Computing approach of cathodic process within solid oxide electrolysis cell: Experiments and continuum model validation

Classical solid oxide fuel cell anode (Ni–cermet) could be employed as solid oxide electrolysis cell cathode. Ni–cermet has been synthesized and tested as solid oxide electrolyzer cathode using three-electrode techniques between 700 °C and 900 °C. yttria stabilized zirconia was used as the electrolyte and Pt as the counter electrode. Polarization curves and impedance spectra have been analyzed for two gas compositions. The presented results demonstrated an influence of Ni–cermet electrode behavior upon gas composition and temperature. The present results highlight a mechanism changing on Ni–cermet electrode upon gas composition. In a second part, a one-dimensional steady state model is developed to predict the cathodic behavior of Ni–cermet. This model takes into account mass and charge conservation, transport of species and reaction kinetics. It considers the porous electrode to be a homogeneous medium characterized. The influence of varying chemical and electrochemical steps kinetic on the shape of polarization curves is discussed. At high overpotential values the model with two rate-limiting steps has been validated using numerical optimization method.

► Ni–cermet electrode tested in electrolysis mode.
► Three-electrode techniques and electrochemical impedance spectroscopy were used.
► Electrode behavior depends on steam/hydrogen ratio.
► Continuum model was solved for two reaction paths.
► Modeling was validated and there is more than one rate-limiting step.