An Investigation On The Electrolyte-supporting Direct Carbon Solid Oxide Fuel Cells

The direct carbon solid oxide fuel cell(DC-SOFC)is an electrochemical power generation device with all solid state structure,and it can use solid carbon as fuel directly.It has attracted considerable attention from researchers for development and application because it has a significant advantage in the clean use of coal.The research on DC-SOFC has made more progress so far,but there are still some problems to be solved in small applications,such as the choice of suitable electrode material and the development of portable stack.And the chip YSZ electrolyte support has been widely used for SOFC because of simple preparation process,high strength,low cost and so on.So in this paper,a series of research on the selection of DC-SOFC electrode material and development of portable DC-SOFC stack was carried out,which based on the chip YSZ electrolyte support.The electrode material determines directly the advantage and disadvantage of the battery performance.So it is necessary to select a suitable electrode material for the preparation of high performance battery.Because DC-SOFC would be the phenomenon of carbon deposition when using Ni-YSZ as anode,and the performance of DC-SOFC was not high when using LSM-YSZ as cathode.Ag-GDC was prepared and used as anode and cathode materials of battery.YSZ electrolyte-supporting SOFC with the construction of Ag-GDC/YSZ/Ag-GDC(Ag-GDC for cathode)was fabricated.And the electrochemical performance was test successively by using humidified H2 and activated carbon loaded with Fe as fuel.At the same time,the battery performance was compared to SOFC with the construction of Ag-GDC/YSZ/LSM-YSZ(LSM-YSZ for cathode).The results show that SOFC with the construction of Ag-GDC/YSZ/Ag-GDC has a better output performance when using directly solid carbon as fuel.The highest power density of 265 mW cm-2 at 825 ?C,is about 1.4 times as much as SOFC with the construction of Ag-GDC/YSZ/LSM-YSZ.What's more,DC-SOFC was not reduced and there is no carbon deposition when using Ag-GDC as the anode material.In addition,the preparation process of DC-SOFC with the construction of Ag-GDC/YSZ/Ag-GDC is simple.Therefore,Ag-GDC is a suitable material for DC-SOFC electrode.In order to promote the process of DC-SOFC in small application,YSZ electrolyte support with a length of 5.5 cm,a width of 2.8 cm,a thickness of 0.5 mm and an opening diameter of 1 mm,was prepared by tape casting.And based on this,the electrolyte-supporting DC-SOFC stack was designed.According to the position of the holes of YSZ electrolyte substrate,Ag-GDC was brushed orderly on both sides of the substrate.And each electrode area is 20 mm ? 5 mm.Next,the cathodes and anodes on both sides of the substrate were connected by using silver conductive blocking the holes.Then,the electrolyte-supporting DC-SOFC stack with effective area of 4 cm2 was prepared,by using activated carbon loaded Fe as fuel and alumina ceramic boat as a fuel carrier.Finally,the electrochemical performance of the stack was test by using four-electrode method at different temperatures.The results show that the trends of the stack were consistent with the trends of a single DC-SOFC.The open circuit voltage and highest power density of the stack were gradually increased with the increase of temperature.At the same time,the total resistance and ohmic resistance of the stack were gradually reduced.The open circuit voltage reached 3.8 V,the highest power density reached 170 mW cm-2,the highest output reached 680 mW,the total resistance reached 24 ? cm2 and the ohmic resistance reached 15 ? cm2 at 820 ?C.Besides,it was found that the stack could run for 15 h stably at 2.8 V when the discharge current of 0.15 A was selected to test its stability at 820 ?C.The device was relatively complete and no obvious crack after the test,which proved that electrolyte-supporting DC-SOFC stack had certain feasibility in small application.In the last part of the paper,segmented-in-series DC-SOFC stack was prepared by two SOFCs with the same specifications and the construction of Ag-GDC/YSZ/Ag-GDC.Primarily,two circular YSZ electrolyte supports with a diameter of 3.2 cm and a thickness of 0.5 mm,were fabricated by tape casting.Secondly,circular Ag-GDC electrodes with a diameter of 1.3 cm were brushed on both sides of the supports.Then two-cell-stack was assembled by using activated carbon loaded Fe as fuel and quartz tube as a fuel carrier.Finally,it was found that the open circuit voltage and highest output of the stack were gradually increased with the increase of temperature by electrochemical performance test.The open circuit voltage reached 2.1 V and the highest output reached 1.1 W at 800 ?C.The results show that the stack has good air tightness,and the working principle is the same with a single DC-SOFC.Herein the stack also has certain feasibility.