Mechanisms of Proton Conductance in Polymer Electrolyte Membranes

Eikerling, Michael; Kornyshev, A. A.; Кузнецов, А. М.; Ulstrup, Jens; Walbran, S.

doi:10.1021/jp003182s

Cited by 346 publications

(299 citation statements)

References 40 publications

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“…5. It can be seen that the predicted anode-free cell performance exhibits similar trend as the measured cell performance with a constant difference throughout the current density range, indicating the difference originating from the potential difference between the calculated thermodynamic reversible cell potential and the measured open-circuit cell potential at zero load, also referred to as the mixed electrode potential in the literature [58][59][60]. It is reported to be in the order of 0.1-0.2 V, and arises due to unavoidable parasitic reactions and fuel crossover through the membrane [53,60].…”

Section: Model Validationsupporting

confidence: 52%

Modeling an ordered nanostructured cathode catalyst layer for proton exchange membrane fuel cells

Hussain

Song

Liu

et al. 2011

Journal of Power Sources

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Modeling an ordered nanostructured cathode catalyst layer for proton exchange membrane fuel cells Hussain, M.M.; Song, D.; Liu, Z.-S.; Xie, Z.This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. abstract A 3D mathematical model of an ordered nanostructured cathode catalyst layer (CCL) has been developed for proton exchange membrane (PEM) fuel cells. In an ordered nanostructured CCL, carbon nanotubes (CNTs) are used as support material for Pt catalyst, upon which a thin layer of proton-conducting polymer (Nafion) is deposited, which are then aligned along the main transport direction (perpendicular to the membrane) of various species. The model considers all the relevant processes in different phases of an ordered nanostructured CCL. In addition, the effect of Knudsen diffusion is accounted in the model. The model can predict not only the performance of an ordered nanostructured CCL at various operating and design conditions but also can predict the distributions of various fields in different phases of an ordered nanostructured CCL. The predicted nanostructured CCL performance with estimated membrane overpotential is validated with measured data found in the literature, and a good agreement is obtained between the model prediction and measured result. Moreover, a parametric study is conducted to investigate the effect of key design parameters on the performance of an ordered nanostructured CCL. In the absence of liquid water, it is found that oxygen diffusion in the pore phase is not the limiting factor for the performance of an ordered nanostructured CCL, owing to its parallel gas pores and high porosity. However, the transport of dissolved oxygen through the Nafion phase has a significant effect on the performance of an ordered nanostructured CCL. Further, it is found that increasing the spacing between CNTs results in a considerable drop in the performance of an ordered nanostructured CCL at the base case conditions considered in the simulation.

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Section: Model Validationsupporting

confidence: 52%

Modeling an ordered nanostructured cathode catalyst layer for proton exchange membrane fuel cells

Hussain

Song

Liu

et al. 2011

Journal of Power Sources

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“…The Grotthuss mechanism and vehicular diffusion are believed to be the predominant modes of proton conduction [45,46]. In the vehicle mechanism, the proton diffuses together with solvent molecules by forming a complex s u c ha sH 3 O + ,C H 3 OH 2 + , and H 5 O 2 + .…”

Section: The State Of Water In the Membranementioning

confidence: 99%

Increases in the proton conductivity and selectivity of proton exchange membranes for direct methanol fuel cells by formation of nanocomposites having proton conducting channels

Liu

Wang

et al. 2009

Journal of Power Sources

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We explore an approach to effectively enhance the properties of cost-effective hydrocarbon protonexchange membranes for application in the direct methanol fuel cell (DMFC). This approach utilizes sulfonated silica nanoparticles (SA-SNP) as additives to modify sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK). The interaction between the sulfonic acid groups of SA-SNP and those of SPAEEKK combined with hydrophilic-hydrophobic phase separation induce the formation of proton conducting channels, as evidenced by TEM images, which contribute to increases in the proton conductivity of the SPAEEKK/SA-SNP nanocomposite membrane. The presence of SA-SNP nanoparticles also reduces methanol crossover in the membrane. Therefore, the SPAEEKK/SA-SNP nanocomposite membrane shows a high selectivity, which is 2.79-fold the selectivity of Nafion ® 117. The improved selectivity of the SPAEEKK/SNP nanocomposite membrane demonstrates potential of this approach in providing hydrocarbon-based PEMs as alternatives to Nafion in direct methanol fuel cells.

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“…The proton transport mechanism in Nafion membrane has been described as a combination of surface diffusion, Grotthuss (hopping) and vehicular/en-mass diffusion. [29][30][31][32][33][34] Each mechanism has a characteristic activation energy and the dominant transport mechanism is known to vary with Nafion water content, which depends both on the local environmental conditions (temperature and relative humidity) and polymer nanostructure. Therefore, the variation either in the nano-structure/orientation or in the transport mechanism may change the activation energy.…”

mentioning

confidence: 99%

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

Paul

McCreery

Karan

2014

J. Electrochem. Soc.

180

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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Mechanisms of Proton Conductance in Polymer Electrolyte Membranes

Cited by 346 publications

References 40 publications

Modeling an ordered nanostructured cathode catalyst layer for proton exchange membrane fuel cells

Modeling an ordered nanostructured cathode catalyst layer for proton exchange membrane fuel cells

Increases in the proton conductivity and selectivity of proton exchange membranes for direct methanol fuel cells by formation of nanocomposites having proton conducting channels

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

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