In Situ Kinetics Studies in All-Vanadium Redox Flow Batteries

Aaron, Douglas; Sun, Che-Nan; Bright, Michael; Papandrew, Alexander B.; Mench, Matthew M.; Zawodzinski, Thomas A.

doi:10.1149/2.001303eel

Cited by 161 publications

(110 citation statements)

References 12 publications

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“…The polarization of the V(ii)/V(iii) couple exceeds that of the V(iv)/V(v) couple for this particular set of materials and activation procedures. This observation is consistent with the recent findings of Aaron et al(4).…”

supporting

confidence: 94%

Half-Cell, Steady-State Flow-Battery Experiments

Darling

Perry

2013

ECS Trans.

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An experimental approach designed to separately test the positive and negative sides of a redox flow battery is discussed. Circulating a single electrolyte through a cell so that oxidation occurs on one electrode and reduction occurs on the other electrode eliminates the problem of reactant crossover that occurs when different electrolytes are placed on either side of the cell. This approach allows phenomena associated with the positive and negative electrode-electrolyte combinations to be studied in isolation. Polarization curves, steady-state potential holds, and potentialcycling experiments are presented as examples of results that can be obtained with this approach. The impact of side reactions on the results is also discussed.

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supporting

confidence: 94%

Half-Cell, Steady-State Flow-Battery Experiments

Darling

Perry

2013

ECS Trans.

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“…Most studies in the past, however, report overall battery parameters (cell resistance or efficiency) and hence conclude with rather general statements. More detailed investigations using reference electrodes or non‐symmetric felt combinations at the positive and negative electrodes have shown that the negative electrode is more problematic with respect to the kinetic overpotential. In fact, recent systematic studies of the electrochemical pretreatment of various carbons (glassy carbon, carbon fibers, graphite) have even revealed opposing effects for both redox couples when subjected to anodic or cathodic pre‐treatment .…”

Section: Introductionmentioning

confidence: 99%

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

2017

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Carbon felts based on rayon and polyacrylonitrile (PAN) precursors constitute the most widespread porous electrode material for vanadium redox‐flow batteries. Since the raw materials exhibit rather poor wettability, it has become common practice to apply oxidative surface treatments prior to use in flow batteries. This study investigates the electrode‐specific effects of raw and thermally oxidized (PAN and rayon‐based) carbon felts on their electrochemical behavior at the negative and the positive electrode in all vanadium redox‐flow batteries. By means of steady‐state single cell measurements, it is verified that oxidative surface treatment has opposite effects on negative and positive redox couples and that the beneficial influence on the vanadium redox‐flow battery performance is mainly brought about by substantially improved charge‐transfer kinetics at the negative electrode. Similarly, the type of carbon precursor and the degree of graphitic character have a particular impact on the electrode behavior.

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“…Unlike the aforementioned four-tank and two-tank EFC approaches, these experiments were performed using only a single tank. This approach is analogous to the symmetric cell experiments of flow batteries; 18,19 instead of storing the positively and negatively charged slurries for subsequent discharge, the outflows from both half cells are simply remixed to a uniform uncharged state in the single reservoir. Doing so allows for consistent uncharged conditions at the inlets of the EFC half-cells.…”

Section: Methodsmentioning

confidence: 99%

Current Density Scaling in Electrochemical Flow Capacitors

Hoyt

Wainright

Savinell

2015

J. Electrochem. Soc.

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Electrochemical flow capacitors (EFCs) are a recently developed energy storage technology. One of the principal performance metrics of an EFC is the steady-state electrical current density that it can accept or deliver. Numerical models exist to predict this performance for specific cases, but here we present a study of how the current varies with respect to the applied cell voltage, flow rate, cell dimensions, and slurry properties using scaling laws. The scaling relationships are confirmed by numerical simulations and then subsequently by comparison to results from symmetric cell EFC experiments. This modeling approach permits the delimitation of three distinct operational regimes dependent on the values of two nondimensional combinations of the pertinent variables (specifically, a capacitive Graetz number and a conductivity ratio). Lastly, the models and nondimensional numbers are used to provide design guidance in terms of criteria for proper EFC operation. The electrochemical flow capacitor is a new energy storage technology that has gained interest for grid-scale applications.1-4 EFCs store energy by charging the double layers that exist at the interfaces between the particles and an electrolyte solution in a flowable slurry electrode. The slurry particles with their charged surfaces are then subsequently transferred to external tanks for energy storage. The stored energy can be recovered by pumping these particles back through the cell during discharge. As is the case for flow batteries, external storage of the charged slurry allows for decoupling of power and energy capacity.A schematic of a four-tank EFC is shown in Figure 1. This design consists of two half cells separated by a membrane. The membrane prevents electronic charge transfer between the negative and positive half-cells but permits the exchange of ions. During charging, slurry is pumped from tanks of uncharged particles through the cell in order to be charged; after passing through the cell this slurry is then stored in a separate set of tanks for charged particles.For this four-tank implementation, discharge then requires reversal of the pumps to redirect the charged particles back into the cell. This approach requires the double layer capacity of the entire slurry flow to be charged as fully as possible upon leaving the cell (i.e. the slurry needs to be fully utilized such that all of the available surfaces are charged to half of the voltage applied across the entire EFC cell). This four-tank approach allows immediate extraction of energy at the charging potential as all of the stored slurry at any point in time is fully charged. However, the necessity of fully charging the entire slurry stream can place severe restrictions on the maximum achievable current density. An alternative two-tank approach, 5 foregoes the separate storage tanks for the charged and uncharged slurries and instead operates in a continuous mode. This approach is similar to the charging/discharging of conventional (non-flowing) capacitors. When operating in this mode la...

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In Situ Kinetics Studies in All-Vanadium Redox Flow Batteries

Cited by 161 publications

References 12 publications

Half-Cell, Steady-State Flow-Battery Experiments

Half-Cell, Steady-State Flow-Battery Experiments

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

Current Density Scaling in Electrochemical Flow Capacitors

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