Investigation and Quantification of Irreversible Degradations and Their Sensitivities during the Start-up Phases of PEMFC By an Accelerated Emulation Approach

Abstract

In automotive application, frequent Start-up/Shut-down (SU/SD) phases of PEMFC system are prone to cause severe degrading conditions. Many studies have been achieved over the past decades to better understand and to mitigate MEA aging and performance decay due to the well-identified reverse current mechanism1. Indeed, the H2|Air front during H2 injection at the air-filled anode creates two sub-cells: H2/Air sub-cell operating in Fuel Cell mode and Air/Air sub-cell operating in Electrolysis Cell mode. This second sub-cell is subjected to high potential at cathodic side (about 1.6 V vs RHE), leading to harsh corrosion of both Pt nanoparticles and carbon support within the cathode catalyst layer. Two main mitigating solutions are generally proposed in the literature: (i) development of more stable materials and (ii) improvement of system control 2,3. Experimental DOE AST4 is usually performed only on small single cell to evaluate MEA component durability. Nevertheless, these tests cannot be fully correlated with real automotive operating conditions to predict PEMFC stack lifetime.In this work, more realistic AST protocols in regard to PEMFC stack/system configuration during start-up phase are proposed. Our experimental approach consists in emulating a representative transient cathodic potential profile (Figure a and b) during the H2|Air front formation and propagation along anodic channel using a 100 cm² single cell with a real stack active area design5. A comprehensive investigation and quantification of degradations caused by reverse current was carried out under SU cycling. Additional sensitivity study on the main operating parameters (potential profile, relative humidity and temperature) was performed to evaluate their respective impact on the cathode degradation and the performance losses. Periodic measurements such as polarization curves and cyclic voltammetry (Figure c) are coupled with CO/CO2 gas emission analysis (Figure d) during cycling at cathode to monitor and quantify the physical and electrochemical modifications within the MEA during our aging SU cycles.On the whole, this original experimental study proposes an overall degradation mechanism and these results are compared with model prediction to validate the most impactful parameters during reverse current phases at the real cell size and design. Ultimately, it will provide key-data to propose and optimize finely different mitigation strategies to be used in PEMFC stack and systems. References Reiser, C. A. et al. A reverse-current decay mechanism for fuel cells. Electrochemical and Solid-State Letters 8, A273–A276 (2005).Zhang, T., Wang, P., Chen, H. & Pei, P. A review of automotive proton exchange membrane fuel cell degradation under start-stop operating condition. Applied Energy 223, 249–262 (2018).Yu, Y. et al. A review on performance degradation of proton exchange membrane fuel cells during startup and shutdown processes: Causes, consequences, and mitigation strategies. Journal of Power Sources 205, 10–23 (2012).Fuel Cell Tech Team Accelerated Stress Test and Polarization Curve Protocols for PEM Fuel Cells. Energy.gov https://www.energy.gov/eere/fuelcells/downloads/fuel-cell-tech-team-accelerated-stress-test-and-polarization-curve.Randrianarizafy, B. Multi-physics modeling of startup and shutdown of a PEM fuel cell and study of the carbon support degradation : mitigation strategies and design optimization. (Université Grenoble Alpes, 2018). Figure 1