2017 Spring Symposium
Maureen Tang, Chemical and Biological Engineering, Drexel University, Philadelphia, PA
Abstract – Hydrogen is a potential low cost, scalable energy storage medium for renewable electricity generation. More importantly, study of the hydrogen electrode reactions has led to the discovery of many of the fundamental concepts in electrochemistry and electrocatalysis. It has long been recognized that the reaction rates of the hydrogen oxidation and hydrogen evolution reactions (HOR and HER) are slower in basic than acidic electrolytes, even though the surface intermediate of adsorbed hydrogen is independent of solution pH. Understanding the root of this observation is critical to designing catalysts for a multitude of electrochemical reactions with relevance to energy conversion and storage. In this work, we undertake both applied and fundamental efforts to understand the mechanisms and develop low-cost, active catalysts for the hydrogen reactions in base.
In the first part of the talk, we utilize a theory-guided approach to develop nickel-silver catalysts for alkaline hydrogen evolution and oxidation. Density-functional-theory calculations predict these alloys will be active for hydrogen evolution and oxidation. To circumvent the thermodynamic insolubility of these two metals and isolate catalytic activity, we employ an uncommon physical vapor codeposition synthesis. Our measurements show that the alloy is indeed more active for hydrogen evolution than pure nickel. In the second part of the talk, we examine specifically the hypothesis that water orientation governs the rate of hydrogen adsorption and thus the overall HER/HOR kinetics by modulating the potential of zero charge of oxide supports in acid and base. Finally, we combine microkinetic modeling and single-crystal measurements to determine if adsorbed hydroxide functions as an active intermediate or spectator in the reaction. The results of these studies highlight the importance of kinetic barriers, as well as adsorption energies, and contribute to resolving a long-standing paradox in electrocatalysis and surface science.
Biography – Maureen Tang joined the faculty of Chemical and Biological Engineering at Drexel University in Fall 2014. She received her B.S. in Chemical Engineering from Carnegie Mellon University and her Ph. D. from the University of California, Berkeley. While at Berkeley, she received a NSF Graduate Research Fellowship, an NSF East Asia Pacific Summer Fellowship, and the Daniel Cubiciotti Student Award of the Electrochemical Society. Dr. Tang has completed postdoctoral work at Stanford University and research internships at Kyoto University, the University of Dortmund, and Dupont. Her research at Drexel develops materials, architectures, and fundamental insight for electrochemical energy storage and conversion.