Giant Thermoelectric Effect in Graded Micro-Nanoporous Materials

Abstract

In this work we report on opportunities for a colossal reduction in lattice thermal conductivity (LTC) of graded micro-nanoporous structures with inhomogeneous porosity which leads to the considerable improvement in thermoelectric figure of merit ZT. We employ the effective medium theory to calculate the LTC of a porous media with hole pores of variable radius and show that porous materials with inhomogeneous porosity are expected to have stronger reduction (about 30 times!) in thermal conductivity than those with pores of equal sizes. Such a reduction is caused by enhanced scattering of thermal phonons with the pore boundaries. We have studied the variations of the LTC as a function of porosity, pore sizes, geometry and the number of pore groups with different sizes. Our theoretical results show excellent agreement with experimental data.

Thermal conductivity reduction in three dimensional graphene-based nanofoam

“…Alternatively, a recent report by Dimitris et al suggested that it may be possible to obtain a strong reduction in thermal conductivity values with graded porous materials having inhomogeneous porosity, compared to that of materials with homogenous porosity. 15 Inhomogeneous porosity denotes random/different pore size throughout the structure. However, it is difficult to experimentally engineer inhomogeneous porous materials.…”