A novel ultrathin nanocrystalline CeO ₂ coating achieving high hydrogen permeation barrier performance

Abstract Hydrogen embrittlement is a serious issue faced by the structural metal materials in hydrogen infrastructures. Developing protective coatings as efficient hydrogen permeation barriers is an urgent need. 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 condition, 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 ultra-low permeability of 1.64×10-15 mol·m-1·s-1·Pa-1/2 at 500 ℃, three orders of magnitude lower than that of the 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 nano-coatings 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 contained 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.