Dr. Stephen J. Paddison

The concept of the fuel cell, a device that electrochemically converts fuel into electrical current, has been known for more than 150 years dating back to the independent work of both Schönbein and Grove.  However, during the past two decades the polymer electrolyte membrane (PEM) fuel cell has been the focus of intense and broad based research for applications including: portable, stationary, and vehicular power sources. Central to this research has been the investigation of how the structure and composition of the various components determine their function. The integration of synthesis, characterization, and modeling is proving to be the route to a molecular level understanding of existing fuel cell materials and the pathway to novel high performance materials.
Our research focuses on the central component of the PEM fuel cell: the proton exchange membrane. We are interested in developing understanding of:

1. the functional dependence of the membrane morphology on water content, density and distribution of protogenic groups, and the chemistry of the backbone and/or side chains
2. the molecular features governing the dissociation, transfer, and diffusion of protons in perfluoro and hydrocarbon ionomers.

A multi-scale modeling approach is used which encompasses: the formulation and application of statistical mechanical based models, dissipative particle dynamics simulations, classical and ab initio molecular dynamics, and electronic structure calculations. We work very closely with experimental groups undertaking both the synthesis and characterization of fuel cell components and materials and pay particular attention to validation of the modeling results over all scales.

•Modeling of morphology & proton transport in PFSA membranes. J. A. Elliott and S. J. Paddison, Physical Chemistry Chemical Physics, 9, 2602-2618 (2007).
•About the choice of the protogenic group in polymer electrolyte membranes: Ab initio modeling of sulfonic acid, phosphonic acid, and imidazole functionalized alkanes. S. J. Paddison, K. D. Kreuer, and J. Maier, Physical Chemistry Chemical Physics, 8, 4530-4542 (2006).
•On the consequences of side chain flexibility and backbone conformation on hydration and proton dissociation in perfluorosulfonic acid membranes. S. J. Paddison and J. A. Elliott, Physical Chemistry Chemical Physics, 8, 2193-2203 (2006).
•Effects of dielectric saturation and ionic screening on the proton self-diffusion coefficients in perfluorosulfonic acid membranes. R. Paul and S. J. Paddison, Journal of Chemical Physics 123, 224704-1-14 (2005).
•Molecular modeling of the ‘short-side-chain’ perfluorosulfonic acid membrane. S. J. Paddison and J.A. Elliott, Journal Physical Chemistry A, 109, 7583-7593 (2005).
•Transport in Proton Conductors for Fuel Cell Applications: Simulations, Elementary Reactions, and Phenomenology. K.-D. Kreuer, S. J. Paddison, E. Spohr, and M. Schuster, Chemical Reviews 104, 4637-4678 (2004).
•Proton conduction mechanisms in Polymer Electrolyte Membranes at low degrees of hydration. S. J. Paddison, Annual Review of Materials Research 33, 289-319 (2003).
•Defect structure for proton transport in triflic acid monohydrate solid. M. Eikerling, S. J. Paddison, L. R. Pratt, and T.A. Zawodzinski Jr., Chemical Physics Letters 368, 108-114 (2003).