In Situ Formation of Ba 3 CoNb 2 O 9 /Ba 5 Nb 4 O 15 Heterostructure in Electrolytes for Enhancing Proton Conductivity and SOFC Performance.

The in situ formation of a heterostructure delivers superior electrochemical properties as compared to the mechanical mixing, which shows great promise for developing new electrolytes for solid oxide fuel cells (SOFCs). Herein, in an SOFC constructed by the Ba 5 Nb 4 O 15 electrolyte and Ni 0.8 Co 0.15 Al 0.05 LiO 2-δ anode, an in situ formation of Ba 3 CoNb 2 O 9 /Ba 5 Nb 4 O 15 heterostructure is designed by Co-ion diffusion from the anode to the electrolyte during cell operation, resulting in improved ion conductivity and fuel cell performance. An abnormal phenomenon is observed that the SOFC based on the Ba 3 CoNb 2 O 9 /Ba 5 Nb 4 O 15 electrolyte delivered a peak power density of 703 mW/cm 2 at 510 °C, which is higher than that at 550 °C. Characterization in terms of X-ray photoelectron spectroscopy and X-ray diffraction verifies that the operating temperature affected the Co doping concentrations, leading to different conducting behaviors of the heterostructure. Furthermore, it is found that the heterojunction of Ba 3 CoNb 2 O 9 and Ba 5 Nb 4 O 15 can restrict the electron migration to avoid current leakage of the cell and simultaneously enhance the proton conductivity. These findings manifest the developed in situ Ba 3 CoNb 2 O 9 /Ba 5 Nb 4 O 15 heterostructure as a promising electrolyte for SOFCs.