Humidity dependent structure of water at the interfaces between perfluorosulfonated ionomer thin film and Pt and HOPG studied by sum frequency generation spectroscopy

Noguchi, Hidenori; Taneda, Kento; Naohara, Hideo; Uosaki, Kohei

doi:10.1016/j.elecom.2012.10.041

Cited by 8 publications

(13 citation statements)

References 27 publications

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“…While the acid treatment for cleaning is the standard procedure for the thick membrane, to the best of our knowledge it has not been widely adopted in the literature for the thin films for studying their properties. A few exceptions exist where the electrode with Nafion coating was dipped in 0.5 M H 2 SO 4 before performing electrochemical experiments and the film was boiled in 0.5 M H 2 SO 4 . However, in both cases films were not annealed at high temperatures.…”

Section: Discussionmentioning

confidence: 99%

Reversible Tuning of Chemical Structure of Nafion Cast Film by Heat and Acid Treatment

Singhal

Datta

2014

J. Phys. Chem. B

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Effects of annealing have been studied on the chemical structure, water uptake, and acidity of the cast Nafion thin film of thickness ∼ 6 μm using a fluorescent probe, 2-(3'-pyridyl)benzimidazole (3PBI), and attenuated total reflactance infrared (ATR-IR) spectroscopy. Nonannealed films and thick Nafion 117 membrane have been used as reference materials, in order to develop a complete understanding of the effect. Annealing has been found to cause a decrease in acidity of otherwise highly acidic ionomer, as sensed by the fluorescent probe and loss of water, as reflected in the ATR-IR spectrum. This observation is surprising and cannot be explained in the light of previous reports of physical changes. Our ATR-IR study has revealed changes in the chemical structure of the hydrophilic part of the ionomer, leading to the formation of sulfonic acid anhydrides. This phenomenon can rationalize the decreased acidity reported in our fluorescence study. Interestingly, acid treatment of the annealed film restores the acidity of the unannealed films. This cannot be rationalized simply by a greater proton uptake from the solution, as the film has to be electroneutral. It appears that the anhydrides formed during the annealing process undergo acid hydrolysis, leading to an increase in the number of SO3(-) groups and, consequently, an increase in the number of H3O(+) ions in the water channels. Besides, the films can be hydrated to an extent that is much greater than Nafion membranes, but the water uptake of acid treated annealed film is slightly less than that of nonannealed films. Hence, we conclude that, along with annealing, acid treatment, a procedure that is generally not performed on the cast films, is an important pretreatment procedure to improve the acidity and hence the transport properties of the cast film.

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Section: Discussionmentioning

confidence: 99%

Reversible Tuning of Chemical Structure of Nafion Cast Film by Heat and Acid Treatment

Singhal

Datta

2014

J. Phys. Chem. B

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“…By using sum frequency generation spectroscopy (SFG), Noguchi and coworkers [20] show that the interface between the PFSA thin film and the Pt surface is different from the interface between PFSA and a HOPG surface. A peak ca.…”

Section: Resultsmentioning

confidence: 99%

Paradox phenomena of proton exchange membrane fuel cells operating under dead-end anode mode

Jiang

Zeng

Wang

et al. 2014

Journal of Power Sources

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“…Using sum frequency generation (SFG) spectroscopy, Noguchi et al demonstrated that water aggregation at ionomer/highly oriented pyrolytic graphite (HOPG) and ionomer/Pt interfaces is different. 32 In their models, water molecules were more widespread outside the proton channels for ionomer/Pt interfaces than for ionomer/HOPG interfaces under high relative humidity (RH) conditions. Our results indicated better proton conductivity for films on Pt substrates than those on other carbon substrates.…”

Section: Pccp Papermentioning

confidence: 99%

Effect of interface on surface morphology and proton conduction of polymer electrolyte thin films

Ohira

Kuroda

Hamed

et al. 2013

Phys. Chem. Chem. Phys.

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To understand the relationship between surface morphology and proton conduction of polymer electrolyte thin films, perfluorinated ionomer Nafion® thin films were prepared on different substrates such as glassy carbon (GC), hydrophilic-GC (H-GC), and platinum (Pt) as models for the ionomer film within a catalyst layer. Atomic force microscopy coupled with an electrochemical (e-AFM) technique revealed that proton conduction decreased with film thickness; an abrupt decrease in proton conductance was observed when the film thickness was less than ca. 10 nm on GC substrates in addition to a significant change in surface morphology. Furthermore, thin films prepared on H-GC substrates with UV-ozone treatment exhibited higher proton conduction than those on untreated GC substrates. However, Pt substrates exhibited proton conduction comparable to that of GCs for films thicker than 20 nm; a decrease in proton conduction was observed at ∼5 nm thick film but was still much higher than for carbon substrates. These results indicate that the number of active proton-conductive pathways and/or the connectivity of the proton path network changed with film thickness. The surface morphology of thinner films was significantly affected by the film/substrate interface and was fundamentally different from that of the bulk thick membrane.

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Humidity dependent structure of water at the interfaces between perfluorosulfonated ionomer thin film and Pt and HOPG studied by sum frequency generation spectroscopy

Cited by 8 publications

References 27 publications

Reversible Tuning of Chemical Structure of Nafion Cast Film by Heat and Acid Treatment

Reversible Tuning of Chemical Structure of Nafion Cast Film by Heat and Acid Treatment

Paradox phenomena of proton exchange membrane fuel cells operating under dead-end anode mode

Effect of interface on surface morphology and proton conduction of polymer electrolyte thin films

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