UC Irvine

To achieve net-zero emissions by 2050, electrolysis is one of the most promising pathways for decarbonization. Valuable products, such as hydrogen, generated through this green process can significantly mitigate CO2 emissions. The proton exchange membrane electrolyzer (PEMWE) converts electricity to value added products via electrochemical reactions. The versatile configurations of PEMWEs, such as zero-gap and gap, are selectively employed depending on the phases of the desired product. The primary challenges of PEMWEs include optimizing the anode compartment by reducing the use of Iridium (Ir)-based catalysts for the oxygen evolution reaction (OER) and gaining a deeper understanding of the water/oxygen two-phase transport phenomena within the porous transport layer (PTL). In this work, we primarily investigate the anode compartment of PEMWE (zero-gap electrolyzer) and modified PEMWE (gap electrolyzer) as the extensive application of PEMWE for the green production of cement precursor. The anode electrocatalyst Ir is considered as one of the most expensive components in PEMWEs. Its outstanding OER activity and durability in acid medium makes it indispensable. However, its scarcity significantly hinders the development of PEMWEs. Reducing the Ir use in PEMWE has become a top priority to address this challenge. Several studies have reported a decline in activity and durability when the loading of Ir decreases below 0.1 mgIr cm-2. Modified Ir-based catalysts present a promising strategy to decrease the loading of Ir, while maintaining or enhancing the OER activity and durability. The first objective of this study focuses on investigating the activity and stability of three different Ir-based catalysts evaluated in a single-cell electrolyzer. A custom-designed operando electrolyzer cell is employed to monitor crystallite changes in Ir-based catalysts under real PEMWE operating conditions using synchrotron X-ray diffraction (XRD). Titanium-based PTL is deployed as a porous layer in the anode of PEMWE, ensuring uniform water distribution to the catalyst layer and efficient removal of generated oxygen gas from catalyst layer to the channel. The second objective seeks to correlate the oxygen contents in the PTL and channel with different current densities and locations within the electrolyzer. We first designed and manufactured two operando electrolyzers to observe two-phase flow in the PTL and channel under ambient and high-pressure conditions using synchrotron X-ray micro computed tomography (CT). A 10-cm long channel design featuring multiple observation windows enables the monitoring change of oxygen contents in the channel and the steady-state oxygen distribution in PTL from inlet to outlet. This thesis also introduces the first-generation high-pressure operando electrolyzer, capable of withstanding pressures of up to 30 bar without water or gas leakage. The cell has already been successfully utilized in synchrotron X-ray micro-CT experiments. Finally, this thesis explores the extensive application of PEMWEs with a serpentine flow-through precipitation reactor and an anion exchange membrane (AEM) to produce cement precursors. By incorporating a flow-through precipitation reactor as the chemical compartment, the system transitions into a gap configuration, enabling the production of solid-phase products via electrolysis at room temperature. Calcium hydroxide (Ca(OH)2), used as the cement precursor, is produced via the combination of electrolysis and chemical reactions at a room temperature. This approach offers a low-carbon alternative to conventional cement manufacturing by mitigating CO2 emissions from calcination and limestone decomposition. However, the solubility of calcium carbonate as one of the reactants in the anode compartment poses a limitation of the Ca(OH)2 production. To address this issue, critical factors such as the pH of anolyte and electrolyte, the solubility of CaCO3 and Ca(OH)2, and wettability of the flow-through precipitation reactor, are comprehensively analyzed to optimize the production rate of Ca(OH)2 and enhance the efficiency of the electrolyzer.