An empirical fuel cell polarization curve fitting equation for small current densities and no-load operation

A logarithmic term is applied to account for the charge transfer overvoltage with most empirical polarization curve fitting equations for polymer electrolyte membrane fuel cells. The logarithmic term applied with state-of-the-art fitting equations is proportional to the logarithm of the cell output current density. This provides good fitting characteristics with large current densities, but results in significant deviations from measured current/ voltage characteristics if small current densities or no-load operation are investigated. A modified logarithmic charge transfer overvoltage term utilising the exchange current density and an internal cell current density is therefore introduced to provide accurate fitting characteristics with small current densities and no-load operation. Fitting characteristics of this modified polarization curve fitting equation are investigated and compared to standard fitting equations.