A novel ultrathin nanocrystalline CeO₂ coating achieving high hydrogen permeation barrier performance

Hydrogen embrittlement is a serious issue faced by structural metal materials in hydrogen infrastructures. The development of protective coatings as efficient hydrogen permeation barriers is urgently needed. Here, we report a new nanocrystalline CeO₂ coating with a thickness of ~40 nm successfully fabricated via the coordination-assisted deposition method. By optimizing the annealing conditions, the resultant CeO₂ coating has a uniform and dense structure, albeit with a high density of dislocations and grain boundaries. Its hydrogen permeation barrier performance was evaluated by a gas-driven deuterium permeation test, achieving an ultralow permeability of 1.64×10⁻¹⁵ mol·s⁻¹·m⁻¹·Pa^−1/2 at 500 °C, which is three orders of magnitude lower than that of stainless steel. The corresponding hydrogen permeation reduction factor (PRF) reaches an ultrahigh value of 2355, which is 4–75 times that of the other oxide nanocoatings, such as ZrO₂, Al₂O₃, Cr₂O₃, and Er₂O₃. The intrinsic hydrogen diffusion mechanism in the single-crystal coating is revealed by first-principles calculations. In the polycrystal coating, the dense dislocation and boundary-containing nanocrystalline structure not only provides abundant hydrogen traps but also prolongs the diffusion pathway to effectively impede hydrogen permeation. This study demonstrates the great potential of CeO₂ as a new type of hydrogen-resistant material and, most importantly, the roles of microstructure in the design of ultrathin hydrogen permeation barriers with high performance.