Fuel Cell Catalyst Layers: A Polymer Science Perspective

Holdcroft, Steven

doi:10.1021/cm401445h

Cited by 423 publications

(479 citation statements)

References 118 publications

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“…Different analysis methods were used for detection of ionomer size in electrodes. 19,35,36 In catalytic layers of fuel cells an operation-induced thinning of the ionomer films that partly encapsulate the platinum covered carbon (Pt/C) agglomerates has been reported. 13,37,38 The observed stronger thinning of the ionomer layers in the anode at samples cut close to the hydrogen inlet and with the use of thin membranes was explained by the higher concentration of highly active hydrogen radicals.…”

Section: F3140mentioning

confidence: 99%

High-Resolution Analysis of Ionomer Loss in Catalytic Layers after Operation

Morawietz

Handl

Oldani

et al. 2018

J. Electrochem. Soc.

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The function of catalytic layers in fuel cells and electrolyzers depends on the properties of the ionically conductive phase, which are most commonly perfluorinated ionomers based on Nafion and Aquivion. An analysis by atomic force microscopy reveals that the ultrathin ionomer films around Pt/C agglomerates have a thickness distribution ranging from 3.5 nm to 20 nm. Their conductivity and gas permeation properties determine the fuel cell performance to a large extend. For electrodes in Aquivion-based membraneelectrode-assemblies operation-induced structure changes were investigated by means of material-and conductivity-sensitive atomic force microscopy, infrared spectroscopy and electron-dispersive X-ray analysis. The observed thinning of the ultrathin ionomer films was mainly caused by polymer degradation deduced from reduced swelling after long-time operation and a significant loss of ionomer with operation time detected by infrared spectroscopy. From the linear thickness increase of the ultrathin films with rising humidity, a mainly layered structure of the ionomer was deduced. An influence of thickness of such ultrathin ionomer films on fuel cell lifetime was found by analysis of differently prepared membrane-electrode-assemblies, where a linear increase of irreversible degradation rate with ionomer film thickness in the electrodes of unused membrane-electrode-assemblies was found.

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Section: F3140mentioning

confidence: 99%

High-Resolution Analysis of Ionomer Loss in Catalytic Layers after Operation

Morawietz

Handl

Oldani

et al. 2018

J. Electrochem. Soc.

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“…In the CL, the ionomer forms a semi-continuous, web-like nanothin film (4-10 nm) covering the aggregates of Pt/C. 1,6 The thickness of such nanothin Nafion films in the CL is comparable to the ionic domain size (∼4 nm) in the bulk Nafion membrane. 7,8 It is obvious that the ionomer structure and property will affect both the proton and mass transport, which in turn will impact the local electrochemical reaction rate and, thereby, the overall PEFC performance.…”

mentioning

confidence: 99%

“…Proton transport is a key functional property of the ionomer used in polymer electrolyte based energy conversion and storage devices including polymer fuel cells (PEFC), 1 polymer electrolyte membrane (PEM) water electrolyzers, 2 photo electrochemical cells 3,4 and artificial photosynthesis device. 5 For PEFCs and PEM electrolyzers, Nafion is the most extensively employed.…”

mentioning

confidence: 99%

Proton Transport Property in Supported Nafion Nanothin Films by Electrochemical Impedance Spectroscopy

Paul

McCreery

Karan

2014

J. Electrochem. Soc.

176

206

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The proton transport property of Nafion nanothin films (4-300 nm) has been investigated by electrochemical impedance spectroscopy (EIS) using interdigitated array (IDA) of gold electrodes on SiO 2 substrate. The proton conductivity has been investigated as a function of film drying/heating protocol, relative humidity, temperature and film thickness. It is found that the film treatment protocol makes a difference in film transport property. Ultimately, the proton conductivity and capacitance of the Nafion nanothin film is thicknessdependent, where the former decreased and the latter increased exponentially with decreasing film thickness. Moreover, the activation energy increased exponentially with decreasing film thickness. The proton conductivity of the thin films of Nafion is significantly lower than that of the membrane counterpart regardless of the thickness, which is consistent with the high activation energy found in the thin films. These differences are likely related to the polymer confinement and morphological differences between the thin films and the freestanding membrane. Proton transport is a key functional property of the ionomer used in polymer electrolyte based energy conversion and storage devices including polymer fuel cells (PEFC), 1 polymer electrolyte membrane (PEM) water electrolyzers, 2 photo electrochemical cells 3,4 and artificial photosynthesis device.5 For PEFCs and PEM electrolyzers, Nafion is the most extensively employed. As a freestanding film of thickness (25-100 μm thick), Nafion serves the function of the electrolyte membrane separating the anode and the cathode. The ionomer is also present in the electrochemically active component of these energy conversion devices as a thin film coating the electrocatalyst. For example, the conventional PEFC catalyst layer (CL) is a porous composite layer (10-25 μm thick) of Platinized carbon (Pt/C) and ionomer. In the CL, the ionomer forms a semi-continuous, web-like nanothin film (4-10 nm) covering the aggregates of Pt/C. 1,6 The thickness of such nanothin Nafion films in the CL is comparable to the ionic domain size (∼4 nm) in the bulk Nafion membrane. 7,8 It is obvious that the ionomer structure and property will affect both the proton and mass transport, which in turn will impact the local electrochemical reaction rate and, thereby, the overall PEFC performance. In fact, researchers of the electrochemical energy research laboratory at General Motors (GM) 9 examined the electrode performance as a function of catalyst loading and found that low-Pt loading catalyst layers exhibited higher transport losses, which they attributed to the transport resistance of ionomer thin film covering the catalyst. The proton conductivity of Nafion membrane is widely investigated and discussed in the literature. [10][11][12][13] In contrast, the proton conductivity of thin Nafion film has remained relatively unexplored, especially for ionomer films of thickness comparable to ionic domain size (∼4-5 nm). The ionic conduction property of materials is highly reg...

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“…above 45 wt.%, concomitant with the decrease of the relative amount of carbon in the catalyst the ionomer decreases the ECSA. This observation therefore indicates that above a certain ionomer to carbon ratio the ionomer blocks the accessible carbon surface area and thus increases NP agglomeration or blocks the Pt surface itself [40,43].…”

Section: Impact Of Nafion Ionomer On Pt/ec-300j Catalystsmentioning

confidence: 93%

The colloidal tool-box approach for fuel cell catalysts: Systematic study of perfluorosulfonate-ionomer impregnation and Pt loading

2016

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In this study the correlation between the impregnation of proton exchange membrane fuel cell catalysts with perfluorosulfonate-ionomer (PFSI) and its electrochemical and electrocatalytic properties is investigated for different Pt loadings and carbon supports using a rotating-disk electrode (RDE) setup. We concentrate on its influence on the electrochemical surface area (ECSA) and the oxygen reduction reaction (ORR) activity. For this purpose platinum (Pt) nanoparticles are prepared via a colloidal based preparation route and supported on three different carbon supports. Based on RDE experiments, we show that the ionomer has an influence both on the Pt utilization and the apparent kinetic current density of ORR. The experimental data reveal a strong interaction in the microstructure between the electrochemical properties and the surface properties of the carbon supports, metal loading and ionomer content. This study demonstrates that the colloidal synthesis approach offers interesting potential for systematic studies for the optimization of fuel cell catalysts.

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Fuel Cell Catalyst Layers: A Polymer Science Perspective

Cited by 423 publications

References 118 publications

High-Resolution Analysis of Ionomer Loss in Catalytic Layers after Operation

High-Resolution Analysis of Ionomer Loss in Catalytic Layers after Operation

Proton Transport Property in Supported Nafion Nanothin Films by Electrochemical Impedance Spectroscopy

The colloidal tool-box approach for fuel cell catalysts: Systematic study of perfluorosulfonate-ionomer impregnation and Pt loading

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