The innovation engine for new materials

Solid Oxide Fuel Cell Materials: Interface Dynamics, Microstructure Optimization and Performance Degradation

Seminar Group: 


Professor Daniel R. Mumm


Chemical Engineering & Material Science
University of California, Irvine


Friday, November 15, 2013 - 4:00pm


ESB 1001


Professor Carlos Levi

Solid Oxide Fuel Cells (SOFCs) and rlated Solid Oxide Electrolysis Cells (SOECs) are solid-state electrochemical devices that allow for (1) direct conversion between chemical energy and electrical energy, and/or (2) drive chemical reactions such as electrolysis or fuels production. Despite the unique benefts of SOFC/SOEC systems for environmentally-friendly electricity production, energy storage used in conjunction with other alternative energy technologies (wind, solar, etc.), and chemical synthesis, there remain several obstacles to commercial viability. In particular, SOFC/SOEC systems must meet defined metrics in terms of cost, performance and durability to achieve widespread adoption as components of a comprehensive energy conversion and storage system. In this talk, I will first discuss efforts to maximize electrochemical performance through microstructural design of composite electrode systems. Focused ion beam serial sectioning and reconstruction have been used in conjunction with systematic variation of microstructural parameters to explore correlations between (1) the intrinsic properties of the composite electrode constituents, (2) the relevant microstructural length scales, and (3) the continutity of the individual phases. We directly quantify the volumetric density of key triple phase boundaries (TPBs), and quantify the fraction of these microstructural elements that are electrochemically active. The electrochemical performance of the electrode systems are then correlated with controllable microstructural features. Keeping the focus on TPBs and electrochemically active interfaces, we then explore factors controlling materials stability by exploring interfacial dynamics (cation interdiffusion and new phase formation) under simulated service environments. The stability and degradation mechanisms of perovskite cathode/electrolyte interfaces were systematically investigated by correlating long term electrochemical performance change to the nano-scale structural and chemical evolution, assessed using advanced electron and X-ray characterization techniques. A significant increase in cathode polarization resistance was observed over the duration of testing, and the performance degradation was attributed to the formation of a less catalytic phase and a change in perovskite stoichiometry at the interface. The mechanisms underpinning the structural and chemical evolution revealed characteristics with strong diffusion related kinetics. Based on the mechanistic understanding of factors that constitute interfacial instability, approaches to stabilize perovskite cathode/electrolyte interfaces were experimentally explored. Lastly, I will discuss our efforts to understand factors controlling the kinetics of oxidation of metal interconnects used in these systems, and illustrate that the electric fields play an important role in determining ohmic loss increases with the development of thermally grown oxides at the interconnect/electrode interfaces. We will conclude by putting these efforts in context relative to developing advanced SOFC/SOEC systems, and discuss the implications of the observed degradation mechanisms.