Composition And Performance Modification Of The Ni-SDC Anode Materials For Solid Oxide Fuel Cells With Carbon Based Fuels

Solid oxide fuel cell(SOFC)has attracted worldwide attentions because of its high energy conversion efificiency,good fuel adaptability and environmental friendship.Hydrogen is the widely used fuel for SOFC.However,its high cost limits the commercial application,while hydro-carbon fueled SOFC is more likely to realize the industrialization because of the relatively low lost.Now Ni based cermets are commonly employed to use as anode material of SOFC,but this anode material is liable to form carbon deposition and leads to the decrease of cell performance in hydrocarbon fuel.Therefore,it is now one of the research hot topics to enhance the anti-coking property of the nickel based anodes in hydrocarbon fuels.It has been shown that addition of some alkaline earth metal or rare earth metal oxides into the Ni based anode materials can improve the catalytic performance of Ni and decrease carbon deposition when using hydrocarbon fuels,accordingly increase the electrochemical performance and long term stability of the cells.Also some catalytic layers on the anode surface are beneficial to the reform of hydrocarbon fuels,and reduce coking.Considering these,this dissertation try to add Ikaline earth metal or rare earth metal oxides into Ni-SDC anode and prepare LaNi0.6Co0.4O3(LNC)catalytic layer on to the surface of the Ni-SDC anode to improve the electrochemical and anti-coking performance of the anode in hydrocarbon fuels.In the third chapter of this thesis,Ni-Sm0.2Ce0.8O1.9(SDC)composite powers added with La2O3-CaO(0-6mol%)was prepared by the glycine nitrate method.The phase composition,microstructure,physical properties and Ni catalytic properties of the composite anode and the electrochemical performance of the single cell under H2 fuel were investigated.The results show that the Ni-SDC composite anodes added with La2O3-CaO mainly contain Ni and SDC phases,and La3+incorporated into SDC lattice,while CaO exists alone.Electrical conductivity of the Ni-SDC anode decreases with the addition of La2O3-CaO.The conductivity of Ni-SDC anode added with 1 and 6 mol%La2O3-CaO at 800? was 1875.40 and 869.31 Scm-1,respectively.With the increase of La2O3-CaO addition,the reduction temperature of NiO increases from 492?to 532?,indicating that the interaction between Ni and SDC was enhance,and maximum power density of the single cells increases from 375.25mWcm-2 to 401.12mWcm-2 at 750? under the wet H2 fuel,indicating that the addition of La2O3?CaO could improve the catalytic activity of Ni and the power output of the single cell in H2.In the fourth chapter,microstructure and performance of the Ni-SDC anodes was investigated at different temperatures in ethanol fuels.Anti-coking resistance of single cells with La2O3-CaO(0-6mol%)/Ni-SDC anode in ethanol fuel was also tested.The results show that morphology of the coke in Ni-SDC anode change from 20-60nm carbon fiber into 200-400nm spherical amorphous carbon between 650-800?,and the degree of graphitization gradually increases.The addition of La2O3-CaO increases the electrochemical performance and long-term stability of single cell in ethanol fuel.Maximum power density of single cell with Ni-SDC anode is 158.86mWcm-2 at 800?,which increases to 377.79 mWcm-2 for cells with La2O3-CaO(2mol%)/Ni-SDC anode.And the cells operate stably for 20h at 650?.The addition of La2O3-CaO reduces the carbon deposition in Ni-SDC anode from 17.18wt%to 8.91wt%,and the carbon graphitization degree decreases after the single cell operates at 650? for 12h.In the fifth chapter,LaNi0.6Co0.4O3(LNC)catalytic layer were prepared onto the surface of NiO-SDC anode by screen printing.Phase constitution and morphology of the catalytic layers were characterized.Also performance of single cells with the LNC coated NiO-SDC anode under different fuels were tested.The results show that the LaNi0.6Co0.4O3 catalytic layers are mainly La2O3 and Ni-Co alloys in reduction atmosphere,and match well with the NiO-SDC anode support.La3+diffusion is not observed during the preparation and operation of the single cell.The LaNi0.6Co0.4O3 catalytic layer can significantly improve the performance of the single cell under H2 fuel.Maximum power density of single cell with LNC coated NiO-SDC anode is 660.43mwcm-2 in H2 fuel at 750?,which is only 375.25 mwcm-2 for single cell with pure Ni-SDC anode.Power density of single cell with Ni-SDC anode is 121.13mwcm-2 at 750? in ethanol fuel,which increases to 160.39 m Wcm-2 and 136.66 mWcm-2 in methanol fuel,indicating that the catalytic activity of LaNi0.6Co0.4O3 changes in different fuelsl.