Load Cycling Durability Protocols for Predictive MEA Lifetime Modeling for Long-Life PEMFC Applications
Authors: Coms Frank D. , LaLonde Ashley , Gu Wenbin , Tylena Joel 
Published: December 2024

As the large-scale commercialization of proton exchange membrane fuel cells (PEMFC) for numerous heavy-duty applications draws nearer, there is an increasing emphasis on the delivery of highly robust membrane electrode assemblies (MEAs) capable of achieving upwards of 25,000 hours of on-road durability (1). A particular area of MEA durability focus is that of the proton conducting perfluorosulfonic acid (PFSA) membrane which is subjected to varying degrees of oxidative stress during fuel cell operation. The development of highly durable membranes necessitates the implementation of accelerated testing protocols that can be used to determine the sensitivity of membrane lifetime to a number of operational parameters such as cell temperature and membrane humidification. The objective of sensitivity studies is to develop robust and predictive degradation models using state-of-the-art (SOA) MEAs under the accelerated operational space that can be subsequently applied to the milder operational space of a long-lifetime application. Traditionally, open circuit voltage (OCV) degradation studies have been employed to assess membrane durability. While OCV degradation experiments can be highly accelerating from a chemical degradation perspective, producing high fluoride release and membrane thinning rates, the operating conditions do not sufficiently emulate the dynamic chemical stresses generated under load nor do they provide RH cycling and concomitant mechanical stresses that accompanies load cycling (2). At the other end of the cell load continuum, constant current durability tests have consistently failed to produce high degradation rates, even in the presence of Fe accelerants.

In response to the recognized shortcomings of OCV and related accelerated durability tests, we have developed a suite of flexible, single-cell, load-cycling durability tests that more closely emulate stresses experienced in variety of real-world, on-load applications. Test protocols enable the variation numerous operational parameters including temperature, inlet RH, high and low cycling current densities and the ratio of time spent at the high and low current densities. In-situ degradation rates are assessed by monitoring emitted fluoride concentrations at regular intervals. Cerium-mitigated (3), SOA PFSA membranes fabricated with PtCo/HSC cathode electrodes are quite robust even under the harshest load cycling conditions (110 °C/ 30% RH), producing fluoride release rate (FRR) values less than 1x10-8 gF/cm-2h-1. The creation of predictive chemical degradation models requires significant and quantifiable chemical degradation signals to occur across accelerated the reaction space continuum. Therefore, given the high stability of SOA membranes, the degradation rates are further accelerated by the addition of Fe2+ Fenton’s catalysts. The Figure below shows the FRR profiles obtained from a series of four MEAs, differing only in the amount of added Fe2+ prior to the durability test conducted at 95 °C/30% RH with load cycling between 0.02-1.5 A/cm². In addition to Fe sensitivity findings, we will present data regarding sensitivities of degradation rates with respect to temperature, inlet RH, high current density values and time ratios at high and low current densities.

(1) D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers, A. Kusoglu, Nature Energy, 6, 462–474 (2021)

(2) C. S. Gittleman, F. D. Coms, Y.-H. Lai, In Polymer Electrolyte Fuel Cell Degradation, M. Matthew, K. E. Caglan, T. N. Veziroglu, Editors, p. 15, Academic Press, Boston (2012)

(3) F. D. Coms, H. Liu, and J. E. Owejan, ECS Transactions, 16, 1735 (2008)

Figure 1