טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZhegur Khais Avital
SubjectCharacterization of Anion Exchange Membranes for Fuel
Cells Applications
DepartmentDepartment of Chemical Engineering
Supervisor Professor Dario Dekel
Full Thesis textFull thesis text - English Version


Abstract

Anion exchange membrane fuel cells (AEMFCs) are highly efficient electrochemical devices that convert the chemical energy of its reactants directly into electric energy. AEMFCs are clean energy sources which only produce water and heat as a byproduct. AEMFC utilizes anion exchange membrane (AEM) as a solid electrolyte to transport hydroxide (OH‾) ions from the cathode, where they are produced, to the anode side, where they are consumed. AEM is a polymeric membrane with a fixed cationic group, mostly nitrogen-based quaternary ammonium. AEMFCs offer several advantages over the more established proton exchange membrane fuel cells (PEMFCs). Those advantages include an alkaline environment which enables the use of non-Platinum group metals as the catalyst and facile reactions kinetics.

AEMFC is compatible with the initial performance of the state-of-art PEMFC however, there are still challenges to overcome. One of them is the chemical stability of the AEM under the operating conditions. AEM's quaternary ammonium group decomposes in the presence of OH‾ ions, causing a reduction of its number and in turn, decreasing the AEM's conductivity reducing the overall performance of the AEMFC. Another major challenge is the undesirable reaction of OH‾ with CO2 when the fuel cell is operated under ambient air (~400ppm CO2). The OH‾ fast reaction with CO2 result in converting OH‾ to bulkier and less mobile CO32‾/HCO3‾ ions which harm AEM conductivity.

In this work, the effect of chemical degradation on AEM properties was studied. It was found that conductivity has a different trend than water uptake (WU) with ion exchange capacity (IEC). Degradation has a significant influence on the AEM conductivity, as conductivity is dropping significantly after a critical degradation point. Besides, a novel method was used to convert the AEM to its fully OH‾ form to study the kinetics of the de-carbonation process for different structure AEMs. Overall, this work may be used as a reference study for future research in the AEMFC community.