Committee Members:
Prof. Meilin Liu, Advisor, MSE
Prof. Preet Singh, MSE
Prof. Hamid Garmestani, MSE
Prof. Matthew McDowell, MSE/ME
Prof. Angus Wilkinson, CHEM/MSE
Development of Proton Conducting Electrolytes with Enhanced Performance and Stability for Reversible Solid Oxide Cells
Abstract:
Reversible solid oxide cells (ReSOCs) that efficiently operate under both fuel cell (fuel to energy) and electrolysis (energy to fuel) modes in a switchable manner are a promising technology for energy storage and conversion. Proton-conducting electrolytes are attracting increasing attention due to their promising conductivity at intermediate temperatures, enabling operation of ReSOCs with high efficiency. However, one of the reasons that they have not been widely adopted is the lack of an electrolyte material that possesses both high ionic conductivity and sufficient stability, especially against high concentrations of steam and carbon dioxide. This objective of this work is to develop novel proton-conducting electrolyte materials for high-performance ReSOCs.
To achieve high proton conductivity, acceptor doping with rare earth elements is a commonly used strategy, which is critical to the formation of protonic defects. The results reveal that conductivity, ionic transference number (tion), chemical stability, and compatibility with NiO (a common fuel-electrode material) are all closely correlated with dopant size. In particular, the reactivity with NiO is found to strongly affect the properties of the electrolytes and hence cell performance. Among all compositions studied, an electrolyte with proper acceptor dopant shows excellent chemical stability and minimal reactivity towards NiO, as predicted from density functional theory (DFT)-based calculations and confirmed by experimental results. In addition, proton-conducting reversible solid oxide cells (P-ReSOCs) based on the optimized electrolyte demonstrate excellent stability and exceptional performance.
Donor doping is an effective strategy for improving the chemical stability of BaCeO3-based proton conductors. However, donor-doped materials often exhibit very low conductivity. The enhanced proton conductivity of donor-doped barium cerate is demonstrated by compensating the incorporation of donor dopants with excess acceptor doping, highlighting the potential of defect chemistry engineering for enhancing conductivity and durability simultaneously. When compared to the state-of-the-art proton conductors with similar conductivity, the optimized donor-doped electrolyte materials demonstrate a significantly enhanced chemical stability, especially against high concentrations of steam, which is vital to water electrolysis for hydrogen production.
While the development of new materials is the focus of this thesis, the technical approach is composed of various electrochemical techniques, surface characterization, and computational modeling to understand the rationale behind the difference in properties. It is hoped that the concepts developed in my studies can offer insights into the rational design of novel materials for chemical and energy transformation technologies.