Towards highly-efficient thermoelectric power harvesting generators

Abstract

Power harvesting from thermoelectric generators is considered as a viable route towards sustainable energy generation by the conversion of thermal gradients occurring naturally or from waste heat sources into useful electrical energy. This thesis investigates the electrodeposition of n-type binary, ternary and doped thermoelectric materials, with the aim of demonstrating that electrodeposition can be used as a cost-effective and simple technique to fabricate highly-efficient thermoelectric materials. In order to achieve this, the thermoelectric and electrical properties of such materials must be related to their microstructural properties. Therefore, a detailed and systematic study of their microstructural properties, including morphology, crystal structure, composition and crystallite size, is undertaken whilst also measuring the electrical and thermoelectric properties. It is found that the potential of the working electrode, employed as the substrate during the electrodeposition of bismuth telluride, is one of the most effective variables in the fabrication process. More anodic potentials such as 0 V vs. SCE offer the best microstructural and thermoelectric properties. The addition of a surfactant, sodium lignosulphonate, to the electrolyte further improves the microstructural properties of bismuth telluride thin films, by levelling the deposits and inducing greater crystallographic orientation in growth planes perpendicular to the substrate. This is believed to be preferential for improving thermoelectric properties. The electrodeposition of the ternary thermoelectric material bismuth tellurium selenide shows that the microstructural and hence the thermoelectric and electrical properties of the thin films can be optimised by use of more positive electrode potentials. The thin films fabricated exhibit a thermoelectric efficiency of up to two orders of magnitude greater than similar materials prepared by electrodeposition previously and equal efficiency to those prepared by methods which are more costly and difficult to undertake. Doping these materials with copper, by electrochemical means, further improves the thermoelectric efficiency by over another order of magnitude.

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ORCID for Iris S. Nandhakumar: orcid.org/0000-0002-9668-9126

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