Study On Preparation And Electrochemical Properties Of BSCF-GDC Cathode Materials For Solid Oxide Fuel Cell

Solid oxide fuel cell?SOFC?is an energy conversion device that could cleanly convert chemical energy to electrical energy with high efficiency,but the high operating temperature?800¹000??hinders its further commercial development.It has been concerned issues for science researchers to develop the intermediate-temperature?600⁸00??solid oxide fuel cell?IT-SOFC?.However,the lower operating temperature would commonly result in the rapid increase of polarization resistance for the traditional SOFC cathode materials,eventually influence the output performance for overall cell.Therefore,it is critical to develop new cathode materials with high-performance for developing IT-SOFC.In this thesis,through the preparation of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-?-Ce_0.9Gd_0.1O_2-??BSCF-GDC?nano-micron cathode composite materials with different structure and morphology,the ionic and electronic conduction region of cathode composites were rationally distributed,and the length of the three-phase boundaries?TPBs?were increased,which could reduce the polarization resistance of cathode materials,and thus achieve the purpose of reducing the SOFC operating temperature.The main study were divided into the following three parts.?1?The BSCF-xGDC?x=30,40,50;refer to the GDC addition content of 30,40,50wt.%?cathode composites were prepared by the solid-phase mixing method.The crystal structure and morphology of the composites,the polarization resistance of the electrode and the performance of the single cell were studied.The results showed that in the BSCF-xGDC composites prepared by the solid-phase mixing method,the GDC powders had good chemical compatibility with BSCF powders,but the distribution of different powders weren't enough uniform.Under the 650? operating temperature,the BSCF-40GDC had the smallest polarity?0.455?·cm²?.The tesing results of NiO-GDC|GDC|BSCF-xGDC single cells further showed that the single cell with 40wt.%GDC addition in the cathode showed the best electrochemical performance with the maximum power density(0.472 W·cm^-2)and the polarization resistance?0.0734?·cm²?in wet hydrogen?3%H₂O?at 650?.?2?The BSCF powders prepared by the sol-gel method were coated with GDC sol,and then calcined to obtain the core/shell structured BSCF-xGDC?x=30,40,50?,which consisted of the BSCF core and the nano-sized GDC continuous conductive shell.This core-shell structure with the ionic conductive particles surrounded by electronic conductive particles could effectively broaden the three-phase boundary area and enhance the oxygen-ionic conductivity,which made the polarization resistance of the cathode composites down to 0.443?·cm² at 650?.The tesing results of NiO-GDC|GDC|BSCF-xGDC single cells further showed that with 40 wt.%GDC addition in the cathode,the single cell showed the excellent electrochemical performance with the maximum power density(0.514 W·cm^-2)and the polarization resistance?0.0588?·cm²?in wet hydrogen?3%H₂O?at 650?.?3?Through the electrostatic spinning method,BSCF nano-powders with clear and complete cubic perovskite crystal phase could be prepared by calcining at 850?.Subsequently,the three-dimensional network structured BSCF-40GDC cathode composites was prepared by Pechini method by calcining at 800?.The GDC particles were uniformly distributed around the BSCF three-dimensional network fibers,which presented a reasonable layout of continuous ion-conducting and electron-conducting regions,and then further improve the electrocatalytic activity and gas permeability of the cathode materials.The electrochemical testing results showed that the polarization resistance of three-dimensional network structured BSCF-GDC composite cathode was only 0.292?·cm² at 650?,and the maximum power density of the NiO-GDC|GDC|BSCF-GDC single cell was increased to 0.672 W·cm^-22 and the polarization resistance is down to 0.055?·cm² in wet hydrogen?3%H₂O?at 650?.