Interaction of hydrogen with actinide dioxide (111) surfaces

Area of Science:

• Surface science
• Computational chemistry
• Materials science

Background:

• Actinide dioxides (AnO2) are crucial in nuclear fuel cycles.
• Understanding hydrogen interactions with AnO2 surfaces is vital for safety and performance.
• Previous studies often simplified surface interactions and electronic behaviors.

Purpose of the Study:

• Investigate atomic and molecular hydrogen interactions with actinide dioxide (111) surfaces.
• Consider noncollinear antiferromagnetic behavior and spin-orbit interactions.
• Determine adsorption energies and reaction barriers.

Main Methods:

• Density Functional Theory with Hubbard U (DFT+U) calculations.
• Inclusion of noncollinear magnetism and spin-orbit coupling.
• Analysis of atomic and molecular hydrogen adsorption and dissociation.

Main Results:

• Atomic hydrogen adsorption leads to hydroxide formation and actinide ion reduction.
• Calculated adsorption energies: UO2 (0.82 eV), NpO2 (-0.10 eV), PuO2 (-1.25 eV).
• Molecular hydrogen dissociation is kinetically limited, not thermodynamically.
• An unusual charge distribution hinders further hydroxyl group formation.
• Hydrogen ion recombination is favored over new hydroxide formation.

Conclusions:

• Atomic hydrogen readily interacts with AnO2 surfaces, forming hydroxyl groups.
• Kinetic barriers significantly impact molecular hydrogen reactivity.
• Surface charge distribution plays a critical role in reaction pathways.
• Hydrogen ion recombination is the preferred outcome on these surfaces.