Suspension Electrodes Research Articles

20-Fold Increased Limiting Currents in Oxygen Reduction with Cu-tmpa by Replacing Flow-By with Flow-Through Electrodes.

Electrochemical oxygen reduction is a promising and sustainable alternative to the current industrial production method for hydrogen peroxide (H2O2), which is a green oxidant in many (emerging) applications in the chemical industry, water treatment, and fuel cells. Low solubility of O2 in water causes severe mass transfer limitations and loss of H2O2 selectivity at industrially relevant current densities, complicating the development of practical-scale electrochemical H2O2 synthesis systems. We tested a flow-by and flow-through configuration and suspension electrodes in an electrochemical flow cell to investigate the influence of electrode configuration and flow conditions on mass transfer and H2O2 production. We monitored the H2O2 production using Cu-tmpa (tmpa = tris(2-pyridylmethyl)amine) as a homogeneous copper-based catalyst in a pH-neutral phosphate buffer during 1 h of catalysis and estimated the limiting current density from CV scans. We achieve the highest H2O2 production and a 15-20 times higher geometrical limiting current density in the flow-through configuration compared to the flow-by configuration due to the increased surface area and foam structure that improved mass transfer. The activated carbon (AC) material in suspension electrodes, which have an even larger surface area, decomposes all produced H2O2 and proves unsuitable for H2O2 synthesis. Although the mass transfer limitations seem to be alleviated on the microscale in the flow-through system, the high O2 consumption and H2O2 production cause challenges in maintaining the initially reached current density and Faradaic efficiency (FE). The decreasing ratio between the concentrations of the O2 and H2O2 in the bulk electrolyte will likely pose a challenge when proceeding to larger systems with longer electrodes. Tuning the reactor design and operating conditions will be essential in maximizing the FE and current density.

Influences of the vibration frequency and phase of the core of ultra-high voltage shunt reactors on suspended discharge in oil-paper insulation

Severe vibration of the core of ultra-high voltage (UHV) shunt reactors under operating conditions often leads to the occurrence of suspension electrode, and such a suspended discharge defect will destroy the oil-paper insulation. It is necessary to investigate the influence of vibration on suspended discharge when determining the best operating condition of UHV shunt reactors. The vibration frequency of the suspension electrode and the phase difference between the applied voltage and the vibration are studied by simulation and experiment. The simulation results show that the phase difference between the voltage and the vibration parameters will lead to an increase in the surface maximum field strength. The distortion of the field intensity caused by several typical vibration frequencies of reactor vibration is ranked (in ascending order) thus: 100, 300, 50, and 200 Hz. There is a coupling relationship between the phase difference and the vibration frequency on the suspended discharge, which will lead to an inconsistency between the field intensity and each single factor. The partial discharge test results of the collision between the suspension electrode and the high-voltage electrode show that the discharge generated by vibration at 100 Hz is much higher than that at other frequencies, followed by those at 300 and 50 Hz, and the discharge generated by vibration at 200 Hz is very small. When the phase difference of voltage advance vibration is between 0° and 90°, the quantity of local discharge is large. When the phase difference is between 90° and 180°, the local discharge is small.

A Ground-Based Electrostatically Suspended Accelerometer.

In this study, we have developed an electrostatically suspended accelerometer (ESA) specifically designed for ground use. To ensure sufficient overload capacity and minimize noise resulting from high suspension voltage, we introduced a proof mass design featuring a hollow, thin-walled cylinder with a thin flange fixed at the center, offering the highest surface-area-to-mass ratio compared to various typical proof mass structures. Preload voltage is directly applied to the proof mass via a golden wire, effectively reducing the maximum supply voltage for suspension. The arrangement of suspension electrodes, offering five degrees of freedom and minimizing cross-talk, was designed to prioritize simplicity and maximize the utilization of electrode area for suspension purposes. The displacement detection and electrostatic suspension force were accurately modeled based on the structure. A controller incorporating an inverse winding mechanism was developed and simulated using Simulink. The simulation results unequivocally demonstrate the successful completion of the stable initial levitation process and suspension under ±1g overload.

Practical potential of suspension electrodes for enhanced limiting currents in electrochemical CO2 reduction.

CO2 conversion is an important part of the transition towards clean fuels and chemicals. However, low solubility of CO2 in water and its slow diffusion cause mass transfer limitations in aqueous electrochemical CO2 reduction. This significantly limits the partial current densities towards any desired CO2-reduction product. We propose using flowable suspension electrodes to spread the current over a larger volume and alleviate mass transfer limitations, which could allow high partial current densities for CO2 conversion even in aqueous environments. To identify the requirements for a well-performing suspension electrode, we use a transmission line model to simulate the local electric and ionic current distributions throughout a channel and show that the electrocatalysis is best distributed over the catholyte volume when the electric, ionic and charge transfer resistances are balanced. In addition, we used electrochemical impedance spectroscopy to measure the different resistance contributions and correlated the results with rheology measurements to show that particle size and shape impact the ever-present trade-off between conductivity and flowability. We combine the modelling and experimental results to evaluate which carbon type is most suitable for use in a suspension electrode for CO2 reduction, and predict a good reaction distribution throughout activated carbon and carbon black suspensions. Finally, we tested several suspension electrodes in a CO2 electrolyzer. Even though mass transport limitations should be reduced, the CO partial current densities are capped at 2.8 mA cm-2, which may be due to engineering limitations. We conclude that using suspension electrodes is challenging for sensitive reactions like CO2 reduction, and may be more suitable for use in other electrochemical conversion reactions suffering from mass transfer limitations that are less affected by competing reactions and contaminations.

Toward constructing high-specific-energy sulfur suspension catholyte for lithium flow battery

Semi-solid suspension electrode is a new approach to develop flow batteries for large-scale energy storage technology, understanding the evaluation behaviors of rheological properties and their relationship with electrochemical performance is of great importance in constructing high-specific-energy suspension electrodes. Herein, sulfur suspension catholyte was employed to investigate the effects of combination mode and content of conductive additive, active material concentration, surfactant on the rheology and electrochemistry of suspension electrodes. The suspension using sulfur and Ketjenblack (KB) codeposition composite (S@KBCC) exhibited lower viscosity and higher sulfur utilization compare with mechanical mixture (S/KB) and sulfur impregnated KB (S-KB). The conductive percolation networks formed when KB content was 0.5 g L−1 in suspension, increasing KB content improved electronic conductivity and sulfur utilization, but leaded to increased viscosity and stress; conductivity, sulfur utilization and viscosity reached the inflection points by modulating KB content. The effects of surfactant Triton X-100 were evaluated in regulating rheological and electrochemical properties, sulfur catholyte with high specific energy of 602 Wh L−1 and power density of 56.6 mW cm−2 was achieved in flow modes. This work proposed the procedures as guides to construct high-energy-density sulfur suspension catholyte, and also offers a reference for other semi-solid electrodes.

Current collectors’ effects on the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 suspension electrodes for lithium slurry battery

Take after the advantages of lithium-ion battery (LIB) and redox flow battery (RFB), semi-solid flow battery (SSFB) is a promising electrochemical energy storage device in renewable energy utilization. The flowable slurry electrode realizes decouple of energy and power density, while it also brings about new challenge to SSFBs, electron transport between active material and the out circuit. In this consideration, three types of current collectors (CCs) are applied to study the resistance and electrochemical performances of slurry cathodes within pouch cells for the first time. It proves that the electronic resistance (Re) between slurry electrode and the CC plays a decisive role in SSFB operation, and it is so large when Al foil is adopted that the cell cannot even work. Contact angle between Ketjen black (KB) slurry without active material (AM) and the CC is a preliminarily sign for the Re, the smaller the angle, the lower the resistance, and the better electrochemical performance of the cell.

Micro-aeration assisted with electrogenic respiration enhanced the microbial catabolism and ammonification of aromatic amines in industrial wastewater

Improvement of refractory nitrogen-containing organics biodegradation is crucial to meet discharged nitrogen standards and guarantee aquatic ecology safety. Although electrostimulation accelerates organic nitrogen pollutants amination, it remains uncertain how to strengthen ammonification of the amination products. This study demonstrated that ammonification was remarkably facilitated under micro-aerobic conditions through the degradation of aniline, an amination product of nitrobenzene, using an electrogenic respiration system. The microbial catabolism and ammonification were significantly enhanced by exposing the bioanode to air. Based on 16S rRNA gene sequencing and GeoChip analysis, our results indicated that aerobic aniline degraders and electroactive bacteria were enriched in suspension and inner electrode biofilm, respectively. The suspension community had a significantly higher relative abundance of catechol dioxygenase genes contributing to aerobic aniline biodegradation and reactive oxygen species (ROS) scavenger genes to protect from oxygen toxicity. The inner biofilm community contained obviously higher cytochrome c genes responsible for extracellular electron transfer. Additionally, network analysis indicated the aniline degraders were positively associated with electroactive bacteria and could be the potential hosts for genes encoding for dioxygenase and cytochrome, respectively. This study provides a feasible strategy to enhance nitrogen-containing organics ammonification and offers new insights into the microbial interaction mechanisms of micro-aeration assisted with electrogenic respiration.

Enhanced Direct Electron Transfer Mediated Contaminant Degradation by Fe(IV) Using a Carbon Black-Supported Fe(III)-TAML Suspension Electrode System.

Iron complexes of tetra-amido macrocyclic ligands (Fe-TAML) are recognized to be effective catalysts for the degradation of a wide range of organic contaminants in homogeneous conditions with the high valent Fe(IV) and Fe(V) species generated on activation of the Fe-TAML complex by hydrogen peroxide (H2O2) recognized to be powerful oxidants. Electrochemical activation of Fe-TAML would appear an attractive alternative to H2O2 activation, especially if the Fe-TAML complex could be attached to the anode, as this would enable formation of high valent iron species at the anode and, importantly, retention of the valuable Fe-TAML complex within the reaction system. In this work, we affix Fe-TAML to the surface of carbon black particles and apply this "suspension anode" process to oxidize selected target compounds via generation of high valent iron species. We show that the overpotential for Fe(IV) formation is 0.17 V lower than the potential required to generate Fe(IV) electrochemically in homogeneous solution and also show that the stability of the Fe(IV) species is enhanced considerably compared to the homogeneous Fe-TAML case. Application of the carbon black-supported Fe-TAML suspension anode reactor to degradation of oxalate and hydroquinone with an initial pH value of 3 resulted in oxidation rate constants that were up to three times higher than could be achieved by anodic oxidation in the absence of Fe-TAML and at energy consumptions per order of removal substantially lower than could be achieved by alternate technologies.

Ammonia Removal from Simulated Wastewater Using Ti3C2T x Mxene in Flow Electrode Capacitive Deionization

The energy-water nexus poses an integrated research challenge with crucial global implications. The nexus highlights the need to adopt a proactive approach by focusing on the conservation and management of both resources. As global freshwater supply continues to deplete, a larger number of people in the world will need to rely on recycled water. One of the ways to address this concern is by focusing efforts on the development and deployment of energy efficient water remediation technologies. Ammonia is one of the most common contaminants found in domestic and industrial wastewater. Concurrently, it is also one of the most liberally produced chemicals because of its widespread use in the agricultural and textile industries. In 2020, approximately 144 million metric tons of ammonia were produced globally (1). Despite that, biological nitrification remains the most widespread method for treating ammonia wastewater (2). Aside from being cumbersome and slow, it also fails to recover ammonia, which is otherwise a valuable product. In pursuit of sustainability, product conservation directly translates to energy conservation and there remains a need for a water purification and ammonia recovery technology that is energy, water, and resource efficient. Capacitive deionization (CDI) is a separation technology that removes ions from water by applying a small voltage below the dissociation potential of water (1.23 V). The ions are temporarily stored in the electrodes and later released to a separate concentrated stream upon voltage removal or reversal. Flowing electrode CDI systems (FE-CDI) have proven advantageous because of their ability to prevent cross contamination, and to run in uninterrupted cycles ad infinitum . The performance of FE-CDI systems relies on the selection of suitable electrode materials with desired properties of high electrical conductivity, high surface area, colloidal stability, and surface sensitivity (3). MXenes are an emerging class of two-dimensional (2D) materials that are highly conductive, hydrophilic, tunable, and possess attractive charge storage and ion transport properties (4,5). In this work, we developed a flowing electrode capacitive deionization (FE-CDI) system using Ti3C2T x MXene suspension electrodes for the removal and recovery of ammonia from synthetic wastewater. A custom-built FE-CDI unit using titanium current collectors with an effective transfer area of 10 cm2 was used to test system efficiency. The electrode performance was evaluated by operating the CDI system with a feed solution of 500 mg/L NH4Cl running in batch mode at a constant voltage of 1.2 and -1.2 V in charging and discharging stages respectively. Despite low loading (1 mg/ml), Ti3C2T x flow electrodes showed a markedly improved performance by achieving 60% ion removal efficiency (Fig. 1a) in a short saturation time of 115 minutes, and an unprecedented ion adsorption capacity of 460 mg/g (Fig. 1b). This is ~ 7× higher than the currently reported value using Ti3C2 in a conventional CDI system targeted at sodium chloride (NaCl) desalination (6). Post-mortem characterization of the suspension electrodes by X-ray diffraction revealed that Ti3C2T x MXene sequestered high amounts of pollutants due to its ability to intercalate ions between its 2D layers. The electrodes possessed favorable electrochemical properties with a high specific capacitance of 148 F/g. The system proved to be a green technology by exhibiting satisfactory charge efficiency of 58-70% while operating at a relatively low energy consumption of 0.45 kWh/kg (Fig. 1c), which is about an order of magnitude lower than the 4.6 kWh/kg used by commercial wastewater treatment plants (7). The results demonstrate that the Ti3C2T x MXene electrodes have the potential to improve the FE-CDI process for energy-efficient removal and recovery of ammonia. IEA, Ammonia Technology Roadmap, International Energy Agency, Paris, (2021).F. Jaramillo, M. Orchard, C. Muñoz, M. Zamorano, and C. Antileo, J. Environ. Manage., 218, 154–164 (2018).Y. Oren, Desalination, 228, 10–29 (2008).Y. Gogotsi and B. Anasori, ACS Nano, 13, 8491–8494 (2019).P. Singh et al., J. Power Sources, 506 (2021).J. Ma, Y. Cheng, L. Wang, X. Dai, and F. Yu, Chem. Eng. J., 384 (2020).M. Ekman, B. Björlenius, and M. Andersson, Water Res., 40, 1668–1676 (2006). Figure 1

Core–Shell Fe3O4@C Conductive Additives for Magnetic Flow-Electrode Capacitive Deionization: Reconstruction of Charge Percolation Networks

Flow-electrode capacitive deionization (FCDI) based on suspension or semisolid electrodes is a promising alternative for large-scale applications, yet precise control over their transport behavior has not yet been accomplished. Here, we report a general approach for remotely manipulating the transport of the hybrid suspension electrodes composed of core–shell Fe3O4@C nanoparticles and powdered activated carbon (AC) simply by employing a magnetic field. Benefiting from the reconfiguration of the charge percolation networks, the average salt removal rate (ASRR) of magnetic FCDI was increased by 61.7% compared to that of FCDI without the magnetic field. The mechanism of magnetic field-magnetic carbon (MC) coupling includes three main pathways: (i) increasing the local concentration of active electrodes on the current collector surface, (ii) increasing the contact sites available to the current collector, and (iii) shortening the ion transport distance. It was also demonstrated that MC could be used as a novel active electrode by further increasing the adsorption capacity of the carbon shell. Under a moderate magnetic flux (Φ = 45 mT), the ASRR and charge efficiency reached 0.16 μm cm–2 min–1 and 94.3%, respectively. In addition, MC is mechanically and chemically robust and can be recovered and reused in long-term operation by magnetic separation. In brief, our study introduces a general strategy to enhance charge transport in suspension electrodes and demonstrates the promising potential of magnetic FCDI for efficient and low-cost desalination.

Precise manipulation of the charge percolation networks of flow-electrode capacitive deionization using a pulsed magnetic field

Magnetic field is a simple and powerful means that enables controlled the transport of electrode particles in flow electrode capacitive deionization (FCDI). However, the magnetic particles are easily stripped from hybrid suspension electrodes and the precise manipulation of the charge percolation network remains challenging. In this study, a programmable magnetic field was introduced into the FCDI system to enhance the desalination performance and operational stability of magnetic FCDI, with core-shell magnetic carbon (MC) used as an alternative electrode additive. The results showed that the pulsed magnetic field (PMF) was more effective in enhancing the average salt removal rate (ASRR) compared to the constant magnetic field (CMF), with 51.6% and 67.7% enhancement, respectively, compared to the magnetic field-free condition. The outstanding advantage of the PMF lies in the enhancement in the trapping and mediating effects in the switching magnetic field, which keeps the concentration of the electrode particles near the current collector at a high level and greatly facilitates electron transport. In long-term operation (20,000 cycles), the pulsed magnetic FCDI achieved a stable desalinating rate of 0.4–0.68 μmol min–1 cm–2 and a charge efficiency of >96%. In brief, our study introduces a new approach for the precise manipulation of charge percolation networks of the suspension electrodes and provides insight into the charging mechanism of the magnetic FCDI.

Electroplating technology of suspended diamond particles surface based on rotating electrode

In view of the difficulty of fine-grained diamond surface electroplating, a method of diamond barrel plating based on rotating electrode is proposed, which is to make the cathode rotate during the rolling process. The mechanism of dynamic contact between fine-grained particle in suspension electroplating solution and electrode is analyzed. And the force model and motion equation of diamond abrasive particles in electroplating fluid were established. The single factor experiments were carried out to study the effects of the rotation speed of the plating bottle, the rotation speed of the electrode, and the diameter of the diamond particles on the weight gain rate and the surface morphology of the suspended fine-grained diamond. The results show that the contact time between the suspended particles and the electrode can be increased when the electrode direction is opposite to that of the plating bottle, and the rotation speed should be matched with the flow rate of the plating solution to obtain a good electroplating result. The weight gain rate decreased with the decrease of particle size. For 25–36 μm diamond particles, the optimal process parameters are as follows: the rotation speed of plating bottle is 20 r/min, the electrode speed is 50 r/min, and the electrode turns opposite to the plating bottle. The smallest size range of diamond particles that can be electroplated by this method is 5–10 μm.

Promising aqueous dispersions of carbon black for semisolid flow battery application

In this systematic study, we attempt to thoroughly understand the aggregation mechanism of conductive carbon black in aqueous dispersing medium and optimize the formulation of suspension electrodes for aqueous sodium–ion semisolid flow battery applications. For the first time, we present branched micelle solution as an electrolyte that introduces the widest electrochemical stability window of 3.5 V, from –3 to + 0.5 V vs. Ag/AgCl, with relatively low viscosity, rendering it as promising aqueous dispersing medium for suspension electrodes (anolytes). The simultaneous rheo-electrical measurements revealed that the aggregation of conductive ketjenblack (KB) particles was controlled by the electrostatic repulsion forces that doubly originate from the inter-aggregate soft interaction and bulk micelle interactions. This remarkable interaction rendered the dispersions electrically percolated at low carbon content (0.9 wt%) and importantly able to conserve the electrical conductivity under extremely high shear rates. Under the quiescent conditions, the percolated KB dispersion could sustain higher load of active material (up to 30 wt% Na2Ti3O7 as an active material) without severe influence on the rigidity (rheological plateau modulus G0) and electrical conductivity (Σ) of the suspensions. These promising findings propound further investigation for the electrochemical performance of these aqueous sodium–ion suspension electrodes under flow conditions.

Hydrogen production by microwave discharge in liquid: Study on the characteristics effect of suspended electrode

In order to further improve the hydrogen production efficiency of microwave liquid-phase discharge, a three-electrode reactor was designed and a suspended electrode was added. The internal structure of the three-electrode reactor was optimized. The formation of bubbles during the discharge and the change characteristics of plasma morphology were studied after adding the suspended electrode. In addition to investigating the physical influence of the suspended electrode on the discharge plasma, the influences of the different electrode materials and specific surface area of the suspension electrode on the composition of the gas products, the hydrogen flow rate and the hydrogen energy yield were also investigated. The experimental results show that the suspended electrode can increase the formation time of plasma and bubble. In this study, the highest flow rate of total gas is 29.5 NL/min with the 80 PPI-Cu foamed metal suspended electrode which is an increase of 31.5% than no suspended electrode.

Effects of conductive additives on the percolation networks and rheological properties of LiMn0.7Fe0.3PO4 suspensions for lithium slurry battery

In depth understanding the evaluation behaviors of conductive percolation networks and rheological properties is important for developing high performance suspension electrodes. Herein, three kinds of conductive additives, Ketjen Black, multi-walled carbon nanotubes and graphene nanoplatelets, are utilized to systematically investigate the impacts of dimension and content on the rheological and electrochemical properties of LiMn0.7Fe0.3PO4 suspensions. The percolation threshold ranges are found to be 0.5–0.6 wt.%, 0.2–0.3 wt.% and 2.3–2.4 wt.% for KB, MWCNT and GNP-based suspensions, respectively. The inflection points for electronic conductivities of different conductive additives based suspensions are situated at 1.0 wt.%, 0.5 wt.% and 2.5 wt.%, respectively, and the static viscosities and yield stresses of KB and MWNCT-based suspensions possess the same inflection points as those of electronic conductivities. Nevertheless, GNP-based suspensions deliver a distinguishing tendency due to their relatively poor dispersion. Electrochemical characterizations indicate that 1.5 wt.% KB-based suspension delivers superior cycle and rate performances. Especially, the successful application of LMFP suspension to lithium slurry battery was demonstrated by a relatively stable cycle over 230 h. Our findings will be helpful for the development of lithium slurry batteries with robust conductive networks and high energy density.

Suspended hydrophilic carbon anodes to enable fully flowable cerium–metal hybrid flow batteries

Hybrid redox flow batteries (RFBs) are a special type of RFBs that involve depositing reactions on negative electrodes. The available volume in negative electrodes for cell stacks limits the totally energy-storing capability of these batteries. This paper introduces the first fully flowable Ce–metal flow battery operated with a semisolid, flowable anolyte. Using the semisolid fuel cell concept, we incorporate the sustainable and deposit-abundant features of non-Li-based batteries into the structure of RFBs to develop a fully flowable RFB system. Solid suspension electrodes of hydrophilic carbon particles deposited by earth-abundant metals with redox activity are investigated as alternatives to the redox-active molecules employed in typical RFBs to decouple the power delivery capability from the energy storage capacity in fully flowable RFBs. While being charged, earth-abundant redox-active metal (Cu, Pb or Zn) is electrodeposited on the carbon particle suspension, which is dissolved in the sequent discharging process. On the basis of the proposed contact-charge-transfer mechanism, the electrical contact to the solid suspension electrode is fed by the redox-inert hydrophobic current collector that restrains direct metal deposition on their surfaces due to the hydrophobicity.

Carbon nanotubes/activated carbon hybrid as a high-performance suspension electrode for the electrochemical desalination of wastewater

In this study, we employed carbon nanotubes (CNTs) to improve the performance of flow-electrode capacitive deionization (FCDI) for wastewater desalination in isolated closed-cycle (ICC) mode. The effects of CNTs loading and initial salt concentration on FCDI desalination were evaluated with energetic performance analysis. FCDI was carried out for the desalination with real wastewater for technology demonstration. The addition of CNTs significantly improved the average salt removal rate (ASRR), associated with a decrease in the flow-electrode flowability. FCDI with 0.25 wt% CNTs had an ASRR of 1.59 μmol/cm2–min, which was 1.7-fold higher than that without CNTs. This was attributed to the bridging effect of CNTs for more rapid charge transfer. Increasing the initial salt concentration from 0.05 to 0.30 M led to a higher ASRR, resulting from a reduction in the electrical resistance in the cell. After further increasing the salt concentration to 0.50 M, the charge efficiency was relatively decreased due to co-ion leakage. Notably, FCDI for the desalination of real saline wastewater achieved a high decrease in conductivity (94%), a high charge efficiency (>99%), and low energy consumption (0.034 kWh/mol). Our results demonstrated that adding CNTs is a feasible approach to achieve high-performance FCDI for sustainable wastewater desalination.

Characterization of Agglomerated Particles in a PEFC Electrode Slurry by Soft X-Ray Radiography

Polymer electrolyte fuel cells (PEFCs) have been commercialized for various applications, such as automobiles and household power sources, because of their low operating temperature and high power density. A PEFC comprises a polymer electrolyte membrane as the electrolyte and electrodes consisting of a catalyst layer and a gas diffusion layer. The catalyst layer plays a role as an electrochemical reaction field with a porous structure and is generally prepared by mixing platinum-supported carbon and ionomer in a solvent to make a suspension (electrode slurry), which is then coated on a substrate and dried. Mixed particles aggregate in the electrode slurry, which affects the porous structure of the catalyst layer. In order to improve the cell performance of PEFCs by controlling the structure of catalyst layers, it is necessary to understand and characterize the electrode slurry [1-2].In this study, we carried out a temporal visualization of the electrode slurry by a soft X-ray radiography system (Mars-Tohken X-ray Inspection, TUX-9000D) to clarify the agglomeration/dispersion state and migration phenomena of particles in the electrode slurry. PEFC electrode slurry is a black opaque suspension and its structure is hardly probed by visible light. In order to observe the electrode slurry by soft X-ray radiography, we used a house-made PTFE container. The container was placed on the sample stage of the soft X-ray imaging system for observation. In order to investigate the effect of interaction between particles, four types of electrode slurries with different non-volatile ratios (7.0, 0.70, 0.40, and 0.11%) were prepared for observation. The ionomer-to-carbon ratio of all electrode slurries was kept at 1.0. The dispersions were prepared by a planetary centrifugal mixer for 30 minutes (2000 rpm for the revolution and 800 rpm for the rotation) just before soft X-ray visualization.Figure 1 shows a soft X-ray radiograph of electrode slurry (non-volatile ratio: 7.0%). The image captured a spatial variation of X-ray absorption in the electrode slurry. High X-ray absorption regions correspond to high density in the slurry, attributed to agglomerates of platinum-supported carbon particles and ionomers. Their diameters were about 10 – 40 μm, and less variation was found in the non-volatile ratio of the electrode slurry from 0.11 to 7.0%. However, the number of agglomerated particles varied depending on the non-volatile ratio of the electrode slurry. The less the non-volatile ratio, the less the number of agglomerated particles observed, suggesting that migrations in the electrode slurry were much affected by the non-volatile component in the slurry. We performed a time-series visualization of the electrode slurry placed in the X-ray radiography system for several hours. Sedimentation behaviors of the agglomerated particles were observed in all electrode slurries. The captured images were processed to quantitatively characterize sedimentation rates in the slurry. It was found that the less the non-volatile ratio, the more the sedimentation rate of the agglomerated particles.AcknowledgmentsThis work was supported by JSPS KAKENHI Grant Number 18K13702 and 21H04540.[1] T. Suzuki et al., ECS Trans., 86-13 (2018), 193.[2] S. Khandavalli et al., ACS Appl. Mater. Interfaces, 10 (2018), 43610. Figure 1

MXene-based suspension electrode with improved energy density for electrochemical flow capacitors

The development of high capacitance materials with high packing density and low viscosity in suspension electrodes is critical for progressing towards high-efficiency, low-footprint electrochemical flow capacitors (EFCs). Here, we report on the first electrochemical and rheological characterization of MXene-based suspension electrodes, using multilayer Ti3C2Tx as the active material and carbon black (CB) as the conductive additive in symmetric and asymmetric EFC devices. In the case of symmetric Ti3C2Tx devices, the Ti3C2Tx concentration is fixed to 22 vol.% in the slurry and the CB concentration is varied from 0.5 to 2.0 vol.%. The symmetric device arrangement offers a high capacitance of 240 F ml−1 (2 mV s−1) and volumetric energy density of 2.65 Wh l−1 @ power density of 47.82 W l−1. Additionally, to extend the potential window, an asymmetric device assembly of activated carbon and Ti3C2Tx is investigated. This arrangement allows a stable operating potential window of 1 V with an energy density of 4.12 Wh l−1 and power density of 31.73 W l−1. Overall, multilayer Ti3C2Tx seems to be excellent candidate for flowable electrode applications, offering high capacitance, energy density and low viscosity due to its high electrochemical activity, excellent electrical conductivity, and versatile surface chemistry.

High Performance Aqueous Li-Ion Flow Capacitor Realized Through Microstructure Design of Suspension Electrode.

Suspension electrode is the core of flowable electrochemical energy storage systems, which are considered suitable for large-scale energy storage. Nevertheless, obtaining suspension electrodes with both low viscosity and high conductivity is still a big challenge. In present work, spinel LiMn2O4 was chosen as an example to make suspension with low viscosity and high conductivity through microstructure morphology control of solid particles and the contact mode between active materials and conductive additives in suspension electrode. By coating a thin layer of polyaniline on the surface of spherical spinel LiMn2O4, the resulting suspension showed much higher electronic conductivity (about 10 times) and lower viscosity (about 4.5 times) as compared to irregular and bare spinel LiMn2O4-based suspension counterpart. As a result, the Li-ion flow capacitor based on LiMn2O4 and activated carbon suspensions exhibited a record energy density of 27.4 W h L−1 at a power density of 22.5 W L−1 under static condition to date, and can be smoothly work under an intermittent-flow mode. The strategy reported in this work is an effective way for obtaining suspension electrodes with low viscosity and high electronic conductivity simultaneously. It can not only be used in the flow capacitors, but also can be extended to other flowable electrochemical energy storage systems.