Unveiling Active Sites for the Hydrogen Evolution Reaction on Monolayer MoS₂

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Molybdenum disulfide (MoS2) is a promising material for catalysis.
• Understanding the specific active sites in MoS2 is crucial for optimizing its performance.
• The hydrogen evolution reaction (HER) is a key process in sustainable energy technologies.

Purpose of the Study:

• To investigate and compare the HER activities of edge and basal-plane sites in monolayer MoS2.
• To quantify the catalytic performance of different MoS2 sites using turnover frequencies (TOFs).
• To explore the catalytic mechanism of MoS2 in comparison to traditional metal catalysts.

Main Methods:

• Synthesis of monolayer MoS2 using chemical vapor deposition (CVD).
• Site-specific analysis using selected-area lithography and electron-beam lithography.
• Local probe measurements to determine HER activity at distinct MoS2 sites.
• Calculation of TOFs based on estimated active site densities.

Main Results:

• MoS2 edge sites (both 1T' and 2H phases) show significantly higher HER activity than basal-plane sites.
• TOF values for 1T'-MoS2 edges and 2H-MoS2 edges are 3.8 ± 1.6 × 10^-4 s^-1 and 1.6 ± 1.2 × 10^-4 s^-1, respectively.
• TOF values for 1T'-MoS2 basal planes and 2H-MoS2 basal planes are 0.008 ± 0.002 × 10^-4 s^-1 and 1.9 ± 0.8 × 10^-4 s^-1, respectively.
• Edge sites exhibit catalytic activity comparable to platinum.

Conclusions:

• MoS2 edge sites are the primary active centers for HER catalysis.
• The HER mechanism on MoS2 may differ from that of conventional metal catalysts, as indicated by its position on the HER volcano plot.
• These findings highlight the potential of MoS2 as an efficient electrocatalyst for hydrogen production.