First-Principles Characterization of Potassium Intercalation in Hexagonal 2H-MoS₂

Periodic density functional theory calculations were performed to study the structural and electronic properties of potassium intercalated into hexagonal MoS 2 (2H-MoS 2 ). Metallic potassium (K) atoms are incrementally loaded in the hexagonal sites of the interstitial spaces between MoS 2 layers of the 2H-MoS 2 bulk structure generating K x MoS 2 (0.125 ≤ x ≤ 1.0) structures. To accommodate the potassium atoms, the interstitial spacing c parameter in the 2H-MoS 2 bulk expands to 15.871 Å in K 0.125 MoS 2 . The second lowest potassium loading concentration (K 0.25 MoS 2 ) results in the largest interstitial spacing expansion (to c = 16.617 Å). Our calculations show that there is a small gradual contraction of the interstitial spacing as the potassium loading increases with c = 14.785 Å for KMoS 2 . This interstitial contraction is correlated with an in-plane expansion of the MoS 2 layers, which is in good agreement with experimental X-ray diffraction (XRD) measurements. The electronic analysis shows that potassium readily donates its 4 s electron to the conduction band of the MoS 2, and is largely ionic in character. As a result of the electron donation, the K x MoS 2 system changes from a semiconductor to a more metallic system with increasing potassium intercalation. For loadings 0.25 ≤ x ≤ 0.625, triangular Mo–Mo–Mo moieties are prominent and tend to form interlayer rhombitrihexagonal tessellated patterns. Intercalation of H 2 O molecules that solvate the K cations is likely to occur in catalytic conditions. The inclusion of two H 2 O molecules per K atom in the K 0.25 MoS 2 structure shows good agreement with XRD measurements.