Work

Temperature-dependent hydrogen uptake in pure iron: The role of the native oxide and interfacial trapping

Year: 2026

Type: article

Abstract: The role of the native iron oxide with regards hydrogen uptake in iron remains insufficiently understood, particularly under gaseous hydrogen at elevated temperature, where oxide reduction can modify the surface state during exposure. Here, pure iron was exposed to 1 bar H₂ using either uniform heating from room temperature to 700 °C or a two-stage protocol involving pre-reduction at 700 °C followed by exposure at lower temperature. Hydrogen depth profiles were measured by ToF-SIMS, while XPS and in situ XRD were used to characterize the nature of the initial oxide and its evolution under hydrogen. Under uniform heating, no significant hydrogen penetration into the iron substrate was detected up to 400 °C, confirming the barrier effect of the native oxide. Hydrogen uptake became measurable at 450–550 °C but was not enhanced at 650–700 °C. In contrast, pre-reduction at 700 °C markedly increased hydrogen uptake during subsequent exposure at 400–600 °C. In situ XRD showed that direct heating at 400 °C produced only partial hematite reduction, with magnetite, wüstite and metallic iron detected, whereas heating to 700 °C led to complete reduction to metallic iron. Hydrogen uptake is therefore governed not only by temperature, but also by the surface state established during exposure. Samples exhibiting hydrogen uptake also showed local enrichment near the oxide/metal interface. Degassing experiments indicated rapid hydrogen release from the substrate but slower depletion at the interface, consistent with transient interfacial trapping. Overall, the native oxide and its thermal evolution govern both hydrogen entry and near-surface redistribution in iron.

Source: Corrosion Science

DOI: 10.1016/j.corsci.2026.114286