Impact of Pt and Pt–Alloy Catalysts on Membrane Life in PEMFCs

Sulek, Mark; Mueller, Steffen; Paik, C. H.

doi:10.1149/1.2889000

Cited by 12 publications

(12 citation statements)

References 23 publications

(7 reference statements)

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“…10,11 Sulek et al have also reported that Nafion lifetime could be extended by 65% when Pt/C catalyst was replaced with Pt-Ni/C. 12 The effect of the gas diffusion electrode (GDE) on membrane stability has also been investigated. Kreitmeier et al reported that a membrane with a GDE exhibited better stability than the bare membrane when exposed to reactive oxygen species.…”

Section: +mentioning

confidence: 99%

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The Effect of Cathode Structures on Nafion Membrane Durability

Choi

Langlois

Mack

et al. 2014

J. Electrochem. Soc.

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The effect of cathode structures on the chemical stability of Nafion membranes is investigated. Membrane electrode assemblies (MEAs) were prepared by using Nafion 212 membrane and commercially available carbon supported Pt electro-catalysts. The cathode structures were controlled by the use of long side chain (LSC) and short side chain (SSC) perfluorosulfonic acids (PFSAs) as well as three dispersing solvents for the electrode fabrication (a water-isopropanol mixture, N-methyl-2-pyrrolidone, or glycerol). The membrane durability was evaluated by the H 2 crossover current density after a 200-hour open circuit voltage accelerated stress test. The MEA with a glycerol-processed SSC PFSA-bonded cathode exhibited a 200-fold less H 2 crossover current density than the MEA with a water-isopropanol-processed LSC PFSA-bonded cathodes. The analyzes by electrochemical impedance spectroscopy and microscopy suggest that the structural uniformity of cathodes play the most significant role in the chemical stability of the Nafion membranes. This study emphasizes the importance of cathode structures on the durability of Nafion membranes. Polymer electrolyte membranes (PEMs) are a critical cell component for polymer electrolyte membrane fuel cells (PEMFCs). The durability of PEMs are important because the life of PEMFCs is often determined by PEM failure.1 The chemical stability of PEMs have been discussed since the 1960s, notably by engineers and scientists at GE.2 LaConti proposed a chemical degradation mechanism for perfluorosulfonic acids (PFSAs):3 oxygen molecules permeate through the membrane from the cathode and are reduced at the anode Pt catalyst to form hydrogen peroxide. Although PFSA membranes are stable in the presence of hydrogen peroxide, metal ions such as Fe 2+ and Cu 2+ in the catalyst layers greatly accelerate the membrane degradation rate by forming reactive oxygen species such as hydroxyl (HO·) and hydroperoxyl (HO 2 ·) radicals.Since the reactive oxygen species are generated in the catalyst layer, the membrane degradation is greater with a supply of H 2 and O 2 in the catalyst layers. Liu et al. reported about the substantially short lifetime for Nafion membranes when H 2 and O 2 gases were supplied to the catalyst-coated membrane, while no degradation is detected when H 2 /O 2 is decoupled to H 2 /N 2 or N 2 /O 2 .7 Later, Burlatsky et al. suggested that an extended catalyst layer between the cathode and the membrane could consume reactive oxygen species to produce water, thereby mitigating the membrane degradation. 8 The effect of gas permeability on membrane degradation has been also demonstrated. Sethuraman et al. compared the durability of wholly aromatic membranes, BPSH-35 and Nafion 112, under accelerated stress conditions. 9 Although the BPSH-35 membranes showed poor chemical stability in ex-situ Fenton tests, the membrane electrode assemblies (MEAs) Because the chemical degradation of membranes is related to the formation of reactive oxygen species in the catalyst layers and their access throug...

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Section: +mentioning

confidence: 99%

“…The effects of electrocatalysts on PEM stability have been investigated. [10][11][12] The chemical degradation of Nafion membranes were reduced by 50% when Pt/C catalyst was replaced with Pt-Co/C. 10,11 Sulek et al have also reported that Nafion lifetime could be extended by 65% when Pt/C catalyst was replaced with Pt-Ni/C.…”

mentioning

confidence: 99%

The Effect of Cathode Structures on Nafion Membrane Durability

Choi

Langlois

Mack

et al. 2014

J. Electrochem. Soc.

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“…alloys have demonstrated that the improved stability previously attributed to alloy effects is often a consequence of catalyst particle size. 7,8 Nevertheless, the enhanced initial mass activity of Pt alloys, coupled with a gradual decay in activity associated with metal area loss and base metal leaching, still results in a retained kinetic activity benefit compared to Pt only, during accelerated durability tests. 2,9−12 A calculation of the amount of leachable Co from PtCo systems has been made, 13 and the fact that while Co ions could saturate the proton conduction sites available in ionomer within the catalyst layer, these effects become less significant once the reservoir of ion exchange sites within the membrane is also considered.…”

Section: Introductionmentioning

confidence: 99%

“…Several recent studies using more appropriate heat treated Pt/C catalysts as comparisons for PtX/C (X = Co, Ni, etc.) alloys have demonstrated that the improved stability previously attributed to alloy effects is often a consequence of catalyst particle size. , …”

Section: Introductionmentioning

confidence: 99%

Evolution of Structure and Activity of Alloy Electrocatalysts during Electrochemical Cycles: Combined Activity, Stability, and Modeling Analysis of PtIrCo(7:1:7) and Comparison with PtCo(1:1)

Balbuena

Ball

et al. 2013

J. Phys. Chem. C

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This study explores the changes in bulk composition/ structure and oxygen reduction activity of two alloys, Pt 7 IrCo 7 and PtCo, caused by Co leaching during electrochemical cycles and as a result of membrane electrode assembly (MEA) fabrication procedures. Exposure to liquid electrolyte and electrochemical cycles in a rotating disc electrode (RDE) environment resulted in substantial Co loss and no stabilization from the low levels of Ir used in the ternary material. The true composition of the ternary material was determined as Pt 8 IrCo 3 following initial exposure to 0.1 M HClO 4 (before cycling) and Pt 11 IrCo 4 after 5000 cycles. Density functional theory (DFT) modeling of the cycled catalyst compositions indicated that structures with Pt-rich upper layers would show the highest stability; however, addition of 0.25 ML oxygen adsorption favored Co segregation from second and third atomic layers. The high initial activities (>0.44A/mgPt) achieved in the RDE environment decreased with cycles and were not reproduced in MEAs. X-ray diffraction (XRD) analysis revealed a measurable increase in lattice parameter caused by the MEA preparation procedure, consistent with Co (and some Ir) leaching into the ionomer phase and relaxation of the lattice. MEA fabrication procedures and cycling in 1 M H 2 SO 4 at 80 • C showed greater changes to catalyst structure and increased Ir and Co loss compared to exposing the catalyst to RDE like conditions (0.1 M HClO 4 , RT) explaining the observed discrepancy in activity between RDE and MEA.

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“…The durability and aging of these cells have therefore been investigated [3][4][5]. Reports show that catalyst aggregation, degradation of the carbon electrodes, and decomposition of the polymer electrolyte could cause reductions in performance [6][7][8][9][10]. In particular, the polymer electrolyte membrane (PEM) has a strong influence on cell performances and lifetimes.…”

Section: Introductionmentioning

confidence: 99%