Fig. 3

Selective intercalation from the top surface of sealed-edge MoS₂. a In situ optical microscopy images show uniform color change of MoS₂ upon Na⁺ intercalation and de-intercalation for sealed-edge MoS₂ through the top surface. b The color of MoS₂ remains unchanged when lowering the potential from 3 V to 0 V, indicating that K⁺ cannot intercalate through the top surface of sealed-edge MoS₂. c-d In situ optical microscopy images show prominent color changes due to Na⁺ and K⁺ intercalation through the edges of MoS₂. Scale bars in a-d, 5 µm. e-f In situ Raman spectra demonstrate Na⁺ intercalates into both sealed-edge MoS₂ and open-edge MoS₂. g-h In situ Raman spectra demonstrate K⁺ does not intercalate into sealed-edge MoS₂ but intercalate into open-edge MoS₂. The voltages in a, c, e, and f were with respect to NaCoO₂. The voltages in b, d, g, h were with respect K/K⁺