  Molybdenum sulfide (MoS$_2$) has attracted significant attention due to its
great potential as a low-cost and efficient catalyst for the hydrogen evolution
reaction. Developing a facile, easily upscalable, and inexpensive approach to
produce catalytically active nanostructured MoS$_2$ with a high yield would
significantly advance its practical application. Colloidal synthesis offers
several advantages over other preparation techniques to overcome the low
reaction yield of exfoliation and drawbacks of expensive equipment and
processes used in chemical vapor deposition. In this work, we report an
efficient synthesis of alloyed Re$_x$Mo$_{1-x}$S$_2$ nanoflakes with an
enlarged interlayer distance, among which the composition
Re$_{0.55}$Mo$_{0.45}$S$_2$ exhibits excellent catalytic performance with
overpotentials as low as 79 mV at 10 mA/cm2 and a small Tafel slope of 42
mV/dec. Density functional theory calculations prove that enlarging the
distance between layers in the Re$_x$Mo$_{1-x}$S$_2$alloy can greatly improve
its catalytic performance due to a significantly reduced free energy of
hydrogen adsorption. The developed approach paves the way to design advanced
transition metal dichalcogenide-based catalysts for hydrogen evolution and to
promote their large-scale practical application.
