Investigations of interfaces for electrochemical devices using tunable block copolymer electrolytes
dc.contributor.advisor | Herring, Andrew M. | |
dc.contributor.author | Buggy, Nora C. | |
dc.date.accessioned | 2022-07-18T20:12:12Z | |
dc.date.available | 2022-07-18T20:12:12Z | |
dc.date.issued | 2021 | |
dc.identifier | Buggy_mines_0052E_12266.pdf | |
dc.identifier | T 9223 | |
dc.identifier.uri | https://hdl.handle.net/11124/14245 | |
dc.description | Includes bibliographical references. | |
dc.description | 2021 Fall. | |
dc.description.abstract | Polymer electrolyte-based electrochemical energy conversion devices, such as electrolyzers or fuel cells, are of interest for large scale hydrogen production and conversion, respectively. Much eort has gone toward improving the anion exchange membrane (AEM), the solid polymer electrolyte which separates the anode and cathode and transports anions and water across the electrochemical device. In addition to the AEM, device performance is dictated in part by sluggish reaction kinetics that can result from poorly formed structures in the electrode catalyst layer (CL). The CL is comprised of a heterogeneous mixture of conductive supporting material, catalyst particles, and anion exchange ionomer (AEI). Electrode design can be improved by synergistically developing ionomer chemistry with fundamental knowledge of their interactions with catalysts and supporting materials. The limited work carried out in this area has focused on using platinum group metal catalysts, which can be replaced with cheaper more abundant catalysts in AEM-based devices due to the enhanced reaction kinetics realized in base. Hence, in this work, tunable block copolymer-based AEIs are developed and their interactions, structure and performance with a silver catalyst are investigated. First, a novel polyethylene-based block copolymer AEM was developed. The polycyclooctene midblock of the ABA triblock copolymer polychloromethylstyrene-b-polycyclooctene-b-polychloromethylstyrene (PCMS-b-PCOE-b-PCMS) was hydrogenated to yield a polyethylene (PE) midblock. The new PE-based AEM had high ionic conductivity, moderate water uptake, and decent alkaline stability. Notably, the mechanical strength of the AEM improved in liquid water. X-ray scattering studies revealed that in liquid water the PE backbone rearranges to form larger crystalline domains, leading to enhanced mechanical properties. Next, interactions between silver nanoparticles (AgNPs) and block copolymer-based ionomers were investigated. This study utilized the PCMS-b-PCOE-b-PCMS triblock copolymer precursor and ionomers derived from quaternization with trimethylamine or N-methylpiperidine. Using FTIR, interactions with AgNPs were determined to occur more strongly with the phenyl groups, vinyl groups, and the pendant quaternary ammonium cations (QACs). Changes in thermal characteristics and crystallinity were highly dependent on the QAC, uncovering differences in the nature of the interactions between silver and trimethylammonium or methylpiperidinium. Ionomer thin film morphology was characterized on a silver surface to model an idealized catalyst interface using grazing incidence small angle X-ray scattering. This work utilized two diblock and two triblock copolymer precursors of PCMS and polyisoprene (PIp). The morphology of the block copolymer precursor was found to align vertically to the interface, but after quaternization, the morphology became more disordered due to dipole-dipole interactions between pendant QACs. Environmental studies were used to elucidate water uptake via changes in the radius of gyration. The final set of studies implemented a half-cell to study the kinetics of the oxygen evolution reaction (OER) on electrodes coated in a silver-ionomer ink. Optimization of the ionomer chemistry is realized through a series of backbone and QAC modifications. The best performing electrode was integrated in a water electrolyzer with the PE-based AEM developed in the first study. In the final chapter, the hypotheses and structure-property-performance relationship are revisited, and future work is proposed. | |
dc.format.medium | born digital | |
dc.format.medium | doctoral dissertations | |
dc.language | English | |
dc.language.iso | eng | |
dc.publisher | Colorado School of Mines. Arthur Lakes Library | |
dc.relation.ispartof | 2021 - Mines Theses & Dissertations | |
dc.rights | Copyright of the original work is retained by the author. | |
dc.subject | anion exchange membranes | |
dc.subject | block copolymers | |
dc.subject | electrochemistry | |
dc.subject | ionomer | |
dc.subject | oxygen evolution reaction | |
dc.subject | thin film | |
dc.title | Investigations of interfaces for electrochemical devices using tunable block copolymer electrolytes | |
dc.type | Text | |
dc.date.updated | 2022-07-18T16:42:34Z | |
dc.contributor.committeemember | Knauss, Daniel M. | |
dc.contributor.committeemember | Wu, Ning | |
dc.contributor.committeemember | Samaniuk, Joseph R. | |
thesis.degree.name | Doctor of Philosophy (Ph.D.) | |
thesis.degree.level | Doctoral | |
thesis.degree.discipline | Chemical and Biological Engineering | |
thesis.degree.grantor | Colorado School of Mines |