Copper-hydroxyl interactions drive water-promoted copper surface oxidation and mobility

The reactions of oxygen (O₂) and water (H₂O) molecules with metal surfaces are critical to heterogeneous catalysis, corrosion, and electrochemical energy conversion. However, disentangling their individual roles remains challenging because both pathways yield the same dissociation product, atomic oxygen (O), and share the hydroxyl (OH) intermediate, thereby obscuring the molecular origin of metal oxidation. In this study, we combine in-situ transmission electron microscopy techniques and ReaxFF reactive force field molecular dynamics (MD) simulations to elucidate the promotional role of H₂O in copper (Cu) surface oxidation. Our results reveal that the structurally disordered Cu/CuO_x interface preferentially adsorbs OH derived from H₂O dissociation. The resulting strong Cu-OH interaction causes dynamic disorder in the topmost Cu layer while enriching electron density in the sublayer. This coupled structural and electronic modulation lowers the resistance for oxygen incorporation, promoting deeper lattice penetration, accelerating oxidation, and enhancing Cu atomic mobility. In contrast, oxidation under pure O₂ produces a comparatively ordered interface that suppresses sustained oxygen ingress, rendering further oxidation kinetically less favorable. These findings identify OH-mediated interfacial dynamics as a key driver of water-assisted metal oxidation and provide mechanistic guidance for controlling oxidation processes in catalytic and corrosion-resistant materials.