Alkaline manganese electrochemistry studied by<i>in situ</i>and<i>operando</i>spectroscopic methods – metal dissolution, oxide formation and oxygen evolution

Rabe, Martin; Toparlı, Çiğdem; Chen, Ying‐Hsuan; Kasian, Olga; Mayrhofer, Karl Johann Jakob; Erbe, Andreas

doi:10.1039/c9cp00911f

Cited by 35 publications

(68 citation statements)

References 52 publications

(104 reference statements)

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“…The role of (octahedral) Mn 4+ for the OER is better understood. Mn 4+ forms at voltages below the onset of the OER [38,46]. While many of the more active Mn-based electrocatalysts contain Mn 4+ in addition to Mn 3+ [10,39,40,[81][82][83][84], those with predominately Mn 4+ are inactive [3].…”

Section: Samplementioning

confidence: 99%

“…Au) induce Mn oxidation after the OER to such a mixed Mn 3+/4+ oxide [41,43]. Moreover, the voltage range in CV can have drastic influence on the observed redox features and thus the nature of the Mn oxide [46,48]. Post-mortem and in situ experiments on many Mn oxides show clear valence changes during electrocatalytic experiments in alkaline media [37][38][39][40], often accompanied by structural changes [35,36].…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, studies including low voltages in addition to those supporting the OER often show the formation of Mn 3 O 4 (Mn 2+ Mn 3+ 2 O 4 ), which was not present in the pristine material [35,38,46]. The exact role of tetrahedral Mn 2+ in Mn 3 O 4 is unknown but Rabe et al [46] show that it hinders Mn dissolution using a combination of in situ Raman spectroscopy and ICP-MS.…”

Section: Introductionmentioning

confidence: 99%

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Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction

Villalobos

Golnak

et al. 2020

J. Phys. Energy

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Manganese oxides have received much attention over the years among the wide range of electrocatalysts for the oxygen evolution reaction (OER) due to their low toxicity, high abundance and rich redox chemistry. While many previous studies focused on the activity of these materials, a better understanding of the material transformations relating to activation or degradation is highly desirable, both from a scientific perspective and for applications. We electrodeposited Na-containing MnO x without long-range order from an alkaline solution to investigate these aspects by cyclic voltammetry (CV), scanning electron microscopy (SEM) and X-ray absorption spectroscopy (XAS) at the Mn-K and Mn-L edges. The pristine film was assigned to a layered edge-sharing Mn 3+/4+ oxide with Mn-O bond lengths of mainly 1.87 Å and some at 2.30 Å as well as Mn-Mn bond lengths of 2.87 Å based on fits to the extended X-ray fine structure (EXAFS). The decrease of the currents at voltages before the onset of the OER followed power laws with three different exponents depending on the number of cycles and the Tafel slope decreases from 186±48 to 114±18 mV dec-1 after 100 cycles, which we interpret in the context of surface coverage with unreacted intermediates. Post-mortem microscopy and bulk spectroscopy at the Mn-K edge showed no change of the microstructure, bulk local structure or bulk Mn valence. Yet, the surface region of MnO x oxidized toward Mn 4+ , which explains the reduction of the currents in agreement with literature. Surprisingly, we find that MnO x reactivates after 30 minutes at open-circuit (OC), where the currents and also the Tafel slope increase. Reactivation processes during OC are crucial because OC is unavoidable when coupling the electrocatalysts to intermittent power sources such as solar energy for sustainable energy production.

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Section: Samplementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction

Villalobos

Golnak

et al. 2020

J. Phys. Energy

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“…[115]. At +1.0 V our spectrum also resembles the features observed during polarization of metallic Mn in alkaline media, which were attributed to the formation of α-MnO2 [119]. The narrowing of the band at decreasing positive potential has also been previously observed [23], and has been assigned to lattice distortions en route to MnOOH.…”

Section: Characterization Of Mnoxsupporting

confidence: 82%

“…However, likely not all modes are enhanced to the same extent by surface plasmon resonance and charge transfer [120]. A phase with a strong Raman response may dominate a more numerous phase with a weaker response [119]. Finally, the SERS effect enhances the signal from the part of the film close to the electrode, not that at the film-electrolyte interface, so spectra may not fully correspond to voltammetric features [115].…”

Section: Characterization Of Mnoxmentioning

confidence: 99%

Understanding selective thin films in the chlorate process

Smulders¹

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This chapter provides context and background information for the work in this thesis. First, chlorate is introduced and its applications are described. Then, an overview of the chlorate production process is provided, describing the reactions involved, the conditions in the industrial process, and a history of its development. 1.1.4 History of chlorate production and research Chlorate is one of the oldest electrochemical processes, with the first confirmed electrosynthesis dating back to 1802 [12]. The process was discovered by Wilhelm von Hisinger and Jöns Jakob Berzelius [12], hobbyist scientists, only two years after Alessandro Volta first invented the pile, a source of electrical current [13]. The first electrochemical plant opened in 1886 in Villers-St. Sépulcre, Switzerland, using a diaphragm setup in a reactor made of wood. It was not very successful due to cathodic losses, and production ended in 1898 [12]. Around the same year, plants opened in Buckingham and Niagara in Quebec, Canada. These had no diaphragm and used bipolar electrodes with a small cell gap (1.5 to 3 mm), already remarkably similar to today's designs [14]. At the turn of century there were also factories in Switzerland, Sweden, and France. Surprisingly, there were no factories in Germany, despite most chlorate research being performed there [12]. Research focused on developing an understanding of the formation of chlorate. Initially it was believed that the formation was a purely chemical process, but within a few years this theory was completely upended several times. The revisions were driven by thorough experiments and reportedly accompanied by "sometimes violent discussions" [12]. Several papers and discussions in rude tones were exchanged between Foerster and Wohlwill [15], [16] in particular. Foerster insisted there was no electrochemical aspect to chlorate formation, while Wohlwill, a student of Nernst, held that there was. The matter was eventually clarified in 1900 when Lorenz and Wehrlin published extensive experimental results that showed chlorate could be formed electrochemically under certain circumstances [17], although Foerster nevertheless maintained his stance [12]. Regardless of the exact mechanism, it was generally agreed that hypochlorite plays an important part in chlorate formation, and that its Finally, Chapter 7 summarizes my findings and provides a perspective on the future of this topic.

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Combination of Highly Efficient Electrocatalytic Water Oxidation with Selective Oxygenation of Organic Substrates using Manganese Borophosphates

et al. 2021

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One of the key catalytic reactions for life on earth, the oxidation of water to molecular oxygen, occurs in the oxygen‐evolving complex of the photosystem II (PSII) mediated by a manganese‐containing cluster. Considerable efforts in this research area embrace the development of efficient artificial manganese‐based catalysts for the oxygen evolution reaction (OER). Using artificial OER catalysts for selective oxygenation of organic substrates to produce value‐added chemicals is a worthwhile objective. However, unsatisfying catalytic performance and poor stability have been a fundamental bottleneck in the field of artificial PSII analogs. Herein, for the first time, a manganese‐based anode material is developed and paired up for combining electrocatalytic water oxidation and selective oxygenations of organics delivering the highest efficiency reported to date. This can be achieved by employing helical manganese borophosphates, representing a new class of materials. The uniquely high catalytic activity and durability (over 5 months) of the latter precursors in alkaline media are attributed to its unexpected surface transformation into an amorphous MnOx phase with a birnessite‐like short‐range order and surface‐stabilized MnIII sites under extended electrical bias, as unequivocally demonstrated by a combination of in situ Raman and quasi in situ X‐ray absorption spectroscopy as well as ex situ methods.

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Alkaline manganese electrochemistry studied byin situandoperandospectroscopic methods – metal dissolution, oxide formation and oxygen evolution

Abstract: During the oxygen evolution reaction, manganese rapidly dissolves, however, it has a disordered oxide layer with a steady state thickness.

Cited by 35 publications

References 52 publications

Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction

Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction

Understanding selective thin films in the chlorate process

Combination of Highly Efficient Electrocatalytic Water Oxidation with Selective Oxygenation of Organic Substrates using Manganese Borophosphates

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