Physical Chemistry Seminar: Professor Mark Tuckerman, New York University (Host: Tom Markland)
**This seminar is available for in-person attendance.**
About the Seminar
"First-principles molecular dynamics investigations of proton and hydroxide transport in low-hydration nanoconfined environments: Idealism leads to realism"
Fuel cell-based anion-exchange membranes (AEMs) and proton exchange membranes (PEMs) have considerable potential as cost-effective, clean energy conversion devices. However, a fundamental atomistic understanding of the hydroxide and hydronium diffusion mechanisms in AEM and PEM environments is an ongoing challenge. In recent years, nano-confined structures have been exploited in the study of cost-effective and reliable polymer architectures for electrochemical devices. In this study, first-principles molecular dynamics simulations, in which interatomic forces are computed “on the fly” from electronic structure calculations, are employed to investigate the influence of the water distribution, temperature, and internal geometry on the diffusion rate of protons and hydroxide ions in nanoconfined geometries that serve as mimics of PEM and AEM environments. The simulations indicate that the water distribution is a determinative factor in the diffusion process. Moreover, it is found that hydroxide diffuison in AEMs is eithe largely vehicular or a combination of vehicular and structural while proton diffusion in PEMs is largely structural. Pairs of cations in AEMs create bottlenecks for hydroxide diffusion while the anion groups in PEMs become active participants in proton diffusion. We uncover an unusual phenomenon, namely, that the temperature dependence of hydroxide diffusion in AEMs is non-monotonic, exhibiting a “kink” over a particular temperature range at which dDOH─/dT < 0, a finding that is confirmed experimentally. Finally, we investigate the influence of the presence of CO2 in AEMs, which leads to a suppression of hydroxide diffusion, a result also in line with experimental observations, and we suggest a physical chemical origin for this suppression.
About the Speaker
Mark Tuckerman obtained his B.S. in physics from the University of California at Berkeley in 1986 and his Ph.D. from Columbia University in 1993, working in the group of Bruce J. Berne. From 1993-1994, he held an IBM postdoctoral fellowship at the IBM Forschungslaboratorium in Rüschlikon, Switzerland in the computational physics group of Michele Parrinello. From 1995-1996, he held an NSF postdoctoral fellowship in Advanced Scientific Computing at the University of Pennsylvania in the group of Michael L. Klein. He is currently Professor of Chemistry and Mathematics at New York University. His research program spans a variety of topics including the use of theoretical and computational chemistry techniques to study electrolyte liquids and model AEM and PEM environments, the development of large time-step algorithms for molecular dynamics, free-energy based enhanced sampling tools for predicting the conformational equilibria of complex molecules and the exploration of structure and polymorphism in molecular crystals, and development of machine learning models for electronic structure theory and statistical mechanics applications. Honors and awards include the Japan Society for the Promotion of Science Fellowship, the Friedrich Wilhelm Bessel Research Award from the Alexander von Humboldt Foundation, the Camille Dreyfus Teacher-Scholar Award, an NSF CAREER Award, and the NYU Golden Dozen Teaching Excellence Award, the Andreas C. Albrecht Lectureship from Cornell University, and the Institute Lectureship from the Indian Institute of Technology, Kanpur. He was recently appointed Chair of the Department of Chemistry at NYU.