Single Cell Regeneration Investigations on Ruthenium Poisoned Cathode Electrocatalysts for PEMFC
Authors: Schwendler Luana , Guo Qiang , Hasché Frédéric , Oezaslan Mehtap 
Published: December 2024

PEMFCs operating with reformate gases (a mixture of H2, CO2, and CO) are a promising alternative for CO2-neutral and environmentally friendly maritime transportation. [1] However, even trace amounts of CO in the hydrogen feed rapidly deactivate the platinum (Pt) electrocatalysts, leading to a high anode overpotential. [2] Pt-ruthenium (Ru) alloy nanoparticles (NPs) supported on carbon (PtRu/C) are among the most widely used anode electrocatalyst materials due to their high CO tolerance during the hydrogen oxidation reaction (HOR). [2, 3] Nevertheless, the PtRu/C anode catalysts suffer from the Ruz+ dissolution followed by crossover through the membrane and re-deposition onto the Pt/C cathode catalyst surface during the long-time PEMFC operation. [3] These phenomena are the main degradation processes in PEMFCs operated with reformate gas. Even at a Ru coverage of the Pt/C cathode catalyst surface of less than 20 %, there is an 8-fold decrease in the kinetics of the oxygen reduction reaction (ORR). [4, 5] Hence, the development of electrochemical regeneration procedures to mitigate or remove Ru-poisoning of the cathode catalyst surface on cell level is essential to extend the lifetime of PEMFCs, e.g. for maritime applications. [6]

Based on our previous work in a three-electrode setup [6], we transferred a selective set of regeneration protocols for Ru-poisoned ORR catalysts using a fully automatic single-cell PEMFC test station. Therefore, catalyst coated membranes (CCMs) with a 12 cm2 geometric surface area were prepared by using two commercial Pt-Ru/C catalysts with different atomic ratios on the cathode side, maintaining the Pt loading of 0.2 - 0.3 mgPt cm-2
geo, while the anode electrode layer contained Pt/C with around 0.1 mgPt cm-2
geo. The anode side was exposed to successive H2/air fronts with different residence times as part of a regeneration strategy of the cathode electrode. The effect of the H2/air front and their residence time were investigated through electrochemical characterization methods, such as polarization curves, Tafel slope, ECSA, HFR, and impedance spectroscopy. Electrochemical performance results were correlated with PEMFC operating conditions (H2/air front, residence times) and structural data to evaluate changes in particle size, structure, and chemical composition of two different Pt-Ru/C catalysts using several techniques like cross-section scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and microscopic X-ray fluorescence spectroscopy (µ-XRF).

Our work evaluated different electrochemical recovery protocols of Ru-poisoned ORR catalyst materials to identify the most promising set of parameters for their re-activation procedure and therefore improve the lifetime of PEMFCs.

References

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