Cloth Electrode Research Articles

Simultaneous detection of dihydroxybenzene isomers in the environment by a free-standing flexible ZnCo2O4 nanoplate arrays/carbon fiber cloth electrode

The simultaneous determination of dihydroxybenzene isomers is highly valuable for early environmental monitoring, but it is still a challenge. In this work, a free-standing flexible electrode was prepared for the simultaneous detection of hydroquinone (HQ), catechol (CC), and resorcinol (RC). The bimetallic zinc/cobalt zeolitic imidazolate frameworks nanoplate arrays (Zn/Co-ZIF NPAs) grown in situ on the carbon fiber cloth (CFC) was fabricated by a facile static synthesis method, and the porous ternary ZnCo2O4 NPAs derived from Zn/Co-ZIF NPAs were formed by annealing in air. Due to the fast electron transmission, abundant active sites and excellent electrocatalytic properties with enzyme-like kinetic performance of the ZnCo2O4/CFC electrode, the as-proposed sensor showed a wilder linear response (2–500 μM), a lower detection limits (0.03 μM HQ, 0.06 μM CC and 0.15 μM RC) and a higher sensitivity (23.58 μA μM−1 cm−2 HQ, 17.72 μA μM−1 cm−2 CC, and 15.18 μA μM−1 cm−2 RC), respectively. More importantly, the proposed electrochemical sensor exhibited excellent detection performance in complex water samples, providing a strategy for the detection of other toxic substances in the ecological environment.

High performance supercapacitors using selenium partially reduced Co3O4 on carbon cloth electrode with 3D interconnected architecture nanowires

The electrodes with high conductivity, large specific surface area and homogeneous pore size distribution are greatly desirable for supercapacitors applications. Herein, a hydrothermal and subsequent annealing approach was adopted to fabricate 3D interconnected nanowires architecture of selenium partially reduced spinel Co3O4 grew on the carbon cloth (COS@CC). The binder-free COS@CC electrode displays excellent specific capacitance, 1046.9 C g−1 at 1 A g−1, superior rate capability, 51.6% capacitance retention and superior cyclic stability, 92.0% capacitance retention after 15,000 cycles. These electrochemical performances were found to be better than that of the Co3O4@CC electrode. The enhanced electrochemical performance was ascribed to the fact that 3D interconnected architecture nanowires could shorten the ion transfer distance and heighten the rate of the redox reaction. In addition, increased specific surface area and homogeneous mesopore size distribution could assist effective diffusion and transfer of OH– between electrodes and electrolyte. The enhancement of conductivity, which is caused by the selenium partial reduction and more oxygen vacancies in the structure, facilitates electrons transfer and consequently improves the electrochemical properties of supercapacitors. These remarkable electrochemical performances indicate that the CSO@CC can be employed for developing high-energy and power-density supercapacitors.

Taurine Electrografting onto Porous Electrodes Improves Redox Flow Battery Performance

The surface properties of porous carbonaceous electrodes govern the performance, durability, and ultimately the cost of redox flow batteries (RFBs). State-of-the-art carbon fiber-based electrode interfaces suffer from limited kinetic activity and incomplete wettability, fundamentally limiting the performance. Surface treatments for electrodes such as thermal and acid activation are a common practice to make them more suitable for aqueous RFBs; however, these treatments offer limited control over the desired functional properties. Here, we propose, for the first time, electrografting as a facile, rapid, and versatile technique to enable task-specific functionalization of porous carbonaceous electrodes for use in RFBs. Electrografting allows covalent attachment of organic molecules on conductive substrates upon application of an electrochemical driving force, and the vast library of available organic molecules can unlock a broad range of desired functional properties. To showcase the potential of electrografting for RFBs, we elect to investigate taurine, an amine with a highly hydrophilic sulfonic acid tail. Oxidative electrografting with cyclic voltammetry allows covalent attachment of taurine through the amine group to the fiber surface, resulting in taurine-functionalized carbon cloth electrodes. In situ polarization and impedance spectroscopy in single-electrolyte flow cells reveal that taurine-treated cloth electrodes result in 40% lower charge transfer and 25% lower mass transfer resistances than off-the-shelf cloth electrodes. We find that taurine-treated electrode interfaces promote faster Fe3+ reduction reaction kinetics as the electrochemical surface area normalized current densities are 2-fold and 4-fold higher than oxidized and untreated glassy carbon surfaces, respectively. Improved mass transfer of taurine-treated electrodes is attributed to their superior wettability, as revealed by operando neutron radiography within a flow cell setup. Through demonstrating promising results for aqueous systems with the model molecule taurine, this work aims to bring forth electrografting as a facile technique to tailor electrode surfaces for other RFB chemistries and electrochemical technologies.

An integrated process for wet scrubber wastewater treatment using electrooxidation and pressure-driven membrane filtration

In this study, the electrooxidation (EO) and membrane processes were used for chemical oxygen demand (COD) and total phenol (TPh) removal from wet scrubber wastewater (WSW). EO experiments were carried out using Al, Fe, SS, Ti, graphite, active carbon cloth electrodes and Box-Behnken design were used for optimization of maximum COD and TPh removal efficiency. Moreover, membrane filtration experiments were conducted to EO process using nanofiltration (NF270) and reverse osmosis membranes (SW30 and BW30). The maximum COD (55%) and TPh (50%) removal efficiency was achieved at pH of 8, 150 A/m2 current density, and 180 min reaction time in EO process. Membrane filtration results showed that COD removal efficiency was the highest for SW30 membrane (95.18%) compared to BW30 (91.15%) and NF270 (80.11%) membranes. TPh removal efficiency in the NF270, BW30, and SW30 membranes was 27.08%, 96.06%, and 98.02%, respectively. The effect of microbial cell viability of the raw and treated wet scrubber wastewater after electrooxidation and membrane filtration was also investigated using E. coli. In addition to these, biofilm inhibition of the raw wet scrubber wastewater and the treated WSW after EO and membrane filtration were tested and the highest biofilm inhibition was found as 76.43% and 72.58% against S. aureus and P. aeruginosa, respectively, in 1/20 diluted samples of the raw WSW. This study suggests that the integrated process using EO and pressure-driven membrane methods are an efficient strategy for COD and TPh removal from WSW.

Tungsten oxide/fullerene-based nanocomposites as electrocatalysts and parasitic reactions inhibitors for VO2+/VO2+ in mixed-acids

The relatively high cost of all-vanadium redox flow batteries (VRFBs) limits their widespread deployment. Enhancing the kinetics of the electrochemical reactions is needed to increase the power density and energy efficiency of the VRFB, and hence decrease the kWh cost of VRFBs. In this work, hydrothermally synthesized hydrated tungsten oxide (HWO) nanoparticles, C76, and C76/HWO were deposited on carbon cloth electrodes and tested as electrocatalysts for the VO2+/VO2+ redox reactions. Field Emission Scanning Electron Microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscope (HR-TEM,), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements were used to characterize the electrodes’ material. The addition of the C76 fullerene to HWO was found to boost the electrode kinetics towards the VO2+/VO2+ redox reaction, by enhancing the conductivity and providing oxygenated functional groups at its surface. A composite of HWO/C76 (50 wt% C76) was found to be the optimum for the VO2+/VO2+ reaction, showing a ΔEp of 176 mV, compared to 365 mV in the case of untreated carbon cloth (UCC). Besides, HWO/C76 composites showed a significant inhibition effect for the parasitic chlorine evolution reaction due to the W-OH functional groups.

Bioinspired synthesis of hematite nanoparticles-reduced graphene oxide composite for application in bisphenol a detection: A new in-sight

Bisphenol A (BPA), one of the well-known environmental endocrine-disrupting compounds, has an effective estrogenic activity that badly impacts the environment and human health. Therefore, an urgent need arises to develop a simple and effective method for BPA detection. Herein, we report novel, disposable and flexible nanoplatforms for electrochemical determination of BPA using carbon cloth electrode supported hematite nanoparticles (α-Fe2O3NPs) on reduced graphene oxide (rGO) composite. The α-Fe2O3NPs@rGO composite was synthesized through a green route using leaves extract of Cinnamomum tamala that acted as a reducing and stabilizing agent for α-Fe2O3NPs followed by the addition of graphene oxide to convert it into rGO. The nanoplatform was fabricated using the electrophoretic deposition technique on carbon cloth (CC) substrate, i.e., (α-Fe2O3NPs@rGO/CC). The analytical performance of α-Fe2O3NPs@rGO/CC nanoplatform is ascribed to the synergistic effect of α-Fe2O3NPs and rGO that resulted in a larger active surface to volume ratio, superior conductivity, and enhanced electrochemical behavior. The fabricated α-Fe2O3NPs@rGO/CC nanoplatform exhibited a broad linear range from 1.9 × 10−10 to 1.00 μM having a higher sensitivity of 33.04 μA (log μM)−1 cm−2 and a low limit of detection of 0.23 μM. It also displayed excellent selectivity, repeatability, reproducibility, and stability with satisfying results. Moreover, the electrochemical nanoplatform helped analyze the real samples to detect BPA with acceptable results. Hence, this nanoplatform could be further utilized to detect other estrogenic analytes.

A flexible supercapacitor with high capacitance retention at an ultra-low temperature of -65.0°C

A novel anti-freezing organo-hydrogel electrolyte is developed to improve capacitance retention of flexible supercapacitor at the ultra-low temperature. The electrolyte is composed of graphene/polyvinyl alcohol matrix and methyl sulfoxide/water/sulfuric acid mixture. It simultaneously possesses a high tensile strength of ca.2.58 MPa and a high ionic conductivity of ca.3.9 S/m. Furthermore, the electrolyte can still maintain high flexibility and high ionic conductivity (ca.1.0S/m) at -65℃. In addition, a flexible supercapacitor with sandwich structure was assembled from the organo-hydrogel electrolyte and two polyaniline fiber/carbon cloth electrodes. The supercapacitor exhibits a high specific capacitance of 252.0F/g and excellent capacitance retention of 93% at -65℃. The excellent capacitance retention is attributed to the synergistic effect of methyl sulfoxide, concentrated sulfuric acid and graphene nanosheets. This study provides a new way to design and prepare anti-freezing electrolyte with high-performance for application in the flexible solid-state electrochemical energy storage at ultra-low temperatures.

Interfacial Engineering of Heterostructured Co(OH)2/NiPx Nanosheets for Enhanced Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) remains a bottleneck for the overall water splitting. Electrocatalysts with superior activity and stability are still highly desired. Herein, a stepwise electrochemical strategy is developed to prepare Co(OH)2/NiPx nanosheet arrays with intimate and abundant heterostructures. The Co(OH)2 nanosheets, which are first electrodeposited on a blank carbon cloth electrode, serve as the substrate for the nucleation and growth of NiPx. The resultant heterointerfaces are well regulated by altering the loading of NiPx. The heterostructured Co(OH)2/NiPx with optimal NiPx loading demonstrate significantly enhanced conductivity and hydrophilicity, which greatly facilitate electron and mass transfer. In addition, strong electronic interaction between Co(OH)2 and NiPx is observed, favoring the generation of high‐valence cobalt center, thus the electrocatalytic performances toward OER are remarkably improved. The heterostructured Co(OH)2/NiPx nanosheets achieve the current density of 10 mA cm−2 at an overpotential of 236 mV, while the corresponding values for Co(OH)2 and the benchmark Ir/C are 292 and 262 mV, respectively. This study provides a facile and effective strategy to fabricate transition metal hydroxide/phosphide composite nanomaterials with intimate heterostructures, enhanced conductivity, and improved wettability, which opens a new direction for the design of highly active electrocatalysts.

Microbial Electrosynthesis Inoculated with Anaerobic Granular Sludge and Carbon Cloth Electrodes Functionalized with Copper Nanoparticles for Conversion of CO2 to CH4.

Microbial electrosynthesis (MES) can sustainably convert CO2 to products and significant research is currently being conducted towards this end, mainly in laboratory-scale studies. The high-cost ion exchange membrane, however, is one of the main reasons hindering the industrialization of MES. This study investigates the conversion of CO2 (as a sole external carbon source) to CH4 using membraneless MES inoculated with anaerobic granular sludge. Three types of electrodes were tested: carbon cloth (CC) and CC functionalized with Cu NPs, where Cu NPs were deposited for 15 and 45 min, respectively. During the MES experiment, which lasted for 144 days (six cycles), methane was consistently higher in the serum bottles with CC electrodes and applied voltage. The highest CH4 (around 46%) was found in the second cycle after 16 days. The system’s performance declined during the following cycles; nevertheless, the CH4 composition was twice as high compared to the serum bottles without voltage. The MES with Cu NPs functionalized CC electrodes had a higher performance than the MES with plain CC electrodes. Microbial profile analysis showed that the Methanobacterium was the most dominant genus in all samples and it was found in higher abundance on the cathodes, followed by the anodes, and then in the suspended biomass. The genus Geobacter was identified only on the anodes regarding relative bacterial abundance at around 6–10%. Desulfovibrio was the most dominant genus in the cathodes; however, its relative abundance was significantly higher for the cathodes with Cu NPs.

Understanding the Interaction between Flow Field Geometries and Porous Electrode Microstructures in Redox Flow Batteries

Redox flow batteries are a promising technological option to integrate the growing supply of renewable energies into the electricity grid, however their deployment is hampered by high costs. To increase cost competitiveness, research efforts have targeted design of new electrolytes, high performance materials, and alternative electrochemical reactor concepts [1]. One powerful strategy is to increase the overall efficiency of the electrochemical stack, which can be achieved by improving the electrochemical performance and reducing the pumping power requirements. Selecting and optimizing the flow field design and electrode microstructure is crucial to accomplish an optimum trade-off. Drawing inspiration from polymer electrolyte fuel cells, current flow battery technologies leverage flow-through, interdigitated and serpentine flow field designs [2]. However, while functional, these designs have not been tailored for the specific requirements of redox flow batteries where single-phase reactive flows are sustained. Recent studies have investigated the influence of the channels and ribs dimensions [3], branched channel geometries [4], as well as the electrode microstructure on the reactor performance [5]. However, the interaction between the flow field geometries and the electrode microstructure determines the accessible surface area, mass transfer phenomena, and pressure drop; but remains poorly understood. With this in mind, we are poised to answer the following scientific question: What is the optimal combination of flow field and electrodes in redox flow batteries? In this work, we evaluate the interaction between geometrically diverse flow field geometries and porous electrode microstructures. We study seven different flow field designs in combination with two commonly used fibrous electrode structures – a carbon paper and a cloth (Figure 1). Flow-through, serpentine, and multiple variations of interdigitated flow fields were designed and fabricated by graphite milling. We employ a suite of polarization, electrochemical impedance spectroscopy, capacitance, and pressure drop measurements to elucidate structure-property-performance relationships. We find that the interdigitated designs perform better with high density of channels (i.e. shorter rib-channel width), even though this leads to higher pressure losses. Interestingly, pressure drop measurements show a similar relative contribution of the flow field and the electrode to the pumping losses, which motivates engineering of flow field geometries and electrode structures in tandem. Mass transfer overpotentials and pressure losses in cloth electrodes are reduced when using flow field geometries that force electrolyte flow into an in-plane direction in the electrode (i.e. parallel to the membrane plane), such as flow-through and interdigitated designs with wider ribs between channels. On the contrary, carbon paper electrodes perform better with interdigitated designs that force electrolyte flow into the through-plane direction (i.e. perpendicular to the membrane plane). Based on these findings, we have undertaken the engineering of innovative flow fields designs by combining interdigitated and branched patterns using 3D-printing, obtaining promising results that will be discussed in the final part of my talk.Figure 1. Polarization results for the combination of cloth and paper electrodes with three different flow field designs, at 5 cm·s-1 in the electrode. References Sánchez-Díez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, Journal of Power Sources, 481, 228804 (2021).D.Milshtein, K.M.Tenny, J.L.Barton, J.Drake, R.M.Darling and F.R.Brushett, J. Electrohcem. Soc., 164, E3265-E3275 (2017).R.Gerhardt, A.A. Wong, M.J. Aziz, J. Electrohcem. Soc., 165, A2625-A2643 (2018).Zeng, F. Li, F. Lu, X. Zhou, Y. Yuan, X. Cao, B. Xiang, Applied Energy, 238, 435-441 (2019).Forner-Cuenca, E.E. Penn, A.M. Oliveira, F.R.Brushett, J. Electrohcem. Soc., 166, A2230-A2241 (2019). Acknowledgments This work has been partially funded by the Agencia Estatal de Investigación (PID2019-106740RB-I00 and RTC-2017-5955-3/AEI/10.13039/501100011033). Figure 1

Exploring the Effectiveness of Carbon Cloth Electrodes for All-Vanadium Redox Flow Batteries

Redox flow batteries (RFBs) have proven to be a promising technology for the integration of intermittent renewable energy sources into the existing electrical grid due to their ability to decouple energy and power ratings, and the associated cost-effectiveness in long-duration energy storage [1]. Among various flow battery chemistries, vanadium redox flow battery (VRFB) is one of the most prominently studied flow battery system [2]. In comparison to other chemistries, four soluble oxidation states of vanadium are available and accessible. This characteristic of VRFBs eliminates cross-contamination between the positive and negative half-cells that would otherwise deteriorate the life and durability of the battery [3]. In a flow battery cell, porous electrode is the key component that determines the performance of the system by delivering liquid electrolytes, facilitating ion/charge transfer, and providing sites for electrochemical reactions [4]. Recently, it has been found that significant performance improvements can be achieved with fabric (carbon cloth) electrodes when coupled with a wetting electrolyte [5].In this talk, we will report our experimental approach to evaluate the short- and long-term effectiveness of various carbon cloth electrode samples for use in VRFBs. Results generated from symmetric flow cell cycling coupled with electrochemical impedance spectroscopy and polarization curve measurements will be discussed. The key physico-chemical properties and their evolution during cycling will be elucidated.

Electrografting As a Versatile Approach to Engineer Porous Electrode Interfaces for Redox Flow Batteries

The intermittent nature of renewable sources can be alleviated by grid-scale energy storage technologies, such as redox flow batteries (RFBs). However, these systems are currently not cost-competitive for widespread deployment. The system costs are linked to stack performance that is limited by kinetic, ohmic and mass-transfer overpotentials as well as materials stability. Carbon fiber-based porous electrodes, ubiquitous in electrochemical reactors, strongly influence these limiting phenomena as they facilitate redox reactions on their surface, conduct electrons, and provide flow paths for reactant transport. Unfortunately, the inherently hydrophobic and inert carbon surface is not optimal for aqueous electrolytes with kinetically sluggish redox couples such as vanadium and iron1. In these systems, controlling the surface chemical state of the electrode is vital to attain significant performance gains. Popular strategies to modify surface chemistry are thermal and acid treatments with a general aim to increase the heteroatom content and number of functional groups of the carbon surface2. These functional groups increase the surface energy of inherently hydrophobic carbon electrode and can serve as active sites for redox-reactions3. However, these treatment strategies can cause embrittlement of the electrode4, mass-loss5, and the formed functional groups, especially in the case of oxygen, can manifest in multiple chemical forms, hindering proper structure-property relationships to be established. Thus, to correlate the surface chemical state to the battery performance, there is a need to develop methodologies to synthesize homogenous, conformal, and stable interfaces onto three-dimensional porous electrodes6.Here we propose electrografting as a surface modification strategy for carbon fiber-based RFB electrodes with a model molecule, taurine. Electrografting is the electrochemical analogue of chemical grafting where covalent bonds are formed between species and the conductive substrate7, with an added advantage that the charge transfer reactions responsible for bond formation can be controlled with applied voltage. We selected taurine as a model molecule to graft on carbon cloth electrodes as its amine group can undergo oxidative electrografting and we hypothesize its sulfonic acid group to be beneficial for electrode wetting, allowing coverage of the electrode surface with a thin layer of desired functional groups. We performed diagnostic studies on glassy carbon electrodes by hydrodynamic voltammetry, where the kinetic rate for the reduction of Fe3+ on taurine treated electrodes is revealed to be an order of magnitude faster than untreated electrodes (1.23 x 10-4 vs 1.84 x 10-5 cm s-1). In-situ flow cell studies in single cell configuration revealed improved performance for mixed Fe2+/3+ electrolyte, especially at lower flow rates (Figure 1). Also, for the first time, we visualized wetting dynamics of porous RFB electrodes in flow cells using neutron radiography. We find that treated electrodes imbibe the acidic electrolyte instantaneously even at low flow rates, which indicates the electrode interfaces feature hydrophilic character. Finally, we performed extended in-situ stability tests under mixed Fe2+/3+ electrolyte flow at open-circuit and applied voltage conditions. Impedance spectroscopy revealed performance degradation with pristine electrodes but not with taurine treated electrodes, confirming the formation of a stable interface with electrografting of taurine. In summary, we show that electrografting of taurine is a facile and environmentally benign approach to functionalize porous electrodes for aqueous redox flow batteries. Beyond this specific application, the possibility to extend the molecular library makes electrografting a suitable approach to engineer interfaces for next-generation electrochemical devices. References P. Chen and R. L. McCreery, Anal. Chem., 68, 3958–3965 (1996).K. Jae Kim et al., Journal of Materials Chemistry A, 3, 16913–16933 (2015).R. H. Bradley and P. Pendleton, Adsorption Science & Technology, 31, 113–133 (2013).L. Yue, W. Li, F. Sun, L. Zhao, and L. Xing, Carbon, 48, 3079–3090 (2010).K. V. Greco, A. Forner-Cuenca, A. Mularczyk, J. Eller, and F. R. Brushett, ACS Appl. Mater. Interfaces, 10, 44430–44442 (2018).A. Forner-Cuenca and F. R. Brushett, Current Opinion in Electrochemistry, 18, 113–122 (2019).D. Bélanger and J. Pinson, Chem. Soc. Rev., 40, 3995–4048 (2011). Figure 1

(Digital Presentation) Electrochemical Characterization of Microbial Fuel Cell Electrodes Using Cyclic Voltammetry and Electrochemical Impedance Spectroscopy

Renewable energy sources are required to lessen energy generation's reliance on fossil fuels. Microbial fuel cells (MFC) exploit microbial metabolic processes to oxidize organic matter to generate energy from wastewater; they serve as a low-cost, sustainable form of wastewater management. Despite the development of effective MFCs, low efficiency and power density have prevented their widespread adoption over traditional fuel cells. Modification of MFC electrodes has been investigated as a means to improve their limited power output. Here we assessed the MFC carbon cloth electrodes and compared them to a traditional glassy carbon, and clean carbon cloth. The electrochemical properties of the electrode surfaces were explored using a three electrode cell consisting of a platinum wire counter electrode and Ag/ AgCl/ 1M KCl reference electrode. Electrolyte dependent studies were conducted in phosphate buffered saline (PBS) in the presence of ferri/ferrocyanide. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV) of the solution redox couple with various working electrode were performed in order to characterize electrode surface, prior, and post MFC use. The ultimate goal is to optimize the electrode surface chemistry to promote optimal MFC performance.

Effect of Tungsten Oxide Structure on Enhancing the V(II)/(VIII) Reaction and Inhibiting H2 Evolution for All-Vanadium Redox Flow Battery

Renewable energy sources require high-efficiency storage systems to allow for its integration within the electrical grid and to supply that energy when needed. All-vanadium redox flow batteries (VRFBs) are very promising for this application because they can store high amounts of energy, are designed to work for long periods, and their solutions can be used indefinitely.1 VRFBs have various advantages when combined with renewable energy sources. The relatively high cost of VRFBs limits their widespread deployment. Enhancing the kinetics of the electrochemical reactions is needed to increase the power density and energy efficiency of the VRFB, and hence decrease the kWh cost of VRFBs. Different carbon materials are used as electrodes in VRFBs (carbon felt, paper and cloth), and each of these materials affects the performance of the battery differently either through sluggish kinetics or a high chance for parasitic reactions catalyzation.2 Modification of these electrodes by carbon-based3 or metal oxides2 nanomaterials can increase the power density of the battery and suppress the parasitic reactions. Some metal oxides like tungsten oxide4 can enhance vanadium reactions alone or when used as composites with nanocarbon materials.This work aims at enhancing the VRFBs negative half-cell reaction (V2+/V3+) kinetics and inhibiting the hydrogen evolution parasitic reaction. Carbon cloth electrodes were modified, using different tungsten oxide nanostructures such as nanowires, nanoflakes, and nanospheres, and tested at different loadings. The results suggest that the change in tungsten oxide structure would lead to a change in the electrode overall performance as a result of changing the electrical conductivity, the wettability of the electrodes, the coverage of the carbon cloth, and the number and nature of the active sites available to catalyze the V2+/V3+ reaction, with the tungsten oxide nanowires showing to be the best electrode modifier.

Three dimensional integrated architecture of Sr[sbnd]Fe LDH on hierarchical NiS framework as a flexible electrode for efficient energy storage and conversion applications

It is vital to examine the abundance of non-precious transition metal di-chalcogenides (TMDs) and layered double hydroxides (LDH) with greater storage capability and excellent electrocatalytic activity. Nowadays, the robust coupling of TMDs and LDH based materials emerged as an efficient electrocatalyst for significant electrochemical applications. The binder-free, flexible, bi-functional catalysts, 3D hybrid nanostructures of coupled TMDs/LDH on the carbon cloth (CC) electrode substrate. Initially, the hierarchical NiS nanoflowers were self-assembled on a flexible CC substrate via hydrothermal approach. Herein, the SrFe LDH nanosheets are vertically anchored on high conductive and flexible NiS/CC electrodes without destroying the original architecture by the electrodeposition method. This enriched 3D hybrid NiS@ SrFe OH/CC nanostructure provides enormous nucleation active sites with interconnected layers leading to the enhancement of electrocatalytic behaviour. The outstanding structural and morphological advantages accelerate the electrochemical activities and reaction kinetics of prepared NiS/CC, SrFe OH/CC and NiS@ SrFe OH/CC flexible electrode based supercapacitor exhibits the specific capacitance of 556, 1151 and 1553 F g−1 at 1 A g−1 current density respectively. NiS@ SrFe OH/CC//AC/CC device has a favourable energy density of 53.07 Wh kg−1 at a high power density of 4.4 kW kg−1. Additionally, these 3D flexible hybrid electrodes also favour oxygen evolution reaction at an extremely lower overpotential (ƞ) of 131 mV @ 10 mA cm−2 current density with a Tafel slope of 53 mV dec−1. The electrodeposited NiS@ SrFe OH/CC electrodes exhibit a bi-functional catalyst with better performance due to their greater surface area of 76.304 m2 g−1, pore volume of 0.113 nm, fast electron transfer-kinetic, hierarchical nanostructures and function as a promising candidate for future energy storage and conversion applications.

A Comparative Study of Compressive Effects on the Morphology and Performance of Carbon Paper and Cloth Electrodes in Redox Flow Batteries

Compressing porous carbon electrodes is a common approach to improve flow battery performance, but the resulting impact on electrode structure, fluid dynamics, and cell performance is not well understood. Herein, microtomographic imaging, load cell testing, and flow cell diagnostics are employed to characterize how compression‐induced changes impact pressure drop, polarization, and mass‐transfer scaling. Five different compressions are tested, spanning ranges typically used in literature, for AvCarb 1071 cloth (0%, 9%, 20%, 25%, 32%) and Freudenberg H23 paper (0%, 8%, 12%, 17%, 22%). It is found that the two electrode structures have distinct responses to compression, resulting in differing optimal conditions identified for each material; specifically, the Freudenberg H23 exhibits lower combined ohmic, charge‐transfer, and mass‐transport values at 8% compression, resulting in improved electrochemical performance across all compressive values, as compared to the optimal AvCarb 1071 compression (20%). Overall, Freudenberg H23 exhibits a greater sensitivity to compression with peak electrochemical activity correlating with increased permeability, whereas AvCarb 1071 is insensitive to compressive loads but produces lower electrochemical performance. Herein, the trade‐offs of mechanical robustness on fluid‐dynamic and electrochemical performance between the two electrodes are demonstrated by the aforementioned findings, suggesting each could be used for specific operating environments.

Efficient Electrochemical Reduction of CO2 to Formate in Methanol Solutions by Mn‐Functionalized Electrodes in the Presence of Amines**

Carbon cloth electrode modified by covalently attaching a manganese organometallic catalyst is used as cathode for the electrochemical reduction of CO2 in methanol solutions. Six different industrial amines are employed as co‐catalyst in millimolar concentrations to deliver a series of new reactive system. While such absorbents were so far believed to provide a CO2 reservoir and act as sacrificial proton source, we herein demonstrate that this role can be played by methanol, and that the adduct formed between CO2 and the amine can act as an effector or inhibitor toward the catalyst, thereby enhancing or reducing the production of formate. Pentamethyldiethylentriamine (PMDETA), identified as the best effector in our series, converts CO2 in wet methanolic solution into bisammonium bicarbonate. Computational studies revealed that this adduct is responsible for a barrierless transformation of CO2 to formate by the reduced form of the Mn catalyst covalently bonded to the electrode surface. As a consequence, selectivity can be switched on demand from CO to formate anion, and in the case of (PMDETA) an impressive TONHCOO− of 2.8×104 can be reached. This new valuable knowledge on an integrated capture and utilization system paves the way toward more efficient transformation of CO2 into liquid fuel.

Polyaniline/Small‐Sized MXene/Carbon Cloth Electrodes with 3D Hierarchical Porous Structure for All‐Solid‐State Flexible Supercapacitors

The porous structure of electrodes can exert a significant impact on electrochemical performances of supercapacitors. Herein, the polyaniline/small‐sized MXene/carbon cloth (PANI/S‐MXene/CC) electrodes with 3D hierarchical porous structure are fabricated by a facile single‐step pulsed electrodeposition. First, the PANI/S‐MXene nanowires closely overlap each other and form a nanosized pore structure, which provides large specific surface area and abundant ion diffusion channels. Second, the CC with a large pore structure can facilitate permeation of gel electrolyte. S‐MXene with small lateral size not only decreases charge transfer resistance of electrodes, but also ensures an interconnected porous framework. Consequently, the assembled all‐solid‐state flexible device delivers a high areal capacitance (478.4 mF cm−2 at 0.5 mA cm−2), a superior rate capability (307.5 mF cm−2 at 10 mA cm−2), a remarkable energy density (42.5 μWh cm−2), favorable cycle stability (75.4% capacitance retention after 4000 cycles), as well as 93.2% capacitance retention after 180° mechanical bending with 1000 cycles. Herein, it is revealed that size selection of nanomaterials is a priority when the porous structure is designed.

Oxygen/fluorine-functionalized flexible carbon electrodes for high-performance and anti-self-discharge Zn-ion hybrid capacitors

Zn-ion hybrid capacitors (ZHCs) are considered promising electrochemical energy storage devices for flexible/wearable electronics. However, the unsatisfactory Zn2+ ions energy storage capability of current carbon electrodes seriously restricts its development. Herein, we effectively increase the electrochemical active surface area (also introducing pores) of the carbon nanotube (CNT) fiber bundles electrode and simultaneously introduce oxygen/fluorine functional groups with abundant C–OH and semi-ionic C–F bonds on the CNT fiber bundles electrode for facilitating the chemical adsorption of Zn2+ ions to produce pseudo-capacitance and enhance electrode kinetics, by adopting a simple electrochemical exfoliation and activation process in fluorine-containing solution. The prepared OFCNT-5 fiber bundles electrode achieves an ultrahigh areal capacitance of 1556.8 mF cm−2 (volumetric capacitance of 593.1 F cm−3), impressive long-cycling stability with capacity retention of 91.8% after 90,000 cycles. Moreover, the fiber-shaped Zn//OFCNT-5 device also delivers a high energy density of 553.53 μW h cm−2 (210.86 mW h cm−3), a high power density of 26.83 mW cm−2 (10.22 W cm−3), and outstanding anti-self-discharge capability. Our method also possesses a good universality and can extend to carbon cloth or carbon paper electrodes, and acts as one general strategy to design high performance of flexible carbon electrodes for ZHCs application.

Paired formate and H2 productions via efficient bifunctional Ni-Mo nitride nanowire electrocatalysts

Electrocatalytic water splitting provides a potentially sustainable approach for hydrogen production, but is typically restrained by kinetically slow anodic oxygen evolution reaction (OER) which is of lesser value. Here, free-standing, hetero-structured Ni3N-Ni0.2Mo0.8N nanowire arrays are prepared on carbon cloth (CC) electrodes for hydrogen evolution reaction (HER) and glycerol oxidation reaction (GOR) to formate with a remarkably high Faradaic efficiency of 96%. A two-electrode electrolyzer for GOR-assisted hydrogen production operates with a current density of 10 mA cm−2 at an applied cell voltage of 1.40 V, 220 mV lower than for alkaline water splitting. In-situ Raman measurements identify Ni (III) as the active form of the catalyst for GOR rather than Ni (IV) and in-situ Fourier transform infrared (FTIR) spectroscopy measurements reveal pathways for GOR to formate. From density functional theory (DFT) calculations, the Ni3N-Ni0.2Mo0.8N heterostructure is beneficial for optimizing adsorption energies of reagents and intermediates and for promoting HER and GOR activities by charge redistribution across the heterointerface. The same electrode also catalyzes conversion of ethylene glycol from polyethylene terephthalate (PET) plastic hydrolysate into formate. The combined results show that electrolytic H2 and formate production from alkaline glycerol and ethylene glycol solutions provide a promising strategy as a cost-effective energy supply.