Impact of substitution on reactions and stability of one-electron oxidised phenyl sulfonates in aqueous solution

Németh, Tamás; Wild, Tym de; Gubler, Lorenz; Nauser, Thomas

doi:10.1039/d1cp04518k

Cited by 9 publications

(37 citation statements)

References 30 publications

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“…This finding is in direct support of the notion that equilibrium (2) is pH-dependent. At high pH, it is shifted toward the less stable HO-adduct, in accordance with its reported p K a ,Ar •+ ≈ 2–3 . As a result, fewer cation radicals are available for DMPO oxidation, reaction (), directly affecting the ratio.…”

Section: Discussionsupporting

confidence: 91%

“…We established that if cation radicals are formed, they are in a dynamic equilibrium with HO-adducts through reaction (2) . Both HO-adducts and cation radicals decay via desulfonation or dealkylation/dearylation.…”

Section: Discussionmentioning

confidence: 99%

“…Model compounds potassium phenyl sulfonate ( PS ), potassium 4-( tert -butyl) phenyl sulfonate ( BPS ), potassium 4-( tert -butyl)-2-methoxyphenylsulfonate ( BMPS ), potassium 4,4′-oxydiphenylsulfonate ( 4SPPS ), potassium 4-phenoxybenzenesulfonate ( 4PPS ), and potassium biphenyl-4-sulfoante ( 4DPS ) were synthesized as described earlier. ,, Sulfuric acid 95% (Fischer Scientific) was used as received and diluted as necessary. Potassium phosphate buffer (KPi) was prepared from potassium phosphate dibasic and potassium phosphate monobasic.…”

Section: Methodsmentioning

confidence: 99%

“…Attack on alkyl substituents of the membrane is at least an order of magnitude slower and therefore of little relevance . The formed HO-adducts have been identified and characterized by electron paramagnetic resonance (EPR) and pulse radiolysis methods. − …”

Section: Introductionmentioning

confidence: 99%

“…Chain cleavage (dealkylation/dearylation) and the loss of protogenic sulfonate groups have been proposed as follow-up or parallel degradation reactions, leading to inevitable membrane failure. − Theoretical studies involving DFT calculations hypothesized that desulfonation is the energetically favorable degradation route for polyaromatic model compounds and that moieties containing heteroatoms are possible weak points susceptible to chain scission . We recently showed that an increase in electron density of the aromatic ring has a favorable impact on the stability against radical-induced degradation …”

Section: Introductionmentioning

confidence: 99%

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EPR Study on the Oxidative Degradation of Phenyl Sulfonates, Constituents of Aromatic Hydrocarbon-Based Proton-Exchange Fuel Cell Membranes

et al. 2022

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Sulfonated aromatic hydrocarbon-based ionomers are potential constituents of next-generation polymer electrolyte fuel cells (PEFCs). Widespread application is currently limited due to their susceptibility to radical-initiated oxidative degradation that, among other intermediates, involves the formation of highly reactive aromatic cation radicals. The intermediates undergo chain cleavage (dealkylation/dearylation) and the loss of protogenic sulfonate groups, all leading to performance loss and eventual membrane failure. Laser flash photolysis experiments indicated that cation radicals can also be formed via direct electron ejection. We aim to establish the major degradation pathway of proton-exchange membranes (PEMs). To this end, we irradiated aqueous solutions of phenyl sulfonate-type model compounds with a Xe arc lamp, thus generating radicals. The radicals were trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and the formed adducts were observed by electron paramagnetic resonance (EPR). The formed DMPO spin adducts were assigned and relative adduct concentrations were quantified by simulation of the experimental EPR spectra. Through the formation of the DMPO/•SO3 – adduct, we established that desulfonation dominates for monoaromatic phenyl sulfonates. We observed that diaryl ether sulfonates readily undergo homolytic C–O scission that produces DMPO/•aryl adducts. Our results support the notion that polyphenylene sulfonates are the most stable against oxidative attack and effectively transfer electrons from DMPO, forming DMPO/•OH. Our findings help to identify durable moieties that can be used as building blocks in the development of next-generation PEMs.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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EPR Study on the Oxidative Degradation of Phenyl Sulfonates, Constituents of Aromatic Hydrocarbon-Based Proton-Exchange Fuel Cell Membranes

et al. 2022

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On the Radical‐Induced Degradation of Quaternary Ammonium Cations for Anion‐Exchange Membrane Fuel Cells and Electrolyzers

2022

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Four benzylic‐type quaternary ammonium (QA) compounds with different electron density at the phenyl group were evaluated for their susceptibility against degradation by radicals. Time‐resolved absorption spectroscopy indicated that radicals with oxidizing and reducing character were formed upon oxidation by HO⋅ and O⋅− (conjugate base of HO⋅). It was estimated that, dependent on the QA, 18–41 % of the formed radicals were oxidizing with standard electrode potentials (E0) above 0.276 V and 13–23 % exceeded 0.68 V, while 13–48 % were reducing with E0<−0.448 V. The stability of these model compounds against oxidation and reductive dealkylation was evaluated at both neutral and strongly alkaline conditions, pH 14. Under both conditions, electron‐donating groups promoted radical degradation, while electron‐withdrawing ones increased stability. Therefore, durability against radical‐induced degradation shows an opposite trend to alkaline stability and needs to be considered during the rational design of novel anion‐exchange membranes for fuel cells and electrolyzers.

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A Nature‐Inspired Antioxidant Strategy based on Porphyrin for Aromatic Hydrocarbon Containing Fuel Cell Membranes**

et al. 2023

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The use of hydrocarbon‐based proton conducting membranes in fuel cells is currently hampered by the insufficient durability of the material in the device. Membrane aging is triggered by the presence of reactive intermediates, such as HO·, which attack the polymer and eventually lead to chain breakdown and membrane failure. An adequate antioxidant strategy tailored towards hydrocarbon‐based ionomers is therefore imperative to improve membrane lifetime. In this work, we perform studies on reaction kinetics using pulse radiolysis and γ‐radiolysis as well as fuel cell experiments to demonstrate the feasibility of increasing the stability of hydrocarbon‐based membranes against oxidative attack by implementing a Nature‐inspired antioxidant strategy. We found that metalated‐porphyrins are suitable for damage transfer and can be used in the fuel cell membrane to reduce membrane aging with a low impact on fuel cell performance.

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Impact of substitution on reactions and stability of one-electron oxidised phenyl sulfonates in aqueous solution

Abstract: Functional groups can be used to modify the equilibrium position and tune the reactivity of one electron oxidised aromatic compounds.

Cited by 9 publications

References 30 publications

EPR Study on the Oxidative Degradation of Phenyl Sulfonates, Constituents of Aromatic Hydrocarbon-Based Proton-Exchange Fuel Cell Membranes

EPR Study on the Oxidative Degradation of Phenyl Sulfonates, Constituents of Aromatic Hydrocarbon-Based Proton-Exchange Fuel Cell Membranes

On the Radical‐Induced Degradation of Quaternary Ammonium Cations for Anion‐Exchange Membrane Fuel Cells and Electrolyzers

A Nature‐Inspired Antioxidant Strategy based on Porphyrin for Aromatic Hydrocarbon Containing Fuel Cell Membranes**

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