Design And Performance Control Of Iron-based Perovskite Cathode Materials For Solid Oxide Fuel Cells

Solid oxide fuel cell(SOFC)are getting more and more attention from researchers due to their low pollutant emissions and higher energy conversion efficiency.However,higher operating temperatures are the main factors limiting their development.In order to develop SOFC and promote its commercialization process,it is imperative to lower the operating temperature of the SOFC.For the cathode polarization resistance,lowering the SOFC operating temperature will rapidly increase the cathode polarization resistance.Compared with other components,the oxygen reduction on the cathode side requires the highest activation energy,and the kinetics of chemical reactions is slower.Therefore,the development of cathode materials with high oxygen reduction activity at low temperatures is the top priority to promote the low temperature of SOFC,so we take the cathode materials as the research center.Among the cathode materials,cobalt-based materials can still maintain good electrochemical performance at low temperatures,but the cobalt-based perovskite cathode materials have poor thermal matching with the electrolyte,the cell is prone to cracking when working at high temperatures,and the raw materials are expensive.In view of the shortcomings of cobalt-based cathodes,iron-based perovskite oxides are expected to become alternatives to SOFC cathodes due to their good thermal expansion coefficient and low cost.However,they have poor electrochemical performance at lower temperatures(<700?),which has become the main bottleneck for the future development of iron-based materials.Based on iron-based perovskite cathode materials,we found that Ba_0.5Sr_0.5FeO_3-?iron-based materials have been reported in the literature,but their oxygen reduction ability is low and electrochemical activity is poor.We designed a part of yttrium ion doped at the B site to improve its catalytic activity and electrochemical activity.Ba_0.5Sr_0.5Fe_0.875Y_0.125O_3-?(BSFY)was successfully prepared by the sol-gel method,testing and characterization can prove that BSFY has a good pure-phase perovskite structure.The subsequent test shows that BSFY has more oxygen vacancies,and the conductivity in the range of 400?800? is acceptable in iron-based materials.The SDC is used as the electrolyte to form a symmetrical cell,and its area specific resistance is only 0.020?cm² at 700?.It was assembled into an anode-supported single cell with a structure of Ni-SDC/SDC/BSFY,with a peak power density of1052mWcm^-2 at 700?.Such electrochemical performance is better in iron-based materials.Use the Ba FeO₃as the parent material,a new type of cobalt-free perovskite cathode co-substituted by strontium and gallium at the A/B site was designed and developed,and Ba_0.75Sr_0.25Fe_0.875Ga_0.125O_3-?(BSFG)was prepared using a simple solid-state reaction.Using Rietveld refinement shows that BSFG has a good cubic perovskite phase.In the working temperature range(500-700?),the non-stoichiometric oxygen value of BSFG is about 0.49?0.57,which is a relatively high oxygen vacancy value.The measured thermal expansion coefficient(TEC)is 17.8×10^-6K^-1,such a small value can prove that BSFG has good thermal compatibility with the electrolyte.At 600?,area specific resistance of the symmetrical cell is only 0.074?cm²,and the peak power density of the anode-supported single cell is as high as 1145mWcm^-2,which is much higher than those of recently reported iron-based materials and even competitive with those of top-performing cobalt-based cathodes materials.A short-term constant current mode(1000mAcm^-2)test of the BSFG-based single cell was performed at 600? to verify its durability.The single cell provided a stable output voltage within 3000minutes without significant performance degradation.First-principles calculations were used to explore the reasons for the excellent activity and durability of the BSFG electrode regarding the oxygen reduction reaction.This provides a new idea for the rational development of high-activity,high-performance perovskite-type low-temperature SOFC cathode materials,and proves the broad potential application space of BSFG cathode materials.