Preparation Of Cathode-supported Tubular Solid Oxide Fuel Cell With Liquid Antimony Anode And Study Of Electrolyte Stability

Traditional anodes materials of solid oxide fuel cells?SOFC?can not meet the practical application requirements when using solid carbon fuel directly,it is difficult for fuel particles to diffuse into the anode due to the difference of size between the fuel particles and the anode pores,which makes the conversion rate of solid state fuel lower than that of gas fuels.SOFC with liquid metal as anode has attracted wide attention on account of its excellent electronic conductivity,good mass transport and impurity tolerance with solid carbon fuels.Among metal materials,In,Sn,Sb,Pb and Bi can be used as liquid anode candidates for they all have lower melting point compared with the operating temperature of solid oxide fuel cells.The metal Sb and its oxides are both liquid in the working temperature range of SOFC,and Sb₂O₃ has oxygen ionic conductivity at the operating temperature,so Sb is considered as a liquid metal anode with a rising prospects.In this study,cathode-supported tubular cells were fabricated and successfully assembled into cathode-supported tubular liquid Sb anode solid oxide fuel cells?LAA-SOFC?.Their electrochemical properties were characterized at different temperatures to verify the possibility of assembling them into integrated stacks.Meanwhile,the stability of liquid Sb anode while using different solid electrolytes?GDC,SDC,YSZ?was studied.The corrosion mechanism of solid electrolyte under different experimental conditions was summarized and the corresponding improvement methods were put forward.The main research contents were as follows:?1?LSM tube cathode support with length of 4.5-5 cm,diameter of 1 cm and wall thickness of 0.5⁰.7 mm was successfully prepared by slurry-casting,and LSM-YSZ cathode functional layer and YSZ electrolyte were prepared on the surface of support by dip-coating method with liquid antimony?Sb?as metal anode.The peak power of LAA-SOFC was 12 mW·cm^-2,19.6 mW·cm^-2,27.7 mW·cm^-2 and 32 mW·cm^-2 at 650,700,750 and 800°C,respectively.The analysis of the electrochemical impedance spectra showed that the high cathode impedance was the main reason for the poor performance of LAA-SOFC.?2?The stability of GDC electrolyte in liquid Sb and Sb₂O₃ two corrosive media under chemical mode was studied.The residual metal Sb or Sb₂O₃ on the surface of electrolyte after the experiment was cleaned with HNO₃ and HCl solution,respectively,and scanning electron microscopy?SEM?and electron probe microanalyzer?EPMA?were used to observe the surface morphology,cross-section morphology and element distribution of electrolyte.It was found that the main reason for the corrosion of GDC electrolyte was the diffusion of liquid Sb and Sb₂O₃ along the grain boundary of electrolyte,which resulted in the grain falling off.The corrosivity of Sb₂O₃ to GDC electrolyte was obviously weaker than that of Sb.The stability of SDC electrolyte in liquid Sb was also studied under the same experimental conditions.The corrosion mechanism was verified the same as that of GDC.With La_0.6Sr_0.4Co_0.2Fe_0.8O_3-??LSCF?as cathode,liquid Sb as anode,the stability of GDC electrolyte in liquid Sb anode SOFC under electrochemical mode was studied by simulating the working environment of direct carbon fuel cell?DCFC?at 750°C.And the corrosion mechanism of electrolyte under chemical mode and electrochemical mode is put forward.The stability of the electrolyte decreases with the increase of current density.?3?The stability of YSZ electrolyte in chemical and electrochemical modes was studied,using the same experimental conditions and corrosive media as that of GDC electrolyte.The surface morphology,phase structure and element distribution of YSZ electrolyte after test were characterized,and Sb and Sb₂O₃ was found along YSZ electrolyte accompanied with the diffusion of Y₂O₃ and the phase transition of YSZ electrolyte were found.Difference from CeO₂ based electrolyte,the corrosion of YSZ is caused by the permeation of Sb and the diffusion of Y₂O₃.The corrosion of electrolyte in electrochemical mode mainly come from Sb₂O₃ and intensified with the increase of current density.