Structure/Performance Relations for Ni/Yttria-Stabilized Zirconia Anodes for Solid Oxide Fuel Cells

Abstract

The relations between morphology and electrochemical performance of Ni/yttria-stabilized zirconia (YSZ) anodes are investigated. Four types of anodes are prepared on YSZ electrolyte three-electrode pellets. A fine cermet of 0.5-1 m particles, a coarse cermet of 2-3 m particles, a porous Ni-paste anode, and a Ni-felt anode. The anodes are characterized by impedance spectroscopy at open-circuit potential, and the electrode relevant part (polarization resistance, R P ) of the spectra is identified and investigated. The active thickness of the fine cermet anode is demonstrated to be about 10 m and is believed to relate to the conductivity of the YSZ network. In the temperature range 850-1000ЊC, R P exhibits an apparent activation energy which increases with coarseness of the anode. No significant dependence on p H2 (0.01-0.97 atm) at 1000ЊC is observed. A dependence on p H2O of about R P ϰ p H2O Ϫ1/2 is found. Physical transport limitations are suggested as possible causes for the observed anode polarization.

Solid Oxide Electrolysis Cells: Microstructure and Degradation of the Ni/Yttria-Stabilized Zirconia Electrode

“…The thickness of the electrochemically active layer varies with temperature and microstructure of the electrode. The microstructures of the electrodes used by Brown et al 42 were coarser than those of the SOECs tested here and the thickness of the electrochemically active layer for the tested SOECs is presumably 5-10 m.…”

“…For the Ni particle size distributions presented here a layer of 10 m from the electrolyte was investigated as this constitutes the active electrode layer from a production point of view. Further, Brown et al 42 found a thickness of the electrochemically active layer of ϳ10 m for Ni/YSZ cermet electrodes at 1000°C. The thickness of the electrochemically active layer varies with temperature and microstructure of the electrode.…”

Kinetic Studies on State of the Art Solid Oxide Cells – A Comparison between Hydrogen/Steam and Reformate Fuels

“…f < 100 Hz. The frequency range f > 100 Hz contains the well-studied LSC/CGO composite oxygen electrode 38,39 in the range 100 Hz < f < 1 kHz with an activation energy of 123 kJ/mol 39 and the well investigated 19,26,40 Ni/8YSZ fuel electrode (f > 1 kHz) with an activation energy of 105 kJ/mol. 25 Considering Cell B alone, Figure 12(b_i) displays the known 20,41 negative thermal activation for the gas conversion process (peak frequency at 1 Hz at 900 • C).…”

Novel SOFC Anodes for the Direct Electrochemical Oxidation of Hydrocarbons

“…If ions from the electrolyte cannot reach the reaction site, if gas-phase fuel molecules cannot reach the site, or if electrons cannot be removed from the site, then that site cannot contribute to the performance of the cell. While the structure and composition clearly affect the size of the TPB, various theoretical and experimental methods have been used to estimate that it extends no more than approximately 10 µm from the electrolyte into the electrode [19,21,22]. Essentially, so long as the diffusion of ions through the electrolyte partially limits the performance, the concentration of excess ions in the oxide phase of the anode will be insignificant.…”