Date of Award
2025-12-01
Degree Name
Doctor of Philosophy
Department
Chemistry
Advisor(s)
Dino Villagran
Abstract
Hydrogen and oxygen generation through electrochemical water splitting represents a promising and sustainable route for clean fuel production. However, the widespread implementation of this technology requires earth-abundant, low-cost, and stable catalysts capable of driving both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) efficiently. Molecularly based catalysts such as porphyrins offer structural tunability, well-defined active sites, and high electronic versatility, enabling systematic exploration of structure and activity relationships. This dissertation focuses on the rational design and advancement of metalloporphyrin-based heterogeneous catalysts for energy conversion and environmental remediation. The work integrates four major chapters: (1) the synthesis of metalloporphyrin polymers for electrochemical water splitting, (2) the electrografting of porphyrins onto conductive substrates to generate stable and electrochemically active modified electrodes, (3) the design of porphyrin-MOF composites for bifunctional catalysis, and (4) the electrochemical reduction of perfluorooctanoic acid (PFOA) using metalloporphyrin-based polymers as reactive catalytic sites. In the first part, four metalloporphyrin polymers were synthesized via the condensation of poly-p-phenylene terephthalamide (PPTA) with amino-functionalized porphyrins incorporating Fe, Co, Ni, or Cu centers. Microscopic and spectroscopic characterization (SEM, TEM, XPS, XRD, FT-IR, and UV-Vis) revealed ordered lamellar structures stabilized by hydrogen bonding and p–p stacking interactions. Among them, the cobalt-based polymer exhibited the best bifunctional performance with low overpotentials for HER, long-term operational stability, and a cell voltage of 1.64 V at 10 mA cm-2 for overall water splitting. These findings demonstrate how polymeric scaffolds can immobilize and stabilize molecular catalysts without compromising electronic communication, offering a platform that bridges homogeneous and heterogeneous catalysis. Building on this concept, the second study explored electrode-immobilized porphyrin films prepared by electrochemical grafting of the free-base and cobalt porphyrins (H2TAPP and CoTAPP) on glassy carbon electrodes. The electropolymerized networks formed robust, covalently bonded architectures that significantly enhanced electrochemical surface area and charge-transfer properties. The resulting electrodes showed moderate Tafel slopes and overpotentials for both half-reactions, maintaining stability over extended electrolysis. These results suggest electrografting as an effective strategy to anchor molecular catalysts while preserving their activity and improving durability under operational conditions. The third study expanded the molecular stabilization strategy by constructing a hybrid composite between cobalt(II) meso-tetrakis(4-carboxyphenyl)porphyrin (CoTcPP) and a conductive zinc-based 2,3,6,7,10,11-hexahydroxytriphenylene (ZnHHTP) metal-organic framework. The resulting CoTcPP@ZnHHTP composite combined the high catalytic activity of cobalt porphyrin sites with the excellent conductivity and large surface area of the MOF scaffold. Characterization confirmed successful incorporation of CoTcPP into the layered ZnHHTP matrix. The composite exhibited remarkable bifunctional catalytic behavior, with low overpotentials and fast kinetics for both HER and OER, achieving near-quantitative Faradaic efficiency and long-term operational stability. The synergy between the redox-active porphyrin and the conductive MOF backbone highlights a rational pathway toward designing composite materials. Finally, the catalytic versatility of these porphyrin-based materials was extended to environmental remediation through the electrochemical degradation of perfluorooctanoic acid (PFOA) as a model PFAS contaminant. Five Porphvlar-type metalloporphyrin polymers were synthesized and evaluated, with Ni-Porphvlar demonstrating the highest defluorination efficiency. Fluoride ion quantification, LC-MS, and UV-Vis spectroscopy confirmed extensive C-F bond cleavage, the formation of unsaturated intermediates, suggesting a sequential hydrogenation-defluorination mechanism while reaching full mineralization with extended degradation time. This work establishes the potential of porphyrin-based molecular frameworks as tunable platforms for PFAS degradation under mild electrochemical conditions, offering an environmentally benign route for addressing persistent pollutants. Overall, this research advances the molecular design of porphyrin-derived materials across various small molecule activation using electrochemical methods. By unifying principles of coordination chemistry, polymer design, and interfacial engineering, these studies demonstrate how molecular catalysts can be rationally heterogenized to achieve enhanced activity, selectivity, and stability. The insights gained provided a basis for the future development of scalable, sustainable electrocatalysts for both renewable fuel production and pollutant degradation.
Language
en
Provenance
Received from ProQuest
Copyright Date
2025-12
File Size
148 p.
File Format
application/pdf
Rights Holder
Neidy Ocuane
Recommended Citation
Ocuane, Neidy, "Rational Design of Molecular Based Catalysts for Water Splitting and Environmental Remediation" (2025). Open Access Theses & Dissertations. 4575.
https://scholarworks.utep.edu/open_etd/4575