Abstract
The simultaneous changes occurring in the internal materials of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) under dynamic operating conditions make characterizing the inherent resistance of each material under different operating conditions highly complex. Therefore, the isolation of the internal resistance of components and the identification of the resistance elements that significantly affect PEMFC performance are essential, but comprehensive studies analyzing the internal resistance under different operating conditions have been scarce.This study proposes a complex resistance analysis methodology capable of isolating the oxygen resistance of a PEMFC single cell under different operating conditions (relative humidity, temperature, supply gas). The Knudsen diffusion within the catalyst layer is calculated according to the operating conditions using a catalyst agglomerate model. This calculation is combined with the dissection of the oxygen transport resistance to distinguish between molecular diffusion, Knudsen diffusion and ionomer film resistance under limiting current density conditions. In addition, an equation has been developed that accurately predicts the ionomer film resistance as a function of changes in temperature and RH, proposing a new approach to mapping ionomer film resistance. Then, by inputting three forms of resistance from the dissection of the oxygen transport resistance analysis as percentages into the distribution of relaxation time analysis, the newly developed methodology gives insight into the contributions of seven different resistance elements at different current densities. This provides an indicator for determining ionomer resistance without the need for temperature and RH experiments. In addition, this research identifies the design of the ionomer within the catalyst layer as a key determinant of PEMFC cell performance, highlighting the significant impact that molecular or Knudsen diffusion can have depending on operating conditions. Consequently, through an in-depth analysis of oxygen stability under different operating conditions, this study will provide essential insights for future PEMFC cell design.
Published Version
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