Study On The Electrode And Electrolyte Materials For Medium And Low Temperature SOFCs

Lowering the operating temperature of solid oxide fuel cell?SOFC?has become a trend in this field,and developping excellent electrode and electrolyte materials for low temperature application is the key.Sr₂CoRO₆?R=Mo,Nb?double perovskite oxide is a potential medium and low temperature electrode material,and their conductivity and conducting mechanism were studied in this dissertation.In addition,La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85?LSGM?is a promising electrolyte material at intermediate temperature,but its performance is still not satisfactory at lower temperatures,so in this dissertation we proposed a method based on two-phase combination to improve the performance of LSGM.Solid state method was used to synthesize Sr₂CoRO₆ double perovskite materials,and their valence state,crystal structure and conductivity were analyzed.Their conducting mechanisms were proposed.X-ray photoelectron spectra revealed that the dominated oxidation state was Co2+ in Sr₂CoMoO₆ but Co3+ in Sr₂CoNbO₆.The crystal lattice structures of Sr₂CoRO₆ were identified by XRD,and their corresponding parameters were calculated by using Rietveld method.The refined crystal structures of Sr₂CoRO₆ have been used to construct their own conducting channel model.And the electrical conductivities under different oxygen partial pressure?PO2?were measured by using a four-probe method.The results show that the electrical conductivity of Sr₂CoMoO₆ in air(0.36 S·cm^-1,973 K)is much lower than that of Sr₂CoNbO₆(7.81 S·cm^-1,973 K).The conductivity of Sr₂CoMoO₆ increased with the decrease of PO2 and reached 2.05 S·cm^-1 while PO2 = 10^-21 atm.However,the conductivity of Sr₂CoNbO₆ decreased significantly while the oygen partial pressure decreased.This phenomenon has been well explained by the conducting channel model.?100-x?wt.% La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85?LSGM?-x wt.% Ce_0.8Gd_0.2O_1.9?GDC??x=0,5,10,20?electrolytes were prepared by solid-state reaction.The composition,microstructure and electrical conductivity of the samples were investigated.At300⁵00 °C,the grain resistances and grain boundary resistances of electrolytesincrease with the increase of x;above 650 °C,the total resistances first decrease and then increase with the increase of x,reaching the highest value while x=5.The battery test revealed that the performance of single cell using 95 wt.% LSGM-5 wt.% GDC as the electrolyte reached the highest,with the maximum power density and current density of 192 mW·cm^-2 and 720 mA·cm^-2 at 800 °C,respectively.La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85-(Li_0.48Na_0.52)₂CO₃ composite electrolytes were prepared by infiltration method.The effect of different contents of PMMA pore forming agent on the morphology and conductivity was discussed.The results show that the porosity of the LSGM matrix increases with the increase of PMMA content;and the conductivity of the composite electrolytes also increases with the increase of PMMA content,reaching 0.09 S·cm^-1 while the content of PMMA was 40 wt.% at 600 ?.