DFT +UStudy of the Adsorption and Dissociation of Water on Clean, Defective, and Oxygen-Covered U₃Si₂{001}, {110}, and {111} Surfaces

Abstract

The interfacial interaction of U 3 Si 2 with water leads to corrosion of nuclear fuels, which affects various processes in the nuclear fuel cycle. However, the mechanism and molecular-level insights into the early oxidation process of U 3 Si 2 surfaces in the presence of water and oxygen are not fully understood. In this work, we present Hubbard-corrected density functional theory (DFT + U) calculations of the adsorption behavior of water on the low Miller indices of the pristine and defective surfaces as well as water dissociation and accompanied H 2 formation mechanisms. The adsorption strength decreases in the order U 3 Si 2 {001} > U 3 Si 2 {110} > U 3 Si 2 {111} for both molecular and dissociative H 2 O adsorption. Consistent with the superior reactivity, dissociative water adsorption is most stable. We also explored the adsorption of H 2 O on the oxygen-covered U 3 Si 2 surface and showed that the preadsorbed oxygen could activate the OH bond and speed up the dissociation of H 2 O. Generally, we found that during adsorption on the oxygen-covered, defective surface, multiple water molecules are thermodynamically more stable on the surface than the water monomer on the pristine surface. Mixed molecular and dissociative water adsorption modes are also noted to be stable on the {111} surface, whereas fully dissociative water adsorption is most stable on the {110} and {001} surfaces.

Coordination-induced bond weakening of water at the surface of an oxygen-deficient polyoxovanadate cluster

“…Instead, aquo ligands either rapidly dissociate from the O-atom vacancy, 69 or alternatively undergo dissociative adsorption at the surface of the material. [28][29][30][31] To the best of our knowledge, there are no examples in which surface coordinated aquo ligands are capable of facilitating H-atom transfer to small molecule substrates. Our findings constitute the first indication of an alternative pathway by which MO x surfaces can hydrogenate small molecule substrates.…”

Atomistic Simulation of Water Incorporation and Mobility inBombyx moriSilk Fibroin

“…In order to understand the interactions between the water molecules and the polymer chains, the incorporation energy for water into a number of different positions in the simulation supercells was calculated using DFT. − Locations for a single water molecule were selected randomly and the incorporation energy, E inc , calculated (eq ). where E (SF + H 2 O), E (SF), and E (H 2 O) are the energies of the energy minimized silk supercell containing the water molecule, the dehydrated silk structure, and the water molecule, respectively.…”

Structural and Phase Evolution in U3si2 During Steam Corrosion

“…The confirmation of Si-rich phases by both in situ NPD and ex situ XRD match progressive corrosion mechanisms where Si dissociates from U3Si2 and migrates inwards to form Si-rich phase [33]. U reacts with O from water molecules undergoing release hydrogen [37]. 1: Lattice parameters and volume fractions for post experiment samples obtained from XRD, from the literature [22,34], and from last-measured in situ NPD patterns.…”