The Role of the Platinum Band for Membrane Degradation in PEMFC – An Investigation using an Artificial Platinum Band

Abstract

The impact of the Pt band on ionomer degradation is controversial. Many studies found increased degradation in the presence of Pt deposits. However, in a recent publication, it was reported that the Pt band suppressed ionomer degradation.3 In their theoretical work, Gummalla et al. explained this discrepancy by the distribution of Pt particles: at low particle density, radicals are free to attack the ionomer, at high density, they are scavenged.4 Experimental results based on membranes in which Pt was deposited chemically support this theory.5,6 However, in those membranes, Pt particles were dispersed homogeneously, not locally as a thin band. In order to examine the influence of the Pt band more accurately, it is necessary to prepare membranes containing Pt particles which are distributed similarly to the Pt band. In this work, we investigated the role of Pt concentration in the Pt band on membrane degradation. For this purpose, we conducted a degradation experiment with membrane electrode assemblies (MEAs) containing an artificial Pt band with different amount of Pt. The MEAs contained two Nafion® membranes between which Pt was deposited mechanically. In the degradation test, they were operated with H2/O2 for ca. 100 h at open circuit voltage. Degradation was investigated based on electrochemical characterization and fluoride emission. In addition, Pt particle distribution at the membrane cross sections was analyzed with scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). 1. A. B. LaConti et al., in Handbook of Fuel Cells: Fundamentals, Technology and Applications, Vol. 3, 647–663, Chicester, England (2003). 2. J. Aragane, J. Appl. Electrochem., 26, 147–152 (1996). 3. N. Macauley et al., ECS Electrochem. Lett., 2, F33–F35 (2013). 4. M. Gummalla et al., J. Electrochem. Soc., 157, B1542–1548 (2010). 5. M. P. Rodgers et al., J. Electrochem. Soc., 160, F1123–F1128 (2013). 6. S. Helmly et al., ECS Trans., 58, 969–990 (2013)