Thermoelectric properties of the modified natural aluminosilicates

Abstract

Natural layered bentonite and its artificial modifications have attracted growing interest in converting low-grade thermal energy into electricity. However, a substantial improvement in the thermoelectrical performance of modified clay remains a significant challenge. Modification is one way to solve the rising thermoelectrical efficiency of clays. Natural bentonite is a promising material for modifications by phosphate ions and magnetite because it is easily prepared in the water media. Such modifications demonstrated high thermoelectrical performance (increasing the Seebek coefficient by two times), thermostability, and durability. IR spectroscopy, X-ray diffraction analysis, atomic absorption spectroscopy, surface area measurements, SEM microscopy, and electrochemical impedance spectroscopy measurements have given the possibility to detect differences in the thermoelectric behavior of the natural and modified bentonite. Magnetite in bentonite enhances the Seebeck coefficient via localization of charge distribution and change in the size of pores, enlarging the non-linear distribution of the electrostatic capacitance due to changing the distribution of the absorbed water, surface, and structure's OH– groups in the natural bentonite. The modification by magnetite decreases the size of the pores to 50–100 nm in bentonite and increases the Seebeck coefficient by 30% on average. The incorporation of phosphate ions causes the decrease of the thermoelectric effect under rising the temperature. Design by PO43– increases the pore sizes more than two times and drops the Seebeck coefficient by 70% on average.