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Optimization of Capacitive Deionization Systems: An Electrochemical Approach

Carmona Orbezo, Aranzazu

[Thesis]. Manchester, UK: The University of Manchester; 2020.

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Abstract

The work presented on this thesis investigates the role of different electrochemical mechanisms that happen within capacitive deionization (CDI) systems in order to optimise the desalination performance and to propose methods that can be widely used to standardize research done in this area. Available literature shows that there is a lack of understanding on how the applied potential is distributed within a CDI pair of electrodes, and several reports even increase the used voltage to desalinate a water stream, regardless of the potential degradation that could happen in the surface of the electrodes. This work highlights the importance of correctly defining an electrochemical stable potential window for salt adsorption, as well as choosing the correct mass for both electrodes in order to avoid any Faradaic effects on the surface of the electrodes. In the case of flow-electrode CDI systems, previous works have neglected the Non-Newtonian nature of slurries used as flow electrodes, as well as how the physical properties and charge transfer mechanisms are affected by the use of different flow rates. Therefore, hydrodynamic voltammetry is used in this work to fully understand the performance of flow-electrode suspensions prepared with different carbon loadings and suspension concentrations at a variety of flow rates. A dimensionless number is proposed in order to be able to predict the electrochemical behaviour of the slurries to be used within the cell. Finally, most FCDI literature focuses on incorporating different types of additives to flow-electrodes in order to improve the conductivity and charge percolation mechanisms. This work shows the incorporation of graphene nanoplatelets as active material in the flow-electrode slurries.