(Reminder) PhD Oral Examination, Cheng-Chieh Chao, TODAY, Monday, Feb 14, 2011, 3:15 pm, McCullough 335

Stanford University Oral Examination

Cheng-Chieh Chao
Department of Mechanical Engineering
Advisor: Prof. Fritz B. Prinz

Monday Feb 14th, 3:15 pm (refreshments at 3 pm)
McCullough Building, Room 335

Atomic layer deposition for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are attractive for their high energy conversion efficiency in the usage of fuels ranging from hydrogen to hydrocarbons. Nevertheless, they have limited applications because this high efficiency cannot be achieved without high operating temperatures, which pose significant engineering challenges, diminishing the SOFCs practicality for applications such as portable power sources. Lowering the operating temperatures of SOFCs may improve thermal stability and offer shorter start-up times, which in turn might broaden their use as auxiliary power units for automobiles. Although many studies have aimed at lowering the SOFC operating temperatures, this temperature reduction has been inevitably accompanied by a decrease in the electrochemical performance, which is contributed by a larger activation loss and ohmic loss. These two losses are related to sluggish reaction kinetics at the electrode/electrolyte interface (interfacial resistance) and poor ionic conductivity in the electrolyte (electrolyte resistance) at reduced temperatures. In this talk, I will present the approaches to reduce both losses with the help of atomic layer deposition (ALD).

In the first approach, ALD was used to fine-tune the electrolyte surface properties, which improved the reaction kinetics at the electrode/electrolyte interface. In the second approach, the nucleation of ALD platinum catalyst was investigated by TEM to improve the catalyst nanostructure, which reduced the activation loss during fuel cell operation. In the third approach, ALD was used to fabricate an ultra-thin SOFC electrolyte, which reduced the ohmic loss during fuel cell operation. In the last approach, by combining the nanosphere lithography (NSL) and ALD process, a corrugated thin-film electrolyte was fabricated to provide a larger area for interfacial reactions. By reducing activation loss and ohmic loss with these approaches, the electrochemical performance of SOFC was improved at low temperatures.