Modelling and Simulation of Electro-catalysts for Green Energy : From Solvated Complexes to Solid-Liquid Interfaces

Abstract: In this thesis, I have worked with solid-liquid interfaces, adsorbed molecules on the surface, and solvated complexes using Density Functional Theory (DFT) calculations to find possible signatures that could help design suitable energy materials. More specifically, I have explored hybrid electrocatalysts for hydrogen evolution reaction (HER), XPS fingerprints of gas-phase melamine (monomer, dimer, trimer, and hexagonal packed arrangement), hexagonally packed melamine adsorbed on the Au(111) surface, and high-valence Ruthenium complexes along a reaction pathway in aqueous solution through a joint theory-experiment approach. First, I have explored single layer and hybrid-type systems as micro-reactors (current collector/catalysts) for HER with site-dependent calculations of the hydrogen binding free energy ΔGH to estimate the HER activity, electronic structure, and Schottky Barrier Height (SBH) to measure the resis-tance for charge injection across the interface. Furthermore, we have predicted a new hybrid electrocatalyst Td-WTe2/2H-MoS2 employing DFT-based trends. Additionally, we have built carbon-based hybrid systems from a bilayer of g-C3N4 coupled with Td-WTe2, 2H-MoS2, and Graphene, and used an implicit solvation model to obtain more realistic signatures. The results show that g-C3N4/Td-WTe2 has filled states in the Fermi level, which is a good indication of higher charge mobility. The SBH was evaluated with both GGA and HSE06, and Td-WTe2/g-C3N4 has shown lower resistance for charge injection across the interface. Further, the induced dipole (driving force for electron injection) increases under higher hydrogen coverages, enhanc-ing the catalytic activity. Finally, our results indicate that Td-WTe2/g-C3N4 could be classified as an efficient electrocatalyst for HER. In the last two papers, we have estimated XPS finger-prints of molecular and solid-state systems by calculating the core-level binding energy shifts using the Janak-Slater transition state approximation. Also, we have developed a new methodology by combing DFT calculations with Monte Carlo Simulations using explicit solvation to resolve the XPS and understand the chemical shifts of the [RuII -OH2]2+ species, as well as of multiple PCET oxidation states. This work also shows that the chemical shift of [RuIV =O]2+ is affected by the polarization of the explicit solvation model, and that we could only capture the experimental trend by using the complete first solvation shell and an XPS averaged spectra over a certain amount of snapshots from the Monte Carlo simulation. To the end, we also show that the nearest-neighbor potential contributions to the Ru 3d binding energies arising from atoms around the metallic center explain the higher 3d-state shifts of the oxo complex.