Experimental Analysis of Oxygen Transport Resistance for Different Types of Ionomer in PEFC Catalyst

Abstract

To improve the performance of polymer electrolyte fuel cells (PEFC), it is important to reduce the oxygen transport resistance in the cathode catalyst layer (CL). The authors have been conducted detailed analysis of the oxygen transport resistance elements: the diffusion resistances in the CL pores, the dissolution resistance into the ionomer, and the transport resistance at the Pt surface. This study improved the method to determine the limiting current density in the analysis, and the cell performances with two types of ionomer, Nafion and Aquivion, based CLs were compared from the viewpoint of the oxygen transport resistance. It was shown that Aquivion based CLs have the lower limiting current densities than those with Nafion, while the voltage is higher in the middle current density range. The analysis suggested that this is due to the higher oxygen transport resistance at the Pt surface, caused by aggregation of Aquivion near the Pt.

Impedance Spectroscopy Measurements of Ionomer Film Oxygen Transport Resistivity in Operating Low-Pt PEM Fuel Cell

“…The effective thickness of the ionomer films estimated using O 2 mass transport resistance was found to be significantly higher than that observed by transmission electron microscopy of 1-10 nm [6,7,9]. This finding suggested that the physical properties of the thin ionomer films in confinements such as water uptake and elastic modulus differed from the properties of bulk ionomer, and the additional interaction of ionomer and Pt negatively affected mass transport [6,7,9,[17][18][19][20][21][22]. In spite of the fact that the limiting current approach is widely used for PEMFCs characterization, its implementation typically requires a cell with an active area of 1-5 cm 2 and high stoichiometry of reagents to reach currents relevant for PEMFCs.…”