Research On The Durability Of The Interface And The Tolerance To Sulfur Of Solid Oxide Fuel Cells

The prior requirement for the sustainable development is to develop clean and efficient energy technology.Solid oxide fuel cells（SOFCs）are one of the most efficient energy-conversion devices that can directly convert chemical fuels into electrical power.In order to commercialize the SOFCs,it is necessary to reduce the cost and prolong the service life.It is important to increase the stability of the SOFCs.Electrolyte,cathode and anode are the most important parts in SOFCs,so increasing their durability is the priority.Based on the electrochemical measurement techniques theories,cathode pellets was prepared to find out the reason of the degradation of the interface between the electrolyte and the cathode,and the Sm0.2Ce0.8O1.9（SDC）interlayer was designed and prepared to increase the durability of the interface between the La0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ（LSGM）electrolyte and the Sm_0.5Sr_0.5CoO_3-δ（SSC）cathode in this work.Then,taking the advantage of nanofibers,the combination of Mg/Fe protective layer and the SSC-nanofibers cathode was used to increase the durability to sulfur.Finally,the LST-Mg/Fe composite protective layer was designed and prepared to protect the triple-phase boundaries（TPBs）and the inner anode,because of which the LST-Mg/Fe composite protective layer could keep the sulfur only on the surface of the Ni-based anode.For the Pt（WE）/LSGM/Pt（CE）single cell test,the current density is set at 200 m A·cm-2 under 800 ℃ in air atmosphere.It is proved that some substances are separated from the grain boundry in the LSGM electrolyte at the working electrode side after 150 h constant current polarization.Based on the EDX results,it is confirmed that element Ga separated from the grain boundry in the LSGM electrolyte and element Sr increased at the the grain boundry.However,there are not parent changes at the counter electrode side through the SEM and EDX results.Based on the results above,it is believed that the reason of the degradation of LSGM electrolye is the migration of the elemente in LSGM electrolyte.For the SSC（WE）/LSGM/Pt（CE）and LSCF（WE）/LSGM/Pt（CE）single cell tests,the current density is set at 200 m A·cm-2 under 800 ℃ in air atmosphere.It is proved that some substances separated from the grain boundry in the LSGM electrolyte at the working electrode side after 150 h constant current polarization,and the elemental distributions are almost the same as those in the Pt（WE）/LSGM/Pt（CE）single cell.In order to avoid the influence during the sintering process,[Pt/SSC（pellet）]（WE）/LSGM/Pt（CE）and [Pt/LSCF（pellet）]（WE）/LSGM/Pt（CE）are prepred by the SSC and LSCF pellets.It is proved that some substances are separated from the grain boundry in the LSGM electrolyte at the working electrode side after 150 h constant current polarization in [Pt/SSC（pellet）]（WE）/LSGM/Pt（CE）single cell.It can be confirmed that the elements migration is the reason of the degradation of the interface between the LSGM electrolyte and the SSC cathode.Moreover,some small paricle substance deposite on the surface of the interface between the LSCF（pellet）and LSGM in the [Pt/LSCF（pellet）]（WE）/LSGM/Pt（CE）single cell.It is believed that the SSC cathode has better compatibility with LSGM electrolyte than the LSCF cathode.A SDC interlayer was designed and prepared to increase the durability of the interface between the LSGM electrolyte and the SSC cathodeThe method to increase the durability of SSC and LSCF cathode to sulfur has been researched.For a cell test,three-electrode setup is used for the tests.The tests are conducted at a constant voltage of 0.3 V^RE.in SO₂–air mixture atmosphere.It is proved that SO₂ leads to the degradation of the performance of the nanoparticle and nanofiber morphology of SSC and LSCF cathodes,and the rate of degradation of the performance of the nanofiber morphology of SSC and LSCF cathodes decrease faster than that of nanoparticle SSC and LSCF cathodes.It is due to the fact that the nanofiber cathode has more access for the SO₂ to the TPBs.Mg/Fe layer is used to protect the SSC and LSCF cathode from sulfur,it is confirmed that the Mg/Fe layer works very well.Particularly,the combination of the Mg/Fe layer and the SSC and LSCF nanofiber cathode can protect the cathode from SO₂.It is probably because that the nanofibers have a specific network space for the Mg/Fe layer to surround the entire cathode,the Mg/Fe layer will react with SO₂ first to protect the TPBs and the cathode.This method slows down the rate of the SSC cathode from 33.677 m A·h-1 to 15.934 m A·h-1 and the rate of the LSCF cathode from 27.477 m A·h-1 to 18.563 m A·h-1.It is believed that the combination of nanofiber structure and the Mg/Fe protective layer can protect the SSC and LSCF cathode from SO₂.The method to increase the durability of Ni-based anode to sulfur has been researched.For a cell test,C₁₂H₂₆+H2O and C₁₂H₂₆+H2O+C4H4S are respectively feeding to the cells at a constant voltage of-0.75 V^CE.with direct internal reforming.It shows that the current density drops rapidly and the results shows that the TPBs has been destroyed.Nanoparticle and nanofiber LST protective has been coated on the surface of the Ni-based anode to increase the durability of Ni-based anode to sulfur,respectively.Based on the SEM results,this method can keep the TPBs from sulfur.LST-Mg/Fe composite protective has been coated on the surface of the Ni-based anode to increase the durability of Ni-based anode to sulfur,it shows that the LST（nanofibers）-Mg/Fe composite protective layer can maintain the current density up to 40 h.Based on the results of electrochemical measurement and SEM,it is believed that the combination of the Mg/Fe and the LST-nanofiber can make the sulfur stay in the LST-Mg/Fe composite layer and increase the durability of Ni-based anode to the sulfur.LST（nanofibers）-Mg/Fe composite protective layer can make the sulfur on the surface of the anode and protect the TPBs and the inner anode effectively.