transfer, thus enhancing the performance of the associated bioelectrochemical system. In this study, a porous N-doped carbon cloth electrode was obtained via a simple thermal reduction and etching treatment, and then used as the anode in a bioelectrochemical system. The electrode has a high nitrogen-to‑carbon (N/C) ratio (~3.9%) and a large electrochemically active surface area (145.4 cm², about 4.4 times higher than that of the original carbon cloth), which increases the bacterial attachment and provides more active sites for extracellular electron transfer. Electrochemical characterization reveals that the peak anodic current (0.71 mA) of the porous N-doped carbon cloth electrode in riboflavin is 18 times higher than that of the original carbon cloth electrode (0.04 mA), confirming the presence of more electroactive sites for the redox reaction. We also obtained a maximum current density of 0.29 mA/cm² during operation of a bioelectrochemical system featuring the porous N-doped carbon cloth electrode, which is 14.5 times higher than that of the original carbon cloth electrode. This result demonstrates that the adoption of our new electrode is a viable strategy for boosting the performance of bioelectrochemical systems.

Rational Design of Microfabricated Electroconductive Hydrogels for Biomedical Applications

Electroconductive hydrogels (ECHs) are highly hydrated 3D networks generated through the incorporation of conductive polymers, nanoparticles, and other conductive materials into polymeric hydrogels. ECHs combine several advantageous properties of inherently conductive materials with the highly tunable physical and biochemical properties of hydrogels. Recently, the development of biocompatible ECHs has been investigated for various biomedical applications, such as tissue engineering, drug delivery, biosensors, flexible electronics, and other implantable medical devices. Several methods for the synthesis of ECHs have been reported, which include the incorporation of electrically conductive materials such as gold and silver nanoparticles, graphene, and carbon nanotubes, as well as various conductive polymers (CPs), such as polyaniline, polypyrrole, and poly(3,4-ethylenedioxyythiophene) into hydrogel networks. Theses electroconductive composite hydrogels can be used as scaffolds with high swellability, tunable mechanical properties, and the capability to support cell growth both in vitro and in vivo. Furthermore, recent advancements in microfabrication techniques such as three dimensional (3D) bioprinting, micropatterning, and electrospinning have led to the development of ECHs with biomimetic microarchitectures that reproduce the characteristics of the native extracellular matrix (ECM). In addition, smart ECHs with controlled structures and healing properties have also been engineered into devices with prolonged half-lives and increased durability. The combination of sophisticated synthesis chemistries and modern microfabrication techniques have led to engineer smart ECHs with advanced architectures, geometries, and functionalities that are being increasingly used in drug delivery systems, biosensors, tissue engineering, and soft electronics. In this review, we will summarize different strategies to synthesize conductive biomaterials. We will also discuss the advanced microfabrication techniques used to fabricate ECHs with complex 3D architectures, as well as various biomedical applications of microfabricated ECHs.

Fate of three bioluminescent pathogenic bacteria fed through a cascade of urine microbial fuel cells

Microbial fuel cell (MFC) technology is currently gaining recognition as one of the most promising bioenergy technologies of the future. One aspect of this technology that has received little attention is the disinfection of effluents and the fate of pathogenic organisms that find their way into the waste stream. In this study, three independent trials were carried out to evaluate the fate of three bioluminescent pathogenic bacteria (Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa and Staphylococcus aureus) introduced into the anodic chamber of a urine-fed cascade of 9 MFCs with matured, electroactive biofilms. These are common examples of enteric human pathogens, which could contaminate urine or waste streams. The results showed that the average power generation in the closed circuit cascade reached 754 ± 16 µW, with an average pathogen log-fold reduction of 6.24 ± 0.63 compared to 2.01 ± 0.26 for the open circuit cascade for all three pathogens. The results suggest that the bio-electrochemical reactions associated with electricity generation were the primary driving force for the inactivation of the introduced pathogens. These findings show that pathogenic organisms introduced into waste streams could be inactivated by the power-generating process within the MFC cascade system, thereby preventing propagation and thus rendering the effluent safer for possible reuse.

A facile synthesis of molybdenum carbide nanoparticles-modified carbonized cotton textile as an anode material for high-performance microbial fuel cells

A novel macroscale porous structure electrode, molybdenum carbide nanoparticles-modified carbonized cotton textile (Mo2C/CCT), was synthesized by a facile two-step method and used as an anode material for high-performance microbial fuel cells (MFCs). The characterization results show that the carbonized cotton textile modified with Mo2C nanoparticles offers a great specific surface area (832.17 m2 g-1) for bacterial adhesion. The MFC using Mo2C/CCT anode delivers the maximum power density of 1.12 W m-2, which is 51% and 116% higher than that of CCT and unmodified carbon felt anodes under the same conditions. The high power density is mainly due to the Mo2C nanoparticles with good biocompatibility and high conductivity and superior electrochemical activity, as well as the macroscale porous structure of carbonized cotton textile, which facilitate the formation of electroactive biofilm and improve the electron transfer. This paper introduces a feasible way to synthesize cost-effective and high-performance anode materials for MFCs.

Toxicity of imidazoles ionic liquid [C16mim]Cl to Hela cells

Our study aimed to evaluate the toxicity of 1-hexadecyl-3-methylimidazolium chloride ([C₁₆min]Cl) on the human cervical carcinoma (Hela) cells. We evaluated toxicity, cell viability, genotoxicity, oxidative stress, apoptosis, and apoptosis-related gene expression in Hela cells following exposure to [C₁₆min]Cl. The results indicated that [C₁₆min]Cl inhibited the growth of Hela cells, decreased cell viability, induced DNA damage and apoptosis, inhibited superoxide dismutase, decreased glutathione content, as well as increased the cellular malondialdehyde level of Hela cells. Moreover, [C₁₆min]Cl induced changes in the transcription of p53, Bax and Bcl-2, suggesting that the p53 and Bcl-2 family might have been involved in the cytotoxicity and apoptosis induced by [C₁₆min]Cl in Hela cells. Taken together, these results revealed that [C₁₆min]Cl imparts oxidative stress, genotoxicity, and induces apoptosis in Hela cells; hence, it is not a green solvent.

Quick start-up and performance of microbial fuel cell enhanced with a polydiallyldimethylammonium chloride modified carbon felt anode

It is of significant importance to simultaneously shorten the start-up time and enhance the electricity generation performance for practical application of microbial fuel cell (MFC). In this paper, the polydiallyldimethylammonium chloride (PDDA) modified carbon felt (PDDA-CF) electrode was prepared and used as the anode of PDDA-MFC. The anode significantly enhanced the start-up speed and electricity generation and dye wastewater degradation performances of the PDDA-MFC. The start-up time of PDDA-MFC is only 9 h, which is only 7.5% that of the unmodified carbon felt anode MFC (CF-MFC). The charge transfer resistance, the maximum output voltage and the maximum output power density of PDDA-MFC were 9.7 Ω, 741 mV and 537.8 mW m^-2 respectively, which were 70.3% lower than, 1.7 times and 3.3 times greater than those of CF-MFC respectively. In addition, the color and chemical oxygen demand (COD) removal rates of Reactive Brilliant Red X-3B for PDDA-MFC reached 95.94% and 64.24% at 24 h respectively, which were 41.5% and 51.2% higher than those of CF-MFC respectively. Due to the electrostatic attraction of PDDA, the adhesion and metabolic mass transfer rate of exoelectrogens are accelerated, thus the PDDA-CF electrode has excellent electrochemical properties and bio-affinity. This paper provides a new idea to enhance the start-up speed and performance of MFC simultaneously.