Fabrication Of Tubular Direct Carbon Solid Oxide Fuel Cell With High Capacity And Its Potential Application In Portable Power Sources

A direct carbon solid oxide fuel cell?DC-SOFC?can convert the chemical energy of carbon into electrical power.It is attracting increasing attention because of its all-solid-state structure,high capacity,environment friendliness,and high theoretical conversion efficiency.Fabrication and portable application of tubular electrolyte-supported DC-SOFCs are studied in this thesis.Tubular electrolyte-supported DC-SOFCs are fabricated by dip-coating technique and the detailed process is invested.A high capacity DC-SOFC system,with the anode fabricated on the outside of the tubular cells,is developed for portable application.The present work contributes to establishing an experimental and theoretical foundation for the practical application of DC-SOFCs.The fabrication technique of the electrolyte has great influence on the electrochemical performance of an electrolyte-supported DC-SOFC.Dip-coating technique,which is fast and low-cost,is especially suitable for fabricating ceramic component such as the electrolyte tubes used in the present work.To solve the problems of cracking and low density of the electrolyte fabricated by dip-coating technique,electrolyte slurries with a variety of solid loading?YSZ powder?are prepared and applied to make solid oxide fuel cells?SOFCs?.Experiments show that the optimal solid loading of the electrolyte slurry is 37 wt.%.The YSZ electrolyte tubes made from the optimized slurry are dense,having a wall thickness of 180 ?m.A SOFC prepared the electrolyte tube,with a configuration of Ag-GDC/YSZ/Ag-GDC,operated by using 3 vol.% H2 O hydrogen as fuel ambient oxygen as oxidant,gives a maximum power density of 296 mW·cm^-2 at 800°C.Segmented-in-series tubular electrolyte-supported SOFC stacks were fabricated by connecting one tubular SOFC unit with the next one in electrical and gas flowing series.The stacks were operated with humidified hydrogen?3 vol.% H₂O?and activated carbon loaded with 5 wt.% Fe as the fuel,respectively.With the total area 10.4,17.6 cm2,a 3-cell-stack and a 5-cell-stack,operated with the humidified hydrogen,give an open circuit voltage of 3.21 and 5.43 V,and maximum power of 3.6 and 4.35 W,respectively,at 800°C.The 3-cell-stack and the 5-cell-stack,operated with 3.0 g and 5.0 g activated carbon loaded with 5 wt.% Fe as fuel?DC-SOFC?,reveal a peak power of 3.2 and 3.8 W at 800°C,respectively.The 3-cell and 5-cell DC-SOFC stacks discharge at a constant current of 1 A for 3.5 and 2.6 h,respectively.A high capacity DC-SOFC stack system,with the anode on the outside of the tubular cells,is designed and fabricated to enable more carbon fuel loaded in a container surrounding the stack.At a constant current of 1 A,the discharging time of a 3-cell-stack with the anode outside the tubular cells,loaded with 17 g activated carbon is 19 h and that of a 5-cell-stack,loaded with 30 g carbon fuel,is 14 h.The 3-cell-stack and the 5-cell-stack achieve a power of 3.7 and 6.3 W at 800°C,respectively.A new heating system which is suitable for tubular DC-SOFC stack was fabricated for the purpose of portable application.With a total activated area of 3.1 cm²,a DC-SOFC which use 1.0 g activated carbon loaded with 5 wt.% Fe as fuel reveals a peak power density of 220 mW·cm^-2 at 800°C.Then a 2-cell-stack,tested at 830°C by using the heating system,shows an output power of 1.06 W.This work provides an experimental foundation and a theoretical model for developing DC-SOFCs for portable applications.