defended her PhD thesis on 11 december 2023
TUNING, ASSESSMENT, AND OPTIMIZATION OF AN ELECTROCHEMICAL WATER DESALINATION PROCESS THROUGH FLOW-ELECTRODE CAPACITIVE DEIONIZATION: MATERIAL, PROCESS, AND PHYSICO -CHEMICAL CONSIDERATIONS
In front of the jury composed of:
– Patrick DROGUI, Professeur, Institut National de la Recherche Scientifique – Rapporteur
– Pierre-Henri AUBERT, Professeur, CY Cergy Paris Université – Rapporteur
– Christel CAUSSERAND, Professeur, Université de Toulouse – Examinatrice
– Ouassim BOUJIBAR, Maitre de Conférences, Université de Tours – Examinateur
– François ZAVISKA, Maitre de Conférences, Université de Montpellier – Co-encadrant
– Philippe SISTAT, Maitre de Conférences, Université de Montpellier – Co-encadrant
– Roland HABCHI, Professeur, Université Libanaise – Co-directeur
– Marc CRETIN, Professeur, Université de Montpellier – Directeur
The ongoing worldwide water scarcity represents a widespread danger to communities in the world. In addressing this issue, crucial purification technologies offer a hopeful path to secure clean water. In particular, desalination, which involves transforming brackish or seawater into freshwater, stands out as a crucial solution for ensuring sustainable futures. Capacitive Deionization (CDI) is emerging as a promising technology that utilizes electrochemical processes to effectively desalinate brackish water, providing a sustainable means for freshwater production. In a typical CDI cell, the feed saline water transverses a separator layer situated between two solid carbon electrodes, each endowed with electric charges. The electrode’s solid-state nature limits performance by constraining surface area and ion adsorption sites. It also hinders continuous operation due to regeneration constraints. Flow-electrode capacitive deionization (FCDI) is an innovative adaptation of traditional CDI, enabling continuous desalination processes. Unlike static electrodes in CDI, FCDI incorporates dynamic flowable electrodes
constituted of active materials and electrolytes, allowing continuous and prolonged ion removal from the saline water stream. This thesis optimized and employed activated carbon-based flow electrodes in a laboratory-scale FCDI system, providing a cost-effective alternative and enhancing the desalination performance of this innovative technology. Initially, a novel approach implemented dry ball-milling to reduce the particle size of commercial activated carbon (AC), producing fine activated carbon (FAC). When employed as the flow electrode material at a 10% weight fraction in FCDI, FAC outperforms unmodified AC in desalination. This superiority is attributed to increased contact area, favorable pore structures, and accelerated charge transfer within the interconnected carbon particle network resulting from the reduced particle size. However, the FAC flow electrode shows increased viscosity, leading to higher pressure drop and consequently higher pumping energy. To address this limitation, our subsequent study explored the impact of particle size distribution on the viscosity and desalination performance of activated carbon flow electrodes in FCDI. A strategic approach was employed by blending FAC particles (0.65-0.92 μm) with AC particles (1.5-2.3 μm). FAC/AC bimodal mixtures preserved the superior desalination performance of FAC while significantly lowering the apparent viscosity, improving flow properties and mitigating pressure drop concerns. The ratio of AC to FAC particles significantly influenced rheological characteristics and desalination performance. A balance between desalination performance and system viscosity was found crucial for practical applications. Furthermore, hydrothermal method was employed to fabricate a cost-effective ACZnO composite for FCDI electrodes. The resulting composite displayed a specific capacitance surpassing pristine AC. This along with the enhanced hydrophilicity contributed to superior FCDI performance. The success is attributed to reduced internal resistance, improved wettability, increased capacitance, enhanced electrical conductivity, and superior charge transfer characteristics, underscoring its potential for FCDI applications.
Moreover, the physicochemical and electrochemical attributes of the flow electrodes materials, encompassing both pristine and modified variants, were assessed through scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray
diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectrometry (FT-IR), dynamic light scattering (DLS), static multiple light scattering (SMLS), rheological measurements, electrophoretic light scattering (ELS), water contact angle measurement (WCA), cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS).