Voltage generation induced by thermo-driven ion solution flow in CNTs for low-grade thermal energy harvesting

The flow induced voltage generation has been regarded as an advanced energy harvesting technology at nanoscale with broad application prospects. The ionic liquid flow inside carbon nanotubes (CNTs) can be potential to harvest the low-grade thermal energy. In this work, the flow of aqueous solution of sodium chloride (NaCl) driven by the temperature gradient and the performance of voltage generation in CNT are investigated with the non-equilibrium molecular dynamics (MD) simulations. The accumulated displacement and the number density distribution of ions and water molecules are recorded in the simulations. The average flow velocities of ions are obtained and the flow-induced voltage is then predicted. The results show the thermal gradient along the axial direction of CNT drives the NaCl solution to flow from its hot end to cold one, which can drag the free charge carriers of CNT with a directional shift and generate a considerable voltage output. Moreover, the effects of temperature difference, CNT diameter and solution concentration on the ions flow and the flow-induced voltage are also studied. It is found the influence of the average flow velocity difference between Na+ and Cl− plays a dominant role on the flow-induced voltage, the different influencing factors show different rules in the variation of voltage generation. The findings in this work can contribute to the development of new energy-harvesting nano-devices for the low-grade thermal energy.