PNNL

Abstract

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The strong drive to commercialize fuel cells for portable as well as transportation power sources has led to the tremendous growth in fundamental research aimed at elucidating the catalytic paths and kinetics that govern the electrode performance of proton exchange membrane (PEM) fuel cells. Advances in theory over the past decade coupled with the exponential increases in computational speed and memory have enabled theory to become an invaluable partner in elucidating the surface chemistry that controls different catalytic systems. Despite the significant advances in modeling vapor-phase catalytic systems, the widespread use of first principle theoretical calculations in the analysis of electrocatalytic systems has been rather limited due to the complex electrochemical environment. Herein, we describe the development and application of a first-principles-based approach termed the double reference method that can be used to simulate chemistry at an electrified interface. The simulations mimic the half-cell analysis that is currently used to evaluate electrochemical systems experimentally where the potential is set via an external potentiostat. We use this approach to simulate the potential dependence of elementary reaction energies and activation barriers for different electrocatalytic reactions important for the anode of the direct methanol fuel cell. More specifically we examine the potential-dependence for the activation of water and the oxidation of methanol and CO over model Pt and Pt alloy surfaces. The insights from these model systems are subsequently used to test alternative compositions for the development of improved catalytic materials for the anode of the direct methanol fuel cell.