Electrospinning Preparation And Properties Study Of Pr₂NiO₄-based SOFCs Cathode Materials

Solid oxide fuel cells（SOFCs）technology can effectively convert the chemical energy in fuel into electricity through electrochemistry process,which has attracted researchers’attention due to its high conversion efficiency and zero production of pollutants.At present,in order to meet the high performance of fuel cells at medium-low temperature,electrodes of different materials and optimized the microstructure of electrode materials were developed.Among these systems,Ln₂Ni O_4+δ（Ln:Lanthanide）with K₂Ni F₄type structure consists of alternating layers of perovskite and halite,which can be used as highly mixed oxidation/electron conductors due to interstitial oxygen and electron conduction in perovskite layers.In the family of Ln₂Ni O_4+δoxides,Pr₂Ni O_4+δhas been widely studied because of its highest diffusion coefficient of oxide ions and surface exchange coefficient.However,most studies were focused on the preparation of powder materials and these materials possessed the low electrocatalytic activity.Therefore,in order to solve these problems,In this thesis,Pr₂Ni O_4+δwas selected as the cathode material to prepare nanofibers by electrospinning process,together with the strategy of element doping and surface modification,the microstructure and electrocatalytic activity of electrode materials were enhanced.The main research process and conclusions were as follows:（1）Pr₂Ni O_4+δ（PNO）hollow nanofibers were prepared by controlling the ratio of PVP to solute via electrospinning technology.The results show that the porous network fiber structure contributes more specific surface area and increased the number of active sites,compared with PNO powders prepared by traditional methods.In addition,the unique hollow tubular structure could accelerate the adsorption and dissociation of oxygen,providing a channel for oxygen transport,thereby demonstrating excellent electrochemical performance.In addition,the symmetrical cell PNO fiber cathode shows a lower polarization impedance than the powder material,with an R_Pof only 0.29Ω·cm²at 700°C,and accelerated ionic mobility,with a lower activation energy（1.02 e V）.Meanwhile,the power density of as-prepared Ni O-SDC|SDC|PNO nanofibers cathode single cell is up to 567 m W/cm².（2）Pr cationic defective nanofibers(Pr_0.9La_0.1)_1.9(Ni_0.7Cu_0.3)_0.9Mn_0.1O_4+δ(（PL）_1.9NCMn)electrode materials were prepared by electrospinning combined with A/B element doping.The introduction of Cu elements in the B-site lattice can lower the synthesis temperature and reduce the polarization impedance,and the high-valence Mn element is used to increase the interstitial oxygen concentration in the lattice.Conductivity relaxation（ECR）analysis proves that higher oxygen vacancy concentration and interstitial oxygen in lattice structure could improve the hydration properties of materials,thereby increasing the proton conductivity of materials.The results show that the R_Pof（PL）_1.9NCMn nanofiber cathode is only 0.101Ω·cm²at 700℃in wet air（3vol.%H₂O）.In addition,the power density of Ni O-BZCY|BZCY|（PL）_1.9NCMn single cell under the condition of fuel mode（FC）reaches 894 m W/cm²,and the current density is about 1563 m A/cm²under the electrolytic model（EC）of 1.3 V voltage.In the subsequent 60h stability test,no obvious voltage attenuation can be observed.（3）On the basis of（PL）_1.9NCMn nanofiber electrode,different concentrations of nickel nitrate solution were impregnated,and the improved the electrocatalytic activity can be observed under the condition with the impregnation concentration of 0.6 mol/L.The microstructure of the nanofibers was optimized by a reduction treatment under the following H₂atmosphere.The cationic defects at Pr site generate a general driving force to precipitate Ni/Mn elements at B site,which are reduced on the surface of nanofibers in the form of metal Ni and Ni Mn alloy particles,and the electrochemical performance is improved by the synergistic effect of the Ni O formed under heat treatment and Ni/Mn alloy particles.The oxygen partial pressure test results show that the existence of nanoparticles changes the main reaction process of the electrode,accelerates the dissociation rate of gas molecules,and improves the overall electrochemical performance.The R_Pvalue of symmetrical cell is 0.125Ω·cm²at 650℃,and the power density of single cell can reach 684 m W/cm².Similarly,the voltage is basically stable at 600℃for 60 h,showing a good short-term stability.