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-delta/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 degrees C shows the lowest polarization resistance of 0.23 Omega.cm(2) at 800 degrees C. Three DRT peaks determined, and an LR Omega(QR(H))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 degrees C to 800 degrees C, Gerischer resistance (R-G) reduces by 91%. Introduction of Pd nanoparticles into the electrode reduces the R-G by 48% and 10% at 650 degrees C and 800 degrees 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.