Electrocatalytic Reactivity of Hydrocarbons on a Zirconia Electrolyte Surface

Nguyen, B. C.; Lin, Tingrui; Mason, David M.

doi:10.1149/1.2109027

Cited by 58 publications

(30 citation statements)

References 30 publications

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“…It was shown earlier that the polarization loss at the electrodes can be reduced by using mixed-conducting ceria electrolytes, 12 or by introducing the mixed-conducting (reduced zirconia or ceria) layer on the conventional zirconia electrolyte surface. 4,5,[13][14][15] There is, however, no report available exclusively on the effect of ionic conductivity of the electrolyte on the electrode polarization behavior, except our work. 16,17 High ionic conductivity of the electrolyte can, of course, lead to reduced ohmic losses.…”

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confidence: 75%

“…Diffusion of O 2 (gas) in gas phase through porous LSM layer [11] Dissociative adsorption of O 2 to form O ad on LSM: O 2 (gas) r 2 O ad (LSM) [12] Surface diffusion of O ad to TPB: O ad (LSM) r O ad (TPB) [13] Charge transfer at TPB: O ad (TPB) ϩ 2e Ϫ (LSM) r O 2Ϫ (TPB) [14] Ionic transfer of O 2Ϫ from TPB into zirconia electrolyte: O 2Ϫ (TPB) r O 2Ϫ (zirconia) [15] With an additional reaction path, "mixed-conducting path," a charge transfer may occur at the LSM surface after step 12…”

Section: Discussionmentioning

confidence: 99%

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Effect of Ionic Conductivity of Zirconia Electrolytes on the Polarization Behavior of Various Cathodes in Solid Fuel Cells

Uchida

Yoshida

Watanabe

1999

J. Electrochem. Soc.

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The polarization behaviors of porous platinum and La(Sr)MnO 3 (LSM) cathodes coupled with zirconia electrolytes with various ionic conductivities ( ion ) were investigated. The exchange current density, j 0 , on Pt cathode was not influenced by the ion at 900 and 1000ЊC, whereas j 0 increased proportionally to ion at a lower temperature of 800ЊC. However, the j 0 on LSM cathodes increaesd in proportion to the ion in the temperature region between 800 and 1000ЊC. The dispersion of nanometer-sized Pt catalysts on LSM particles greatly enhanced the performance, the magnitude of which depended on the temperature, the ion , and the microstructure of LSM. The observations are well explained kinetically, i.e., the cathode performance is controlled by the transport rate of O 2Ϫ at the interface when the surface reaction rate is sufficiently high. Consequently, the use of high-performance electrodes in combination with the solid electrolyte having high ion is very important for achieving the high performance of solid oxide fuel cells. © 1999 The Electrochemical Society. S0013-4651(98)03-090-0. All rights reserved.Manuscript submitted March 18, 1998; revised manuscript received September 1, 1998.Solid oxide fuel cells (SOFCs) have been intensively investigated since they are expected to yield fairly high energy conversion efficiencies. At present, the operating temperature of SOFC is restricted to temperatures of about 1000ЊC because of insufficient performance of the state-of-the-art electrolyte and electrodes at low temperatures. Lowering the operating temperature to around 800ЊC is desirable to overcome a limited choice of the component materials resistant to mechanical degradation due to thermal heat shock or to physical and chemical degradation due to oxidation/reduction of materials or to solid-phase reaction at an interface between different materials. However, two major obstacles must be solved to operate SOFCs at medium temperatures. The first is to reduce ohmic losses in solid electrolytes. Progress in this direction has been achieved by the development of a very thin film zirconia electrolyte 1-7 or novel solid electrolytes with higher ionic conductivity. [8][9][10][11] Besides the reduction of ohmic losses, it is very important to develop high performance electrodes since the electrode reaction rates at both anode and cathode are affected detrimentally at medium temperature range.We have been conducting a series of studies with the objective of developing high performance SOFC electrodes operating at relatively lower temperatures than those of the present level. Thus, it becomes essential to clarify the factors that control the polarization properties of these electrodes. It was shown earlier that the polarization loss at the electrodes can be reduced by using mixed-conducting ceria electrolytes, 12 or by introducing the mixed-conducting (reduced zirconia or ceria) layer on the conventional zirconia electrolyte surface. 4,5,[13][14][15] There is, however, no report available exclusively on the effect of ionic ...

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mentioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Effect of Ionic Conductivity of Zirconia Electrolytes on the Polarization Behavior of Various Cathodes in Solid Fuel Cells

Uchida

Yoshida

Watanabe

1999

J. Electrochem. Soc.

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“…In contrast, measurements on scandia-stabilized zirconia electrolytes indicate similar anodic overpotentials and activation energies for porous Pt and Au electrodes in CO, H 2 , and CH 4 in the temperature range 700 to 850°C. 4,16,17 A proposed explanation hypothesizes oxygen vacancies in the electrolyte to act as electrochemical reaction sites, with electrons migrating along the electrolyte surface to or away from these active sites. 17 Finally a wide variety of experimental conditions ͑gas-phase composition and temperature͒ and electrolytes ͑types and amount of dopants in ZrO 2 ) results in different reaction mechanisms being proposed and renders comparison difficult.…”

Section: -H 2 O)mentioning

confidence: 99%

Electrochemical Oxidation of CO on Pt and Ni Point Electrodes in Contact with an Yttria-Stabilized Zirconia Electrolyte

Lauvstad

Tunold

Sunde

2002

J. Electrochem. Soc.

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The steady-state and impedance response of a solid metal point electrode in contact with a solid, oxygen-ion conducting electrolyte in CO-CO 2 atmospheres was derived for three reaction mechanisms, involving gaseous species or species adsorbed on the surface of the electrode and/or the electrolyte. The overall electrochemical reaction was assumed to proceed in elementary steps, such as adsorption, diffusion of adsorbed species, and charge transfer. Eliciting the reaction mechanism from the steady-state response may require an extensive analysis in terms of temperature, gas-phase composition, and overpotential dependence. The impedance response, on the other hand, can in favorable cases be more distinctively dependent on the number of adsorbed species involved in the reaction and on the role of diffusion. Thus, if only one adsorbed intermediate species is involved, the impedance spectrum will always appear in the first quadrant of the impedance plane plot irrespective of experimental conditions. If two adsorbed intermediates are involved, however, this may lead to appearance of fourth-quadrant data.From a thermodynamic point of view it would be desirable to use natural gas directly as fuel in a solid-oxide fuel cell ͑SOFC͒, but the inherent kinetic stability of the main constituent, methane (CH 4 ), and problems related to degradation of the fuel electrode due to carbon formation make this difficult. 1,2 One way of avoiding the problem of carbon formation is to use steam-reformed methane as fuel. At sufficiently high temperatures ͑approximately 1000°C͒, the electrochemical reactions probably involve the reformed gases, H 2 and CO, rather than CH 4 , 3 while for lower temperatures ͑700°C͒, no effect of the water-shift reaction was seen. 4 In the literature, some dissension appears to exist regarding the relative rates of the electrode reactions involving CO-CO 2 and H 2 -H 2 O. 5 Several workers report that the reactions involving CO or CO-CO 2 exhibit lower current or exchange current densities and higher anodic overpotentials than do the reactions involving H 2 or H 2 -H 2 O, both for Pt 4,6-9 and for cermets of Ni and yttria-stabilized zirconia ͑YSZ͒. 10 Due to this, H 2 -H 2 O is used in most of the fuel electrode studies. 11-14 According to Setoguchi et al. 15 however, the anodic polarization conductivity of the Ni-YSZ cermet electrode/ YSZ electrolyte interface depends strongly on the oxygen partial pressure, p O2 , in the fuel, but is independent of the kind of fuel (CO-CO 2 , H 2 -H 2 O, and CH 4 -H 2 O).In addition, the role of the fuel-electrode material in the reaction mechanism is not well understood. Setoguchi et al. 15 observed that the anodic overpotential, a , of a range of metal electrodes in H 2 at 800°C is be correlated with the metal/oxygen bonding strength, which is smallest for Ni ͓ a (Au) Ͼ a (Pt) Ͼ a (Ni)͔. In contrast, measurements on scandia-stabilized zirconia electrolytes indicate similar anodic overpotentials and activation energies for porous Pt and Au electrodes in CO, H 2 , and CH 4...

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“…Solid oxide fuel cells (SOFCs) provide advantages of high energy conversion efficiency, such as heat utilization and ability to use a variety of fuels, due to their high operating temperature in the range between 800 and 1000 • C. [1][2][3] An SOFC consists of three essential components: a porous cathode, a dense electrolyte and a porous anode. The most commonly used materials are lanthanum strontium manganite as cathode, yttria stabilized zirconia (YSZ) as the electrolyte and Ni-YSZ cermet as anode.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and property evaluation of barium aluminosilicate glass–ceramic sealant for anode-supported solid oxide fuel cell

Ghosh

Kundu

Sharma

et al. 2008

Journal of the European Ceramic Society

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Electrocatalytic Reactivity of Hydrocarbons on a Zirconia Electrolyte Surface

Cited by 58 publications

References 30 publications

Effect of Ionic Conductivity of Zirconia Electrolytes on the Polarization Behavior of Various Cathodes in Solid Fuel Cells

Effect of Ionic Conductivity of Zirconia Electrolytes on the Polarization Behavior of Various Cathodes in Solid Fuel Cells

Electrochemical Oxidation of CO on Pt and Ni Point Electrodes in Contact with an Yttria-Stabilized Zirconia Electrolyte

Microstructure and property evaluation of barium aluminosilicate glass–ceramic sealant for anode-supported solid oxide fuel cell

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