Date of Award
2026-05-01
Degree Name
Doctor of Philosophy
Department
Chemistry
Advisor(s)
Sreeprasad S. Sreenivasan
Abstract
Electrochemical energy conversion through reactions such as the hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction (ORR) reactions underpins water electrolysis, fuel cells, and metal-air batteries. While HER proceeds with low overpotential on platinum-group metal catalysts, the corresponding anodic and cathodic oxygen reactions remain kinetically constrained, with overpotentials on state-of-the-art OER catalysts of order 250-320 mV at 10 mA cm⁻² in acidic media. The efficiency of these systems therefore depends critically on the electronic structure of the catalyst, the energetics of intermediate adsorption, and the dynamics of interfacial transport. Conventional catalyst design has focused largely on adsorption-energy descriptors and on tuning the electronic structure of the active site through alloying, strain, defect engineering, or heteroatom doping. Emerging evidence, however, indicates that catalytic activity also reflects coupled contributions from charge polarization, spin configuration, interfacial built-in fields, and externally applied perturbations such as magnetic fields. Designing materials platforms in which these contributions can be introduced and examined systematically is therefore a key open problem. This thesis develops covalent organic frameworks (COFs) as programmable platforms for introducing charge-controlled, spin-dependent, and field-sensitive contributions to electrocatalytic activity progressively, and for studying how these contributions combine through comparative molecular design and controlled external perturbation. Four chapters develop the strategy stepwise, building from metal-free systems to metal-containing, chiral, and heterostructure-coupled architectures. Chapter 2 establishes a metal-free baseline by combining two structural strategies in a single COF: donor-acceptor electronic asymmetry, achieved through alternating electron-rich benzene and electron-deficient triazine units within amide-linked frameworks, and interfacial built-in fields generated through heterostructure formation with carbon nanotubes (CNTs). The first introduces intramolecular charge transfer that biases the electronic environment at catalytic sites; the second adds an asymmetric interface whose electrostatic structure is resolved by Kelvin probe force microscopy and electrochemical impedance spectroscopy (EIS). Together, they show that meaningful catalytic activity can be programmed into a transition-metal-free framework. Under applied magnetic field, this system responds reversibly and with a clear orientation dependence, consistent primarily with magnetohydrodynamic transport and field-induced perturbation of the interfacial environment - establishing the transport-dominated baseline against which field-coupled response in metal-containing systems is interpreted in subsequent chapters. Chapter 3 introduces metalloporphyrin-metallophthalocyanine COFs that incorporate two distinct metal centers - Ni and Co, with Zn as a redox-inactive control - within a single crystalline lattice, allowing site-specific catalytic roles to be examined within a common architecture. Ni sites support the high-valent redox chemistry that drives OER, while Co sites stabilize the oxygen intermediates relevant to ORR. Together, they provide bifunctional oxygen electrocatalysis from a single material. Magnetic-field experiments on these systems reveal a response that combines transport-related contributions with field-sensitive interfacial behavior, marking a clear departure from the transport-dominated baseline established in Chapter 2 and pointing to additional mechanisms specific to redox-active metal sites. Chapter 4 introduces chirality as an intrinsic, structurally encoded source of spin selectivity through Ir-porphyrin COFs in which the chiral element is placed independently within the framework linker, at the axial coordination environment of the metal, or at both positions simultaneously. This structural decoupling allows local and extended chiral environments to be examined separately and in combination through chiroptical response, magnetoconductive AFM, and OER activity. The dual-chiral frameworks show the strongest combined transport-asymmetry and catalytic signatures, indicating that chirality at the framework and chirality at the metal contribute cooperatively rather than redundantly. The results establish chirality as an addressable structural parameter for controlling spin-related charge transport. Chapter 5 shifts the locus of spin control from the framework to the metal active site itself. Axial ligand coordination produces two distinct Fe(III) coordination environments within a common framework architecture - a high-spin environment (S = 5/2) through chloride coordination and a low-spin environment (S = 1/2) through 1-methylimidazole coordination - providing a chemically matched pair of materials in which the d-orbital occupancy at the active site is the principal variable. The high-spin framework shows improved activity relative to the low-spin analogue at near-identical electrochemically accessible surface area, identifying the Fe coordination environment as the dominant origin of the activity difference. Integration with Ti₃C₂Tx MXene produces a further enhancement, due to improved electrical addressing of the Fe sites and possible interfacial electronic modulation. Under a 300 mT applied magnetic field, the heterostructure shows an additional reproducible response that combines transport, interfacial, and possible spin-related contributions. The chapter establishes field sensitivity as a robust observation and identifies the specific control experiments needed to resolve its mechanistic origin. Together, this thesis treats spin - through chirality, spin-state control, and field response - as an explicit design variable in COF electrocatalysis, on the same footing as charge polarization and adsorption energetics, rather than as a secondary effect to be inferred after the fact. By bridging molecular chemistry, condensed matter physics, and electrocatalysis, the work establishes chemically programmable platforms for charge-, spin-, and field-coupled electrocatalysis and identifies the structural and experimental controls through which their mechanistic decomposition can be carried forward.
Language
en
Provenance
Received from ProQuest
Copyright Date
2026-05
File Size
232 p.
File Format
application/pdf
Rights Holder
Lissette Garcia Enriquez
Recommended Citation
Garcia Enriquez, Lissette, "Disentangling Electronic Structure, Spin, And Field Effects In Covalent Organic Framework Electrocatalysts" (2026). Open Access Theses & Dissertations. 4676.
https://scholarworks.utep.edu/open_etd/4676