An electrode kinetics study of H2 oxidation on Ni/Y2O3-ZrO2 cermet electrode of the solid oxide fuel cell

Hydrogen oxidation on Ni/3 mol% Y(2)O(3)-ZrO(2) (Ni/Y-TZP) cermet electrodes has been studied in moist H(2) environments. The impedance behaviour is characterised by two clearly separated arcs in the frequency domain, indicating that the overall electrode reaction is controlled by at least two rate limiting processes in series. The electrode process associated with the low frequency arc is mainly dependent on the H(2) concentration. Moreover, the electrode conductivity of the low frequency arc (sigma(L)) is independent of temperature and the polarisation potential. Based on these observations, the electrode process associated with the low frequency arc has been attributed to hydrogen dissociative adsorption/diffusion on the surface of Ni particles. The electrode process of the high frequency arc is also affected by the H(2) concentration and by oxygen partial pressure (P(O2)), however in contrast to the low frequency arc, the electrode conductivity associated with the high frequency electrode process (sigma(H)) showed a strong temperature dependence with an activation energy of similar to 162 kJ mol(-1) and it increases with increasing polarisation potential. This arc has been attributed to hydrogen transfer from the Ni electrode surface to the Y-TZP electrolyte surface, followed by a charge transfer process on the electrolyte surface near the interface region. The results of this study clearly demonstrate that the Y-TZP in the Ni cermet electrodes has little effect on the reaction mechanism, but plays an important role in modifying the electrode microstructure and kinetics of the fuel oxidation reaction. (C) 1999 Elsevier Science B.V. All rights reserved.