On the origin of the non-faradaic electrochemical modification of catalytic activity (NEMCA) phenomena. Oxygen isotope exchange on Pt electrode in cell with solid oxide electrolyte

Sobyanin, V. A.; Соболев, В. И.; Belyaev, V. D.; Marina, Olga A.; Demin, A.; Липилин, А. С.

doi:10.1007/bf00769508

Cited by 19 publications

(24 citation statements)

References 9 publications

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“…As it can be seen in Figure 3, there is no influence of the electrode polarization on the rate of equilibration. It reinforces the previous result of Sobyanin et al [16] who reported the same conclusion at 510°C and P(O 2 ) = 0.5 mbar. In this range of temperature, there is no effect of the polarization on the oxygen activation process which is likely limited by the dissociative adsorption energy.…”

Section: Resultssupporting

confidence: 93%

“…Early works of Sobyanin et al demonstrated the feasibility of such an experiment by performing homomolecular oxygen isotope exchange on a Pt/8-YSZ/Pt cell. [16] They concluded that at a moderate temperature of ca. 500°C, electrode polarization has no effect on the rate of oxygen homomolecular exchange with respect to its open circuit value.…”

Section: Introductionmentioning

confidence: 99%

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Operando Isotopic Exchange in Solid Oxide Fuel Cells: Oxygen‐Transport Dependency on Applied Potential

2020

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The oxygen isotopic exchange technique is a powerful tool to investigate the oxygen transport kinetics in an oxide solid. In a solid oxide fuel cell, isotopic surface exchange and diffusion coefficients are classically determined by using the Isotopic Exchange Depth Profiling method followed by ex situ SIMS characterizations. Despite its relevance, the utilization of in situ or operando techniques to measure the isotopic exchange under an electrical bias remains marginal. We developed here a setup which enables operando monitoring of oxygen exchange in SOFC type cells under polarization. The system has been used for studying the oxygen mobility dependency upon polarization on a symmetrical Pt/YSZ/Pt cell (YSZ: yttriastabilized zirconia). Homomolecular and heterolytic exchange reactions were undertaken to investigate the oxygen activation step and discriminate the limiting step among the sequence of elementary steps which constitute the oxygen transport process in the SOFC system. Oxygen ions incorporation into the dense ionic conductor was identified to be the rate determining step, and its first order rate constant dependency on applied potential was established.

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Section: Resultssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Operando Isotopic Exchange in Solid Oxide Fuel Cells: Oxygen‐Transport Dependency on Applied Potential

2020

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“…[8] The same conclusion was also reached by Sobyanin et al who studied the oxygen isotope exchange over Pt/YSZ catalysts and found no change in the PtÀO bond strength upon electrochemical polarization. [18][19][20][21] This result is in agreement with physical intuition because oxygen spilling over from the tpb onto the surface of the metal electrode the oxygen should lose its memory of where it came from originally. On can thus formulate the following steps [Eqs.…”

Section: Identity Of the Oxygen Spillover Speciessupporting

confidence: 83%

“…[4-6, 8, 16, 17] An alternative concept for the NEMCA effect was proposed by Sobyanin and co-workers, who explained the non-Faradayicity by a chain mechanism initiated by an electrochemically generated charged surface oxygen species. [18][19][20][21] Herein we investigate the C 2 H 4 + O 2 reaction on Pt/YSZ in an UHV environment. The reason for this choice is the huge Lfactor of 3 10 5 of this system and the paradigmatic role this system therefore had in numerous review papers and monographs on the EPOC effect.…”

Section: Introductionmentioning

confidence: 99%

The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst

2010

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The electrochemical promotion of the C(2)H(4)+O(2) reaction to form CO(2) and H(2)O is studied in the 10(-5) and 10(-4) mbar range with a Pt catalyst interfaced as working electrode to yttrium-stabilized zirconia (YSZ). Photoemission electron microscopy (PEEM) was used as spatially resolving method. Under open-circuit conditions, that is, without an external voltage applied, the CO(2) production exhibits a pronounced hysteresis upon cyclic variation of p(C(2)H(4)). The hysteresis is attributed to the build-up of a carbonaceous CH(x) layer inhibiting O(2) adsorption and hence poisoning the reaction. It is shown that the application of a positive potential of 1 V triggers a transition from the unreactive branch of the reaction to an active branch. The large non-Faradayicity reported in the literature for this reaction system is explained as an ignition effect caused by the partial removal of the inhibiting carbonaceaous layer.

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“…In fact, there have been isotopic exchange experiments with Pt/YSZ conducted by Sobyanin et al in the mbar range and the authors concluded that the results give no indication that a different more strongly bonded oxygen species exists under EPOC conditions. [10] We followed a different approach, asking whether a special spillover species is really required to explain the large non-Faradaic effects found in many EPOC experiments. The answer is "No".…”

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confidence: 99%

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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On the origin of the non-faradaic electrochemical modification of catalytic activity (NEMCA) phenomena. Oxygen isotope exchange on Pt electrode in cell with solid oxide electrolyte

Cited by 19 publications

References 9 publications

Operando Isotopic Exchange in Solid Oxide Fuel Cells: Oxygen‐Transport Dependency on Applied Potential

Operando Isotopic Exchange in Solid Oxide Fuel Cells: Oxygen‐Transport Dependency on Applied Potential

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”

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