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 H2/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 VRHE. The performance penalties arising from a decrease of the kinetics of the hydrogen oxidation reaction (HOR) and growing H2 mass-transport resistances are measured via H2-pump experiments. The thus projected anode voltage losses for low anode Pt loadings (25 μgPt 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 H2 mass-transport related overpotentials were identified and attributed to carbon corrosion, indicated by a thinning of the anode catalyst layer upon aging.
Highlights
Proton exchange membrane fuel cells (PEMFCs) present themselves as viable alternative to internal combustion engines for automotive applications, and are currently at the edge of commercialization, as evidenced by the recent launch of PEMFC powered vehicles by Hyundai,[1] Toyota,[2] and Honda.[3]
Engl et al recently showed that start-up or shut-down (SUSD) in high temperature phosphoric acid fuel cells leads to significant amounts of carbon corrosion on the anode, along with a loss of Pt electrochemical surface area (ECSA), a finding which the authors attributed to the change of the anode potential upon switching the gas atmosphere between H2 and air.[18]
In order to quantify the voltage losses due to anode degradation, we will first compare the anode ECSA-loss during SUSD cycling with that observed during square-wave voltage-cycling of the anode potential between 0.05 and 1.05 VRHE, which mimics the potential profile experienced by the anode catalyst during the passage of a H2/air front
Summary
Proton exchange membrane fuel cells (PEMFCs) present themselves as viable alternative to internal combustion engines for automotive applications, and are currently at the edge of commercialization, as evidenced by the recent launch of PEMFC powered vehicles by Hyundai,[1] Toyota,[2] and Honda.[3].
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