Tunable 3D/2D MoS 2 /Ni 3 S 2 nanocomposites as an Efficient Electrocatalyst for Hydrogen Evolution Reaction

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMD), such as molybdenum disulfide (MoS₂), have high potential to replace noble metals as electrocatalysts for hydrogen evolution reaction (HER) from water splitting, owing to their much lower cost. Although MoS₂ nanosheets have some active sites located mostly on their edges, their relatively large basal planes have high hydrogen adsorption free energy, limiting their HER activity. Doping of TMD with other transition metals such as Ni is an effective strategy to enhance their electrocatalytic property. Herein, we adopted Ni₃S₂ with a high Ni/S ratio for doping MoS₂ nanoflowers that were produced in a one-pot hydrothermal process for forming 2D/3D Ni₃S₂/MoS₂ nanocomposites. The fabricated MoS₂:Ni₃S₂ heterostructure only needs to incorporate a small amount of Ni₃S₂ for producing excellent HER activity. The optimized MoS₂:Ni₃S₂ nanocomposite with a molar ratio of 1:0.125 (NMS1) in 0.5 M H₂SO₄ provides a dramatically lowered overpotential of 135 mV at 10 mA cm⁻² and a small Tafel slope of 51 mV dec⁻¹, as compared to the pristine MoS₂ nanoflower that was produced by a hydrothermal process with an overpotential of 233 mV and a Tafel slope of 53 mV dec⁻¹.. Based on the X-ray absorption near-edge structure (XANES) analysis of the MoS₂/Ni₃S₂ heterostructure, the partial substitution of Ni for Mo occurred in the MoS₂/Ni₃S₂ heterostructure that has induced a highly expanded surface and thus induced active sites, leading to enhanced HER efficiency. This approach of designing bimetallic sulfide 2D/3D composites involving transition metals provides high potential for HER applications.