| Solid oxide fuel cell?SOFC?is a device that can directly convert the chemical energy of fuel to electrical energy.It has the characteristics of high efficiency,low pollution,fuel flexibility and so on.It has received extensive attention in the background of energy crisis and environmental pollution in the 21st century.Traditional Ni-based anodes of SOFC have encountered many problems when using the hydrocarbon as fuels.The main problems are carbon deposition and sulfur poisoning.Therefore,developing a new electrode material with resisting carbon deposition and tolerating sulfur poisoning is crucial for the commercialization of SOFC.In order to develop an electrode material with resisting carbon deposition and toleranting sulfur poisoning,two types of double perovskite anode materials Sr1.9VMoO6–?and Sr2TiMoO6–?,and a double perovskite symmetric electrode material Sr2TiFe1–xMox O6–??x=0.1,0.2?.The cubic Sr1.9VMoO6–?anode was obtained by solid-state reaction sintering at 1200? in 5?H2/Ar for 10 h.The anode material has good chemical compatibility with common SOFC electrolytes LSGM and SDC below 1000? in 5?H2/Ar.The average thermal expansion coefficient of SVMO anode at 30–1000? in 5?H2/Ar is 13.3×10–6 K–1,which is close to that of common SOFC electrolyte materials.The eletrical conductivity SVMO anode reached 1364–499 S cm–1 at 100–800? in dry H2,which is significantly higher than the existed anode materials and even higher than some Ni-based anode materials.Electrochemical performance of the SVMO anode can be improved by impregnating precious metal Pd nanoparticles,the reasons are that the coexistence of Pd/PdO/PdOx in Pd–SVMO anode and the partial Pd ions doped into the SVMO lattice,which can provide oxygen vacancies and improve the oxygen ionic conductivity.The polarization resistance is reduced by about 56?at 850? when impregnated Pd nanoparticles.The single cell with SVMO anode shows an acceptable power density when the dry H2 as fuel.Impregnating Pd nanoparticles significantly improves the output power density of the cell.The maximum power density of Pd–SVMO anode reached 529,664,794 mWcm–2 with dry H2 as fuel at 750–850?.The 80-h stability test of Pd–SVMO anodes with syngas containing H2S as fuel showed that the maximum power density decreased slightly from 526 mWcm–2 to 513 mWcm–2,indicating a good stability.The anode surface after the stability test was subjected to Raman test,and no forms of carbon were detected.Stability test of Ni–SDC anode under the same conditions showed that the cell performance of the anode was significantly degraded and the Raman spectroscopy indicated that carbon deposition and sulfur poisoning are appeared.It can be seen that the Pd–SVMO anode is a potential SOFC anode material with good resistance to carbon deposition and sulfur poisoning.The double perovskite STMO anode combines the characteristics of two single perovskite materials SrTiO3 and SrMoO3.The cubic structure of STMO anodes was obtained sintering at 1200? for 10 h in 5?H2/Ar.STMO anode shows good chemical compatibility with LSGM and SDC electrolytes at 1000? in 5?H2/Ar.The XPS results indicate that the Ti element in the STMO anode is+4 valence state and the Mo element has the+4,+5,and+6 three valence states,which is consistent with the valences of Ti and Mo elements in the SrTiO3 and SrMoO3 materials,which is also one of the reasons that the characteristics of STMO anode combining these two single-perovskite materials.STMO anode shows electrical conductivity of about 190 S cm–1 at 450–850? in dry H2,demonstrating excellent conductivity.At 30–1000?,the average thermal expansion coefficient of STMO anodes is 11.2×10–6 K–1 in 5?H2/Ar,which indicates STMO anode should have good thermal compatibility with common electrolytes.The polarization impedance of STMO anode at 800? is 2.916?cm2 in H2.After impregnated Pd nanoparticles into STMO anode,the polarization impedance decreased to 1.338?cm2,about 54?decreased at 800?.The maximum power densities of single cell with STMO and Pd–STMO anodes at 800? reach 317 and 884 mWcm–2 using H2 as fuel and 164 and482 mWcm–2 when use syngas containing H2S as fuel.The 60-h stability test of the STMO and Pd–STMO anodes were carried out in syngas,the cell performance did not degrade obviously,indicating a good stability.Raman detection on the anode surface after the stability test revealed that no forms of carbon deposition.It can be seen from the above results that STMO anode possesses good resistance to carbon deposition and sulfur poisoning.Impregnation of Pd nanoparticles only improves the electrochemical performance.The STMO anode has good resistance to carbon deposition and sulfur poisoning,but the electrochemical performance is not sufficient.We introduce Co element at the Ti site and expect to improve the electrochemical performance of STMO anode.Sr2Ti1–xCoxMoO6–??x=0.1,0.2?anodes were synthesized by solid-state reaction.The pure phase of STC0.1MO sample was obtained after sintering at 1200? for 10 h in 5?H2/Ar.A little impurities are detectd in STC0.2MO sample,so the followed studies are not carried out for STC0.2MO sample.The STC0.1MO anode has good physical and chemical compatibility with the common electrolytes LSGM and SDC.The electrical conductivity of STC0.1MO anodes in dry H2 is lower than that of STMO anode due to the increased oxygen vacancy concentration as the introduction of low-valent Co elements into STMO anode,and the oxygen ion conductivity will be increased thus the electronic conductivity will be decreased.The polarization impedance of STC0.1MO anode at 800? is 1.222?cm2,which is obviously lower than 2.916?cm2 of STMO anode.The maximum power density of single cell has also been increased.In syngas,the single cell with STC0.1MO anode continuously operated for 40 h,and the performance did not significantly degrade.No forms of carbon deposition were deteced by Raman test on the anode surface after stability test.The above results show that the doped of Co element improves the electrochemical performance of the STMO anode and keeps other properties unchanged.Sr2TiMo1–xFexO6–??STMF,x=0.1,0.2,0.3,0.4,0.5?were synthesized by incorporating Fe at the Mo site of STMO anode.STMF series anode materials were sintered at 1200? in5?H2/Ar for 10 h.Taking SFMF05 anode as an example,the chemical compatibility tests with LSGM and SDC electrolytes were carried out at 1000? in 5?H2/Ar and the results were satisfied.The average thermal expansion coefficient of STMF anodes at 30–1000°C in 5?H2/Ar are 11.0–11.5×10–6 K–1,which is close to that of common SOFC electrolyte materials.The polarization impedance of STMF04 anode is the smallest,which are 1.848,1.100 and 0.722?cm2 in the temperature range of 750–850?,respectively,which are lower than 4.668,2.916 and 1.915?cm2 of STMO anode.The maximum power densities of single cell with STMF04 anode reached 247,492,and 761 mW cm-2 using H2 as fuel and 129,233,and 422 mW cm-2 using syngas containing H2S as fuel at 750–850°C,which are higher than those of STMO anodes.The single cell with STMF04 anode in syngas continuously operated for 40 h,the cell performance did not show significant attenuation.The Raman test was performed on the anode surface after stability test,and no carbon deposition was detected.It can be seen from the above results that the incorporation of Fe element improves the electrochemical performance of STMO anode and achieves our goal.Moreover,the introduction of Fe did not affect the ability of STMO anode to resist carbon deposition and sulfur poisoning.Symmetrical solid oxide fuel cells?SSOFCs?show many advantageous features of simplifying fabrication process,minimizing interdiffusion between components and enhancing coking and sulfur tolerance by operating the anode as cathode.The double perovskite Sr2TiFe0.9Mo0.1O6–??STFM01?and Sr2TiFe0.8Mo0.2O6–??STFM02?oxides are synthesized by the solid-state reaction and assessed as symmetrical electrodes.Both of the two materials show cubic double perovskite structure with outstanding structural stability,and that well chemical compatibility and matched thermal expansion coefficients with the common electrolytes in oxidizing and reducing atmospheres under SOFC working temperature.From the electrochemical performance,the STFM01 electrode of electrolyte-supported single cell presents the maximum power densities of 573 mW cm–2 in H2 and 361 mW cm–2 in complex hydrocarbon fuels containing H2S at 850°C.The electrochemical stability test exhibits that STFM01 sample showed no any degradation in H2 and acceptable degradation in hydrocarbon fuels,and STFM02 sample showed no any deterioration during 30-h test in hydrocarbon fuels,which implies that the STFM01 and STFM02 materials have acceptable structural stability and remarkable ability of resisting carbon deposition and sulfur poisoning than the traditional anode material. |
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