(452a) Efficient Surface Chemistry Simulations and Applications to Pem Fuel Cell Electrochemistry

A wide range of chemical and electrochemical systems in surface catalysis exhibits non-linear behavior. One of the common causes for such interesting behavior is the interaction among the chemical species adsorbed on the surface. In polymer electrolyte membrane (PEM) fuel cells, nano-particles are typically used as electrocatalyst. The specific topology of such particles, which can be assumed to have cubo-octahedral geometry, can further lead to local non-linearities. Specifically, the edge/corner sites of such nano-particles can behave very differently from the sites located on the faces. Environment-averaged approaches, such as the mean-field approximation, often fail to accommodate the details of such local phenomena. An accurate approach for such complex chemical systems is the Dynamic Monte Carlo (DMC) method. DMC is computationally much more demanding than conventional approaches, and a number of DMC simulations algorithms have been proposed in the past. An example is the popular Variable Step Size Method (VSSM). VSSM has the advantage that the computational cost of a single time step is independent of the lattice size for problems with time-independent rate parameters, but scales with the square of the number of lattice sites otherwise. Another method, the First Reaction Method (FRM), can be applied for time-varying rate coefficients, but the computational cost per time step depends still linearly on the logarithm of the number of lattice sites. Here we present a new DMC algorithm that can be applied for time-varying rate coefficients and has a computational cost per time step that is independent of the lattice size.

To demonstrate the capabilities of the new method, DMC simulations of cyclic voltammetry experiments of PEM fuel cell electrochemistry will be presented and compared with experimental observations. The importance of non-linear adsorbent interactions will be discussed.