Date/Time: Wednesday August 19^th at 5 p.m.

Location:  Room 3515, Hightower Conference Room, MRDC

Committee:

•            Faisal Alamgir (Advisor, Materials Science and Engineering)

•            Meilin Liu (Materials Science and Engineering)

•            Preet Singh (Materials Science and Engineering)

•            Eric Vogel (Materials Science and Engineering)

•            Krista Walton (Chemical & Biomolecular Engineering)

Thesis Title: Near Surface Evaluation of Structural, Electronic and Chemical Properties of Templated Pt Monolayers

Abstract: Platinum group metals are the choice catalysts for a wide variety of catalytic reactions, including oxygen reduction. The focus of this study is to explore the dimensional aspect of both electronic and structure-driven surface properties of Pt monolayers grown via templating on Au. Surface limited redox replacement is used to provide precise layer-by-layer growth of Pt to synthesize well-controlled ‘core-shell’ catalyst architectures.

The interaction between core and shell manifests itself through both a structural contribution of epitaxial strain and d-electron orbital mixing. The cumulative effect of the secondary support on the surface Pt and its interaction with adsorbate species is referred to as a ligand effect. The main goal of the research is to investigate how these ligand effects contribute to the structural and electronic properties of Pt monolayer catalysts.

One focus of our study is to explore the incorporation of two dimensional materials into the core-shell catalyst architecture. Materials such as single-layer graphene and transition metal dichalcogenides have shown potential for increased activity and stability when used as supports. We have found that fully wetted 4-5 monolayer Pt films can be grown on graphene, maximizing the exposed catalyst surface with high Pt utilization. The research also looks to investigate the use of single-layer graphene as an intimate capping sheet to prevent surface dissolution of electrode metals into the electrolyte, without adversely affecting activity.

X-ray photoelectron spectroscopy and extended x-ray absorption fine structure techniques are used to examine surface composition and local atom-atom correlations (bond distance, strain, coordination) as well as core-shell charge transfer effects. Cyclic voltammetry and the oxygen reduction reaction are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively.