Pristine Basal- and Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Molybdenum disulfide (MoS2) possesses a layered structure with distinct basal and edge planes.
• Theoretical predictions suggest higher electroactivity for the edge plane compared to the basal plane.
• Experimental evidence directly comparing the electrochemical properties of MoS2 basal and edge planes is limited.

Purpose of the Study:

• To experimentally compare the electrochemical properties of the basal and edge planes of macroscopic molybdenum disulfide (MoS2) crystals.
• To provide direct experimental validation for theoretical predictions regarding MoS2 surface electroactivity.

Main Methods:

• Utilized macroscopic MoS2 pristine crystals with controlled exposure of basal or edge planes.
• Characterization included Atomic Force Microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry.
• Employed digital simulations and Density Functional Theory (DFT) calculations to support experimental findings.

Main Results:

• Raman spectroscopy revealed anisotropic phonon mode excitation between basal (E2g) and edge (A1g) planes.
• The edge plane exhibited significantly higher heterogeneous electron transfer rate constants (k(0)) for [Fe(CN)6](3-/4-) and [Ru(NH3)6](3+/2+) redox probes compared to the basal plane.
• The basal plane showed negligible activity for the hydrogen evolution reaction, while the edge plane demonstrated higher activity, mirroring the [Fe(CN)6](3-/4-) redox probe results.

Conclusions:

• The edge plane of MoS2 is experimentally confirmed to be substantially more electrochemically active than the basal plane.
• The findings support theoretical predictions and highlight the importance of surface orientation for MoS2 electrochemical applications.
• MoS2 basal planes are largely inactive for key electrochemical reactions like hydrogen evolution, emphasizing the superior performance of edge sites.