Synthesis of New Protic Ionic Liquids for Fuel Cells on the Basis of In Situ FT-IR Measurements

Munakata, Hirokazu; Tashita, Takamitsu; Haibara, Masaki; Kanamura, Kiyoshi

doi:10.1149/1.3484805

Cited by 19 publications

(19 citation statements)

References 12 publications

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“…[25][26][27][28][29] Quite recently, high O 2 solubility in some ILs has been utilized to address the issues of insufficient O 2 concentration near the Pt surface. Snyder et al pioneered the studies of using ILs as an ORR promoter.…”

mentioning

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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mentioning

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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“…As increasing the temperature from 30°C to 120°C, E onset shifted from 0.43 V to 0.55 V which might be due to the weak anion adsorption on the catalytic sites at elevated temperatures. 60 The enhancement of oxygen reduction current density from 0.14 mA cm ¹2 to 1.15 mA cm ¹2 at 0.1 V vs. RHE can be attributed to the higher oxygen diffusion in dema-TfO (5.5 © 10 ¹5 mol cm 2 s ¹1 at 120°C) due to lower viscosity of dema-TfO along with the enhanced kinetics of ORR at elevated temperatures. 34 Figure 5a again shows the comparison between the LSVs of NG at room temperature as well as at 120°C in dema-TfO.…”

Section: Resultsmentioning

confidence: 93%

“…It has been reported that the overpotential for ORR on Pt catalyst increases in ionic liquids by anion adsorption on the electrode surface. 60 Therefore, the larger overpotential of NG in dema-TfO may be attributed to the poisoning of ORR active centeres by anion adsorption. 34 In addition, the low oxygen diffusion coefficient (1.1 © 10 ¹5 mol cm 2 s ¹1 ) 31 and high viscosity of dema-TfO 31 at room temperature result in lower mass transport and lower ORR activity than those in aqueous electrolyte.…”

Section: Resultsmentioning

confidence: 99%

Highly Durable Non-Platinum Catalyst for Protic Ionic Liquid Based Intermediate Temperature PEFCs

Peediyakkal

Munakata

et al. 2019

Electrochemistry

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We firstly report remarkable stability and performance of non-precious catalyst, nitrogen doped graphene (NG) towards oxygen reduction reaction (ORR) in a protic ionic liquid (N,N-diethylmethylammonium trifluoromethanesulfonate(dema-TfO)) at intermediate temperatures. Our electrochemical results indicate that an elevated operating temperature has an enhancing effect on ORR activity of NG in dema-TfO. In addition, even after 2000 cycles of potential sweep in the potential range from 1.0 V to 1.5 V vs. RHE at 120°C in dema-TfO, NG keeps the same ORR onset potential with 14% decrease in oxygen reduction current, showing the excellent stability of NG. Whereas commercially available Pt/C (Pt 37.5% in weight) shows 13% negative ORR onset potential shift along with 56% loss of oxygen reduction current during the stability test. TEM and EDS observations taken after durability test were also in agreement with the higher durability of NG over Pt/C at 120°C in dema-TfO. Raman and XPS results taken after the durability test also substantiated the structural stability of NG in dema-TfO at intermediate temperatures. The greater durability and comparable electrochemical activity of NG with Pt/C can unfold the possibilities of non-precious catalyst for intermediate temperature PEFCs.

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“…Munakata et al also investigated the effect of fluorination on ILs. [ 112 ] They extended the fluorinated chain of ammonium‐based ILs ( Table 5 ) and observed the effect on ORR, using the IL as an electrolyte. They observed an increase in ORR activity with fluorination, which could be attributed to the enhanced oxygenophilicity.…”

Section: Solid Catalysts With An Il Layermentioning

confidence: 99%

“…During the experiment, they observed an increase in the peak associated with the SO 2 –N group, suggesting gradual desorption of the IL from the surface of the catalyst. [ 112 ] From the magnitude of this increase, they deduced that ILs with longer fluorinated chains adsorb more weakly on the catalyst surface, allegedly due to the dispersion of negative charge in the anion, and are responsible for the increase in activity. [ 112 ]…”

Section: Solid Catalysts With An Il Layermentioning

confidence: 99%

Engineering the Electrochemical Interface of Oxygen Reduction Electrocatalysts with Ionic Liquids: A Review

Favero

Stephens

Titirici

2020

Adv Energy and Sustain Res

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Hydrogen fuel cells are a promising technology for the environmentally sustainable production of electricity. However, their commercialization is hindered by the sluggish kinetics of the oxygen reduction reaction and by the high cost of the state‐of‐the‐art platinum catalysts. To address these challenges, research has focused on the enhancement of the activity of platinum and platinum group metal (PGM)‐free electrocatalysts, by modifying their composition and topology. Recently, a new approach has emerged to boost the activity of ORR catalysts, based on engineering the electrochemical interface. Herein, the recent developments in the use of ionic liquids (ILs) to modify the triple‐point interface of ORR catalysts are summarized. In this review, the current understanding in the literature of the effect of IL layers is presented, along with the open questions and remaining challenges. A short perspective on the applicability of this simple and effective modification to other electrochemical reactions is discussed.

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Synthesis of New Protic Ionic Liquids for Fuel Cells on the Basis of In Situ FT-IR Measurements

Cited by 19 publications

References 12 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

Highly Durable Non-Platinum Catalyst for Protic Ionic Liquid Based Intermediate Temperature PEFCs

Engineering the Electrochemical Interface of Oxygen Reduction Electrocatalysts with Ionic Liquids: A Review

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