Ba0·5Sr0·5(Co0·8Fe0.2)1-xTaxO3-δ perovskite anode in solid oxide electrolysis cell for hydrogen production from high-temperature steam electrolysis

Abstract

Among perovskite anodes in solid oxide electrolysis cell (SOEC), Ba0·5Sr0·5Co0·8Fe0·2O3-δ (BSCF) has gained much attention due to its dominantly high performance. However, the BSCF still suffers from chemical instability. In this study, the B-site of BSCF is partially substituted by a higher valence Ta5+ (5, 10, 15 and 20 mol%) to improve its structural stability - Ba0·5Sr0·5(Co0·8Fe0.2)1-xTaxO3-δ (BSCFTax, 0 ≤ x ≤ 0.20). It is found that doping with higher valence Ta5+ increases both chemical stability and electrochemical performance of BSCF. Although the BSCFTa0.10 shows the lowest oxygen vacancies indicating by the ratio of adsorbed oxygen vacancies (Oadsorbed) to lattice oxygen (Olattice), the electrochemical performance increases. The decrease in Co3+/Co4+ ratio results in increasing electronic conductivity in the anode. It is likely that proper amount of Ta5+ doping provide a balance between ionic and electronic conductivity in the anode and improved electrochemical performance. The symmetrical half-cells with electrolyte support (BSCFTa/YSZ/BSCFTa) are fabricated to determine the area specific resistance (ASR) and activation energy of conduction - BSCFTa0.10 shows the best performance. Cathode-supported Ni-YSZ/YSZ/BSCFTa0.10 also shows higher durability than Ni-YSZ/YSZ/BSCF (operating at current density −0.45 A cm−2 in electrolysis mode, 80 h, 800 °C and H2O to H2 ratio of 70:30).