Design of novel flow cell architectures for enhanced transport in flowable electrode systems

Jonathan C. Ehring

doi:10.17918/00011486

Flowable electrodes have gained increasing attention as a promising electrochemical platform for energy storage and ion-selective water treatment processes. These systems use multi-phase suspensions of electrochemically active particles dispersed in liquid electrolytes, allowing traditionally static electrode materials to be fluidized, regenerated, and scaled through flow-assisted reactor architectures. By circulating active material through the reactor, flowable electrodes decouple storage capacity from power output, enabling capacity to scale with suspension volume while power is governed by reactor size. However, suspension electrodes contain non-dissolved electroactive particles whose performance depends on coupled electrochemical and hydrodynamic transport processes that are not present in single-phase electrolyte systems. Despite its significance, flow-cell architecture designed specifically for multi-phase suspension electrodes remains largely unexplored, limiting the ability to control particle transport, charge transfer, residence time, and interfacial renewal within the reactor. This thesis aims to address the existing gap in flow-cell architecture design by developing reactor concepts that are inherently suited for multiphase suspension electrodes and that enhance electrochemical utilization through controlled particle interactions. This is accomplished through systematic experimental evaluation of actively driven flow-cell architectures that impose particle mixing within the reactor volume. A pulsatile static mixing design is used to establish the role of particle mixing in improving charge transfer and salt removal by coupling localized particle redistribution with reduced charge-transport distance. This particle-mixing concept is then transferred to a screw-driven tubular flow cell, where the slurry is actively propelled through the reactor volume while simultaneously participating in electrochemical energy conversion processes. Lastly, the screw-driven tubular cell is adapted for flow-electrode capacitive deionization in a single-cycle configuration, enabling the effects of controlled screw-induced mixing to be evaluated under salt-removal and regeneration conditions. Across these systems, electrochemical characterization, conductivity measurements, hydrodynamic analysis, and energy metrics connect reactor-induced particle motion with overall system performance. The results demonstrate that flowable electrode performance is enhanced when effective mixing promotes particle renewal at electrochemically active interfaces. By identifying the coupling between mixing, residence time, current collector contact, and ion transfer, this work highlights the importance of reactor designs that create dynamic, internally renewing electrode environments for scalable and energy-efficient multiphase electrochemical flow systems.

Design of novel flow cell architectures for enhanced transport in flowable electrode systems

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Design of novel flow cell architectures for enhanced transport in flowable electrode systems

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