Carbon Felt Electrode Research Articles

Tunisian hypersaline sediments to set up suitable halotolerant microbial bioanodes for electrostimulated biodegradation of thiabendazole

This study investigated for the first time the performance of microbial halotolerant bioanodes designed from two Tunisian Hypersaline Sediments (THS) for simultaneous electrostimulated biodegradation of synthetic fruit packaging wastewater containing thiabendazole (TBZ), and recovery of an anodic current signal. Halotolerant bioanodes formation has been conducted on 6 cm2 carbon felt electrodes polarized at −0.1Vvs Saturated Calomel Electrode (SCE), inoculated with 80% (v:v) of synthetic wastewater containing 50 ppm of irradiated or not irradiated TBZ and 20% (v:v) of THS for a period of 7 days. Microbial bioanodes, and the corresponding anolytes, i.e., synthetic wastewater, were studied comparatively by electrochemical, microscopic, spectroscopic, molecular and microbial ecology tools. Despite the low maximum current densities recorded in the 50 ppm TBZ runs (3.66 mA/m2), more than 80% of the TBZ was degraded when non-irradiated TBZ (nTBZ) was used as the sole carbon energy by the microorganisms. Nevertheless, the degradation in the presence of irradiated TBZ (iTBZ) was greatly reduced by increasing the irradiation dose with maximum current density of 0.95 mA/m2 and a degradation rate less than 50% of iTBZ. In addition, chemical changes were observed in TBZ as a result of gamma irradiation and bioelectrochemical degradation. FT-IR and UV-Vis techniques confirmed the degradation of TBZ structural bonds producing novel functional groups. Culture-dependent approach and 16S ribosomal RNA sequencing demonstrated that bacterial community of halotolerant bioanodes formed with nTBZ were dominated by Proteobacteria (75%) and Firmicutes (25%). At species level, enrichment of Halomonas smyrnensis, Halomonas halophila, Halomonas salina, Halomonasor ganivorans and Halomonas koreensis on carbon felt electrodes were correlated with maximal current production and nTBZ degradation. As a result, THS halotolerant bacteria, and specifically those from Chott El Djerid (CJ) site certainly have well established application for the electrostimulated microbial biodegradation of fungicide in the real fruit and vegetable processing industries.

Boosting catalytic activities of carbon felt electrode towards redox reactions of vanadium ions by defect engineering

Boosting catalytic activities of carbon felt electrode towards redox reactions of vanadium ions by defect engineering

Construction and Electrochemical Properties of Solid-state Supercapacitors with Redox Additives.

Adding redox additives to conventional electrolytes is considered to be an effective method to improve electrochemical performance of the supercapacitors, which is ascribed to the additional Farady capacitance derived from the reversible redox reaction. Here, the influence of K3 Fe(CN)6 on electrochemical properties for single electrode system and the assembled solid-state supercapacitor are investigated. The carbon felt (CF) electrode in the mixed solution of K3 Fe(CN)6 /KCl exhibits remarkable specific capacitance of 2.45 F cm-2 after 5000 cycles, obviously much higher than conventional electrolyte KCl. The capacitance retention and the coulombic efficiency of the solid-state supercapacitor maintains 86.5% and 97% after 2500 cycles, symmetric supercapacitor shows a high energy density of 58 mWh L-1 at power density of 660 mW L-1 . Furthermore, the solid-state SCs exhibit excellent flexibility and four supercapacitors are capable of lighting up an LED lamp, demonstrating the potential of practical applications of the as-prepared solid-state SCs.

Improved electricity production and nitrogen enrichment during the treatment of black water using manganese ore-modified anodes

The decline of fossil fuel availability is calling for alternative energy such as electricity produced by degradation of waste in microbial fuel cells. The performance of microbial fuel cells is controlled by the anode because microorganisms grow and attach on the anode. Here, we prepared carbon felt electrodes modified with manganese ore based on the hypothesis that manganese and silicon oxides would improve the cell performance to treat simulated black water. We compared properties of the manganese ore-modified electrodes with properties of classical carbon felt electrodes modified with magnetic ferroferric oxide. We also studied the removal of the chemical oxygen demand and the enrichment in ammonia nitrogen. Results show that the maximum voltage of the manganese ore-modified carbon felt electrode is 1.7 times higher than that of the magnetic ferroferric oxide-modified carbon felt electrode. The start-up time to reach the maximum voltage is reduced by 68%. The removal of chemical oxygen demand reached 91.2%. Up to 68.0% of ammonia nitrogen can be enriched at the cathode, implying that ammonia nitrogen can be highly reduced in the effluent. Overall, the manganese ore-modified carbon felt electrode showed excellent redox performance, excellent corrosion resistance and low electron transfer resistance.

Electrochemical Determination of Hemoglobin by the İmmobilization of the Analyte into a Carbon Felt Electrode (CFE) Using Cyclic Voltammetry (CV)

A practical and sensitive electrochemical sensor for hemoglobin (Hb) detection was developed. The main electrochemical reaction was the reduction of Fe (III) in the Hb structure. For the construction of the sensor, Hb was physically immobilized onto a carbon felt electrode (CFE) without using any linker or applying any pre-functioning or electrochemical procedures. After examining the electrochemical mechanism, the experimental conditions, such as pH, were optimized and the analytical characteristics were investigated. A linear range of 0.05 µM to 3.00 µM with a detection limit of 4.4 nM was obtained for Hb. The relative standard deviation value for 3 replicate determinations of 0.05 µM Hb was calculated as1.35%. The developed sensor was successfully applied for Hb detection via standard addition method in synthetic physiological serum sample. Meanwhile, the influences of interfering reagents, such as cysteine, ascorbic acid, bovine serum albumin, and glucose, on Hb detection were also examined.

Lignin as redox-targeted catalyst for the positive vanadium electrolyte

Vanadium Redox Flow Batteries (VRFBs) are promising candidates for large- scale energy storage applications however, there are still some obstacles that need to be overcome such as their low energy density (25–30 Wh L−1 for a 1.8 M electrolyte), high cost and large environmental impact due to corrosiveness and the unsustainability of vanadium. To address these challenges, we introduce lignin as a low-cost electrocatalyst and capacity booster for the positive electrolyte. Coated on a glassy carbon electrode, lignin showed electrocatalytic abilities and improved the electrochemical reversibility of the VO2+/VO2+ redox couple significantly. In charge and discharge cycles volumetric capacities of 28 Ah L−1 (charge) and 23.5 Ah L−1 (discharge) were achieved with a 0.9 M concentrated vanadium electrolyte which surpassed the maximum theoretical capacity of 24.1 Ah L−1 in the charge. This demonstrates an increase of 7.5 Ah L−1 and 9 Ah L−1 for the charge and discharge cycles, respectively, compared to a pristine carbon felt electrode. This work showcases the noteworthy influence of lignin on vanadium and opens new possibilities for VRFB chemistry.

Carbon felt electrode modified by lotus seed shells for high-performance vanadium redox flow battery

Vanadium redox flow batteries (VRFBs) have attracted considerable attentions for their promising applications as large-scale energy storage devices. However, the widespread implementation of VRFBs is still hindered by the severe overpotentials of redox reactions, due to the poor electrochemical activities of conventional carbon felt (CF) electrodes. Herein, we present the fabrication of biomass lotus seed shells-modified CF (Bio-CF) electrode, which exhibits remarkable electrocatalytic effects on both the V2+/V3+ and VO2+/VO2+ redox reactions. The influences of auxiliary sucrose concentration and pyrolysis temperature were investigated to optimize the Bio-CF electrodes. Meanwhile, molecular dynamic simulations were employed to verify the experimental data. Furthermore, high performance VRFBs were achieved with the optimized Bio-CF electrode, affording high energy efficiency (83.14 %) and outstanding cycling stability under a current density of 100 mA cm−2. It is believed that the strategy to improve electrochemical performance of CF modified by cost-effective biomass materials provides a promising route for developing high performance VRFBs.

Half-wave rectified alternating current electrochemical-assembled devices for high-capacity extraction of Pb2+ from dilute wastewater

The selective capacitive removal (SCR) of toxic but valued lead ions (Pb 2+ ) from dilute wastewater is challenging for water purification since valueless and nontoxic alkali metal ions (like Na + ) often dominate typical metal-containing industrial effluents . Herein, novel devices were assembled based on the half-wave rectified alternating current electrochemical (HWACE) method, and a self-support chitosan-modified carbon felt (Chitosan/ CF ) electrode was constructed to boost the SCR of (Pb 2+ ) from dilute wastewater. The characterization results of the Chitosan/CF electrodes indicated robust mechanical stability, good hydrophilia, and highly capacitive properties owing to the presence of abundant surface functional groups (-NH 2 , –OH). The assembled devices exhibited high extract performances under various conditions. Nearly complete removal of Pb 2+ was achieved in a binary solution containing 50 ppm Pb 2+ and 100 ppm Na + at power supply parameters of the voltage of 5 V, frequency of 600 Hz, and flow rate of 8 mL/min within 24 h with a maximum removal efficiency reaching ∼99.4% and barely changed the concentration of Na + . Here, the fast growth of lead dendrites on the electrode surface was readily visible with naked eyes after 6 h. The characterization data of the Chitosan/CF electrode after HWACE extraction showed the presence of metallic lead (Pb0), suggesting further electroreduction of Pb 2+ into neutral particles after adsorption on the electrode surface. The mechanism taking place at the cathode during the whole HWACE extraction process can best be described by Pb 2+ reduction as the dominant process in early-stage and layered double hydroxide (LDH) precipitation at the late stage. The neutralized lead particles alleviated the Coulombic repulsion for sequent Pb 2+ transformation, instantaneously leading to a nucleation mechanism for the continuous revival of lead particles. As a result, a rather high capacity >2500 mg/g was recorded, outperforming traditional SCR methods. Therefore, the constructed devices provided a new promising way for SCR of Pb 2+ from typical metal-containing wastewater. In addition, the suggested process can be scalable and integrable with dilute wastewater treatment or full resource recovery sewage treatment plant .

Validating role of different enzymes (laccases and catalases) based voltammetric biosensors in detection of pesticide and dye

The widespread utilization of hazardous and tenacious pesticides and azo dye in agriculture as well as textile industry respectively has sparked research into new, high-performing, low-cost and quick analytical strategies to mitigate their residue levels in the environment and food. An enzyme based biosensor has been considered as rapid biosensing tool for detection of toxicity and environmental monitoring of different contaminants as compared to previously existing conventional. Pesticide detection based on enzyme inhibition have been reported previously, however, for the dye it is reported for the first time in this study. This research focuses on the construction and testing of a novel biosensor based on fungal laccase and bacterial catalase for monitoring the chlorpyrifos and Reactive Red 195 (RR195). Partially purified laccase obtained from fungus (Aspergillus niger) and Catalase from bacteria (Staphylococcus aureus) was initially immobilized in a chemically and thermally treated carbon felt (CF) electrodes by physical adsorption. Biosensing of different concentration of pesticide and dye was carried out in terms of enzyme activity inhibition corresponding to electric signal (I) generation at an applied voltage of −1 to +1 through voltammetric analysis. Increase in concentrations of pollutants (10 ugL−1-30 mgL−1) was significantly correlated with decline in current (I) output. Effectiveness of biosensors is depicted by good repeatability, stability, and low limit of detection with insignificant interference of other compounds. The reusability of the enzyme based electrode was confirmed even after 90 days with a slight variation in current (I) peaks. The determination of varying chlorpyrifos and RR195 concentrations by developed biosensors indicated outcomes reliable with those attained via other studies, which authenticate the technique and its benefit for the quantification of these pollutants in less time.

Regulating flow field design on carbon felt electrode towards high power density operation of vanadium flow batteries

Flow batteries promise a great practice to integrate with renewable energy sources in electric grid applications. However, high power density operation of flow batteries remains a challenge due to mass transport limitation and flow resistance in porous carbon felt electrode, which urges the need of advanced flow design to synergistically lower concentration polarization and reduce pressure drop. Herein, we realize a remarkably enhanced power density operation for vanadium flow batteries by regulating flow field design on carbon felt electrodes. Finite element analyses firstly reveal significantly reduced pressure drop, well-distributed reactant and promoted flow velocity on carbon felts with parallel and interdigitated flow designs. On the basis of measured local mass transfer coefficients, both interdigitated and parallel based felts exhibit a notable reduction in simulated concentration polarization at 200 mA cm−2 with parallel flow outperforming interdigitated design. Experimental validations further confirm a superior voltage efficiency of 78 % and significantly enhanced discharge capacity at 200 mA cm−2 for the flow cell adopting parallel based felts. Finally, dynamic modelling and simulation of an industrial-scale 32 kW stack highlight a desirable system efficiency of ca. 70 % for the parallel flow felt design at 200 mA cm−2, signifying a great potential of regulating flow field on carbon felts for design and scale-up of practical flow battery stacks.

(Digital Presentation) High-Temperature Ammonia Treatment for Carbon Felt Electrodes in All-Vanadium Redox Flow Batteries

Ammonia gas treatments of varying temperature were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without processing, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to improve performance, which has been historically accomplished with thermal treatments ostensibly to promote oxygen functional groups, although this has been the subject of debate as morphological impacts have also been observed. [1-3] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [4-6] Previous research at the University of Tennessee Knoxville suggests edge sites play a role in improving performance. Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. Additional experiments were performed at 900°C by varying length of treatment time, finding four hours to be optimal. [3] New experiments have been done to investigate the kinetic effects of temperature.For these experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at (500°C, 700°C, 900°C, and 1100°C) varying temperatures for four hours. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. This was done to study the mechanism and kinetic effects of ammonia on the carbon felt material as temperature increases during the treatment itself. Samples treated at the highest temperatures exhibited a notable loss of mass, which is observed in the SEM images in Figure 1. This resulted in a significant increase in edge sites and active surface area, along with a substantial increase in cell performance, which was achieved with the ammonia-modified carbon felts described in this work, with over three times the current density at 80% voltage efficiency compared to untreated felt. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment.Electrochimica Acta, 1992. 37(7): p. 1253-1260.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016.Gass, K., High Performance Vanadium Redox Flow Battery Electrodes. [manuscript under submission], 2021.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces.Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries.Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries.Energy Storage Materials, 2020. 25: p. 885-892. Figure 1. SEM images at 30,000X magnification of carbon felt electrodes: a) untreated, b) 4 hours NH3 treated at 500°C, c) 4 hours NH3 treated at 700°C, d) 4 hours NH3 treated at 1100°C. Scale was identical for all micrographs Figure 1

(Digital Presentation) The Influence of Post-Processing on Dynamic Hydrogen Bubble Templated Bi Modified Graphite Felt in Vanadium Redox Flow Batteries

Graphite felts (GFs) are a widely used electrode material in vanadium redox flow batteries (VRFB) by virtue of their high porosity, chemical stability, low cost and good electrical conductivity. However, the hydrophobicity and the low electrochemical activity are the main obstacles for the use of pristine GF in VFRB applications. To tackle such problems, bismuth has been reported to be a promising catalyst for V2+/ V3+ redox reactions [1]. Post-processing parameters, such as air/vacuum drying, exposure time to water during rinsing step, etc. can impact the performance of the Bi modified GFs, which will correspondingly affect morphology, purity and distribution of the catalyst leading to different kinetics. These parameters are rarely studied and reported in the literature.In this work, an effective synthesis method, the so-called dynamic hydrogen bubble template (DHBT) electrodeposition, has been employed for the deposition of high surface area Bi on GFs [2]. This method involves galvanostatic deposition of the metal at high current densities which is accompanied by hydrogen evolution, and the hydrogen bubbles serve as dynamic template for metal deposition. Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were carried out in a half-cell setup. The kinetics of Bi modified GFs could be obtained qualitatively by using Friedl’s method [3], in which the charge transfer resistance and double layer capacitance from impedance measurements are correlated, and quantitatively from the CV fitting routine in Polarographica developed by Tichter et al. [4]. The kinetic trends derived from both methods are consistent, with Polarographica exhibiting specific quantitative values as compared to Friedl’s method.It has been found that the post processing and drying conditions after Bi electrodeposition affect the performance of the GFs significantly. Therefore, the impacting parameters including electrochemically active surface area, Bi distribution, impurity, etc. are further studied by excluding certain parameters under different conditions. By the two previously mentioned methods of obtaining kinetics and the characterization of SEM and XRD, it is demonstrated that long time exposure to water during the rinsing step combined with vacuum drying after synthesis will promote a relatively higher kinetics than the other post-processing treatments on the Bi modified GFs.Full-cell tests with a VRFB test bench have been carried out. According to the polarization curves and charge-discharge curves at 25 mA/cm2 and 50 mA/cm2, the electrodes with Bi show pronounced advantages over pristine GF, namely, lower overpotential, lower charge voltage, higher discharge voltage and higher electrolyte utilization. Long term cycling will be compared and discussed in detail as well.[1] B. Li et al., “Bismuth Nanoparticle Decorating Graphite Felt as a High-Performance Electrode for an All-Vanadium Redox Flow Battery,” Nano Lett., vol. 13, no. 3, pp. 1330–1335, Mar. 2013, doi: 10.1021/nl400223v.[2] M. Yang, “Fern-shaped bismuth dendrites electrodeposited at hydrogen evolution potentials,” J. Mater. Chem., vol. 21, no. 9, p. 3119, 2011, doi: 10.1039/c0jm03213a.[3] J. Friedl and U. Stimming, “Determining Electron Transfer Kinetics at Porous Electrodes,” Electrochimica Acta, vol. 227, pp. 235–245, Feb. 2017, doi: 10.1016/j.electacta.2017.01.010.[4] T. Tichter et al., “Real-space simulation of cyclic voltammetry in carbon felt electrodes by combining micro X-ray CT data, digital simulation and convolutive modeling,” Electrochimica Acta, vol. 353, p. 136487, Sep. 2020, doi: 10.1016/j.electacta.2020.136487.

Close Contact without Mixing: All-Aqueous Membrane-Free Flow Battery

The accumulation of energy produced by renewable sources to be used when demand is high is a key aspect of a truly decarbonized grid. Among all energy accumulation technologies, Redox Flow Batteries (RFBs) are specially promising due to its safety, flexibility of design and the ability to decouple capacity and power of the system. In a standard configuration, both redox electrolytes that are stored in external tanks are pumped in the electrochemical reactor separated only by an ion-selective membrane. This membrane is a critical part of the battery as it allows the selective pass of certain ions that compensate the charge imbalances while maintaining separated the active species in their respective compartments. Membranes used in RFB are expensive (up to 25% of the total cost in vanadium RFB), contribute greatly to the ohmic resistance of the battery, and the undesired crossover through it is never fully avoided which produces a performance decay of the battery over time. These issues are addressed by membrane-free RFB designs developed in our group.The idea behind MFreeB ERC project is to take advantage of the immiscibility of certain liquids to naturally separate redox active species in a membrane-free battery design [1]. Aqueous Biphasic Systems (ABSs) are a special example of all-aqueous natural occurring immiscible phases made by mixing water with two compounds that can be either polymers, inorganic salts or both. The two redox active species added to the biphasic system can be rationally selected and optimized so that they partition specifically to one of the two phases used as anolyte and catholyte [2]. These types of batteries have been proposed by several groups, including us, mostly as “static batteries” because filter-press reactors, typically used in conventional RFB, cannot be easily adapted to this membrane-free concept. In order to develop truly flowing systems, a totally different electrochemical reactor should be designed.Here, we report on the development of an electrochemical reactor that allows the formation of the two immiscible phases making possible the testing of immiscible batteries under flowing conditions for the first time. A counterflow flow-through configuration was used since it reduces flow instabilities while at the same time it allows high conversion rates in the carbon felt electrodes avoiding mass transport issues [3]. Several tests were performed in the battery; e.g. polarization curves, charge and discharge cycling and efficiency over time were measured. Moreover, the self-discharge phenomena, occurring near the interface when charged species enter in contact and provoking a loss of efficiency, was evaluated as a function of operating conditions. Special attention was given to the study of the different processes occurring in the region near the interface in order to mitigate losses and further optimize the design. Acknowledgments This work has been partially funded by project MFreeB which have received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 726217).

Electrical Resistive Tomography to Analyse the Flow Behaviour in Redox Flow Batteries

Redox flow batteries (RFBs) are re-emerging as a safe, scalable, efficient and versatile means of large-scale energy storage. Growing adoption of renewable energy generation has ushered a new optimism regarding future reduction in fossil fuel dependency; limiting further harm dealt to the climate and wider environment. However, this momentum demands more efficient energy storage solutions to reconcile power demand and the intermittent nature of wind, solar and tidal energy generation [1]. Without proper storage, reliable back-up generation – largely provided by fossil fuels – will continue to be an unavoidable reality [2]. RFBs utilise the electrochemical properties of dissolved metal ions to store and release energy. Independent sizing of electrolyte storage tanks and flexible power delivery contributes to the flexibility of RFBs compared to alternative battery technologies [3].RFB reactions occur at the electrode-electrolyte interface, and thus the mass transport at this interface is a critical factor in determining the overall RFB performance. Most RFBs use porous electrodes, with a popular choice of material being carbon felt (CF) due to its low cost, chemical stability and high conductivity [4], although the hydrophobic nature of some CF can cause poor electrode ‘wettability’- decreasing the contact area between the electrode and the electrolyte. Further, electrolyte depletion and asymmetric flow can lead to the presence of ‘dead spots’ where the interface is inactive. Many studies have been conducted on CF to improve the electrochemical performance, using surface treatments, compression and channel flow to improve active area, wettability, and species transport [5-7]. These each have direct impact on current density, pressure drop, overpotentials, and energy efficiency. While the flow of electrolyte in the RFB porous electrodes can be modelled using computational fluid dynamics (CFD) [8], and experimentally assessed using x-ray tomography [9,10] and some optical visualisation methods [11], there are limited experimental methods which can be used on entire RFB stacks.In this study, we explore the use of electrical resistive tomography (ERT) to probe the flow of electrolyte through RFB electrodes. ERT has the advantage that it can provide a non-intrusive means of investigating the hydrodynamics of the otherwise opaque cell stack. Measurements were performed using an array of electrodes place around the perimeter of an RFB electrode chamber which contained conventional carbon felt electrodes. Sensitivity maps were generated using the COMSOL Multiphysics platform and compared with experimental measurements. The flow distribution was evaluated by using injections of concentrated KCl solutions into the background electrolyte. Overall, ERT demonstrated promise as a technique for characterising real-time flow dynamics in RFB stacks and for future research into porous electrode and flow field modifications.

Nitrogen‐Doped Carbon Felt as an Electrode Material for Vanadium Flow Batteries

AbstractVanadium flow batteries (VFBs) are well suited for energy storage due to the attractive features of high safety and long cycle life. Electrodes are a key component of a VFB, directly affecting the energy efficiency and power density of the battery. However, the carbon felt electrode commonly used suffers from poor hydrophilicity and electrochemical activity. Herein, a simple ammonium sulfate hydrothermal method was presented to improve the electrochemical activity and hydrophilicity of carbon felt. In the design, hydrophilic nitrogen‐containing and oxygen‐containing functional groups were introduced in the hydrothermal process, in favor of optimizing the hydrophilicity of carbon felt. The doping of nitrogen with negative charge density and the increasing defects promoted the electrochemical reactions of vanadium ions. Furthermore, the effects of the experimental parameters on the performance of the carbon felt and the battery were carefully studied. As a result, the VFB with 90‐1 nitrogen‐doped carbon felt exhibited the best performance; the energy efficiency achieved 87.34 % at the current density of 80 mA/cm2, which was 3.91 % higher than that with the original one.

Enhancement of bioelectricity and hydrogen production from xylose by a nanofiber polyaniline modified anode with yeast microbial fuel cell

In this study, modification of carbon felt (CF) electrode using polymerized nanofiber polyaniline (PANI) was developed for increasing the conductivity of anodic electrode toward efficient adherence of exoelectrogenic yeast cells of Cystobasidium slooffiae JSUX1 and further enhancing both bioelectricity and hydrogen production from xylose in MFCs. The morphology analysis with SEM images verified the formed nanofiber structure of PANI on the surface of the PANI/CF electrode. Nanofiber PANI with a higher surface area could improve the conductivity of the PANI/CF anode for a durable attachment of yeast C. slooffiae JSUX1 to form a dense biofilm and boost a high-performance in MFCs. The maximum derived power output of MFCs with PANI/CF (119.35 ± 3.27 mW/m2) was about 2.2 times higher than that of MFCs with the bare CF (50.41 ± 6.9 mW/m2) and the maximum hydrogen yield reached 25.83 mL by using xylose as the sole carbon source. The obtained results of PANI/CF modified electrodes compared to the bare CF anode suggested that the extracellular electron transfer (EET) and energy production by yeast cell C. slooffiae JSUX1 have an excellent capability to be improved by PANI polymers in MFCs.

Improved Magnetite Nanoparticle Immobilization on a Carbon Felt Cathode in the Heterogeneous Electro-Fenton Degradation of Aspirin in Wastewater.

Toward the improvement of the application of heterogeneous electro-Fenton in water treatment, we report a new strategy of enhancing the immobilization of a magnetite nanoparticle catalyst on a carbon felt cathode. Exploiting the intrinsic ferrimagnetic properties of magnetite nanoparticles, magnet bars were used to attach the magnetite into the void spaces of the porous carbon felt (CF) cathode. The magnetite nanoparticles were prepared by coprecipitation with variations in the molar ratios of Fe2+/Fe3+. The magnetite was characterized, attached onto the CF electrode with magnetic bars, and used in the heterogeneous electro-Fenton (EF) degradation of aspirin. The effects of the following on the degradation were studied: Fe2+/Fe3+, pH, catalyst loading concentration, and voltage. The heterogeneous EF degradation of aspirin in wastewater improved by 23% when magnetic bars were used to enhance the immobilization of the magnetite catalysts. The 1:4 Fe2+/Fe3+ ratio resulted in the highest hetero-EF catalytic degradation of aspirin with complete degradation (100%) achieved after 140 min. For a mixture of pharmaceuticals, degradation percentages of 94.3% (aspirin), 88% (ciprofloxacin), and 80% (paracetamol) in 3 h were obtained. The magnetized magnetite on the cathode was reusable for 10 cycles. Thus, the use of magnets shows a promising strategy to avoid the leaching of ferrimagnetic nanoparticle catalysts embedded in the cathode for heterogeneous EF processes.

Hydrothermal Synthesis of Flexible Fe‐Doped Polyaniline/Dye‐Functionalized Carbon Felt Electrode for Supercapacitor Applications

AbstractIn this study, Fe‐doped polyaniline/dye‐functional composite modified carbon felt electrode was synthesized using hydrothermal method and a supercapacitor exhibiting 1.5 V was obtained with 3.0 M KCl aqueous electrolyte. In order to improve supercapacitor performance easily and effectively, the effect of Lanaset Green B (LGB) acidic dye concentration on supercapacitor performance in polyaniline polymerization was investigated. Electrochemical, morphological and structural characterizations of the synthesized electrodes (CFt/Fe‐PANI/LGB) were carried out. The results showed that the capacitance increases due to the strong interaction of functional groups between PANI and dye molecules and improves the properties of pseudocapacitive supercapacitors by providing potential redox materials. The CFt/Fe‐PANI/LGB(3 mM) electrode displayed a high specific capacitance of 1543 F g−1 at a scan rate of 5 mV s−1 in half‐cell electrode system. In full‐cell, the assembled symmetric supercapacitor has a maximum energy density of 32.7 Wh kg−1 and power density of 1250 W kg−1. The supercapacitor electrode and symmetric supercapacitor display retention of capacitance performances 82.3 % and 78.8 % after 2400 and 5000 cycles in 3.0 KCl electrolyte, respectively. CFt/Fe‐PANI/LGB(3 mM), flexible, wearable carbon felt electrode material and improved redox behavior of the polymer material play an important role for textile electronics applications.

Direct In Situ Vertical Growth of Interlaced Mesoporous NiO Nanosheets on Carbon Felt for Electrocatalytic Ammonia Synthesis.

Metal oxide nanomaterials directly grown on conductive substrates are optimal electrode materials because their structures allow for rapid ion and electron transport and thereby reduce internal resistance in the electrode. The development of such binder-free, self-supporting electrodes is of great significance for applications in electrocatalysis. In this work, a simple hydrothermal in situ self-assembly reaction and annealing process was developed to prepare three kinds of nickel oxide @ carbon felt (NiO@CF) nanocomposites with different morphologies. The influence of different precipitators (strong or weak bases) on the morphology of the resulting nano-sized nickel oxide nanocomposites was investigated. The microstructures of the NiO@CF samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). When ammonia was used as the precipitator, NiO grew vertically on the surface of the carbon felt and formed a mesoporous nanosheet-like structure (NiO NSs@CF). As an electrocatalytic nitrogen reduction reaction (e-NRR) electrode, the NiO NSs@CF sample showed an excellent NH3 yield (71.3 μg h-1 mg-1 cat. ) and Faradaic efficiency (17.9 % at -0.5 V vs. RHE) in 0.1 M Na2 SO4 . The good performance was attributed to the vertical interleaved mesoporous sheet-like structure (with the pore size of 15 nm and the thickness of ∼30 nm) and the relatively high concentration of oxygen vacancies. First-principles calculations with strong on-site Coulomb interactions demonstrated that the presence of oxygen vacancy on NiO sample leads to a significantly stronger N binding over the surface, benefiting for the nitrogen gas adsorption and reduction. The e-NRR performance of this binder-free, flexible electrode material is superior to that of other reported nickel-based nanomaterials. This study highlights the potential of such binder-free carbon felt electrodes for use in e-NRR that could meet the needs of industrial production.

Reduced graphene oxide improves the performance of a methanogenic biocathode

Microbial electrosynthesis (MES), a sub-branch of bioelectrochemical processes, takes advantage of a certain type of electroactive microorganism to produce added value products (such as methane) from carbon dioxide (CO2). The aim of this study is to quantify the benefits of using a carbon felt electrode modified with reduced graphene-oxide (rgoCF) as a methanogenic biocathode. The current density generated by the rgoCF was almost 30% higher than in the control carbon felt electrode (CF). In addition, charge transfer and ohmic resistances were, on average, 50% lower in the rgoCF electrode. These improvements were accompanied by a larger presence of bacteria (31% larger) and archaea (18% larger) in the rgoCF electrode. The microbial communities were dominated by hydrogenotrophic methanogenic archaea (Methanobacterium) and, to a lesser extent, by a low-diversity group of bacteria in both biocathodes. Finally, it was estimated that for a CO2 feeding rate in the range 15–30 g CO2 per m2 of electrode per day, it is possible to produce a high-quality biogas (>95% methane concentration).