Study On Electrochemical Performance Of LaPrNiO Cathode Of RP Type At Modified GDC Electrolyte

Cathode and electrolyte are important components of SOFC and their performance has great influence on the SOFC. Recently, Ruddlesden –Popper(RP)type of layered perovskite cathode materials have been gradually being valued, because it has high ionic conductivity, high oxygen diffusion capacity and high surface exchange capacity in intermediate temperature, and it will become one of the most promising cathode materials in IT-SOFC. Because Gd0.1Ce0.9O1.95(GDC) has higher ionic conductivity in intermediate temperature with RP type cathode material matching higher, scholars pay more attention to it. But the inevitable existence of Si O2 impurities in GDC materials of business greatly affect the grain boundary resistance, which leads to the decrease of the performance. Studies show that adding proper amount of Fe2O3 can effectively clear the Si O2, however, the negative effect is that the polarization resistance becomes larger and the surface property becomes worse, this is very detrimental to the application of cathode materials. This dissertation will improve the surface properties of GDC electrolyte, and La Pr Ni O cathode of RP stype was obtained by Pr doped A position of La3Ni2O7. Then the GDC is combined with the RP cathode structure to expect a higher performance.Firstly, the electrochemical properties of GDC electrolyte add Fe2O3 were studied.The results indicated that Fe2O3 and Si O2 can occur chemical reaction, and because the melting point of reaction product is lower than 1400 o C, it is precipitate on the surface of GDC electrolyte which seriously affect the performance of GDC surface and electrode. Al2O3 plate was covered on the two surfaces of the GDC electrolyte respectively, in order to remove Fe2 Si O4 on the surface, the electrode and the electrolyte can be more in good contact and improve the electrochemical performance.The polarization resistance of GDC electrolyte is reduced by about 50%.Secondly, the La3-x Prx Ni2O7(x=0.0-3.0) cathode materials were synthesized under the same conditions with sol-gel and XRD phase analysis showed that,the crystal structure of La3Ni2O7 was transformed into Pr2 Ni O4 with the increase of Pr doping amount. The test of high temperature conductivity by DC four terminal method found that a small amount of Pr(x=0.4) doped casued the highest conductivity, and its maximum value is 70 Scm-1. When the content of Pr increases to x=2.2, the crystal structure changed which led to the decrease of the maximum conductivity ratio of La3Ni2O7 phase by nearly 50%. Fitting Arrhenius curve showed that low temperature region close to linear, which is consistent with the small polaron hopping mechanism.Thermal expansion performance analysis shows that the La3Ni2O7 structure has themost similar thermal expansion coefficient(TEC) with GDC.The cathode material La3-x Prx Ni2O7 was made into a half cell test on the GDC electrolyte that electrochemical performance was improved. AC impedance test results show that when the doping amount of Pr is x=1.0, the minimum polarization impedance of the La3Ni2O7 structure is obtained, and the polarization resistance is0.22 Ωcm2 under 800 o C. The impedance analysis under different oxygen partial pressure shows that the main effect of the electrode process is the transfer of the charge in the three phase reaction zone(TPB). Polarization curves show that the higher the temperature, the greater the current density under the same over potential,and when the doping amount of Pr is x=1.0, the current density is 260 m Acm-2 under the over potential of 0.1 V. The cross section test of the half cell shows that the electrode is in good contact with the electrolyte, and the cathode thickness of each ratio is almost the same, which shows that the electrochemical performance test is basically true and effective.Finally, because the La2 Pr Ni2O7 cathode has the best electrochemical performance under the La3Ni2O7 structure. So, Ni-GDC for anode, La2 Pr Ni2O7 as the cathode, GDC electrolyte that electrochemical performance was improved made of electrolyte supported single cell. Test results show that the open circuit voltage is about 0.8-0.9 V,and the maximum output power density is 223 m Wcm-2 at 800 o C.In summary, the La2 Pr Ni2O7 cathode is used to the GDC electrolyte, which makes the electrochemical performance of the electrode and the electrode electrochemical performance and battery performance has greatly improved, the polarization resistance reduced 60% to La3Ni2O7. The determining step of the electrode reaction process is the charge transfer process in TPB, which indicates that the conductivity of the material should be improved in order to improve the performance further.