|M.Sc Student||Guyes Eric|
|Subject||Electrode Permeability Enhancement and Desalination|
Performance Characterizations for Flow-Through
Electrode Capacitive Deionization
|Department||Department of Mechanical Engineering||Supervisor||Assistant Professor Matthew E. Suss|
|Full Thesis text|
The world is facing an ever-increasing demand for clean water, and strategies to combating water scarcity include technological development to increase water treatment efficiency and widening the pool of available water resources. A promising emerging technology to address this issue is capacitive deionization (CDI), a research field that has witnessed considerable development in the previous decade. At its core, the CDI process utilizes a cell with two porous electrodes (usually carbon-based) electrically isolated by a separator. A constant voltage or current is applied between the electrodes while salty feedwater flows through the cell, which causes ion electromigration into the electrode pores while the desalted water flows out of the cell.
In the flow-between electrodes (FB) architecture, the separator between the electrodes serves as both the electrical isolator and the water flow channel. As a consequence of these differing functions, a competition arises with respect to the width of the separator channel. The electric field strength and desalination rate are larger in a narrow channel due to the minimal interelectrode distance; however, hydraulic resistance is also larger in a narrow channel, which can limit the water flow rate and increase pumping energy requirements. Alternatively, a wide separator channel allows for higher water throughput but reduces the desalination rate via a weaker electric field and an increased diffusion length for ions to travel from the channel to the electrodes.
In contrast, feedwater passes directly through the porous structures of the electrodes and separator in the flow-through electrodes (FTE) architecture. As the separator does not serve as the flow channel, its width may be minimized, leading to fast desalination and a compact cell in FTE relative to the FB design. However, flow pressures tend to be greater due to the generally low permeability of porous electrode media, limiting the available selection of electrode materials to those with large, micron-scale pores. We here propose and demonstrate a promising solution via the laser perforation of flow channels into commercial CDI electrode material, which we show dramatically reduces flow pressure, increases electrode permeability, and leaves electrode salt storage capacity and electric capacitance unaffected in constant-voltage charging mode. We further provide basic characterization data from a custom-built FTE CDI cell that demonstrated good agreement with a one-dimensional engineering model. This shows that FTE CDI cells can be modeled with a one-dimensional approach, unlike more typical FB cells where more complex two-dimensinoal approaches are required. The demonstrated electrode permeability increase and one-dimensional model-to-data comparison constitute meaningful advances in FTE CDI research.