A5: Molecular dynamics studies at fluid interfaces in nanoporous solids.

Supervision:

Prof. Dr.-Ing. Robert Horst Mei├čner, Prof. Dr.-Ing. Irina Smirnova

Objective:

Research project A5 is focused on modeling solid-liquid interfaces at the molecular level using molecular dynamics simulations. Of particular interest are interfaces in nanoporous media with their characteristically high accessible surfaces. These materials have a wide range of applications, especially in electrochemistry as electrode materials and novel energy conversion processes. By studying the behavior at these interfaces, valuable insights into the key factors that determine the properties of fluids in nanoporous materials will be gained, enabling the optimization of a wide range of corresponding applications.

In total, four different solid materials are studied: platinum and gold as conventional metals, and graphene and molybdenum disulfide (MoS2) as two-dimensional (2D) materials. These materials were chosen for their importance in electrochemistry and as representative examples of different types of surfaces.

While structures made of platinum and gold are already widely used as catalysts and electrodes in electrochemical processes, the newer 2D materials graphene and MoS2 hold promise for novel forms of energy conversion and filtration in nanofluidics due to their unique mechanical and electrical properties.

In the first part of the research project, the structural and dynamic properties of water at the interfaces of these materials will be investigated, as water is present in a large number of technical as well as natural processes in contact with these surfaces. Furthermore, with a special focus on graphene, the behavior of confined aqueous solutions and ionic liquids will be investigated, as they occur in diffusio-osmosis (Fig. 1 (left)) and supercapacitors (Fig. 1(right)), respectively.

Figure 1: Schematic representation of (left) diffusio-osmotic transport of an aqueous solution in a nanochannel and (right) a supercapacitor filled with an ionic solution.

The insights thus obtained into behavior at the nanoscale should subsequently provide information on correlations with properties that can be observed macroscopically.

Materials and Methods:

The molecular dynamics simulations are performed within the frame of the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) and CP2K. The simulations are based on different level-of-theories depending on the complexity of the system under consideration, ranging from classical force field simulations to quantum mechanical state calculations using density functional theory.

To investigate the dynamic and structural behavior of the water-contact layer (Figure 1) on the above materials, an atomistic interaction potential is first developed based on second-generation High-Dimensional Neronal Network Potentials (2G-HDNNP).