Optimization Of High-temperature Electrochemical Properties Of NdBaCo 2 O 6-? Cathode Materials With Double Perovskite Structure

Solid oxide fuel cell?SOFC?is a kind of promising power generation device because of its high efficiency,no pollution and no restriction of Kano cycle.As the key component of solid oxide fuel cell,cathode has been the focus of researchers.In this paper,NdBaCo₂O_6-? with double perovskite structure is used as the research object,the composition of the electrode material and the microstructure of the electrode are optimized and the physical and chemical properties and electrochemical properties of these cathode materials are studied in detail.The main research contents are as follows:NdBaCo₂O_6-?-xCe_0.9Gd_0.1O_1.95?CGO??x = 0-10 wt.%?composite cathode material was prepared by in-situ sol-gel method.NdBaCo₂O_6-? and CGO has good chemical compatibility at 950 ?.The composite CGO electrolyte material in NdBaCo₂O_6-?electrode material remarkably improves the catalytic performance of the electrode.With the increase of the amount of CGO,the polarization resistance of the electrode decreases at first and then increases.The NdBaCo₂O_6-?-5CGO cathode exhibits the lowest polarization resistance at 700 ??only 0,038 ? cm2?.Study on the oxygen reduction reaction mechanism shows that the rate control step of the oxygen reduction reaction on the electrode is the charge transfer process.At 700?,the single cell output power is 0.354 W cm-2.The Nd_1-xBaCo₂O_6-??x = 0,0.02,0.04,0.06?cathode materials are prepared by conventional high temperature solid state method,and the effects of cation vacancy on the electrochemical properties of the materials were investigated.These cathode materials have good chemical compatibility with CGO electrolyte at 1100 ?.With the increase of the concentration of cation vacancy,the conductivity of the electrode material decreases gradually,and the thermal expansion coefficient increases gradually.The polarization resistances of the vacancy materials are significantly lower than that of the parent material.The polarization resistance of Nd_0.96BaCo₂O_6-? is the smallest?about 0.043 cm2 at 700 ??,which is about 80%lower than that of the parent material NdBaCo₂O_6-?.The mechanism of oxygen reduction reaction?ORR?was investigated under different temperature and oxygen partial pressure conditions.The results show that the rate controlling step of the oxygen reduction reaction is the charge transfer process.The introduction of cation vacancy did not change the rate control step of the ORR reaction.The polarization test results show that the current density of Nd_0.96BaCo₂O_6-? electrode can reach-200 mA cm-2 when the cathodic overpotential is-20 mV at 700 ?,which is much higher than that of the parent material.The output of the electrolyte supported cell with Nd_0.96BaCo₂O_6-? is 0.334 W cm-2 at 700 ?.The electrode microstructure is optimized on the Nd_0.96BaCo₂O_6-? electrode using polystyrene?PS?microspheres as the pore forming agent.The effect of different PS ball diameter and different PS content on the microstructure of electrode and electrode reaction process are investigated.The results show that the porosity of the electrode increases with the amount of PS.The polarization resistances of the cathode prepared by using PS as the pore former are significantly lower than those without the PS microspheres.The cathodic surface resistance of the cathode with 2.3 ?m PS sphere is the smallest,0.0148 ? cm2 at 700?.The mechanism of oxygen reduction reaction of the electrode shows that the diffusion process of oxygen on the electrode is improved by the introduction of the PS microspheres.The low frequency arc in the impedance,which represents the oxygen gas diffusion process disappears and the process of oxygen reduction is accelerated.The rate control step of the ORR reaction on the cathode is the charge transfer process.At 700 ?,when the cathode over-potential is-25 mV,the current density can reach-200 mA cm-2,which is much higher than that of the parent material.The output of the electrolyte supported cell is 0.436 Wcm-2 at 700 ?,which is about 31%higher than that of the Nd_0.96BaCo₂O_6-? cell without PS pore-forming agent.