Judith C. Yang, PhD

Professor

208 Benedum Hall | 3700 O’Hara Street | Pittsburgh, PA 15261 P: 412-624-8613

judyyang@pitt.edu

Dynamic Surface Reactions: Bridging the Gaps

The rational design of new and improved materials, such as for corrosionresistance or catalysis, requires an understanding of the relationship between their processing, structure, and performance and the underlying reaction mechanisms. The spatial and temporal scales of these processes span orders of magnitude, and no one technique covers them all. Another gap lies in the disconnect between the simple, idealized materials used for computation and the ill-defined “messy” materials of experiment. Our research focuses on bridging these gaps by coupling computational modeling with a host of experimental techniques. Of particular importance for this task is the environmental transmission electron microscope (ETEM), which enables the direct observation of the structure, chemistry, and composition of these materials at the meso- to atomic-scale in real time and under reaction conditions. Some of our current projects include:

Metal and Metal Alloy Oxidation

Understanding metal of metal oxidation is critical to corrosion control, catalysis, and advanced materials engineering. Classical oxidation theories assume a uniform oxide film growth; however, in situ TEM studies reveal this is far from the case. It is a complex set of (often coupled) processes involving physical and chemical changes at multiple scales. A great knowledge gap exists between the oxygen-induced surface reconstructions of the early stages and the formation of the subsequent oxide structure. We are using ETEM in concert with DFT calculations to study early-stage oxidation to determine the structure of these reconstructed surfaces and how they depend on the metal surface faceting and environmental conditions (O2 pressure, temperature), such as the Cu(110) “sawtooth” reconstruction under O2 (Fig. 1).

Heterogeneous Catalysts and Nanomaterials

Bimetallic nanoparticle catalysts can exhibit enhanced activity and selectivity over their single-metal constituents, since each part can be tailored for a specific function. However, adding a second metal greatly increases the complexity of the bimetallic system, especially under environmental conditions; variation in the elements’ mixing patterns and reconfiguration (e.g., NiCo nanoparticles, Fig. 2) can affect the reaction mechanisms and thus catalytic performance. Our design cycle iterates between theory (DFT, MM), synthesis, characterization (TEM, X-ray), and testing to discover and optimize new catalysts. This mutually supportive approach yields insights that could not be achieved separately.

Fig. 2 Fig. 1