PrBa _1-x Sr _X Co _2-y Ni _Y O _{5 + δ And Cation Vacancy Synthesis And Properties Of The Cathode}

The cathode materials with highly electrochemical performance plays one of keycomponents in Solid Oxide Fuel Cells (SOFCs)。At low operating tamperatures(400-600oC), the cathode materials with highly electrocatalytic activity have animportant significance for improved power in SOFC. In this thesis, PrBa1-xCo2O5+δ,Pr1-xBaCo2O5+δ, PrBa1-xSrxCo2O5+δ, and PrBaCo2-xNixO5+δcathodes have beensynthesized based on mixed ionic and electronic conductor (MIEC) PrBaCo2O5+δwithdouble perovskite structure, through the cation-deficiency and doping strategy. In orderto develop new cathode materials with highly electrochemical performance, goodcompatibility between cathode amd electrolyte, and strong stability, these materials havebeen investigated systematically, and evaluated as cathodes for intermediate-orlow-temperature SOFCs,Firstly, PrBa1-xCo2O5+δ(x=0-0.1) cathode materials were synthezied by aconventional solid-state reaction. These compounds have the good compatibility withCGO electrolyte at high temperature. The Ba-deficiency leads to an increase inelectrical conductivity, a decrease in the thermal expansion coefficient, andimprovement of electrochemical performance for cathode. PrBa0.94CoO5+δcathodeexhibits the lowest polarization resistance,0.042Ω cm2at600oC. The cathodicoverpotential of-15mV was obtained at the cathodic current density of-152mA cm-2.Secondly, Pr1-xBaCo2O5+δ(x=0.02-0.1) cathode materials were synthesized. Thesematerials show the high electrical conductivity and highly electrochemical performance.At550oC, Pr0.96BaCo2O5+δcathode has a polarization resistance of0.25Ω cm2. Thecathodic overpotential of-56mV was obtained at the current density of-78mA cm-2at550oC. Impedance spectra at various oxygen partial pressures at different temperaturesdetermine the rate-limiting process for oxygen reduction reaction on PrBa0.94CoO5+δandPr0.96BaCo2O5+δcathodes.PrBa1-xSrxCo2O5+δ(x=0.1-0.5) cathode materials were synthesized by solid-state reaction. The Sr dopant effectively enhances the electricalconductivity. In the temperature of100-750oC, the electrical conductivities of theseoxides reach700-3000S cm-1, which is responsible for the high performance ofcathodes. At550oC, PrBa0.7Sr0.3Co2O5+δcathode has a polarization resistance of0.14Ωcm2, which is lower than that of classic perovskite cathode BSCF (0.25Ω cm2). Thisindicates that it is a potential cathode for application at low temperatures. In order tofuther study the effect of doping on electrochemical performance, PrBaCo2-xNixO5+δ(x=0.02-0.1) cathode materials were synthesized. It is found that the Ni dopant makes anincrease in the thermal expansion coefficient. This affects the compatibility betweencathode and electrolyte. However, these materials still show the highly electrochemicalperformance. PrBaCo21.96Ni0.04O5+δcathode has a polarization resistance of0.16Ω cmat600oC。Oxyge reduction kinetics proves that the rate-limiting step for oxygenreduction reaction on PrBa0.7Sr0.3Co2O5+δand PrBaCo1.96Ni0.04O5+δcathodes changesfrom charge transfer reaction to the conduction of O2-at TPB to electrolyte, withreducing the temperatures.