High-Valent Iron Redox-Mediated Photoelectrochemical Water Oxidation

Jeon, Tae Hwa; Han, Seungmok; Kim, Bupmo; Park, Cheolwoo; Kim, Wooyul; Park, Hyunwoong; Choi, Wonyong

doi:10.1021/acsenergylett.1c02430

Cited by 12 publications

(15 citation statements)

References 56 publications

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“…In addition, in acid, the Co 3+ /Co 2+ redox couple has rarely been used as a homogeneous cocatalyst for PEC or electrochemical water oxidation except for a few case studies on the oxidation-degradation of organic or inorganic compounds [16][17][18]. Very recently, high-valent Fe ions have been demonstrated to mediate water oxidation, but the performance decay mechanism has not been considered [19]. Therefore, although the valence band energy level of WO 3 near 3 V vs. standard hydrogen electrode (SHE) is higher than the potential of the Co 3+ /Co 2+ (1.92 V vs. SHE) redox couple (i.e., the charging of Co 2+ /Co 3+ is energetically favorable) [10,18], it remains unknown whether homogeneous Co ions could mediate the water oxidation process, thus alleviating the performance decay issue observed for WO 3 photoanodes in acidic electrolytes.…”

Section: Introductionmentioning

confidence: 99%

Improving WO3/SnO2 photoanode stability by inhibiting hydroxyl radicals with cobalt ions in strong acid

Shi

Cui

2022

Sci. China Mater.

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Photoelectrochemical (PEC) water splitting in acid is promising, but its development has been hindered by the lack of stable photoanodes and effective nonprecious cocatalysts. WO 3 is one of the few acid-stable semiconductors, but its fast performance decay under illumination remains elusive and unsolved. Herein, we present that the fast photocurrent decreases of both WO 3 and WO 3 /SnO 2 photoanodes were caused by the hydroxyl radicals (OH•) generated at the electrode/electrolyte interfaces, and we solved this issue by introducing cobalt (Co 2+ ) ions into the electrolyte at pH 0.3, allowing for the efficient oxidation of H 2 O to O 2 rather than to detrimental OH• radicals, with the Faradaic efficiency toward oxygen evolution increasing from 40% to 95% and the photocurrent density increasing from 0.6 to 0.8 mA cm −2 and being stable for 25 h at 1.2 V (reversible hydrogen electrode). Importantly, the scavenging of OH• radicals by vitamin C demonstrated the same photocurrent stability as the introduction of Co 2+ ions, further implying the crucial inhibiting role of Co 2+ ions. In-situ ultraviolet-visible and Raman spectroscopy indicated the trapping of surface holes by the oxidation of Co 2+ to Co 3+ , and electron paramagnetic resonance revealed the role of Co 2+ ions in the inhibition of OH• radicals. This study provides an ideal model for combining a homogeneous redox-active Co 2+ /Co 3+ couple with a photoanode for water oxidation in strong acid.

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Section: Introductionmentioning

confidence: 99%

Improving WO3/SnO2 photoanode stability by inhibiting hydroxyl radicals with cobalt ions in strong acid

Shi

Cui

2022

Sci. China Mater.

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“…H.HanS.KimB.ParkC.KimW.ParkH.ChoiW. Jeon, T. H. Han, S. Kim, B. Park, C. Kim, W. Park, H. Choi, W. ACS Energy Lett.202275966 …”

Section: Key Referencesmentioning

confidence: 99%

“…A stable oxide overlayer can eliminate surface defect sites and act as a passivation layer, which enhances photooxidation of water by improving hole transfer (Figure b). , On the other hand, water photooxidation usually proceeds via direct hole transfers, but it can be mediated by the redox mediator that shuttles the holes between the semiconductor VB and water molecules. We recently reported a couple of unconventional cases of water photooxidation in the presence of Fe(III) or Ag(I) ions that mediate the hole transfer. , Although Fe(III) and Ag(I) ions are commonly believed to serve as electron acceptors, they can play the role of hole acceptor on the contrary to generate high-valent iron or silver species (e.g., Fe(IV), Ag(II)) that subsequently oxidize water (Figure c).…”

Section: Controlling Hole Transfer-mediated Water Oxidationmentioning

confidence: 99%

“…Time profiles of O 2 evolution through (b) the direct hole transfer in the absence and presence of the passivation layer (WO 3 vs Al 2 O 3 /WO 3 ; N-TNT vs TaO x N y /N-TNT) and (c) the metal ion-mediated (Ag + and Fe 3+ ) hole transfer on WO 3 . Reproduced with permission from refs , − . Copyright 2021 American Chemical Society, 2013/2015 Royal Society of Chemistry, 2020 Springer Nature.…”

Section: Controlling Hole Transfer-mediated Water Oxidationmentioning

confidence: 99%

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Selective Control and Characteristics of Water Oxidation and Dioxygen Reduction in Environmental Photo(electro)catalytic Systems

Lee¹,

Bae

Choi³

2023

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS: Employing semiconductor materials is a popular engineering method to harvest solar energy, which is widely investigated for photocatalysis (PC) and photoelectrocatalysis (PEC) that convert solar light to chemical energy. In particular, environmental photo(electro)catalysis has been extensively studied as a sustainable method for water treatment, air purification, and resource recovery.Environmental PC/PEC processes working in ambient conditions are initiated mainly through hole transfer to water (water oxidation) and electron transfer to dioxygen (O 2 reduction) and the subsequent photoredox transformation of water and dioxygen serves as a base of various PC/PEC systems. Through the redox transformations, different products can be generated depending on the number of transferred electrons and holes. The single electron/hole transfer generates radical species and reactive oxygen species (ROS) which initiate the degradation/ transformation of various pollutants in water and air, while the multicharge transfer can generate energy-rich chemicals (e.g., H 2 , H 2 O 2 ). Therefore, understanding the characteristics of the photoredox reactions of water and dioxygen on the semiconductor surface is critically important in controlling the selectivity and efficiency of photoconversion processes.In this Account, we describe various environmental PC/PEC conversions with a particular focus on how the phototransformation of dioxygen and water is related to the overall processes occurring on diverse semiconductor materials. The activation of water or dioxygen can be controlled by modifying the properties of semiconductors, changing the kind of counterpart half-reaction and the experimental conditions. If water can be used as a ubiquitous reductant under solar irradiation, many kinds of reductive transformations can be carried out under ambient environmental conditions. For example, various toxic oxyanions (or metal ions) can be reductively transformed to harmless or less harmful species or useful chemicals/fuels can be synthesized under ambient conditions if water can provide electrons and protons via solar water oxidation. On the other hand, dioxygen can turn into reactive oxygen species (ROS) as a versatile oxidant or to a chemical like H 2 O 2 . There should be many more possibilities of utilizing the photoconversion of water and dioxygen for environmentally significant purposes, which are yet to be further developed and demonstrated. In this Account, we highlight the recent strategies and the novel functional materials for effective activation of water and dioxygen in environmental PC/PEC systems. Design of environmentally functional PC/PEC systems should be based on better understanding of water and dioxygen activation.

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“…Indeed, Boettcher and co-workers show that various chemical and electronic factors can play different roles in creating charge-carrier-selective junctions at the electrolyte interface . Electrochemical methods can be used to control the morphology of the semiconductor surface and to explore new semiconductor materials and co-catalystsestablishing their interfacial charge-transfer processes under bandgap irradiation or applied bias. − A common theme in PEC cell development is the optimization of charge separation efficiency by modification of interlayers and interfaces. Indeed, in recent work from Jeon, Park, and co-workers, minimizing ohmic contact losses in a lead halide perovskite, buried junction PEC device afforded a significant enhancement in photoconversion efficiency .…”

Section: Photocatalysismentioning

confidence: 99%