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Zirconium phytate-based proton conductors for high-temperature fuel cell applications
Nimir, Wessam Ahmed Mohamed
Nimir, Wessam Ahmed Mohamed
Date
2023-04
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Thesis
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Description
A Master of Science thesis in Chemical Engineering by Wessam Ahmed Mohamed Nimir entitled, “Zirconium phytate-based proton conductors for high-temperature fuel cell applications”, submitted in April 2023. Thesis advisor is Dr. Amani Al-Othman and thesis co-advisor is Dr. Muhammad Tawalbeh. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Abstract
Hydrogen fuel cells are regarded among clean power sources. They yield almost zero emissions with water being the only product. A functional membrane is the heart of the proton exchange membrane (PEM) fuel cell. This thesis describes the development of novel composite membranes for high-temperature PEM fuel cells (HT-PEMFCs) in particular. PEM fuel cells usually operate around 80°C. HT-PEMFCs operating above water’s boiling point are preferred due to their improved kinetics, heat recovery, superior water management, and enhanced tolerance to hydrogen fuel impurities. Nafion, the current conventional membrane in PEMFCs, cannot be used above 100°C, as its proton conductivity decreases dramatically. In this thesis, high-temperature and Nafion-free membranes are reported. These membranes are based on zirconium phytate (ZrPA), Silicotungstic acid (STA), and ionic liquids (ILs). Porous polytetrafluoroethylene (PTFE) polymer was used as a support. Various mass percentages of STA, and ILs were utilized and investigated. The membranes were characterized by electrochemical spectroscopy (EIS) and showed promising proton conductivity upon the addition of ILs. The unmodified ZrPA membrane had a proton conductivity of 6.65×10⁻⁴ S/cm. The inclusion of STA resulted in a ten-fold increase, raising it to 2.23×10⁻³ S/cm. This work investigated the effect of adding a plasticizer agent, polyethylene glycol (PEG). Further modification with PEG raised the proton conductivity to 3.81×10⁻² S/cm. The maximum proton conductivity (0.1 S/cm), similar to Nafion's conductivity, was obtained with 5.86 wt% of the IL ([HMIM][C₄N₃⁻]). A high-temperature test up to 150°C showed a decrease in conductivity by two orders of magnitude (10⁻ᵌ S/cm) but, promising conductivity. Water uptake analysis revealed that the modified ZrPA/STA/PEG/ILs membranes could hold more than 60 wt% of water. The modified membranes were further characterized by TGA, SEM, EDX, and XRD. The TGA results showed a decrease of 34 wt% at 600°C. FTIR and XRD analysis indicated a change in their crystalline and revealed substantial changes in particle diameter and morphology. The previous results showed that the synthesized membranes in this thesis are of great potential for HT-PEMFC applications.