Rational design of three-dimensional MoS₂ nanoflower-rGO heterostructure for high-performance electrocatalytic...

Developing efficient and low-cost non-noble-metal electrocatalysts for the hydrogen evolution reaction (HER) is essential for sustainable hydrogen production. Herein, we report the hydrothermal synthesis of a three-dimensional MoS₂ nanoflower/reduced graphene oxide (MoS₂ NF-rGO) hybrid heterostructure, where MoS₂ nanoflowers are uniformly anchored onto rGO nanosheets. The as-prepared MoS₂ NF-rGO exhibits superior HER activity, delivering a low overpotential of 172 mV at a cathodic current density of 10 mA cm^-2 with a remarkably low Tafel slope of 54 mV dec^-1 in 0.5 M H₂SO₄. In alkaline medium (1.0 M KOH), the catalyst achieves a cathodic current density of 10 mA cm^-2 at an overpotential of 406 mV with a Tafel slope of 190 mV dec^-1, while retaining nearly 100% activity after a continuous 50 h chronoamperometry stability test. These values significantly outperform pristine MoS₂, which requires overpotentials of 309 mV and 475 mV to achieve the cathodic current density of 10 mA cm^-2 in acidic and alkaline media, respectively. Comparative analysis further reveals that the MoS₂-rGO composite with spherical morphology exhibits inferior HER performance despite having a nearly similar composition to MoS₂ NF-rGO, highlighting the important role of MoS₂ morphology in determining the catalytic activity. Cross-referencing the microscopic, spectroscopic, and electrochemical results suggests that the enhanced HER performance of MoS₂ NF-rGO is associated with its hierarchical nanoflower architecture, which provides abundant exposed edge sites and a larger electrochemically active surface area, while EIS measurements show that MoS₂ NF-rGO exhibits the lowest charge-transfer resistance relative to bare MoS₂ nanoflowers and MoS₂-rGO, consistent with more facile electrochemical charge-transfer kinetics.