Cathode Loading Impact on Voltage Cycling Induced PEMFC Degradation: A Voltage Loss Analysis

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Bimetallic alloys based on Pt and Y are potential cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their high oxygen reduction reaction (ORR) activity. Nevertheless, the synthesis of carbon supported Pt x Y catalysts is challenging due to the low standard reduction potential of yttrium compared to platinum. Hence, extended electrochemical testing in actual PEMFCs remains elusive, especially with respect to catalyst degradation upon voltage-cycling. In this publication, we present the synthesis of a bimetallic Pt x Y/C catalyst via impregnation of commercial Pt/C with an yttrium halide precursor and subsequent heat-treatment in H 2 at 1200 • C. This catalyst showed a high specific ORR activity, at a mass activity similar to Pt/C due to its comparably low electrochemical surface area (ECSA). On the other hand, the large particle size of the here synthesized Pt x Y/C catalyst (≈10 nm) resulted in a significantly enhanced stability versus degradation in an accelerated stress test (AST) based on voltage-cycling between 0.6 and 1.0 V RHE at 50 mV s −1 , showing a superior ECSA, ORR activity and H 2 /air performance after 30000 cycles compared to a standard Pt/C catalyst.

Section: Particle Size Distribution Of Pt X Y/c-the Leached Ptmentioning

confidence: 78%

Section: Thermogravimetric Analysis (Tga)mentioning

confidence: 99%

Activity and Stability of Carbon Supported Pt_xY Alloys for the ORR Determined by RDE and Single-Cell PEMFC Measurements

Schwämmlein

Harzer

Pfändner

et al. 2018

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“…Here, the thickness at each position for a given MEA was determined from the area divided by the length to obtain a more precise average, whereby the area integration was executed semi-automatically based on the contrast between Pt rich electrodes and their less dense neighboring materials using the program ImageJ (as described by Harzer et al). 20 Furthermore, high resolution field-emission SEM images were taken to compare the morphology of the MEA cross-section (JSM-7500F, JEOL GmbH, Germany).…”

Section: Methodsmentioning

confidence: 99%

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

Schwämmlein

Rheinländer

Chen

et al. 2018

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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.

“…For each catalyst, two independent fuel cell measurements were conducted under differential-flow conditions using a 5 cm 2 flow-field (see References 17 and 18), and the mean absolute deviation between both is shown as error bars in all figures (for more details on the fuel cell testing conditions see our previous publications). 15,16 Results and Discussion…”

Section: Samplementioning

confidence: 99%

Tailoring Catalyst Morphology towards High Performance for Low Pt Loaded PEMFC Cathodes

Harzer

Orfanidi

El‐Sayed

et al. 2018

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121

151

The effect of the catalyst synthesis method on the location of platinum nanoparticles on a high surface area Ketjenblack is investigated with respect to the high current density performance in low loaded proton exchange membrane fuel cells (PEMFC). Catalysts were prepared using various synthetic methods to deposit platinum nanoparticles at different locations on the carbon surface, e.g. inside or outside the pores of the primary particle. Transmission electron microscopy (TEM) suggested, that the Pt-particle deposition can be controlled to be preferentially on the outer carbon surface or within the pores. Electrochemical characterization was performed in thin-film rotating disk electrode (RDE) setup as well as in 5 cm 2 single cell MEA tests. Although the carbon support was identical for all catalysts, the one with more Pt particles deposited on the outer carbon surface performed superior at high current which was attributed to a lower oxygen mass transport resistance. From the presented data, it can be concluded that not only the type or the surface area of the carbon black support affects the fuel cell performance, but that the synthesis approach is an additional parameter to tune the fuel cell performance at high current density.