Trust is good, control is better: a review on monitoring and characterization techniques for flow battery electrolytes

Nolte, Oliver; Volodin, Ivan A.; Stolze, Christian; Hager, Martin D.; Schubert, Ulrich S.

doi:10.1039/d0mh01632b

Cited by 64 publications

(54 citation statements)

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“…[7][8][9][10] Understanding modes of performance loss requires diagnostic tools that can monitor the RFB throughout its operating lifetime. 11 Such insights into the state of the system would allow researchers to interrogate mechanisms of component failure and operators to improve asset utilization and maintenance planning.…”

Section: Introductionmentioning

confidence: 99%

A microelectrode-based sensor for measuring operando active species concentrations in redox flow cells

Neyhouse

Tenny

Chiang

et al. 2021

Preprint

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The assessment of candidate materials for redox flow batteries requires effective diagnostic techniques for monitoring the evolution of electrolyte state of charge and state of health to interrogate time-dependent changes in system behavior. Further, such tools can be applied in practical embodiments to inform maintenance schedules and optimize energy utilization. In this work, we develop and test a flow-through, microelectrode-based electrochemical sensor to

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Section: Introductionmentioning

confidence: 99%

A microelectrode-based sensor for measuring operando active species concentrations in redox flow cells

Neyhouse

Tenny

Chiang

et al. 2021

Preprint

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“…Accurate and reliable online SOC determination is necessary to improve battery control and to achieve efficient long term operation of the system [7]. A number of methods exist for estimation of the SOC, including potential measurement, UV-Vis spectroscopy, density or conductivity [8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Half-Cell State of Charge Monitoring for Determination of Crossover in VRFB—Considerations and Results Concerning Crossover Direction and Amount

Haisch

Holtz

et al. 2021

Membranes

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Membranes play a crucial role in efficiency and longevity of flow batteries. Vanadium flow batteries suffer self-discharge and capacity fading due to crossover of electrolyte components through the membrane from one battery half-cell to the other. We consider the impact of vanadium species crossing ion exchange membranes on state of charge of the battery and we present a simple method to determine crossover characteristics using half-cell open circuit potential measurements. State of charge for the negative and positive half-cell is simulated based on assumptions and simplifications for cation and anion exchange membranes and different crossover parameters. We introduce a crossover index "IndXovr" which enables the determination of crossover direction from state of charge data for the negative and positive half-cell and therewith identification of the half-cell in which predominant self-discharge occurs. Furthermore IndXovr allows statements on crossover amount in dependence on state of operation. Simulated case studies are compared to experimental state of charge values estimated from half-cell potential measurements. Our results reveal that half-cell potential monitoring respectively half-cell SOC estimation, is a simple and suitable tool for the identification of crossover direction and relative amount of crossover in VFB.

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“…[3] Thus, methods to accurately assess the key electrolyte state variables state of charge (SOC) and state of health (SOH) are of paramount importance for these RFB concepts.As recently reviewed by our group, the most established SOC monitoring methods for RFBs are represented by Coulomb counting (CC) and measurements of the electrolytes' redox potential. [4] Both methods require either relatively simple measurement equipment (open circuit voltage (OCV) cells) or are implemented into a battery management system (CC) and can therefore be used independently of the RFB chemistry. Nevertheless, both methods are prone to error accumulation and long-term changes and, thus, require frequent recalibration.…”

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confidence: 99%

“…Apart from the aforementioned methods, spectroscopic methods have as well been used to determine flow battery state variables, in particular for the VRFB, although other chemistries have been investigated as well. [4,5] Especially UV-vis spectroscopic measurements have been used in this context, due to the relatively simple and reliable setup as well as their ability to provide half-cell resolution. However, due to the nonlinearity of the absorption for optically dense mixtures, as described by the Beer-Lambert law, the hitherto published methods generally rely on empirically-derived calibrations or extremely thin transmittance measurement cells.…”

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confidence: 99%

“…However, due to the nonlinearity of the absorption for optically dense mixtures, as described by the Beer-Lambert law, the hitherto published methods generally rely on empirically-derived calibrations or extremely thin transmittance measurement cells. [4] Furthermore, UV-vis data of molecular compounds usually bear limited structural information, as the The transition from fossil to renewable energy sources requires adequate storage technologies due to the intermittency of the supplied energy. With respect to this, organic redox-flow batteries (ORFBs) represent a promising concept for the storage of electricity on a large scale at economically justifiable costs.…”

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confidence: 99%

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IR Spectroscopy as a Method for Online Electrolyte State Assessment in RFBs

Nolte

Geitner

Hager

et al. 2021

Advanced Energy Materials

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viability. However, this shift in energy production has a major drawback: While conventional power plants are designed to produce energy on demand with constant output, the intrinsic intermittency of wind, and solar energy productions calls for suitable energy storage solutions, in which redox flow batteries (RFBs) represent a promising solution. [1] Compared to the current commercially available inorganic systems based on vanadium (VRFB) or zinc-bromine/zinc-iron, the use of organic active materials in RFBs promises a decoupling from commodity prices as well as an environmentally and socially responsible production of the storage materials. [2] However, organics are prone to decomposition reactions on the molecular level that inevitably occur within the pursued decadal lifetimes required for an economic operation of RFBs. [3] Thus, methods to accurately assess the key electrolyte state variables state of charge (SOC) and state of health (SOH) are of paramount importance for these RFB concepts.As recently reviewed by our group, the most established SOC monitoring methods for RFBs are represented by Coulomb counting (CC) and measurements of the electrolytes' redox potential. [4] Both methods require either relatively simple measurement equipment (open circuit voltage (OCV) cells) or are implemented into a battery management system (CC) and can therefore be used independently of the RFB chemistry. Nevertheless, both methods are prone to error accumulation and long-term changes and, thus, require frequent recalibration. Furthermore, the CC method can only provide full-cell resolution (i.e., battery state variables) instead of a more informative half-cell resolution, that is able to provide an electrolyte-based state assessment. Apart from the aforementioned methods, spectroscopic methods have as well been used to determine flow battery state variables, in particular for the VRFB, although other chemistries have been investigated as well. [4,5] Especially UV-vis spectroscopic measurements have been used in this context, due to the relatively simple and reliable setup as well as their ability to provide half-cell resolution. However, due to the nonlinearity of the absorption for optically dense mixtures, as described by the Beer-Lambert law, the hitherto published methods generally rely on empirically-derived calibrations or extremely thin transmittance measurement cells. [4] Furthermore, UV-vis data of molecular compounds usually bear limited structural information, as the The transition from fossil to renewable energy sources requires adequate storage technologies due to the intermittency of the supplied energy. With respect to this, organic redox-flow batteries (ORFBs) represent a promising concept for the storage of electricity on a large scale at economically justifiable costs. However, these storage technologies can only be operated reliably if parameters representing the actual condition of the storage medium (i.e., the electrolyte) can be accurately assessed. These so-called electrolyte state variables are ...

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Trust is good, control is better: a review on monitoring and characterization techniques for flow battery electrolytes

Abstract: Flow Batteries (FBs) currently are one of the most promising large-scale energy storage technologies for energy grids with a large share of renewable electricity generation. Among the main technological challenges...

Cited by 64 publications

References 531 publications

A microelectrode-based sensor for measuring operando active species concentrations in redox flow cells

A microelectrode-based sensor for measuring operando active species concentrations in redox flow cells

Half-Cell State of Charge Monitoring for Determination of Crossover in VRFB—Considerations and Results Concerning Crossover Direction and Amount

IR Spectroscopy as a Method for Online Electrolyte State Assessment in RFBs

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