Operando Imaging Reveals Active Wrinkled Regions for Hydrogen Evolution in MoS₂ Electrocatalysts

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Understanding structure-activity relationships in non-metallic electrocatalysts is crucial but challenging due to coupled charge-transfer and chemical steps.
• Local structural distortions significantly influence electrocatalytic performance, yet their specific roles remain poorly understood under operando conditions.

Purpose of the Study:

• To investigate the influence of local structural distortions on electrocatalysis in monolayer molybdenum disulfide (MoS2) during the hydrogen evolution reaction (HER).
• To spatially resolve the active sites and understand the underlying mechanisms responsible for enhanced HER activity in MoS2.

Main Methods:

• Operando atomic force microscopy-scanning electrochemical microscopy (AFM-SECM) to identify active domains.
• Combined AFM-SECM and scanning transmission electron microscopy (STEM) for high-resolution imaging of structural features.
• Operando electron-transfer (ET) imaging to assess charge-transfer kinetics.

Main Results:

• Wrinkled regions in monolayer MoS2 were identified as highly active domains for HER.
• Enhanced HER activity was localized at wrinkle edges with folded edge structures, demonstrating a clear structure-activity relationship.
• Limited enhancement in charge-transfer kinetics was observed, suggesting improved chemical steps as the primary driver of activity.

Conclusions:

• Folded edge structures within wrinkled regions of MoS2 play a key role in promoting HER activity.
• The enhanced activity is attributed to the promotion of subsequent chemical steps rather than solely improved electron transfer.
• These findings provide mechanistic insights for designing advanced non-metallic electrocatalysts.