Electrochemical Modification Of PrBa_0.94Co₂O_5+? Cathode In Solid Oxide Fuel Cell

One of the key components in intermediate-temperature solid oxide fuel cells?IT-SOFCs?is the electro-catalytic activity of the cathode materials,which plays an important role in controlling the performance of fuel cell at intermediate-and low-temperatures?400-700 ^oC?.In this thesis,A-site Ba-deficient mixed ionic and electronic conductor PrBa_0.94Co₂O_5+??A-PBC?with double perovskite structure is selected as research aim.The simple perovskite nanorods-decorated PrBa_0.94Co₂O_5+??SPN-A-PBC?,transition metal Ta⁵⁺-doped PrBa_0.94Co_2-xTa_xO_5+?and alkaline earth metal Ca²⁺-doped Pr_1-x-x Ca_xBa_0.94Co₂O_5+?cathode materials have been successfully synthesized by heating treatments,and their electro-catalytic activity are systematically investigated toward oxygen reduction reaction?ORR?to develop new cathode materials with stable and excellent electrochemical performance.The heterostructured simple perovskite nanorods-decorated double perovskite?SPN-A-PBC?cathode has been synthesized using PrBa_0.94Co₂O_5+?as precursor prepared by solid-state reaction through in situ exsolving strategy.Combined with X-ray diffraction?XRD?,selected area electron diffraction?SAED?,high-resolution transmission electron microscopy?HRTEM?and elemental energy-dispersive spectroscopy?EDS?analysis,it is demonstrated that A-PBC has a layered double perovskite structure and the simple perovskite nanorods are formed on the surface of A-PBC.The electrochemical measurements indicate that the SPN-A-PBC cathode exhibits excellent catalytic ORR activity.The polarization resistance of SPN-A-PBC is0.025?cm² at 700 ^oC,which is much lower than that?0.1?cm²?of A-PBC.This value can remain steadily over a period of 120 h.The single fuel cell with the SPN-A-PBC cathode delivers a peak power density of 1100 mW cm^-22 at 700 ^o C,and the current density can be operated at a constant voltage of 0.6 V without an obvious decay.These results confirm that SPN-A-PBC may be used as a high-performance and stable cathode material for IT-SOFCs.The double perovskite PrBa_0.94Co_2-xTa_xO_5+??x=0-0.05?oxides have been synthesized by a solid-state reaction.The electrochemical properties of the PrBa_0.94Co_2-x-x Ta_xO_5+?materials are systematically studied.The results indicate that the doping of Ta⁵⁺on B-site not only stabilizes the A-site ordering layered perovskite structure but also significantly enhance the catalytic ORR activity.The high electrical conductivity and fast surface oxygen kinetics of PrBa_0.94Co_2-xTa_xO_5+?lead to the excellent electrochemical performance.Among all of components,the PrBa_0.94Co_1.96Ta_0.04O_5+?cathode gives a lowest polarization resistance?0.020?cm² at700 ^oC?.The single fuel cell with the PrBa_0.94Co_1.96Ta_0.04O_5+?cathode delivers a peak power density of 1050 mW cm^-22 at 700 ^oC,and is operated steadily for 100 h at a loading voltage of 0.6 V.Moreover,the PrBa_0.94Co_1.96Ta_0.04O_5+?cathode shows a good CO₂-durability.The double perovskite Pr_1-xCa_xBa_0.94Co₂O_5+??x=0-0.3?oxides have been synthesized by a solid-sate reaction.It is found that the concentration of oxygen vacancies increases resulting from the doping of Ca²⁺.The electrochemical measurements confirm that the Pr_0.8Ca_0.2Ba_0.94Co₂O_5+?cathode possesses the best electrochemical performance.The polarization resistance of the Pr_0.8Ca_0.2Ba_0.94Co₂O_5+?cathode is 0.037?cm² at 700 ^oC,and remains for 60 h without a change.The single fuel cell with the Pr_0.8Ca_0.2Ba_0.94Co₂O_5+?cathode delivers a peak power density of 906mW cm^-2.