Experimental modeling of magnetic field-induced interfacial instabilities in electrolysis cells and liquid metal batteries.

• Applicant: Dr.-Ing. Gerrit Maik Horstmann
• Subject Area: Fluid Mechanics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512131026

Today, there is a strong consensus that the challenges of climate change can only be addressed with holistic and integrative solution strategies. The increase in share of renewable energies as well as the exploitation of energy efficiency potentials are two of the key drivers in this process. Within this context, magnetic field-induced interfacial instabilities are of major significance for not just one but two important technologies: electrolysis cells (ECs), which are widely used in the immensely energy-intensive Hall-Héroult process (~ 3 % of the electricity generated worldwide) for extracting aluminum, as well as liquid metal batteries (LMBs), which are discussed today as a low-cost energy storage, as required for the deployment of fluctuating renewable energies. Both technologies, which can be described as multi-layer systems in terms of fluid mechanics, are exposed to strong cell currents, which, in interaction with induced or external magnetic fields, can destabilize the liquid-liquid interfaces and provoke rotational wave motions. In ECs, such rotational waves are generally undesirable and limit the cell’s energy efficiency. In LMBs, however, excessive wave sloshing may also be dangerous and provoke short circuits in the worst case, but soft and controlled wave motions also have the potential to improve mixing and the degree of efficiency with it. For these reasons, such wave motions have been intensively studied in literature as early as the 1970s. Nevertheless, today there is a severe discrepancy between a large number of available simulation environments and analytical models, but as yet hardly existing experiments. Due to the high operating temperatures and the chemical aggressiveness of the active materials, laboratory experiments have been difficult to implement so far. This is exactly where this project intends to start. It is the aim to realize a novel, easy-to-use model experiment, which requires only one layer of GaInSn and can therefore be carried out at room temperature. By means of a feedback loop between injected currents and wave elevations, it is possible to fully model both the wave mechanics as well as the magnetic instability mechanism on laboratory scale. The experiment should therefore not only serve as a basis for validation of the various theoretical models, but also grant new insights into as yet largely not understood sub-aspects, e.g., understanding the exact influence of magnetic damping or the aspect ratio on the stability behavior. Moreover, such an experiment is ideally suited to test recently developed stabilization methods for the suppression of wave motion, which are based on a smart modulation of the cell current. Even small increases in efficiency through the Hall-Héroult process could yield a significant contribution towards global energy reduction.

• DFG Programme: Research Grants