The Woodruff School

SUMMARY

Thermo-electrochemical cells (TECs) are devices that could convert waste heat to electricity inexpensively. However current TECs have low conversion efficiencies. As a starting point, I developed a comprehensive multiscale model that couples the governing equations in TECs (mass and heat transfer, electro-kinetics and fluid dynamics). The simulation results using an aqueous potassium ferri/ferrocyanide solution showed that TECs are limited by the ionic diffusion at the cold electrode. In addition, the model was used to find the optimum cell thickness, aspect ratio and number of cells in a series stack. In light of this ionic diffusion limitation, I investigated the current approaches used in the literature for other electrochemical devices to overcome this limit and improve performance. In particular, the addition of carbon nanotubes (CNTs) to a solvent-free ionic liquid (IL) electrolyte showed an efficiency improvement of 300% in dye-sensitive solar cells (DSSCs).

The main objective of this proposal is to understand the ionic transport mechanisms in CNT/IL mixtures. There are two questions to consider. Do CNTs affect the intrinsic physical diffusion of the ions by breaking the ion-associated pairs? Or do the nanotubes participate in homogenous reactions with the ions, thus setting an exchange-like ionic transport? The research plan involves the electrochemical characterization of ionic diffusion and conductivity of CNT/IL mixtures, and their dependence on other properties or material characteristics. Some conditions to evaluate are temperature, surface chemistry of the CNTs, CNT length, concentration of CNTs and redox couples. The research plan extends to evaluate a novel IL, BMIFeCN, as electrolyte for TECs. It is possible that BMIFeCN can maintain the fast electrokinetics and high redox entropy of ferri/ferrocyanide, and also experience the conductivity enhancement with the addition of CNTs. Another objective of this proposal is to extend the TEC model to porous electrodes and consider two more designs, tubular and flow cell.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Pablo Salazar Zarzosa

TIME:	Thursday, May 2, 2013, 1:30 p.m.

PLACE:	Love Building, 210

TITLE:	THERMO-ELECTROCHEMICAL CELLS: NUMERICAL OPTIMIZATION AND ENGINEERING OF NOVEL ELECTRODES AND ELECTROLYTES

COMMITTEE:	Dr. Baratunde Cola, Co-Chair (ME) Dr. Satish Kumar, Co-Chair (ME) Dr. Peter Hesketh (ME) Dr. Todd Sulchek (ME) Dr. Sankar Nair (CHBE) Dr. Thomas Fuller (CHBE)

SUMMARY Thermo-electrochemical cells (TECs) are devices that could convert waste heat to electricity inexpensively. However current TECs have low conversion efficiencies. As a starting point, I developed a comprehensive multiscale model that couples the governing equations in TECs (mass and heat transfer, electro-kinetics and fluid dynamics). The simulation results using an aqueous potassium ferri/ferrocyanide solution showed that TECs are limited by the ionic diffusion at the cold electrode. In addition, the model was used to find the optimum cell thickness, aspect ratio and number of cells in a series stack. In light of this ionic diffusion limitation, I investigated the current approaches used in the literature for other electrochemical devices to overcome this limit and improve performance. In particular, the addition of carbon nanotubes (CNTs) to a solvent-free ionic liquid (IL) electrolyte showed an efficiency improvement of 300% in dye-sensitive solar cells (DSSCs). The main objective of this proposal is to understand the ionic transport mechanisms in CNT/IL mixtures. There are two questions to consider. Do CNTs affect the intrinsic physical diffusion of the ions by breaking the ion-associated pairs? Or do the nanotubes participate in homogenous reactions with the ions, thus setting an exchange-like ionic transport? The research plan involves the electrochemical characterization of ionic diffusion and conductivity of CNT/IL mixtures, and their dependence on other properties or material characteristics. Some conditions to evaluate are temperature, surface chemistry of the CNTs, CNT length, concentration of CNTs and redox couples. The research plan extends to evaluate a novel IL, BMIFeCN, as electrolyte for TECs. It is possible that BMIFeCN can maintain the fast electrokinetics and high redox entropy of ferri/ferrocyanide, and also experience the conductivity enhancement with the addition of CNTs. Another objective of this proposal is to extend the TEC model to porous electrodes and consider two more designs, tubular and flow cell.