PhD Oral Exam, Joong Sun Park, Wed, April 20th, 2011, 2:00 pm, CIS auditorium
Joong Sun Park
mrjpark at stanford.edu
Wed Apr 20 10:58:00 PDT 2011
Stanford University Ph.D. Dissertation Defense
Title: “Nano Electrochemistry in Energy Conversion Devices”
Joong Sun Park
Department of Mechanical Engineering
Advisor: Prof. Fritz B. Prinz
Date: Wednesday, April 20th, 2011
Time: 2:00 pm (Refreshments at 1:45pm)
Location: CISX 101X (Auditorium)
The overall efficiency of energy conversion devices such as batteries, fuel cells, and biological cells is often limited by charge transfer reactions at electrode-electrolyte interfaces. Because interfaces are the site of nearly all chemical (and electrochemical) reactions, understanding and improving their characteristics and structures can lead to significant reductions in both catalytic and interfacial losses. To this end, nano electrochemistry may offer us ways to understand details of charge transfer reaction at nanoscale resolution and open opportunities to engineer the interface with better kinetics. This talk presents in three parts the results of three studies aimed at lowering the electrochemical reaction losses in both ceramic fuel cells and biological systems.
The first part of talk discusses a study of oxide ion incorporation and transport at the cathode of solid oxide fuel cells (SOFC). SOFCs are an attractive clean energy technology because of the low to zero emissions from their operation and their potentially high efficiency. For wider applications, it is desirable to lower the operation temperature of SOFCs, but this causes significant increase of interfacial loss due to sluggish kinetics of oxygen reduction reaction at the cathode. In this study, I demonstrated both spectroscpic (AC impedance spectroscopy) and spectrometric (Nano secondary ion mass spectrometry) evidence that oxygen incorporation from the cathode into the electrolyte is significantly enhanced at grain boundaries of the electrolyte.
The second part of the talk discusses a study focused on proton transport in proton-conducting ceramic fuel cells. Acceptor-doped perovskites have attracted recent attention as potential electrolyte materials for the next generation protonic devices, including fuel cells, because of their high ionic conductivity at intermediate temperatures. The chemical instability of most of proton-conducting ceramics in acidic gas environments such as carbon dioxide, however, compromises their practical use. I discuss the evidence of proton conduction in nanoscale yttria-stabilized zirconia, well known oxide ion conductor; this points to its possible usage as a chemical barrier layer for proton-conducting ceramics.
The third part of the talk presents a study of the possibility of extracting electricity from plant cell and the economic feasibility. Plants have developed sophisticated solar energy capture mechanisms that may be adapted to be less expensive or to perform better than current photovoltaic solar energy collectors. I discuss direct extraction of photosynthetic electrons from a single plant cell done by inserting nanoscale electrodes into their chloroplasts in vivo; these results may represent an initial step in generating “high efficiency” bioelectricity.
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