Hydrogen as a fuel has been considered promising for a more sustainable economy once it possesses high energy density and is considered a clean energy source. In this area, Brazil has the potential to become the largest producer of green hydrogen in the world, generating revenue for the country, in addition to receiving investment for infrastructure facilities and technological development. A promising route for green hydrogen production is through water electrolysis. However, the best catalysts currently found are based on noble metals such as platinum, which are expensive and scarce. With these considerations, molybdenum disulfide (MoS2) has been studied for application as a catalyst due to its high abundance and low cost. As it is well known for this MoS2, its activity is related to edge sites while the predominant basal plane is inert to such a process. Therefore, different works in the literature have proposed different methods to generate defects in the basal plane of MoS2. However, it is still challenging to control the position, size, and defective areas on the basal plane of MoS2 monolayers through most defect engineering routes. In this work, we report for the first time the fabrication of etched arrays in ultra-large MoS2 monolayers using focused ion beam (FIB). By adjusting the dose of Ga+ ions, it is possible to confine defects near the etched areas or spread them along the basal plane. The catalytic activity of FIB-produced etched arrays towards the hydrogen evolution reaction (REH) was measured by fabricating microelectrodes using a new method that preserves the catalytic sites. We demonstrate that the overpotential can be lowered to 290 mV by accessing basal plane activity only. Transmission electron microscopy images obtained for freestanding MoS2 monolayers patterned with FIB revealed the presence of amorphous regions and analysis by X-ray photoelectron spectroscopy indicated an excess of sulfur in these regions. The obtained results demonstrate a rational way to control the amorphous-crystalline boundaries on the surface and future insights for the optimization of defects in MoS2 monolayers. In addition to the creation of defects by FIB, additional tests were carried out for the first time regarding the creation of defects in MoS2 monolayers adsorbed on a gold surface by a mild chemical etching through hydrogen peroxide. These results revealed that conditions applied to generate defects in multilayer MoS2, previously described in the literature, cause complete etch of the monolayer. On the other hand, at lower concentrations, a redshift of the E12g peak, referring to in-plane vibration mode, was observed by Raman spectroscopy, indicating the generation of defects. In addition, HER measurements showed a reduction of about 200 mV in overpotential.
Bem-vindo(a) aos Anais do VII NanoMat, evento organizado pela Pós-graduação em Nanociências e Materiais Avançados da Universidade Federal do ABC (UFABC) com o intuito de reunir e debater trabalhos desenvolvidos por alunos e pós-doutorandos em Materiais e áreas afins.
Comissão Organizadora
Pedro Alves da Silva Autreto
Andre Luiz Martins de Freitas
Aryane Tofanello
Comissão Científica
Ferramenta completa de submissão, avaliação e publicação de anais para eventos científicos.
