Electrodes For Flow Batteries Research Articles

Acetylacetonate-modified TiO2 nanoparticles coated on the carbon felt as the negative electrode of vanadium redox flow battery for reducing HER and enhancing V3+/V2+ redox reactions

The occurrence of the hydrogen evolution reaction (HER) on the surface of the carbon-based negative electrode of the vanadium redox flow battery (VRFB) causes high charge transfer resistance (RCT) for the desired V3+/V2+ redox reaction leading to irreversible capacity loss. To this effect, we have synthesized acetylacetonate-modified TiO2 (SGTA) and unmodified TiO2 (SGT) coating colloidal solutions as electrocatalysts for enhanced V3+/V2+ redox reaction on the carbon-felt negative electrodes of VRFB. The SGTA particles exhibit significantly higher homogeneity with sizes of ≤15 nm, in comparison to the severely aggregated SGT particles with diameters of ∼23–75 nm in colloidal solution. When coated on the pristine carbon felt (P-CF), the surface morphology of the SGTA@CF electrode exhibits relatively dense, uniformly coated particles, in comparison to the sparse, non-even coating of aggregated particles on the SGT@CF electrode surface. Consequently, the charge transfer for V3+ → V2+ reduction reaction and charge storage capacity are determined to be in the order SGTA@CF > SGT@CF > P-CF, confirming that the competitive and irreversible HER was higher on the surface of non-evenly coated fibers and bare carbon felt, respectively.

High‐performance Porous Electrodes for Flow Batteries: Improvements of Specific Surface Areas and Reaction Kinetics

High‐performance Porous Electrodes for Flow Batteries: Improvements of Specific Surface Areas and Reaction Kinetics

High-performance composite electrode based on polyaniline/graphene oxide carbon network for vanadium redox flow batteries

In this study, an electrode wrapped in a carbon network is fabricated using a straightforward hydrothermal technique. Conducting polymers such as polyaniline (PANi) have been used to form carbon networks on the surfaces of carbon fibers. However, the cycling instability of PANi, which is a consequence of structural modifications, is a significant obstacle to its commercial application. This study presents an innovative and effective approach for synthesizing carbon networks using PANi/reduced graphene oxide (PANi-rGO-CF) composites to enhance the performance of vanadium redox flow battery (VRFB) electrodes. PANi-rGO was deposited on carbon felt using a hydrothermal method, followed by calcination under an argon atmosphere. The presence of graphene oxide facilitated the uniform distribution of PANi and enhanced its stability. PANi-rGO-CF demonstrated superior electrocatalysis toward vanadium redox couples owing to the abundant heteroatom active sites, affording VRFBs with extraordinary stability and outstanding energy efficiency after 100 cycles at 100 mA/cm2.

Effect of Hydrogen Pressure on The Mass Transfer Characteristics of Hydrogen-Bromine Flow Battery Electrodes

The mass transfer characteristics of porous carbon electrodes in the liquid side of a hydrogen bromine redox flow battery (H2-Br2 RFB) were investigated under compressive deformation caused by operation at elevated hydrogen pressure. Here, flow cell measurements of permeability and micro-particle image velocimetry (μPIV), alongside electrochemical measurements of capacitance and battery discharge were used to characterize changes in the liquid side electrode compression, in-plane liquid flow, accessible surface area, polarization, and mass transfer scaling brought by hydrogen pressure. We studied two electrode types with different structures, carbon paper and carbon cloth, in untreated well as heat-treated forms in the pressure range 0–8 bar H2. It was found that pressure-induced compression of the liquid side electrode increases the accessible area of untreated electrodes, with little effect on heat-treated electrodes, but decreases the electrochemical performance of the battery in all cases by increasing the ohmic resistance of the cell and decreasing the mass transfer coefficient of the porous electrode. Overall, heat treatment is shown to affect the rigidity, saturation behavior, and generalized mass transfer of paper electrodes but not of cloth electrodes. Our findings will guide the selection of electrode materials and operation parameters for the H2-Br2 RFB.

Deconvoluting Surface Modification Effects on Flow Battery Electrode Performance by Impedance Spectroscopy

Flow batteries have proliferated over the past decade, both in installed capacity and in the diversity of systems being developed for grid storage applications. As a long duration energy storage technology, flow batteries offer the distinct advantage of independent scaling of energy capacity through their liquid electrolytes, and of power capacity through stack design. Across flow battery systems, improving the design of reactor stacks to achieve high power densities at acceptable energy conversion efficiencies remains an important lever for lowering overall levelized costs of storage. In pursuit of this aim, understanding the reaction kinetics on the surfaces of porous carbon electrodes is key [1]. However, traditional techniques such as voltammetry, impedance spectroscopy, and cell performance must be utilised with caution to avoid convoluting observations of surface kinetics with other effects.Previous studies on vanadium flow batteries have used impedance spectroscopy to circumvent this issue, utilising the shared dependence of double layer capacitance and charge transfer conductance [2]. In recent years, DRT analysis of impedance spectra has also been used to further study electrode treatments for vanadium systems [3]. Building on these works, we use impedance spectroscopy combined with other techniques to deconvolute the effects of electrode treatments ex-situ before demonstrating the modified electrode performance in flow cells. The accompanying abstract image illustrates how different electrode modifications can manifest comparative differences in identified faradaic features in impedance spectra. As the most well studied system, we first apply our analysis to electrodes for vanadium electrolytes, validating our method and previous studies on electrode modifications. Following this, we apply our approach to capture a range of behaviours by studying redox active species with faster kinetics, such as recently developed organic species [4].The results of this work aim to improve the evaluation of reaction kinetics for different redox active species and electrode treatments. By doing so, we seek to further understand surface reaction mechanisms and how they can be harnessed to improve stack and electrolyte performance.[1] T. V. Sawant, C. S. Yim, T. J. Henry, D. M. Miller, and J. R. McKone, ‘Harnessing Interfacial Electron Transfer in Redox Flow Batteries’, Joule, vol. 5, no. 2, pp. 360–378, Feb. 2021, doi: 10.1016/j.joule.2020.11.022.[2] H. Fink, J. Friedl, and U. Stimming, ‘Composition of the Electrode Determines Which Half-Cell’s Rate Constant is Higher in a Vanadium Flow Battery’, J. Phys. Chem. C, vol. 120, no. 29, pp. 15893–15901, Jul. 2016, doi: 10.1021/acs.jpcc.5b12098.[3] K. Köble et al., ‘Revealing the Multifaceted Impacts of Electrode Modifications for Vanadium Redox Flow Battery Electrodes’, ACS Appl. Mater. Interfaces, vol. 15, no. 40, pp. 46775–46789, Oct. 2023, doi: 10.1021/acsami.3c07940.[4] J.-M. Fontmorin, S. Guiheneuf, T. Godet-Bar, D. Floner, and F. Geneste, ‘How anthraquinones can enable aqueous organic redox flow batteries to meet the needs of industrialization’, Current Opinion in Colloid & Interface Science, vol. 61, p. 101624, Oct. 2022, doi: 10.1016/j.cocis.2022.101624. Figure 1

Carbon Structure Regulation Strategy for the Electrode of Vanadium Redox Flow Battery.

Vanadium redox flow battery (VRFB) is a type of energy storage device known for its large-scale capacity, long-term durability, and high-level safety. It serves as an effective solution to address the instability and intermittency of renewable energy sources. Carbon-based materials are widely used as VRFB electrodes due to cost-effectiveness and well-stability. However, pristine electrodes need proper modification to overcome original poor hydrophilicity and fewer reaction active sites. Adjusting the carbon structure is recognized as a viable method to boost the electrochemical activity of electrodes. This review delves into the advancements in research related to ordered and disordered carbon structure electrodes including the adjusting methods, structural characteristics, and catalytic properties. Ordered carbon structures are categorized into nanoscale and macroscale orderliness based on size, leading to improved conductivity and overall performance of the electrode. Disordered carbon structures encompass methods such as doping atoms, grafting functional groups, and creating engineered holes to enhance active sites and hydrophilicity. Based on the current research findings on carbon electrode structures, this work puts forth some promising prospects for future feasibility.

Surfactant Effects in Porous Electrodes for Microemulsion Redox Flow Batteries

The effect of surfactant additives on electrochemical behavior in porous electrodes was investigated using vanadium redox flow battery half-cells and the dependence of volumetric kinetics and mass transport on electrolyte, surfactant, and electrode type was explored. Without surfactant added, carbon paper electrodes demonstrated greater kinetics and transport compared to carbon felt, for a given electrolyte. Additionally, posolyte kinetics are greater than negolyte kinetics by one to three orders of magnitude, depending on the electrode type. Addition of surfactant increased electrode wettability and possibly electrochemical surface area. However, this was accompanied by a decrease in volumetric mass transport, due to stronger electrolyte-electrode interactions. The presence of sodium dodecyl sulfate (SDS) influenced posolyte and negolyte kinetics differently. Kinetics showed a dependence on electrode type and surfactant. On carbon felt, volumetric kinetics decreased for both posolyte and negolyte with SDS addition. On carbon paper, SDS decreased volumetric kinetics for the posolyte but increased (>2X) kinetics for the negolyte! This kinetic enhancement depends on surfactant chemistry: cetyltrimethylammonium bromide, a cationic surfactant, failed to increase kinetics. Furthermore, SDS did not increase areal specific resistance. These findings show the superior performance of carbon paper compared to carbon felt and suggest SDS as a possible VRFB negolyte additive.

Modulating single-atom sulfur-vacancy defect in MoS2-x catalysts to boost cathode redox kinetics for vanadium flow batteries

Vanadium flow batteries (VFBs) have great potential for application in energy storage systems. However, the sluggish cathode redox kinetics still greatly restricts their operation at high current densities. Herein, we boost cathode redox chemistry by modulating single-atom sulfur-vacancy (S-vacancy) defect of MoS2-x in-situ grown on carbon felts via a facile chemical etching method. Firstly, the optimized S-vacancy concentration is figured out via high throughput calculations based on d-band center theory. By precisely controlling etching duration, we achieve a tailored S-vacancy concentration, leading to highly dispersed S-vacancies, increased specific surface area, and improved hydrophilicity. Electrochemical characterizations demonstrate that optimized S-vacancy state can significantly facilitate the VO2+/VO2+ kinetics. Moreover, analysis of electron density difference and integrated crystal orbital Hamiltonian group further reveals that dispersed S-vacancy distribution also contribute to efficient surface electronic structure and enhanced adsorption process. Benefiting from enhanced VO2+/VO2+ kinetics, VFB single cell achieves a superior EE of 78.73 % at 300 mA cm−2 and is able to last for 500 cycles without decay. This work demonstrates the promising potential of single-atom S-vacancies catalysts in the fabrication of flow battery electrodes and more importantly sheds light on the fundamental modulation essence of d-band center in MoS2-x towards enhanced cathode redox kinetics.

In situ growth of CoO on MXene sheets for modification of all‑vanadium redox flow battery electrodes

In order to greatly improve the energy efficiency and electrolyte utilization efficiency of vanadium redox flow batteries (VRFBs) and to enable them to operate at high current densities, MXene/CoO composites were used for the first time in this research as electrocatalysts for the V3+/V2+ reaction. The catalytic effect of the materials was characterized by cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) tests. Then battery performance of MXene/CoO composite modified plasma-treated graphite felt (GF) negative electrodes (MXene/CoO/GF) were tested in a VRFB. The results show that MXene/CoO composites can improve the catalytic activity. There is a 22.93 % increase in energy efficiency and 124.94 % increase in electrolyte utilization efficiency when MXene/CoO/GF is applied as VRFB negative electrode at a current density of 200 mA cm−2 compared to GF. At a current density of 250 mA cm−2, the energy efficiency of MXene/CoO/GF is maintained at 75.55 %. The excellent performance is attributed to the addition of MXene/CoO, which increases the active sites for redox reactions and thus improves the kinetics of the V3+/V2+ reaction.

Upscaling of Reactive Mass Transport through Porous Electrodes in Aqueous Flow Batteries

Porous electrodes (PEs) are an important component of modern energy storage devices, such as lithium-ion batteries, flow batteries or fuel cells. Their complicated multiphase structure presents a considerable challenge to modeling and simulation. In this paper, we apply the volume-averaging method (VAM) as an efficient approach for the evaluation of effective macroscopic transport parameters in PEs. We consider the transport of electro-active species coupled to heterogeneous Butler-Volmer type reactions at the electrode surface. We identify the characteristic scales and dimensionless groups for the application to aqueous flow batteries. We validate the VAM-based model with direct numerical simulation results and literature data showing excellent agreement. Subsequently, we characterize several simplified periodic PE structures in 2D and 3D in terms of hydraulic permeability, effective dispersion and the effective kinetic number. We apply the up-scaled transport parameters to a simple macroscopic porous electrode to compare the overall efficiency of different pore-scale structures and material porosity values over a wide range of energy dissipation values. This study also reveals that the Bruggeman correction, commonly used in macroscopic porous electrode models, becomes inaccurate for realistic kinetic numbers in flow battery applications and should be used with care.

Multiple‐dimensioned defect engineering for graphite felt electrode of vanadium redox flow battery

AbstractThe scarcity of wettability, insufficient active sites, and low surface area of graphite felt (GF) have long been suppressing the performance of vanadium redox flow batteries (VRFBs). Herein, an ultra‐homogeneous multiple‐dimensioned defect, including nano‐scale etching and atomic‐scale N, O co‐doping, was used to modify GF by the molten salt system. NH4Cl and KClO3 were added simultaneously to the system to obtain porous N/O co‐doped electrode (GF/ON), where KClO3 was used to ultra‐homogeneously etch, and O‐functionalize electrode, and NH4Cl was used as N dopant, respectively. GF/ON presents better electrochemical catalysis for VO2+/VO2+ and V3+/V2+ reactions than only O‐functionalized electrodes (GF/O) and GF. The enhanced electrochemical properties are attributed to an increase in active sites, surface area, and wettability, as well as the synergistic effect of N and O, which is also supported by the density functional theory calculations. Further, the cell using GF/ON shows higher discharge capacity, energy efficiency, and stability for cycling performance than the pristine cell at 140 mA cm−2 for 200 cycles. Moreover, the energy efficiency of the modified cell is increased by 9.7% from 55.2% for the pristine cell at 260 mA cm−2. Such an ultra‐homogeneous etching with N and O co‐doping through “boiling” molten salt medium provides an effective and practical application potential way to prepare superior electrodes for VRFB.

Tin Hybrid Flow Batteries with Ultrahigh Areal Capacities Enabled by Double Gradients.

Tin-based hybrid flow batteries have demonstrated dendrite-free morphology and superior performance in terms of cycle life and energy density. However, the quick accumulation of electrodeposits near the electrode/membrane interface blocks the ion transport pathway during the charging of the battery, resulting to a very limited areal capacity (especially at high current density) that significantly hinders its deployment in long-duration storage applications. Herein, a conductivity-activity dual-gradient design is disclosed by electrically passivating the carbon felt near the membrane/electrode interface and chemically activating the carbon felt near the electrode/current collector interface. In consequence, the tin metals are preferentially plated at the region near electrode/current collector, preventing the ion transport pathway from being easily blocked. The resultant gradient electrode demonstrated an unprecedentedly high areal capacity of 268 mAh cm-2 at a current density of as high as 80mA cm-2. Numerical modeling and experimental characterizations show that the dual-gradient electrode differs from conventional electrodes with regard to their reaction current density distribution and electrodeposit distribution during charging. This work demonstrates a new design strategy of 3D electrodes for hybrid flow batteries to induce a desirable distribution of electrodeposits and achieve a high areal capacity at commercially relevant current densities.

Optimization Framework for Redox Flow Battery Electrodes with Improved Microstructural Characteristics

This research significantly advances the field of vanadium redox flow batteries (VRFBs) by introducing a pioneering approach to optimize the microstructural characteristics of carbon electrodes. Addressing the traditional challenge of...

Recent advances and perspectives of practical modifications of vanadium redox flow battery electrodes

Electrode modification of VRFB with “3Es”.

Sintered Electrospun Fibrous Electrodes via Compression and Laser Perforation for Redox Flow Battery

The principal sources of new renewable energy, such as solar and wind power, depend strongly on the weather conditions, leading to the unstable electric power supply. Energy storage systems (ESS) has been developed to address this problem. One of the most promising technologies for energy storage device is redox flow batteries due to its high capacity and design flexibility. In particular, the vanadium redox flow battery is considered as a next-generation battery because of its safety and high efficiency, but not yet widely deployed owing to its low power density. The carbonized electrospun fibrous materials have been utilized as electrodes to overcome the flaw, because of their high specific surface area for reaction, high porosity to support flow and diffusion, and good electrical conductivity through the interconnected fibers. Typically, smaller fiber is preferential due to the exponential increase of surface area, but the small pores among the fibers reduce the permeability, limiting the electrolyte transportation or increasing parasitic pumping costs. In this study, flow battery electrodes made of electrospun carbon fibers were synthesized by applying compression during the stabilization stage. The objective was to create flow battery electrodes with higher volumetric surface area to support the electrochemical reaction while retaining the permeability. A porosity reduction of 12% was attained by this method, yielding a 50% increase of volumetric surface area, while the in-plane permeability and tortuosity were found to remain consistent. In addition, the holes perforated by a carbon dioxide laser addressed the issue of low through-plane permeability caused by the compacted fibers. All electrospun samples outperformed commercial carbon mats in flow cell tests. The compressed samples showed markedly better performance in the activation region but showed serious mass transport polarization at higher current density. The laser perforations significantly eliminated this flaw, yielding the best performance over the entire range of current density. Figure 1

(Invited) Effect of Electrochemical Treatment and pH on the Kinetics of VII-VIII Reactions on Glassy Carbon Electrodes

Vanadium flow batteries (VFBs) are known for their long cycle life, high efficiency, and scalability, which make them suitable for various energy storage applications, including grid-scale energy storage, renewable energy integration, and remote power systems. There are several areas of active research on VFBs. These include electrolyte chemistry, electrode materials, cell design, system integration, modeling and simulation, performance optimization, scale-up and commercialization1.Carbon felts are often used as electrodes in VFBs due to their high electrical conductivity, chemical stability, and availability2. However, the surface properties of carbon materials can be influenced by the surrounding environment, leading to changes in their surface chemistry and reactivity. These changes in the environment can alter the kinetics of the vanadium reactions at the carbon surfaces, which in turn can impact the performance and efficiency of the battery system. Various electrochemical, chemical, and thermal treatments have been reported to have a significant impact on the carbon electrode kinetics3. It is thus important to investigate electrode kinetics to improve the performance of VFBs.Previously our group has reported that electrochemical treatments of carbon electrodes at different potentials significantly affect the electrode kinetics of VIV-VV and VII-VIII redox reactions4,5. The cathodic treatment of carbon electrode enhances the kinetics of VIV-VV redox reaction but inhibits the kinetics of VII-VIII redox reaction, while anodic treatment inhibits the kinetics of the VIV-VV redox reaction but enhances the kinetics of the VII-VIII redox reaction6-9. We have further investigated the effect of electrochemical treatment on the VIV-VV kinetics at glassy carbon electrodes following treatment in electrolytes of various pH. For all pHs investigated (pH 0 – pH 6), VIV-VV kinetics are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. The activating effect of cathodization increased markedly with increasing pH, whereas the deactivating effect of anodization appears approximately the same for all pHs. The observed effects are attributed to changes to electrode surface states by electrochemical polarization reactions, the rates of which appear to be pH dependent10.We have extended our investigation into the VII-VIII reaction kinetics. We will present results on the effect of electrochemical treatment and pH on the kinetics of VII-VIII reactions on glassy carbon electrodes. The kinetic rates for the VII-VIII couple on these electrodes are measured and compared using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Acknowledgements Varsha Sasikumar S P would like to thank the Irish Research Council (IRC) for a postgraduate scholarship to perform this research and acknowledge facilitation of this research by University of Limerick (UL), Ireland and South East Technological University (SETU), Ireland. References Aluko and A. Knight, IEEE Access, 11, 13773-13793 (2023).Kim et al., Scientific Reports, 4, 6906 (2014).K. Sankaralingam et al., Journal of Energy Storage, 41, 102857 (2021).N. Buckley et al., ECS Transactions, 98(9), 223-239 (2020).N. Buckley et al., Electrodes for Vanadium Flow Batteries (VFBs) In Flow Batteries: From Fundamentals to Applications, Chapter 24, Edited by. C. Roth et al., Wiley-VCH, ISBN 978-3-527-34922-7 (2023).Bourke et al., Journal of Electrochemical Society, 163, A5097 (2016).Bourke et al., Journal of Electrochemical Society, 162, A1547 (2015).A. Miller. et al., Journal of Electrochemical Society, 163, A2095-A2102, (2016).Bourke et al., Journal of Electrochemical Society, 170, 030504 (2023).Sasikumar et al., ECS Transactions, 109, 107 (2022).

Stereolithography 3D Printing As a Versatile Tool to Manufacture Porous Electrodes for Redox Flow Batteries

Redox flow batteries show potential for large-scale energy storage; yet their current costs limit widespread implementation. As the porous electrode microstructure defines the available surface area for electrochemical reactions, electrolyte transport, and fluid pressure drop [1], enhancing the electrode performance is a promising strategy to increase power density and thus reduce system costs. Conventional fibrous porous electrodes are repurposed from fuel cell gas diffusion electrodes and have not been tailored to sustain the requirements of liquid-phase electrochemistry. Therefore, new manufacturing techniques offering high control over the electrode microstructure and resulting properties need to be developed [2]. In this context, 3D printing techniques are uniquely suited to manufacture controlled and deterministic architectures, enabling the tuning of electrochemical performance and hydraulic resistance [3].In this work, we employ stereolithography 3D printing using a commercial desktop printer, followed by carbonization, to manufacture model grid structures and investigate their potential as redox flow battery electrodes. We use microscopy, tomography, spectroscopy, fluid dynamics, and electrochemical diagnostics, to evaluate the thermal behavior, manufacturing fidelity, and fluid and mass transport performance of ordered lattice structures in non-aqueous redox flow cells. We find that the flow field geometry (flow through versus interdigitated), printing orientation with respect to the printing platform, and pillar geometry (Figure 1a) influence the flow cell performance. The printing orientation impacts the surface roughness and resin spreading, which determines the electrode morphology, influencing the internal surface area, shrinking direction after carbonization, and thus the charge transfer, mass transfer, and hydraulic resistances. Moreover, mass transfer rates within the electrode are increased by altering the pillar shape to a helical or triangular design, or by using an interdigitated flow field design, providing directions to improve electrolyte mixing through the electrode. Although the commercial electrodes feature a greater internal surface area and therefore a better electrochemical performance, the area-normalized mass transfer coefficients and pressure drop can be reduced by utilizing 3D printed electrodes (Figure 1b-c). Going forward, 3D printing technologies that enable finer features combined with carbonization at elevated temperatures can be used to manufacture multi-scale electrode structures simultaneously providing excellent electrochemical performance and low hydraulic resistance. We anticipate that combining 3D printing with emerging computational topology optimization approaches could enable the bottom-up design of advanced electrode materials for electrochemical devices [4]. Acknowledgments The authors gratefully acknowledge the Dutch Research Council (NWO) through the Talent Research Program Veni (17324) and the 4TU.HTM grant for financial support.

Expanding the Scanning Electrochemical Microscopy Toolset for Evaluating Electron Transfer Kinetics of Concentrated and Specialized Redox Electrolytes on Carbon Surfaces

Performing quantitative measurements of heterogeneous electron transfer reactions at electrodes (e.g., determining k0 and a) under conditions of high redox active molecule concentration in solution, such as those encountered in electrolytes for redox flow batteries (RFBs), presents significant technical challenges. For example, attempting to use transient voltammetry methodology quickly leads to limitations imposed by iR drop, as currents can be large and resistance, especially in non-aqueous systems, can be high. Additionally, using steady-state techniques based on convective principles, such as the rotating disk electrode (RDE), involve the use of relatively large equipment, with moving parts, and usually with requirements of tens to hundreds of mL of solution, which may be limiting for exploring new compounds at high concentration.To address these issues, here we introduce the use of scanning electrochemical microscopy (SECM) for the determining the rates of electron transfer of redox active species at high concentration in non-aqueous [1] and other unconventional systems, such as deep eutectic solvents. SECM enables the resolution of higher rates of electron transfer compared to transient voltammetry and RDE, and it also enables experiments with spatial resolution, enabling the exploration of reactivity on various sites of a heterogeneous electrode. In this presentation, we will describe theoretical and practical aspects of these measurements, and we will demonstrate their utility using two model systems. The first one consists on the observation of inherent rate asymmetries observed for ferrocene derivatives, ubiquitous redox probes, at the graphite/carbonate solvent interface. These asymmetries are not present on aqueous systems or metallic electrodes, demonstrating the ability of the SECM technique to capture unique behaviors. In the second case, we will discuss how SECM measurements can be used on deep eutectic solvents such as ethaline to address how interactions between redox actives and the electrode or the solvent systems modulate the rate of electron transfer. By systematically modifying the strength of interactions by means of molecule choice, solvent composition, and electrode type and structure, we can gain insight into the processes that determine reactivity at redox flow battery electrodes. This insight is critical for exploring the interfacial aspects such as adsorption, passivation, and double-layer effects on kinetics of electron transfer.[1] Gaddam, R.; Sarbapalli, D.; Howard, J.; Curtiss, L.A.; Assary, R.S.; Rodríguez-López, J. An SECM-Based Spot Analysis for Redoxmer-Electrode Kinetics: Identifying Redox Asymmetries on Model Graphitic Carbon Interfaces Chem: Asian J., 2023, 18, 2, e202201120. Figure 1

Scaling up Electrode Manufacturing with Non-Solvent Induced Phase Separation Technology

Grid-scale energy storage technologies must be deployed at a massive scale to balance the mismatch between energy generation using renewable technologies and demand. Redox flow batteries are an emerging technological option for large-scale and multi-hour electrochemical energy storage thanks to their ability to decouple energy and power1. Despite their intrinsic advantages, the current elevated costs of this technology hinders commercialization2. To improve cost competitiveness, research efforts have focused on developing novel electrolyte chemistries and optimized reactor concepts. To the latter, optimizing the porous electrode microstructure and surface chemistry offers a promising pathway to increase the performance of flow batteries. However, porous electrodes design is challenging as they must fulfil contradictory requirements such as providing high surface area for electrochemical reactions, facilitating mass transport of reactive species, and maintaining low operational pressure drop. Furthermore, state-of-the-art porous electrodes have been repurposed from other mature electrochemical technologies but have not been tailored for the unique requirements of redox flow batteries3.Non-solvent induced phase separation (NIPS) has been recently introduced as a versatile method to synthesize porous structures suitable for RFBs with unique properties, which are unattainable with current fibrous materials4,5. Drawing inspiration from membrane fabrication techniques, we reengineered the method for the synthesis of porous electrodes for use in redox flow batteries. The porous electrodes synthesized with NIPS were tested in a single-electrolyte cell configuration and then in an all-vanadium redox flow battery, showing promising electrochemical performance in comparison with existing commercial fibrous carbon materials. In this presentation, I will discuss our current efforts to scale up the NIPS method to manufacture electrodes at industrial scale. We believe that non-solvent induced phase separation is a cost-effective alternative to traditional carbon fibrous materials thanks to the few simpler steps required for the electrode preparation. Based on technoeconomic modeling, we estimate that the production cost of the NIPS electrodes can be less than half of the production costs of traditional carbon fibrous electrodes6. Moreover, the phase separated electrodes do not require post-manufacturing heat treatment to increase the surface area and wettability, which further translates into savings on energy costs. In this project, we aspire to scale-up the NIPS materials to a final size, after carbonization, of 30·30 cm2 while retaining similar microstructural and electrochemical performance properties as in laboratory scale. We perform a suite of microscopy, spectroscopic and flow cell diagnostics to correlate the electrode microstructure, surface chemistry and device performance. In this presentation, I will discuss the scalability of the method, reproducibility based on statistical analysis of sample properties and performance, and finally electrochemical performance on two flow battery chemistries.References Markard, J. (2018). The next phase of the energy transition and its implications for research and policy. Nature Energy, 3(8), 628-633.Darling, R. M. (2022). Techno-economic analyses of several redox flow batteries using levelized cost of energy storage. Current Opinion in Chemical Engineering, 37, 100855.Forner-Cuenca, A., and Brushett, F. R. (2019). Engineering porous electrodes for next-generation redox flow batteries: recent progress and opportunities. Current Opinion in Electrochemistry, 18, 113-122.Wan, C. T. C., Jacquemond, R. R., Chiang, Y. M., Nijmeijer, K., Brushett, F. R., & Forner‐Cuenca, A. (2021). Non‐Solvent Induced Phase Separation Enables Designer Redox Flow Battery Electrodes. Advanced Materials, 33(16), 2006716.Jacquemond, R. R., Wan, C. T. C., Chiang, Y. M., Borneman, Z., Brushett, F. R., Nijmeijer, K., & Forner-Cuenca, A. (2022). Microstructural engineering of high-power redox flow battery electrodes via non-solvent induced phase separation. Cell Reports Physical Science, 3(7), 100943.Minke, Christine, Ulrich Kunz, and Thomas Turek. "Carbon felt and carbon fiber-A techno-economic assessment of felt electrodes for redox flow battery applications." Journal of Power Sources342 (2017): 116-124.

Elucidating in-situ heat generation of LiFePO4 semi-solid lithium slurry battery under specific cycling protocols

Semi-solid lithium slurry battery combines the advantages of the high energy density of lithium-ion battery and the flowability of flow battery electrodes and has attracted attention in energy storage. Elucidating the heat generation during cycling is crucial for evaluating the safety. However, there is a relative lack of research in this field of semi-solid lithium slurry battery. Herein, the heat generation of lithium iron phosphate (LiFePO4) semi-solid lithium slurry battery during cycling under specific cycling protocols is investigated in this work. The results show that the battery has lower heat generation when cycling at an ambient temperature of 35–50 ℃ and a charging cutoff voltage below 4.0 V, meanwhile, it maintains considerable capacity. However, when the charging cutoff voltage exceeds 4.4 V, the cyclic heat generation of the battery increases significantly, and the capacity attenuates significantly. Meanwhile, the classical equation for calculating battery heat generation of lithium-ion battery is no longer reliable. This is mainly because the electrolyte content of the semi-solid lithium slurry battery is too high (over 80 %), and at high charging cutoff voltage, the side decomposition reactions of the electrolyte increase significantly. Subsequent characterization of electrode materials also confirms this inference. This study can provide a clearer understanding of the safety of semi-solid lithium slurry battery and has guiding implications for industrial applications.