Electrocatalytic Performance Of Ruddlesden-Popper Layered Iron-based Perovskites

Solid oxide fuel cell(SOFC),as an energy conversion device with high energy conversion efficiency,clean and environmental protection,and wide range of fuel choices,is considered to be one of the promising power generation methods in the future.Reducing the operating temperature of solid oxide fuel cells is the current research trend.However,reducing the working temperature will also greatly reduce the catalytic activity of the electrode.Therefore,the development of electrode materials with good catalytic activity and stability at medium and low temperatures has become the focus of current research on medium temperature solid oxide fuel cells.Ruddlesden-Popper(R-P)type oxide Sr₃Fe₂O_7-?is a mixed ionic-electronic conductor(MIEC)with high oxygen concentration,catalytic activity and stability,and is considered to be a very promising cathode material for IT-SOFC.In this study,Sr₃Fe₂O_7-?cathode material was used as the matrix,and the A-site and B-site and co-doping methods of A-site and B-site were used to improve the material properties.In this paper,the effects of La doping on the structure and properties of Sr₃La_xFe₂O_7-?(SLFx)oxide were systematically studied first.The experimental results showed that the conductivity of the samples increased with the increase of La doping amount.The electrical conductivity of SLF10 at 450?is 112.79 S cm^-1.At 700?,the polarization impedance of SLF10 is the smallest(0.14?cm~2),and the maximum power density is0.77 W cm^-2.The cathode overpotential of SLF10 was the lowest at the same current density,and the current density was-213.3 and 146.3 m A cm^-2 when the cathode overpotential of SLF10 was-21.5 and 45.1 m V at 700?,respectively.Secondly,the effects of La/Ni co-doping on the structure and electrochemical properties of Sr₃Fe₂O_7-?were studied.La/Ni co-doping can significantly increase the oxygen vacancy concentration and electrical conductivity of the cathode,and reduce its polarization resistance.The conductivity of Sr_2.9La_0.1Fe_1.9Ni_0.1O_7-?(SLFN)reaches112.6 S cm^-1 at 400°C.The polarization resistance of SLFN is only 0.11?cm~2 at700?,and the maximum power density can reach 1.01 W cm^-2.The current densities of SLF10 were-121.6 and 121.4 m A cm^-2 when the cathode overpotentials were-21.0and 21.4 m V at 700?,respectively.Finally,the effect of Pr doping on the structure and electrochemical properties of Sr₃Fe₂O_7-?was investigated.Through the test of electrical conductivity,it is found that the electrical conductivity of the material increases with the increase of Pr content.Sr_2.9Pr_0.1Fe₂O_7-?showed the best electrochemical performance,with a polarization impedance of 0.09?cm~2 and the maximum power density of 0.95 W cm^-2 at 700?,and there was no obvious decline in continuous operation for 60 h.