טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKafri Bar
SubjectGlobal Modeling of an Alkaline Membrane Fuel Cell System
DepartmentDepartment of Chemical Engineering
Supervisors Professor Simon Brandon
Dr. Nir Haimovich
Full Thesis textFull thesis text - English Version


Abstract

Fuel cells are devices that convert chemical energy from a fuel (most commonly hydrogen) into electricity through a chemical reaction with an oxidizing agent (most commonly oxygen), much like the reaction in common batteries, but with a continuous supply of reactants (fuel and oxidizer). Alkaline fuel cells are a class of fuel cells which use a redox reaction that produces/consumes hydroxide ions in the two half-cell reactions. Alkaline Membrane Fuel cells (AMFCs) are a particular type of alkaline fuel cells which use an ionomeric immobilized membrane as an electrolytic layer, between the two half cells.

  Good water management is an inherent necessity, as due to the cell's half-reactions there is production of water on the anode side, where only half of this water is consumed on the cathode side, and where portions of the excess may go out of either. Thus, there could be an accumulation of water on one side of the cell, a situation which might lead to "flooding" in the ACL (Anode Catalytic Layer), being destructive for both the cell's function and its materials. On the other hand, the opposite situation, "dry-out" in the CCL (Cathode Catalytic Layer), is just as harmful, and may independently occur or co-exist with ACL "flooding".

  Therefore, the main goal of this study is to analyze dynamic heat and water transport in an AMFC using an appropriate model, as these processes are crucial to both cell electrical performance and stability.  Hence, as far as mass transfer is concerned - only the water component is modeled using a one-dimensional spatio-temporal approach. Heat transfer is then analyzed based on a piece-wise lumped parameter approach. The cell is divided into several control volumes, representing its main regions, where each (isothermal) volume thermally interacts with its neighbors in a manner dependent on (and thus coupled with) local water content.

  The model is used to describe the effect of several parameters on the electric performance of the cell, its temperature and the water content along the cell, providing a decision making tool for designers in order to optimize the cell's performance with respect to these parameters.  The model products include polarization (I/V) curves, water spatial distribution along the cell, and temperature transients of every control volume.