Mechanical properties of membrane-electrode assemblies (MEAs) are most relevant for the durability of proton-exchange membrane fuel cells (PEMFCs) [1]. During operation, the MEA must endure eventual changes in the static pressure of anodes and cathodes caused by changes in power demand, gases flow rate, and/or water generation, accompanied by hygrothermal cycles, that cause mechanical stresses in the membrane, leading to cracks and possible fatal failure [2]. In parallel, the mechanical properties of MEAs change irreversibly during power production as a consequence of membrane and electrodes corrosion [3]. Therefore, it is of interest to characterize the mechanical properties of MEAs before assembly, and after operation.

The small-punch is a new technique for testing mechanical properties of solids. It consists of measuring the deformation of a disc of the testing material with a ‘small puncher’, while recording the load (force) exerted by the puncher and the deflection produced on the specimen (Fig. 1a) [4]. The plot load vs deflection allows estimating mechanical strength, fracture toughness, impact, and tensile properties. Most interesting is that the disk specimen can be as small as a few millimeters, which makes the small-punch technique very appropriate when the amount of sample is limited, and for localized studies of mechanical properties.

In this communication, results of the small-punch technique are shown for the study of MEAs operated in single PEMFCs (Fig. 1b). The analysis is carried out of the local mechanical properties on new and degraded MEAs. First results show that local mechanical properties of the aged MEA correlate well with gas feeding conditions and reflect laterally inhomogeneous degradation (Fig. 1b).

Acknowledgement: The work is partially financed by the ELHYPORT project (PID2019−110896RB-I00), Spanish Ministry of Science and Innovation.

[1] X. Huang, R, Solasi, Y. Zou, M. Feshler, K. Reifsnider, D. Condit, S. Burtlatsky, T. Madden, J. Polymer Science: Part B: Polymer Physics, Vol. 44, 2346–2357 (2006).

[2] Z. Lu, M. Lugo, M.H. Santare, A.M. Karlsson, F.C. Busby, P. Walsh, J. Power Sources 214 (2012) 130-136.

[3] M. Pestrak, Y. Li, S.W. Case, D.A. Dillard, M.W. Ellis, Y-H. Lai, C. S. Gittleman, J. Fuel Cell Sci. Technol. (2010), 7(4): 041009.

[4] EN 10371:2021 Metallic materials - Small punch test method. CEN, Brussels (2021)