Defect Engineering of Ultra-large MoS₂ Monolayers by Electron Beam Lithography Toward the Hydrogen Evolution Reaction

The search for clean, renewable, and environmentally friendly hydrogen sources has made water an excellent feedstock candidate to produce hydrogen. Green H₂ production from water occurs by a system known as water splitting, however, a major challenge for this process is its unfavorable energy demand in bare electrodes, requiring a catalyst. Among the most studied materials in recent years, transition metal dichalcogenides (TMDs) stand out for their high performance in the hydrogen evolution reaction (HER). Among the TMDs, MoS₂ has shown promising catalytic properties with excellent stability and non-toxicity [1]. 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 [2]. In this work, the fabrication of defective arrays with resolution of approximately 250 nm on high aspect ratio MoS₂ monolayers using nanolithography is reported for the first time. By adjusting the size and distance of the patterns, it is possible to establish a quantitative relationship between the number of defects, i.e. edges created in the basal plane, and their electrocatalytic performance. The electrocatalytic activity of the arrays toward the hydrogen evolution reaction (HER) was measured by fabricating microelectrodes using a recently reported method that preserves the catalytic sites [2,3]. This catalyst showed outstanding activity, with an onset overpotential of 437 mV. Characterization analysis by Raman spectroscopy, AFM, KPFM, SEM and EDS revealed that the exposed regions underwent effective corrosion, resulting in ultra-large defect arrays on the basal plane.<br/>Acknowledgments<br/>We thank the São Paulo Research Foundation (FAPESP, 2022/00955-0), and Brazilian System of Laboratories in Nanotechnologies (SisNano).<br/>References<br/>[1] <i>Nanoscale</i>, 14, (2022) 6811.<br/>[2] <i>J. Mater. Chem. A</i>, 11, (2023) 19890.<br/>[3] <i>J. Mater Chem. A</i>, (2024) doi.org/10.1039/D4TA02042A