434542 Rational Design of Catalytic Sites for Energy Applications

Sunday, November 8, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Timothy Van Cleve, Department of Chemical Engineering, University of Michigan, Ann Arbor, MI

The rapidly increasing global demand for energy coupled with large population growth necessitates the development of increasingly efficient systems for utilizing our finite energy and chemical resources.  While no single approach will address these complex issues, I strongly believe that catalysts have an important role to play in addressing these challenges.  Our society is already heavily reliant on these materials to produce the chemicals that we need to sustain our lifestyles.  Catalysts are incredible because of their ability to facilitate selective chemical transformations while converting between chemical, thermal, radiant, and electrical forms of energy.  Coupling catalytic systems with renewable energy sources presents a unique opportunity to regenerate useful high value chemicals from low value feed stocks like CO2 and H2O.  In order to develop these technologies, it is vital to understand the pathway through which these chemical transformations proceed and how catalytic systems respond to different energetic stimuli.  It is also vital to identify key characteristics of active and stable catalysts to enable the design of materials with optimal sites for a particular reaction. This strategy was implemented during my PhD studies for the development of hydrogen fuel cell electrocatalysts.

Over the course of my graduate studies under Prof. Suljo Linic, we have investigated how geometric and chemical manipulations of catalytic sites influence overall catalytic performance.  Specifically, we focused on understanding how changing the size, shape, and composition of Ag and Pt alloy electrocatalysts affects their activity towards the oxygen reduction reaction (O2+4H+/e-→2H2O, ORR) in alkaline and acidic electrolytes.  First, kinetics studies of the oxygen reduction mechanism on these surfaces allowed us to identify key chemical descriptors (like OOH or OH adsorption energies) that are correlated with catalytic activity.  We then utilized quantum chemical calculations to determine how these descriptors could be selectively influenced in platinum based catalysts through perturbations such as alloying or inducing geometric strain.  After identifying promising catalysts, we developed sophisticated synthesis strategies to prepare these materials.  We then tested their activity, with rigorous experimental protocol allowing us to obtain valid kinetic rates from the observed rates, and found that improved activity was achieved. Finally, we performed extensive in situ and ex situ characterization to confirm both that the atomic structure of the electrocatalyst matches that of our model and that the observed activity enhancement is a direct result of the improved key chemical descriptors of this particular nanostructure.

My future research interests focus on the design of cheap, active, and stable catalysts for hydrogen evolution, CO2 reduction, and nitrogen fixation.  My knowledge and experience with rational design, chemical synthesis, activity testing, and material characterization equips me with the skills to tackle these challenges.

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