Electrochemical Characterization of Ni/ScYSZ Electrodes as SOFC Anodes

Investigations of Ni/ScYSZ cermets were performed by electrochemical impedance spectroscopy (EIS) using different symmetric designs: electrolyte supported (ESC) and anode supported (ASC) cells. The obtained spectra were analyzed using distribution of relaxation times (DRT), and complex non-linear least squares fitting (CNLS). Depending on the cell design, one or two low frequency gas transport related processes have been identified, and fitted with generalized finite Warburg (GFW) elements. One was related to gas diffusion in a stagnant layer above the anode (ESC+ASC), and the other to gas diffusion in the anode support layer (ASC). A higher frequency process has also been identified, and correlated to the charge transfer (CT) combined with ionic conduction in the ceramic matrix. This has been fitted using a transmission line model (TML), which correlates the exhibited responses with the expected physical processes. Values of the ionic conductivity of the backbone structure, as well as the line specific resistance (LSR) for the charge transfer process have been determined. The impact of cell design on performance was found to be non-negligible. The cells with anode supports showed significantly lower resistance values associated with the TML electrode related processes.