Design, Fabrication, and Characterization of Proton Exchange Membrane Liquid-fed Energy Conversion Electrodes
Creators: name: Abdelrahman, Mohamed
Publisher: name: Carnegie Mellon University
Year: 2023
Subjects: subject: Mechanical Engineering
subject: FOS: Mechanical engineering

description: The negative impact of climate change due to the continuous use of fossil fuels is becoming very apparent in our daily lives. Therefore, it is necessary to transition from a fossil fuel-based economy to one based on renewable energy sources. However, renewable energy sources are characterized by intermittent power supply due to their dependency on weather conditions and time of day. To resolve this, large-scale energy storage solutions are required as we transition to an era of increasing renewable penetration. Polymer electrolyte membrane water electrolyzers (PEMWEs) are promising candidates to store electricity as hydrogen at relatively high efficiencies and power densities. However, the cost is a major limitation that hinders PEMWE market adoption. A strategy to address this is to increase the system's efficiency, thereby decreasing the amount of material in a stack required to generate the same quantity of hydrogen. This can be done by optimizing the structure and morphology of the individual components used in the system. Studies have shown that the structural and material properties of the anode PTL and CL impact the kinetic, ohmic, and mass transport losses of the PEMWE system. Another approach to reducing the cost is to enhance the durability of components used in the system, thereby reducing the overall life-cycle cost of the system. The method of PEMWE operation heavily impacts the durability of the system. After the hydrogen is produced through electrolysis, it can be transported where it is needed, either as a transportation fuel or for use in industrial applications. However, our current infrastructure does not support the transportation of the gaseous fuel nationwide. Therefore, hydrogen can be converted into carbon-neutral methanol according to the Power-to-Liquid concept, allowing the energy to be stored in the chemical bonds of the liquid fuel. A clean and energy-efficient method to convert the chemical energy in the methanol to useful work is using a direct methanol fuel cell (DMFC). DMFCs have several advantages for a broad spectrum of energy-demanding applications, ranging from portable devices to stationary backup power. This versatility is due to methanol's high gravimetric energy density. Therefore, a DMFC is a suitable replacement for hydrogen proton exchange membrane fuel cells (PEMFCs) when storage and fuel delivery are issues. However, DMFC technology has yet to be widely adopted within the market due to its high cost originating from technological barriers such as 1/ methanol crossover from the anode to the cathode and 2/ sluggish kinetics of the methanol oxidation reaction (MOR). This thesis starts by revealing some of the improvements and limitations of platinum group metal (PGM)-free cathodes in a DMFC. Next, it shows how the kinetics of vapor-fed methanol oxidation differ from liquid-fed methanol, resulting in the discovery of some unique kinetic characteristics for vapor-fed DMFCs, which could potentially serve as a gateway for further unique kinetic discoveries of other vapor-fed electrochemical devices. Additionally, it discusses the effects of operating voltage values, anode catalyst loadings, and feedwater dissolved oxygen concentrations on the performance and stability of PEMWE anodes. Furthermore, it presents the development of a novel PEMWE anode catalyst support using a porous polymer electrolyte with a unique structure. Lastly, it provides insights into the choice of the porous transport layer (PTL) for the PEMWE anode and insights into water saturation levels in the PTL during cell operation.