H–Cu vacancy co-segregation and H diffusion in Cu grain boundaries

Hydrogen embrittlement is a critical challenge in structural and electronic applications of copper (Cu), yet its atomistic mechanism remains incompletely understood. Here we combine density functional theory (DFT) and bond-order potential (BOP) simulations to determine hydrogen adsorption, incorporation, diffusion, and interaction with vacancies at Cu grain boundaries (GBs). Undercoordinated regions, such as surfaces and GB cores, act as preferential adsorption and incorporation sites for atomic hydrogen, especially in the presence of Cu vacancies. Hydrogen in the GB further enhances vacancy segregation, leading to stable H–V complexes with co-segregation energy gains of up to eV. Hydrogen migration barriers within the GB network are as low as 0.2 eV, significantly lower than in bulk Cu (0.42 eV), establishing GBs as fast transport pathways. Together, these results propose an atomistic mechanism that links H 2 exposure at Cu surfaces to H accumulation and H–V complexes formation at grain boundaries, clarifying the early stages of hydrogen-induced degradation in polycrystalline Cu. • Combined DFT and bond-order potential methodology provided an atomistic mechanism that links H 2 exposure at Cu surfaces to H accumulation and H–V Cu complexes formation at grain boundaries in Cu. • In the grain boundary, hydrogen migrates along low-barrier pathways (down to 0.2 eV) compared with bulk Cu ( 0.4 eV). • Hydrogen and V co-segregate at the grain boundary, forming stable H–V complexes with up to eV gain in energy.