Abstract
This report focuses on a novel strategy for the preparation of transition metal–MoS2 hybrid nanoclusters based on a one-step, dual-target magnetron sputtering, and gas condensation process demonstrated for Ni-MoS2. Aberration-corrected STEM images coupled with EDX analysis confirms the presence of Ni and MoS2 in the hybrid nanoclusters (average diameter = 5.0 nm, Mo:S ratio = 1:1.8 ± 0.1). The Ni-MoS2 nanoclusters display a 100 mV shift in the hydrogen evolution reaction (HER) onset potential and an almost 3-fold increase in exchange current density compared with the undoped MoS2 nanoclusters, the latter effect in agreement with reported DFT calculations. This activity is only reached after air exposure of the Ni-MoS2 hybrid nanoclusters, suggested by XPS measurements to originate from a Ni dopant atoms oxidation state conversion from metallic to 2+ characteristic of the NiO species active to the HER. Anodic stripping voltammetry (ASV) experiments on the Ni-MoS2 hybrid nanoclusters confirm the presence of Ni-doped edge sites and reveal distinctive electrochemical features associated with both doped Mo-edge and doped S-edge sites which correlate with both their thermodynamic stability and relative abundance.
Highlights
Transition metal dichalcogenides (TMDs) have emerged as promising materials for electrocatalytic applications
A lower sputtering power of only 3W on the Ni target was used in the preparation of the hybrid Ni-MoS2 nanoclusters in order to avoid an excess of Ni nanoclusters, whereas 8W of sputtering power was used on the
The activity of Ni-MoS2 hybrid nanoclusters is on par with previous reports of electrocatalytic enhancement to hydrogen evolution reaction (HER): an almost 3-fold increase in exchange current densities along with a significant shift in the onset potential, as well as an almost unaffected Tafel slope (≈ 120 mVdec−1)
Summary
Transition metal dichalcogenides (TMDs) have emerged as promising materials for electrocatalytic applications. The weakening of the S-doping metal bond on the MoS2 edge strengthens the H−S binding on the S-edge up to an optimal level for catalyzing the HER.[10] Experiments on MoS2 nanoparticles and MoS3 thin films reported an HER enhancement upon nonselective edge doping,[11,12] and later tests on edge-terminated MoS2 nanofilms correlated the 2-fold (in the case of Cu dopant) and almost 3-fold (for Fe, Co, Ni) HER enhancement observed with the activation of the S-edge sites.[13] Surprisingly, TM-doping on MoS2 nanoparticles (NPs) is scarcely reported probably due to the difficulty in separating the effects of surface area and morphology changes from the electrocatalytic enhancement.[14,15]
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