Single-atom nickel anchored on surface of molybdenum disulfide for efficient hydrogen evolution

Abstract Owing to the advantages with both uniform dispersity of active sites like liquid and recycling of solid catalysts, single-atom electro-catalysts improve their catalytic activities remarkably over conventional catalysts. Herein, single-atom nickel was assembled on surface of MoS2 to form Ni-anchored MoS2 (Nisa-MoS2) electro-catalyst by means of thermal balance at 200 ℃ for 24 h. High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and Energy dispersive X-ray (EDX) mapping displayed single-atoms of nickel were uniformly dispersed on MoS2. X-ray diffraction (XRD) indicated the hexagonal structure of crystalline MoS2 with space group of P 36/mmc was formed and the thermal balance treatment facilitated the crystallization of plane (002) in the presence of Ni(II) solution. X-ray photoelectron spectrometry (XPS) detected the Ni(II) 2p binding energy on surface of MoS2. The over-potential of 196 mV and Tafel slope of 87 mV dec-1 for Nisa-MoS2 electrocatalyst has been achieved for hydrogen evolution reaction (HER) in 1.0 mol/L KOH solution, whereas pristine MoS2 possessed an over-potential of 462 mV and Tafel slope of 433 mV dec-1 for HER, indicating the single-atoms of Ni improved the HER activity significantly. HER on Nisa-MoS2 electro-catalyst follows Volmer-Heyrovsky mechanism in alkaline electrolyte. Ethylenediaminetetraacetic acid (EDTA) and thiocyanate (SCN-) are used to identify the active sites. The results displayed the over-potentials remarkably shifted negatively by ∼50 mV in the presence of EDTA and SCN-, suggesting the single-atoms of nickel were active sites. The impact structure of MoS2 was fabricated after single nickel atoms were anchored on MoS2, the new electronic states led to the high catalytic performance of the confined single nickel atoms, and the confined single nickel atoms could in turn affect the intrinsic activity of MoS2. It is the synergistic effect between Ni and MoS2 that reduced the energy barrier and promoted the HER effectively.