Investigations on the Corrosion Behavior of a 20 Cell PEMFC Automotive Short Stack Caused By Air/Air Start-Ups at Different Operating Conditions Utilizing a Segmented Current Mapping Board
Authors: Jurjević Adrian , Mohrdieck Christian , Weidler Natascha 
Published: December 2024

The Polymer Electrolyte Membrane Fuel Cell (PEMFC) emerges as one of the key technologies for the future of energy and mobility landscapes by offering a clean, efficient, and sustainable power generation. To ensure the commercial viability of PEMFCs, the components, particularly the Membrane Electrode Assembly (MEA), and its operation must be designed to minimize the impact of degradation processes over their entire lifetime and to maximize durability.
It is known that the oxidation or corrosion of the cathode catalyst support material resulting from the so-called reverse current decay mechanism caused by gas atmosphere changes when starting up from an inactive state (air/air situation) or shutting down from the active state (H2/air situation) is one of the most significant degradation processes. The Carbon Oxidation Reaction (COR) can lead to a detachment of the supported catalyst particles from the rest of the electrical network or to a delamination from the ionic network and therefore ultimately result in a reduction of the Effective Catalyst Surface Area (ECSA) and in increasing mechanical instability up to the collapse of the catalyst layer [1].
In previous work, different approaches have been taken to simulate this degradation mechanism using accelerated stress tests, usually at half-cell or sub-scale level, with active areas <50 cm² [2][3]. The aim of this work is to investigate the effect of Air/Air Start-Ups (AASUs) on a higher integration level using a 20 cell short stack with a single full-size automotive cell active area of >200 cm². AASUs were executed after different air soak durations and under different operating conditions with focus on relative humidity, coolant inlet temperature, hydrogen concentration and inflow rate to vary the gas front residence time within the active area. The short stack is equipped with a Cell Voltage Monitoring (CVM) of each individual cell and a high-resolution segmented Current Mapping Board (CMB) next to the anode Interface Plate (IFP) to record local and internal current density changes, particularly during the passage of the gas atmosphere front, as exemplified and illustrated in Figure 1.
After the fundamental investigation of the impact of different operating parameters, a specific parameter set was chosen to assess the degradative effects on an identical stack in a continuous AASU sequence operation until failure. Throughout the stress testing, the cell performances including the local current distribution as well as the ohmic resistance of the stack by Electrochemical Impedance Spectroscopy (EIS) were monitored. Furthermore, morphological investigations using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) were performed after disassembly of the stack on different cells in the stack and at different positions within the active area. The formation of degradation gradients within the active cell area and along the stack, induced by AASU stress testing, is demonstrated through changes in local current densities measured with the CMB, accompanied by a loss of overall cell performance and supported by in-depth morphological investigations.

References

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[2] Wu, Jinfeng; Yuan, Xiao Zi; Martin, Jonathan J.; Wang, Haijiang; Zhang, Jiujun; Shen, Jun et al. (2008): A review of PEM fuel cell durability: Degradation mechanisms and mitigation strategies. In Journal of Power Sources 184 (1), pp. 104–119. DOI: 10.1016/j.jpowsour.2008.06.006.
[3] Marcu, A.; Toth, G.; Kundu, S.; Colmenares, L. C.; Behm, R. J. (2012): Ex situ testing method to characterize cathode catalysts degradation under simulated start-up/shut-down conditions – A contribution to polymer electrolyte membrane fuel cell benchmarking. In: Journal of Power Sources 215, S. 266–273. DOI: 10.1016/j.jpowsour.2012.05.010.

Figure 1