Microstructure of Pt electrodes and its influence on the oxygen transfer kinetics

Badwal, S. P. S.; Ciacchi, F.T.

doi:10.1016/0167-2738(86)90308-5

Cited by 62 publications

(70 citation statements)

References 8 publications

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“…6. Such a large difference in the value of the equilibrium exchange current density was previously found in studies of the Pt,Q/stabilized zirconia interface and results partly from different electrode morphologies [25,26,29].…”

Section: Steudy Vute Polorisutiotimentioning

confidence: 72%

Electrode polarization at the Au, O2 (g) / yttria stabilized zirconia interface. Part II: electrochemical measurements and analysis

1991

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The impedance of the Au,O,(g)/yttria stabilized zirconia interface has been measured as function of the overpotential, temperature and oxygen partial pressure. At large cathodic overpotentials (vi -0. I V) and large anodic overpotentials (7~ +O. I V) inductive effects are observed in the impedance diagram at low frequencies. Those inductive effects result from a charge transfer mechanism where a stepwise transfer of electrons towards adsorbed oxygen species occurs. A model analysis shows that the inductive effects at cathodic overpotentials appear when the fraction of coverage of one of the intermediates increases with more negative cathodic overpotentials.The steady state current-voltage characteristics can be analyzed with a Butler-Volmer type of equation. The apparent cathodic charge transfer coefficient is close to 01, =0.5 and the apparent anodic charge transfer coefficient varies between I .7 < (Y, -C 2.8. The logarithm of the equilibrium exchange current density ( lo ) shows a positive dependence on the logarithm ofthe oxygen partial pressure with a slope of m = (0.602 0.02). Both the apparent cathodic charge transfer coefficient and the oxygen partial pressure dependence of I,, are in accordance with a reaction model where a competition exists between charge transfer and mass transport of molecular adsorbed oxygen species along the electrode/solid electrolyte interface. The apparent anodic charge transfer coefficients deviate from the model prediction.

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Section: Steudy Vute Polorisutiotimentioning

confidence: 72%

Electrode polarization at the Au, O2 (g) / yttria stabilized zirconia interface. Part II: electrochemical measurements and analysis

1991

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Section: Conventional Solid Oxide Fuel Cell Electrolytesmentioning

confidence: 99%

“…Since then stabilised zirconia has been the electrolyte that has received most attention by fuel cell developers. Most zirconia electrolytes are based upon either yttria or scandia stabilisation of the tetragonal polymorph 6,7,13 , commonly referred to as YSZ andScSZ respectively, although a number of alternative dopants have been investigated, Table 1. Conventionally the substitution level is between 3 and 8 mol % for the yttria based materials and at 10-12 mol% for the Sc based materials.…”

mentioning

confidence: 99%

Advanced Inorganic Materials for Solid Oxide Fuel Cells

Skinner¹,

Laguna‐Bercero²

2011

Energy Materials

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PC-SOFC -Proton conducting solid oxide fuel cell IT-SOFC -Intermediate temperature solid oxide fuel cell IntroductionFuel cells are widely regarded as a next generation technology that will contribute to reductions in emissions of gases responsible for climate change such as CO 2 . There are several modifications to the basic concept of a fuel cell that allow operation over a wide variety of temperatures and with differing fuels. One of the most promising types of fuel cell for large scale power generation and combined heat and power applications is the solid oxide fuel cell (SOFC). The solid oxide fuel cell offers many advantages over conventional combustion-based power generation technologies and has been the subject of intensive investigation for many years. As with all other fuel cells the SOFC is an electrochemical energy conversion device that converts the chemical energy contained within a fuel (for example, H 2 ) to useful electrical energy through an electrochemical oxidation process. Using the simplest fuel as an example the overall chemical reaction occurring is: To achieve this overall reaction it is essential that we consider the basic components of the fuel cell. A SOFC consists of three ceramic functional components (anode "fuel side", cathode "air side" and electrolyte) plus an electrical interconnect that is either ceramic or metallic depending upon the operating environment. These 4 components are referred to as the fuel cell and to achieve suitable power outputs these individual cells are connected to form a fuel cell stack. Schematics of two alternative designs of a single fuel cell are shown in Figure 1.At the anode the fuel is oxidised with the oxidant (oxygen) reduced at the cathode.These two components are separated by a gas tight electrolyte membrane that is a pure ionic conductor, transporting the oxide ion species from the cathode to the fuel side. This process releases electrons to an external circuit, providing the useful electrical power. These reactions are summarised as:cathode reaction Evidently these electrode reactions are significantly more complex than shown in equations 1.1. and 1.2 and fuller discussions of the proposed fuel oxidation and oxygen reduction electrode reactions are given in [1][2][3][4].It is therefore clear that in a solid oxide fuel cell there are many processes that require optimised materials, and consequently the SOFC is a complex solid state device. As a summary, it is essential that the electrolyte is a gas tight, pure ionic conductor stable over a wide pO 2 range (>10 -24 atm). Anodes have to possess stability in reducing conditions with both high ionic and electronic conductivity, and chemical compatibility with the electrolyte material. Similar properties are required for the cathode with the exception that stability is now in oxidising environments.Additionally the cathode has to be catalytically active towards oxygen reduction, which is often a rate limiting process, particularly at lower temperatures of operation (<650 o C). These are demanding pr...

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“…Here O represents the oxidized ~Rg~ species, ne is the number of electrons transferred, and R is the reduced species. This mechanism is modelled [27,28] by the Butler-Volmer equation [30] I (~aF~) (-:~oF~c) ] Je = Jo.e exp RT exp R~ (8) and occurs at the three-phase line and/or at the twophase contact area. In this relation, Jo,e is the exchange current density, e, and ~c are the anodic and cathodic transfer coefficients; r& and r/~ are the anodic and cathodic overpotentials.…”

Section: Rtamentioning

confidence: 99%

“…For the temperature range, oxygen pressure, and current density associated with each of these morphologies, the rate-limiting or polarization mechanisms were discussed. A more recent investigation [27] considered the effects of temperature, film thickness and gas atmosphere on the surface area, particle size, and three-phase-line length of sputtered platinum electrodes.…”

Section: Introductionmentioning

confidence: 99%

A morphological investigation of electrodes for solid electrolytes

Canaday

Wheat

Haley³

et al. 1989

J Mater Sci

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using the techniques of image analysis, profilometry, gas permeability, mercury porosimetry, and gas adsorption, the morphological properties of porous electrode film (1 to 300/~m) materials are discussed. The materials include platinum paste which is utilized as electrodes for high-temperature oxygen-ion-conducting ZrO 2 electrolytes and for low-temperature solid-state protonic electrolytes. Also considered are plasma-sprayed nickel layers and silver membranes. It is shown that each of the five methods can be used to make quantitative evaluations of film electrodes. The electrode morphological parameters measured include particle diameter, pore diameter, porosity, three-phase line, thickness, surface texture, gas-flow/pressure, pore area, and surface area. A discussion of these properties as they relate to activation and concentration polarization of electrochemical cells is also presented. IntroductionThe morphology of the electrodes used in certain types of electrochemical cells has been known [1-9] to affect the performance of these devices. Of particular interest here is the three-phase cell consisting of a solid (ceramic) electrolyte (in which mobile ionic species migrate or diffuse), porous metal electrodes and reactant gas species. This structure may be compared with two-phase electrochemical cells containing a liquid or solid electrolyte and non-porous metal electrodes.A number of three-phase cells has been under intensive study. The cell with doped ZrO2 [1-9] as the electrolyte is an anionic conductor, having 02 ions as the mobile species. The operating temperatures of this cell is 800 to 1000 ° C. A cationically conducting cell based on the SrCeO3 electrolyte [10-13] also operates in this temperature range and has protons as its mobile species.Two protonic conductors which operate at 25 to 300°C have also been developed. The fl/fl"-A1203 [14][15][16] and Nasicon [17,18] formulations show promise as precursor electrolytes for fuel cells, electrolysers and sensors. In order for these materials to be used in hydrogen cells, it is necessary for the mobile cationic species to be exchanged for hydronium, H30 + , ions. A method for ion-exchanging the precursor material in powder form and then bonding the exchanged powder with an inorganic substance has been developed [19].A number of electrochemical devices have been reported which utilize the hydronium electrolyte;

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Microstructure of Pt electrodes and its influence on the oxygen transfer kinetics

Cited by 62 publications

References 8 publications

Electrode polarization at the Au, O2 (g) / yttria stabilized zirconia interface. Part II: electrochemical measurements and analysis

Electrode polarization at the Au, O2 (g) / yttria stabilized zirconia interface. Part II: electrochemical measurements and analysis

Advanced Inorganic Materials for Solid Oxide Fuel Cells

A morphological investigation of electrodes for solid electrolytes

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