  Single- and few-layered InSe flakes are produced by the liquid-phase
exfoliation of beta-InSe single crystals in 2-propanol, obtaining stable
dispersions with a concentration as high as 0.11 g/L. Ultracentrifugation is
used to tune the morphology, i.e., the lateral size and thickness of the
as-produced InSe flakes. We demonstrate that the obtained InSe flakes have
maximum lateral sizes ranging from 30 nm to a few um, and thicknesses ranging
from 1 to 20 nm, with a max population centred at ~ 5 nm, corresponding to 4
Se-In-In-Se quaternary layers. We also show that no formation of further
InSe-based compounds (such as In2Se3) or oxides occurs during the exfoliation
process. The potential of these exfoliated-InSe few-layer flakes as a catalyst
for hydrogen evolution reaction (HER) is tested in hybrid single-walled carbon
nanotubes/InSe heterostructures. We highlight the dependence of the InSe flakes
morphologies, i.e., surface area and thickness, on the HER performances
achieving best efficiencies with small flakes offering predominant edge
effects. Our theoretical model unveils the origin of the catalytic efficiency
of InSe flakes, and correlates the catalytic activity to the Se vacancies at
the edge of the flakes.
