Thomas-Fermi model improves electrode simulations

Molecular dynamics simulations of electrode and electrolyte interfaces have allowed researchers insight into electrochemical systems, which in turn has enabled breakthroughs in fields such as supercapacitance and metal surface hydration. However, these simulations treat all electrodes as perfect conductors – a limiting oversimplification.

Scalfi et al. propose an improved model that takes into account the screening of the electric field at the interface. The researchers felt a new model was necessary, since previous studies found different metals respond differently to adsorbed ions.

Scalfi et al. extended the previous model, which used an extended Hamiltonian framework, where electrode charges were represented as degrees of freedom, with a Thomas-Fermi electrode model. This model uses an extra term involving the Thomas-Fermi screening length of the material, which brings an energy penalty and allows for conductive metals, such as gold, to be differentiated from imperfect conductors, such as graphite. The improved model was found to produce different results for the structure, and dynamics of the simulated electrolyte compared to the old model.

“We observed that the new model is in agreement with analytical expressions for simple system,” said author Mathieu Salanne. “We also observed a large difference in the charge distribution within the electrode and within the liquid when a potential is applied, which means that these effects at play should not be neglected.”

The improved model, where one can tune the metallicity of the electrode, will allow researchers to predict the capacitive properties of materials used for energy storage. The researchers plan to continue expanding the model to cover various electrode types, including electrodes made of different atomic species and nanoporous electrodes, which are important for supercapacitor applications.

Source: “A semiclassical Thomas-Fermi model to tune the metallicity of electrodes in molecular simulations,” by Laura Scalfi, Thomas Dufils, Kyle Reeves, Benjamin Rotenberg, and Mathieu Salanne, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0028232 .