From fundamentals of transport in flow electrodes at membrane interfaces to application

  • Von den Grundlagen des Transports in fließfähigen Elektroden an Membrangrenzflächen zur Anwendung

Linnartz, Christian Jürgen; Wessling, Matthias (Thesis advisor); Elimelech, Menachem (Thesis advisor)

1. - Düren : Shaker Verlag (2022)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik series - AVT.CVT - chemical process engineering 25 (2022)
Page(s)/Article-Nr.: xi, 209 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

Reducing our negative, human induced impact on planet Earth is the most vital task of our time. Facing that global challenge, essential aspects to be tackled are recycling water-soluble compounds, degradation of harmful contaminates, and new pathways for the electrification of the chemical industry. Most electro-membrane processes targeting these task rely on solid electrodes and an ion-exchange membrane interface. Thus, the active surfaces are fixed and are prone to transport limitations in the boundary layers at the rigid structures. Mounted in a module, the electrodes cannot be replaced and possess a fixed storage capacity for adsorption. Thus, water treatment processes are usually in-efficient batch processes that need to switch between adsorption and adsorption modes. A fruitful and until now unappreciated innovative approach is the use off lowable electrodes which make the processes continuous. In this work, flow electrodes as complex fluids are applied for water desalination and valuable salt concentration using the technology flow-electrode capacitive deionization (FCDI). New materials for shortening charge transport paths are developed and applied in modules, starting from studying the charge transport and particle cluster formation. Subsequently, the global effects during scale-up are researched. Consequently, optical and electrical analysis of flow electrodes is conducted, accompanied by FCDI desalination experiments and simulations determining the course of ion concentrations in a module. Results showed that charge transport within the flow electrodes is fostered by creating particle percolation networks, yet the used electrolyte also triggers it. Shorter charge transport paths by combining ion-exchange membrane and cur-rent collector reduced overpotentials. Adjusting the salt contraction in the flow-electrode electrolyte, the unwanted water crossover across the adjacent ion-exchangemembranes is mitigated, which is essential for long-term stability. Hence, the particle concentration of the flow electrode and the unwanted osmotic dilution of the concentrates were controlled. Based on this, module configurations were pro-posed and tested. Flow electrodes open a new field of continuous electrochemical processes. Understanding the fundamentals of charge transport and their impact on large-scaleflow-electrode modules, the foundations are laid to put the technology into operation.

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