Single-Atom Ni/MoS₂ Nanomaterial Produced by Thermal Shock for Gas-Phase Formic Acid Decomposition

A single-atom nickel doped molybdenum disulfide (2H-phase) nanomaterial/catalyst with a high Ni content (4.3 wt %) was synthesized using a thermal shock treatment of a Ni(OAc)2/(NH4)2MoS4 mixture in an Ar flow at 873 K. The X-ray photoelectron and X-ray absorption near-edge structure spectroscopy data indicated that Ni is present in a single Ni2+ cationic state. According to extended X-ray absorption fine structure spectroscopy, the coordination of the Ni atom in this Ni/MoS2 catalyst corresponds to four S atoms with Ni–S distances of 2.22 Å. These bond lengths suggest that the Ni atom substitutes for the Mo atom in the 2H–MoS2 structure. Therefore, Ni2+–S4 sites were formed. The catalyst was tested in gaseous formic acid decomposition and exhibited significantly higher hydrogen production at 413–513 K compared to both Ni-free MoS2 and 3 wt % Ni catalyst supported on porous carbon with the mean Ni particle size of 3.2 ± 1.7 nm. The Ni/MoS2 catalyst demonstrated only slight deactivation during 5 h of reaction testing at 483 K. Density functional theory (DFT) calculations showed that the formic acid molecule interacts more strongly with the Ni-doped MoS2 model than with the Ni-free MoS2 model. The results of the work could be useful for the development of MoS2-based nanomaterials for catalysis and electrochemistry applications.