Niobium sulfides as catalysts for hydrotreating reactions

MoSx-coated NbS2 nanoflakes grown on glass carbon: an advanced electrocatalyst for the hydrogen evolution reaction

Recent experimental and theoretical studies have demonstrated that two-dimensional (2D) transition metal dichalcogenide (TMDC) nanoflakes are one of the most promising candidates for non-noblemetal electrocatalysts for hydrogen evolution reaction (HER). However, it is still challenging to optimize their conductivity and enrich active sites for highly efficient electrochemical performance. Herein, we report a chemical vapor deposition (CVD) and thermal annealing two-step strategy to controllably synthesize hybrid electrocatalysts consisting of metallic NbS₂ nanoflake backbones and a highly catalytic active MoS_x nanocrystalline shell on polished commercial glass carbon (GC). In addition, the amount of MoS_x in the hybrids can be easily adjusted. We first demonstrate that a small amount of MoS_x significantly promotes the HER activity of 2D NbS₂ nanoflakes, which is in good agreement with the density functional theory (DFT) calculation results. Moreover, the optimized MoS_x@NbS₂/GC electrocatalyst displays superior HER activity with overpotential of -164 mV at -10 mA cm^-2, a small Tafel slope of 43.2 mV dec^-1, and prominent electrochemical stability. This study provides a new path for enhancing the HER performance of 2D TMDC nanoflakes.

Large-scale synthesis of NbS2 nanosheets with controlled orientation on graphene by ambient pressure CVD

We report ambient pressure chemical vapor deposition (CVD) growth of single-crystalline NbS2 nanosheets with controlled orientation. On Si and SiO2 substrates, NbS2 nanosheets grow almost perpendicular to the substrate surface. However, when we apply transferred CVD graphene on SiO2 as a substrate, NbS2 sheets grow laterally lying on the graphene. The NbS2 sheets show the triangular and hexagonal shapes with a thickness of about 20-200 nm and several micrometres in the lateral dimension. Analyses based on X-ray diffraction and Raman spectroscopy indicate that the NbS2 nanosheets are single crystalline 3R-type with a rhombohedral structure of R3m space group. Our findings on the formation of highly aligned NbS2 nanosheets on graphene give new insight into the formation mechanism of NbS2 and would contribute to the templated growth of various layered materials.