Doctoral defence: Faiza Summer “Development and optimization of flow electrode capacitor technology”

On 10 May at 14:00 Faiza Summer will defend her doctoral thesis “Development and optimization of flow electrode capacitor technology”.

Supervisors:
Researcher Janno Torop, University of Tartu
Professor Veronika Zadin, University of Tartu
Professor Alvo Aabloo, University of Tartu

Opponent:
Associate Professor Pekka Eero Peljo, University of Turku (Finland)

Summary
An electrochemical flow capacitor (EFC) is a conceptual approach to meet large-scale electricity storage. This device is similar in operation to a supercapacitor but uses a concentrated solution of carbon micro and nanoparticles and an electrolyte instead of solid electrodes. It typically flows in channels with a diameter of a few millimeters, the wall of which is a flow collector and through which the liquid electrode material is pumped. A porous ion-conducting membrane separates the electrodes. Using carbon-based liquid electrodes in the device under development will allow the technology to be significantly scaled up and integrated into existing electricity grids and used effectively to support renewable energy production.

The central goal of the work presented is to understand the fundamental properties of EFC technology. As a result, EFC laboratory tests and computer simulations have been performed to design and optimize the device architecture. In the field of simulations, both existing electrochemical models have been adapted for EFC modeling, and a new stochastic model based on Monte-Carlo principles has been developed. Both implemented and developed models were thoroughly calibrated and validated against laboratory experiments and used to understand the flow electrode charging process in three fundamental EFC device designs.

Models based on Nernst-Planck equations or concentrated solution theories are often used to model similar electrochemical devices. Second-order differential equations systems with partial derivatives describe both the ion concentrations and the charge exchange processes occurring in the device. The application of these models was characterized by the limitations of charge storage and transport processes in the device due to diffusion. If the electrode material circulation and sufficiently fast charge transport are critical processes, then a sufficiently large diameter of the electrode flow channels is important. Otherwise, it is necessary to minimize the diameter of the same channel. At the same time, the experimental work showed that the phenomena caused by diffusion are critical side effects and have a significant effect on electrode charging processes. The models based on the Nernst-Planck equations and the stochastic model developed successfully matched the experimental results. Moreover, the developed stochastic model allows to simulate the convection and mixing processes of liquid electrodes successfully and to apply the effects of side reactions. Thus, the developed approach opens the possibility to find a solution to the central problem of the flow capacitor design - how to ensure sufficient flow of electrode material from the device and at the same time avoid limiting the transport of charge due to diffusion.

Due to the development of EFC technology, a significant increase in the storage capacity of energy from renewable sources can be expected. At the same time, to improve the power density of EFCs without compromising their high energy density and cyclicality, it is necessary to monitor the coherence of developments with other energy storage and conversion technologies. Important factors are the choice of operating conditions of the device, the design of the electrodes, the materials of the electrolyte, as well as suitable catalysts.

The defence will be held in Zoom: https://ut-ee.zoom.us/j/98528706611?pwd=d0JWQjN1MUdQQVNVVUg4TXprVnM0dz09.
Meeting ID: 985 2870 6611, Passcode: 279098.

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