International Journal of Hydrogen Energy, Vol.42, No.8, 5284-5294, 2017
Oxygen transportation, electrical conductivity and electrochemical properties of layered perovskite SmBa0.5Sr0.5Co2O5+delta
Oxygen transportation properties of SmBa0.5Sr0.5CO2O5+delta (SBSC55) layered perovskite has been investigated as a potential cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This research includes the following items: (1) structural characteristics, thermogravimetric behavior, oxygen permeation, chemical bulk diffusion coefficient (D-chem), and (2) the electrochemical performance of long-term testing carried out to evaluate its electrochemical stability. The D-chem values for SBSC55 cathode are 2.6 x 10(-6), 9.1 x 10(-6) and 1.8 x 10(-5) cm(2) s(-1) at 500 degrees C, 600 degrees C, and 700 degrees C, respectively. The oxygen permeation flux for SBSC55 membrane with 1.0 mm thickness increased from 0.143 mL min(-1) cm(-2) at 500 degrees C to 0.406 mL min(-1) cm(-2) at 800 degrees C under synthetic air at a flow rate of 50 mL min(-1), helium at a rate of 25 mL min(-1). The activation energies of oxygen permeation for the high temperature region (700-800 degrees C) and low temperature region (500-650 degrees C) are 23.67 and 6.96 kJ mol(-1), respectively. It suggested that oxygen diffusion for high temperature range is surface exchange process, low temperature range is bulk diffusion process. The long-term test of cathodic polarization resistance for SBSC55 vertical bar SDC vertical bar SSBSC55 half-cell at 600 degrees C during 96 h has been carried out with an increase rate of 0.30% h(-1). Based on the impedance spectra with various oxygen partial pressure results, the rate-limiting process of ORR is determined that the oxygen ion transfer from triple-phase boundary (TPB) and/or two-phase boundary (2PB) sites of cathode is major with the minority of charger transfer reaction. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.