  This is the first report on the enhanced thermoelectric (TE) properties of
novel Bi2S3-Bi nanocomposites synthesized using a one-step polyol method at
different reaction temperatures (TRe) and time. They are well-characterized as
nanorod-composites, coexistent with orthorhombic Bi2S3 and rhombohedral Bi
phases together in which the latter coats the former forming Bi2S3-Bi
core-shell type structures along with independent Bi nanoparticles (NPs). There
is a very significant observation of systematic reduction in electri-cal
resistivity \r{ho} with reaction temperature and time duration increase,
revealing a promising approach for reduction of \r{ho} in this highly resistive
Bi2S3 and hence resolving the earlier obstacles for its thermoelectric
application potentials for the past few decades. Most astonishingly, TE power
factor at 300 K of highest Bi content nanocomposite pellet, made at 27 oC using
~900 MPa pressure, is 3 orders of magnitude greater than that of hot-pressed
Bi2S3, or even 23% better than that of spark plasma-sintered core-shell
Bi2S3@Bi sample reported earlier (Tarachand et al. Nano Res. 2016, 9, 3291; Ge
et al. ACS Appl. Mater. Interfaces 2017, 9, 4828). Considering the probable
greatly reduced thermal conductivity due to their complex nanostructures, the
significantly improved TE performance potential near 300 K is highly
anticipated for these toxic- and rare earth element-free TE nanocomposites,
making the present synthesis method as a pioneering approach for developing
enhanced thermoelectric properties of Bi2S3-based materials without using extra
sintering steps.
