Committee:

Prof. Nazanin Bassiri-Gharb (Advisor, ME/MSE)

Dr. Raymond R. Unocic (ME)

Prof. Meilin Liu (MSE)

Prof. Rosario Gerhardt (MSE)

Prof. Faisal Alamgir (MSE)

Title: 

Probing Complex Ionic Dynamics on the Nanoscale via Energy Discovery Platforms

Abstract: 

Ionic dynamics underpin the functionalities of a broad spectrum of materials and devices ranging from energy storage and conversion, to sensors and catalytic devices. Electrochemical reactivity and ionic transport in these systems is, however, a complex process, controlled by the interplay of charge injection and field-controlled and diffusion-controlled transport. These processes are often very sensitive to the environmental conditions and defect structures. To understand the fundamental mechanisms underpinning electrochemical functionality, it is vital to separate the spatial localization of reaction and transport processes on the nanoscale. 

This proposal aims to uncover complex ionic dynamics in functional oxides via energy discovery platforms, which combine nano/micro-fabricated lateral devices with in-situ characterization method. To be specific, the electrochemical reactivity and proton conduction mechanisms are investigated by time resolved Kelvin probe force microscopy (tr-KPFM) in two case studies: nanostructured ceria (NC) and yttrium-doped barium zirconate (Y-BZO). Through tr-KPFM, the surface potential variation is obtained in a sub-micron spatial resolution, and 10^-2 to 10^2 s temporal resolution. The effects of environmental conditions such as temperature and humidity, and the role of defects and triple phase boundaries (TPBs) on the electrochemical and transport processes are investigated. Finite element modeling is performed to correlate the observed surface potential variation to local generation and migration of mobile charged species on the nanoscale. In addition, scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) are used to correlate structural defects such as oxygen vacancies to the proton conduction mechanisms.