Semester

Fall

Date of Graduation

2019

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Edward M. Sabolsky

Committee Member

Xingbo Liu

Committee Member

Bruce S. Kang

Committee Member

John W. Zondlo

Committee Member

Shiwoo Lee

Abstract

Development of solid oxide fuel cell (SOFC) electrodes with nano-structured grains can show enhanced power density with high catalytic activity owing to the higher surface area to volume ratio of the particles. However, the addition of nano-particles during the conventional electrode manufacturing process causes inevitable structural changes due to the coarsening of nano-particles at sintering temperatures. Wet impregnation/ infiltration methods are a practical and well-utilized method to form nanoparticles within the porous electrode microstructure of solid oxide fuel cells (SOFC) which requires relatively low calcination temperatures. Critical factors that impact the reduction of the electrode polarization using the nano-catalyst impregnation strategy include catalyst loading, decoration type, and volumetric distribution homogeneity through the porous electrode microstructure. These can mostly be tuned by performing repetitive infiltration cycles followed by a co-firing step after each cycle for calcination. This labor and time-intensive method continues until the desired nano-catalyst loading is achieved. The factors that may degrade the performance as inter-particle interactions, pore-clogging, and/or inhomogeneous deposition result in gas diffusion related to rapid cell voltage degradation issues.

The objective of this work is to investigate organic electrode modifiers to enhance nano-catalyst infiltration efficiency and uniformity within a commercial nickel oxide (NiO)/ yttria stabilized zirconia (YSZ) anode support and lanthanum strontium manganite (LSM)/YSZ cathode systems. The aim is to reduce the process to minimal processing steps while increasing both the performance and stability of the SOFC by decorating the nano-catalyst deposition. In this study, nano-CeO2, ceria, was used as a redox catalyst system and efficiently inserted throughout both porous SOFCs electrodes simultaneously by using a bio-inspired surfactant-assisted infiltration protocol. The process includes the initial modification of the electrode pore walls with a catechol-based surfactant film, i.e., poly-dopamine (pDA), poly epinephrine (pNE) or other alternative surfactants from the catechol family. The nano-ceria layer is then deposited uniformly over the bio-template surfactant layer during a single submersion of the SOFC into a cerium salt solution. Voltage-current-power curves and impedance spectroscopy were used to characterize the electrochemical performance of the impregnated anode-supported SOFC button cells. The end-goal of the work was to develop an infiltration protocol that performs boosted initial power density (performance) with high-stability by mitigating the nano-catalyst coarsening. The infiltrated cells displayed up to 35% reduction in polarization over the baseline cell with high electrochemical stability during 300 hours of testing at 750oC.

The catechol surfactant deposition kinetics and the degree of polymerization of the surfactants on planar substrates were investigated. The adhered catechol thickness was fitted to exponentially decreasing function of time. The growth of the fired ceria particles over the pNE coated substrates showed that the growth of ceria particles can be both by forming new nuclei or growing over the existing nuclei.

Embargo Reason

Publication Pending

Available for download on Saturday, December 05, 2020

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