| Cathode is one of the most important components of the solid oxide fuel cells (SOFCs). And the performance of cathode plays a decisive role on the output performance of SOFCs. In recent years, people have been tried their best to find a kind of novel cathode material which has better catalytic activity at low temperature and higher stability at high temperature. Recently, more and more attention has been focused on K2NiF4-type perovskite-like oxide made up of the alternating ABO3perovskite layers and AO rock salt layers. This kind of material exhibited good mixed ion and electron conductivity in combination with higher surface diffusion coefficient for oxygen and higher catalytic ability for oxygen reduction reaction in the medium temperature area. Thus K2NiF4-type perovskite-like oxide are potential candidates for SOFC cathode materials.A mixing of SOFC cathode materials and electrolyte materials with a certain ionic conductivity can make the TEC of cathode materials matched better with electrolyte, and triple-phase boundary (TPB) at cathode electrolyte interface could be expanded to the whole cathode, thus effectively reduce the internal resistance losses caused by polarization on the cathode. Pr-doped ceria Ce1-xPrxO2-δ is a kind of low ionic transference number mixed conductors, when Pr molar ratio excess0.2it could give higher oxygen ionic conductivity than traditional electrolyte Ce0.8Gd0.2O1.9. While the oxygen ionic conductivity of Ce0.8Pr0.2O2-δ is not the highest in Ce1-xPrxO2-δ series, it has appropriate TEC and mechanical behavior. For this reason, we expect to introduce Ce0.8Pr0.2O2-δ into Lao.6PrSro.4Ni04+s could obtain composite cathodes with better electrochemical performance.We synthesized LPSN and CPO powder materials by sol-gel method, and then prepared (1-xwt%)LPSN-(xwt%)CPO (x=0,10,20,30,40,50) series composite cathodes by means of mechanical mixture, abbreviated as LPSN-xCPO (x=0,10,20,30,40,50). There were good chemical compatibility between LPSN and CPO (GDC), but GDC and CPO reacted with each other at1000℃. The conductivity of composite cathodes all decreased inordinately compared with pure LPSN, and activation energy fitting from conductivity data all increased slightly. The average thermal expansion coefficient of the composite cathodes all increased slightly compared with LPSN, but still matched well with GDC.LPSN-40CPO exhibited the minimum polarization resistance among the LPSN-CPO series. The polarization impedance of LPSN-40CPO tested at700℃in air was0.22Qcm2, which was only1/8of pure LPSN under the same conditions. Impedance spectroscopy measured under different oxygen partial pressure consists of two arc, high frequency arc was contributed by oxygen adsorption, dissociation and diffusion process, and low frequency arc represents the oxygen transport inside the porous cathode. Ball-milling could open the aggregate inside the CPO powder, thus CPO powder could more evenly attached to the surface of LPSN, so we can get composite cathode with better electrochemical performance. The research of the electrochemical performance of the composite cathodes prepared under different sintering temperature and sintering time determined the optimum preparation conditions of the composite cathode was1050℃sintering3h.LPSN-40SDC exhibited the best electrochemical performance in LPSN-SDC (prepared by GNP method) series, but the pre-sintering temperature of GDC (SDC) prepared by glycine-nitrate combustion method was only800℃, the GDC (SDC) particle was sintered seriously after a1000℃high temperature calcined in the process of preparing cathode. Instead of expanding the TPB, the GDC (SDC) blocked the pores thus hindered the transport of the gas, which caused LPSN-SDC(GDC)(prepared by GNP method) showed poor electrochemical performance. The polarization resistance of LPSN-40SDC(GDC)(prepared by sol-gel method) composites decreased in a large distant than pure LPSN, at700℃the polarization resistance of LPSN-40GDC and LPSN-40SDC tested in air were separately0.18Qcm2and0.22Qcm2, the comparison of electrochemical performance of LPSN-CPO and LPSN-GDC(SDC)(prepared by sol-gel method) composite cathodes on GDC electrolyte showed that due to the existing of cracks on the LPSN-CPO and GDC contact surface, although the CPO ionic conductivity was higher than GDC and SDC, the electrochemical performance of LPSN-CPO series was worse than LPSN-GDC(SDC) series.The open circuit voltage of a single GDC electrolyte support type cell with LPSN-40CPO as cathode at700℃was0.78V, due to the larger electrolyte ohm impedance, the maximum output power density of the cell was only85mWcm-2. YSZ-GDC double-layer membrane anode support type single cell due to the introduction of GDC isolation layer which has better chemical compatibility and thermal matching with the composites, thus not only guaranteed a higher open circuit voltage, but also reduced the ohm impedance and polarization impedance effectively, at700℃the maximum output power density of the cell increased to317mWcm-2... |
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