Modeling and experiments to develop thermo-electrochemical cells

Abstract

Low-temperature waste heat recovery is an important component of generating a more efficient, cost-effective and environmentally-friendly energy source. To meet this goal, thermo-electrochemical cells (TECs) are cost-effective electrochemical devices that produce a steady electric current under an applied temperature difference between their electrodes. However, current TECs have low conversion efficiencies. On this project, I developed a comprehensive multiscale model that couples the governing equations in TECs. The model was used to understand the fundamental principles and limitations in TECs, and to find the optimum cell thickness, aspect ratio and number of cells in a series stack. Doped multiwall carbon nanotubes (MWCNTs) were then explored as alternative electrodes for TECs. One of the main objectives of this dissertation is to study multiwall carbon nanotube/ionic liquid (MWCNT/IL) mixtures as alternative electrolytes for TECs. Previous authors showed that the addition of carbon nanotubes (CNTs) to a solvent-free IL electrolyte improves the efficiency of dye solar cells by 300%. My research plan involved a spectroscopy analysis of imidazolium-based ionic liquids (IILs) mixed with MWCNTs using impedance spectroscopy and nuclear magnetic resonance. The results show that the combination of interfacial polarization and ion pair dissociation effects reduces mass transfer resistances and enhances the power of TECs at low wt% of MWCNTs. This happens in spite of reduced open circuit voltage due to percolated networks.