Abstract:
Among perovskite anodes in solid oxide electrolysis cell (SOEC), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) has gained much attention due to its relatively high performance. However, the BSCF still suffers from chemical instability. In this study, partial substituting higher valance Ta5+ (5, 10, 15 and 20 mol%) at the B-site (Co2+/Fe3+) of BSCF was investigated to improve its structural stability. The Ba0.5Sr0.5(Co0.8Fe0.2)1-xTaxO3-δ (BSCFTax, 0 ≤ x ≤ 0.20) were synthesized by citrate-EDTA complexing method. The BSCF and BSCFTa0.05 exhibited the single phase perovskite while segregation of Ta2O5 and Ta3N5 were observed in other samples. The symmetrical half-cell having the yttria stabilized zirconia (YSZ) as an electrolyte (BSCFTa/YSZ/BSCFTa) were fabricated to determine the area specific resistance (ASR) of the electrode. BSCFTa0.10 shows the lowest ASR of 2.32 Ω·cm2 at 600°C. Comparing electrochemical performance and durability of single cells having undoped BSCF, BSCFTa0.10 and LSM-YSZ a basic anode, Ni-YSZ/YSZ/BSCFTa0.10 exhibited the highest performance and durability. The degradation rate of Ni-YSZ/YSZ/BSCF, Ni-YSZ/YSZ/BSCFTa0.10 and Ni-YSZ/YSZ/LSM-YSZ were 0.0123V·h-1, 0.0027V·h-1 and 0.0204V·h-1, respectively (operating at current density 0.45A·cm-2 in electrolysis mode, 80 h, 800°C and H2O to H2 ratio of 70:30). Doping with higher valence Ta5+ increased durability and chemical stability in BSCF but also decreased oxygen vacancy due to decreasing defect in the perovskite. However, electrochemical performance increased in Ta5+ doped BSCF, likely due to a proper balance between electronic and ionic conductivity in doped BSCF.
