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

Abstract

Hydrogen (H) removal in plasma-facing materials (PFMs) has been an important issue in the field of manually controllable fusion reactions. The tungsten nitride (WNx) 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 WNx. 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 WNx film on the surface of the PFMs, the nanochannels will be helpful in removing and recycling hydrogen isotopes in the PFMs.