Journal of Power Sources 196 (2011) 8234–8240 Contents lists available at ScienceDirect Journal of Power Sources jou rnal h omepa g e: www.elsevier.com/locate/jpowsour Mechanical durability of proton exchange membranes with catalyst platinum dispersion Ruiliang Jia a,b , Binghong Han b , Kemal Levi b , Takuya Hasegawa c , Jiping Ye d , Reinhold H. Dauskardt b,∗ a Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA b Department of Materials Science and Engineering, Stanford University, 496 Lomita Mall, Durand Bldg., Room 121, Stanford, CA 94305-2205, USA c Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka 237-8523, Japan d Research Department, Nissan ARC LTD., 1 Natsushima-cho, Yokosuka 237-0061, Japan a r t i c l e i n f o Article history: Received 15 April 2011 Received in revised form 25 May 2011 Accepted 25 May 2011 Available online 1 June 2011 Keywords: Proton exchange membrane Fuel cell platinum Bulge test Tearing test Nafion ® a b s t r a c t The durability of proton exchange membrane (PEM) fuel cells remains a challenging issue for their long term operational use. Degradation of the PEM related to dissolution of the adjacent catalyst and re- deposition into the PEM significantly reduces cell efficiency. We investigate the effects of platinum (Pt) dispersions intended to simulate the re-deposited catalyst on the mechanical durability of the PEM. The bulge technique was applied to characterize the mechanical properties of PEMs simulating pressure loading on fully hydrated membranes in fuel cells. The results showed that with increasing Pt dispersion concentration the stiffness of the PEMs increased, and the membranes became less ductile and inclined to fracture at lower stresses under pressure loading. We also used the out-of-plane tearing test to char- acterize membrane fracture behavior which revealed the harmful effects of Pt dispersion on the fracture resistance under different environmental conditions. Deterioration in fracture resistance was explained in terms of the Pt distribution and aggregation as defects inside the membranes as characterized by elec- tron microscopy. Fracture was shown to initiate preferentially at the interface of Pt particles and the polymer matrix, and propagate through the defect regions in polymer with lower energy, thus reducing the overall fracture resistance of the PEM. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Proton exchange membrane fuel cells (PEMFCs) are a promising power source in stationary, portable, and automotive applications [1–3]. Despite significant improvements in efficiency of these fuel cells in recent years, the durability of current PEMFCs is still a challenging issue for their practical use [4]. In particular, degra- dation of proton exchange membranes (PEMs), including chemical decomposition induced by a hydrogen peroxide byproduct [5–12] and mechanical damage of the membranes under pressure loading [13–20], represents common failure modes that limit the lifetime of fuel cells. The performance of PEMFCs is also significantly dependent on the electrocatalytic activity of catalysts such as platinum (Pt) and Pt alloys in both electrodes [21]. The deleterious effect of cat- alyst degradation on fuel cells efficiency has been investigated [22–25], and the phenomenon of Pt dissolution in the adjacent Abbreviations: PEM, proton exchange membrane; PFSA, perfluorosulfonic acid; DIW, distilled water. ∗ Corresponding author. Tel.: +1 650 725 0679; fax: +1 650 725 4034. E-mail addresses: dauskardt@stanford.edu, rhd@stanford.edu (R.H. Dauskardt). catalyst layer and subsequent re-deposition into the PEM after long-term operation was also reported [26]. On the other hand, it has also been reported that Pt dispersions in PEMs suppress chem- ical degradation of the molecular structure of the membranes [27]. Notwithstanding such observation, however, the effects of such Pt dispersions on the mechanical durability of PEMs are currently unknown. Accordingly, in this study we investigated the mechanical prop- erties of PEMs with Pt dispersions intended to simulate the effect of re-deposited Pt catalyst. The bulge testing method was applied to simulate pressurized loading on hydrated membranes in fuel cells. This method was previously used with a gas pressure medium to characterize PEMs’ strength and resistance to gas leakage [17–19], and was also applied to analyze the effect of foreign cation con- tamination on the mechanical reliability of hydrated PEMs using water as a pressure medium [20]. Here we studied not only the biaxial stress–strain behavior of the PEM-Pt with various Pt concen- trations, but also their fracture toughness under hydrated pressure loading. The results showed that with increasing Pt dispersion con- centration the stiffness of the membranes increased. Pt dispersion also made the membranes less ductile and inclined to fracture at lower stresses. In addition, we used the tearing test to characterize the out-of-plane fracture behavior of PEM-Pt. Pt dispersions had 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.05.069