Figure - available from: Journal of Physics D: Applied Physics
This content is subject to copyright. Terms and conditions apply.
X-ray CT imaging of the flow cell containing static electrolyte obtained using a lab-based CT system with a 4× objective lens (effective pixel size of 3.8 µm) comprising 1601 projections of 7 s exposure. Areas of incomplete wetting of the felt can be seen in the orthoslice (a) and segmentation of the Ti current collector (grey), felt (red) and felt containing electrolyte (purple) is possible (b). The electrolyte volume has been removed in image (c) and a Ti mesh current collector was employed in this instance.
Source publication
Flow batteries represent a possible grid-scale energy storage solution, having many advantages such as scalability, separation of power and energy capabilities, and simple operation. However, they can suffer from degradation during operation and the characteristics of the felt electrodes are little understood in terms of wetting, compression and pr...
Similar publications
Flow batteries represent a possible grid-scale energy storage solution, having many advantages such as scalability, separation of power and energy capabilities, and simple operation. However, they can suffer from degradation during operation and the characteristics of the felt electrodes are little understood in terms of wetting, compression and pr...
Citations
... As shown in Figure 10c, R. Jervis et al. designed a mini flow battery for in situ X-ray computed tomography (CT) to study CF materials. [93] The in situ characterization method enabled nondestructive characterization of a range of microstructures of CF fibers, electrolytes and pore phases. This device correlated electrode degradation and microstructural changes with electrochemical performance in flow batteries, providing a basis for evaluating the performance of flow batteries and electrode materials. ...
Flow batteries (FBs) have been demonstrated in several large‐scale energy storage projects, and are considered to be the preferred technique for large‐scale long‐term energy storage in terms of their high safety, environmental friendliness, and long life, including all‐vanadium flow batteries (VFBs) and Fe‐Cr flow batteries (ICFBs). As the electrochemical reaction site, the electrode parameters, such as the specific surface area, active site, and so on, have a significant impact on the flow battery performance and reliability. Extensive research has been carried out on electrode modification to improve the current density and energy efficiency of the FBs. In this review, the reaction mechanisms of VFBs and ICFBs are discussed in detail firstly, and then the electrodes modification methods are overviewed and summarized from four aspects: self‐modification, carbon‐based electrocatalysts, metal‐based electrocatalysts and composite electrocatalysts. Finally, the recent catalytic mechanism, in situ characterization technology, and future research directions are presented.
... Among the techniques used so far to image RFB electrodes, fluorescence measurements require transparent cells and cannot image the electrode through the thickness, 80 while Xray tomography offers high in-plane resolution but necessitates cell modifications. 81 Neutron radiography, on the other hand, is highly sensitive to water molecules and neutrons are not attenuated strongly by most housing materials (e.g., aluminum, steel, carbon), enabling imaging under representative conditions with minimal cell modifications. More importantly, neutrons allow imaging of the entire electrode thickness and can probe the internal wettability of electrodes, offering a powerful tool to compare different electrode treatments. ...
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.
... In 2016, Jervis et al. designed a miniature flow cell to conduct in situ imaging of RFB electrodes with synchrotron X-ray CT [47]. This work proved the capability of synchrotron CT to image electrode structure and electrolyte variation under an operating environment. ...
... The cell was built in a rotational symmetry as shown in Figure 3a, where the attenuation of the beam at all angles was kept constant to reduce the artefacts from the reconstructions. This work compared CT images by SRS and lab-based CT systems, showing that the former achieved higher signal-to-noise ratio and better segmentation of electrode fibres from the electrolyte phase in a significantly reduced time frame, which enables imaging of RFBs with in situ/operando X-ray CT [47]. ...
Operando and in situ characterisation studies with the assistance of high energy light produced by synchrotrons are becoming increasingly attractive in the energy storage area, allowing for nondestructive investigations of material properties and device behaviour in realistic working environments, and with high temporal resolution afforded by the latest generation of high-flux beamlines. Many operando synchrotron techniques are well suited to redox flow batteries, which undergo redox changes of the active species in their electrolytes when flowed through porous electrodes. There is a large variety of redox flow battery designs and chemistries, spanning transition metal solutions, hybrid gas-liquid devices, plating and stripping mechanisms and organic redox species. This review presents an overview of recent progress and preponderance of synchrotron techniques in investigating the current issues of redox flow batteries. For each synchrotron X-ray analytical approach, practical examples and breakthrough findings are outlined and the potential applications on the newly developed redox flow batteries are discussed.
... Other technologies, such as MABs, fuel cells, and electrolysers utilize this same fundamental "sandwich" type architecture. (Reproduced, with permission, from Jervis et al.[20]) ...
Society already possesses an array of technologies that can decarbonize the U.S. power grid, but social, economic, and political barriers may impinge their deployment in the timescales necessary to thoroughly curb climate change. This perspective emphasizes two of the largest barriers specific to battery adoption: cost and materials. Battery costs, particularly for more nascent storage technologies, are generally still prohibitively high, largely due to an inability to overcome small-scale production; we explore an array of political and economic strategies to more rapidly promote deployment and reduce costs. One key contributor to elevated costs is the relatively higher value of essential battery materials. Smaller scale, concentrated supply chains result in materials criticality, which raises prices and challenges rapid scale-up. Here, both technical and economic solutions exist, and some are reviewed in this work. Generally, there is a tension between a company’s competitive advantage (i.e., proprietary design and manufacturing) and more cost-efficient production (i.e., centralization, standardization, etc.), that must be overcome via political and economic incentivization. Ultimately, greater urgency is needed in the public and private investment spaces to combat climate change by enabling the rapid development and deployment of the best solutions.
... Imaging techniques offer a good alternative, as they allow operando measurements while the wetting and non-wetting phase within the porous material can be tracked. Among the techniques used so far to image RFB electrodes, fluorescence measurements require transparent cells and cannot image the electrode through thickness [58] while X-ray tomography offers high in-plane resolution but necessitates heavy cell modification [59]. Neutron radiography, on the other hand, is highly sensitive to water molecules and neutrons are not attenuated strongly by most housing materials (e.g., aluminum, steel), enabling imaging under representative conditions with minimal cell modification. ...
The surface properties of porous carbonaceous electrodes govern the performance, durability, and ultimately the cost of redox flow batteries. As prepared, commercially available carbon fiber electrode interfaces suffer from limited kinetic activity and incomplete wettability, fundamentally limiting the performance. Here, we propose electrografting as a versatile and facile technique to enable task-specific functionalization of the ubiquitous carbon fiber-based porous electrodes. We elect to investigate taurine as a model molecule as the sulfonic acid group is anticipated to provide hydrophilic and active interfaces whereas the amine group allowing covalent attachment to the carbon surface would enhance stability. We perform hydrodynamic voltammetry and find enhanced kinetic rates of taurine treated model electrodes and flow cell experiments reveal superior mass-transport properties of taurine treated porous cloth electrodes. Additionally, we perform operando neutron radiography to visualize electrolyte infiltration within the electrode in a flow cell setup and find superior wettability of porous electrodes functionalized with taurine. Electrografting emerges as a promising technique to functionalize three-dimensional porous electrodes for redox flow batteries and other electrochemical technologies for energy conversion and storage.
... Jervis et al. [176] employed X-ray computed tomography (CT) to study the carbon felt material during the operation of a VRFB cell. To maximize the X-ray penetration, the cell was constructed from polypropylene. ...
Progress in renewable energy production has directed interest in advanced developments of energy storage systems. The all-vanadium redox flow battery (VRFB) is one of the attractive technologies for large scale energy storage due to its design versatility and scalability, longevity, good round-trip efficiencies, stable capacity and safety. Despite these advantages, the deployment of the vanadium battery has been limited due to vanadium and cell material costs, as well as supply issues. Improving stack power density can lower the cost per kW power output and therefore, intensive research and development is currently ongoing to improve cell performance by increasing electrode activity, reducing cell resistance, improving membrane selectivity and ionic conductivity, etc. In order to evaluate the cell performance arising from this intensive R&D, numerous physical, electrochemical and chemical techniques are employed, which are mostly carried out ex situ, particularly on cell characterizations. However, this approach is unable to provide in-depth insights into the changes within the cell during operation. Therefore, in situ diagnostic tools have been developed to acquire information relating to the design, operating parameters and cell materials during VRFB operation. This paper reviews in situ diagnostic tools used to realize an in-depth insight into the VRFBs. A systematic review of the previous research in the field is presented with the advantages and limitations of each technique being discussed, along with the recommendations to guide researchers to identify the most appropriate technique for specific investigations.
... In addition to the visualization of structural changes in dry carbon electrodes [26,29,42], X-ray radiography and tomography can be applied to trace the electrolyte flow path, including possible hindrances, during the cell operation. In 2016, Jervis et al. [43] presented a cylindrical miniature flow cell that could resolve the carbon material, the static electrolyte, and air residues. Tariq et al. [30] used time-resolved X-ray μ-CT to visualize the imbibition of vanadium electrolyte into dry carbon paper electrodes. ...
A porous carbon electrode fully saturated with electrolyte is one crucial aspect of vanadium redox flow battery efficiency. It determines the electrochemically active surface area, provides more active sites for the reaction during operation, and prevents local degradation due to inhomogeneities in electrolyte distribution. We investigate the electrolyte invasion and distribution at open-circuit potential in heat-treated carbon felt electrodes at varying compression ratios and flow field configurations, using synchrotron X-ray radiography. The quantitative analysis yields time-resolved saturation values of the injection and resolves local changes in saturation to detect areas of lower electrolyte accessibility. Compression ratios of 50% and above lead to a high electrode utilization with more than 97% saturation over the felt thickness. In contrast, carbon felts at 25% and 17% compression only reach 49% and 15% saturation near the flow fields. However, increasing the flow velocity after the injection causes the boundary area next to the flow field to fill even at low compressions. This area is especially critical for the electrode utilization since it is invaded after the bulk. Depending on the compression level, it does not reach full saturation.
... Consequently, it is somewhat surprising that they are not yet widely applied in recent VRFB studies to validate the hypothesis on the electrocatalytic effect of bismuth. To the best of our knowledge the only studies exploiting X-ray imaging techniques in context of the VRFB system are the following ones focusing on the electrolyte and metal free carbon felt electrode behaviour [32][33][34][35]. ...
Decorating carbon felt electrodes with bismuth and bismuth oxide nanoparticles is proposed to be a promising strategy for enhancing the sluggish electron transfer kinetics of the negative half-cell reaction in vanadium redox flow batteries. However, regarding the highly corrosive electrolyte solution, major concerns on the stability of the solid bismuth phase and thus on the local catalyst distribution and catalyst functionality emerge. With this study we present a novel in-operando cell design allowing for X-ray imaging during battery tests in laboratory scale dimensions. In this manner, we verify a dissolution of the bismuth/bismuth oxide particles in open circuit potential condition at SOC = 0 (SOC: state of charge) as well as a re-deposition during the charging process of the battery. No dissolution during the discharging process can be detected. With this knowledge, the effect of the bismuth/bismuth oxide distribution on the electrochemical performance of the battery is investigated. By performing the deposition during the charging process at different electrolyte flow rates, different deposition patterns are obtained. However, independent of the deposition pattern, similar cell performances are achieved that put the enhancement effect by bismuth as heterogeneous catalyst into question.
... Recent developments in transmission x-ray microscopy (TXM) techniques such as x-ray radiography and computed tomography (CT) have enabled the acquisition of high-resolution images at both the micro and nano scales with relatively short scan times [1][2][3][4][5][6][7][8]. These advances in TXM, have enabled imaging of processes within electrochemical energy devices such as batteries, fuel cells and electrolyzers. ...
Synchrotron x-ray imaging techniques, like x-ray computed tomography (CT) and radiography have proven instrumental in expanding the communities knowledge of complex transport and reaction kinetics in electrochemical devices such as fuel cells and electrolyzers. This work presents the development of novel x-ray CT imaging techniques for operando visualization of water within low temperature fuel cells at spatial resolutions spanning the micro and nano scales. The design of operando sample holders, for both micro x-ray CT and nano CT experiments is described in depth, and prototypes of these sample holders were evaluated across a set of requirements, the most important of which are x-ray transmissibility, electrical conductivity and mechanical stability. Water segmentation from micro x-ray CT data was enabled by an image subtraction method, where the image without water is subtracted from the one with water. Through iterative experimentations, the operando nano CT cell was developed to optimize mechanical compression, electric conductivity and gas flow. While three-dimensional fuel cell reconstructions were shown possible, there remain challenges to overcome at typical lower energies (8 keV) due to beam damage, whereas it is not as significant for higher energies (>17.5 keV)
... 252 Methods such as 3D X-ray tomography and radiography (Fig. 10) 253 can be used to reveal the internal structure of electrodes over a range of length scales(tens of cm to sub-nm). 254,255 The application of tomography to carbon-based materials for energy storage application has been slowly growing. Traditionally, the relatively low Z number of carbon challenge the rendering of electrode images using X-ray computed tomography (XCT). ...
In this article, the different approaches reported in the literature for modelling electrode processes in redox flow batteries (RFBs) are reviewed. Models for RFBs vary widely in terms of computational complexity, research scalability and accuracy of predictions. Development of models of RFBs have been quite slow in the past but in recent years researchers have reported on a range of modelling approaches for the optimization of RFB systems. Flow and transport processes, and their influence on the electron transfer kinetics, play an important role in the performance of RFBs. Macro-scale modelling, typically based on a continuum approach for the porous electrode modeling, have been used to investigate current distribution, to optimize cell design and to support techno-economic analyses. Microscale models have also been developed to investigate the transport properties within porous electrode materials. These microscale models exploit experimental tomographic techniques for characterization of the three-dimensional structures of different electrode materials. New insights into the effect of the electrode structure on transport processes are being provided from these new approaches. Modelling the flow, transport, electrical and electrochemical processes within the electrode structure is a developing area of research, and there are significant variations in the requirements of models for different redox systems, in particular for multiphase chemistries (gas-liquid, solid-liquid etc.) and for aqueous and nonaqueous solvents. Further development is essential to better understand the kinetic and mass transport phenomena in the porous electrodes, and multiscale approaches are also needed to enable optimization across the relevent length scales.
