Electrocatalytic Reduction of N₂ to NH₃ Over Defective 1T′-WX₂ (X=S, Se, Te) Monolayers

Defects in transition metal dichalcogenides (TMDs) can serve as active sites in catalytic reactions. In this work, by means of first-principles calculations, the catalytic activities of WX₂ (X=S, Se, Te) monolayers in the 1T′ phase with both vacancy defects (missing chalcogen atoms, ^XV_d) and antisite defects (replacing chalcogen atoms with W atoms, ^XA_d) were evaluated for the nitrogen reduction reaction (NRR). Results showed that all these defective catalysts had great potential toward electrocatalytic ammonia synthesis by exhibiting low limiting potentials (U_L). Over 1T′-WTe₂@^TeV_d, 1T′-WS₂@^SA_d, 1T′-WSe₂@^SeA_d, and 1T′-WTe₂@^TeA_d, the corresponding U_L values were −0.49, −0.21, −0.19, and −0.15 V, much smaller than that of the benchmark catalyst, the Ru (0001) surface (U_L=−0.98 V). Furthermore, the hydrogen evolution reaction (HER) was inhibited. 1T′-WX₂ monolayers with the antisite defects showed better NRR activity than those with the vacancy defects because of the smaller steric hindrance at the former. Results suggest that the steric effect at the active surface sites should be utilized to develop better catalysts.