  Hypothesis: Nanofluidic systems provide an emerging and efficient platform
for thermoelectric conversion and fluid pumping with low-grade heat energy. As
a basis of their performance enhancement, the effects of the structures and
properties of the nanofluidic systems on the thermoelectric response (TER) and
the thermoosmotic response (TOR) are yet to be explored. Methods: The
simultaneous TER and TOR of electrolyte solutions in nanofluidic membrane pores
on which an axial temperature gradient is exerted are investigated numerically
and semi-analytically. A semi-analytical model is developed with the
consideration of finite membrane thermal conductivity and the
reservoir/entrance effect. Findings: The increase in the access resistance due
to the nanopore-reservoir interfaces accounts for the decrease of short circuit
current at the low concentration regime. The decrease in the thermal
conductivity ratio can enhance the TER and TOR. The maximum power density
occurring at the nanopore radius twice the Debye length ranges from several to
dozens of mW K$^{-2}$ m$^{-2}$ and is an order of magnitude higher than typical
thermo-supercapacitors. The surface charge polarity can heavily affect the sign
and magnitude of the short-circuit current, the Seebeck coefficient, and the
open-circuit thermoosmotic coefficient, but has less effect on the
short-circuit thermoosmotic coefficient. Furthermore, the membrane thickness
makes different impacts on TER and TOR for zero and finite membrane thermal
conductivity.
