Imaging Reactivity of the Pt–Ionomer Interface in Fuel-Cell Catalyst Layers

Martens, Isaac; Melo, Lis G. A.; West, Marcia; Wilkinson, David P.; Bizzotto, Dan; Hitchcock, Adam P.

doi:10.1021/acscatal.0c01594

Cited by 21 publications

(12 citation statements)

References 70 publications

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“…[13,27] However, the mechanism by which this oxidation occurs is poorly understood. [13,28,29] Oxidation could be occurring directly at the catalyst/ionomer surface or chemically through reactivity with OER intermediates or other reactive oxygen species formed, for example, through radical reactivity. [30,31] These degradation phenomena may or may not depend on catalyst type.…”

Section: Ionomer Degradation By the Catalyst Surfacementioning

confidence: 99%

Anode Catalysts in Anion‐Exchange‐Membrane Electrolysis without Supporting Electrolyte: Conductivity, Dynamics, and Ionomer Degradation

et al. 2022

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Anion‐exchange‐membrane water electrolyzers (AEMWEs) in principle operate without soluble electrolyte using earth‐abundant catalysts and cell materials and thus lower the cost of green H2. Current systems lack competitive performance and the durability needed for commercialization. One critical issue is a poor understanding of catalyst‐specific degradation processes in the electrolyzer. While non‐platinum‐group‐metal (non‐PGM) oxygen‐evolution catalysts show excellent performance and durability in strongly alkaline electrolyte, this has not transferred directly to pure‐water AEMWEs. Here, AEMWEs with five non‐PGM anode catalysts are built and the catalysts’ structural stability and interactions with the alkaline ionomer are characterized during electrolyzer operation and post‐mortem. The results show catalyst electrical conductivity is one key to obtaining high‐performing systems and that many non‐PGM catalysts restructure during operation. Dynamic Fe sites correlate with enhanced degradation rates, as does the addition of soluble Fe impurities. In contrast, electronically conductive Co3O4 nanoparticles (without Fe in the crystal structure) yield AEMWEs from simple, standard preparation methods, with performance and stability comparable to IrO2. These results reveal the fundamental dynamic catalytic processes resulting in AEMWE device failure under relevant conditions, demonstrate a viable non‐PGM catalyst for AEMWE operation, and illustrate underlying design rules for engineering anode catalyst/ionomer layers with higher performance and durability.

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Section: Ionomer Degradation By the Catalyst Surfacementioning

confidence: 99%

Anode Catalysts in Anion‐Exchange‐Membrane Electrolysis without Supporting Electrolyte: Conductivity, Dynamics, and Ionomer Degradation

et al. 2022

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“…64 Martens et al observed thin films of damaged ionomers close to the Pt surface upon electrochemical oxidation driven by formed hydrogen peroxide. 65 Although they applied potentials above 1.0 V RHE , ionomer degradation may also have taken place to a minor extent in our experiments. Yano et al observed increased H 2 O 2 formation on Pt/C catalysts after ASTs which could eventually cause ionomer degradation towards the end of ASTs.…”

Section: Resultsmentioning

confidence: 73%

Towards a realistic prediction of catalyst durability from liquid half-cell tests

Imhof,

Della Bella,

Stühmeier

et al. 2023

Phys. Chem. Chem. Phys.

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“…Yoshimune and Harada attribute this phenomenon to the stronger hydrophobic attraction of the ionomer backbone to the carbon than active interactions between ionomer sulfonate groups and Pt. However, in the dried catalyst ink, ionomers were almost observed to cover the Pt particles instead of the carbon substrate . We considered that the adsorption preference of ionomers depends on the presence of water because the hydrophilic sulfonic groups have strong interactions with both water and Pt particles; the amphiphilic ionomers can form a more stable adsorption structure on the carbon substrate than on Pt, which will be discussed later.…”

Section: Resultsmentioning

confidence: 99%

Morphology Evolution and Adsorption Behavior of Ionomers from Solution to Pt/C Substrates

Guo

Mabuchi

et al. 2022

Macromolecules

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Coarse-grained molecular dynamics simulations were performed to understand the morphological evolution and adsorption mechanism of Nafion ionomers from the aqueous solutions to the Pt/C substrate surface under various solution compositions and substrate properties. We found that the ionomer coverage did not increase with the increasing ionomer-to-carbon ratio but was related to the size and concentration of the ionomer aggregates, following the Langmuir adsorption model that shows a wettability switching behavior due to their changed morphology from solution to the surface. Ionomer aggregates in the solution tended to unfold and spread on the carbon substrate rather than Pt particles, although the cylindrical ionomer aggregates were easily attracted by Pt particles initially due to their hydrophilic ionic shells. The smaller Pt particles had a greater effect on ionomer adsorption. With the increasing number of Pt particles, ionomer coverage increased first and then decreased, depending on whether there was enough carbon surface to anchor the ionomer backbone. A balanced Pt/C ratio and the appropriate distribution of the Pt particles were required for tuning the ionomer coverage and distribution toward the design of the catalyst ink structure to improve the power performance.

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Imaging Reactivity of the Pt–Ionomer Interface in Fuel-Cell Catalyst Layers

Cited by 21 publications

References 70 publications

Anode Catalysts in Anion‐Exchange‐Membrane Electrolysis without Supporting Electrolyte: Conductivity, Dynamics, and Ionomer Degradation

Anode Catalysts in Anion‐Exchange‐Membrane Electrolysis without Supporting Electrolyte: Conductivity, Dynamics, and Ionomer Degradation

Towards a realistic prediction of catalyst durability from liquid half-cell tests

Morphology Evolution and Adsorption Behavior of Ionomers from Solution to Pt/C Substrates

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