Ambient pressure X-ray photoelectron spectroscopy during electrochemical promotion of ethylene oxidation over a bimetallic Pt–Ag/YSZ catalyst

Toghan, Arafat; Arrigo, Rosa; Knop‐Gericke, Axel; Imbihl, R.

doi:10.1016/j.jcat.2012.09.006

Cited by 19 publications

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“…[11][12][13][14][15] With a differentially pumped XPS, we extended the p-range of ethylene oxidation up to 1 mbar, which is even about two orders of magnitude higher in p(O 2 ) than in the studies of Vayenas et al We found absolutely the same picture as at low p: EPOC was only observed beyond the rate maximum when a carbon layer starts to build up. [16] Compared to the L factors reported by Vayenas et al which go as high as 3 10 5 , the values in our UHV-type study are quite modest, reaching only 2.4. Most likely, the discrepancy is largely due to the about two-orders-of-magnitude higher pressure of the reactants used in the older studies.…”

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“…[9] How about TPD? Right at the beginning of their note, Vayenas and Vernoux present in Figure 1 O 2 TPD spectra from Pt/YSZ obtained after 18 O 2 adsorption from the gas phase, followed by electrochemical pumping of 16 O from YSZ. Again, the authors are convinced that this figure "leaves little room for any reasonable doubts about the validity of the sacrificial promoter, i. e. two oxygen species mechanism".…”

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Comment on the Note by Vayenas and Vernoux on “The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst”

Imbihl

Toghan

2011

ChemPhysChem

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The essential point of the note by Vayenas and Vernoux is to defend the "sacrificial promoter" mechanism, which involves two oxygen species and has been advocated in numerous papers and monographs by Vayenas et al., against the ignition mechanism suggested by us in two recent papers. [1,2] The basic idea of the "ignition concept" is to explain the huge non-Faradaic effect found in the electrochemical promotion of catalytic (EPOC) ethylene oxidation and many other reaction systems exhibiting an EPOC effect without having to invoke the special oxygen spillover species postulated by Vayenas et al. In their "sacrificial promoter" mechanism, besides regular chemisorbed oxygen, a special oxygen spillover species should exist on Pt/ YSZ (YSZ = yttria-stabilized ZrO 2 ), with particular properties that differ from those of regular chemisorbed oxygen on Pt. [3,4] There is insofar agreement as the identity of chemisorbed oxygen and the spillover species at low coverage/low pressure is accepted, that is, under these conditions, only one oxygen species exists. [5][6][7] In contrast to that, the issue of a special spillover species at high coverage/high pressure remains controversial. In the second last paragraph one can read the following statement about the two-oxygen species mechanism: "This mechanism has been confirmed beyond any reasonable doubt by numerous techniques, e. g. XPS, TPD (temperature-programmed desorption) and temperature-programmed oxidation (TPO)." A strong statement, but if one actually goes into the details of these "proofs", one does not find a single proof which withstands a detailed examination (for more details, see ref. [7]). The O1 s BE at 528.8 eV often cited as evidence for O dÀ with (d % 2) stems from oxygen of YSZ which floats with the applied potential, [7,8] the peak assigned in cyclic voltametry to the spillover species was shown to be caused by Si contamination. [9] How about TPD? Right at the beginning of their note, Vayenas and Vernoux present in Figure 1 O 2 TPD spectra from Pt/YSZ obtained after 18 O 2 adsorption from the gas phase, followed by electrochemical pumping of 16 O from YSZ. Again, the authors are convinced that this figure "leaves little room for any reasonable doubts about the validity of the sacrificial promoter, i. e. two oxygen species mechanism". What one sees in their Figure 1 are two adsorption states as they are common in practically all O 2 adsorption experiments on noble-metal surfaces. The two states arise typically due to energetic interaction of the adsorbed particles which become dominant at high coverage and, in addition, due to different grain orientations on the polycrystalline material. As expected for dissociative chemisorption, one finds isotopic mixing. The amount of mixing varies for the two states but this is no surprise because depending on the distance from the tpb (three-phase boundary) where the spillover species originates, the oxygen coverage . Schematic representation of the ignition mechanism proposed for the electrochemical activation of catal...

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Comment on the Note by Vayenas and Vernoux on “The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst”

Imbihl

Toghan

2011

ChemPhysChem

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“…The correlations found between surface chemistry on electrode and electrochemical device performance have started to provide mechanistic insight for us to improve electrochemical devices. The use of AP‐PES by electrochemical research community is growing rapidly and new AP‐PES instruments and new model cells are being developed for electrochemical research at several synchrotron facilities . Most of the current studies are limited to the gas‐solid interfaces.…”

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confidence: 99%

Recent Progress on Synchrotron‐Based In‐Situ Soft X‐ray Spectroscopy for Energy Materials

2014

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Soft X-ray spectroscopy (SXS) techniques such as photoelectron spectroscopy, soft X-ray absorption spectroscopy and X-ray emission spectroscopy are efficient and direct tools to probe electronic structures of materials. Traditionally, these surface sensitive soft X-ray techniques that detect electrons or photons require high vacuum to operate. Many recent in situ instrument developments of these techniques have overcome this vacuum barrier. One can now study many materials and model devices under near ambient, semi-realistic, and operando conditions. Further developments of integrating the realistic sample environments with efficient and high resolution detection methods, particularly at the high brightness synchrotron light sources, are making SXS an important tool for the energy research community. In this progress report, we briefly describe the basic concept of several SXS techniques and discuss recent development of SXS instruments. We then present several recent studies, mostly in situ SXS experiments, on energy materials and devices. Using these studies, we would like to highlight that the integration of SXS and in situ environments can provide in-depth insight of material's functionality and help researchers in new energy material developments. The remaining challenges and critical research directions are discussed at the end.

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“…In the last decade the progress in this field has been gigantic and we will now briefly provide a non-exhaustive list of proposed approaches. Depending on the type of synchrotron radiation employed, different methodologies have been put forward: The research using soft X-rays initially was focused on cells using solid oxide electrolytes [6,19,20] as well as on room [10,16,17] and higher [11] temperature proton exchange membrane (PEM)-based electrode assemblies in (wet) gaseous atmospheres. To investigate electrochemical reactions in liquid electrolytes by soft X-ray spectroscopies, an alternative approach uses electron-transparent graphene membranes to separate the liquid reaction environment from the vacuum section of the analysis chamber [13,21].…”

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In Situ Electrochemical Cells to Study the Oxygen Evolution Reaction by Near Ambient Pressure X-ray Photoelectron Spectroscopy

Streibel

Hävecker

et al. 2018

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In this contribution, we report the development of in situ electrochemical cells based on proton exchange membranes suitable for studying interfacial structural dynamics of energy materials under operation by near ambient pressure X-ray photoelectron spectroscopy. We will present both the first design of a batch-type two-electrode cell prototype and the improvements attained with a continuous flow three-electrode cell. Examples of both sputtered metal films and carbon-supported metal nanostructures are included demonstrating the high flexibility of the cells to study energy materials. Our immediate focus was on the study of the oxygen evolution reaction, however, the methods described herein can be broadly applied to reactions relevant in energy conversion and storage devices.

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Ambient pressure X-ray photoelectron spectroscopy during electrochemical promotion of ethylene oxidation over a bimetallic Pt–Ag/YSZ catalyst

Cited by 19 publications

References 58 publications

Comment on the Note by Vayenas and Vernoux on “The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst”

Comment on the Note by Vayenas and Vernoux on “The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst”

Recent Progress on Synchrotron‐Based In‐Situ Soft X‐ray Spectroscopy for Energy Materials

In Situ Electrochemical Cells to Study the Oxygen Evolution Reaction by Near Ambient Pressure X-ray Photoelectron Spectroscopy

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