Degradation and Performance of Oxygen Electrodes for Low and Intermediate Temperature Reversible Solid Oxide Cells for Energy Storage

Lu, Matthew Yunching

doi:https://doi.org/10.21985/n2-4nsv-an62

Work

Degradation and Performance of Oxygen Electrodes for Low and Intermediate Temperature Reversible Solid Oxide Cells for Energy Storage

Public

Download PDF

Download All Files (.zip)

Rapid changes in global climate are pushing nations to reduce CO2 emissions and adopt clean energy technologies for renewable energy generation and storage. As wind and solar are implemented worldwide, a commensurate response in energy storage will need to be installed to meet fluctuations in peak energy demands and generation from intermittent wind and solar sources. Currently, pumped hydro dominates energy storage, but is geographically confined to locations with substantial elevation differences. Lithium-ion battery technology may be appropriate for small-scale energy storage, but the scalability and cost structure of this technology is inadequate to meet future needs as both the population and the demand for renewable energy continue to grow. Reversible solid oxide cells are a promising technology for targeting large-scale energy storage due to the ease of scalability and storage of hydrogen, hydrocarbons, or other reactant fuels. In these systems, however, the sluggish kinetics of the oxygen reduction and evolution reactions provide great challenges to improve upon before implementation. These reactions occur in the oxygen electrode and represent the largest resistive component of the solid oxide cell, in addition to being a major source of degradation affecting the lifetimes of these devices. Thus, this dissertation investigates oxygen electrodes in reversible solid oxide cells for energy storage applications, primarily focusing on degradation mechanisms and methods to enhance performance at low and intermediate temperatures. La0.6Sr0.4Co0.2Fe0.8O3-δ is the most widely studied oxygen electrode with good intermediate temperature performance (650-800 °C) and reasonable stability. An encyclopedic study on the effects of temperature and reversing current density on La0.6Sr0.4Co0.2Fe0.8O3-δ electrodes is presented, shedding light on the degradation mechanisms and the resulting impacts on electrochemical performance. The results show that Sr surface segregation can result in substantial degradation, but that there is an operating window of relatively high temperature (750 °C) and current density where polarization resistance is stable. A Sr surface cleaning method is developed that effectively, but only temporarily, improve electrochemical performance. Additional results on attempts to enhance performance and stability by nanoparticle infiltrations are also presented. A new mixed ionic and electronic conducting oxygen electrode material, Sr(Ti1-x-yFexCoy)O3-δ, is developed with performance and stability surpassing benchmarks set by state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-δ oxygen electrodes. PrOx is added in a single-step infiltration into La0.6Sr0.4Co0.2Fe0.8O3-δ and SrTi0.3Fe0.55Co0.15O3-δ scaffolds to achieve substantial performance and stability enhancements at low and intermediate temperatures, with PrOx-infiltrated SrTi0.3Fe0.55Co0.15O3-δ achieving an order of magnitude performance improvement over La0.6Sr0.4Co0.2Fe0.8O3-δ at low temperatures (450 to 550 °C). These improvements on the oxygen reduction and evolution processes are carefully evaluated by analyzing the electrochemical impedance spectra using a distribution of relaxation times method and a transmission line model. Advancements on developing SrTi0.3Fe0.55Co0.15O3-δ-Ce0.9Gd0.1O2-δ composite oxygen electrodes to improve the compatibility of SrTi0.3Fe0.55Co0.15O3-δ with existing electrolyte and fuel electrode materials is presented along with preliminary results on the stability of Sr(TixFe1-x)O3-δ in reducing conditions.

Creator