PERFORMANCE MODELING OF THE BALLARD-MARK-IV SOLID POLYMER ELECTROLYTEFUEL-CELL .1. MECHANISTIC MODEL DEVELOPMENT

A parametric model predicting the performance of a solid polymer elect rolyte, proton exchange membrane (PEM) fuel cell has been developed us ing a combination of mechanistic and empirical modeling techniques. Th is paper details the mechanistic model development. Mass transport pro perties are considered in the mechanistic development via Stefan-Maxwe ll equations. Thermodynamic equilibrium potentials are defined using t he Nernst equation. Activation overvoltages are defined via a Tafel eq uation, and internal resistances are defined via the Nernst-Planck equ ation, leading to a definition of ohmic overvoltage via an Ohm's law e quation. The mechanistic model cannot adequately model fuel cell perfo rmance, since several simplifying approximations have been used in ord er to facilitate model development. Additionally, certain properties l ikely to be observed in operational fuel cells, such as thermal gradie nts, have not been considered. Nonetheless, the insights gained from t he mechanistic assessment of fuel cell processes were found to give th e resulting empirical model a firmer theoretical basis than many of th e models presently available in the literature. Correlation of the emp irical model to actual experimental data was very good.