  Graphite nanofibers (GNFs) have been demonstrated to be a promising material
for hydrogen storage and heat management in electronic devices. Here, by means
of first-principles and transport simulations, we show that GNFs can also be an
excellent material for thermoelectric applications thanks to the interlayer
weak van der Waals interaction that induces low thermal conductance and a
step-like shape in the electronic transmission with mini-gaps, which are
necessary ingredients to achieve high thermoelectric performance. This study
unveils that the platelet form of GNFs in which graphite layers are
perpendicular to the fiber axis can exhibit outstanding thermoelectric
properties with a figure of merit ZT reaching 3.55 in a 0.5 nm diameter fiber
and 1.1 for a 1.1 nm diameter one. Interestingly, by introducing 14C isotope
doping, ZT can even be enhanced up to more than 5, and more than 8 if we
include the effect of finite phonon mean-free path, which demonstrates the
amazing thermoelectric potential of GNFs.
