Mechanical behaviour of hydrogenated nanoporous palladium†

Nanoporous materials, unique materials with characteristic nanoscale effects in a macroscopic format, have been highlighted for their solid-state hydrogen storage capabilities. However, an atomic-level description devoted to understand nanoscale size effects is still missing. In the present paper, molecular dynamics and Monte Carlo simulations were performed to investigate the hydrogen absorption and mechanical behavior under tensile stress of nanoporous palladium (np Pd). The results reveal that np Pd with ligament sizes on the nanometer scale exhibits a hydrogen absorption isotherm similar to that of nanoparticles of comparable size, showing nearly continuous growth, unlike bulk samples or flat thin films. Tension simulations showed a hydrogen softening effect on the np Pd, reducing Young's modulus and yield stress. Small amounts of hydrogen delay dislocation nucleation, contributing to the material ductile behavior. In contrast to the brittle behavior often observed in metallic systems with hydrogen, np Pd undergoes homogeneous plastic deformation that prevents fracture, even at high strain levels. This behavior is attributed to densification, with dislocation density increasing alongside hydrogen content. These findings suggest that np Pd has unique mechanical properties, presenting a promising potential for solid-state hydrogen storage applications.