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

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 ΔG H 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-WTe 2 /2H-MoS 2 employing DFT-based trends. Additionally, we have built carbon-based hybrid systems from a bilayer of g-C3N4 coupled with Td-WTe 2 , 2H-MoS 2 , and Graphene, and used an implicit solvation model to obtain more realistic signatures. The results show that g-C 3 N 4 /Td-WTe 2 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-WTe 2 /g-C 3 N 4 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-WTe 2 /g-C 3 N 4 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 [Ru II -OH 2 ] 2+ species, as well as of multiple PCET oxidation states. This work also shows that the chemical shift of [Ru IV =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 she