| dc.description.abstract | In flowable slurry electrodes, charge is transferred from stationary electrodes to particle clusters through hydrodynamic interactions; however, so far little is known about the particle dynamic behavior under continuous flow. This dissertation aims to uncover new understandings about these behaviors and their effects on the electrochemical performance of flowable electrodes through numerical and experimental methods.
Using Stokesian dynamics, we explore the effects of conductive additive on the charging of a slurry electrode and present a unified expression for the dynamically varying electrical network of particles. The results suggest that at lower concentrations of activated carbon particles, the conductive additive enhances charge transfer by filling interstitial spaces and establishing contacts between carbon particles; however, at higher concentrations, the benefits are not as clear since direct contacts between particles dominate the charge transfer process.
Next, a novel microfluidic electrochemical flow capacitor (µ-EFC) platform was constructed using transparent materials to directly visualize particle hydrodynamics and measure electrochemical charging and discharging performance. It is found that as the flowrate varies, particle distribution along the channel height is significantly affected as particles tend to migrate away from the stationary electrodes where the shear is high; however, higher rates of shear also increase the number of interactions between particle clusters. These competing effects lead to a non-monotonic trend in the normalized charging and discharging current versus flowrate plot.
Finally, the µ-EFC design was iterated to include three-dimensional (3D) gold electrodes of varying lengths to directly visualize particle behavior in the boundary layer around stationary electrodes and the resulting electrochemical performance. These experiments revealed distinct particle flow behaviors at each 3D electrode length, and the electrochemical data is clearly affected by the inclusion of 3D electrodes. Specifically, the average resting charging current was increased by a factor of 4.8 and the discharging current was increased by a factor of 2.8.
These novel findings have significantly enhanced our understandings of the hydrodynamic effects on the electrochemical performance of flowable electrodes and pave the road for optimal operation of EFCs with slurry electrodes. | |
