Patterning edge-like defects and tuning defective areas on the basal plane of ultra-large MoS₂ monolayers toward the hydrogen evolution reaction

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Florindo, Bianca Rocha ; Hasimoto, Leonardo H. ; de Freitas, Nicolli ; Candiotto, Graziani ; Lima, Erika Nascimento ; de Lourenco, Claudia ; de Araujo, Ana B. S. ; Ospina, Carlos ; Bettini, Jefferson ; Leite, Edson R. ; Lima, Renato S. ; Fazzio, Adalberto ; Capaz, Rodrigo B. ; Santhiago, Murilo

• Document type: Journal article
• Source: JOURNAL OF MATERIALS CHEMISTRY A; v. 11, n. 37, p. 10-pg., 2023-09-26.

Abstract

The catalytic sites of MoS2 monolayers towards hydrogen evolution are well known to be vacancies and edge-like defects. However, it is still very challenging to control the position, size, and defective areas on the basal plane of MoS2 monolayers by most of the defect-engineering routes. In this work, the fabrication of etched arrays on ultra-large supported and free-standing MoS2 monolayers using a focused ion beam (FIB) is reported for the first time. By tuning the Ga+ ion dose, it is possible to confine defects near the etched edges or spread them over ultra-large areas on the basal plane. The electrocatalytic activity of the arrays toward the hydrogen evolution reaction (HER) was measured by fabricating microelectrodes using a new method that preserves the catalytic sites. We demonstrate that the overpotential can be decreased up to 290 mV by assessing electrochemical activity only at the basal plane. High-resolution transmission electron microscopy images obtained on FIB patterned freestanding MoS2 monolayers reveal the presence of amorphous regions and X-ray photoelectron spectroscopy indicates sulfur excess in these regions. Density-functional theory calculations enable identification of catalytic defect sites. Our results demonstrate a new rational control of amorphous-crystalline surface boundaries and future insight for defect optimization in MoS2 monolayers. (AU)

• FAPESP's process: 22/00955-0 - Study of the influence of mechanical deformations on the performance of stretchable devices based on MoS2 for application in the energy area
• Grantee: Leonardo Hideki Hasimoto
• Support Opportunities: Scholarships in Brazil - Doctorate