Oxygen Vacancy Formation on Boron-Contaminated Ti-V-Nb Non-Evaporable Getter Surfaces for Fusion Applications and Its Implications for Hydrogen Adsorption

The influence of boron surface contamination on oxygen activation and subsequent hydrogen adsorption on Ti-V-Nb non-evaporable getter (NEG) surfaces was investigated using density functional theory (DFT). A series of boron concentrations from 0 to 66.7 at.% was systematically introduced into the surface layer, spanning dilute perturbation to strong surface reconstruction regimes. Chemisorbed oxygen was fixed in a consistent configuration to simulate the passivating oxide overlayer formed under realistic conditions. Two independent performance criteria were considered. These were ease of activation, assessed by oxygen vacancy formation energy, and hydrogen pumping capability, assessed by H2 adsorption energy. The results reveal that moderate boron contamination at 41.7 at.% reduces the average oxygen vacancy formation energy by 1.232 eV, promoting easier oxygen removal, while excessive boron loading leads to oxygen trapping. Screening the concentrations by this descriptor therefore identifies 5B as the least detrimental to activation within the investigated range. On this surface, H2 adsorption is strongly site-dependent, with bridge and hollow sites exhibiting dissociative chemisorption. PDOS analysis shows that B 2p states mediate hydrogen activation either directly through B 2p-H 1s hybridization at the hollow site or indirectly by modifying the neighbouring metal centres at the bridge site, while the elevated work function of the 5B surface reflects enhanced surface dipole strength rather than a barrier to H2 adsorption. LST/QST calculations reveal a forward barrier of 0.422 eV for hydrogen migration from the surface into the subsurface, with the subsurface state thermodynamically more stable by 0.531 eV. These findings establish that moderate boron contamination does not severely hinder oxygen removal or eliminate hydrogen uptake, providing atomic-scale insight for fusion-relevant environments where boronization is routinely applied as a wall conditioning technique to suppress plasma contamination and sustain high-quality plasma confinement.