Symmetrical cells consisting of Ni-Y_0.20Ti_0.18Zr_0.62O_1.90 (Ni-YZT) cermet electrodes on a Ni-YSZ support have been investigated with respect to the hydrogen/water partial pressures. Impedance spectra at open circuit potential were obtained as function of temperature and analysed in terms of a fractal finite length Gerischer Impedance. For fine and coarse microstructures of the Ni-YZT electrodes, a consistent set of model parameters could be obtained. The results indicate that surface diffusion rather than bulk diffusion plays a role in the hydrogen/water reaction but also that a fine-grained fraction in the mixed conducting YZT phase is advantageous for the overall electrode performance and the surface exchange reaction.