The electrochemistry of Ni pattern anodes used as solid oxide fuel cell model electrodes

Ni pattern electrodes with well-defined triple phase boundary (TPB) lengths were prepared in order to investigate the reaction mechanisms at solid oxi de fuel cell (SOFC) anodes. The anode microstructures were stable during th ermal treatment and electrochemical measurements. Electrochemical impedance spectroscopy was used to study the influence of the overpotential, of the gas atmosphere, of the temperature, and of the pattern geometry on the elec trochemical behavior of SOFC anodes. It is found that the reaction kinetics are dominated by one main process. This process is thermally activated wit h an activation of energy of E-A = 0.88 +/- 0.04 eV. At overpotentials high er than 300 mV, a second process becomes relevant. The partial pressure of water in the fuel gas atmosphere has a catalytic effect on the anode perfor mance, whereas variations of the patrial pressure of hydrogen in the fuel g as atmosphere have no significant influence on the electrode behavior. A mo del was established in order to explain the catalytic effect of water. The direct proportionality between the relaxation frequency and the TPB length suggests a TPB limitation of the anode kinetics. (C) 2001 The Electrochemic al Society.