Atomic-level insights into single-layer Co-promoted MoS2 clusters supported on a rutile TiO2(110) model oxide support

Abstract

Single-layer mixed metal transition metal dichalcodenides (TMDCs), such as Co-promoted MoS2 supported on metal oxide supports like TiO2, have a wide range of applications in heterogeneous, electro- and photocatalysis, energy harvesting, and energy storage. In this work, we present atomic-level insights into the interaction between single-layer Co-promoted MoS2 clusters and a model oxide rutile TiO2(110) support. We have used physical vapor deposition (PVD) to synthesize a precursor containing bimetallic Co-Mo nanoparticles supported on (1 × 1) TiO2(110). We sulfide this precursor using an H2S background of 1 × 10−3 mbar at 650 K to synthesize the Co-promoted MoS2 clusters. We use a combination of scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to analyze the Co-promoted MoS2 clusters. We compare our results with that of pristine MoS2 clusters supported on TiO2(110), synthesized by an identical procedure, but without the Co atoms. We demonstrate that Co addition enhances the yield of (Co-promoted) MoS2 clusters, in comparison to sulfidation of Mo nanoparticles to form MoS2 clusters. Additionally, we also find that the Co-promoted MoS2 clusters have predominantly high-index edge terminations which likely are stabilized by Co-S-Ti and Mo-S-Ti linkages to an (3 × 1) S-TiO2 structure formed during the sulfidation. This causes an increase in the local density of states (LDOS) at the BRIM sites, thereby increasing their contrast in the STM images at the linkage sites. We have used our experimental results to propose a candidate atomic model for the Co-promoted MoS2 clusters supported on TiO2(110).