A new type of electrode called a "flowable electrode" has been used in several emerging energy- and environment-related technologies, such as the electrochemical flow capacitor for storing electrical energy and capacitive deionization for treating brackish water. During the operation of a flowable electrode, a slurry of small, highly porous carbon beads mixed with an aqueous electrolyte flows into an electrochemical cell and is charged with an applied voltage. Ions are adsorbed to the interior surface of the carbon beads through their pores to store electrical charge. Because the porous carbon beads have enormous interior surface area relative to their mass, they can store or release a tremendous amount of ions and electrons in a very short time. This process allows more rapid charging and discharging compared with conventional rechargeable batteries. The flow capacitor has the potential to achieve 100 times faster charging and 1000 times longer lifetime than Li-ion batteries. Furthermore, the flow architecture makes it scalable for grid energy storage. Achieving these potentials requires detailed knowledge about how the detailed configuration of the slurry affects electrical conductivity and charging. The electrical network within the slurry consists of carbon particles in intermittent contact causing electrical pathways to be rapidly disrupted and reformed. Thus, the entire slurry displays unique behavior in electrical conductivity and charging characteristics, which are key to the performance of the flowable electrode. This project will investigate how hydrodynamic interactions at the carbon particle level affects the critical properties of flowable electrodes. The results will help improve efficiency of flow electrodes, which will contribute to sustainable developments in energy and water resources. The interdisciplinary nature of the project provides rich opportunities for students from high-school to graduate levels to participate in the research.
This project combines experimental and computational approaches to explore the hydrodynamic interactions of activated carbon particles with diameters from 1 to 10 micrometers, and the electrochemical processes of flowable electrodes. Novel microfluidic devices will be constructed to directly observe particle interactions and, simultaneously, to measure the electrical or electrochemical properties of the slurry. Dielectric-rheo setups will be used to measure properties at the macroscopic level. The computational efforts will employ a new numerical model to simulate the micro-hydrodynamics of the particles, the topology-varying electrical circuit of the particle network, and their coupling. The experimental data will provide critical parameters such as the electrical resistance and capacitance of the particle network to the computational model. The computational model will extract effects of shear rate and particle concentration on the particle cluster characteristics, including cluster sizes, lengths, and orientations, and their effects on the anisotropic conductivity and transient charging behavior of the flowable electrode. The studies will produce knowledge to improve the performance of flowable electrodes in energy and environment technologies.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
