Chemical degradation by radicals limits the durability of aromatic hydrocarbon-based proton exchange membranes used in fuel cells and water electrolyzers. While hydroxyl radicals (HO • ) are recognized as important degradation agents, the roles of hydrogen (H • ) and peroxyl radicals (HOO • /ROO • ) remain poorly understood. Here, γ-radiolysis of water was used to selectively generate H • and HOO • /ROO • along with HO • under acidic conditions relevant to device operation. Two aromatic sulfonate model compounds representing structural motifs of hydrocarbon ionomers were exposed to radicals in N 2 saturated and O 2 containing solutions at pH 0 and 2. In the presence of HO • , degradation increased with radical dose and was enhanced by oxygen and increasing pH, consistent with established HO • -induced degradation pathways. Selective suppression of HO • using tert -butanol showed that H • radicals cause negligible degradation of the aromatic substrates, while HOO • and organic peroxyl radicals (ROO • ) exhibit only minor reactivity. These results indicate that HO • is the principal radical responsible for degradation of the investigated aromatic hydrocarbon model compounds, whereas H • and HOO • /ROO • contribute little to substrate loss. The findings improve the mechanistic understanding of radical-induced degradation and provide guidance for the development of more durable hydrocarbon membranes.

Radicals formed during operation of polymer electrolyte fuel cells, particularly during accelerated stress tests (AST), chemically degrade hydrocarbon proton exchange membranes (HC PEMs). In HC PEMs, the path from initial chemical attack over the evolution of membrane damage to failure is not yet well understood. This is evident when assessing different classes of HC PEMs in OCV hold ASTs: while chemical degradation occurs in all systems, expression of the evolution of membrane damage can differ vastly. This work combines an extensive OCV hold study with a complimentary gamma-radiolysis investigation on model small molecules for the first time. Our experiments reveal that the in-situ AST lifetime trends of HC PEMs correlate with the susceptibility of phenyl sulfonates-featuring to some extent comparable electronic configurations-to undergo degradative chain-reactions when exposed to the highly oxidizing radicals generated during the radiolysis of aqueous solutions. Our conclusions aim to incite the discussion on underlying radical stability of different HC PEMs, and we propose that electron-rich, poly(phenylene) type materials more likely undergo chemical degradation pathways that delay OCV failure, i.e. "suppress" membrane damage, when compared to electron-poor poly(phenylene sulfone) and poly(ether ether ketone) type materials.

We adapted two photochemical methods to generate radicals and assess their impact on anion exchange membrane stability, independent of base-induced degradation. By exposure of aqueous solutions of potassium nitrite or suspensions of TiO₂ to UV-light at 365 nm, we generated hydroxyl radicals or a combination of hydroxyl and superoxide radicals. The methods’ applicability to anion exchange membranes (AEMs) is demonstrated on three commercial AEMs: PiperION-40, FM-FAA-3-PK-75, and PNB-R45. Changes in ion-exchange capacity, along with FT-IR, and NMR analyses revealed significant degradation in thinner, non-reinforced membranes, while thicker and reinforced membranes showed greater resistance. We attribute this to the limited penetration depth of highly reactive radicals into the membrane. Both methods are practical and inexpensive tools for benchmarking AEM stability against radical attack.

We adapted two photochemical methods to generate radicals and assess their impact on anion exchange membrane stability, independent of base-induced degradation. Through the exposure of aqueous solutions of potassium nitrite or suspensions of TiO2 to UV light at 365 nm, we generated hydroxyl radicals or a combination of hydroxyl and superoxide radicals. The methods’ applicability to anion exchange membranes (AEMs) is demonstrated on three commercial AEMs: PiperION-40, FM-FAA-3-PK-75, and PNB-R45. Changes in ion-exchange capacity, along with FT-IR and NMR analyses, revealed significant degradation in thinner, non-reinforced membranes, while thicker and reinforced membranes showed greater resistance. We attribute this to the limited penetration depth of highly reactive radicals into the membrane. Both methods are practical and inexpensive tools for benchmarking AEM stability against radical attack.

The increase in regulations on per- and polyfluoroalkyl substances (PFAS) due to health and environmental concerns,1 has resulted in an increasing need for alternatives to polyfluoroalkylsulfonic acid (PFSA) based proton exchange membranes (PEMs). An alternate class of polymers are functionalized polyarylenes, such as sulfonated polyphenylenesulfone (sPPS)2, sulfonated phenylated polyphenylenes (sPPP)3, and the co-polymer sulfonated polyphenylene quinquephenylene (SPP-QP)4. Despite good progress made in reaching comparable performance to Nafion, radical induced degradation of phenyl(sulfonate) rings during fuel cell operation remains prevalent. In a recently published study,5 we investigated the potential of using a Cu(II)-porphyrin complex as an antioxidant for aromatic sulfonate compounds. First, γ-radiolysis was used on aqueous solutions containing the model aromatic compound potassium 4-(tert-butyl)-2-methoxyphenylsulfonate with varying amounts of antioxidant. The exposure of water-based solutions to high-energy radiation results in the formation of hydroxyl radicals, which in turn react with the model compound. Resulting degradation of the compounds was analyzed using high performance liquid chromatography (HPLC). In the second part of the study, we incorporated the Cu(II)-porphyrin into PEMs to test membrane stability during fuel cell operation using an accelerated degradation protocol. The measurements combined with post-mortem analysis show that membranes containing antioxidants have a five-fold increased stability compared to reference non-stabilized membranes. References: (1) Ackerman Grunfeld, D.; Gilbert, D.; Hou, J.; Jones, A. M.; Lee, M. J.; Kibbey, T. C. G.; O’Carroll, D. M. Underestimated Burden of Per- and Polyfluoroalkyl Substances in Global Surface Waters and Groundwaters. Nat. Geosci. 2024, 17 (4), 340–346. https://doi.org/10.1038/s41561-024-01402-8. (2) Araujo, C. C. de; Kreuer, K. D.; Schuster, M.; Portale, G.; Mendil-Jakani, H.; Gebel, G.; Maier, J. Poly(p-Phenylene Sulfone)s with High Ion Exchange Capacity: Ionomers with Unique Microstructural and Transport Features. Phys. Chem. Chem. Phys. 2009, 11 (17), 3305–3312. https://doi.org/10.1039/B822069G. (3) Adamski, M.; Skalski, T. J. G.; Britton, B.; Peckham, T. J.; Metzler, L.; Holdcroft, S. Highly Stable, Low Gas Crossover, Proton-Conducting Phenylated Polyphenylenes. Angew. Chem. Int. Ed. 2017, 56 (31), 9058–9061. https://doi.org/10.1002/anie.201703916. (4) Miyake, J.; Taki, R.; Mochizuki, T.; Shimizu, R.; Akiyama, R.; Uchida, M.; Miyatake, K. Design of Flexible Polyphenylene Proton-Conducting Membrane for next-Generation Fuel Cells. Sci. Adv. 2017, 3 (10), eaao0476. https://doi.org/10.1126/sciadv.aao0476. (5) de Wild, T.; Wurm, J.; Becker, P.; Günther, D.; Nauser, T.; Schmidt, T. J.; Gubler, L.; Nemeth, T. A Nature-Inspired Antioxidant Strategy Based on Porphyrin for Aromatic Hydrocarbon Containing Fuel Cell Membranes**. ChemSusChem 2023, 16 (21), e202300775. https://doi.org/10.1002/cssc.202300775.

Laser ablation in combination with an inductively coupled plasma time-of-flight mass spectrometer (LA-ICP-TOFMS) is an upcoming method for rapid quantitative element mapping of various samples. While widespread in geological applications, quantification of elements in biotissues remains challenging. In this study, a proof-of-concept sample preparation method is presented in which plant-tissues are fossilized in order to solidify the complex biotissue matrix into a mineral-like matrix. This process enables quantification of elements by using silicone as an internal standard for normalization while also providing consistent ablation processes similar to minerals to reduce image blurring. Furthermore, it allows us to generate a quantitative image of the element composition at high spatial resolution. The feasibility of the approach is demonstrated on leaves of sunflowers (Helianthus annuus), soy beans (Glycine max), and corn (Zea mays) as representatives for common crops, which were grown on both nonspiked and cadmium-spiked agricultural soil. The quantitative results achieved during imaging were validated with digestion of whole leaves followed by ICP-OES analysis. LA-ICP-TOFMS element mapping of conventionally dried samples can provide misleading trends due to the irregular ablation behavior of biotissue because high signals caused by high ablation rates are falsely interpreted as enrichment of elements. Fossilization provides the opportunity to correct such phenomena by standardization with Si as an internal standard. The method demonstrated here allows for quantitative image acquisition without time-consuming sample preparation steps by using comparatively safe chemicals. The diversity of tested samples suggests that this sample preparation method is well-suited to achieve reproducible and quantitative element maps of various plant samples.

Hydrocarbon-based materials are of interest as next-generation proton exchange membranes (PEMs) for polymer electrolyte fuel cells (PEFCs). The biggest drawback of aromatic hydrocarbon PEMs is the presence of aromatic groups contained within the polymer, which make these materials susceptible to radical induced degradation reactions. In the fuel cell community antioxidant action is usually equated with scavenging of potent radicals, i.e. HO•, by various additives. In this work, however, we report on the repair of damaged membranes. This is tested by performing in situ accelerated stress tests at open circuit voltage with high H2 and O2 partial pressures. Membranes with aromatic sulfonate groups are synthesized as these are common constituents in hydrocarbon-based membranes. Two different approaches to incorporate the repair agent, cerium(III), are explored: 1) ionic bonding of Ce(III) to sulfonate groups and 2) covalent attachment through stable complexes of crown ether and Ce(III). We report that, during fuel cell operation, polymer degradation can be significantly reduced by Ce(III) when immobilized in the membrane. Ionic attachment did not yield in the desired repair effect as a result of cerium loss from the membrane.

AbstractHiermit stellen wir einen elektrochemisch unterstützten Prototypen für die Erzeugung von Nitrylradikalen aus Eisen(III)‐nitrat unter milden Reaktionsbedingungen vor, wobei eine einfache Vorrichtung mit kostengünstigen Graphit‐ und Edelstahlelektroden verwendet wurde. Die einzigartige Reaktionsweise wurde durch detaillierte spektroskopische und experimentelle Studien mechanistisch bewiesen. Die synthetische Vielseitigkeit dieses Konzepts wurde durch die Entwicklung hocheffizienter Nitrierungsprotokolle für verschiedene ungesättigte Kohlenwasserstoffe demonstriert, die durch Elektrizität betrieben und durch Elektronen angetrieben werden. Diese Protokolle haben nicht nur einen breiten Anwendungsbereich, sondern lassen sich auch leicht auf Dekagramme skalieren und weisen eine außergewöhnliche Substratvielfalt und Kompatibilität mit funktionellen Gruppen auf.

Herein, we introduce an electrochemically assisted generation of nitryl radicals from ferric nitrate under mild reaction conditions using a simple setup with inexpensive graphite and stainless-steel electrodes. The mechanism of the reaction is supported by detailed spectroscopic and experimental studies. Powered by electricity and driven by electrons, the synthetic diversity of this reaction has been demonstrated through the development of highly efficient nitration protocols of various unsaturated hydrocarbons. In addition to a broad application area, these protocols are easy to scale for decagram quantities, and exhibit exceptional substrate generality and functional-group compatibility.

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.

In an operating polymer electrolyte fuel cell (PEFC) radical intermediates are formed as a result of the interaction of H 2 and O 2 on the surface of the Pt-based electrocatalyst. Of the various radical intermediates, • OH is of particular concern owing to its high oxidative strength, E °( • OH,H + /H 2 O) = 2.72 V) [1]. In PFSA ionomers, • OH reacts relatively slowly with the polymer and has a lifetime on the order of microseconds. This leaves sufficient time for additives, such as Ce(III), to scavenge the radicals and thus mitigate radical induced damage of the ionomer. In hydrocarbon-based ionomers containing aromatic units, • OH reacts within nanoseconds with polymer constituents [2]. Radical scavenging can therefore not be effective. In the development of alternative antioxidant strategies for hydrocarbon-based ionomers, it is crucial to elucidate polymer degradation mechanisms triggered by radical attack. In addition to studying the initial reactions of primary radicals, i.e. • OH, it is equally important to characterize the nature of the formed polymer intermediates, their lifetime, stability and reactivity. Sufficiently long-lived intermediates can be repaired by suitable additives, thereby restoring the original ionomer [3]. In the fuel cell, the thus protected membranes show a much lower rate of degradation in an accelerated stress test (AST) at open circuit voltage (OCV) [4]. In this contribution, we provide an overview of methods to study reaction of radicals with small-molecule model compounds and ionomer constituents [5, 6]. The interaction of ionizing radiation (MeV electrons or photons) with water leads to the formation of radicals, such as • OH, at known rates. Water radiolysis can therefore be used to study the kinetics of radical attack and follow-up reactions as a function of pH, electron density of the aromatic ring, and presence of additives. Examples relevant to the acidic conditions in the proton exchange membrane (see Figure, Panel a) as well as the alkaline conditions in an anion exchange membrane (AEM) will be given. Moreover, the use of suitable antioxidants to mitigate degradation through the repair of intermediates will be discussed. Fuel cell tests with hydrocarbon-based membranes containing polymer-bound antioxidants will be shown (see Figure, Panel b) and prospects for long-term stability of non-fluorinated ionomers assessed. Figure caption: a) Analysis of the effect of Ce(III) ions on the extent of degradation of 1 mM of 4-cumenesulfonate (4CS) and 4-(tert-butyl)phenylsulfonate (BPS) at pH 0 (1 M H 2 SO 4 ) in 1 mM H 2 O 2 upon exposure to a radiolytic dose provided by a 60 Co-source of 800 Gy (corresponding to a cumulative amount of • OH of 0.22 mM). ‘Excess degradation’ indicates the difference to the extent of degradation in the absence of Ce(III) and H 2 O 2 . Data for BPS from [5]. b) Ohmic resistance of single cells (average of several experiments) with partially fluorinated membrane containing a tethered crown ether with and without Ce(III) metal center during an accelerated stress test. Ion exchange capacity at the end of test was measured to represent remaining membrane state of health. Conditions: open circuit voltage (OCV), H 2 /O 2 , 80 °C, 2.5 bar a , and 100% R.H. [4]. References: H. A. Schwarz, R. W. Dodson, J. Phys. Chem., 88, 3643 (1984). L. Gubler, W.H. Koppenol, in: The Chemistry of Membranes Used in Fuel Cells: Degradation and Stabilization, S. Schlick (Ed.), 107-138, John Wiley & Sons (2018). T. De Wild, T. Nemeth, T.M. Nolte, T.J. Schmidt, T. Nauser, L. Gubler, J. Electrochem. Soc., 168, 054514 (2021). T. de Wild, T. Nemeth, P. Becker, D. Günther, T. Nauser, T.J. Schmidt, L. Gubler, J. Power Sources 560, 232525 (2023). T. Nemeth, T. de Wild, L. Gubler, T. Nauser, Phys. Chem. Chem. Phys. 24, 2, 895 (2022). T. Nemeth, T. de Wild, L. Gubler, T. Nauser, J. Electrochem. Soc. 169, 054529 (2022). Figure 1

An antioxidant strategy for aromatic hydrocarbon based proton exchange membranes for fuel cells and electrolyzers requires an understanding of the mechanisms of radical attack and follow-up reactions. We provide experimental evidence that radical scavenging is ineffective. Instead, focus has to be placed on repairing intermediates. Recent studies of exposure of model compounds to radicals formed in a γ-irradiation cell are reported. Fuel cell tests of membranes containing polymer-bound antioxidants with cerium and copper metal complexes show improved chemical stability in an accelerated stress test. Requirements for a successful implementation of a damage-repair mechanism in hydrocarbon membranes are discussed.

The Front Cover shows that during the operation of a proton exchange membrane fuel cell harmful radical species (HO⋅, H⋅ and HOO⋅) form that attack the membrane. The use of hydrocarbon-based proton-conducting membranes in fuel cells is currently hampered by the insufficient durability of the material in the device. In our work, we implement a nature-inspired antioxidant strategy by covalently modifying the membrane with metalated porphyrins. Porphyrin-based antioxidants are suitable for transferring damage and thus greatly enhance membrane stability against radical-induced degradation with a minimal impact on fuel cell performance. More information can be found in the Research Article by T. de Wild et al.

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.

Hydrocarbon-based materials are of interest as next-generation proton exchange membranes (PEMs) for the polymer electrolyte fuel cell (PEFC). The biggest drawback of aromatic hydrocarbon PEMs is the presence of aromatic groups contained within the polymer, which make these materials susceptible to radical induced degradation reactions.In this work, we test the hypothesis whether transition metal ions, such as Ce(III), can act as a repair agent in hydrocarbon-based membranes by reducing harmful radical intermediates formed during operation. This is tested by performing in situ accelerated stress tests at open circuit voltage with high H 2 and O 2 partial pressures. Membranes with aromatic sulfonate groups are synthesized as these are common constituents in hydrocarbon-based membranes. Two different approaches to incorporate cerium are explored: 1) ionic bonding of Ce(III) to sulfonate groups and 2) covalent attachment through stable complexes of crown ether and Ce(III). We report that, during fuel cell operation, polymer degradation can be significantly reduced by Ce(III) when immobilized in the membrane. Ionic attachment did not yield in the desired repair effect, most likely due to cerium migration effects.

Harmful radical species (HO•, HOO•) are formed during fuel cell operation. Out of these species, the highly electrophilic hydroxyl radical is the most reactive (1.8 – 2.7 V vs. NHE). Consequently, the most electron-rich constituents, aromatic rings, are preferentially attacked and undergo rapid degradation. Hydroxyl radical formation rates depend on operating conditions and cell parameters, but even with low formation rates the damage accumulates over time and can lead to thinning or embrittlement of the membrane, and will cause irreversible damage to the cell. Due to these effects, long-term operation becomes challenging. Therefore, membranes with enhanced radical stability are increasingly desirable. In our previous work, we have shown, using kinetics measurements, that it should be possible for Ce(III) to act as a repair agent for formed damaged intermediates (cf. Figure).[1] In our follow-up work we demonstrate that Ce(III) can indeed reduce degradation rates.[2] These experiments were performed in a fuel cell setup using accelerated stress tests at open circuit voltage (OCV), a cell temperature of 80 °C, 100% RH and high H2 and O2 partial pressures of 2 bar. In-situ measurements and post-test analyses unequivocally show that bound Ce(III) can mitigate degradation of poly(α-methylstyrene sulfonate)-based membranes. We believe that this approach could also be applicable for other aromatic-based polymers if a sufficiently long-lived intermediate is formed upon radical attack. References: [1] T. de Wild et al., J. Electrochem. Soc. 2021, 168, 054514. [2] T. de Wild et al., J. Power Sources, submitted Figure 1

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.

During the operation of aromatic hydrocarbon-based proton exchange membrane fuel cells, formed radical species attack the membrane. The most deleterious radical formed is HO · , both strongly electrophilic and oxidising. Oligomers of α -methylstyrene sulfonates (PAMSS) were used as model compounds. We report on the complex reaction cascade following the oxidative attack on aromatic cores bearing proton conductive sulfonate groups. UV-absorption bands of initial oxidation products indicate the formation of radical adducts and aromatic cation radicals. Subsequently, a transformation associated with an absorbance build-up at 580 nm is observed, presumably also related to aromatic cation radicals. Build-up and decay are significantly accelerated at high ionic strength levels that are also typical in fuel cells. Increased ionic strength causes phase separation: dynamic light scattering experiments indicate particle formation that is dependent both on chain length and on ionic strength. Aromatic cation radicals are known strong oxidants. With a presumed redox potential of E °((PAMSS-580 nm) ·+ /PAMSS) ∼ 2 V this oxidizing species should react also with mediocre reductants. Here, Mn(II) was oxidised to Mn(III) with rate constants of (5–10) × 10 6 M −1 s −1 . Implications for experimental design of kinetics experiments and understanding chemical mechanisms are discussed.

Ionizing radiations cause chemical damage to proteins. In aerobic aqueous solutions, the damage is commonly mediated by the hydroxyl free radicals generated from water, resulting in formation of protein radicals. Protein damage is especially significant in biological systems, because proteins are the most abundant targets of the radiation-generated radicals, the hydroxyl radical-protein reaction is fast, and the damage usually results in loss of their biological function. Under physiological conditions, proteins are initially oxidized to carbon-centered radicals, which can propagate the damage to other molecules. The most effective endogenous antioxidants, ascorbate, GSH, and urate, are unable to prevent all of the damage under the common condition of oxidative stress. In a promising development, recent work demonstrates the potential of polyphenols, their metabolites, and other aromatic compounds to repair protein radicals by the fast formation of less damaging radical adducts, thus potentially preventing the formation of a cascade of new reactive species.

Highly reactive aromatic cation radicals have been invoked lately in synthetic routes and in the degradation pathways of hydrocarbon-based polymers. Changes in the electron density of aromatic compounds are expected to alter the reaction pathway following one electron oxidation through altering the pKa of the formed intermediate cation radical. Electron-donating groups increase its stability, however, little experimental data are known. While, in theory, the cation radical can be repaired by simple electron transfer, electron transfer to or from its deprotonated form, the hydroxycyclohexadienyl radical, will cause permanent modification or degradation. Time-resolved absorption spectroscopy indicates a pKa ≈ 2-3 for the 4-(tert-butyl)-2-methoxyphenylsulfonate (BMPS) radical cation, while its parent compound 4-(tert-butyl) phenylsulfonate (BPS) is much more acidic. The stability of both compounds towards oxidation by HO˙ was evaluated under air at pH 5 and pH 0. At pH 5, both BMPS and BPS are unstable, and superstoichiometric degradation was observed. Degradation was slightly reduced for BPS at pH 0. In contrast, the more electron rich BMPS showed 80% lower degradation. We unambigously showed that in the presence of Ce(III) and H2O2 at pH 0 both BMPS and BPS could be catalytically repaired via one electron reduction, resulting in further damage moderation.