Graphite Felt Research Articles

Superhydrophilic cobalt-doped NiFe LDH graphite felt with enriched oxygen vacancy as an efficient oxygen evolution electrocatalyst in alkaline media

Efficient non-precious metal electrocatalysts are crucial for hydrogen production through water electrolysis. Combining a superhydrophilic electrocatalyst with oxygen vacancy and a conductive carbon matrix is significant for NiFe LDH-based oxygen evolution reaction (OER) applications. In this study, NiFe LDH nanoflowers and Co-doped NiFe LDH nanoneedles were synthesized on graphite felt through an in-situ self-assembly strategy. Further results have shown that doping Co into NiFe LDH nanoarrays significantly enhances the specific surface area and oxygen vacancy density, while the graphite felt serves as a conductive scaffold and prevents active sites detachment. Oxygen vacancies in Co3–Ni7Fe3 LDH/TGF adjust the electronic configuration, and superhydrophilicity promotes effective electrolyte diffusion. This synergy endows Co3–Ni7Fe3 LDH/TGF with excellent OER performance, lower overpotential of 252 mV (10 mA cm−2), a Tafel slope (63.13 mV), and stability at high current densities. This research provides a new perspective for utilizing non-precious metal catalysts on carbon substrates for hydrogen production.

3-Dimensional numerical study on carbon based electrodes for vanadium redox flow battery

Electrode materials are critical in determining the performance of Vanadium redox flow batteries (VRFB). This work aims at elucidating the difference between carbon-based electrodes for VRFB. The electrodes considered for the present study are Graphite felt, Carbon felt, Carbon paper, and Carbon cloth. To study the characteristic behavior of different electrode materials, a 3D unit cell numerical model was developed by coupling electrolyte flow and electrochemical reactions and mass transfer module apart from considering the electrode structural and material information such as porosity, permeability, thickness, conductivity, and specific area. The simulation results of this study suggest that the Graphite felt is the optimum choice as an electrode material for VRFB as it offers higher electrocatalytic activity, lower pressure drop, better performance, and lower cost. The study is also extended to a multilayer configuration of Carbon Paper and Carbon Cloth. The performance of multi-layered electrodes by stacking single sheets of Carbon Paper and Carbon Cloth electrodes are matched to meet the performance obtained with the Graphite felt electrode. It has been shown with the help of polarization curve and the pressure drop study that the performance of five layers of carbon cloth and nine layers of carbon paper match the performance of Graphite felt, approximately. The present study provides practical guidance for the design and optimization of VRFB electrodes.

Methodology for fast testing of carbon-based nanostructured 3D electrodes in vanadium redox flow battery

Progress in material chemistry is manifested daily by the variety of prepared functional materials, often with nanodimensional structuring. The electrodes for vanadium redox flow batteries have been shown to benefit from incorporating nanostructured materials such as carbon nanotubes. However, the methods of such incorporation are far from optimal, relying mainly on physical deposition or insertion into a binder. Here, we describe a technique for integrating carbon-based rod-like nanomaterials into a vanadium redox flow battery and a methodology for fast nanomaterial performance testing. The technique is based on creating a fixed nanomaterial bed sandwiched between two graphite felt electrodes, forming a 3D flow-through electrode in the battery. Performing various positive and negative control experiments, we show the beneficial effect of a nanostructured bed on the primary battery characteristics obtained from short-term electrochemical experiments. We characterize carbon nanotubes exhibiting promising electrochemical behavior in vanadium electrolytes, as observed in our previous study. The load curves obtained from charge-discharge steps at various current densities and electrolyte flow rates revealed considerable differences in the performance of the tested materials, with few-walled carbon nanotubes reaching unsurpassable characteristics. At room temperature, with 50 %-SOC-working solutions and the highest tested linear velocity of 14.6 cm/min, the evaluated power density for this material reached values above 500 mW/cm2. For comparison, thermally treated graphite felt, used as a benchmark material, provided a power density of around 300 mW/cm2 under identical conditions. Although developed for vanadium redox flow batteries, the method enables testing tube-like and rod-like (nano-)materials for flow electrochemical systems.

CVD Grown CNTs-Modified Electrodes for Vanadium Redox Flow Batteries.

Vanadium redox flow batteries (VRFBs) are of considerable importance in large-scale energy storage systems due to their high efficiency, long cycle life and easy scalability. In this work, chemical vapor deposition (CVD) grown carbon nanotubes (CNTs)-modified electrodes and Nafion 117 membrane are utilised for formulating a vanadium redox flow battery (VRFB). In a CVD chamber, the growth of CNTs is carried out on an acid-treated graphite felt surface. Cyclic voltammetry of CNT-modified electrode and acid-treated electrode revealed that CNTs presence improve the reaction kinetics of V3+/V2+ and VO2+/VO2+ redox pairs. Battery performance is recorded for analysing, the effect of modified electrodes, varying electrolyte flow rates, varying current densities and effect of removing the current collector plates. CNTs presence enhance the battery performance and offered 96.30% of Coulombic efficiency, 79.33% of voltage efficiency and 76.39% of energy efficiency. In comparison with pristine electrodes, a battery consisting CNTs grown electrodes shows a 14% and 15% increase in voltage efficiency and energy efficiency, respectively. Battery configured without current collector plates performs better as compared to with current collector plates which is possibly due to decrease in battery resistance.

Exploring the viability of peracetic acid-mediated antibiotic degradation in wastewater through activation with electrogenerated HClO

Electrochemical advanced oxidation processes (EAOPs) face challenging conditions in chloride media, owing to the co-generation of undesirable Cl−disinfection byproducts (Cl−DBPs). Herein, the synergistic activation between in-situ electrogenerated HClO and peracetic acid (PAA)-based reactive species in actual wastewater is discussed. A metal-free graphene−modified graphite felt (graphene/GF) cathode is used for the first time to achieve the electrochemically-mediated activation of PAA. The PAA/Cl− system allowed a near−complete sulfamethoxazole (SMX) degradation (kobs =0.49 min−1) in only 5 min in a model solution, inducing 32.7− and 8.2−fold rise in kobs as compared to single PAA and Cl− systems, respectively. Such enhancement is attributed to the occurrence of 1O2 (25.5 μmol L−1 after 5 min of electrolysis) from the thermodynamically favored reaction between HClO and PAA-based reactive species. The antibiotic degradation in a complex water matrix was further considered. The SMX removal is slightly susceptible to the coexisting natural organic matter, with both the acute cytotoxicity (ACT) and the yield of 12 DBPs decreasing by 29.4 % and 37.3 %, respectively. According to calculations, HClO accumulation and organic Cl−addition reactions are thermodynamically unfavored. This study provides a scenario-oriented paradigm for PAA−based electrochemical treatment technology, being particularly appealing for treating wastewater rich in Cl− ion, which may derive in toxic Cl−DBPs.

Electrocatalytic removal of gaseous elemental mercury from modified graphite felt gas diffusion electrode

H2O2 is the cornerstone of the modern chemical industry and has a wide range of applications. Graphite felt coated with carbon oxide black can be used as an efficient cathode material to produce H2O2. The electrode can be used to remove Hg0 in the gas phase. Through the characterization of the catalyst, it was observed that oxidized carbon black has more functional groups and defects than carbon black. The increase of −C = O can promote oxygen reduction reaction, and then produce H2O2 through electrochemical two-electron oxygen reduction, and finally show better Hg0 removal performance. The oxidative removal of Hg0 was 81.5 % after 60 min at current density = 9.2 mA/cm2, electrolyte concentration = 0.06 mol/L and pH = 4.6. which is 33.5 % higher than that of original graphite felt, and it still has good stability and repeatability after 7 repetitions. At the same time, DFT calculation revealed that the incorporation of CB into C = O promoted the conversion of O2 to H2O2. Finally, this study opens up a new way for efficient, rapid, green, clean, and sustainable removal of Hg0 from the gas phase.

Electrochemically‐Enabled Construction of N‐Acyl Iminophosphoranes

AbstractN‐acyl iminophosphoranes have shown significant potentials in various areas. This paper presents two electrochemical strategies for the successful construction of a series of substituted N‐acyl iminophosphoranes using electrochemical activation of hydroxylamines or dioxazolones to generate unprotected amide radicals and radical anions. The simple undivided cell with inexpensive electrode setups (graphite felts, carbon rods, and copper sheets) provides excellent substrates tolerance under mild conditions. This simple electrochemical construction of N‐acyl iminophosphoranes also has good scalability, practicability and extensibility. Furthermore, synthetic transformations of the N‐acyl iminophosphorane products have demonstrated the application potentials of the P=N bond.

Bioelectricity production and bioremediation potential of Withania somnifera in plant microbial fuel cells

In p-MFCs living plants photosynthesize within a bio-electrochemical circuit. The plant exudes organic waste material from the roots. In the rhizosphere, bacteria consume these wastes by oxidizing them in contrast to the atmosphere that reduces it. This redox reaction along with photosynthesis can be harnessed as bioelectricity. In this work, the plant Withania somnifera (L.) Dunal was used for generating bioelectricity from the root exudates and organic matter available in the soil. An open circuit voltage of 930±21 mV was achieved between multiple cycles of operation. The cell voltage further increased to 1260±140 mV with enrichment in the form of discards from vegetable matter. The peak recorded voltage was 1400 mV. Graphite fibre felt electrodes ensured uniform microbial growth with power densities that were achieved at 57 mW/m2 and 84 mW/m2 with and without enrichment respectively. ATR-FTIR demonstrated complete degradation of specific compounds attached to the carbon matrix in the soil along with the polysaccharide content from the enrichments. Additionally, this work also monitored the changes in soil pH and its homogeneity, the impact of photosynthetically active radiation, humidity, and the presence of CO2 in the air, and how it affects plant growth and ultimately the microbes at the rhizosphere which accounted for the bioremediation and the resultant bioelectricity production. SEM imaging provided additional evidence that the presence of electrochemically active soil bacteria, an anaerobic environment, and electrode characteristics are crucial for the development of conductive biofilms.

Inducing three-phase interface to enhance hydroxyl radical production via green atomic H*-mediated electro-Fenton process for highly-efficient tetracycline degradation

Electro-Fenton system, a pivotal advanced oxidation process in wastewater treatment, inherently grapples with dual challenges of O2/solute transfer contradiction and Fe-dissolution deactivation. To surmount these obstacles, a sandwich Pd/C electrode (SE-Pd/C) featuring a three-phase interface (TPI) was fabricated by coating hydrophilic Pd/C catalyst layers onto hydrophobic graphite felt substrate for enhanced hydroxyl radical production through a green H*-mediated Fenton process. SE-Pd/C demonstrated superior performance with an 88.9% TC removal rate, outperforming hydrophilic (HIE, 68.4%) and hydrophobic (HOE, 47.9%) Pd/C electrodes. The underlying rationale for its high performance includes: (1) The TPI in SE-Pd/C optimized the concurrent mass transfer of O2 and TC, enabling an improved electrostatic TC adsorption capacity of 31.2% (versus 27.3% for HIE-Pd/C and 20.3% for HOE-Pd/C), alongside elevated H2O2 production reaching 8.6 g·L−1 (compared to 0.02 g·L−1 for HIE and 2.0 g·L−1 for HOE); (2) The hydrophilic catalyst layer ensured a rich availability of electrochemically active Pd-sites, facilitating H* generation and subsequent H2O2 activation to form •OH (13.4 × 10−12 M·S > 6.7 × 10−12 M·S of HOE > 4.3 × 10−12 M·S of HIE). As H* could be electro-generated from both H+ and H2O, the SE-Pd/C system manifested robust adaptability across a wide pH range of 3−11, consistently achieving ≥ 88.9% TC removal. Thus, this research pioneered the synergy of TPI with the H*-mediated Fenton process, outlining a potent strategy for bolstered treatment of antibiotic-laden wastewater.

Recent Progress in our Understanding of the Degradation of Carbon‐Based Electrodes in Vanadium Redox Flow Batteries – Current Status and Next Steps

AbstractThis mini‐review summarises and discusses recent findings form the literature on the degradation of carbon‐based electrodes for vanadium redox flow batteries (VRFBs). It becomes evident that the focus of current investigations is on carbon paper, carbon felt and graphite felt electrodes, which is understandable from a practical point of view. However, the structural complexity of these materials often prohibits doubtless attribution of observed performance reduction (or increase) to changes in the electrode materials. Among the discussed major causes for degradation are formation or change of surface functional groups, changes in the carbon sp2/sp3 ratio, intercalation of ions as well as formation of inhibiting adsorbates. In order to gain deeper insight into the changes of carbon electrodes in VRFBs under relevant operation conditions, the authors suggest reducing complexity of the investigated materials and applying in situ‐studies under well‐defined and controllable conditions on model electrodes. These studies then should be extended towards more practical systems and may finally help to reduce degradation phenomena including enhanced overvoltages and thus could improve cycling and energy efficiency as well as long‐term stability of vanadium redox flow batteries.

Microstructure evolution and densification behavior of ultrafast high-temperature sintered Li6.5La3Zr1.5Ta0.5O12 ceramics

Increasing the heating rate during the sintering process of Li6.5La3Zr1.5Ta0.5O12 (LLZTO) solid-state electrolyte is an effective method for suppressing lithium volatilization, tailoring grain growth, and achieving rapid densification. However, the ultrafast heating rate can lead to uneven surface temperature distribution of the electrolyte, subsequently affecting its microstructure and performance. Herein, we systematically investigate the microstructural evolution and densification behavior of LLZTO ceramics under rapid heating conditions using the ultrafast high-temperature sintering (UHS) method. An intercalibration technique combining finite element simulations and experimental data from infrared spectral measurements is used for prediction of the temperature distribution of the sample. Adjustment of the size ratio of the graphite felt to the sample diameter resulted in uniform temperature distribution, which aids in improving sintering quality. The densification mechanism of the samples during the UHS process is revealed by thermodynamics. Under sintering conditions with a current of 25 A applied for 30 s, the ultrafast heating rate (up to 104 °C/min) results in fine grains with a diameter of approximately 3.4 μm and a relative density of 93.2 %. The preferred samples finally exhibit good ionic conductivity stability, maintaining 3.09 × 10−4 S cm−1 at dynamic pressures of 5–50 MPa at room temperature.

Electrochemical Bioconjugation of Tryptophan Residues: A Strategy for Peptide Modification.

Interest in electrocatalytic bioconjugation reactions has surged, particularly for modifying tryptophan and tyrosine residues in proteins. We used a cost-effective graphite felt electrode and low-current methodology to achieve selective bioconjugation of tryptophan with thiophenols, yielding up to 92%. This method exclusively labeled tryptophan residues and incorporated fluorinated tryptophan for NMR analysis. Eight polypeptides, including lanreotide and leuprorelin, were effectively coupled, demonstrating the method's versatility and potential for novel diagnostic and therapeutic agents.

Advances in Redox Flow Batteries – A Comprehensive Review on Inorganic and Organic Electrolytes and Engineering Perspectives

AbstractDevelopment and application of large‐scale energy storage systems are surging due to the increasing proportion of intermittent renewable energy sources in the global energy mix. Redox flow batteries are prime candidates for large‐scale energy storage due to their modular design and scalability, flexible operation, and ability to decouple energy and power. To date, several different redox couples are exploited in redox‐flow batteries; some are already commercialized. This battery technology is facing a lot of challenges in the science, engineering, and economic front. Issues plaguing flow batteries are low energy density, high overall cost, poor stability of electrolytes, shifting of solvent from anolyte to catholyte while using cation exchange membrane, reverse flow with anion exchange membrane, and corrosion of graphite felt in the catholyte side. Significant research efforts are ongoing to address these challenges. This comprehensive and critical review summarizes the recent progress in electrolyte technologies, including electrochemical performance and stability, strategies to enhance the energy and power densities and, in the end, the levelized and life‐cycle cost of these batteries analyzed. A comprehensive outlook on this technology with respect to practical energy storage applications is also provided.

Unravelling the mechanisms of organic micropollutant removal in bio-electrochemical systems: Insights into sorption, electrochemical degradation, and biodegradation processes

Bio-electrochemical systems (BESs) have recently been proposed as an efficient treatment technology to remove organic micropollutants from water treatment plants. In this study, we aimed to differentiate between sorption, electrochemical transport/degradation, and biodegradation. Using electro-active microorganisms and electrodes, we investigated organic micropollutant removal at environmentally relevant concentrations, clarifying the roles of sorption and electrochemical and biological degradation. The role of anodic biofilms on the removal of 10 relevant organic micropollutants was studied by performing separate sorption experiments on carbon-based electrodes (graphite felt, graphite rod, graphite granules, and granular activated carbon) and electrochemical degradation experiments at two different electrode potentials (−0.3 and 0 V).Granular activated carbon showed the highest sorption of micropollutants; applying a potential to graphite felt electrodes increased organic micropollutant removal. Removal efficiencies >80 % were obtained for all micropollutants at high anode potentials (+0.955 V), indicating that the studied compounds were more susceptible to oxidation than to reduction. All organic micropollutants showed removal when under bio-electrochemical conditions, ranging from low (e.g. metformin, 9.3 %) to exceptionally high removal efficiencies (e.g. sulfamethoxazole, 99.5 %). The lower removal observed under bio-electrochemical conditions when compared to only electrochemical conditions indicated that sorption to the electrode is key to guarantee high electrochemical degradation. The detection of transformation products of chloridazon and metformin indicated that (bio)-electrochemical degradation occurred. This study confirms that BES can treat some organic micropollutants through several mechanisms, which merits further investigation.

In Situ Growth of Amorphous MnO2 on Graphite Felt via Mild Etching Engineering as a Powerful Catalyst for Advanced Vanadium Redox Flow Batteries.

Owing to the advantages of low cost, high safety, and a desirable cycling lifetime, vanadium redox flow batteries (VRFBs) have attracted great attention in the large-scale energy storage field. However, graphite felts (GFs), widely used as electrode materials, usually possess an inferior catalytic activity for the redox reaction of vanadium ions, largely limiting the energy efficiency and rate performance of VRFBs. Here, an in situ growth of amorphous MnO2 on graphite felt (AMO@GF) was designed for application in VRFBs via mild and rapid etching engineering (5 min). After the etching process, the graphite felt fibers showed a porous and defective surface, contributing to abundant active sites toward the redox reaction. In addition, formed amorphous MnO2 can also serve as a powerful catalyst to facilitate the redox couples of VO2+/VO2+ based on density functional theoretical (DFT) calculations. As a result, the VRFB using AMO@GF displayed an elevated energy efficiency and superior stability after 2400 cycles at 200 mA cm-2, and the maximum current density can reach 300 mA cm-2. Such a high-efficiency and convenient design strategy for the electrode material will drive the further development and industrial application of VRFBs and other flow battery systems.

In-situ synthesis of bimetallic Co/Zn-ZIF on the graphite-felt for electrocatalytic degradation of pharmaceutical pollutants

In the electro-Fenton process, one of the important challenges is to adjust the pH of the environment in the acidic region so that the system's performance is not affected by side reactions. In this case, it will be necessary to neutralize the solution after the process. One of the solutions is to use a heterogeneous catalyst to widen the pH range. However, recovering the used catalyst itself can be another challenge. Modifying the electrode using electroactive materials can answer both of these challenges. This work modified the bare graphite-felt (GF) electrode using zeolitic imidazolate frameworks (ZIF)-derived carbon material doped with Co and Zn through a rapid, room-temperature, and water-based synthesis method. Various analyses, including XRD, SEM, XPS, and LSV, confirmed the proper modification of bare GF carbon fibers. The modified Co/Zn-N-C@GF electrode showed good performance in removing rifampicin (RFP) during the electro-Fenton process, so about 90 % of the pollutant was removed within 30 min without adding a homo-/heterogeneous catalyst. Optimum conditions for this process were 1.0 V for applied voltage, 40 mg/L for initial concentration of RFP, and 5.6 for pH. Also, LC-MS analysis was performed to confirm the degradation of RFP and investigate its degradation pathway.

Joule heat mediated by graphite felt enhances peroxymonosulfate activation and carbamazepine degradation: Efficiency and mechanism

Thermal activation of persulfate (PS) is a simple and effective method to generate sulfate radicals (SO4̇‾) for pollutant degradation but its practical application was severely restricted by the excessive energy consumption. In this study, a low energy consumption but efficient Joule heat-activation strategy was developed. The temperature of the reaction solution (TRS) rose to 76.9 °C within 30 min after 5 V external voltage (Uex) was applied onto the two sides of a graphite felt (GF) with the thickness of 6 mm (GF-6). Correspondingly, the peroxymonosulfate (PMS) decomposition ratio and the degradation efficiency of carbamazepine (CBZ) reached 82.6 % and 97.5 %. The catalytic activation of PMS on the surface of GF was the dominant pathway to generate free radicals during the Joule heating process rather than the heat-activation pathway. More importantly, removing per milligram of CBZ only consumed 5.6 kJ electric energy which was significantly lower than that of the common heating methods (namely, 80 °C water bath heating and electrical heating at 5 V using a commercially available ceramic electric heating rod). Impressively, this Joule heating system exhibited wide applicability and prominent reusability. Overall, this work developed an effective PMS thermal activation strategy with low power consumption using the widely available GF and realized efficient degradation of typical organic pollutants.

A gradient electrospinning electrode structure both in the in/through-plane directions for non-aqueous iron-vanadium redox flow battery

To boost the performance of non-aqueous redox flow batteries (RFBs), it is important to synergistically improve the flow/mass transfer efficiencies and the uniformity of overpotential distribution into the porous electrode. In this work, electrostatic spinning technology is developed to propose a novel porous electrode with gradient pore distribution both in the in-plane and through-plane directions, and applied in deep eutectic solvent (DES) electrolyte-based iron-vanadium RFB. On the one hand, the new in-plane gradient design modifies the distribution of reactive species of electrode near the membrane side, resulting in the decreasing polarization loss. On the other hand, the increasing porosity of electrodes from the flow field side to the membrane side attains a trade-off between the charge transfer and the electrolyte flow resistances. According to the experimental results, compared to the graphite felt electrode, the energy efficiency of this RFB with three-dimensional gradient electrode improves by 74.2 % at a current density of 10 mA·cm−2. Moreover, the numerical simulation reveals the reactive transfer behaviors of three-dimensional gradient porous electrode. The results show that the proposed three-dimensional gradient design can enhance the uniformity of overpotential distribution and achieve the decrease of polarization resistance, thus improving the performance of DES electrolyte-based iron-vanadium RFB effectively.

Air Plasma Modification of Graphite-Based Electrode for Improved Performance of Aqueous Redox Flow Batteries

Graphite felt is widely utilized as a porous carbon electrode in aqueous redox flow batteries (RFBs). However, its inherent hydrophobic nature and limited electrochemical activity present challenges. While the correlation between RFB performance and electrode properties has been extensively studied for vanadium chemistry and other inorganic redox active materials, it remains scarce in literature for organic systems. In this study, we employ air plasma treatment, known for its controllability, solvent-free nature, and short treatment duration, to modify commercially available graphite felt for RFB applications. A comprehensive analysis is conducted to establish correlations between plasma treatment, physical properties, electrochemical characteristics, and overall cell performance in aqueous RFBs. Comparative evaluation reveals a significant enhancement, with treated graphite felt exhibiting an 85% increase in capacity at 140 mA cm−2 compared to its pristine counterpart. By intentionally utilizing authentic RFB electrodes and employing state-of-the-art ferrocyanide posolyte, this study underscores the crucial role of the interface, even for rapid (reversible) redox-active materials utilized in AORFBs.

A bifunctional electrocatalytic graphite felt for stable aqueous zinc-polyiodide flow batteries

The appealing features of high safety, environmental friendliness, and flexible layout make the Zn–I2 flow batteries attractive for implementation in long-duration grid-scale energy storage systems. However, the uncontrollable self-transformation of high-soluble polyiodide species often result in the limited reutilization of I3−/I− redox couple and compromise its theoretical energetic potentials. Herein, FeP nanoclusters embedded in N and P co-dopped carbon layer render the functional graphite felt with strong interaction between polyiodides and substrate in combination with the accelerated I−/I3− redox kinetics under working conditions. The heteroatoms and nanoclusters served synergically as strong chemisorption and electrocatalytic hotspots for iodine and its intermediates conversion. The strong interactions between polar matrix and active species facilitated interfacial physicochemical confinement effect mitigates polyiodide crossover and the electrocatalysis effect promises efficient iodine conversion and stable cycling performance. Consequently, the Zn–I2 flow battery delivers excellent rate performance, ultralong cycling life for 1000 cycles with a recorded average Coulombic efficiency of 98.1 %, and substantially enhanced anti-self-discharge capability. The rational modification of carbon felt represents a promising direction to unlock the practical potentials of Zn–I2 flow chemistry.