(65f) Tailoring Electrode Microstructures for High-Performance Redox Flow Batteries through Non-Solvent Induced Phase Separation

Porous carbon electrodes play critical roles in electrochemical systems by supporting numerous functions which include providing catalytic sites to facilitate faradaic reactions, distributing liquid reactants and products, and conducting electrons and heat.¹ The surface chemistry and microstructure of the porous carbon electrode is particularly relevant for redox flow batteries (RFBs), wherein dissolved redox active species are forced through porous electrodes within a flow cell, oxidizing and reducing on the electrode surface during operation. RFBs hold promise for long duration energy storage for the electric grid due to their decoupling of energy and power, long service life, and scalability.² However, contemporary RFBs are prohibitively expensive, incentivizing further cost reduction for widespread deployment; lowering reactor cost by augmenting power output is a promising approach to bridging the economic gap. While commercial electrodes are functional, they possess suboptimal surface chemistry and microstructure for existent and emerging RFB chemistries.³ Furthermore, the physical properties (i.e., porosity) of commercial electrodes are spatially homogeneous across the through-plane direction of the electrode, although the optimal porosity profiles balancing fluid dynamics, mass transport, and available surface area may be chemistry-specific and non-uniform.

In this presentation, we will systematically demonstrate non-solvent induced phase separation (NIPS) as a facile and versatile method to engineer interconnected porous microstructures with unique porosity profiles unattainable in commercial electrodes.⁴ Combining spectroscopic characterization and fluid dynamic measurements with electrochemical evaluation in two common aqueous redox systems (i.e., Fe^2+/3+ and all-vanadium), we will illustrate the viability of NIPS as a platform for developing structure-function design principles in RFB electrodes. From these findings, we will highlight pathways towards high-performance electrodes, investigating the role of electrochemically accessible surface area and porosity gradients in the through-plane direction in these custom material sets. Further, we will show that the synthetic method can be modified to generate dense and planar carbon films, enabling opportunities to extract fundamental rate constants on bottom-up designed materials using conventional electroanalytical approaches. While the primary focus of this talk will be on RFBs, the methods and findings described are generalizable to convection-driven electrochemical reactors that require spatially engineered electrode layers.

Acknowledgments

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. CTW acknowledges additional funding from the National Science Foundation Graduate Research Fellowship Program under Grant No. 1122374. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

References

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