Electrochemical Study And Microstructural Modification Of Cathode Materials For Proton-Conducting Solid Oxide Fuel Cells

Energy issues are related to the sustainable development of the earth closely.As an efficient energy generator,solid oxide fuel cell(SOFC)has drawn much attention to itself.SOFC can directly convert chemical energy into electric energy without combustion process,and it has the advantages of environmental friendliness,fuel adaptability and simple structure.The high working temperature of conventional oxygen conducting solid oxide fuel cell(O-SOFC),however,often results in high fabrication and operation cost as well as fast-thermal degradation.In contrast,the proton conducting solid oxide fuel cell(H-SOFC)with proton conducting electrolyte needs a lower active energy of proton transport ensures intermediate or lower operating temperatures.To ensure the high efficiency of H-SOFC with operating temperature decreasing,the option of cathode materials is crucial.In this paper,the research on high performance H-SOFC is carried out.The electrochemical and catalytic properties of cathode materials have been improved by microstructural modification,and promising cell performance has been obtained under low/intermediate temperature regime.In Chapter 1,a brief introduction of research background has been given.Emphasis is put on basic principles,proton conducting electrolytes and cathodes of H-SOFC.Meanwhile,electrospinning and infiltration nanofabrication techniques have been introduced.In Chapter 2,La2NiO4+δ(LNO),LaNi0.6Fe0.4O3-δ(LNF)nanofieber cathodes were fabricated by electrospun technique.The nanofiber cathodes with high porosity and specific surface area can not only improve the gas delivery rate,but also increased the triple phase boundary sites.The cell with LNF nanofiber cathode showed the low polarization resistance of 0.128 Ω cm2 and large power output of 551 mWcm-2 at 700℃.Electrochemical studies reveal that the performance of H-SOFC with nanofiber cathode is higher than traditional cathode made through powder combustion method.Chapter 3 introduces the nanostructured LNF infiltrated LNO cathode which was evaluated as a potential cobalt-free cathode for BaZr0.1Ce0.7Y0.2O3-δ(BZCY)-based H-SOFC.The performance of LNO backbone cathodes with different loading amounts of LNF infiltrated phase were also investigated and electrochemical studies implied that 31 wt.%LNF infiltrated cathode exhibited the lowest polarization resistance of 0.027 Ω cm2 and the highest maximum power density of 969 mWcm-2 at 700 °C.This work demonstrated that the infiltrated LNF-LNO cathode had a great potential for H-SOFC.Chapter 4 in this thesis works on the three-phase(H/O2’/e-)conducting cathode obtained with infiltration process.LNF nanoparticles are infiltrated into proton conducting BZCY scaffold,and it reached 1082 mWcm-2 at 700 °C as applied in BZCY electrolyte.In addition,we also exchanged the skeleton and the infiltration material,which is using BZCY nanoparticles modified LNF skeleton.It also obtained a relatively high performance in this way,but lower than the former one.At the meantime,it is found that the selection of suitable infiltration solution is also important for experimental design.Chapter 5 presents a summary of this paper and looks forward to the future work of H-SOFC with the development and utilization of new energy.