Low-temperature Solid Oxide Fuel Cells Based On Doped Ceria And Perovskite Composites

Solid oxide fuel cell(SOFC)is widely considered as one of the most promising energy conversion technologies due to its fuel flexibility,high energy conversion efficiency and low emission.Nowadays,high operational temperature is of the most limitation to the commercialization of SOFC.To address the high-temperature issue,typical solutions includes reducing the thickness of yttrium stabilized zirconia(YSZ)electrolyte and replacing the YSZ electrolyte with alternative material doped ceria.However,because of the complexity of thin-film technique and the reduction of Ce4+,they failed to enable the authentic commercialization of current SOFC technology.Recently,a breakthrough fuel cell technology called "electrolyte free fuel cell(EFFC)" has been successfully developed.In EFFC,through using the ionic and semiconducting materials to replace the electrolyte,the polarization loss resistances between electrolyte and electrodes will decline and the ionic conductivity will increase,thus the cell can function at 550? well.Such fuel cell device has a simple construction and low cost,suggesting a new concept for developing commercialized SOFC.In this study,we develop a series of EFFC devices based on doped CeO2 and perovskite composites to gain an insight into the new technology of EFFC:(1)after testing the performances of the EFFCs based on different ratio SDC-SSC composites in different temperatures,it is found the EFFCs can operate well in the range of 475 ? to 550 ? and the power density ranges from 367-741 mW/cm2.Through studying the influence of ratio between SDC and SSC to the performance of EFFCs,it is found when the ratio between SDC and SSC is 6:4,the balanced ionic and electronic conductivities are achieved and the device output was optimized to be 741 mW/cm2 at 550?.The EIS result illustrate that the improved performance is due to the increasing of TPB by introducing the SSC into SDC.(2)The SDC-SFM composite has been successfully prepared for the electrodes of traditional SOFCs and middle membranes of EFFCs,respectively.A maximum power density of 841 mW/cm2 has been achieved at 550? by the EFFC device and the device can be measured at 550? for about 24h.while the SDC electrolyte SOFC can just reach 326 mW/cm2 at the same temperature.The EIS studies showed a much smaller charge transfer resistance for EFFC than that of the conventional one.The Schottky junction which is identified to be formed at H2 side can certainly prevent the electron from passing through the internal device.Thus the EFFC can get a higher output and avoid the short circuit problem at the same time.(3)N type semiconductor LST and ionic conductor SCDC composite has been successfully demonstrated in EFFC.The EFFC using 6SCDC-4LST composite can reach a high OCV of 1.16V and power output of 840 mW/cm2 at 550 ?,while the conventional SOFC with SDC electrolyte exhibits a highest power output of 462 mW/cm2 at the same operational temperature.The EIS results reveal that the resistances of EFFC for each electrochemical process are smaller than that of conventional SOFC.Besides,PN junction is verified at the air side of the EFFC.Because of the stable existence of junction at air side,the EFFC can operate at 550? for about 14 hours stably.