|M.Sc Student||Douglin John Chris.|
|Subject||The Essential Role of Water Management on the Performance|
and Stability of Anion Exchange Membrane Fuel
|Department||Department of Chemical Engineering||Supervisor||Professor Dario Dekel|
|Full Thesis text|
There is a consensus among researchers that hydrogen fuel cells constitute the core building blocks for sustainable, renewable energy conversion in the automotive industry. To date, proton exchange membrane fuel cells (PEMFCs) have seen great development in terms of research and commercialization. However, they suffer major challenges that prevent their widespread market proliferation. These include the dependence upon rare, platinum-based catalysts and components that can withstand the acidic operating environment. The Anion exchange membrane fuel cell (AEMFC) has recently gained increased visibility in the research community as they are technically similar and have the ability to overcome the cost challenge of PEMFC technology.
The main modification is the alkaline operating environment which offers several advantages including the potential use of low-cost platinum group metal (PGM)-free catalysts and hydrocarbon-based anion exchange membranes (AEMs). The modification in pH changes the electrochemical reactions, thereby exacerbating the issue of water management during fuel cell operation. This aggrandized issue of water management demands further attention within the community to be fully elucidated and serves as the focus of this thesis.
Inherent to its functioning, the AEMFC produces water at the anode which is consumed at the cathode. Therefore, the optimization of the operating conditions is of utmost importance to maintaining ideal performance and long-term stability. As the current (load) on the cell is increased, the water generated in the cell increases making the fuel cell susceptible to catalyst layer flooding. Conversely, membrane drying and catalyst degradation result if the water content is too low. Either condition has a negative impact on cell performance, therefore, a major area of focus in this thesis will be the optimization of operating conditions.
The design of the AEMFC is also critical in which water is managed. Since the field is still in its infancy, researchers throughout the literature have developed various techniques and materials to design AEMFCs. The gas diffusion electrode (GDE) technique, which has yielded the highest performance in the literature to date were utilized throughout this thesis. Additionally, highly conductive membranes and state of the art catalysts for the hydrogen oxidation reaction (HOR) and oxidation reduction reactions (ORR) were employed.
This work shows that dew point optimization has a significant effect on the water balance, both in the anode and the cathode, hence a positive effect on fuel cell performance at 60 °C for three of the four membranes studied. At 70 °C and 80 °C, applying back-pressure to one or both electrodes helped to reduce flooding, and prevent membrane dehydration. The optimum pinch and cathode gas porosity were found to be 20 and 37% respectively which are a function of the Teflon gaskets chosen as well as the ionomer to platinum to carbon ratio (I:Pt:C) ratio in the cathode. As materials for AEMFCs are undergoing extensive and world-wide research, this work will help to further the understanding the key factors that influence effective management of water and their combined impact on performance and long-term stability.
Keywords: fuel cell, alkaline electrolyte, anion exchange membrane, water management