(73e) Modeling Thermodynamics and Kinetics at 2D Material Interfaces: Applications in Synthesis, Nanopore Formation, Wetting, and Catalysis

Two-dimensional (2D) materials, such as, graphene, transition metal dichalcogenides (TMDs) (e.g., molybdenum disulfide (MoS₂)), hexagonal boron nitride (hBN), and layered metal oxyhydroxides (e.g., nickel oxyhydroxide (NiOOH)) have recently received considerable attention, due to their exceptional optoelectronic, mechanical, barrier, and catalytic properties. However, a physical understanding of the controlled synthesis and interfacial behavior of 2D materials is still lacking. In this talk, I will discuss our research in several fundamental areas pertaining to modeling thermodynamics and kinetics at the interfaces formed by 2D materials:

1. Mechanistic models for the chemical vapor deposition growth and etching of 2D materials: I will discuss a generalized theory for the growth of TMD monolayers using chemical vapor deposition (CVD). The combined use of kinetic Monte Carlo (KMC) simulations and a transport model based on chemical engineering principles will be shown to enable the prediction of the experimentally observed shape and size evolution of the MoS₂ morphology inside a CVD reactor. Next, I will discuss the solution of the Isomer Cataloging Problem (ICP) for lattice nanopores in 2D materials. Combining density functional theory (DFT) calculations, KMC simulations, and chemical graph theory, I will present a catalog of unique, most-probable isomers of 2D lattice nanopores, demonstrating remarkable agreement with experimental transmission electron microscopy data for nanopores in graphene and hBN.

2. Development of force field models to understand wetting and friction at 2D material surfaces: I will outline the development of classical force fields for MoS₂ and hBN, for use in mechanical and interfacial applications, using DFT and lattice dynamics calculations. The force fields will be shown to predict the crystal structure and elastic constants of MoS₂ and hBN with good accuracy, and to correctly describe the mild hydrophilicity of the MoS₂ and hBN basal planes. I will also discuss the use of molecular dynamics (MD) simulations to understand the role of dispersion interactions, electrostatics, and entropy in the wetting and frictional properties of 2D materials. Further, I will discuss how our work led to some unexpected findings, including: (i) the dominance of dispersion interactions and entropy over electrostatics in determining the wettability and friction of 2D MoS₂, and (ii) that liquids with lower wettability can demonstrate higher friction on 2D hBN.

3. Understanding catalysis at 2D material interfaces using first-principles simulations: I will outline the use of conventional DFT with Hubbard-like corrections (DFT+U) and hybrid DFT with a fraction of exact exchange to understand the electrocatalytic behavior of pure NiOOH in terms of the oxygen evolution reaction (OER). By calculating Gibbs free energies for various elementary reactions occurring during the simple associative mechanism for water splitting, I will discuss the prediction of a lower bound for the overpotential exhibited by the surface for the OER. Finally, I will discuss the efficacy of dopants such as iron and manganese in enhancing the OER capability of NiOOH, including contrasting and rationalizing results from DFT+U and hybrid DFT.

In conclusion, the theoretical and simulation-based research work discussed in this talk should inform the controlled synthesis of 2D materials, and their use in various applications, including optoelectronic devices, mechanical composites, membranes for gas separation/water desalination, and electrocatalysis for splitting water molecules into oxygen and hydrogen.