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Exoelectrogenic bacteria can transfer the electrons out of the cell body through the extracellular electron transfer (EET) process after consuming various organic matters, which attracts increasing attentions in both academia and industrial communities. In this dissertation, I will focus on a typical exoelectrogenic bacterium Shewanella and its cooperating with inorganic materials such as nano-devices and nanoparticles. In the Shewanella-nano-devices hybrids, the current output features and cell density can be both in-situ monitored and studied. Take a further step, by anchoring the metal nanoparticles into the Shewanella membrane structures and bulk biofilms, we can greatly boost the EET process and achieve record high power output. In the first project, we developed and applied an on-chip approach to study the EET, metabolic activity status and behaviors of microbes for maximal current production with real time in-situ microscope observation. The dissimilatory extroelectrogenic bacteria Shewanella oneidensis MR-1 wild type (WT) and its mutant cells (bfe and mtrC/omcA) were used as the model organisms to understand extroelectrogenic biofilm growth, metabolism rate, and current production. Our goal is to specify the various mechanisms of EET process in Shewanella oneidensis MR-1 and its mutant cells under different conditions.Furthermore, based on the insight developed from the on-chip platform, we further develop a rational strategy to boost the transmembrane and extracellular electron transfer processes by loading Shewanella biofilms on reduced graphene oxide/silver nanoparticles (rGO/Ag) scaffolds. Our systematic studies show that the rGO/Ag can release positively charged silver ions, which facilitate Shewanella attachment to rGO/Ag scaffold to form dense biofilms, while at the same time produce transmembrane and outer-membrane Ag nanoparticles to form the Shewanella-Ag hybrids, with greatly enhanced transmembrane and extracellular electron transfer efficiency to improve the bacteria turn-over frequency (TOFs) and boost the overall Shewanella based microbial fuel cells (MFCs) performance. The resulting MFCs with the rGO/Ag anode can output a current density of 38.5 A/m2, a power density of 6.63 W/m2 and a Coulombic efficiency of 81%, greatly outperforming the best Shewanella MFCs reported to date.In the third project, we further show that rGO/Cu scaffolds can exert a similar enhancement effect to produce high performance in the MFC tests, demonstrating universal applicability of our strategy for enhancing the MFC performance.

Non-noble metal catalyst with high catalytic activity and stability towards oxygen reduction reaction (ORR) is critical for durable bioelectricity generation in air-cathode microbial fuel cells (MFCs). Herein, nitrogen-doped (iron-cobalt alloy)/cobalt/cobalt phosphide/partly-graphitized carbon ((FeCo)/Co/Co2P/NPGC) catalysts are prepared by using cornstalks via a facile method. Carbonization temperature exerts a great effect on catalyst structure and ORR activity. FeCo alloys are in-situ formed in the catalysts above 900 °C, which are considered as the highly-active component in catalyzing ORR. AC-MFC with FeCo/Co/Co2P/NPGC (950 °C) cathode shows the highest power density of 997.74 ± 5 mW m−2, which only declines 8.65% after 90 d operation. The highest Coulombic efficiency (23.3%) and the lowest charge transfer resistance (22.89 Ω) are obtained by FeCo/Co/Co2P/NPGC (950 °C) cathode, indicating that it has a high bio-electrons recycling rate. Highly porous structure (539.50 m2 g−1) can provide the interconnected channels to facilitate the transport of O2. FeCo alloys promote charge transfer and catalytic decomposition of H2O2 to •OH and •O2−, which inhibits cathodic biofilm growth to improve ORR durability. Synergies between metallic components (FeCo/Co/Co2P) and N-doped carbon energetically improve the ORR catalytic activity of (FeCo)/Co/Co2P/NPGC catalysts, which have the potential to be widely used as catalysts in MFCs.

As a sustainable and eco-friendly technology, the benthic microbial fuel cell (BMFC) has been emerged as alternative and potential approach to recover electrical energy by microorganisms, but lower power density and poor long-term life hinder their practical application. Modification of anodic materials is an efficient strategy to solve this problem. Here, a conductive and biocompatible hydrogel electrode, polyaniline-polypyrole-CNTs-Fe3O4 (PANI-PPy-CNTs-Fe3O4) is prepared and applied as anode in a simulated BMFC. The maximum power density of the BMFC with PANI-PPy-CNTs-Fe3O4 hydrogel anode (5901.49 mW/m3) is 1.33, 2.15 and 2.06 times higher than that of PANI-PPy (4413.03 mW/m3), PANI and PPy anodes (2737.12 and 2859.53 mW/m3), respectively. The charge transfer resistance of quaternary hydrogel bioanode in BMFC (3.922 Ω) is much lower than that of the PANI (8.682 Ω), PPy (8.262 Ω) and PANI-PPy (5.772 Ω) hydrogel bioanodes. Moreover, the extracellular electron transfer ability is also enhanced on the composite hydrogel anode, which also exhibits the high biomass. High-throughput sequencing technology indicates that the synergistic effect of bacteria on the quaternary hydrogel made full use of organic matter as available fuel to enable a high electricity-generation anode. Such foregoing mainly ascribed to the composite hydrogel keep the high biocompatibility from components, while the addition of CNTs and Fe3O4 dramatically decreases the internal resistance and provides more electrochemical active surface area on basis of macroporous 3D hydrogel structure. This work explores the composite hydrogel used as anodes to construct high-performance BMFC and provides significant information for the applications of actual BMFCs in the future.

Schematic illustration of the fabrication of CoxNiy alloy nanocubes (ANCs) and hollow CoxNiy alloy nanocubes (HANCs).

Background Unlimited energy demand and rapid urbane development are major deriving forces to generate bioelectricity through microbial fuel cells (MFCs) and have been a hot area for 2-decades. Various advancements have been employed to improve the MFC's efficiency through electrode and membrane materials. Methods Here, we discussed the recent innovations and developments to fabricate the electrode and membrane materials, which play a key role in bio-energy production and performance. Specifically, the morphological aspects, including pure/doped carbon-based electrodes and their large surface area, directly enhanced the oxygen reduction efficiency of MFCs. Findings The impact of organic and inorganic hybrid composite bio-polymer membranes and separators to improve the electron transfer ability and remedies for associated biofouling problems are also highlighted. Numerous enhancements to the material's physical, mechanical, and chemical properties are explored in detail to prevent biofouling issues. In addition, it highlights how the well-ordered mesopores, large surface area, and biocompatibility of MFCs directly affect their stability and performance. Finally, this review article introduces current issues with smart, feasible solutions, stability improvements, and future perspectives of MFCs and critically evaluated recent progress and developments in MFCs technology which can be useful for academic and industrial researchers.

International audience; The present work examines, for the first time, the use of thiolated graphene oxide (TGO), in polyelectrolyte composite membranes as an effective approach to enhance the MFC performance. A new composite membrane based on a sulfonated polyethersulfone (SPES) hybrid with GO, sulfonated GO (SGO), and TGO was fabricated and assessed in MFC. The blend membranes were characterized with various techniques. The sulfhydryl (-SH) and sulfonic (-SO3H) groups enhanced the proton selectivity of the membrane and MFC performance. The MFC using the SPES/SGO1.8% composite membrane generated a power density of 66.4 mW/m2 which was double that produced by MFC using Nafion117 membrane in batch mode which lasted for 8 days. The SPES/SGO membrane was more selective towards H+ rather than other cations (K+, Na+, and Li+). This was also confirmed by the results of proton conductivity analysis, as the SPES/SGO1.8% membranes showed a value of 1.42 mS/cm which was higher than Nafion117 (1.3 mS/cm), SPES/TGO1.8% (1.25 mS/cm), SPES/GO1.8% (0.56 mS/cm), and SPES (0.32 mS/cm). The higher COD removal and coulombic efficiency were obtained in MFC with SPES/SGO membranes. In conclusion, it is our view that the new SPES/SGO and SPES/TGO membranes can be applied favorably in dual-chamber MFCs meeting their needs. © 2021 Elsevier Ltd

Background The design of highly active non-noble metal oxidation reduction catalysts (ORR) for microbial fuel cell (MFC) has always been a challenge. The aim of this study is to develop a highly active low cost cobalt-based ORR catalyst for MFCs cathode. Method Herein, a series of highly active nitrogen doped Co3O4-ZIF/Zn-T catalysts with different calcination temperatures (T) were prepared using bimetallic Co/Zn leaf blade structure Co-ZIF/Zn-67 as template. The Co3O4-ZIF/Zn-T catalysts were characterized by various methods, and the effect of T on the structure and ORR performance of MFC catalyst were studied. Significant findings The results showed that the Co3O4-ZIF/Zn-T derived from bimetallic Co/Zn leaf blade structure Co-ZIF/Zn-67 template exhibited better ORR performance than Co3O4-ZIF-400 derived from the dodecahedral structure Co-ZIF-67 template. The bimetallic Co/Zn Co-ZIF/Zn-67 template promotes more uniformly distributed mesopores, high N content and abundant smaller active Co3O4 sites due to its particular structure and the isolation effect of Zinc. Among Co3O4-ZIF/Zn-T catalysts, the Co3O4-ZIF/Zn-400 calcined at 400 °C demonstrated the highest ORR performance (onset potential was 0.082 V and MFC power density was 656.9 mw/m2), which was much higher than Co3O4-ZIF-400 (0.027 V and 402.8 mw/m2). The output voltage of MFC with Co3O4-ZIF/Zn-T exhibited no significant downward trend in 30 days stability test, indicating that the Co3O4-ZIF/Zn-400 catalyst has great stability.

Microbial fuel cells (MFCs) are capable of converting the chemical energy of biodegradable organic matter directly into electricity, thus they can be applied in various fields: waste elimination, biosensor industry and production of renewable energy. In this study, the efficiency of noble metal free carbon aerogel based cathode catalysts was investigated and compared to plain glassy carbon cloth without catalyst (CC ) and platinum containing carbon powder catalyst ( PtC ) in H-type MFCs. Surface extension by carbon aerogel (CA ) enhanced the maximum power density by 34 % compared to CC, to 14.1 W m−3. With nitrogen doped carbon aerogel (NCA) the performance was further increased to 15.7 W m−3. Co-doping the resorcinol-melamine-formaldehyde based aerogel with graphene oxide (GNCA) resulted in an additional power increase of 70 %, indicating that the electrocatalytic activity of NCAs can be considerably improved by co-doping with graphene oxide. Although the performance of GNCA remained below that of PtC (50.2 W m−3) in our investigations, it can be concluded that GNCA based coatings may provide a noble metal free, and therefore competitive and sustainable alternatives for cathode catalysis in MFC based technologies.

Background Nowadays, the development of biofilm on the cost-effective polymer-based substrate (anode) to be employed in a microbial fuel cell (MFC) is considered important. The present study deals with the formation of Bacillus subtilis 168 biofilm on a pencil lead graphite that was assessed in an MFC using electrochemical impedance spectroscopy (EIS). Method The cylindrical single-chambered MFC was designed by using an air-cathode supported stainless steel mesh as a cathode and pencil lead graphite as an anode. Cyclic Voltammetry (CV) and Scanning Electron Microscopy (SEM) were employed to investigate the biofilm formation. The monitoring of biofilm was conducted by impedance spectroscopy using a new Equivalent Electrical Circuit Model [R(QR)(Q[R(RQ)])]

Microbial fuel cells (MFCs) are recognized as an efficient method to utilize biomass to generate power while simultaneously treats wastewater. Micro-electro-mechanical system (MEMS) technology enables miniaturization of the MFCs system. Miniaturized MFCs through MEMS strengthen the system’s reaction capacity that makes it suitable for environmental sense field applications such as sensors or biomedical actuators. In this work, MEMS technology is employed to deposit metal layers on the surface of the anode/cathode electrode to enhance the power density of the MFC. Hence, micromixers and micro-pillars in the anode tank along with the influence of the electron transport media on MFC performance were evaluated. The introduction of the micro-mixers promotes the full mixing of the anolyte. The inclusion of the micro-pillars increases the surface area of the electrode, thereby enhancing the electrical energy output of the MFC. Results revealed that the introduction of the microstructure and the electron transfer media to the anolyte in the MFC have yielded a maximum current of 66.55 μ A cm−2, a maximum power density of 3.28 μ W cm−2, and an internal resistance value of 2 . 57 k Ω . Moreover, the inclusion of several micro-mixers and micro-pillar structures to the anode tank has shown the performance enhancement of MFC. Relevant research results will provide a reference for future research on the combination of MFCs and sensors.

Microbial fuel cell (MFC) is the most prominent bioelectrochemical approach in electricity generation while metal removal is its secondary application. However, ongoing challenges including low electron transfer rates and unstable biofilm formation on the anode surface need to be addressed. As an attempt to overcome such drawbacks, in the present study, the anode was prepared from graphene oxide (Lg-GO) obtained from lignin and subsequently modified with a metal oxide (i.e., TiO2). Thus, the plain Lg-GO and Lg-GO/TiO2 delivered 57.01 mA/m2 and 70.17 mA/m2 of current density along with 85 % and 90 % of Pb (II) ions removal from synthetic wastewater, respectively within the 90-day operation of MFC. The recorded maximum power density at the Lg-GO anode was 0.44 mW/m2, while the maximum PD at the Lg-GO/TiO2 anode was 0.78 mW/m2. The prepared anodes were characterized, and the operational conditions were optimized to validate their performances. The results showed that the optimum performance of the anode was in normal environmental conditions (e.g., pH 7, room temperature). In conclusion, the obtained results indicated that the prepared electrodes (i.e., Lg-GO and Lg-GO/TiO2) are suitable for energy generation and metal removal via MFC.

The aim of this study is to synthesise SPEEK composite proton exchange membrane with the addition of TiO2 nanofillers for microbial fuel cell application. SPEEK composite membrane with varying weight percentage of TiO2 (2.5, 5, 7.5 and 10%) was prepared to study the effect of TiO2 concentration on membrane performance. Synthesized composite membranes were subjected to various characterization studies such as FT-IR, XRD, Raman spectroscopy, TGA, UTM and SEM. Physico-chemical properties of membrane such as water uptake capacity, ion exchange capacity and thickness were also analyzed. 5% TiO2 – SPEEK composite membrane exhibited the higher water uptake capacity value and Ion exchange capacity value of 31% and 1.71 meq/g respectively. Performance of the MFC system with TiO2 – SPEEK membranes were evaluated and compared with the pristine SPEEK and Nafion membrane. 5% TiO2 – SPEEK membrane produced the higher power density (1.22 W/m2) and voltage (0.635 V) than the other membranes investigated. Efficacy of MFC in wastewater treatment was evaluated based on the chemical oxygen demand (COD), total organic carbon content and turbidity. Biofilm growth over the surface of the electrodes was also analyzed using scanning electron microscopy. HIGHLIGHTS Use of TiO2 – SPEEK composite membrane as alternate for the Nafion 117.; Energy generation from dairy wastewater was investigated using dual chambered MFC.; Low cost membrane.; Green energy.; TiO2 – SPEEK can be used to overcome drawbacks of Nafion 117.

Possibility of pyrolyzing high-density polyethylene (HDPE) waste and activating the HDPE-derived carbon (HDC) to be utilized as an oxygen reduction reaction (ORR) catalyst in microbial fuel cell (MFC) was explored. The Fourier transform infra-red spectrum of synthesized HDC indicated the presence of key surface functional groups that aid in catalyzing ORR, while the X-ray diffractogram indicated carbonization of HDC that enhanced electrical conductivity. Cyclic voltammogram and electrochemical impedance spectroscopy of HDC demonstrated an ORR peak current density of − 2.46 mA cm‒2, which was found to be comparable with commercial activated carbon (AC, − 2.71 mA cm‒2). The MFC with HDC as cathode catalyst (MFC–HDC) rendered a power density (115 mW m‒2) that was only 25% lower than the MFC with commercial AC as a catalyst (MFC–AC). Organic matter removal efficiency of MFC–HDC was comparable to MFC–AC. Thus, the low-cost HDC electrocatalyst (0.025 $ g‒1) exhibited catalytic performance comparable with AC (12 $ g‒1) and difference between the performance of the two MFCs with HDC and AC as catalyst can be attributed to the lower specific surface area (232 m2 g‒1) of the HDC catalyst as compared to AC (1200 m2 g‒1). Thus, for future applications, the specific surface area of HDC catalyst need to be improved to make it competitive with commercial AC.

One of the main challenges faced by microbial fuel cells (MFCs) generating voltage is how to facilitate the oxygen reduction reaction (ORR) process using a specifically designed air cathode, especially by optimizing a three-phase catalytic interface and enhanced O2 diffusion on it. Herein, a three-dimensional porous N-doped graphene aerogel (NGA) is polymerized onto a steel mesh (SM) to construct a simple structure of an air cathode (NGA-x/SM) via hydrothermal synthesis and subsequent freeze-drying treatment; more specifically, NGA was simultaneously used as an efficient ORR catalyst layer and breathable gas diffusion layer to improve the performance of MFCs. In this system, the NGA-5/SM (with a precursor concentration of x = 5.0 mg mL-1) makes itself a perfect candidate to be used as an air cathode. Characterization parameters reveal that sub-micrometer micropores, defective multilayer structures, and the highest proportion of pyridinic-N (48.1%) exist in NGA-5/SM. Furthermore, electrochemical measurements demonstrate that it has an oxygen reduction peak potential of 0.63 V, a Tafel slope of 187 mV dec-1, and closest 4e- transfer pathway (n = 3.2-3.5). These data prove that a three-phase boundary can naturally form in NGA-5/SM, where the ORR occurs. More importantly, this work provides a proof of concept that a Pt-free air cathode could be prepared with high-efficiency NGA by a two-step preparation method to achieve a MFC maximum power density of 1593 mW m-2.

Microfluidic paper based microbial fuel cells (μP-MFCs) have gained considerable popularity due to their compact, quick and low-cost fluid manipulation paradigm. Compared to conventional technologies, paper as a substrate with advanced nanomaterial electrode material has many distinct advantages from point-of-care monitoring to energy harvesting. As a result, these have been used and are more popular in a variety of fields, such as health diagnostics, environmental and food quality management. By this encouragement, herein a portable microbial fuel cell as an origami array has been demonstrated using custom carbon electrodes with a modified the transition metal oxide MnO2 nanomaterial. This customized electrode design was first printed using a tabletop PCB inkjet printer where the anode was further modified with synthesized MnO2 nanoparticles. The entire cell was formed by folding the paper along predefined edges where the fuel, Shewanella putrefaciens, was streamed continuously via inherent capillary cation. Various studies, such as morphological, surface catalyst coating, amount loading and volumetric culture optimization experiments, have also been accomplished to find the most appropriate optimum parameter to enhance power conversion efficiency. The developed origami arrayed microbial fuel generated an open-circuit potential (OCP) for two parallel connected MFCs of 0.534 V and a maximum power density of 15.9 μW/cm2 with a maximum current density of 130 μA/cm2. In the end, the harvested power was used by powering the digital watch circuit through the ultra-low DC-DC booster board. Such an MFC origami array, with simple electrode manufacturing and modification process, has a great potential and bright future in Internet of Things (IoT) applications by making multiple stacks where the data can be monitored.

As a promising energy storage/conversion technology, the microbial fuel cell (MFC) is generally restricted by the biofouling on the cathode and the sluggish kinetics of oxygen reduction reaction (ORR). Consequently, developing bacteriostatic and high-performance ORR catalysts is critical for the large-scale application of MFC. Herein, we prepare an electrocatalyst of porous octahedral zirconium-based metal organic framework (MOF) UiO-66-NH2 with dispersed Ag and Fe3C nanoparticles (Ag/Fe–N–C) through a facile impregnation and pyrolysis method for an efficient alkaline and neutral ORR. Systematic experimental results demonstrate that the synergistic effect of Ag and Fe can optimize the d-band center of catalyst to boost the interfacial charge transfer, thus resulting in an increased ORR kinetics. As expected, the catalyst with Ag/Fe–N–C-2:1 exhibits outstanding onset potential (1.01 V vs. RHE) and half-wave potential (0.58 V vs. RHE) in neutral electrolyte, which is comparable to Pt/C catalyst. Meanwhile, Ag/Fe–N–C-2:1 indicates obvious antibacterial activity, inhibiting the biofouling on the cathode surface. The MFC with the Ag/Fe–N–C-2:1 as the cathode catalyst can achieve a maximum power density of 1261.1 ± 24 mW m−3, outperforms the MFC with Pt/C (1087.5 ± 14 mW m−3). In summary, Ag/Fe–N–C-2:1 composite can serve as a feasible alternative cathode catalyst for MFC.

Developing low-cost and high-performance anodes is of great significance for wider applications of microbial fuel cells (MFCs). In this study, microalgae and pyrite were co-pyrolyzed (P/MC) and then coated on carbon felt (CF) with PTFE as a binder. P/MC modification resulted in increased electroactive surface area, superhydrophilicity and higher biocompatibility. Besides, the P/MC-CF anode reduced the charge transfer resistance from 35.1 Ω to 11.4 Ω. The highest output voltage and the maximum power density of the MFC equipped with the P/MC-CF anode were 657 mV and 1266.7 mW/m2, respectively, which were much larger than that of the MFC with the CF anode (530 mV, 556.7 mW/m2). The P/MC-CF anode also displayed higher columbic efficiency (39.41%) than the CF anode (32.37%). This work suggests that pyrolyzing microalgae with pyrite is a promising method to enhance the performance of MFCs.

The ternary component NiCoAl-layered double hydroxide (NiCoAl-LDH) and carbon nanotube (CNT) nano-composite (CNT/NiCoAl-LDH) were successfully prepared by a simple hydrothermal method. The NiCoAl-LDH nanosheets were effectively and uniformly grown on CNTs, forming a cross-linked conductive network structure, and stainless steel (SS) mesh was used as the base to load CNT/NiCoAl-LDH for microbial fuel cell (MFC) cathode. X-ray diffraction (XRD) results presented that the CNT/NiCoAl-LDH hybrid exhibited the (003), (006), (012), (015), (018), (110) and (113) crystal planes of hydrotalcite reflection. The surface functional groups C-O, C=O, C-H, C-N and M-O of the hybrid were confirmed. The cross-linked network structure of the hybrid was observed and the content and proportion of each element of the hybrid were found. CNT/NiCoAl-LDH showed excellent catalytic oxygen reduction reaction (ORR) ability by cyclic voltammetry (CV) and linear voltammetry (LSV) due to its abundant electrochemical active sites and excellent conductivity. The maximum output voltage of CNT/NiCoAl-LDH catalyst as MFC cathode was 450 mV, the maximum power density was 433.5 ± 14.8 mW/m2, and the maximum voltage stabilization time was 7–8 d. The results indicated that the CNT/NiCoAl-LDH hybrid was full potential as a high-performance, low-cost MFC cathode catalyst in future.

This research proposes an alternative for companies and farmers through the production of electricity using microbial fuel cells (MFCs) using waste from export products. Nine MFCs were manufactured with zinc and copper electrodes; and as substrates, pineapple, potato and tomato pulp wastes were used in the anode chamber, and residual sludge in the cathode chamber. It was observed that the MFCs with pineapple substrate generated higher values of the electrical parameters, resulting in voltage and current values of 0.3484 ± 0.003 V and 27.88 ± 0.23 mA, respectively. It was also observed that the maximum power density was 0.967 ± 0.059 W/cm2 at a current density of 0.04777 A/cm2 for the same substrate. Acid pH values were observed in the three samples, while the conductivity reached its maximum value on day 23 (69.47 ± 0.91 mS/cm) which declined until the last day of monitoring; the turbidity values increased abruptly after day 22 until the last day where a value of 200.3 ± 2.52 UNT was observed for the pineapple substrate. The scanning electron microscopy for the pineapple substrate MFC electrodes shows the formation of a porous biofilm on the zinc and copper electrodes. These results show that a new form of electricity production has been achieved by generating high voltage and current values, using low-cost materials.

It is critical to develop non-noble metal (NNM) electrocatalysts with excellent stability and innovative activity for oxygen reduction reaction (ORR) in the microbial fuel cells (MFCs), which is a promising energy conversion technology. Herein, the preparation of iron carbide electrocatalysts (SrCO3/Fe3C) by the pyrolysis of a bimetal precursor (Sr and Fe) is proposed as a feasible strategy to realize a highly active electrocatalyst for ORR. Based on the catalytic potential of Sr-based materials, Fe species doping can provide more beneficial active sites for ORR. Concisely, the SrCO3/Fe3C(1:12) catalyst achieves the onset potential of 0.197 V (vs. Ag/AgCl) superior than Pt/C catalyst (0.193 V vs. Ag/AgCl) and the half-wave potential of −0.157 V (vs. Ag/AgCl) in 0.1-M KOH solution. Furthermore, the electrocatalyst exhibits nearly four-electron pathway, and generates less than 3% H2O2. Compared with Pt/C catalyst, it possesses preferable stability and superior methanol tolerance. Moreover, a composite electrode with SrCO3/Fe3C(1:12) as a catalyst on the carbon cloth demonstrated a superb air cathode in MFCs with a power density of 398.98 mW m−2, which can outperform than 10 wt% Pt/C catalysts (342.13 mW m−2) on MFCs.

The aim of the present study is to enhance the performance of a microbial fuel cell (MFC) design by making simple interventions. Specifically, terracotta “t” and mullite “m” ceramics are tested as membranes while carbon veil and carbon cloth are used as electrodes. In the case of “m” cylinders different dimensions are examined (m: ID 30 mm x height 11.5 mm; sm: ID 18 mm x height 18 mm). The units operated continuously with urine as the feedstock. The best performing is the sm type (60–100 μW), followed by the t type (40–80 μW) and the m type (20–40 μW). Polarisation experiments indicated that activated carbon on the anode enhances the power output (t: 423 μW, sm: 288 μW). Similarly, the increase of the surface area and the addition of stainless steel mesh on the cathode improves the power performance for the “sm” and the “t” units. Furthermore, it is shown that the design with the smaller internal diameter, performs better and is more stable through time., Graphical abstract Image 1, Highlights • A microbial fuel cell design is optimized by making simple modifications. • The design performs better when its internal diameter is decreased from 30 mm to 18 mm. • Activated carbon on the anode drastically increases the maximum power output. • The increase of the cathodic surface area boosts the power output. • Stainless steel mesh on the carbon cathode electrode enhances the power output.

Microbial fuel cells (MFCs) convert chemical energy to electrical energy via electrochemically active microorganisms. The interactions between microbes and the surface of a carbon electrode play a vital role in capturing the respiratory electrons from bacteria. Therefore, improvements in the electrochemical and physicochemical properties of carbon materials are essential for increasing performance. In this study, a microwave and sulfuric acid treatment was used to modify the surface structure of graphite granules. The prepared expandable graphite granules (EGG) exhibited a 1.5 times higher power density than the unmodified graphite granules (1400 vs. 900 mW/m3). Scanning electron microscopy and Fourier transform infrared spectroscopy revealed improved physical and chemical characteristics of the EGG surface. These results suggest that physical and chemical surface modification using sulfuric acid and microwave heating improves the performance of electrode-based bioprocesses, such as MFCs.

Microbial fuel cells (MFCs) as a renewable energy conversion technology have been attracting increasing attention in the past decades. However, a deeper understanding of bioelectrochemical reaction in electrodes is urgent to improve the cell performance towards practical applications. In this paper, a mathematical model of air cathode MFCs was proposed by coupling mass transport and charge conservation with bioelectrochemical/electrochemical reactions. The model was validated based on experimental results and further used to predict the performance of MFCs. The effect of mass transport including oxygen and substrate on electrode kinetics was studied based on the model. The results showed that enhancing mass transport in both anode and cathode remarkably facilitated the electrode current and hence the cell performance, and oxygen transfer in catalyst layer of cathode is the dominating factor limiting the cell performance. The proposed model can provide a facile avenue to capture the interdependence of electrode variables and help guide electrode design for optimizing the performance of MFCs in practical applications.

In this study, we investigate the effect of heat treatment on the surface properties of carbon cloth electrodes and on the power generation efficiencies of microbial fuel cells (MFCs) configured with the heat-treated carbon cloth electrodes. Water contact angle measurements show that the hydrophobic surfaces of the carbon cloth became super-hydrophilic after heat treatment at a temperature above 500 °C, making it suitable for bacterial propagation. X-ray photoelectron spectrometry revealed that the signal of the C-O functional group of the carbon cloth electrodes increased in intensity after heat treatment. The MFCs configured with heat-treated carbon cloth electrode exhibited high power density of 16.58 mW/m2, whereas that of the untreated MFCs was only 8.86 mW m2. Compared with other chemical modifications, heat treatment does not use any environmentally unsound acidic or toxic solutions during modification and are promising for manufacturing large-scale MFC stacks.

This study shows the effectiveness of titanium dioxide (TiO₂) on a floating microbial fuel cell (FMFC). In the experiment, when a UV cutoff filter attached halogen lamp was used, the power density of the FMFC using pristine TiO₂ (P25) and the FMFC using TiO₂ sintered at 650 °C were was 2.11mW/m2 and 10.44 mW/m2 respectively. Next, when measured without UV cutoff filter, pristine TiO₂ type FMFC and 650°C sintered TiO₂ type FMFC recorded 2.93 mW/m2 and 11.93 mW/m2 respectively. From this result, it was confirmed that the power density was improved up to five times when the UV cutoff filter was used and four times when it was not used. According to the results of X-ray Diffraction (XRD), 650°C sintered TiO₂ is composed of more rutile phase than pristine TiO₂.

Microbial fuel cells (MFCs) have various potential applications. However, anode is a main bottleneck that limits electricity production performance of MFCs. Herein, we developed a novel anode based on a stainless steel cloth (SC) modified with carbon nanoparticles of Chinese ink (CI) using polypyrrole (PPy) as a building block (PPy/CI/SC). After modification, PPy/CI/SC showed a 30% shorten in start-up time (36.4 ± 3.3 h vs. 52.3 ± 1.8 h), 33% increase in the maximum current (12.4 ± 1.4 mA vs. 9.3 ± 0.95 mA), and 2.3 times higher in the maximum power density of MFC (61.9 mW/m2 vs. 27.3 mW/m2), compared to Ppy/SC. Experimental results revealed that carbon nanoparticles were able to cover SC uniformly, owing to excellent dispersibility of carbon nanoparticles in CI. The attachment of carbon nanoparticles formed a fluffy layer on SC increased the electrochemically-active surface area by 1.9 times to 44.5 cm2. This enhanced electron transfer between the electrode and bacteria. Further, embedding carbon nanoparticles into the PPy layer significantly improved biocompatibility as well as changed functional group contents, which were beneficial to bacteria adhesion on electrodes. Taking advantage of high mechanical strength and good conductivity, a large-size PPy/CI/SC was successfully prepared (50 × 60 cm2) demonstrating a promising potential in practical applications. This simple fabrication strategy offers a new idea of developing low cost and scalable electrode materials for high-performance energy harvesting in MFCs.

Noble metal-free and highly efficient electrocatalytic materials with hierarchically porous structures continue to be studied for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). We report bimetal-organic framework (bi-MOF)-derived nanocubic Swiss cheese-like carbons with a novel three-dimensional hierarchically porous structure (3D Co-N-C) prepared by utilizing cetyltrimethyl-ammonium bromide (CTAB) as a structure-directing agent to control the formation of a nanocubic skeleton, and silica spheres as a template to form a mesoporous structure. The elemental composition and chemical morphology of this material can be tuned through the Zn/Co ratio to optimize its ORR catalytic activity. The optimized 3D Co-N-C displays excellent ORR catalytic performance (half-wave potential as high as 0.754 V vs . reversible hydrogen electrode and diffusion-limiting current density of 5.576 mA cm−2) in 0.01 mol L−1 phosphate-buffered saline (PBS electrolyte), showing it can compete with the commercial 20 wt% Pt/C catalysts. The catalytic capability and long-term durability of 3D Co-N-C as an air-filled cathode electrocatalyst in an MFC device are tested, showing that the 3D CoNC-MFC can reach a high power density of 1257 mW m−2 and provide a competitive voltage during a periodic feeding operation for 192 h; these values are much higher than those of the Pt/C-MFC.

Improving the power output and other power generation performance is the technical bottleneck restricting the industrial application of microbial fuel cell (MFC). Modification of the anode using na...

Microbial fuel cells (MFC) are technologies in which microorganisms directly convert organic compounds (sugars, alcohols, effluents) into electricity. In this paper, yeast Saccharomyces cerevisiae is used in microbial fuel cells as a microorganism to produce bioelectricity. First, electron production is simulated using a genome-scale metabolic (GEM) model of the Saccharomyces cerevisiae genome-scale. The GEM model is used to predict the metabolic fluxes for microbial cells. Then, two small and large scale electrodes with 1.5 × 1.5 × 2 cm3 and 2 × 2 × 2 cm3 (4.5 ml and 8 ml) sizes were made and the effect of electrode size on power generation is investigated. Also, to increase the electrical conductivity, carbon/graphite is coated on the electrodes by pyrolysis spray. By changing the size of the electrode in the microbial fuel cell, the current density and the power output level were investigated. The results showed that, due to the reduction of losses in the activation region in the polarization diagram significantly, the density of electric current and the power output level in the microbial fuel cell of a small scale is higher than the large scale. Therefore, by reducing the size of the electrode in the microbial fuel cell, the production of electric current intensity and power output level increases.

Microbial fuel cell (MFC) is a type of bio-electrochemical system, which harvests bioelectricity by oxidizing the organic material present in the wastewater. Performance of a MFC relies on the both anodic and cathodic reaction kinetics. The oxygen reduction reaction (ORR) occurring on the cathode is a sluggish reaction, which majorly diminishes the power generation of a MFC. In this context, the use of metal organic frameworks (MOFs) is appropriate as a cathode catalyst to boost the ORR kinetics, thus enhancing the power generation of MFCs. The higher specific surface area, excellent catalytic activity and precise permeable structure of MOFs render them suitable for the application as cathode catalysts to enhance ORR in MFCs. Hence, there is a wide scope of implementation of different low-cost MOF-based cathode catalysts in MFCs, which would not only enhance its performance but also would diminish the fabrication cost of field-scale MFCs. This review therefore provides the detailed understanding on both the synthesis methods and structural characteristics of MOFs and also explains the mechanism of ORR, role of cathode catalysts and application of MOFs as cathode catalysts in MFCs.

Ceramic separators have recently been investigated as low-cost, robust, and sustainable separators for application in microbial fuel cells (MFC). In the present study, an attempt was made to develop a low-cost MFC employing a clayware ceramic separator modified with silica. The properties of separators with varying silica content (10%–40% w/w) were evaluated in terms of oxygen and proton diffusion. The membrane containing 30% silica exhibited improved performance compared to the unmodified membrane. Two identical MFCs, fabricated using ceramic separators with 30% silica content (MFCS-30) and without silica (MFCC), were operated at hydraulic retention time of 12 h with real rice mill wastewater with a chemical oxygen demand (COD) of 3,200 ± 50 mg/L. The maximum volumetric power density of 791.72 mW/m3 and coulombic efficiency of 35.77% was obtained in MFCS-30, which was 60.4% and 48.5%, respectively, higher than that of MFCC. The maximum COD and phenol removal efficiency of 76.2% and 58.2%, respectively, were obtained in MFCS-30. MFC fabricated with modified ceramic separator demonstrated higher power generation and pollutant removal. The presence of hygroscopic silica in the ceramic separator improved its performance in terms of hydration properties and proton transport. Highlights Ceramic separator modified with silica (30% w/w) outperformed unmodified separator.; 1.5 times more proton mass transfer was observed in ceramic separator with 30% silica.; Internal resistance of the MFC decreased 1.6 times due to better proton mobility.; Volumetric power density of 0.8 W/m3 and COD removal of 76.24% was achieved.; 1.5 times higher coulombic efficiency was obtained in the MFC operated with modified separator.

Materials at the nanoscale show exciting and different properties. In this review, the applications of nanomaterials for modifying the main components of microbial fuel cell (MFC) systems (i.e., electrodes and membranes) and their effect on cell performance are reviewed and critically discussed. Carbon and metal-based nanoparticles and conductive polymers could contribute to the growth of thick anodic and cathodic microbial biofilms, leading to enhanced electron transfer between the electrodes and the biofilm. Extending active surface area, increasing conductivity, and biocompatibility are among the significant attributes of promising nanomaterials used in MFC modifications. The application of nanomaterials in fabricating cathode catalysts (catalyzing oxygen reduction reaction) is also reviewed herein. Among the various nanocatalysts used on the cathode side, metal-based nanocatalysts such as metal oxides and metal-organic frameworks (MOFs) are regarded as inexpensive and high-performance alternatives to the conventionally used high-cost Pt. In addition, polymeric membranes modified with hydrophilic and antibacterial nanoparticles could lead to higher proton conductivity and mitigated biofouling compared to the conventionally used and expensive Nafion. These improvements could lead to more promising cell performance in power generation, wastewater treatment, and nanobiosensing. Future research efforts should also take into account decreasing the production cost of the nanomaterials and the environmental safety aspects of these compounds.

Background Microbial fuel cell (MFC) technology is a promising sustainable future energy source with a renewable and abundant substrate. MFC critical drawbacks are anode surface area limitations and electrochemical loss. Recent studies recommend thick anode biofilm growth due to the synergetic effect between microbial communities. Engineering the anode surface area is the prospect of MFC. In this study, a microbial electrode jacket dish (MEJ-dish) was invented, first time to the authors’ knowledge, to support MFC anode biofilm growth. The MFC reactor with MEJ-dish was hypothesized to develop a variable biofilm thickens. This reactor is called a fragmented electro-active biofilm-microbial fuel cell (FAB-MFC). It was optimized for pH and MEJ-dish types and tested at a bench-scale. Results Fragmented (thick and thin) anode biofilms were observed in FAB-MFC but not in MFC. During the first five days and pH 7.5, maximum voltage (0.87 V) was recorded in MFC than FAB-MFC; however, when the age of the reactor increases, all the FAB-MFC gains momentum. It depends on the MEJ-dish type that determines the junction nature between the anode and MEJ-dish. At alkaline pH 8.5, the FAB-MFC generates a lower voltage relative to MFC. On the contrary, the COD removal was improved regardless of pH variation (6.5–8.5) and MEJ-dish type. The bench-scale studies support the optimization findings. Overall, the FAB improves the Coulombic efficiency by 7.4–9.6 % relative to MFC. It might be recommendable to use both FAB and non-FAB in a single MFC reactor to address the contradictory effect of increasing COD removal associated with the lower voltage at higher pH. Conclusions This study showed the overall voltage generated was significantly higher in FAB-MFC than MFC within limited pH (6.5–7.5); relatively, COD removal was enhanced within a broader pH range (6.5–8.5). It supports the conclusion that FAB anode biofilms were vital for COD removal, and there might be a mutualism even though not participated in voltage generation. FAB could provide a new flexible technique to manage the anode surface area and biofilm thickness by adjusting the MEJ-dish size. Future studies may need to consider the number, size, and conductor MEJ-dish per electrode.

Coal tar pitch, the residue generated from distillation of coal tar, is cheap, abundant, and carbon enriched. This paper evaluates the effects of the surface modification of coal-tar pitch-derived nanoporous carbons (NPCs) as anode materials on the performance of Escherichia coli (E. coli)-based microbial fuel cells (MFCs) for the first time. The coal-tar pitch precursors are heated under N2 to 450 °C (450O) and 750 °C (750X) to obtain NPCs with different concentrations of oxygen-containing functional groups. 750X is, thereafter, doped with nitrogen atoms to generate a nitrogen-doped NPCs (750N). More biofilm is formed on the 750N anode than the 750X or 450O anode because of the higher electrical conductivity and biocompatibility of 750N. As a result, a higher power output of MFC is obtained when the 750N anode is used. The maximum power density of 750N is 3772 mW m−2, while that of 750X and 450O are 2876 mW m−2 and 3562 mW m−2, respectively, demonstrating that 750N is a potential sustainable anode material for high-performance MFC applications.

This study is a contribution to development of material based on transition metal oxides with application in electrochemical devices. A pyrochlore-like solid solution with general chemical formula ...

Microbial fuel cell (MFC) is a device that coverts the chemical energy contents of organic matter to electrical energy by the catalytic action of microorganisms. Cow dungs as organic substrates were used in three sets of dual chambered MFCs to study the effects ofelectrodes on the open circuit voltage (OCV) generation of MFC. The anode and cathode compartments were connected using a protonexchange membrane, 1 kg of the cow dung diluted with 500 ml of water was introduced in the anode compartment of each of the setups. The electrode configurations for set-up 1, 2 and 3 respectively were Carbon-Carbon(C-C), carbon-copper(C-Cu) and carbon- zinc(C-Zn). Samples for microbial load count were collected every two days from the anode compartment of the MFC and analyzed using standard microbiological methods. The OCV of the three setups were measured daily for two weeks using a digital multimeter. The microbial load ranged from 4.2 × 104 to 8.5 × 104 CFU/ml for bacteria and 2.1 × 102 to 2.3 × 103 CFU/ml for fungi. The range (average) of the OCV obtained from the set-ups were 0.06 to 0.72 V (0.42 V) for the C–C; 0.02 to 0.67 V (0.26 V) for C-Cu and 0.11 to 0.78 V (0.39 V) for the C-Zn. The OCV for the C-C electrode combination showed an increasing trend while the OCV of C-Cu and C-Zn showed decreasing trends with increasing number of days. The C-C electrode combination gave the best OCV. Keywords: microbial fuel cell, open circuit voltage, electrodes, organic substrate

In this study, the cathode chamber of the microbial fuel cell (MFC) was aerated using the photosynthetic aeration method and was compared with the mechanical aeration method in terms of power generation. Light energy for photosynthetic aeration was supplied in different regimes. The dissolved oxygen of 8.0–9.0 mg/L in the cathode chamber under mechanical aeration was increased to 10.0–11.0 mg/L under photosynthetic aeration of continuous light supply. The maximum power density obtained in the mechanical aeration was increased by 34.5% when photosynthetic aeration employed. Also, the algal assisted cathodic reaction under photosynthetic aeration reduced the internal resistance of the cell by 13.7%. To simulate with natural sun lighting conditions, 12/12 h of dark/light regime was tested to observe the stability of the MFC. During the light phase, microalgae carried out photosynthesis and provided the oxygen required for the cathodic reaction while in the dark phase, the voltage in the cell dropped due to the respiration by microalgae. The dissolved oxygen level dropped to 6.5–7.5 mg/L during the dark phase. Cathode chamber was also operated under 32/32 h of light/dark regime to observe the voltage variation under longer cycles. A higher voltage drop was observed in 32/32 h light/dark regime, as compared with 12/12 h of light/dark regime. Biomass productivity of 0.58 g/L/day was achieved in the MFC conducted under continuous light. It was reduced to 0.51, and 0.39 g/L/day under 12/12 h, and 32/32 h of light/dark regimes, respectively. The results suggested that photosynthetic aeration has the potential to achieve better power generation in the cell than mechanical aeration with an additional advantage of simultaneous microalgal biomass production.

Microbial fuel cells (MFCs) are a newly emerging technology in bioenergy processing. This research is to replace the use of platinum catalysts. Three types of oxygen reduction catalysts (B12/XC-72, B12/CNT and B12/AC) are analyzed and compared with the other two activated sludge and no catalyst where the performance of activated carbon in MFCs are evaluated. The results show that the catalyst with B12 vitamin as the main body has a higher open-circuit voltage. Among them, the open-circuit voltage of B12/CNT is the highest with 0.667 V, which is about 2 times that of MFCs without catalyst. The highest electrical performance with 0.54 W m−2 is 3.17 times that of catalyst-free MFCs, which shows that the self-made B12/CNT catalyst MFCs have the best performance in this study. The related research will be helpful for the application of wastewater to energy.

The present research demonstrates the design and development of a dual-compartment water purification proto-plant for microbial degradation of organic waste using microbial fuel cell technology and adsorptive removal of inorganic pollutants present in sewage water using highly crystalline chitosan grafted polyaniline (CHIT-g-PANI) and rice husk derived adsorbent. The materials were characterized by UV–Vis, infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and relevant standard methods. The observed results revealed the highly crystalline, biocompatible, porous nature of CHIT-g-PANI as electrode materials for effective microbial degradation of organic wastes of sewage water for generating electricity and water purification. Thus, observed parameters were power density of 6.496 w/m2, sustainable usability for 20 days, and removal of organic waste by 97% from sewage water. Furthermore, the above partially treated water was passed through an adsorption chamber filled with rice husk-derived adsorbents, which removes the 84.5% inorganic impurities of its original concentrations.

The microbial fuel cell (MFC) efficiency was assessed by using biochar electrode. Electrodes were made of silicon (Si0.4), zinc (Zn0.4), and copper (Cu0.4) in 40% proportions mixed with derived waste coconut shell (CS) biochar materials after the carbonization process. The specific surface area of CS-Si0.4 (0.1920 m2 g−1), CS-Zn0.4 (0.2025 m2 g−1), and CS-Cu0.4 (0.2532 m2 g−1) is higher when compared to Graphite Particle (GP) (0.2165 m2 g−1). Electrodes’ power production outputs were CS-Si0.4 ((19.22 ± 0.5) mW m−2), CS-Zn0.4 ((26.40 ± 0.6) mW m−2), and CS-Cu0.4 ((47.04 ± 0.5) mW m−2) similar to GP ((32 ± 0.5) mW m−2). Experimental results show that the CS-Cu0.4 electrode provides maximum power output and efficiency. The inclusion of metals will increase surface area of biochar electrodes, and it increases the microbial fuel cell efficiency. The CS-Cu0.4 electrodes are therefore feasible, biocompatible, and cost-effective for environmentally sustainable systems.

This work aims at providing a simple and effective method to optimize and improve the nitrogen-based defects into intrinsically N-doped carbon-based electrospun nanofibers (CNFs) for achieving highly active catalysts for the oxygen reduction reaction (ORR). To reach this goal, plasma treatments are investigated as an effective method to tune the distribution of the N-doping sites that are vital to improve the ORR catalytic activity of the material. Morphological, physical, chemical as well as electrochemical characterizations were performed on plasma-treated CNFs to demonstrate the effectiveness of such treatments to improve the catalytic behavior of CNFs toward ORR. Finally, Microbial Fuel Cells (MFCs) were selected to test the plasma-treated nanofibers as the cathode catalyst layer demonstrating an increase of the overall performance of the MFCs with respect to the devices using the Pt-based reference catalyst.

Sediment microbial fuel cells (SMFCs) are energy harvesting devices where the anode is buried inside marine sediment, while the cathode stays in an aerobic environment on the surface of the water. To apply this SCMFC as a power source, it is crucial to have an efficient power management system, leading to development of an effective energy harvesting technique suitable for such biological devices. In this work, we demonstrate an effective method to improve power extraction with SMFCs based on anodes alternation. We have altered the setup of a traditional SMFC to include two anodes working with the same cathode. This setup is compared with a traditional setup (control) and a setup that undergoes intermittent energy harvesting, establishing the improvement of energy collection using the anodes alternation technique. Control SMFC produced an average power density of 6.3 mW/m2 and SMFC operating intermittently produced 8.1 mW/m2. On the other hand, SMFC operating using the anodes alternation technique produced an average power density of 23.5 mW/m2. These results indicate the utility of the proposed anodes alternation method over both the control and intermittent energy harvesting techniques. The Anode Alternation can also be viewed as an advancement of the intermittent energy harvesting method.

Sediment microbial fuel cell (SMFC) is a bio-electrochemical device that uses anaerobic bacteria to produce renewable energy. The voltage generated by SMFC is very low, so directly it cannot be applied to modern electronic devices. But, it is feasible to raise the output voltage of SMFC by connecting them in series-parallel combinations. In the present work, four SMFC modules are developed in the laboratory and by connecting in four different ways the output voltage as well as the output current are raised to the utility levels. The primary cause to avoid the practical application of series and parallel connected SMFC is voltage reversal problem. To do away with this problem, in this work each group of SMFCs is first used to charge a super-capacitor (4 F, 5.5 V) and then it has been used to power the dc boost converter. Moreover, in this research work, the effects of charging and discharging times of super capacitors for each module are also investigated. In the final stage, a dc boost converter is presented to step-up the voltage of stacked SMFCs which provides a regulated output voltage (9 V/12 V) at the load. The results obtained, show that module-4 connected boost converter provides higher output current for a longer duration as compared to other super capacitor connected modules. This technique of energy harvesting from SMFCs can be used as a power source (either of 9 V or 12 V) in practical electronic devices.

This work has investigated the scale-up potential of microbial fuel cells (MFCs) under stacking mode. Stacking was done in batch mode and continuous mode. Batch feeding mode stacks were operated in electrical series (S) and parallel (P) mode. Continuous feeding mode stacks were kept in electrically parallel mode with different hydro-dynamic patterns. The two continuous stacks were connected hydro-dynamically in series (i.e. Parallel Dependent; PD) and parallel (i.e. Parallel Independent; PID) configurations. The performance of the continuous stacks was evaluated on the basis of COD consumption rate, power generation and coulombic efficiency. PID obtained highest power (0.47 mW) which was approximately 3.6 times that of PD configuration (0.13 mW). The rate of COD consumption was also highest in PID stack (3091.75 mg·L−1·d−1). Coulombic efficiency of the PID stack was 14.26% which was approximately 292.8% of the PD stack. The results confirmed that the parallel electrical connection hybridized with the independent hydro-dynamic flow gives the best possible results when working with stacking of MFCs.

A novel in situ approach is proposed to visualize biofilm formation in the microchannel for the microfluidic microbial fuel cell (MMFC) anode, which could reflect a more precise biofilm formation during start-up process in real-time. A microchannel reactor was designed and fabricated based on a transparent indium-tin-oxide (ITO) conductive membrane. In situ visualization of biofilm formation under various anolyte flow rates was captured by a phase contrast microscope combined with a custom long working distance objective. The results show that no steady biofilm is formed on the surface of anode under low flow rate of 50 μL min−1 because of the insufficient nutrient supply. With increasing the anolyte flow rate, more attached bacteria on the anode surface and denser biofilm are observed in the microchannel. Less bacteria are attached on the surface of anode along flow direction due to the entrance effect. However, denser biofilm leads to larger mass transfer resistance of the anolyte and product in biofilm. Therefore, a superior bioelectrochemical performance is yielded for the biofilm formed under a moderate flow rate during start-up process.