Defence of doctoral thesis: Shaobo Han– Thermoelectric polymer-cellulose composite aerogels

Abstract:

Thermoelectric materials are scrutinized as energy materials and sensing materials. Indeed, they convert thermal energy into electrical energy. In addition, those materials are actively sensitive to a temperature modification through the generation of an electric signal. Organic thermoelectric (OTE) materials are complementary to inorganic thermoelectric materials, as they possess unique properties such as solution processing, ionic conductivity, flexibility, and softness. While thin-film OTE materials have been widely studied because they are easily manufactured by various coating techniques, little is done in the creation of three-dimensional morphologies of OTE materials; which is important to develop large temperature gradients.

Cellulose is the most abundant biopolymer on the planet. Recently, the applications of cellulose are not only limited in making papers but also in electronics as the cellulose provide 3-D microstructures and mechanical strength. One promising approach to make 3-D OTE bulks is using cellulose as scaffold because of their properties of relativelybhigh mechanical strength, water processability and environmentally friendly performance.

The aims of the thesis have been to enlarge the applications of an OTE material poly(3,4 -ethylenedioxythiophene) (PEDOT), with an approach of making 3-D aerogels composite with nanofibrillated cellulose (NFC), in two main areas: (1) multi-parameter sensors and (2) solar vapor generators. In the first application, we demonstrate that the new thermoelectric aerogel responds independently to pressure P, temperature T and humidity RH. Hence, when it is submitted to the three stresses (T, P, RH), the electrical characterization of the material enables to measure the three parameters without crosstalking effects. Thermoelectric aerogels are foreseen as active materials in electronic skins and robotics. In the second application, the conducting polymer aerogels are employed as solar absorbers to convert solar energy into heat and significantly increased the water evaporation rate. The IR absorption is efficient because of the free-electron in the conducting polymer PEDOT nano-aggregates. Because of the low cost of those materials and the water stability of the crosslinked aerogels, they could be of importance for water desalination.