Anode Aging during PEMFC Start-Up and Shut-Down: H₂-Air Fronts vs Voltage Cycles

Abstract

Start-up and shut-down (SUSD) events in proton exchange membrane fuel cells (PEMFCs) are a major source of cathode degradation, causing a loss of electrochemical surface area (ECSA) and carbon corrosion. Our study reveals that also the anode suffers significant damage during SUSD, dominated by the loss of ECSA, induced by potential cycling between ≈0 and ≈1 V upon the passage of H 2 /air fronts. Furthermore, we demonstrate the analogy of SUSD-induced anode degradation and that originating from quasi-square wave potential cycling between 0.05 and 1.05 V RHE . The performance penalties arising from a decrease of the kinetics of the hydrogen oxidation reaction (HOR) and growing H 2 mass-transport resistances are measured via H 2 -pump experiments. The thus projected anode voltage losses for low anode Pt loadings (25 μg Pt cm −2 ) predict HOR kinetic losses of ≈40 mV at 80 • C and 3 A cm −2 for aged anode catalyst layers, suggesting that anode degradation by SUSD could be a significant durability issue in future PEMFC systems with ultra-low Pt loadings and with more stable cathode catalyst carbon supports. Moreover, SUSD-induced H 2 mass-transport related overpotentials were identified and attributed to carbon corrosion, indicated by a thinning of the anode catalyst layer upon aging.

Characterization methodology for anode starvation in HT-PEM fuel cells

“…5) at which current density repeatedly increased after the decrease in previous intercepts can be due to an in-plane crossover effect passing over the geometry of flow channels [34]. anode side / oxygen reduction reaction (ORR) -cathode side), but also as the galvanic cell (HOR and oxygen evolution reaction (OER) -anode side / ORRcathode side) [35].…”

Anode aging in polymer electrolyte membrane fuel Cells I: Anode monitoring by ElectroChemical impedance spectroscopy

“…It is usually agreed by the research community that most of FC lifetime issues presumably originate from the cathode [20,21], hence anode degradation has been rarely studied in the literature. This common belief may however not apply to all systems and operating conditions: for example, Schwämmlein et al recently showed that anode ageing may be significant in the case of repeated start-up and shut-down -because of potential cycling -and have a measurable impact on the FC performance [22]. In this work, PEMFC ageing is characterized during an AST consisting in load-induced humidity cycling combined with OCV by monitoring various parameters such as FC performance, electrode ECSA, hydrogen permeation and impedance spectra; beyond classical survey of the cathode and membrane alterations, an emphasis on possible anode degradation is also made.…”

Mitigated Start-Up of PEMFC in Real Automotive Conditions: Local Experimental Investigation and Development of a New Accelerated Stress Test Protocol

“…Specifically, also the anode suffers significant degradation during SU/SD, induced by potential cycling as described in Ref. 53. However, as shown by other authors, 8 the SU/SD mechanism introduces heterogeneity in the catalyst layer properties affecting both rib/channel and through the channel, observable at high frequency and attributable to the variation either of the proton conductivity or of the double layer capacitance.…”