Performance equations of polymer electrolyte fuel cells

Performance equations that describe the dependence of cell potential on current density for polymer electrolyte fuel cells (PEFCs) have been developed in algebraic form. The equations are derived from the reduction of a one-dimensional model that takes into account, in detail, the limitations of reactant transport, proton migration and electron conduction, as well as electrochemical reactions within the cathode, anode and membrane electrolyte. Reduction of the one-dimensional model is implemented by approximating the profiles of reactant concentration and ionomer potential with appropriate functions and by lumping the overall reaction rates at the reaction centres of the catalyst layers. Since the performance equations originate from a mechanistic one-dimensional model, all parameters appearing in the equations have a precise physical significance. In addition, individual potential losses caused by the various limiting processes can be clearly quantified in the equation. Particularly, the equations for potential losses relevant to the anode limiting processes are first revealed by the present work. Thus, they can be used as a diagnostic tool for PEFC performance. Computational results show that the performance equations agree well with the original one-dimensional model over an extensive parameter range. The present performance equations allow for an efficient evaluation of PEFC performance since the complexities of the one-dimensional model and the procedures for the numerical solutions are completely avoided. As compared with previously developed performance equations dealing with PEFC cathodes only, the present equations are able to provide accurate interpretation on the polarization behaviour of a complete PEFC.