Influence of Equivalent Weight of Ionomer on Local Oxygen Transport Resistance in Cathode Catalyst Layers

Ono, Yoshiyuki; Ohma, Atsushi; Shinohara, Kazuhiko; Fushinobu, Kazuyoshi

doi:10.1149/2.040308jes

Cited by 101 publications

(116 citation statements)

References 26 publications

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“…Electrochemical Impedance Spectroscopy (EIS) is commonly adopted to measure the effective proton conductivity within the catalyst layer in MEA. 52 While in the rotating disk electrode (RDE) setup, due to the thinness of the catalyst layer and the abundance of electrolyte, the associated protonic resistance has been largely neglected. Nonetheless, it is essential to study the proton diffusion in Pt/C-IL.…”

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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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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“…R pt,int [24] Substitute Equation 19 into 23 and 24, we have, [26] Notice that Equation 26 applies only to a Pt/C catalyst particle. In this case, a lower wt% means less Pt loading, and thus a higher interfacial transport resistance.…”

Section: Ionomer Filmmentioning

confidence: 99%

“…Some research argued a much smaller oxygen diffusivity in the thin ionomer film than that in the bulk membrane in order to obtain a relatively reasonable ionomer thickness. 8,24 Indeed, oxygen diffusivity has not been measured in-situ in very thin film in the catalyst layer. Although a decreased ion conductivity in thin ionomer film was suggested in some studies, [25][26][27] probably due to the decrease of water uptake with decreasing film thickness, extending this conclusion to oxygen diffusivity remains an open question.…”

mentioning

confidence: 99%

Modeling and Experimental Validation of Pt Loading and Electrode Composition Effects in PEM Fuel Cells

Hao

Moriyama

et al. 2015

J. Electrochem. Soc.

139

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A low platinum loading model, considering both the platinum loading and platinum particle distribution on carbon support, is developed. This model takes into account the interfacial transport resistances at ionomer, water film and Pt particle surfaces in order to capture the effects of Pt loading and electrode composition on fuel cell performance. After coupling this electrode model into a comprehensive PEM fuel cell model, i.e. M2 model, experimental validation is performed for a wide range of Pt loading from 0.2 to 0.025 mg/cm 2 for two electrode compositions with and without carbon dilution. Good agreement between the predicted and measured polarization curves is achieved under wide-ranging operating conditions. The agglomerate size effect is also examined and it is shown that the agglomerates have virtually no effect on cell performance for agglomerate radius smaller than 150 nm. Since in realistic fuel cell catalyst layers, agglomerates may not exist, or may only exist with sizes no larger than 150 nm based on SEM observations, the present work suggests that the standard homogeneous electrode model is suitable and sufficient for analyses of transport losses in PEM fuel cell electrodes where interfacial transport resistances exist.

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“…The Nafion ionomer tends to from an agglomerated particle in contact with Pt/C [22]. In general, the Nafion covered the catalyst surface will hinder the oxygen transfer to reaction interface, which has become the major bottleneck for low Pt loading and high current density of PEMFCs [4,7,8]. As our knowledge, it is the first time to investigate the temperature effect on interface property with various Nafion contents in RDE system.…”

Section: Structural Model Of Reaction Interface For Orrmentioning

confidence: 99%

Electrochemical study of temperature and Nafion effects on interface property for oxygen reduction reaction

Chen

Zhong²,

et al. 2018

Ionics

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With the growth of new energy economy, proton exchange membrane fuel cell (PEMFC) has great potential to be success. However, the lack of high-performance catalyst layer (CL) especially at cathode limits its applications. It is becoming increasingly important to understand interface property during electrocatalytic oxygen reduction reaction (ORR). Here, the rotating disk electrode (RDE) method is developed to study the temperature and Nafion ionomer content effects on interface formed between Nafion and Pt/C. The results show that the temperature has the significant influence on electrochemical active sites, charging double capacitance, and reaction polarization resistance at low Nafion content region. Excess Nafion loaded in CLs will turn to self-reunion and increase the exposed active sites. We find that the optimum Nafion loading is in the range of 30 to 40 wt.%. The highest specific activity we achieve is 107.8 μA/cm 2 .Pt at 60°C with 0.4 of ionomer/catalyst weight ratio, corresponding to the kinetic current 283.5 μA at 0.9 V. This finding provides new insights into enhancing the Pt utilization and designing high-efficiency catalysts for ORR.

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Influence of Equivalent Weight of Ionomer on Local Oxygen Transport Resistance in Cathode Catalyst Layers

Cited by 101 publications

References 26 publications

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

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

Modeling and Experimental Validation of Pt Loading and Electrode Composition Effects in PEM Fuel Cells

Electrochemical study of temperature and Nafion effects on interface property for oxygen reduction reaction

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