MATERIALS SCIENCE SEMINAR

ABSTRACT: Nanoporous metals are unique, high surface area materials formed by the selective dissolution of the less noble component(s) from a binary or even multicomponent alloy, a process known as dealloying. The physical mechanism of porosity evolution during dealloying involves a competition between dissolution of the less noble component and surface diffusion of the remaining more noble component(s) leading to the dynamic formation of a ligamentous structure which is characterized by a high surface area to volume ratio. It is this high surface area to volume ratio and inherent conductivity that make nanoporous metals attractive materials for use as catalytic electrodes for many electrochemical reactions. This presentation will focus on application of nanoporous metals in the catalysis of the cathodic oxygen reduction reaction (ORR), which is the primary bottleneck in fuel cell catalysis. Fundamental understanding of the formation mechanism of these nanoporous metals has allowed specific control of morphological features which has shed light on the structure/function relationship and how it relates to the intrinsic catalytic activity of this uniquely structured fuel cell catalyst. The mass activity of our nanoporous, high surface area, Pt-alloy catalyst (np-NiPt) formed by dealloying of Ni rich NiPt alloys is on its own higher than that of the commercial Pt/C catalyst, yet we are able to further enhance this activity by creating a composite catalyst through impregnation with a hydrophobic, protic ionic liquid that chemically and geometrically confines oxygen to the reactive surface region (an architecture impossible to make using solid nanoparticles). The intrinsic catalytic activity of the composite catalyst was first assessed for planar nanoporous electrodes; however, this architecture is not suited for integration into a working fuel cell. For this reason we have developed a novel nanoporous nanoparticle structure through a unique delayed nucleation solvothermal process that will be discussed in detail. These novel nanoporous nanoparticles show potential for application beyond the ORR such as electrochemical reduction, electrochemical capacitors, CO oxidation, water-gas-shift and other surface active catalytic processes not only because of their unique structure but also the ease with which their morphology and composition may be optimized for each specific process.