EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Porous carbon materials are of great interest due to their wide range of applications. They are, for example commonly used as electrode material in Electrochemical Double Layer Capacitors (EDLCs), systems in which energy is stored by reversible ion adsorption. The performance of these devices is largely dependent on the structure of the carbon. As a consequence, the development of a better designing strategy demands a fundamental understanding of the underlying molecular phenomena and precise characterization of these materials. In this regard, NMR spectroscopy has proven to be beneficial. In particular, in-situ NMR experiments can be used to investigate the evolution of the system under charging/discharging conditions. However, the interpretation of the spectra is challenging as it depends on several factors such as ring currents in the carbon and adsorption energy of the ions. A fine interpretation thus necessitates the development of adequate theoretical methods to help in comprehending the spectra.
In this work, we use a combination of molecular and mesoscopic simulations to predict the chemical shifts and NMR spectra of ions diffusing inside the porous carbon electrodes and study the factors affecting them. Thanks to its multi-scale nature, this scheme makes use of data from Molecular Dynamic simulations (free energy profiles) and Density Functional Theory (Nucleus Independent Chemical Shift) to simulate NMR spectra. This model was applied to various electrode-electrolyte combinations and the resulting shifts were in good agreement with the experimental shifts. We were also able to show that the major contribution to the chemical shift comes from ring currents.