Woodruff School of Mechanical Engineering
Faculty Candidate Seminar
Understanding Interfaces in Electrochemical Energy Systems
Dr. Matthew McDowell
California Institute of Technology
Monday, January 26, 2015 at 11:00:00 AM
MRDC Building, Room 4211
Seung Woo Lee
The chemical, structural, and mechanical characteristics of interfaces play a major role in determining the properties and performance of electrochemical systems. In novel materials for electrochemical energy storage and conversion, dynamic processes at internal solid-solid interfaces, as well as at the solid-electrolyte interface, must be understood and controlled for maximized performance. In this talk, the influence of interfaces will be discussed in the context of two different systems, batteries and solar fuels devices. New materials for lithium-ion batteries (such as silicon) offer improved charge storage capacity, but cycle life is often limited because of reaction-induced volume changes and mechanical degradation. Here, in situ transmission electron microscopy (TEM) of the reaction of lithium with single silicon nanostructures reveals that the movement of the two-phase interface between the reacted and unreacted material exerts a controlling influence on the transformation, affecting both the reaction kinetics and particle fracture through the evolution of large internal stresses. These results offer fundamental insight into the nature of this reaction and also provide guidelines for improving battery performance. In photoelectrochemical systems for converting sunlight into fuels, the solid/electrolyte interface at a semiconductor electrode is highly susceptible to photocorrosion, which often prevents long-term operation. Metal oxide overlayers of varying thickness and with controlled electronic properties are shown to effectively protect a number of moderate band gap semiconductors from photocorrosion while also allowing for facile carrier transport, thus enabling stable and efficient photo-driven water oxidation. Together, these results demonstrate the importance of understanding and controlling interfaces in energy systems, and they are a step towards improved electrochemical devices.
Matthew McDowell graduated from Georgia Tech with a B.S. in Materials Science and Engineering in 2008, and he earned his Ph.D. in Materials Science and Engineering from Stanford University in 2013. He is currently a postdoctoral scholar in the Division of Chemistry and Chemical Engineering at Caltech. His research has focused on developing materials for electrochemical energy systems and understanding their properties and functionality at the nanoscale. He was awarded the Materials Research Society Graduate Student Gold Award in 2013 for his thesis research.
Refreshments will be served.