Performance Evaluation Of A-Site Cation-Deficient Non-Cobalt-Based Perovskite Oxides As The Cathode For Intermediate-to-Low Temperature Solid Oxide Fuel Cells

Solid oxide fuel cell（SOFC）is an energy device and is capable of directly converting chemical fuels into electricity.It has attracted much attention due to unique advantages,including fuel flexibility,high energy conversion efficiency,all-solid state and low emission.SOFC nonetheless has not been widely commercialized due to the problems associated with their high operating temperature（800-1000°C）,especially the high cost and poor stability.Lowering the SOFC operating temperature is urgent.With the decrease of operation temperature,the lack of the cathode activity also becomes a major problem,limiting the development of SOFC.Therefore,the development of cathode materials with high activity at low and intermediate temperatures is crucial for practical SOFC application.（1）First,we synthesized cobalt-based perovskite oxide Sr Ta_0.1Fe_0.9O_3-δas the SOFC cathode material by high-temperature solid-phase method.The effects of the doping Ta⁵⁺into the B-site of Sr Fe O_3-δ（SF）perovskite were investigated,which included the effects on crystal structure,electrical conductivity and oxygen reduction reaction（ORR）catalytic activity.It is found that Sr Ta_0.1Fe_0.9O_3-δ（STF）has a good cubic crystal structure at room temperature.The results of thermogravimetric analysis（TGA）and iodometric titration show that Sr Ta_0.1Fe_0.9O_3-δhas a higher oxygen vacancy concentration relative to Sr Nb_0.1Fe_0.9O_3-δ（SNF）and SF.The thermal expansion coefficient（TEC）and electrical conductivity of STF both decrease compared to SF.The STF exhibits good ORR catalytic activity with an area specific resistance（ASR）value of only 0.15Ωcm²at 600°C,which is better than Sr Nb_0.1Fe_0.9O_3-δunder the same test conditions.At 650°C,the peak power density of the STF electrode is 891 m W cm^-2.To further enhance the ORR catalytic activity of the STF cathode material,30 wt%Sm_0.2Ce_0.8O_1.9（SDC）electrolyte powder was mixed with STF.The results show that the introduction of 30 wt%SDC effectively improved the electrochemical performance of STF.The ASR of STF+SDC cathode is only 0.115Ωcm²at 600°C,and the anode-supported single cell obtained the peak power density（PPD）1118m W cm^-2at 650°C.（2）Then,we synthesized A-site cation-deficient perovskite materials,Sr_1-xTa_0.1Fe_0.9O_3-δ（x=0,0.02,0.05,0.10 and 0.20）.All S_1-xTF materials yield a Pm-3m cubic perovskite structures and show good chemical compatibility with the SDC electrolyte.Both TEC and electrical conductivity decrease with the increase of A-site cation deficiency.Among them,S_0.95TF shows the best electrochemical performance,with an ASR value of only 0.095Ωcm²at 600°C,33%lower compared to the STF.S_0.95TF also has good resistance to CO₂poisoning,and the ASR can recover to it’s initial value after removing CO₂in air.Furthermore,the SDC-supported symmetrical cell with the S_0.95TF electrode displayed superior stability of～240 h at 600°C.Single cells consisting of Ni+SDC anode,SDC electrolyte and S_0.95TF cathode were also fabricated and tested,and the PPD reaches1140 m W cm^-2at 650°C,which is significantly better than STF.