Theses

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The theses in UWSpace are publicly accessible unless restricted due to publication or patent pending.

This collection includes a subset of theses submitted by graduates of the University of Waterloo as a partial requirement of a degree program at the Master's or PhD level. It includes all electronically submitted theses. (Electronic submission was optional from 1996 through 2006. Electronic submission became the default submission format in October 2006.)

This collection also includes a subset of UW theses that were scanned through the Theses Canada program. (The subset includes UW PhD theses from 1998 - 2002.)

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Browsing Theses by Author "Ahmed, Khaja Wahab"

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    Development and Evaluation of Nickel and Cobalt-Based Mixed Metal Oxide Catalysts for Anion Exchange Membrane Water Electrolysis
    (University of Waterloo, 2024-12-12) Ahmed, Khaja Wahab
    Hydrogen production using an Anion exchange membrane (AEM) electrolyzer allows the use of non-platinum group metal (PGM) catalysts for oxygen evolution reaction (OER). Nickel and Cobalt-based oxides are active in an alkaline environment for OER and are relatively inexpensive compared to IrO2 catalysts used in Polymer electrolyte membrane (PEM) electrolysis. This study explores the catalytic performance and stability of nickel and cobalt-based oxides, particularly NiFeOx, NiFe2O4, and NiFeCoOx, in OER and AEM water electrolysis. In the first study, mixed metal oxide catalysts NiFeOx and NiFeCoOx catalysts were synthesized by coprecipitation method using NaOH. The catalysts were characterized through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The NiFeCoOx catalysts demonstrated superior performance in AEM water electrolysis compared to NiFeOx and NiO, achieving the highest current density of 802 mA cm−2 at 2 V and 70°C using 1M KOH as the electrolyte. Electrochemical Impedance Spectroscopy (EIS) and equivalent circuit fitting were used to assess ohmic and activation resistances. Results indicated a reduction in both ohmic and activation resistances with increasing electrolyte concentration. Additionally, the performance of commercially available AEMs, Fumasep FAA-3-50, and Sustainion X-37-50 grade T, was evaluated under similar conditions. EIS results showed that the X-37-50 membrane had lower ohmic resistance compared to the FAA-3-50 membrane. The investigation of catalytic activity and performance of nickel cobalt oxide (NiCoOx) catalysts in AEM water electrolysis for hydrogen production was performed in the second study. The catalysts were synthesized with different ratios of Ni to Co and applied to a nickel foam gas diffusion layer (GDL) at the anode. Scanning electron microscopy (SEM) revealed a distinct flaky structure of the NiCoOx catalyst, while X-ray diffraction (XRD) confirmed the presence of a NiCo2O4 spinel crystal structure. Linear sweep voltammetry (LSV) measurements for the Oxygen Evolution Reaction (OER) in a three-electrode system indicated that NiCoOx (1:3) had the highest catalytic activity, with a current density of 238 mA cm-2 at 1.8 V. Tafel analysis showed that NiCoOx (1:3) had the lowest Tafel slope, indicating faster reaction kinetics and a lower overpotential for higher current densities. Chronoamperometry tests demonstrated the stability of the catalysts at different current densities, with long-term stability testing of NiCoOx (1:3) over 500 hours showing minimal voltage increase during OER, confirming its stability in prolonged operation. NiCoOx (1:3) displayed the highest activity among the tested catalysts at different temperatures, achieving current densities of 1700 mA cm-2 at 2.2 V and 70°C in AEM electrolysis. Nyquist plots and equivalent circuit analysis revealed that NiCoOx (1:3) had lower activation resistance compared to other catalyst compositions for AEM electrolysis. Temperature-dependent measurements showed decreased resistances (ohmic, activation, and membrane) with increasing temperature, indicating improved reaction kinetics and ion conductivity. Long-term durability tests confirmed the stable operation of the catalyst, while short-term tests verified its effectiveness at higher current densities in single-cell AEM electrolyzer operation. In the third study, NiCoOx catalysts were modified using Fe in different proportions ranging from 2.5 to 12.5wt.%. and keeping the Ni to Co ratio to 2:1. Evaluation of the catalytic activity of NiFeCoOx catalysts was conducted by linear sweep voltammetry (LSV) and chronoamperometry (CA) experiments for the oxygen evolution reaction (OER). The catalyst containing 5% Fe exhibited the highest catalytic activity, achieving an overpotential of 228 mV at a current density of 10 mA cm-2, with activity declining with further increases in Fe content. Long-term testing for OER at 50 mA cm-2 demonstrated stable electrolysis operation for 100 hours. Further analysis in an AEM water electrolyzer test revealed that the NiFeCoOx catalyst with 5% Fe at the anode demonstrated the highest current densities of 1516 mA cm−2 and 1620 mA cm−2 at 55°C and 70°C at 2.1 V, with a maximum current density of 1880 mA cm−2 achieved at 2.2 V and 70°C. Nyquist plot analysis of electrolysis at 55°C indicated that the NiFeCoOx catalyst with 5% Fe exhibited lower activation resistance compared to other Fe loadings, suggesting enhanced performance. This study compared the performance of NiFeCo(OH)x and NiFeCoOx catalysts for AEM water electrolysis, revealing that NiFeCoOx demonstrated significantly higher current densities at various temperatures compared to NiFeCo(OH)x. The durability test conducted for 8 hours demonstrated stable AEM water electrolysis with minimal degradation, achieving an overall cell efficiency of 70.5% during operation at a higher current density of 0.8A cm-2. The final study investigated the catalytic activity and performance of NiFeOx catalysts in OER and AEM water electrolyzers. These catalysts were synthesized with varying iron content weight percentages and at the stoichiometric ratio for nickel ferrite (NiFe2O4). The stability of NiFe2O4 catalyst over a 600-hour period at 50 mA cm-2 was demonstrated for OER, with a degradation rate of 15 μV/h. In AEM electrolysis using the X-37 T membrane, NiFe2O4 catalyst exhibited high activity, achieving a current density of 1100 mA cm-2 at 45°C, increasing to 1503 mA cm-2 at 55°C. The performance of various membranes was assessed, with Fumatech FAA-3-50 and FAS-50 membranes showing the highest performance, indicating a strong correlation between membrane performance and conductivity. Analysis of Nyquist plots and equivalent circuit analysis revealed that ohmic resistance decreased with increasing temperature, indicating a positive effect on AEM electrolysis. FAA-3-50 and FAS-50 membranes offered lower activation and ohmic resistances, suggesting higher conductivity and faster membrane charge transfer. NiFe2O4 in an AEM water electrolyzer demonstrated strong stability, with a voltage degradation rate of 0.833 mV/h over a 12-hour durability test.