Matthew McDowell
California Institute of Technology

Seminar: Noon, Monday, March 9th, RLE Combined Allen and Haus Conference Rooms (36–462 and 36–428)

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 improved performance. In this talk, the influence of interfaces will be discussed in the context of two different systems, batteries and solar fuels devices. New anode 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 situtransmission electron microscopy (TEM) of the reaction of lithium with single silicon nanostructures reveals that the movement of a 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 unique 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.