Porous Carbon Felt Research Articles

Untreated vs. Treated Carbon Felt Anodes: Impacts on Power Generation in Microbial Fuel Cells.

This research sought to enhance the efficiency and biocompatibility of anodes in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), with an aim toward large-scale, real-world applications. The study focused on the effects of acid-heat treatment and chemical modification of three-dimensional porous pristine carbon felt (CF) on power generation. Different treatments were applied to the pristine CF, including coating with carbon nanofibers (CNFs) dispersed using dodecylbenzene sulfonate (SDBS) surfactant and biopolymer chitosan (CS). These processes were expected to improve the hydrophilicity, reduce the internal resistance, and increase the electrochemically active surface area of CF anodes. A high-resolution scanning electron microscopy (HR-SEM) analysis confirmed successful CNF coating. An electrochemical analysis showed improved conductivity and charge transfer toward [Fe(CN)6]3-/4- redox probe with treated anodes. When used in an air cathode single-chamber MFC system, the untreated CF facilitated quicker electroactive biofilm growth and reached a maximum power output density of 3.4 W m-2, with an open-circuit potential of 550 mV. Despite a reduction in charge transfer resistance (Rct) with the treated CF anodes, the power densities remained unchanged. These results suggest that untreated CF anodes could be most promising for enhancing power output in BESs, offering a cost-effective solution for large-scale MFC applications.

Selective Sensing in Microbial Fuel Cell Biosensors: Insights from Toxicity-Adapted and Non-Adapted Biofilms for Pb(II) and Neomycin Sulfate Detection.

This study introduces the utilization of self-powered microbial fuel cell (MFC)-based biosensors for the detection of biotoxicity in wastewater. Current MFC-based biosensors lack specificity in distinguishing between different pollutants. To address this limitation, a novel approach is introduced, capitalizing on the adaptive capabilities of anodic biofilms. By acclimating these biofilms to specific pollutants, an enhancement in the selectivity of MFC biosensors is achieved. Notably, electrochemically active bacteria (EAB) were cultivated on 3D porous carbon felt with and without a model toxicant (target analyte), resulting in the development of toxicant-resistant anodic biofilms. The model toxicants, Pb2+ ions and the antibiotic neomycin sulfate (NS), were deployed at a concentration of 1 mg L-1 during MFC operation. The influence of toxicity on biofilm growth and power production was investigated through polarization and power density curves. Concurrently, the electrochemical activity of both non-adapted and toxicity-adapted biofilms was investigated using cyclic voltammetry. Upon maturation and attainment of peak powers, the MFC reactors were evaluated individually as self-powered biosensors for pollutant detection in fresh wastewater, employing the external resistor (ER) mode. The selected ER, corresponding to the maximum power output, was positioned between the cathode and anode of each MFC, enabling output signal tracking through a data logging system. Subsequent exposure of mature biofilm-based MFC biosensors to various concentrations of the targeted toxicants revealed that non-adapted mature biofilms generated similar current-time profiles for both toxicity models, whereas toxicity-adapted biofilms produced distinctive current-time profiles. Accordingly, these results suggested that merely by adapting the anodic biofilm to the targeted toxicity, distinct and identifiable current-time profiles can be created. Furthermore, these toxicity-adapted and non-adapted biofilms can be employed to selectively detect the pollutant via the differential measurement of electrical signals. This differentiation offers a promising avenue for selective pollutant detection. To the best of our current knowledge, this approach, which harnesses the natural adaptability of biofilms for enhanced sensor selectivity, represents a pioneering effort in the realm of MFC-based biosensing.

Slurry Based Lithium-Ion Flow Battery with a Flow Field Design

Slurry based lithium-ion flow battery has been regarded as an emerging electrochemical system to obtain a high energy density and design flexibility for energy storage. The coupling nature of electrode thickness and flow resistance in previous slurry flow cell designs, demands a nuanced balance between power output and auxiliary pumping. To address this issue, a slurry based lithium-ion flow battery featuring a serpentine flow field and a stationary porous carbon felt current collector is proposed in this work. The carbon felt serves to provide a stable and efficient pathway for electron transport, while the flow field helps distribute active slurry onto the felt for electrochemical reactions. With such a design, the LiFePO4 (LFP) slurry based flow battery shows a low flow resistance and good flow stability without forming severe filter cakes on the felt surface, similar to cross-flow filtration. A maximum power density of 84.5 mW cm−2 and a stable coulombic efficiency of ∼98% under intermittent flow, and a specific capacity of 164.87 mAh g−1 (based on the total LFP in the tank) in continuous flow are successfully demonstrated. These preliminary yet encouraging results may put forward new avenues for future structural design and optimization of slurry based flow batteries.

Depolymerization of plastics by means of electrified spatiotemporal heating.

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibriumthermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET))by means ofpyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters theincreasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.

Flexible Electrochemical Platform Coupled with In Situ Prepared Synthetic Receptors for Sensitive Detection of Bisphenol A.

A flexible electrochemical sensor based on the carbon felt (CF) functionalized with Bisphenol A (BPA) synthetic receptors was developed. The artificial Bisphenol A receptors were grafted on the CF by a simple thermal polymerization molecular imprinting process. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and electrochemical characterizations were used to analyze the receptors. Characterization results demonstrated that the Bisphenol A synthetic receptors successfully formed on the CFs surface. Because the synthetic receptor and the porous CFs were successfully combined, the sensor displayed a better current response once Bisphenol A was identified. The sensor's linear range was determined to be from 0.5 to 8.0 nM and 10.0 to 300.0 nM, with a detection limit of 0.36 nM. Even after being bent and stretched repeatedly, the electrode's performance was unaffected, demonstrating the robustness, adaptability and viability of installing the sensor on flat or curved surfaces for on-site detection. The designed electrochemical sensor has been used successfully to identify Bisphenol A in milk samples with satisfactory results. This work provided a promising platform for the design of implantable, portable and miniaturized sensors.

Two‐Dimensional MXene as a Nanofluidic Anolyte Additive for Enhancing Performance of Vanadium Redox Flow Batteries

AbstractIn this work, Ti3C2TxMXene was investigated as a nanofluidic anolyte additive in vanadium redox flow batteries to improve the sluggish kinetics of V2+/V3+redox reaction. Numerous electrochemical tests under flow and static conditions were performed to demonstrate the effectiveness of MXenes for VRFB applications. Pressure drop tests and morphology analysis were also conducted to better understand the hydraulic effects of MXene addition into the anolyte. The nanofluidic anolytes with the concentration of 0.10 and 0.15 wt% showed the best electrochemical performance, although the former induced less aggravated hydraulic effects within a reasonable pressure drop range. At a current density of 200 mA cm−2, the nanofluidic analyte containing 0.10 wt% MXene was able to utilize 67 % of the theoretical capacity. Contrarily, with the pristine anolyte, only 10 % of the theoretical capacity could be utilized due to excessive losses. Moreover, the energy efficiency up to 74 % is observed for the nanofluidic electrolyte, which is an increase of 25 % compared to the pristine anolyte. Primarily, the enhanced battery performance was attributed to the improved electrocatalytic activity towards the anodic V2+/V3+redox reaction. Furthermore, a dynamic, web‐like, flowing electrode network is shown to increase the mass transport capacity of porous carbon felt electrodes by creating additional, abundant, and electrochemically active surfaces within the pores.

(Digital Presentation) Evaluating the Performance of Multi-Walled Carbon Nanotube Composite Microporous Layers Deposited on Carbon Felt Gas Diffusion Layers

Electrochemical energy storage devices (EESDs) such as metal-air batteries (MABs) and alkaline electrolyte membrane fuel cells (AEMFCs) have begun to gain vast amounts of attention due to their high theoretical energy densities and open-circuit voltage values. Although these devices present promising aspects for the environment and sustainability, they suffer from the slow reaction kinetics and degradation effects that occur at the catalyst layer interface of the air electrode. Typically, these effects are due to the accumulation of molecular species such as water or oxygen at catalyst active sites because of poor electrode hydrophobicity and fluid management. Herein, we perform experimentation to mitigate these effects by implementing mixed carbon composite microporous layers onto porous carbon felt based air electrodes. This adaptation of the air cathode was predominantly based on the aforementioned downfalls and the lack of availability of commercial carbon felts that have adequate wet proofing and conductivity like some of the related carbon paper gas diffusion layers. Microporous layers (MPLs) enhance electrical conductivity, surface area, and adhesion at the catalyst layer and gas diffusion layer interface. These layers typically consist of a hydrophobic polymer such as polytetrafluoroethylene (PTFE) and a conductive carbon black substrate such as Ketjen Black 600JD (KJB). The incorporation of multi-walled carbon nanotube (MWCNT) and carbon black composites into the structure of the MPLs drastically decreases ohmic polarization with minimal increases in specific resistance. The electrical resistance of the synthesized carbon substrate decreases at high rates of MWCNT dispersion, which corresponds directly to a low MWCNT weight percentage within the composite. The MPL increases the mass transport through the electrode by mitigating flooding effects that typically occur within the pores near the surface of the catalyst layer, ultimately aiding in charge transfer between the gas diffusion layer and catalyst active sites. Preliminary data from AEMFC symmetric cell tests suggests that a microporous layer consisting of a 10 wt.% MWCNT/KJB (m/m) substrate is the optimal loading of carbon nanotubes and leads to better cell performance. There is an increase in current density of 60 mA/cm2 compared to an air electrode with no MPL within the ohmic region of the polarization curve corresponding to approximately 0.7 V, while only an increase of 18 mA/cm2 is seen for an MPL consisting of a 30 wt.% MWCNT/KJB (m/m) carbon substrate. The increase of charge transfer by the 10 wt.% synthesized carbon substrate MPL was attributed to the ability of the nanotubes at high rates of dispersion to act as molecular wires within the electrode. Additionally, zinc-air battery tests using the optimally configured air electrode, determined from previous experiments, show that the current density at an operating voltage of 1.1 V was increased by 2.3 times that of an electrode without an MPL using the same catalyst material and loading. Significantly, this research will lead to a better understanding of optimization of the air electrode used within electrochemical devices and how to eliminate some of the adverse effects associated with it. Figure 1

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.

Concentrated solar-thermal methane pyrolysis in a porous substrate: Yield analysis via infrared laser absorption

In situ compositional analysis via laser absorption spectroscopy is used to characterize the output of a concentrated solar-thermal methane pyrolysis process over a range of test conditions. The novel thermo-chemical process involves directed radiation of a simulated solar source, focused onto a porous carbon felt substrate through which methane flows and decomposes to produce primarily hydrogen gas and graphitic carbon, along with residual hydrocarbons. A mid-infrared laser diagnostic setup has been developed to measure the residual concentrations of light hydrocarbons in the pyrolysis product gas downstream of the reaction zone, with real-time on-line monitoring capability. The infrared absorption sensor utilizes two interband cascade lasers (ICLs) to probe the fundamental C-H stretch vibrational bands, targeting (1) the R(15) manifold of the ν3 band of CH4 as well as one R(14) transition of the ν9 band of C2H4 near 3.16 μm and (2) the RQ3 line cluster of C2H6 near 3.34 μm, respectively. A compositional analysis based on carbon and hydrogen balances is developed to characterize the hydrogen and carbon yields of the pyrolysis process using laser absorption measurements and deposited carbon weight. A range of test conditions are examined with variations of flow rate and solar flux, demonstrating real-time monitoring of product gas composition and sensitivity to operating conditions in variable and transient conditions.

The catalytic effect of trimetallic alloy modified C-felt electrodes on hydrogen evolution reaction

In this study, Ni, NiFe, and Pt are electrochemically deposited on the porous carbon felt for various periods to increase catalytic efficiency and hydrogen gas production, which is investigated in an alkaline medium. The prepared electrodes are characterized by using electrochemical impedance spectroscopy, linear sweep voltammetry, potentiodynamic polarization, cyclic voltammetry, scanning electron microscopy, and X-ray diffraction methods. In addition, hydrogen gas volume is measured by applying the electrolysis process to the electrodes prepared in 1.0 M KOH. It is observed that the most effective Ni deposition time on carbon felt is 20 min. Nickel deposited electrodes were coated with Ni&Fe and Pt in different periods to increase the catalytic effect of the electrode. The highest catalytic effect on the hydrogen evolution reaction was obtained from the C#Ni20NiFe10@Pt45 electrode. Applied of a −0.2 VSHE overpotential, 80 mA cm−2 current density is obtained. The mechanism is determined as Volmer-Heyrovsky and rate determined step is Volmer.

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.

Lattice Boltzmann simulation of liquid water transport in gas diffusion layers of proton exchange membrane fuel cells: Parametric studies on capillary hysteresis

Water management is crucial for reliable operation of Polymer Electrolyte Membrane Fuel Cells (PEMFC). Here, the gas diffusion layer (GDL) plays an essential role as it has to ensure efficient water removal from and oxygen transport to the catalyst layer.In this study water transport through porous carbon felt GDLs was simulated using a 3D Color-Gradient Lattice Boltzmann model. Simulations were carried out on microstructures of plain and impregnated fiber substrates of a Freudenberg H14. The GDL microstructures were reconstructed from high-resolution X-ray micro-computed tomography (μ-CT). For the distinction of carbon fibers and polytetrafluoroethylene (PTFE) in the binarized microstructures an in-house algorithm was developed. The additive was specified heterogeneously in the GDL through-plane direction employing a PTFE loading profile as derived based on μ-CT image data. In the in-plane direction the additive was furthermore defined in a realistic fashion near carbon fiber intersections. Prior to parametric studies on capillary behavior a sophisticated modeling approach for semipermeable membranes had to be developed to account for experimental boundary conditions. Capillary hysteresis was then investigated by simulation of intrusion and drainage curves and subsequent comparison to testbench data.

Application of in-Situ Radiography to Porous Carbon Felt Electrodes in Vanadium Redox Flow Batteries

Porous carbon felts are routinely applied as electrodes in vanadium redox flow batteries. They offer several advantages, such as low cost, low weight, good electron conductivity, and chemical inertness. However, due to their comparatively low activity in catalyzing the vanadium reactions at the anode and cathode side of the battery, an activation treatment is required to enhance the kinetics. In the literature, a heat-treatment at 400 °C in air has been reported as sufficient to introduce more oxygen functional groups at the surface, also improving the wettability of the felt and its contact with the electrolyte significantly. In this context, it is however not clear, which mechanisms are responsible for the observed performance increase. In another approach, bismuth is deposited on the carbon felts to enhance the V2+/3+ reaction in the anolyte. While a better battery performance is indeed observed, the bismuth is assumed to be dissolved and re-deposited during the charge-discharge cycles.The aim of this work is to utilize in-situ X-ray radiography to study both the activation process and the catalytic enhancement effect due to bismuth decoration in more detail. We will highlight the potential of in-situ (synchrotron) radiography for the investigation of electrode/electrolyte interaction, pore filling and electrolyte flow behaviour complementing other more routine characterization techniques nicely [1]. To elucidate the effect of air activation, pristine and heat-treated carbon felts have been brought into contact with water, sulfuric acid and an acidic vanadium solution and ex-situ contact angles determined. This study was complemented by in-situ X-ray radiography, in which an in-house built flow cell served to monitor the electrolyte flow through the porous felt materials (pristine and heat-treated). The effect of the heat-treatment can be clearly discerned in water, see figure 1 (top: pristine felt, bottom: heat-treated felt). In contrast, when the commercial vandium electrolyte was being used, the differences between pristine and heat-treated felt vanished. Consequently, only a negligibly higher pore filling degree was observed for the treated felts, while all felts were flooded in less than 1 minute. [2]Apart from the phenomena described above, we will also highlight the potential of in-situ radiography with respect to Bi-decorated felts during operation. [3][1] L. Eifert, N. Bevilacqua, K. Köble, K. Fahy, L. Xiao, M. Li, K. Duan, A. Bazylak, P.-C. Sui, R. Zeis, ChemSusChem 13 (2020) 3154.[2] M. Gebhard, M. Schnucklake, A. Hilger, M. Röhe, M. Osenberg, U. Krewer, I. Manke, C. Roth, Energy Technol. 8 (2020) 1901214.[3] M. Gebhard, T. Tichter, J. Schneider, J. Mayer, A. Hilger, M. Osenberg, M. Rahn, I. Manke, C. Roth J. Power Sources 478 (2020) 228695. Figure 1

Impact of Varying Bipolar Plates Having Flow-Fields on the Performance of Redox Flow Battery at High Current Density

Redox flow Cell (RFC) stores electricity in the form of chemical energy into the electrolyte. The interface of the electrode surface and electrolyte is responsible for redox reaction and resultantly increase in the state-of-charge (SOC) during charging of the cell. Dispersion of the electrolyte into the electrode (porous carbon felt) and flowrate are important parameters for the performance of the cell. A bipolar plate having flow-field is responsible to disperse electrolyte. Two different configurations of interdigitated flow-field (IFF) and serpentine flow-fields (SFF) were fabricated on the impregnated graphite bipolar plates. The performance was compared with RFC having a conventional bipolar plate without any flow-field.The as-received Fumatech FAP-450 anion exchange membrane was used. All membranes were cleaned in 1M H2SO4 solution at 80oC and stored in DI water. The as-received commercial electrolyte consisted of vanadium solution (1.6 M) was used. Graphite felt electrode (GFE) having a thickness of 4.6 mm was used with a compression ratio of 25%. GFE was boiled in 1M H2SO4 for 12 hours and kept in the same solution for 12 hours. These were washed with DI water and dried at 100oC. Afterward, GFE was thermally treated at 390oC for 12 hrs inside the furnace injected by air and then cooled down in the furnace up to room temperature. Membranes and GFE were used from the same batch for each experiment.The performance of RFC was characterized using charge-discharge cycling (CDC), impedance curves (EIS), and polarization (iV-curve). EIS performed in a range of 100mHz to 50kHz having AC perturbation of 10mV. RFC was charged from SOC of 25% to 75%. It was ensured by recording open-circuit-potential (OCP) after each cycle and the measurement of OCP was co-related with SOC values computed based on concentrations. This allows us to set the cut-off potential from 0.8V to 2.0V and it helps to remain in the safe SOC limits to avoid hydrogen evolution.EIS results of conventional (CFF), IFF, and SFF at the flowrate of 40ml.min-1 were shown in Figure 1(a). The introduction of the new bipolar plates having flow-fields has a significant effect on the area-specific resistance (ASR) which was decreased and charge transfer resistance (CTR) was almost similar. The equivalent circuit analysis of the impedance curve was shown in Figure 1(b). Ohmic & charge transfer resistance of the cell having IFF and SFF is less than conventional whereas capacitance highlighted by CPE is almost double. The effect of varying flowrate on EIS results was tested on the IFF as shown in Figure 1(c) and have a negligible effect. CDC was performed using each flow-field to assess the performance of RFC. Impact of flow-field on the capacity as a function of potential at 120mA.cm-2 having 40ml. min-1 is shown in Figure 1(d) and inset showed the average efficiency of 10 cycles. RFC having IFF reached to higher capacity and overall energy efficiency (EE) of this arrangement is also higher than SFF. However, it was observed that columbic efficiency (CE) is low, but it was the effect of membrane aging after repeated cycles. This observation was eliminated in future studies by using a fresh membrane. The impact of varying flowrate was on the capacity and EE of the RFC having IFF at 80 mA.cm-2 was shown in Figure 1(e). Best capacity and EE results were obtained by using IFF at 20 ml.min-1.Therefore, CDC was performed to check the impact of varying current density having IFF at 20ml.min-1 as shown in Figure 1(f). The current density ranging from 40 to 155mA.cm-2 was tested and EE was decreased from 85% to 60% after increasing the current density up to four times. The CE remains the same which means that no side reactions and least crossover. The voltaic efficiency (VE) was kept on decreasing gradually as the current density was increasing. To further investigate this effect polarization analysis was performed to get limiting current density and peak power as shown in Figure 1(g). It highlights that this arrangement can reach up to a higher current density of 410mA.cm-2 and peak power of 56.25W.l-1 for an RFC having 80ml of electrolyte. Overpotentials were shown in Figure 1(h). It signifies that activation overpotential is negligible, ohmic overpotential is minimum at 10ml.min-1, and mass transport overpotential is minimum at 20ml.min-1.This study highlights that optimization of bipolar plate is significant and has a considerable impact on the performance. It is not a straight-forward isolated process and future researchers need to decide about many trade-offs while optimizing even a single component of RFC. Figure 1

Three‐Dimensional Wettable Carbon Felt Host for Stable Lithium Metal Anode

Lithium (Li) metal possesses a high specific capacity and low electrochemical potential, which is promising as an anode material for Li metal–based batteries. However, dendritic lithium deposition and “dead Li” formation during cycling severely restricte its practical applications. Herein, a nickel (Ni)‐coated carbon felt as the host is used for prefilling Li via a facile thermal infusion strategy, through which a Ni‐coated carbon felt (CFt/Ni–Li) composite anode is achieved. The obtained anode exhibits an ultrastable voltage profile with an ultralow hysteresis (40 mV at 10 mA cm−2) beyond 200 cycles in symmetric cells due to the good confinement of Li metal in the conductive carbon felt frameworks. Moreover, the porous carbon felt not only provides good electronic connection but also the space for accommodating volume expansion which leads to low dimensional change and the inhibition of Li dendrite growth. When paired with a LiFePO4 (LFP) cathode, the CFt/Ni–Li anode shows better rate capability and long‐term cycling stability after 600 cycles at 1C. An important strategy for the design of stable Li metal anodes is provided, which is significant for practical applications of advanced Li metal batteries.

A Simple Aqueous Battery with Potential for Scalable Energy Storage Based on MnO2 Deposition at the Cathode and a Quinoid‐Modified Activated Carbon Anode

AbstractSearching for new materials and battery architecture is highly essential for developing scalable energy storage systems with good reliability, low cost, long cycle life, and high power density. Here, we report the fabrication of a simple and cheap aqueous battery with potential for low‐cost energy storage. In this battery, a quinoid‐modified activated carbon (AC‐AQS) electrode is adopted as the anode and a porous carbon felt is exploited as the current collector in the cathode for reversible MnO2 deposition (MnO2‐C) from Mn2+ in the electrolyte. This MnO2‐C/AC‐AQS battery delivers an outstanding power density (4.4 kW kg−1), excellent cycling stability (99.9 % of the maximum discharge capacity is maintained after 10 000 cycles), and limited self‐discharging. A maximum energy density of 102.5 Wh kg−1 under the charging capacity of 1.2 mAh cm−2 is achieved. Moreover, owing to the ultrafast redox kinetics of cathode and anode, it can be charged to 0.8 mAh cm−2 within 57.6 s, demonstrating excellent rate capability.

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 (Rct) 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.

Porous electrospun carbon nanofibers network as an integrated electrode@gas diffusion layer for high temperature polymer electrolyte membrane fuel cells

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) utilize phosphoric acid imbibed polybenzimide membranes, which allow for improved reaction kinetics due to the higher operating temperatures, but suffer from the corrosive environment and the sluggish oxygen transport and associated transport limitations. The latter issue is addressed in this work by the integration of the gas diffusion layer (GDL) into the gas diffusion electrode (GDE) in an entirely electrospun concept. For this purpose, coaxial electrospinning is applied by spinning two immiscible polymer solutions simultaneously to create a core-shell structure. Porous carbon felt structures are obtained due to phase separation in the shell and a subsequent carbonization treatment (integrated GDE@GDL). Full cell tests (0.6 mgPt cm−2) demonstrate a 21% increase in the power density normalized to the platinum content compared to the spray-coated reference (1 mgPt cm−2). Electrochemical impedance spectroscopy (EIS) measurements coupled with the distribution of relaxation times (DRT) analysis show that the morphology of the GDE@GDL favors oxygen transport inside the electrode. Mass transport limitations were successfully remedied by our electrospun concept rendering an additional GDL sheet obsolete.

Improving the Thermodynamic Energy Efficiency of Battery Electrode Deionization Using Flow-Through Electrodes.

Ion intercalation electrodes are being investigated for use in mixed capacitive deionization (CDI) and battery electrode deionization (BDI) systems because they can achieve selective ion removal and low energy deionization. To improve the thermodynamic energy efficiency (TEE) of these systems, flow-through electrodes were developed by coating porous carbon felt electrodes with a copper hexacyanoferrate composite mixture. The TEE for ion separation using flow-through electrodes was compared to a system using flow-by electrodes with the same materials. The flow-through BDI system increased the recoverable energy nearly 3-fold (0.009 kWh m-3, compared to a 0.003 kWh m-3), which increased the TEE from ∼6% to 8% (NaCl concentration reduction from 50 to 42 mM; 10 A m-2, 50% water recovery, and 0.5 mL min-1). The TEE was further increased to 12% by decreasing the flow rate from 0.50 to 0.25 mL min-1. These findings suggest that, under similar operational conditions and materials, flow-through battery electrodes could achieve better energy recovery and TEE for desalination than flow-by electrodes.

Electrolyte Flow in Vanadium Redox Flow Batteries

The redox reactions inside a Vanadium Redox Flow Battery (VRFB) are catalyzed by a porous carbon felt electrode, through which the vanadium containing electrolyte is pumped. Thus, a high Electrochemically Active Surface Area (ECSA), corresponding to a high saturation of the porous electrode, is beneficial to the performance. Maintaining a low mass transport resistance inside the flow felt is important to reduce parasitic pumping losses, which decrease the overall efficiency of the battery system. The pressure drop was measured, as it is directly related to the pumping losses caused by the flow through the pores. X-ray tomography and X-ray radiography were used to visualize the distribution of the electrolyte inside the pores. The effect of thermal activation (400 °C, 25 h) and compression of the carbon electrode on the wetting behavior of the electrolyte was investigated, as it correlates with the ECSA and the oxygen content on the electrode surface1. Furthermore, the changes in flow behavior of the redox active vanadium species with a different oxidation number are of interest, as it could imply separate optimization parameters for the anode side and the cathode side. The redox-active vanadium species in the electrolyte exist in four different states, V(II), V(III), V(IV), and V(V). In this work, the X-ray based techniques were used in an ex situ injection setup2. VRFB electrolytes (V(IV), V(V), V(II), V(III), all 0.1 M in 2M H2SO4) were injected into a commercially available porous carbon felt electrode ((GFA 6EA) from SIGRACELL® battery electrodes (SGL Carbon, Germany)) under controlled degrees of compression (20%, 50%, 70% of the uncompressed height). After an initial imbibition of the electrode, which was stopped immediately after the electrode wicked the electrolyte, a higher flow-rate was applied to simulate operating conditions. Synchrotron X-ray radiography shows the invasion and progression of the liquid electrolyte into the pores and indicates that capillary forces are initially dominant, but numerical simulation of the flow-through suggests that other forces come into play as well at higher flow velocities3. The study shows that the thermal activation plays the major role in the wetting behavior, increasing the saturation inside the electrode by more than 200% and decreasing the pressure drop by a factor of two when the electrolyte is injected into a thermally activated electrode, in agreement with Banerjee et al.3. The influence of the vanadium species in the electrolyte is relatively weak and it shows a slightly higher saturation for V(III), but this effect is outweighed by a stronger effect of compression. Synchrotron X-ray tomography highlights the occurrence of the Cassie-Baxter effect (the emergence of trapped air bubbles inside the electrode) and implies movement of these bubbles during continuous flow, in agreement with Greco et al.1. Figure 1: a) Saturation after injection of various electrolyte species into thermally activated carbon felt electrodes under different degrees of compression. b) Effect of compression on the pressure during the simulation of continuous flow-through conditions. The bar color corresponds to the color of the electrolyte solution in both figures. 1 Greco, K. V., Forner-Cuenca, A., Mularczyk, A., Eller, J. J. & Brushett, F. R. Elucidating the Nuanced Effects of Thermal Pretreatment on Carbon Paper Electrodes for Vanadium Redox Flow Batteries. ACS Applied Materials & Interfaces 10, 44430-44442, doi:10.1021/acsami.8b15793 (2018). 2 Bevilacqua, N., George, M. G., Galbiati, S., Bazylak, A. & Zeis, R. Phosphoric Acid Invasion in High Temperature PEM Fuel Cell Gas Diffsuion Layers. Electrochim. Acta 257, 89-98, doi:10.1016/j.electacta.2017.10.054 (2017). 3 Banerjee, R., Bevilacqua, N., Eifert, L. & Zeis, R. Characterization of carbon felt electrodes for vanadium redox flow batteries - A pore network modeling approach. Journal of Energy Storage 21, 163-171, doi:10.1016/j.est.2018.11.014 (2019). Figure 1