Structure, Kinetics, and Thermodynamics of Water and Its Ions at the Interface with Monoclinic ZrO₂ Resolved via Ab Initio Molecular Dynamics

Abstract

In this work, we assess the structural, kinetic, and thermodynamic nature of water in contact with the monoclinic ZrO2 (1̅11) surface by ab initio molecular dynamics calculations. We find that water molecules in the first layer immediately facing the solid surface have a preferred orientation, with one water intramolecular bond, Ow–Hw, lying parallel to the surface, and the other water hydrogen Hw atom pointing away from the surface. This originates from the electrostatic attraction between surface Zr and water’s oxygen, Zr–Ow, and from the hydrogen bonding of surface oxygen and water’s hydrogen, Os–Hw. The short-range interactions between interfacial water and the surface ions of ZrO2 lead to an ordered structure for water molecules, with alternating hydrogen-rich and oxygen-rich layers that persist for more than 5 Å away from the surface. The surface structural perturbation also leads to a shortened hydrogen-bond distance and distorted hydronium ion solvation shell, which leads to faster proton hopping dynamics and lowered solvation free energy of the hydronium ion. By analyzing these observations in a spatially resolved way, we demonstrate a clear link between the interfacial water structure, localized dynamics, and thermodynamic effects. This work provides an atomistic understanding of the interaction of hydrated protons with the ZrO2 surface in aqueous environment and allows for further engineering of oxide surfaces for targeted hydrogen activity.

Charged species redistribution at electrochemical interfaces: a model system of the zirconium oxide/water interface

“…In this case of pH-neutral water, we observe an 8-order-of-magitude increase in the H + concentration in the Stern layer compared to bulk water, which is consistent with previous AIMD observation, which also predicts significant H + adsorption. 50 The multi-scale model enables us to quantify the concentration of surface adsorbates and how they change with pH and solid defect chemistry.…”

“…In this case of pH-neutral water, we observe an 8-order-ofmagitude increase in the H + concentration in the Stern layer compared to bulk water, which is consistent with previous AIMD observation, which also predicts significant H + adsorption. 50 Fig. 3 (a) Predicted water chemistry in equilibrium with ZrO 2 as a function of pH at room temperature.…”

“…The adsorption free energies are 0.20 eV for H + and 0.15 eV for OH À as found in our ab initio molecular dynamics (AIMD) study of the ZrO 2 (% 111)/water interface, and the Stern layer width is taken as 3 Å as read from the adsorption energy profiles from our previous work. 50 The atomistic model used for the AIMD calculation is shown in Fig. 2.…”

Pathways for Electron Transfer at MgO–Water Interfaces from Ab Initio Molecular Dynamics

“…DFT studies have just recently begun to unravel the energetics and interfacial hydration structures of radiolytic species at interfaces of aluminum (oxy)­hydroxides, , WGO systems similarly relevant to managing radioactive waste. While equilibrium hydration structures and dynamics of MgO − and ZrO 2 have been elucidated, mechanistic and dynamical studies of ET across semiconducting oxide–water interfaces have largely focused on nanoparticles and/or candidates for solar photocatalysis such as TiO 2 . − Such studies have nonetheless demonstrated that the interplay between electronic energy levels and water dynamics governs interfacial charge transfer. ,, …”

Effect of Elemental Doping on the Adsorption Behavior and the Mechanism of Hydrogen Adsorption on the Zirconium Surface

“…Zirconium alloys are widely used in nuclear reactors as fuel cladding and structural materials because of their lower thermal neutron absorption cross section, excellent corrosion resistance, and good compatibility with UO 2 . − During the operation of the nuclear reactors, the zirconium claddings are oxidized by a primary coolant. Simultaneously, the zirconium claddings also absorb a fraction of hydrogen, which is released by the corrosion reaction of zirconium with water.…”