Proton Conduction and Lithium Extraction in Chromium (III) Phosphonate Metal-Organic Frameworks
Date
2024-01-24
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Abstract
Phosphonate metal-organic frameworks (MOFs) present potential candidates for functional materials due to their inherent structural stability and the capacity for synthetic manipulation. However, a trade-off often arises in the form of compromised crystallinity and structural predictability, which poses a significant hurdle in fabricating porous materials. This thesis focuses on an in-depth investigation into the synthetic approach and the performance of ordered chromium phosphonate MOFs concerning proton conduction and lithium extraction. An approach utilizing a hydrogen-bonded metal-organic framework (HMOF) intermediate was adopted to balance crystallinity and stability and evaluated thoroughly in Chapter 3. Salts made of hexaaquochromium(III) cations and phosphonate anions were dehydrated to form stable MOFs. Intriguingly, this method maintains partial structural crystallinity and engenders a varied pore size distribution during the thermal dehydration conversion step. This variability, in turn, affects the proton conductivity by providing different proton mobility efficiency, with as broad as two orders of magnitude in proton conduction among different MOFs. Chapter 4 explores the use of the HMOF to MOF strategy, focusing on the impact of reagent stoichiometry, ligand geometry, and binary solvent systems on proton conduction. It reveals that fine-tuning reactant stoichiometry is a viable method for enhancing proton mobility channels. The chapter also investigates how ligand geometry influences proton conductor performance, finding that more flexible structures maintain conductivity regardless of structural changes caused by water percolation. Additionally, it highlights the role of binary solvent systems in HMOF synthesis, noting that higher solvent content in HMOFs leads to lower crystallinity and reduced proton conduction after thermal dehydration, though the dehydration process itself minimally affects proton conductivity. Chapter 5 pivoted focus to explore the potential of chromium phosphonates as direct lithium extraction (DLE) adsorbents. To achieve optimal Li+ uptake capacity and selectivity, DLE adsorbents were designed to incorporate a Li+ favorable ’pocket’, templated during synthesis, along with a specific pore aperture for Li+ sieving. The study investigates the influence of pH, contact time, and concentration on adsorption, indicating a pseudo-second order kinetic model and monolayer chemisorption. Durability tests reveal these adsorbents maintain consistent uptake capacity and high stability.
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Keywords
Proton conduction, Lithium extraction, Metal-organic frameworks, Chromium phosphonates, Proton exchange membrane fuel cells
Citation
Zhang, J. (2024). Proton conduction and lithium extraction in chromium (III) phosphonate metal-organic frameworks (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.