Analysis of the Ionomer Coverage of Pt Surface in PEMFC

Ikeda, Kotaro; Nonoyama, Nobuaki; Ikogi, Yoshihiro

doi:10.1149/1.3484612

Cited by 27 publications

(27 citation statements)

References 6 publications

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“…The electrodes with the smallest and largest average ionomer layer thicknesses were both based on Aquivion PFSA. Although the influence of the preparation method on ionomer thickness cannot be revealed in detail here, the great influence of preparation on the average thickness is obvious and corresponds with reports in the literature. − ,,,,, …”

Section: Resultssupporting

confidence: 83%

Quantitative in Situ Analysis of Ionomer Structure in Fuel Cell Catalytic Layers

Morawietz

Handl

Oldani

et al. 2016

ACS Appl. Mater. Interfaces

100

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A quantitative in situ investigation of the structure of the catalytic layer of polymer electrolyte membrane fuel cells using material-sensitive and conductive atomic force microscopy is reported. The distribution and size of the ionomer phase at the surface of the catalytic layer is retrieved from adhesion force mappings, measured at high humidity and up to 75 °C. The average ionomer layer thickness varies between 7 and 13 nm for three differently prepared samples, as concluded from the histograms. Evidence of a lamellar structure of the thinner ionomer layers is presented. A significant thinning of the ionomer layers after long-term fuel cell operation is observed.

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Section: Resultssupporting

confidence: 83%

Quantitative in Situ Analysis of Ionomer Structure in Fuel Cell Catalytic Layers

Morawietz

Handl

Oldani

et al. 2016

ACS Appl. Mater. Interfaces

100

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“…19,56 Also, the carbon structures greatly affect the ionomer dispersion on the catalyst surface. 57,58 In an attempt to estimate IL coverage on the catalyst surface, we note that hydrogen adsorption behavior on low index Pt(hlk) facets differs dramatically in HClO 4 and H 2 SO 4 solutions, such as the Pt(100) and Pt(110).…”

Section: Resultsmentioning

confidence: 99%

Enhancing Pt/C Catalysts for the Oxygen Reduction Reaction with Protic Ionic Liquids: The Effect of Anion Structure

Huang¹,

Song

Morales‐Collazo

et al. 2017

J. Electrochem. Soc.

139

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Protic ionic liquids (ILs) have been recently studied as a potential approach to enhance oxygen reduction reaction (ORR) activity of carbon supported platinum catalysts (Pt/C) for application in polymer electrolyte membrane fuel cells. The high oxygen solubility in the ILs was suggested as one of the main reasons for the accelerated reaction rates. Because the nature of the anion of the IL has been associated with increased oxygen solubility, in this work we survey a number of ionic liquids with various anions to study this effect. While the search for direct correlation between the ORR activities and the oxygen solubilities does not produce any conclusive results, by contrast, the specific activity showed dependence on the availability of oxygenated species free Pt sites. This finding indicates that the inhibition of Pt oxidation and less adsorption of non-reactive species may also play an important role in the enhanced ORR activity. Moreover, the degree of IL coverage on the Pt surface was estimated using (bi)sulfate ions as an indicator. The surface coverage not only affected the ORR activity, but also the Pt dissolution process. This suggests that an optimal balance between activity and stability can be achieved on a partially covered Pt surface. The oxygen reduction reaction (ORR) that occurs on the cathode poses a major hurdle for the efficient utilization of polymer electrolyte fuel cells (PEMFC). Extensive studies have focused on developing novel catalysts to improve the efficiency of this reaction.1,2 The ORR involves multiple steps, among which O 2 + H + + e − ↔ OOH ads and OH ads + H + + e − ↔ H 2 O act as the potential rate determining steps. Simultaneously optimizing the Gibbs free energies for both steps to completely eliminate the overpotential is very challenging, and a ∼350 mV overpotenial is commonly observed, which is independent of the identity of the catalyst.3,4 The large overpotential has been generally attributed to the sluggish kinetics of the ORR and adsorption of oxygenated species (e.g. OH ad ) or other anions. 5 The coverage of the adsorbed oxygenated species (θ OH ad ) is unfavorable for the reaction, and the availability of the free metal surface (as expressed by the (1-θ OH ad ) term) is one of the governing factors for the ORR activity.6,7 As a result, much effort has been dedicated to weakening the bonding of OH to the catalyst surface either by shifting the d-band center of Pt 8,9 or by lateral repulsion from the supports (e.g. metal oxides). 10,11Anion adsorption on Pt also affects the ORR activity, and it is agreed that the occupation of active sites deactivates the sites and reduces the activity.12 In real-world membrane-electrode assembly (MEA), the Nafion membrane and ionomer, constituted by a Teflon-like backbone and an anionic cluster of sulfonic groups, 13 are widely employed as indispensable components. The interface between the Nafion and the metal has received great attention due to the strong irreversible sulfonate anions adsorption on the Pt. 12,[14][15][16] The de...

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“…10 The triplephase boundary (TPB) concept holds that the catalytic reactions-anodic oxidation of hydrogen (Hydrogen Oxidation Reaction -HOR) and cathodic reduction of oxygen (Oxygen Reduction Reaction -ORR)-can only occur at confined spatial regions where proton-conducting electrolyte (Nafion1 or water), reactant gas, and electrically connected catalyst particles are in contact. 9,[11][12][13] Thus, a catalyst layer with an extensive, high-density distribution of triple-phase boundaries is important for the development of high Pt utilisation catalysts.…”

Section: Introductionmentioning

confidence: 99%

Nafion®-stabilised Pt/C electrocatalysts with efficient catalyst layer ionomer distribution for proton exchange membrane fuel cells

2012

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We report a facile method for the preparation of proton exchange membrane fuel cell (PEMFC) electrocatalysts from Nafion1-stabilised colloidal Pt nanoparticles (Nafion1-Pt/C), offering synthetically-directed formation of the Pt-ionomer interface and providing unprecedented control over the morphology of Pt particles on the carbon support. Electrochemical characterisation of the catalysts in aqueous acidic electrolytes using Rotating Disc Electrode (RDE) techniques revealed that Nafion1-Pt/C catalysts possessed similar specific activity and mass activity towards the oxygen reduction reaction (ORR) as commercial Pt/C catalysts, whilst requiring lower overall ionomer loadings. Combined with the near-100% utilisation measured for the Nafion1-Pt/C catalysts, this implies that Pt nanoparticles synthesised with Nafion1 as a stabiliser can be 'tuned' to have simultaneous access to the reactant gas, the electron conducting carbon support and the proton conducting polymer electrolyte in the catalyst layer, thereby optimising the triple-phase reaction zone. By taking advantage of this bottom-up approach, which allows nanoscale control of the Nafion1-Pt-carbon interface, new opportunities exist to lower the Pt loading and the cost of the fuel cell.

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Analysis of the Ionomer Coverage of Pt Surface in PEMFC

Cited by 27 publications

References 6 publications

Quantitative in Situ Analysis of Ionomer Structure in Fuel Cell Catalytic Layers

Quantitative in Situ Analysis of Ionomer Structure in Fuel Cell Catalytic Layers

Enhancing Pt/C Catalysts for the Oxygen Reduction Reaction with Protic Ionic Liquids: The Effect of Anion Structure

Nafion®-stabilised Pt/C electrocatalysts with efficient catalyst layer ionomer distribution for proton exchange membrane fuel cells

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