The Impact of Platinum Reduction on Oxygen Transport in Proton Exchange Membrane Fuel Cells

Key challenges to the acceptance of Proton Exchange Membrane Fuel Cells (PEMFCs) for Fuel Cell Electric Vehicles (FCEVs) are the cost reduction and improvements in power density for compactness. High current density operation is one of the most effective solutions for cost reduction and power density improvements. It contributes to size reduction of PEMFCs as well as lower amounts of Platinum (Pt). However, high current density operation causes an increase in concentration overpotential, resulting in lower cell performance. In addition, the oxygen transport resistance typically increases under lower Pt loadings. The effect of rib/channel widths and Pt loading on oxygen transport resistance and cell performance were investigated by coupled experimental and numerical analyses in this study. Oxygen transport resistance was obtained by measuring limiting current with various rib/channel widths and platinum loadings, and it significantly increased depending on the rib/channel widths as well as platinum loadings. A three-dimensional numerical model was developed by implementing the oxygen transport resistance from the pores in catalyst layer to the platinum surface. Numerical validations showed that the rib/channel widths caused inhomogeneous reaction distributions in both in-plane and through-plane directions. This resulted in an increase in the oxygen transport resistance. Also, the numerical model revealed that the oxygen flux per platinum surface area significantly increased when platinum loading is decreased, causing an increase in the oxygen transport resistance. Moreover, the model could reproduce the cell performances under high current density with different rib/channel widths and platinum loadings. These results suggested that a reduction of oxygen flux per platinum surface area was essential to achieve high current density operation with lower platinum loadings.