Electrochemical evaluation of Sr2Fe1.5Mo0.5O6-δ/Ce0.9Gd0.1O1.95 cathode of SOFCs by EIS and DRT analysis

Employing potent advanced materials to perform as the cathode of SOFC requires a profound investigation on the material's electrochemical response within the oxygen reduction reaction. Accordingly, in this research, electrochemical characteristics of Sr2Fe1.5Mo0.5O6-δ/Gd0.1Ce0.9O1.5 (SFM/GDC) air electrode was studied using electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) technique. SFM/GDC composite electrode sintered at 1050 °C shows the lowest polarization resistance of 0.23 Ω.cm2 at 800 °C. Three DRT peaks determined, and an LRΩ(QRH)G equivalent circuit is proposed for the EIS response, in which the Gerischer element was related to the low-frequency part. Two of the peaks indicated by DRT were associated to the Gerischer response, which reveals simultaneous occurrence of oxygen surface reaction and diffusion sub-processes during ORR. By temperature rising from 650 °C to 800 °C, Gerischer resistance (RG) reduces by 91%. Introduction of Pd nanoparticles into the electrode reduces the RG by 48% and 10% at 650 °C and 800 °C, respectively. The results demonstrate that at the intermediate temperature range, the SFM/GDC composite electrode requires improvement by surface decoration due to its insufficient surface exchange kinetics; however, significantly improved surface exchange kinetics is observed at higher temperature range without any surface modification.