High thermoelectric and mechanical performance in the n-type polycrystalline SnSe incorporated with multi-walled carbon nanotubes

•A high ZT of ∼1.0 at 773 K and a high vickers hardness of >50 are simultaneously achieved in n-type SnSe.•MWCNTs act as “bridges” to accelerate the electron transport between n-SnSe grains.•MWCNTs act as phonon scattering centers to suppress the lattice thermal conductivity.•MWCNTs act as “binders” to bond adjacent n-SnSe grains and strengthen the hardness.