Understanding Effective Electronic Conductivity of Slurry Electrodes Used in Electrochemical Flow Capacitors and All-Iron Redox Flow Batteries
Authors: Ke Xinyou , Wainright Jesse S. , Savinell Robert F. 
Published: February 2020

Slurry electrodes are being considered in electrochemical systems1-5 for decoupling power and energy in electrochemical flow capacitors (EFCs) and for redox flow batteries (RFBs) involving electrodeposition reactions. In our all-iron slurry flow batteries (IFBs)3,4 utilizing very low-cost electrolyte materials, the slurry electrodes are used in the negative side involving iron plating/de-plating. During charging, iron is plated onto the slurry particles and then the particles carry the iron metal out of the electrochemical cell to be stored in the external electrolyte reservoirs. The slurry electrodes are synthesized by dispersing conductive carbon particles into electrolyte contained dissolved iron species. The effective electronic conductivity of slurry electrodes affects current density distributions, over-potential boundary layers, utilizations of slurry and electrochemical performance of EFCs and IFBs4. Therefore, fundamental studies of slurry electronic conductivity are needed. Possible factors affecting the effective electronic conductivity of a slurry include carbon loading, mean linear velocity or shear rate, electrolyte ionic strength, particle size, particle shape, surface chemistry, etc. In this work, we studied the effect of mean linear velocity through the slurry electrode channel ranging from stagnant to 22 cm/s on slurry effective electronic conductivity for various loadings of 660R carbon black dispersed in deionized water. A DC measurement using a chronoamperometry technique was made in a 3.5 cm2 electrode cell design. Figure 1 shows the variations of effective electronic conductivity for three different loadings, 5% w.t., 10% w.t. and 15% w.t. of 660R carbon black slurry under mean linear velocity increasing from 0 to 22 cm/s. The Figure 1 presents evidence that shear rates induced by different mean linear velocities/flow rates have certain effects on effective electronic conductivity of slurry electrodes. This is may be due to changes in the agglomeration patterns5of slurry particles. The motivation of this work is to explore possible mechanisms that lead to a better understanding of slurry electrodes. The ultimate goal is to improve the effective electronic conductivity of slurry electrodes and optimize the electrochemical performance of EFCs and IFBs.
Acknowledgement
This work is supported in-part by the all-iron flow battery project (award number: DE-AR0000352) funded by Department of Energy (DOE) of the United States.
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Figure 1