Carbon Felt Electrode Research Articles

Voltage recovery from frozen microbial fuel cells in the laboratory and outdoor field reactors

Extreme temperature variations are a problem that must be faced in the practical application of microbial fuel cells (MFCs), but MFCs are not extensively described for low and even freezing temperatures. This study assessed the effect of low-temperature shock on the power generation performance and microbial community structure of MFCs. Two scales of MFCs, the small (mL-MFC) and the large (L-MFC), were constructed in the laboratory and their performance was evaluated before and after freezing at −18 °C. The experimental results demonstrate that both MFCs were capable of rapidly restoring their voltage to the previous level after thawing. For the mL-MFC (rGO/Ag), the power density recovered from 194.30 ± 10.84 mW/m2 to 195.57 ± 4.02 mW/m2 after thawing. For L-MFC (carbon felt electrodes), the power density increased significantly from the initial 1.79 mW/m2 to 173.90 mW/m2 after thawing, but the performance degradation problem after reactor amplification still needs to be solved. The sediment microbial fuel cell (SMFC) was successfully constructed and operated in a natural outdoor environment to maintain high voltage output after the period of frost. Microbial analysis indicated after the frost period, psychrotolerant microorganisms enriched on the anode, such as Flavobacterium and Psychrobacter, while the relative abundance of anaerobic methanogenic bacterium decreased. Overall, freeze-thaw operations had a non-negative impact on the performance of MFCs and provided some references for their practical applications.

Electrochemical degradation of carbamazepine in water by a flow-through and pilot-scale reactor with carbon felt electrodes: Parametric study under realistic operational conditions

Carbamazepine (CBZ) is one of the most stable pharmaceutical compounds that is commonly found in the effluents of wastewater treatment plants (WWTP). In this context, this contribution presents a comprehensive analysis of the different operating parameters of a flow-through and pilot-scale cylindrical reactor for hydrogen peroxide (H2O2) generation, in which the degradation of CBZ takes place. The electrochemical system was evaluated using 8 L of electrolytes prepared with tap water in the presence of methanol as dissolved organic matter or spiked tertiary WWTP effluent, at a volumetric flow of 7 L min−1. This reactor (i) improves the mass transport due to its flow-through configuration using fibrous quasi-three-dimensional carbon felt electrodes, (ii) operates without an external oxygen supply to promote the H2O2 electrosynthesis because it is incorporated by a jet aerator (iii) achieves the Fenton reaction at circumneutral pH due to Fe(II) disposition from a cation exchange resin. At first, the carbonaceous materials were electrochemically characterized by cyclic voltammetry measurements. Different operating parameters were evaluated by factorial design methodologies for H2O2 generation, energetic consumption and CBZ removal. The application of a current density of 1.4 mA cm−2, in a cathode-anode-cathode arrangement immersed in a 120 mM ionic strength solution, allowed to obtain up to 6.4 mg H2O2 L−1 after 40 min, consuming 0.44 kWh m−3. Later, the Fenton reaction was validated by a florescence study, and by the incorporation of 0.75 g of granular activated carbon and 5 g of Fe(II) loaded resin, CBZ abatement yields of 68 % and 32 % were obtained using a synthetic solution and a spiked tertiary WWTP effluent, respectively, and up to 28 % of the dissolved total organic carbon was removed. Finally, an analysis of the stability of the carbon felt electrodes was tackled using scanning electron microscopy and energy-dispersive X-ray spectroscopy.

Efficient Decoupled Electrolytic Water Splitting in Acid through Pseudocapacitive TiO2.

Water electrolysis remains a key component in the societal transition to green energy. Membrane electrolyzers are the state-of-the-art technology for water electrolysis, relying on 80°C operation in highly alkaline electrolytes, which is undesirable for many of the myriad end-use cases for electrolytic water splitting. Herein, an alternative water electrolysis process, decoupled electrolysis, is described which performed in mild acidic conditions with excellent efficiencies. Decoupled electrolysis sequentially performs the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), at the same catalyst. Here, H+ ions generated from the OER are stored through pseudocapacitive (redox) charge storage, and released to drive the HER. Here, decoupled electrolysis is demonstrated using cheap, abundant, TiO2 for the first time. To achieve decoupled acid electrolysis, ultra-small anatase TiO2 particles (4.5nm diameter) are prepared. These ultra-small TiO2 particles supported on a carbon felt electrode show a highly electrochemical surface area with a capacitance of 375Fg-1. When these electrodes are tested for decoupled water splitting an overall energy efficiency of 52.4% is observed, with excellent stability over 3000 cycles of testing. This technology can provide a viable alternative to membrane electrolyzers-eliminating the need for highly alkaline electrolytes and elevated temperatures.

A sustainable electrochemical strategy utilizing pulsed alternating current and dual carbon felt electrodes for enhanced degradation of organic pollutants: Oxidation performance and mechanisms

In this work, a novel electrochemical (EC) oxidation system utilizing pulsed alternating current (PAC) and dual carbon felt (CF) electrodes has been established for sustainable degradation of sulfamethoxazole (SMX) with no addition of extra oxidant. The EC/PAC system showed high degradation efficiency and energy efficiency compared to the pulsed direct current (PDC) and direct current (DC) systems. The EC/PAC process was effective across a wide pH range of 3–11 for SMX removal. The results showed that the 1O2 confined to the CF electrode surface was the dominant oxidative specie that was generated from dissolved oxygen in the system. Under PAC conditions, the cathode and anode were rapidly switched on the same CF electrode, increasing the generation of 1O2 for enhanced SMX oxidation. Furthermore, the EC/PAC system demonstrated resistance to interference from various anions of different concentration levels found in natural environment. In contrast to the EC/PDC system, the EC/PAC system emerged as a promising option for more efficient H2O2 production. High-resolution mass spectrometry results revealed the SMX degradation pathways and byproducts, which were then evaluated for toxicity removal. Overall, the EC/PAC system offers a green and sustainable solution to future wastewater treatment, with high degradation rates, energy efficiency, and sustainability.

Additive manufactured metal lattice structures used as flow-through electrodes in a filter-press electrochemical reactor

This study deals with the electrochemical and hydraulic performances of additive manufactured metal periodic lattice structure electrodes. These electrodes are fabricated by Laser Powder Bed Fusion (LPBF) from the titanium alloy TA6V and two structures have been studied: diagonal and octet-truss. They are integrated, as flow-through electrodes, in an electrochemical filter-press reactor. Current–potential curves are experimentally obtained by linear sweep voltammetry when feeding the reactor with a ferricyanide solution. From the measurement of the limiting current of ferricyanide ions reduction, the volumetric mass transfer coefficient kAe is determined for several flow rates. Numerical simulations of fluid flow and mass transfer in these structures are also performed. Results show high values of kAe for these structures (competing with carbon felt electrodes) while maintaining a high permeability (low flow resistance). The surface roughness, inherent to the additive manufacturing process, is found to induce a low (≲10%) enhancement of mass transfer despite the roughness size (Ra in the range 10-20μm) is close to the average thickness of the diffusion layer (for the investigated fluid velocities). As a result, these electrode structures show promising potential to be used in intensified electrochemical reactors by being further optimized to find the optimal internal dimensions that maximize mass transfer while limiting flow resistance.

The effects of different electrode materials on the electric field-assisted co-composting system for the soil remediation of heavy metal pollution

The electric field-assisted composting system (EACS) is an emerging technology that can enhance composting efficiency, but little attention has been given to electrode materials. Herein, an EACS was established to investigate the effects of electrode materials on humic substance formation and heavy metal speciation. Excitation-emission matrix analysis showed that carbon-felt and stainless-steel electrodes increased humic acid (HA) by 48.57 % and 47.53 %, respectively. In the EACS with the carbon-felt electrode, the bioavailability factors (BF) of Cu and Cr decreased by 18.00 % and 7.61 %, respectively. Despite that the stainless-steel electrodes decreased the BF of As by 11.26 %, the leaching of Cr, Ni, Cu, and Fe from the electrode itself is an inevitable concern. Microbial community analyses indicated that the electric field increased the abundance of Actinobacteria and stimulated the multiplication of heavy metal-tolerant bacteria. Redundancy analysis indicates that OM, pH, and current significantly affect the evolution of heavy metal speciation in the EACS. This study first evaluated the metal leaching risk of stainless-steel electrode, and confirmed that carbon-felt electrode is environment-friendly material with high performance and low risk in future research with EACS.

Two-in-one strategy for optimizing chemical and structural properties of carbon felt electrodes for vanadium redox flow batteries

ABSTRACT Vanadium redox flow batteries (VRFBs) have received significant attention for use in large-scale energy storage systems (ESSs) because of their long cycle life, flexible capacity, power design, and safety. However, the poor electrochemical activity of the conventionally used carbon felt electrode results in low energy efficiency of the VRFBs and consequently impedes their commercialization. In this study, a carbon felt (CF) electrode with numerous nanopores and robust oxygen-containing functional groups at its edge sites is designed to improve the electrochemical activity of a carbon felt electrode. To achieve this, Ni metal nanoparticles were initially precipitated on the surface of the CF electrode, followed by etching of the precipitated Ni nanoparticles on the CF electrode using sulfuric acid. The resulting CF electrode had a specific surface area eight times larger than that of the pristine CF electrode. In addition, the oxygen-containing functional groups anchored at the graphite edge sites of the nanopores can act as robust electrocatalysts for VO2+/VO2 + and V2+/V3+ redox reactions. Consequently, the VRFB cell with the resulting carbon felt electrode can deliver a high energy efficiency of 86.2% at the current density of 60 mA cm−2, which is 20% higher than that of the VRFB cell with the conventionally heat-treated CF electrode. Furthermore, the VRFB cell with the resultant carbon felt electrodes showed stable cycling performance with no considerable energy efficiency loss over 200 charge-discharge cycles. In addition, even at a high current density of 160 mA cm−2 , the developed carbon felt electrode can achieve an energy efficiency of 70.1%.

Cationic covalent organic frameworks electrode for 99TcO4- electro-adsorption with enhanced removal property

Electro-adsorption approach has been exhibited enormous promise for radionuclides removal from radioactive wastewater, and the fabrication of functional electrodes is of great significance for achieving efficient and selective removal. Herein, a cationic covalent organic framework (COFs) was synthesized through aldimine condensation reaction between 3,8-diamino-5-methyl-6-phenylphenanthridinium bromide and 1,3,5-tris(p-formylphenyl)benzene and then modified onto carbon felt electrode for efficient separation of TcO4- by electro-adsorption. The cationic COFs functionalized electrode showed efficient separation properties for TcO4- with high selectivity, fast kinetic, and large uptake capacity. The adsorption equilibrium of the functional electrode for ReO4- (a surrogate for 99TcO4-) can be reached within only 60 s by electro-adsorption with 1.2 V applied voltage, much faster than physicochemical adsorption (10 min). The maximum electro-adsorption capacity was calculated to be 990.1 mg/g by Langmuir model, at least 2.1 times larger than the value of 473.9 mg/g acquired via physicochemical adsorption. In the meantime, the cationic COFs functionalized electrode exhibited high selectivity for ReO4-. The sorption mechanism was studied by XPS, EDX and DFT, the results revealed that the adsorption of ReO4- onto the cationic COFs mainly involve an ion exchange process between ReO4- and Br-. This work provides a new method for efficient and selective elimination of TcO4-, which can be extended to eliminate other contaminants through rational electrode design and manufacture.

Nano zero-valent iron functioned 3D printing graphene aerogel electrode for efficient solar-driven biocatalytic methane production

To address the urgent need for developing carbon-neutral technologies, microbial electrosynthesis (MES), as an important contributor to the renewable energy field, can convert carbon dioxide to multi-carbon chemicals using microbes serving as living catalysts at the cathode. However, the performance of the cathode is restricted by the weak electrochemical reaction kinetics of the organisms, the specific area of the electrode, and the mass transfer under high current. Herein, we report a facile 3D-printed graphene aerogel (GA) electrode built with a nanozero-valent iron (NZVI)-functionalized graphene ink. The 3D-printed GA electrode was designed to possess hierarchical pores with an enhanced high specific surface area for microbial colonization while ensuring mass transfer. NZVI can assist in-situ hydrogen generation, facilitating biofilm formation and methane (CH4) production in the indirect electron transfer pathway. Consequently, the optimized 3D-printed electrode achieved a maximum CH4 production rate of 6993 ± 832 mmol/m2/d with a faradaic efficiency of 83.7%, which increased by 3.24-fold to the carbon felt electrode. In addition, integrating the proposed cathode into a PV-electrolyzer cell yielded a solar-to-CH4 efficiency of 4.70%. This study provides a unique method for the development of advanced cathodes and underscores the potential of integrating MES with renewable energy technologies.

Energy Production in Microbial Fuel Cells (MFCs) during the Biological Treatment of Wastewater from Soilless Plant Cultivation

The management of drainage water (DW), which is produced during the soilless cultivation of plants, requires a high energy input. At the same time, DW is characterized by a high electrolytic conductivity, a high redox potential, and is also stable and putrefaction-free. In the present study, the natural properties of drainage water and a biotreatment method employing an external organic substrate in the form of citric acid (C/N 1.0, 1.5, 2.0) were utilized for energy recovery by a microbial fuel cell (MFC). The cathode chamber served as a retention tank for DW with a carbon felt electrode fixed inside. In turn, a biological reactor with biomass attached to the filling in the form of carbon felt served as the anode chamber. The filling also played the role of an electrode. The chambers were combined by an ion exchange membrane, forming an H letter-shaped system. They were then connected in an external electrical circuit with a resistance of 1k Ω. The use of a flow-through system eliminated steps involving aeration and mixing of the chambers’ contents. Citric acid was found to be an efficient organic substrate. The voltage of the electric current increased from 44.34 ± 60.92 mV to 566.06 ± 2.47 mV for the organic substrate dose expressed by the C/N ratio ranging from 1.0 to 2.0. At the same time, the denitrification efficiency ranged from 51.47 ± 9.84 to 95.60 ± 1.99% and that of dephosphatation from 88.97 ± 2.41 to 90.48 ± 1.99% at C/N from 1.0 to 2.0. The conducted studies confirmed the possibility of recovering energy during the biological purification of drainage water in a biofilm reactor. The adopted solution only required the connection of electrodes and tanks with an ion-selective membrane. Further research should aim to biologically treat DW followed by identification of the feasibility of energy recovery by means of MFC.

Nitrogen, phosphorus, and sulfur co-doped carbon nanotubes/melamine foam composite electrode for high-performance vanadium redox flow battery

The high cost and complex modification process of carbon felt electrodes limits its further popularization in vanadium redox flow batteries (VFBs). By introducing low-cost melamine foam, nitrogen, phosphorus, and sulfur co-doped carbon nanotubes/ melamine foam composite electrode (NPS-CNTs-CMF) is designed and fabricated via immersing melamine foam in a solution containing N, P, and S co-doped CNTs. The integration of modified CNTs significantly enhances the conductivity and hydrophilicity of the electrode. Moreover, the composite electrode also demonstrates outstanding electrocatalytic activity owing to the heteroatom doping that further inspired the electrocatalytic activity of CNTs. Density function theory calculations further uncover that introducing heteroatoms on CNTs not only promotes the adsorption of vanadium ions but also facilitates the electron transfer between vanadium ions and MF substrate. As a result, the battery loading with NPS-CNTs-CMF exhibits excellent battery performance, achieving energy efficiency of 80.12 % at 300 mA cm–2. Additionally, the long-term cycling stability is attained over 200 consecutive charge-discharge cycles at 300 mA cm−2. This study provides a novel melamine foam material with low cost and simple modification, and this new composite structure stimulates the development of high-performance electrodes in VFBs.

The Effect of Bismuth and Tin on Methane and Acetate Production in a Microbial Electrosynthesis Cell Fed with Carbon Dioxide.

This study investigates the impacts of bismuth and tin on the production of CH4 and volatile fatty acids in a microbial electrosynthesis cell with a continuous CO2 supply. First, the impact of several transition metal ions (Ni2+, Fe2+, Cu2+, Sn2+, Mn2+, MoO42-, and Bi3+) on hydrogenotrophic and acetoclastic methanogenic microbial activity was evaluated in a series of batch bottle tests incubated with anaerobic sludge and a pre-defined concentration of dissolved transition metals. While Cu is considered a promising catalyst for the electrocatalytic conversion of CO2 to short chain fatty acids such as acetate, its presence as a Cu2+ ion was demonstrated to significantly inhibit the microbial production of CH4 and acetate. At the same time, CH4 production increased in the presence of Bi3+ (0.1 g L-1) and remained unchanged at the same concentration of Sn2+. Since Sn is of interest due to its catalytic properties in the electrochemical CO2 conversion, Bi and Sn were added to the cathode compartment of a laboratory-scale microbial electrosynthesis cell (MESC) to achieve an initial concentration of 0.1 g L-1. While an initial increase in CH4 (and acetate for Sn2+) production was observed after the first injection of the metal ions, after the second injection, CH4 production declined. Acetate accumulation was indicative of the reduced activity of acetoclastic methanogens, likely due to the high partial pressure of H2. The modification of a carbon-felt electrode by the electrodeposition of Sn metal on its surface prior to cathode inoculation with anaerobic sludge showed a doubling of CH4 production in the MESC and a lower concentration of acetate, while the electrodeposition of Bi resulted in a decreased CH4 production.

Enhanced heterogeneous electro-Fenton process for degradation of rhodamine B: FeOCl/CF@AB composite cathode with superior efficiency and sustainability

With the growing environmental concerns and increasing demand for clean energy, the synthesis of Stable and efficient heterogeneous Electro-Fenton catalysts gains significant attention in the market. We present a novel FeOCl/CF@AB composite cathode designed for efficient heterogeneous electro-Fenton degradation of rhodamine B. The composite cathode exhibits remarkable catalytic performance, outperforming the raw carbon felt electrode, and achieving significantly higher rhodamine B degradation rates. The incorporation of acetylene black encapsulation provides excellent stability, preserving the FeOCl active sites from corrosion and ensuring sustained catalytic activity even after multiple reuse cycles. The electron penetration mechanism on the FeOCl/CF@AB cathode is elucidated through density functional theory calculations, revealing spontaneous O2 activation and H2O2 generation. Electron transfer between Fe(II) species and the acetylene black shell facilitates these processes. The presence of •OH species supports the degradation of rhodamine B to intermediates and mineralization to CO2 and H2O. Furthermore, LC-MS analysis unveils the detoxification effect of the electro-Fenton process with FeOCl/CF@AB, presenting reduced developmental toxicity of degradation intermediates. Economic cost analysis demonstrates the feasibility and cost-effectiveness of the FeOCl/CF@AB cathode for large-scale wastewater treatment applications. In conclusion, the FeOCl/CF@AB composite cathode showcases stability and efficiency, offering a promising and sustainable electro-Fenton technology for dye wastewater treatment.

Enhancing microbial fuel cell performance with carbon powder electrode modifications for low-power sensors modules

Microbial Fuel Cell (MFC) is a promising technology for harnessing energy from organic compounds. However, the low power generation of MFCs remains a significant challenge that hinders their commercial viability. In this study, we reported three distinct modifications to the stainless-steel mesh (SSM), carbon cloth, and carbon felt electrodes using carbon powder (CP), a mixture of CP and ferrum, and a blend of CP with sodium citrate and ethanol. The MFC equipped with an SSM and CP anode showed a notable power density of 1046.89 mW.m-2. In comparison, the bare SSM anode achieved a maximum power density of 145.8 mW m-2. Remarkably, the 3D-modified SSM with a CP anode (3D-SSM-CP) MFC exhibited a substantial breakthrough, attaining a maximum power density of 1417.07 mW m-2. This achievement signifies a significant advancement over the performance of the unaltered SSM anode, underscoring the effectiveness of our modification approach. Subsequently, the 3D-SSM-CP electrode was integrated into single-chamber MFCs, which were used to power a LoRaWAN IoT device through a power management system. The modification methods improved the MFC performance while involving low-cost and easy fabricating techniques. The results of this study are expected to contribute to improving MFC's performance, bringing them closer to becoming a practical source of renewable energy.

Extending the lifetime of vanadium redox flow batteries by reactivation of carbon electrode materials.

The degradation and aging of carbon felt electrodes is a main reason for the performance loss of Vanadium Redox Flow Batteries over extended operation time. In this study, the chemical mechanisms for carbon electrode degradation are investigated and distinct differences in the degradation mechanisms on positive and negative electrodes have been revealed. A combination of surface analysis techniques such as X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Electrochemical Impedance Spectroscopy (EIS) was applied for this purpose. In addition to understanding the chemical and physical alterations of the aged electrodes, a thermal method for reactivating aged electrodes was developed. The reactivation process was successfully applied on artificially aged electrodes as well as on electrodes from a real-world industrial vanadium redox flow battery system. The aforementioned analysis methods provided insight and understanding into the chemical mechanisms of the reactivation procedure. By applying the reactivation method, the lifetime of vanadium redox flow batteries can be significantly extended.

Insights into the hydrogen evolution reaction in vanadium redox flow batteries: A synchrotron radiation based X-ray imaging study

The parasitic hydrogen evolution reaction (HER) in the negative half-cell of vanadium redox flow batteries (VRFBs) causes severe efficiency losses. Thus, a deeper understanding of this process and the accompanying bubble formation is crucial. This benchmarking study locally analyzes the bubble distribution in thick, porous electrodes for the first time using deep learning-based image segmentation of synchrotron X-ray micro-tomograms. Each large three-dimensional data set was processed precisely in less than one minute while minimizing human errors and pointing out areas of increased HER activity in VRFBs. The study systematically varies the electrode potential and material, concluding that more negative electrode potentials of −200 mV vs. reversible hydrogen electrode (RHE) and lower cause more substantial bubble formation, resulting in bubble fractions of around 15%–20% in carbon felt electrodes. Contrarily, the bubble fractions stay only around 2% in an electrode combining carbon felt and carbon paper. The detected areas with high HER activity, such as the border subregion with more than 30% bubble fraction in carbon felt electrodes, the cutting edges, and preferential spots in the electrode bulk, are potential-independent and suggest that larger electrodes with a higher bulk-to-border ratio might reduce HER-related performance losses. The described combination of electrochemical measurements, local X-ray micro-tomography, AI-based segmentation, and 3D morphometric analysis is a powerful and novel approach for local bubble analysis in three-dimensional porous electrodes, providing an essential toolkit for a broad community working on bubble-generating electrochemical systems.

(Invited) The Effect of Surfactants on Vanadium Electrochemistry in Porous Carbon Electrodes

We present a study of vanadium electrochemistry in porous electrodes with and without sodium dodecyl sulfate (SDS) additives present. Carbon paper and felt electrodes are compared. Carbon felt electrodes are the de facto standard in flow batteries. There are significant differences in the electronic conductivity of these media. The carbon paper has a much higher conductivity than the felt, which has an electronic conductivity similar to the ionic conductivity of the electrolytes used. The latter fact motivates an extension of available theory for polarization curve fitting to explicitly include both electronic and ionic contributions in the porous electrode. We demonstrate agreement between our model and an existing model evaluated at the limit where electrode conductivity is significantly greater than electrolyte conductivity. Our model uses the product of the electrode surface area per volume ratio and the heterogeneous electron transfer rate constant, and the Damköhler number as fitting parameters for carbon paper and felt electrodes. We discuss the effect of SDS additives on kinetics in the context of the cation hydration shell for the vanadium ions. To this point, we apply Marcus-Hush-Chidsey formalism to our porous electrode model to quantify reorganization energies obtained through polarization curve fitting. This work was supported as part of the Breakthrough Electrolytes for Energy Storage (BEES2), an Energy Frontier Research Center funded by the United States. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

Impact of Power Electronic Converter Ripples on Vanadium Redox Flow Batteries

The worldwide effort to decarbonize the electricity grid has made battery energy storage system (BESS) an essential technology. A promising technology for long duration storage on the grid is Vanadium Redox Flow Batteries (VRFBs), which can support the grid by regulating peak load, reducing intermittency of large-scale renewables, and as emergency power supply. There are two primary methods of integrating a BESS to the grid. Frist, the BESS is directly connected to the DC-link of a DC-AC converter that interfaces with the grid. Second, the BESS is connected to a DC-DC converter that in turn interfaces with the DC-link of a DC-AC converter. These converters all have a characteristic ripple voltage and current during operation. The magnitude and frequency of the ripples depend on topology and switching frequency of a converter, controller design and protocol, type of connection to the grid, voltage magnitude and load characteristics. Currently, studies on the impact of ripples have been limited to Lithium-ion and Lead-Acid batteries. The impact of ripple current and voltage has not been studied in VRFBs. In a VRFB, potential impact includes excessive gassing of hydrogen and carbon corrosion of the bipolar plate and porous electrode and cell heating. To better integrate and operate VRFBs to the electricity grid, the impact of ripples needs to be studied in detail.Using a novel experimental platform, where both magnitude and frequency of ripples will be incorporated, we will emulate the performance of different power electronic converter configurations. It will comprise standard 5cm2 VRFB cells with a carbon felt electrode and Nafion ion exchange membrane. The various converter ripples in an electricity grid setting will be emulated by superimposing the signals from a potentiostat (constant current) and a high frequency transformer (modulated ripples), which will be connected to the cathode of the cells.The experimental testbed will be used to cycle the VRFB cells at various states of charge with ripples that emulate the performance of power electronic converters during grid operations and disturbances. Varied parameters will include ripple amplitude, ripple frequency, electrolyte flow rate, applied current density and state of charge. Measurement data from monitoring voltage of each electrode, cell voltage and current, gas generation, electrolyte crossover and electrolyte loss will be analyzed to determine the impact of ripples on VRFB cells. Finally, the cells will be monitored for signs of gas generation and postmortem signs of carbon corrosion.Our analysis will determine the impact of various ripple magnitude and frequencies on VRFBs in a simulated grid integration environment. This work will facilitate the development of design standards for power electronic converters that are intended for battery applications, while also informing future efforts to optimize VRFB cell and stack performance.

Mitigation of Discharged Capacity Decay and Volume Variation in Vanadium Redox Flow Batteries By Modifying Electrolytes Composition

Vanadium redox flow battery (VRFB) is a promising technology for energy storage because of its independent energy to power ratio and long cycle life. However, VRFB commercialization is still hindered by some technological issues, among which the electrolyte imbalance caused by the undesired vanadium-ions and water transport through the membrane. These phenomena result in battery capacity loss, that can be recovered with periodic re-balancing procedures, thus increasing operating and maintenance costs.In the literature different studies have been dedicated to the analysis of ions and water crossover. In particular, Oh et al [1] evidenced that water and vanadium ions transport across the separator are strictly related. Shin et al [2] tried experimentally to mitigate water imbalance through a modified preparation of the electrolytes; however, the proposed mitigations were experimentally verified for just one charge-discharge cycle.In this work, combining experimental and modelling activity, the evolution of discharged capacity and electrolyte volume were first investigated and then mitigated modifying electrolytes composition for hundreds of cycles. In addition, to increase the validity of the obtained results, three different Solvay® membranes were tested: E98-05 (EW 980, thickness 50 mm), E87-05 (EW 870, thickness 50 mm) and E98-09 (EW 980, thickness 90 mm). Cycles with fixed cut-off voltages at 0.1 A cm-2 were performed in a 25 cm2 cell employing carbon felt electrodes (Sigracell® GFD 2.5 EA thermal activated).Adopting commercial electrolyte, the discharged capacity of the battery dramatically decreased in its first phase of operations, while electrolytes volume continuously varied until the end of the test, as reported in figure 1B for E98-05. This behaviour was showed by all the three different membranes, regardless their thickness or equivalent weight. Thanks to a preliminary modelling analysis with a 1D VRFB physical model, the causes of the initial capacity decay were fully understood and three different mitigation strategies obtained through the modification of electrolyte preparation were proposed and experimentally validated.The first one consisted in the reduction of the initial proton concentration difference between anolyte and catholyte, obtained by increasing the acid molarity at negative side. This led to the mitigation of the initial capacity decay. The second one consisted in the increase of the proton concentration in both the catholyte and anolyte, obtained by increasing their acid molarity. This led to the mitigation of the initial capacity decay and the reduction of the electrolyte volume variation in time.The third mitigation strategy combined the beneficial effect of reducing the initial proton concentration difference between anolyte and catholyte and the one of increasing the proton concentrations in both the electrolytes. The results were promising: as can be seen in figure 1, with E98-05 the initial capacity decay was completely mitigated and no volume variation was experienced in more than 200 cycles. The effectiveness of this mitigation strategy was experimentally validated successfully also with E98-09 and E87-05. Figure 1 - charge-discharge cycle with E98-05 using modified electrolytes: A) discharged capacity; B) electrolyte volume variation.

Polydopamine anchored localized growth of copper nanoparticles on carbon felt electrode for bioelectrochemical dye degradation

Surface functionalized electrodes facilitate easy electron exchange for the redox reactions in microbial fuel cell (MFC). Synthetic binders used for nanomaterial deposition compromises the reproducibility, stability and obstruct the active catalytic sites. Polydopamine (PDA) coating on electrode provides amine and catechol groups for localization of Cu2+ ions. Higher concentration of Cu2+ facilitated faster growth of copper nanoparticles (CuNPs) using Curcuma longa extract as reducing agent. In-situ growth of CuNP@PDA on carbon felt (CF) reduced the charge transfer resistance and provided redox active species for electron transfers. CuNP@PDA CF cathode resulted in methyl red (MR) degradation in aerated cathode MFC by producing Cu catalyzed reactive oxygen species. MR and O2 compete for electrons at cathode which reduced the overall power output of the MFC. CuNP@PDA CF-MFC was able to produce maximum power density of 15.3 and 6.1 mW/m2 with 10 and 50 mg/L MR respectively as compared to bare CF-MFC which produced 5.5 and 2.7 mW/m2. Dye mineralization could be achieved with CuNP@PDA CF-MFC due to bioelectrochemical advanced oxidation process while bare CF-MFC could only achieve dye decolorization. Such strategy is useful for achieving complete dye removal in a single reactor as compared to conventional dye mineralization process mandating sequential steps.