Ying LiuFollow

Date of Completion

12-11-2013

Embargo Period

12-11-2013

Major Advisor

William E. Mustain

Associate Advisor

Brain Willis

Associate Advisor

Yu Lei

Associate Advisor

Jeffrey McCutcheon

Associate Advisor

Ugur Pasaogullari

Field of Study

Chemical Engineering

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

The electrochemical energy conversion devices, fuel cell, have received considerable attention over the past few decades because of their potential to provide high efficiency power since electrochemical processes are not limited by traditional Carnot or Rankine heat cycles. The oxygen reduction reaction (ORR) is an important electrochemical process that is active in low-temperature fuel cells. However, it is also the performance-limiting reaction, since it shows overpotential nearing 300 mV. Thus, currently, the most critical challenge is to discover low cost, stable, high activity catalysts for ORR. Nowadays, the most effective catalysts for ORR are still Pt group metals.

The catalyst support material is one of the most critical components of any electrochemical system. First, they allow for fine dispersion and stabilization of small clusters of electrochemically active noble metals. The resulting small particle size allows access to a much larger number of catalytic sites than the corresponding bulk metal, which is critical for electrochemical applications where current scales linearly with the number of sites. Second, interaction between the catalyst and support can have a significant influence on the catalyst electronic structure. The influence of the catalyst support will be amplified as catalyst dispersion is increased and particle size decreased.

In this study, three materials, tungsten carbide (WC), tungsten oxide (WO3) and tin-doped indium oxide (ITO) are chosen as the support materials, nanosized Pt clusters are deposited on the surfaces of these supports. The activity and stability of these platinum supported electrocatalysts for ORR have been evaluated by the physical characterization and electrochemical experiments, and the objective is to find out: 1) the intrinsic electrocatalytic activity of Pt clusters can be enhanced by tailoring the metal-support interaction between Pt and the catalyst support material; 2) strong interaction between nanosized Pt clusters and the support material can reduce Pt cluster agglomeration.

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