Effects of Atmospheric Trace Species on the Oxygen Reduction Reaction and the Production of Hydrogen Peroxide

Imabayashi, Shin Ichiro; Kondo, Yoko; Komori, Ryotaro; Kawano, Akihiko; Ohsaka, Takashi

doi:10.1149/1.2981931

Cited by 16 publications

(5 citation statements)

References 7 publications

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“…The surface area of these atmospheric droplets is tremendous. This work implies that this vast surface area might have been functioning as previously unknown electrochemical cells for the spontaneous and ultrafast redox reactions that are highly important in many atmospheric chemical processes such as the redox cycling of iron(II/III) and the reduction of O 2 . Furthermore, since most aqueous atmospheric reactions occur in microdroplets, our findings imply that the chemistries previously studied in the bulk might need to be revisited.…”

Section: Resultsmentioning

confidence: 99%

Spontaneous Reduction-Induced Degradation of Viologen Compounds in Water Microdroplets and Its Inhibition by Host–Guest Complexation

et al. 2022

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Water serves as an inert environment for the dispersion and application of many kinds of herbicides. Viologen compounds, a type of widely used but highly toxic herbicide, are stable in bulk water, whose half-life can be up to 23 weeks in natural water, imposing a severe health risk to mammals. In this study, we present the striking results of the spontaneous and ultrafast reduction-induced degradation of three viologen compounds in water microdroplets and provide the concentration, time, temperature dependence, mechanism, and scale-up of the reactions. We postulate that the electrons existing at the air−water interface of the microdroplets due to the unique redox potential therein initiate the reduction, from which further degradation occurs. The host−guest complexation between cucurbit[7]uril and viologens only slightly changes the redox potential of viologens in the bulk but completely inhibits the reactions in microdroplets, adding to the uniqueness of the redox potentials at the air−water interfaces of microdroplets. Taken together, microdroplets might have been functioning as naturally occurring ubiquitous tiny electrochemical cells for a plethora of unique redox reactions that were thought to be impossible in the bulk water.

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Section: Resultsmentioning

confidence: 99%

Spontaneous Reduction-Induced Degradation of Viologen Compounds in Water Microdroplets and Its Inhibition by Host–Guest Complexation

et al. 2022

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“…90 Many of these contaminants are present as impurities in the anodic fuel used for FC (CO, CO 2 , H 2 S, and NH 3 ), while others as air pollutants of the cathode side (NO x , SO x , CO, and CO 2 ). 67,68,[72][73][74]91,92 Among the contaminants, S-containing molecules are the most impacting on performance due to strong adsorption bonds. Nevertheless, using appropriate protocols for FC operations, it is possible to recover the catalytic activity polarizing at high potentials to oxidize the adsorbed S to sulfates that are then desorbed from the catalytic site.…”

Section: Introductionmentioning

confidence: 99%

“…Typical contaminant molecules of Pt surfaces are sulfur dioxides (SO 2 ), − elemental S, hydrogen sulfide (H 2 S), , carbonyl sulfide (COS), , ammonia (NH 3 ), ammonium ion (NH 4 + ), ,, phosphate (H 2 PO 4 – at pH 1), nitrogen oxides (NO x ), , carbon monoxide (CO), , halide ions, − and methanol . Many of these contaminants are present as impurities in the anodic fuel used for FC (CO, CO 2 , H 2 S, and NH 3 ), while others as air pollutants of the cathode side (NO x , SO x , CO, and CO 2 ). ,,− ,, Among the contaminants, S-containing molecules are the most impacting on performance due to strong adsorption bonds. Nevertheless, using appropriate protocols for FC operations, it is possible to recover the catalytic activity polarizing at high potentials to oxidize the adsorbed S to sulfates that are then desorbed from the catalytic site. ,, The problem of sulfur contamination of Pt catalysts is a well-known issue.…”

Section: Introductionmentioning

confidence: 99%

Exchange Current Density as an Effective Descriptor of Poisoning of Active Sites in Platinum Group Metal-free Electrocatalysts for Oxygen Reduction Reaction

et al. 2023

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The oxygen reduction reaction (ORR) is of primary importance for the direct and clean conversion of energy in fuel cells, necessarily requiring an electrocatalyst to be exploited. At the state of the art, platinum group metal-free (PGM-free) electrocatalysts are the most promising alternative to carbon-supported Pt nanoparticles (Pt/C), which are more expensive and more performing but highly prone to deactivation in a contaminated working environment. The comparison of the two materials is at the level of fine-tuning, requiring specific activity descriptors, namely, turnover frequency (TOF) and site density (SD), to understand how to compare the performance of PGM-free electrocatalysts with Pt/C electrocatalysts. Specific probing molecules that bind with the active sites are required to evaluate the SD of PGM-free electrocatalysts. However, PGM-free electrocatalysts possess not a single active site like Pt/C, but a multitude of primary (metal-containing) and secondary (metal-free) sites arising from the pyrolysis synthesis process, eventually complicating SD evaluation. In this work, we propose a method for evaluating the direct interaction through the chemisorption of probing molecules over the PGM-free primary and secondary sites, the discrimination of which is of paramount importance in an effective SD evaluation. Based on the rotating disk electrode technique, the study investigates the electrochemistry of Fe-based PGM-free electrocatalysts poisoned with hydrogen sulfide at pH 1 in comparison with a Pt/C sample. In addition, X-ray photoelectron spectroscopy (XPS) is used to establish a relationship between the electrochemistry and surface chemistry of the poisoned material. The results identify the exchange current density as a meaningful tool that allows the discrimination of poisoning of specific active sites (metal-containing or metal-free). In addition, the understanding of the interaction phenomenon occurring between sites and probing molecules will be paramount for the selection of those contaminants capable of selectively interacting with the active sites of interest, paving the way to a more accurate SD evaluation.

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“…The effect of SO 2 on the oxygen reduction reaction (ORR) of Pt and Pt/C in 0.1 mol dm −3 HClO 4 has been reported by Imabayashi et al [1] and Garsany et al [2]. In their reports, the decrease of ORR activity and increase of H 2 O 2 formation was observed upon addition of SO 2 .…”

Section: Resultsmentioning

confidence: 84%

Effect of Air Contaminants on the Electrolyte Degradation in Polymer Electrolyte Membrane Fuel Cells

Imamura,

Yamaguchi

2009

Meet. Abstr.

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Effects of Atmospheric Trace Species on the Oxygen Reduction Reaction and the Production of Hydrogen Peroxide

Cited by 16 publications

References 7 publications

Spontaneous Reduction-Induced Degradation of Viologen Compounds in Water Microdroplets and Its Inhibition by Host–Guest Complexation

Spontaneous Reduction-Induced Degradation of Viologen Compounds in Water Microdroplets and Its Inhibition by Host–Guest Complexation

Exchange Current Density as an Effective Descriptor of Poisoning of Active Sites in Platinum Group Metal-free Electrocatalysts for Oxygen Reduction Reaction

Effect of Air Contaminants on the Electrolyte Degradation in Polymer Electrolyte Membrane Fuel Cells

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