Preparation And Properties Of M_xO_y-8YSZ (M=Ni, Fe, Zn) Electrolyte For Solid Oxide Fuel Cells

Solid Oxide Fuel Cell（SOFC）is a new type of power generation device that can directly convert the chemical energy of fuel into electrical energy,and has received extensive attention because of its environmental friendliness,high power conversion efficiency and fuel adaptability.SOFC consists of anode,cathode and electrolyte,Among them,electrolyte is the core component of SOFC,which largely determines the performance of SOFC.8 mol%Y₂O₃-stabilized Zr O₂（8YSZ）is commonly used as the electrolyte for SOFC,but it can only obtain good ionic conductivity at high temperature（1000°C）.However,the high operating temperature has caused many negative impacts on the commercial development of SOFC,such as difficulties in selecting materials for other cell components,increased manufacturing costs and deterioration of electrode stability.Therefore,reducing the operating temperature of SOFC is a necessary option to facilitate its commercialization.However,the decrease in operating temperature reduces the ionic conductivity of 8YSZ drastically,which leads to a sharp decrease in cell performance.Therefore,to accelerate the commercialization of SOFC,it is particularly important to improve the ionic conductivity of 8YSZ at low and intermediate temperatures（600-800°C）.In this paper,NiO-doped 8YSZ,Fe₂O₃-doped 8YSZ and ZnO/Fe₂O₃ co-doped 8YSZ electrolytes were fabricated via solid-state reaction.The relative density,phase composition,oxygen vacancy concentration,microscopic morphology and ionic conductivity of the electrolytes and the performance of the prepared cells were investigated using Archimedes drainage method,XRD,XPS,SEM and electrochemical workstation,respectively.The main research contents and results are as follows:（1）The NiO-doped 8YSZ electrolytes were fabricated via solid-state reaction,and the effects of NiO doping amount and sintering temperature on the phase composition,relative density,microscopic morphology,ionic conductivity of 8YSZ electrolytes and the performance of the prepared cells were investigated.The results show that the prepared samples formed a single-phase cubic fluorite structure.With the increase of NiO-doping content from 0 to 2.0 mol%,the relative density of samples first increased from 96.5%to99.0%and then decreased to 97.8%.The ionic conductivity of the samples was mainly affected by the NiO doping content and the sintering temperature,and the maximum electrolyte ionic conductivity was found as 0.064 S·cm^-1（800℃）when the NiO doping content was 0.5 mol%and the sintering temperature was 1500℃,and the peak power density obtained by the assembled single cell was 54.90 m W/cm².（2）The Fe₂O₃-doped 8YSZ electrolytes were fabricated via solid-state reaction,and the effects of Fe₂O₃ doping amount on the phase composition,relative density,microscopic morphology,oxygen vacancy concentration,ionic conductivity of the 8YSZ electrolytes and the performance of the prepared cells were investigated,and the effect of sintering temperature on the performance of Fe₂O₃-doped 8YSZ electrolyte was explored.The results show that the phase composition of 8YSZ electrolyte was not changed by Fe₂O₃doped.With the increase of Fe₂O₃-doping content from 0 to 2.0 mol%,the lattice constant of samples first decreased gradually from 5.1326?to 5.1270?and then increases to5.1358?,which was accompanied with the increase of the relative density from 96.5%to99.0%.In addition,XPS showed that the doping of 0.5 mol%Fe₂O₃ significantly increased the oxygen vacancy concentration of the 8YSZ electrolyte.When the Fe₂O₃ doping content was 0.5 mol%and the sintering temperature was 1400℃,the electrolyte ionic conductivity reached a maximum of 0.050 S·cm^-1（800℃）,which was 2.17 times higher than that of the pure 8YSZ sample(0.023 S·cm^-1)at the same temperature,and the peak power density obtained by the assembled single cell was 74.96 m W/cm².（3）The ZnO/Fe₂O₃ co-doped 8YSZ electrolytes were fabricated via solid-state reaction,and the effects of the ratio of ZnO/Fe₂O₃ co-doping on the phase composition,relative density,microscopic morphology,ionic conductivity of 8YSZ electrolytes and the performance of the prepared cells were investigated.The results showed that the 8YSZ electrolytes prepared with different ZnO/Fe₂O₃ co-doping amounts were all formed a single-phase cubic fluorite structure.With the amount of ZnO/Fe₂O₃ co-doping increases from 1.0 mol%to 2.5 mol%,the lattice constant of the samples gradually decreases from5.1458?to 5.1348?,and the relative density increases from 98.5%to 99.0%.In addition,the maximum electrolyte ionic conductivity was found as 0.049 S·cm^-1（800℃）when the amount of ZnO/Fe₂O₃ co-doping was set as 2 mol%,and the peak power density obtained by the assembled single cell was 62.8 m W/cm².