Engineered MoSe2-Based Heterostructures for Efficient Electrochemical Hydrogen Evolution Reaction

2D transition metal-dichalcogenides are emerging as efficient and cost-effective electrocatalysts for the hydrogen evolution reaction (HER). However, only the edge sites of their trigonal prismatic phase show HER-electrocatalytic properties, while the basal plane, which is absent of defective/unsaturated sites, is inactive. Herein, the authors tackle the key challenge of increasing the number of electrocatalytic sites by designing and engineering heterostructures composed of single-/few-layer MoSe2 flakes and carbon nanomaterials (graphene or single-wall carbon nanotubes) produced by solution processing. The electrochemical coupling between the materials that comprise the heterostructure effectively enhances the HER-electrocatalytic activity of the native MoSe2 flakes. The optimization of the mass loading of MoSe2 flakes and their electrode assembly via monolithic heterostructure stacking provides a cathodic current density of 10 mA cm(-2) at overpotential of 100 mV, a Tafel slope of 63 mV dec(-1), and an exchange current density (j(0)) of 0.203 mu A cm(-2). In addition, thermal and chemical treatments are exploited to texturize the basal planes of the MoSe2 flakes (through Se-vacancies creation) and to achieve in situ semiconducting-to-metallic phase conversion, respectively, thus they activate new HER-electrocatalytic sites. The as-engineered electrodes show a 4.8-fold enhancement of j(0) and a decrease in the Tafel slope to 54 mV dec(-1).