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Research Papers

# Study of the Rate Limiting Step of the Cathodic Process in Anode Supported Solid Oxide Fuel Cell

[+] Author and Article Information
M. P. Carpanese, G. Cerisola

DICheP,  University of Genova, Piazzale Kennedy 1, 16129 Genova, Italy

M. Viviani

Institute for Energetics and Interphases, CNR, Via De Marini 6, 16149 Genova, Italy

P. Piccardo

DCCI,  University of Genova, Via Dodecaneso 31, 16146 Genova, Italy

IEES-BAS, 10 Acad. G. Bonchev, 1113 Sofia, Bulgaria

A. Barbucci1

University of Genova, Piazzale Kennedy 1, 16129 Genova, Italybarbucci@unige.it

1

Corresponding author.

J. Fuel Cell Sci. Technol 5(1), 011010 (Feb 01, 2008) (7 pages) doi:10.1115/1.2784295 History: Received November 30, 2005; Revised January 29, 2007; Published February 01, 2008

## Abstract

The oxygen reduction (OR) mechanism at the Sr-doped $LaMnO3$ (LSM) and yttria stabilized zirconia (YSZ) composite cathode for high temperature solid oxide fuel cells is still uncertain, despite of the great deal of work carried out over the last years about this system. In previous works, we tested a half-cell (with a YSZ electrolyte pellet) in a typical three-electrode configuration: It was observed that the portion of the composite cathode volume involved in the reaction depends on the operating temperature. Moreover, we analyzed part of the impedance data by the differential impedance analysis, which does not need a preliminary working hypothesis. The results suggested that significant limitations in the oxygen ion transport occur in the LSM pure material, which are not observed in the composite YSZ/LSM cathode. In this study, we investigate the behavior of the LSM/YSZ system in a Ni/YSZ cermet anode-supported half-cell with yttria stabilized zirconia (8YSZ) electrolyte and a screen printed LSM/YSZ composite cathode. The aim is to individuate and characterize the cathodic contribution from the overall impedance response, varying the partial pressure of the reactant gases, to obtain additional information about the OR mechanism from the $p(O2)$ dependence. By a possible interpretation of the oxygen reaction mechanism, a comparative study of the cathode behavior with previous results is performed.

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## Figures

Figure 1

Complex plane impedance diagram (a) of the cell and frequency dependence of the real and imaginary parts of the impedance (b) at OCV and different oxygen partial pressures. The anode gas is pure humidified hydrogen. The real part of impedance diagram is corrected for the Ohmic resistance.

Figure 2

Complex plane impedance diagram (a) and frequency dependence of the real part of the impedance (b) at OCV and different temperatures. Anode gas—pure humidified hydrogen; cathode gas—air. The real part is corrected for the Ohmic resistance.

Figure 3

Complex plane impedance diagram (a) of the cell and frequency dependence of the real and imaginary parts of the impedance (b) at OCV and different humidified H2+CO mixture. Cathode gas: O2:Ar=21:79. The real part is corrected for the Ohmic resistance.

Figure 4

Complex plane impedance diagram of the cell at OCV and 800°C. Cathode gas—air; anode gas—pure humidified hydrogen. (○), experimental data; (line), fitting with LR(R1Q1)(R2C2)(R3Q3). L=3.06×10−7H; R=0.11Ω; R1=0.17Ω; Q1=0.012; n1=0.61; R2=0.02Ω; C2=0.043F; R3=0.65; Q3=0.042; n3=0.78.

Figure 5

Values of the resistances—extracted from the fitting with LR(R1Q1)(R2C2)(R3Q3)—versus oxygen partial pressures. (○), R1 (high frequency resistance); (▵): R2 (intermediate frequency resistance); and (□). R3 (low frequency resistance).

Figure 6

Dependence between ln(1∕Rp) and ln[p(O2)] at three different temperatures. The anode gas is humidified hydrogen. The solid lines describe the calculated equations.

Figure 7

OCV Impedance plots at different partial pressures of the oxygen in a mixture with argon at 700°C. The anode gas is pure humidified hydrogen. The real part is corrected for the Ohmic resistance.

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