Novel tungsten nitride crystal providing nanochannels for hydrogen removal and recycling in PFMs

Hydrogen (H) removal in plasma-facing materials (PFMs) has been an important issue in the field of manually controllable fusion reactions. The tungsten nitride (WN_x) film, as a by-product on the divertor surface in the fusion reactor after nitrogen seeding, has rich H retention, and much attention should be given to hydrogen removal from WN_x. In this paper, by using density functional theory calculations, we predicted a novel W₂₄N₄₈ crystal, which possesses nanoscale cavities and channels inside, and studied the interaction between it and hydrogen. We found that the N atoms inside the crystal are favorable for the adsorption of atomic hydrogen. When more hydrogen atoms are injected, the hydrogen atoms adsorbed in the crystal react with the newly entered hydrogen atoms to form hydrogen molecules. These newly formed H₂ molecules can easily move through the nanochannels in W₂₄N₄₈ and serve to remove hydrogen. Our calculations suggest that when this new W₂₄N₄₈ material is embedded in the WN_x film on the surface of the PFMs, the nanochannels will be helpful in removing and recycling hydrogen isotopes in the PFMs.