Electrodeposition of graphene by cyclic voltammetry on nickel electrodes for microbial fuel cells applications

Ni electrode was modified with graphene by the electrodeposition (ED) method to prepare an anode (anode‐ED) for microbial fuel cell (MFC). Electrochemical and morphological characterizations of anode‐ED along with the effects of anode modification on the MFC performance were investigated. The graphene modification based on cyclic voltammetric electrodeposition resulted in the decrease of charge transfer resistance (R_ct) and improved extracellular electron transfer efficiency of anode. The maximum power density obtained from the MFC equipped with anode‐ED was 25.83 and 17.86 times larger than those of MFCs equipped with bare Ni anode and anode modified with graphene by traditional hydrothermal treatment method (anode‐HT), respectively. The electrochemical impedance spectroscopy (EIS) analysis results indicated that the R_ct of anode decreased significantly after inoculation during the MFC operation. The improvement in power density was attributed to the decreasing R_ct and the biocompatibility of graphene modified on anode‐ED surface. This study presented an effective electrodeposition method to make graphene‐modified anodes, which could improve the MFC performance.     

Modification of graphite felt using nano polypyrrole and polythiophene for microbial fuel cell applications-a comparative study

Microbial fuel cells (MFC) are bio-electrochemical devices used for the generation of electricity from biomass. A single chamber membrane less air-breathing cathode microbial fuel cell (SCMFC) with two different anode configurations was investigated for energy generation using shewanella putrifaciens as bio-catalyst. The graphite felt (GF) anode was modified with 0.008 g/cc polypyrrole nanoparticles (Ppy-NPs) and 0.024 g/cc polythiophene nanoparticles (PTh-NPs) by conventional method. The nanoparticles coating improved the properties such as thermal characteristics and electron transfer capabilities of the anodes, which was confirmed by Thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS) and cyclic voltametry (CV). The variation in the cell potential with time under open circuit condition resulted in voltages of 0.842V and 0.644 V for Ppy-NP and PTh-NP modified GF respectively. A maximum power density (1.22 W/m²) was obtained for Ppy-NP modified GF than PTh-NP modified GF (0.8 W/m²). The results showed that GF coated with nano conductive polymers such as Ppy and PTh are the promising candidates for the best performance of a MFC.     

A graphene modified anode to improve the performance of microbial fuel cells

Graphene with a Brunauer-Emmett-Teller (BET) specific surface area of 264 m² g⁻¹ has been used as anodic catalyst of microbial fuel cells (MFCs) based on Escherichia coli (ATCC 25922). The electrochemical activities of plain stainless steel mesh (SSM), polytetra?uoroethylene (PTFE) modified SSM (PMS) and graphene modified SSM (GMS) have been investigated by cyclic voltammetry (CV), discharge experiment and polarization curve measurement. The GMS shows better electrochemical performance than those of SSM and PMS. The MFC equipped with GMS anode delivers a maximum power density of 2668 mW m⁻², which is 18 times larger than that obtained from the MFC with the SSM anode and is 17 times larger than that obtained from the MFC with the PMS anode. Scanning electron microscopy (SEM) results indicate that the increase in power generation could be attributed to the high surface area of anode and an increase in the number of bacteria attached to anode.     

Facile microwave-assisted synthesized reduced graphene oxide/tin oxide nanocomposite and using as anode material of microbial fuel cell to improve power generation

A new nanocomposite material was fabricated by a facile and reliable method for microbial fuel cell (MFC) anode. Tin oxide (SnO₂) nanoparticles were anchored on the surface of reduced graphene oxide (RGO/SnO₂) in two steps. The hydrothermal method was used for the modification of GO and then microwave-assisted method was used for coating of SnO₂ on the modified GO. Nanohybrids of RGO/SnO₂ achieved a maximum power density of 1624 mW m⁻², when used as the MFC anode. The obtained power density was 2.8 and 4.8 times larger than that of RGO coated and bare anodes, respectively. The electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics were also studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The high conductivity and large specific surface of the nanocomposite were greatly improved the bacterial biofilm formation and increased the electron transfer. The results demonstrate that the RGO/SnO₂ nanocomposite was advantageous material for the modification of anode and enhanced electricity generation of MFC.     

Increasing power generation of microbial fuel cells with a nano-CeO2 modified anode

Nano-CeO₂ was used to modify the carbon felt anode in microbial fuel cell (MFC). The MFC with the modified anode obtained the higher closed circuit voltage resulting from the lower anode potential, the higher maximum power density (2.94 W m^?2), and the lower internal resistance (77.1 Ω). Cyclic voltammetry (CV) results implied that the bioelectrochemical activity of exoelectrogens was promoted by nano-CeO₂. Electrochemical impedance spectroscopy (EIS) results revealed that the anodic charge transfer resistance of the MFC decreased with modified anode. This study demonstrates that the nano-CeO₂ can be an effective anodic catalyst for enhancing the power generation of MFC.     

Pyrolyzing pyrite and microalgae for enhanced anode performance in microbial fuel cells

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.     

Novel porous carbon felt cathode modified by cyclic voltammetric electrodeposited polypyrrole and anthraquinone 2-sulfonate for an efficient electro-Fenton process

A novelty two-step synthesized porous carbon felt (PCF) cathode modified by cyclic voltammetric (CV) electrodeposited polypyrrole (Ppy) and anthraquinone 2-sulfonate (AQS) (PCF/Ppy/AQS) for an efficient electro-Fenton process has been investigated. Brunauer Emmett Teller (BET) and scanning electron microscope (SEM) measurements verified the three-dimensional porous structure of the PCF, revealing that the specific surface area was approximately 2.5 times higher than that of the bare carbon felt (CF), which ensured more active sites available for oxygen reduction reaction (ORR). In addition, the electrodeposited Ppy decreases the charge transfer resistance (R_ct) of the PCF cathode. AQS, a type of anthraquinone that can serve as an oxygen reduction catalyzer, could accelerate the ORR process and subsequently improve the performance of the electro-Fenton system. Rotating disk electrode (RDE) analysis confirmed that the ORR catalyzed by AQS was a double-electron reduction process, which contributed to hydrogen peroxide (H₂O₂) generation. The removal efficiency of total organic carbon (TOC) from Rhodamine B (RhB) could reach 51% within 1 h in the electro-Fenton system equipped with the PCF/Ppy/AQS, resulting in an improvement of approximately 24% compared with the bare CF cathode without porous treatment. The cycle experiment showed a good stability of the PCF/Ppy/AQS cathode. Additionally, the possible mechanism of degradation process in the electro-Fenton equipped with the PCF/Ppy/AQS cathode was proposed based on the electron paramagnetic resonance (EPR) analysis and quenching experiment. The novel fabricated PCF/Ppy/AQS provides an alternative as a high-efficiency cathode, yielding energy savings in the electro-Fenton system.     

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

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

Microbial fuel cell constructed with micro-organisms isolated from industry effluent

Three types of aerobic bacteria such as Citrobacter freundii, Proteus mirabilis and Bacillus subtilis were evaluated in terms of bioelectricity production using double chambered microbial fuel cell (MFC) with graphite cloth as anode and cathode and Nafion membrane as proton exchange membrane (PEM). Performance of MFC was studied with addition of glucose. Cyclic voltammetry (CV) experiments showed the presence of peaks at −92 and −163 mV vs Ag/AgCl for C. freundii and P. mirabilis indicating their electrochemical activity without an external mediator. Potential time experiments showed the potential of MFC solely depend on change in anode potential rather than cathode potential. The internal resistance of MFC containing B. subtilis was lower than C. freundii and P. mirabilis. Fuel cell performance was evaluated employing polarization curve and power output along with cell potentials. MFC containing B. subtilis with neutral red mediator showed current output of 112 mA m⁻² at external resistance of 0.3 kΩ which is higher than the current outputs from MFC containing C. freundii and P. mirabilis. The relative efficiency of power generation observed in aerobic microenvironment may be attributed to the effective substrate oxidation and good biofilm growth observed on the anodic surface.     

Enhanced performances of microbial fuel cells using surface-modified carbon cloth anodes: A comparative study

In this study, performances of two-chamber microbial fuel cells (MFCs) with surface-modified carbon cloth anodes by four methods are compared including soaking in aqueous ammonia (CC-A), electrolysis in phosphate buffer (CC-P), electrolysis in nitric acid (CC-N) and electrolysis in nitric acid followed by soaking in aqueous ammonia (CC-NA). It is found that performances of all these modified anodes are better than that of the bare one. The MFC with the anode modified by CC-NA yield the maximum power density of 3.20 ± 0.05 W m⁻², which is 58%, 36%, 35% and 28% higher than those of the MFC with untreated anode (CC-C, 2.01 ± 0.02 W m⁻²), and treated by the CC-A (2.35 ± 0.15), CC-N (2.38 ± 0.02 W m⁻²) and CC-P (2.50 ± 0.08 W m⁻²) methods, respectively. The active biomass and EIS analysis for the anodes indicated that the highest power output of the CC-NA MFC may primarily attributed to the enhanced electron transfer resulting from the existence of quinoid groups on the CC-NA surface, rather than the biomass effect. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopic analyses of the CC-NA anode further demonstrate that the formation of quinoid groups contributes to the improvement in the MFC performance by accelerating the electron transfer between electrochemically active bacteria (EAB) and the anode surface.     

Diphenyloctyl phosphate as a flame-retardant additive in electrolyte for Li-ion batteries

The use of diphenyloctyl phosphate (DPOF) as a flame-retardant additive in liquid electrolyte for Li-ion batteries is investigated. Mesocarbon microbeads (MCMB) and LiCoO₂ are used as the anode and cathode materials, respectively. Cyclic voltammetry (CV), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) are used for the analyses. The cell with DPOF shows better electrochemical cell performance than that without DPOF in initial charge/discharge and rate performance tests. In cycling tests, a cell with DPOF-containing electrolyte exhibited better discharge capacity and capacity retention than that of the DPOF-free electrolyte after cycling. These results confirm the viability of using DPOF as a flame-retardant additive for improving the cell performance and thermal stability of electrolytes for Li-ion batteries.     

Methanol electro-oxidation on Pt/C modified by polyaniline nanofibers for DMFC applications

In the present study, in order to achieve an inexpensive tolerable anode catalyst for direct methanol fuel cell applications, a composite of polyaniline nanofibers and Pt/C nano-particles, identified by PANI/Pt/C, was prepared by in-situ electropolymerization of aniline and trifluoromethane sulfonic acid on glassy carbon. The effect of synthesized PANI nanofibers in methanol electrooxidation reaction was compared by bare Pt/C by different electrochemical methods such as; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Scanning electron microscopy (SEM) was also employed to morphological study of the modified catalyst layer. The test results reveal that introduction of PANI nanofibers within catalyst layer improves the catalyst activity in methanol oxidation, hinders and prevents catalyst from more poisoning by intermediate products of methanol oxidation and improves the mechanical properties of the catalyst layer. SEM images also indicate that PANI nanofibers placed between platinum particles and anchor platinum particles and alleviate the Pt migration during methanol electrooxidation.     

Study on stability of self-breathing DFMC with EIS method and three-electrode system

In this paper, direct methanol fuel cell's (DMFC's) electrochemical process was successfully investigated in situ using Electrochemical Impedance Spectroscopy (EIS) method. Under three-electrode system, anode and cathode's polarization overpotential, charge transferring resistance and active surface were independently measured in order to reveal the degradation factors after 50 h stability testing. The results showed that Ru's dispersing, membrane's swelling and water flooding were main reasons resulting in performance decline. And SEM images confirmed these conclusions. Moreover, cathode's degradation was less serious than anode and it could be recovered. Traditional equivalent circuit model of self-breathing DMFC was modified according to a fact that the dielectric relaxation phenomenon of porous electrode occurred at cathode rather than anode.     

Effect of surface modification of anode with surfactant on the performance of microbial fuel cell

Surface modification of anode using surfactant has great influence on the electrical performance of a microbial fuel cell (MFC). In this study, the effect of surface‐modified exfoliated graphite used for anode fabrication on a cube‐type MFC batch reactor was examined. The surface exfoliated graphite was modified with 5‐mM anionic surfactant, sodium dodecyl sulfate. Anaerobic sludge used as inoculum containing 70% (v/v) of artificial wastewater and 30% (v/v) of seed sludge in an anode chamber and air cathode was used in cathode side. Anode modification was explored as an approach to enhance the start‐up and improve the performance of the reactor. Scanning electron microscopy was used to evaluate the morphology and activity of electrochemically active bacteria. In the study, the start‐up time of MFC required to approach stable voltage was substantially reduced, and the maximum stable voltage was higher than the control. In addition, the activation resistance of the MFC was considerably reduced, and the maximum power density (1640 mW/m²) was 20% higher than control. However, when the surface of exfoliated graphite was modified with over 10‐mM anionic surfactant, some negative effects on start‐up time, activation resistance and maximum power density were observed. This modification also enhanced the bacterial attachment and biofilm formation on the modified anode surface. The result suggested that surface modification anode with surfactant is effective for electrical responses achieved in the MFC. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of catalyst layer with zeolite on the performance of a proton exchange membrane fuel cell operated under low-humidity conditions

Proton exchange membrane fuel cells (PEMFCs) employ a proton conductive membrane as the separator to transport a hydrogen proton from the anode to the cathode. The membrane's proton conductivity depends on the water content in the membrane, which is affected by the operating conditions. A membrane electrode assembly (MEA) that can self-sustain water is the key component for developing a light-weight and compact PEMFC system without humidifiers. Hence, zeolite is employed to the anode catalyst layer in this study. The effect of the gas diffusion layer (GDL) materials, catalyst loading, binder loading, and zeolite loading on the MEA performance is investigated. The MEA durability is also investigated through the electrochemical impedance spectroscopy (EIS) method. The results suggest that the MEA with the SGL28BCE carbon paper, Pt loadings of 0.1 and 0.7 mg cm^?2 in the anode and cathode, respectively, Nafion-to-carbon weight ratio of 0.5, and zeolite-to-carbon weight ratio of 0.3 showed the best performance when the cell temperature is 60 °C and supplies with dry hydrogen and air from the environment. According to the impedance variation measured by EIS, the MEA with zeolite in the anode catalyst layer shows higher and more stable performance than those without zeolite.     

Simultaneous oxygen-reduction and methanol-oxidation reactions at the cathode of a DMFC: A model-based electrochemical impedance spectroscopy study

A model-based electrochemical impedance spectroscopy (EIS) approach that combines an equivalent electrical circuit (EEC) method and a mathematical model derived from the reaction kinetics is proposed to investigate the simultaneous oxygen-reduction reaction (ORR) and methanol-oxidation reaction (MOR) at the cathode of a DMFC. Good agreements between the calculated results and the experimental data validated the proposed method. Detailed kinetic parameters and state variables of the cathode were conveniently extracted and the concerned reaction processes were further analyzed, which demonstrated the comprehensive applicability of this method. The results showed a significant poisoning effect on the ORR by the presence of methanol at the cathode. The results also indicated that whether the methanol permeated from the anode can be completely oxidized by electrochemical reaction at the DMFC cathode depends on the electrode design and operating conditions, even at high potentials.     

β-FeOOH modified carbon monolith anode derived from wax gourd for microbial fuel cells

The preparation of high-performance anode materials is of significance for enhanced power generation in microbial fuel cells (MFCs). Herein, porous carbon monolith was prepared by simple freeze drying of wax gourd and subsequent pyrolysis (WGC). β-FeOOH was coated on WGC to further improve the performance of the anode (β-FeOOH/WGC). The maximum power density of the MFCs with WGC and β-FeOOH/WGC anode was 913.9 and 1355.1 mW/m² respectively, which was much higher than that of the control (558.2 mW/m²). WGC possessed three-dimensional pore structure, nitrogen and oxygen-containing functional groups, which endowed it with satisfactory bacterial loading. Improved MFC performance after β-FeOOH modification could be ascribed to two aspects: β-FeOOH enhanced the electrochemical activity and decrease the transfer resistance; β-FeOOH was conducive to exoelectrogens formation. This study demonstrated that the synthesis of β-FeOOH modified carbon monolith anode offered an efficient route to enhance the power generation of MFCs.     

Fabrication and characterization of gold nanoparticles and fullerene-C60 nanocomposite film at glassy carbon electrode as potential electro-catalyst towards the methanol oxidation

Development of low cost anodic materials and high efficient electro-kinetics of methanol in direct methanol fuel cell (DMFC) has been a promising approach. However it has not been successfully reached to market from laboratory due to its high cost and low kinetic oxidation. Both issues encounter from one of its main components, the catalyst. Therefore, present work focuses upon the development of new catalyst material and optimization of various most significant influencing parameters of a high performance DMFC. We have developed a nanocomposite material employing gold nanoparticles and fullerene-C₆₀ at glassy carbon electrode (AuNP@reduced-fullerene-C₆₀/GCE) as anode for high performance oxidation of methanol. Fullerene-C₆₀ was manually dropped on pre treated GCE and partially electro-reduced in KOH to make it more conductive. Gold nanoparticles (AuNPs) were deposited on reduced-fullerene-C₆₀ modified electrode using cyclic voltammetry (CV). Electrochemical characterization techniques such as CV, electrochemical impedance spectroscopy (EIS) and chronocoulometry were used to characterize modified electrode. Modified electrode was also characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) for morphological properties. The electrochemical behavior of methanol was performed in alkaline medium using CV and chronoamperometry methods. The results revealed good electrocatalytic performance and better stability than previously reported catalysts using AuNP@reduced-fullerene-C₆₀ catalyst, suggesting making promising anodic material for direct methanol oxidation fuel cell.     

Copper-phthalocyanine and nickel nanoparticles as novel cathode catalysts in microbial fuel cells

In this study, four different catalysts (i.e., carbon black, nickel nanoparticle (Ni)/C, Phthalocyanine/C and copper-phthalocyanine/C), were tested in a two-chamber Microbial Fuel Cell (MFC) and their performances were compared with Pt as the common cathode catalyst in MFC. The characterization of catalysts was done by TEM, XPS and EDX and their electrochemical characteristics were compared by cyclic voltammetry (CV) and Linear Sweep Voltammetry (LSV). The results proved that copper phthalocyanine and nickel nanoparticles are potential alternatives catalyst for Pt. Even copper-phthalocyanine generated power is almost the same as Pt. The CV and LSV results reported high electrochemical activity of these catalysts. The maximum power density and coulombic efficiency was achieved by copper-phthalocyanine/C as 118.2 mW/m² and 29.3%.     

A novel battery-supercapacitor system with extraordinarily high performance

In this paper, a battery-supercapacitor system is developed and its electrochemical performance is investigated. The battery-supercapacitor system is composed of a separated LiFePO₄/activated carbon cathode and a separated Li₄Ti₅O₁₂/activated carbon anode onto both sides of a piece of aluminum foil. We demonstrated the superior electrochemical performance of this battery-supercapacitor system, such as its energy density of 4.9–48.5 Wh/kg, power density of 167.7–5243.2 W/kg, rate capability of 73.9% at a current density of 20 A and cycle life (91.5% after 1800 cycles) which outperforms that of a hybrid supercapacitor. This can be explained by the synergistic effect of a Faradaic and non-Faradaic system in a single cell. The results clearly show that the battery-supercapacitor system, including a LiFePO₄ cathode/Li₄Ti₅O₁₂ anode and an activated carbon anode/activated carbon cathode, has great potential for use in advanced energy storage devices.