(7gj) Ion Transport in Charged Porous Media: From Porous Electrodes to Geological Flows
AIChE Annual Meeting
Sunday, October 29, 2017 - 1:00pm to 3:30pm
Teaching Interests: Transport Phenomena, Thermodynamics, Numerical Analysis, Mathematical Physics
Understanding ion transport phenomena and electrochemical processes in porous media is relevant to many applications. Some examples include charge transport and storage in batteries and supercapacitors, water desalination through capacitive deionization, electrokinetic remediation of contaminated soil, and monitoring of fluid flow in underground reservoirs. Although these problems span many orders of magnitude in both length and time scales, the fundamental picture of ion transport and electrokinetic phenomena is remarkably similar. Here, I will discuss some of the underlying physical mechanism and their implications for optimizing existing technologies and possible novel applications.
For my doctoral thesis at UCSB (under the supervision of Prof. Frederic Gibou and Prof. Todd Squires), I studied the effects of pore microstructure on ion transport in porous electrodes. In most existing models, pore morphology is neglected and transport is described using homogenized equations. Despite their popularity and success, these models cannot correctly describe heterogeneous transport which occurs in ordered porous materials, e.g. in mesoporous carbon or CNT-based electrodes. Therefore, pore microstructure can significantly impact the charging kinetics. To test this hypothesis, I developed multi-resolution numerical algorithms for solving the Poisson-Nernst-Planck equations at the pore-scale. Specifically, I showed that surface conduction, which was ignored in previous models, can significantly enhance the charging kinetics by providing additional transport pathways. This discovery may be used for designing better performing electrodes for high power density applications.
During my postdoctoral research at MIT with Prof. Martin Bazant, I have been investigating novel applications of electrokinetic phenomena to underground fluid flow problems. For instance, our recent theory shows that electro-osmotic flows can control, and under certain conditions suppress, viscous fingering. This interfacial instability can lead to residual trapping of oil during secondary recovery process and is hard to control. However, we show that by adjusting the injection ratio of electric current to fluid flow, viscous fingering can be manipulated such that stable displacement is possible. Electro-osmotic flows are also more efficient in submicron pores where hydraulic resistance is very large. Therefore, they can lead to a more uniform displacement even in reservoirs with very large permeability variations. Finally, it might be possible to leverage the large electro-osmotic pressures, generated in tight and dead-end pores, as a new and efficient fracturing technique.