Study on the Electrochemical Behavior and Stability Enhancement of Solid Oxide Electrochemical Cells based on Oxygen- and Proton-conducting ceramics

Abstract

In response to the accelerating climate crisis and environmental threats, the development of clean, efficient, and sustainable energy conversion technologies has become a global necessity. Among various candidates, solid oxide electrochemical cells (SOCs) have attracted considerable attention for their ability to directly convert chemical energy into electricity with high efficiency and minimal emissions. Depending on the type of ionic charge carrier in the electrolyte, SOC systems are generally classified into oxygen-ion conducting fuel cells (SOFCs) and proton-conducting fuel cells, commonly referred to as protonic ceramic fuel cells (PCFCs). SOFCs and PCFCs are commonly designed with anode-supported architectures to minimize ohmic resistance and achieve high electrochemical performance. However, this structure poses inherent limitations in both systems. In SOFCs, the thick Ni-based anode is susceptible to mechanical degradation under redox cycling and carbon deposition during hydrocarbon fuel operation, ultimately hindering long-term durability. Meanwhile, in most PCFC studies employing BaCeO3-based electrolytes, despite their high proton conductivity, the poor chemical and mechanical stability of the electrolyte remains a significant obstacle to their implementation in cell designs suitable for commercialization. To overcome these limitations, this dissertation investigates alternative strategies tailored to the distinct challenges of each system. The first research topic of this dissertation addresses the redox instability and carbon deposition in SOFCs by adopting a cathode-supported cell structure. By introducing a sintering aid into the electrolyte and optimizing pore formers in the cathode layer, the co-sintering temperature was reduced by over 100 °C, minimizing interdiffusion at the electrode/electrolyte interface and preserving gas transport pathways. The resulting cathode-supported cells exhibited peak power densities exceeding 480 mW cm-2 at 650 °C, marking the highest performance reported for cathode-supported SOFCs. Redox cycling and methane-fueled tests confirmed that this configuration can endure oxidation-reduction cycles and recover from carbon deposition, offering a promising platform for robust SOFC operation in variable fuel environments. The second research topic of this dissertation focuses on the development of a chemically and mechanically stable electrolyte-supported PCFC using BaZr0.85Y0.15O3-δ (BZY). By systematically controlling the effects of the setter type and differences in the stoichiometric composition between the setter and electrolyte according to the sintering aids, a stoichiometric BZY electrolyte thick film thinner than 100 μm was successfully fabricated by tape casting. This structure enabled stable operation with competitive performance in both fuel cell and electrolysis modes, demonstrating its potential as a scalable and stable alternative to conventional anode-supported PCFCs. In this dissertation, these two system-specific designs address key limitations of conventional SOCs, offering new design frameworks to improve performance, durability, and commercial viability of next-generation fuel cell technologies.