A SIMPLE ANALYTICAL EQUATION FOR POLYMER ELECTROLYTE FUEL CELL

In recent years, several modelling studies were carried out to elucidate the electrochemical behaviour of a polymer electrolyte fuel cell (PEFC). However, theoretical models based on mechanistic approaches require the knowledge of not readily available parameters such as humidity levels, transfer coefficients, thickness of the membrane and of the catalytic layer. On the other hand, empirical models generally are not able to cover the entire current range when activation, mass transport and ohmic overpotential are simultaneously present and for this reason they are applicable over a restricted range of operating conditions. In this report, a simple empirical expression to determine cell potential (E) vs. current density (i) behaviour in PEFC is proposed. Starting from the experimental evidence that the cell resistance increases with the current density, and taking into account that resistance is the macroscopic evidence of charge transport limitation, using a mechanistic analogy some parameters correlated with cell components characteristics and operating condition were introduced. An attempt to give an interpretation of the introduced parameters was done applying to experimental data obtained with a 50 cm2 single cell using low Pt loading electrodes (~0.1 Pt mg cm-2), H2 and air as reactant gas, at different operating conditions. A good accuracy between theoretical and experimental data over the entire range of current density were found. The proposed equation seems to be able to separate the pure ohmic overpotential from others mass transport contribute.