Rational design of three-dimensional MoS2 nanoflower-rGO heterostructure for high-performance electrocatalytic hydrogen evolution reaction in acidic and alkaline media.

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.