Simultaneous thermoosmotic and thermoelectric responses in nanoconfined electrolyte solutions: Effects of nanopore structures and membrane properties

TL;DR

This study investigates how nanostructure and membrane properties influence thermoelectric and thermoosmotic responses in electrolyte-filled nanopores, revealing key factors that enhance energy conversion efficiency in nanofluidic systems.

Contribution

It introduces a semi-analytical model considering membrane thermal conductivity and interface effects, providing new insights into optimizing nanofluidic thermoelectric performance.

Findings

Access resistance reduces short circuit current at low electrolyte concentrations.

Lower thermal conductivity ratio enhances thermoelectric and thermoosmotic responses.

Maximum power density exceeds that of typical thermo-supercapacitors by an order of magnitude.

Abstract

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.