3D-printed conductive static mixers enable all-vanadium redox flow battery using slurry electrodes

Abstract

State-of-the-art all-vanadium redox flow batteries employ porous carbonaceous materials as electrodes. The battery cells possess non-scalable fixed electrodes inserted into a cell stack. In contrast, a conductive particle network dispersed in the electrolyte, known as slurry electrode, may be beneficial for a scalable redox flow battery. In this work, slurry electrodes are successfully introduced to an all-vanadium redox flow battery. Activated carbon and graphite powder particles are dispersed up to 20 wt.% in the vanadium electrolyte and charge-discharge behavior is inspected via polarization studies. Graphite powder slurry is superior over activated carbon with a polarization behavior closer to the standard graphite felt electrodes.3D-printed conductive static mixers introduced to the slurry channel im-prove the charge transfer via intensified slurry mixing and increased surface area. Consequently, a significant increase in the coulombic efficiency up to 80 % and energy efficiency up to 50 % is obtained. Our results show that slurry electrodes supported by conductive static mixers can be competitive to state-of-the-art electrodes yielding an additional degree of freedom in battery design. Research into carbon properties (particle size, internal surface area, pore size distribution) tailored to the electrolyte system and optimization of the mixer geometry may yield even better battery properties.

On the Resistances of a Slurry Electrode Vanadium Redox Flow Battery

“…The Nyquist plots are presented in Figure b. The anolyte shows overall higher resistances as the catholyte, which is in correlation with previous published research . A direct observation can be made through checking R ohm where the Nyquist plots intersects with y‐axis ( y =0).…”

“…The benefit of using SMs has been shown previously through only full cell polarization experiments . For that reason, EIS experiments are conducted to evaluate the improvements on the cell resistances, and analyzed for each anolyte…”

“…A laboratory sized flow cell was used with an effective area of 19 cm 2 as described in our previous paper . The static mixers (SM) were produced via additive manufacturing with a single layer of twisted filaments (Stratasys Objet Eden 260 V, RGD525).…”

“…Static mixers are flow promoters that induce additional secondary flows to the flow field; therefore, they help to mitigate the mass transport related limitations. As recently shown by our group, static mixers improve the particle movements in the flow cell and enable the slurry electrodes to reach higher polarization current densities . To have a better understanding of resistances that limit the performance, slurry electrodes should be studied thoroughly in a VRB.…”

“…The electrodes do not contribute to the redox reactions, except for the fact that they provide sufficient surface area for electrolyte reactions, leading to higher current densities. Recently, a novel approach has been introduced that renders the traditional concept of static solid porous electrodes to a more dynamic level . In this approach, conductive particle networks, called slurry electrodes, are used to transport the electrons to the electrolyte.…”