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At the Mountains of Modeling

Multiscale Simulations of Desalination by Capacitive Deionization

Time: Fri 2022-12-16 13.00

Location: FB53 AlbaNova, Roslagstullsbacken 22

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Language: English

Subject area: Material and Nano Physics Physics

Doctoral student: Johan Nordstrand , Material- och nanofysik

Opponent: Professor Maarten Biesheuvel, WETSUS, European centre of excellence for sustainable water technology

Supervisor: Professor Joydeep Dutta, Material- och nanofysik; Professor Oscar Tjernberg, Material- och nanofysik

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QC 221125


More than 2 billion people are living in water-scarce areas. Meanwhile, there are enormous amounts of water in the salty oceans. Capacitive deionization (CDI) rises to the challenge with electrochemical cells for desalinating the water. As the CDI field expands, modeling becomes an increasingly important part of the development landscape. Multiscale modeling could bring innovations from the material scale to pilot plants. 

The multiscale work in this thesis has been like climbing a mountain. At the start, we investigate the macroscopic device level. One milestone is the electrolytic-capacitor (ELC) model, which can simulate CDI process dynamics. Whereas previous 2D models were unsteady for a single CDIcell, the ELC model could accurately simulate stacks of over 100 cells at a fraction of the time. It also enables simulations of complex upscaled geometries, such as bipolar electrode stacks, ohmic charging, and asymmetric devices. Going up the mountain, the mesoscopic level reveals the local mechanisms behind the macroscopic behavior. One important stepping stone is the dynamic Langmuir (DL) model, which reveals how isotherm-based modeling can crease stable and tractable simulations. Also, developments in isotherm, double-layer, and circuit modeling make it possible to choose what model structures to lean on depending on the conditions. Near the top of the mountain, the microscopic level shows the fundamental atomic mechanisms behind the mesoscopic material properties. These investigations reveal a ladder mechanism of ion transport in crystals of Prussian blue analogs (PBA), meaning the cations climb frames formed by negative groups in the crystal structure.

In the end, we plant a flag by combining the developments from the journey into a complete multiscale model. That model demonstrated that we could predict CDI charging trends from the atomic structure of PBA electrodes. Having the full multiscale model also made it possible to backtrack and determine atomic-level mechanisms by comparing the output of different mechanism cases with macroscopic experiment data. The multiscale mountain is massive and has big potential. A dream is that future research will expand these concepts, in CDI and beyond.