Papel de la posición del electrodo de referencia en las medidas de sobrepotencial

Figueiredo, F. M.; Frade, J.R.; Marques, F.M.B.

doi:10.3989/cyv.1999.v38.i6.910

Cited by 10 publications

(14 citation statements)

References 9 publications

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“…[13][14][15][16][17][18][19][20][21][22] Still, with proper care, the information that these experiments yield can be valuable for optimization of SOFC electrodes.…”

Section: Discussionmentioning

confidence: 99%

Impedance Spectroscopy for the Characterization of Cu-Ceria-YSZ Anodes for SOFCs

McIntosh

Vohs

Gorte

2003

J. Electrochem. Soc.

129

144

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The performance of electrodes in direct-utilization, solid oxide fuel cells ͑SOFCs͒ has been studied on anode-supported and electrolyte-supported cells using impedance spectroscopy, coupled with calculations of the potential distribution in the electrolyte. The cells in these studies were composed of a Cu-ceria-yttria-stabilized zirconia ͑YSZ͒ anode, a YSZ electrolyte, and a Sr-doped LaMnO 3 ͑LSM͒-YSZ cathode and were operated at 983 K using both H 2 and n-butane as fuel. Both calculations and experiments show that three-electrode measurements on anode-supported electrolytes, with the reference electrode opposite the anode, provide no additional information over two-electrode measurements and cannot be used to estimate the performance of individual electrodes. Three-electrode measurements were able to estimate anode and cathode performance on thick, electrolyte-supported cells, with symmetric placement of the working electrodes. However, both experiments and calculations demonstrate that differences in the kinetics of the two electrodes make perfect separation of anode and cathode processes difficult. The cathode performance of LSM-YSZ in these experiments was described by a single arc in the Cole-Cole plot, with a frequency of 2 kHz and a resistance of 0.4 ⍀ cm 2 . The performance of the anode in H 2 was also characterized by a single arc, with a frequency of 4 Hz and a resistance of 0.8 ⍀ cm 2 . While anode performance in H 2 is only weakly dependent on current density, nonlinear processes are observed with n-butane, so that the area-specific resistances depend strongly on the current density.The focus of research on solid oxide fuel cells ͑SOFCs͒ in our laboratory has been on the development of alternative anodes that allow the direct, electrochemical oxidation of hydrocarbon fuels in the absence of added steam or air. Because Ni, the most commonly used metal for SOFC anodes, 1 catalyzes the formation of carbon filaments when exposed to hydrocarbons at SOFC operating temperatures, 2-5 it must be replaced with a different electronic conductor that is not catalytically active for this reaction. We have focused primarily on replacing Ni with Cu, since Cu is a poor catalyst for carbon formation. 6,7 Ceria is included in the anode to enhance anode performance, in part because of the catalytic activity of ceria for oxidation of hydrocarbon fuels. 8 It has been shown that Cuceria-yttria-stabilized zirconia ͑YSZ͒ anodes are capable of direct, electrochemical oxidation of various fuels, including hydrocarbons that are liquids at room temperature. 9,10 While the performance that has been achieved with the Cu-ceria-YSZ anodes is reasonable, further optimization of the directoxidation SOFC requires better monitoring of the anode performance. Separation of the losses associated with the anode from the losses associated with the electrolyte and the cathode is usually accomplished using reference electrodes, but there is no consensus on what electrode geometry gives the best results. Some groups simply place a reference elec...

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“…[13][14][15][16][17][18][19][20][21][22] Still, with proper care, the information that these experiments yield can be valuable for optimization of SOFC electrodes.…”

Section: Discussionmentioning

confidence: 99%

Impedance Spectroscopy for the Characterization of Cu-Ceria-YSZ Anodes for SOFCs

McIntosh

Vohs

Gorte

2003

J. Electrochem. Soc.

129

144

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“…As has been discussed in detail in several previous studies, proper alignment of the cathode and anode and positioning of the reference electrode are required in order to obtain accurate measurements of overpotentials using both current interruption and impedance spectroscopy [9][10][11][12][13]. For a cell with an ideal configuration the magnitude of the initial drop in the reference to cathode current interruption measurement should be equal to that in the reference to anode measurement at the same current density.…”

Section: Resultsmentioning

confidence: 99%

“…The overpotential, A In order to completely separate the anode and cathode processes a well-placed reference electrode is again required. Several recent experimental and theoretical studies have demonstrated the importance of well-designed cell geometry in order to obtain a reference electrode whose potential is pinned near the center of the electrolyte and independent of cell current [9][10][11][12][13]. These studies show that one needs to use a cell with a relatively thick electrolyte, symmetric coaxial placement of the cathode and anode, and placement of the reference electrode at least three electrolyte thicknesses from the edge of one of the electrodes.…”

Section: Cu-ceria-ysz Cermet Anodes For Solid Oxide Fuel Cells (Sofcsmentioning

confidence: 99%

Measurement of electrode overpotentials for direct hydrocarbon conversion fuel cells

et al. 2004

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Cathodic and anodic overpotentials were measured using current interruption and AC impedance spectroscopy for two separate solid oxide fuel cells (SOFCs). The fuel cells used yttria-stabilized zirconia (YSZ) as the electrolyte, strontium-doped lanthanum manganite (LSM) as the cathode, and a porous YSZ layer impregnated with copper and ceria as the anode. The Cu/CeO 2 /YSZ anode is active for the direct conversion of hydrocarbon fuels. Overpotentials measured using both current interruption and impedance spectroscopy for the fuel cell operating at 700ºC on both hydrogen and n-butane fuels are reported. In addition to providing the first electrode overpotential measurements for direct conversion fuel cells with Cubased anodes the results demonstrate that there may be significant uncertainties in measurements of electrode overpotentials for systems where there is a large difference between the characteristic frequencies of the anode and cathode processes and/or complex electrode kinetics.

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“…This factor may be controlled by an accurate design of the electrode geometry ensuring symmetrical electrode arrangements and keeping them at a convenient distance. Based on finite elements simulations of the potential distribution [14], this distance was found to be of 3-4 mm for a 1 mm thick electrolyte. Finally, an oxygen concentration gradient may occur between the sample inner surface and the pumping electrodes leading to a non-equilibrium sensor reading.…”

Section: Methodsmentioning

confidence: 99%

Microstructural effects on the electrical properties of grain boundary Fe-doped LSGM

2008

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Papel de la posición del electrodo de referencia en las medidas de sobrepotencial

Cited by 10 publications

References 9 publications

Impedance Spectroscopy for the Characterization of Cu-Ceria-YSZ Anodes for SOFCs

Impedance Spectroscopy for the Characterization of Cu-Ceria-YSZ Anodes for SOFCs

Measurement of electrode overpotentials for direct hydrocarbon conversion fuel cells

Microstructural effects on the electrical properties of grain boundary Fe-doped LSGM

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