Abstract

Professor Jonah Erlebacher
Department of Materials Science and Engineering
Johns Hopkins University

Seminar: November 6, 2006
3:30-4:30pm
Mechanical Engineering, Room 339

Gilded Fuel Cells: Interfacial Phenomena and Applications for Dealloying of Binary Alloys

In our group at Johns Hopkins University, we have been studying the
formation of so-called "Nanoporous Gold (NPG)," a mesoporous metal (5-50 nm pores) that holds promise for application in a variety of cutting-edge technologies including materials for fuel cells and biosensing. The complex microstructure of NPG belies the rather simple processing route used to make the material, namely, start with a dense alloy of silver and gold and then selectively dissolve the silver away in a suitably acidic environment, a process called dealloying. The gold atoms left behind are found to have moved from their original lattice sites and reformed into a extended crystalline 3D porous network. While we primarily examine dealloying to form nanoporous gold, our results are applicable to dealloying generally. With this in mind, we study dealloying from a dual perspective -- as a feature useful for creating new materials and as a problem related to corrosion of many important materials in fields varying from aerospace to oil production.

In this presentation, I will first discuss how the intricate nanoscale dance of silver and gold atoms along the acid/alloy interface leads to nanoporosity evolution, and how the this dance is the result of choreography directed by traditional materials thermodynamics and kinetics, just in an (extremely) unusual context. Analytical, computational and experimental approaches to this problem will be discussed, with an eye toward the long term goal of clarifying the formation mechanism of NPG and extending these ideas to other alloy systems to create new materials. I will also discuss the problem of the electrochemical "critical potential" that determines if an alloy is susceptible to corrosion.

I will secondly discuss how we are using nanoporous gold, and composites
based upon nanoporous gold, to develop new catalyst materials for hydrogen/oxygen proton exchange membrane fuel cells. By coating the intricate porous structure of NPG with an atomically thin layer of platinum, we simultaneously solve a number of problems that fuel cells currently possess, namely, inefficient utilization of precious metal (Pt) catalyst materials, lack of tailorability of catalytic activity, and thermal stability problems.

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