PEM Unit Cell Model Considering Additional Reactions

A computational model is developed for a PEM unit cell capable of describing the reactions that occur in the cell in understoich conditions. Such conditions can occur as a result of reactant supply system failure (blockage, leaks, system control, etc.). The model applies to cells with straight channels, and mass transport in the MEA (membrane crossover as well as transport through the GDE) in the channel cross-plane is described only in an average sense assuming linear diffusive mechanisms. Several other major assumptions are made, the most significant being that the cell is always at saturated conditions and is taken to be isothermal. Several electrochemical and mass transport coefficients are not available in the literature and “best guesses” are taken. The results of the model are not yet validated experimentally. However, it is the first model proposed that captures these phenomena in a comprehensive way at the local level and also couples the phenomena through channel flow. Cathode understoich results show the expected Hydrogen evolution at the cathode. Anode understoich results show anode Carbon oxidation. An interesting third run is shown where at low currents, a partial anode understoich condition occurs where the cell voltage remains positive, but the anode is starved of Hydrogen near outlet. Carbon corrosion at the cathode occurs in this case.Copyright © 2006 by ASME