| All social activities are energy conversion,based on several kinds of energy.Therefore,the development of novel energy technology is the only way to solve energy shortage.Fuel cell is an energy source with high efficiency,cleanness,safety,high conversion eff-iciency,no mechanical movement,low noise and flexibility of fuel selection.In this thesis,a systematic studying on diamond introducing SDC(samarium oxide doped cerium oxide)electrolytes and an electrolyte preparation device are presented,the electrochemical properties improvments of alkaline earth metal oxide catalysts were carried out based on LSCF(Lanthanum Strontium Cobalt Iron)cathode.Electrochemical properties improvements on perovskite(nickel and cobalt based)alkaline earth metal oxide catalysts,and anti-pollution properties of optimized BaCoO3 cathode catalyst and anodic fuel catalytic reforming are presented.The SDC electrolyte powder was prepared by the glycine-nitrate method,and then introduced with lwt.%the Nano-diamond(NDs)powder,named SDC/ND.After being pressed and sintered,it was prepared as an electrolyte-supporter(300μm)for single cell.When measured with hydrogen as fuel and air as the cathode oxidant,SDC/ND electrolyte had an output power density of 762 mW/cm2 at 800 ℃(2.4 times of pure SDC electrolyte single cell).SDC electrolyte has lower Ea when introduced with NDs and process better performance even between 600℃ and 800℃.Because NDs can provide widen channels to accelerate the migration of oxygen ions,increase the grain size of electrolyte which provide more oxygen vacuum,and enhance the ionic conductivity inside the grain.Therefore,NDs introduced SDC electrolyte is highly feasible and promising for novel electrolyte materials for high performance SOFC.Besides,one of the best ways to reduce ohmic impedance is to reduce the thickness of the electrolyte layer,which is shortening the transfer distance of oxygen ions in the electrolyte.We have designed an electrolyte preparation mold control device according to the requirement of preparing and control the thickness of the electrolyte between 100 μm and 300 μm.A porous cathode tape was prepared by casting a commercial LSCF cathode material.To prevent Sr separating from LSCF,which lead the Rp increasing,different alkaline earth metal oxide catalysts(MgO,CaO,SrO,and BaO)were infiltrated on LSCF surface to improve ORR and stability.We selected metal nitrate solution as precursor to infiltrate on porous LSCF and sintered in air.The experiment results show that CaO,SrO and BaO catalyst can all reduce Rp and keep it stable.Among them BaO shows the best performance.Rp is higher than bare LSCF after infiltrated CaO and SrO catalyst at the beginning.The diameters of catalyst particle grow to moderate size after sintering at 900℃,which showed the best performance.The experiment showed that 5 uL is the best infiltration amount.Too much catalyst infiltrated hinders the effective area of oxygen molecules through TPB of cathode and electrolyte,which will reduce ORR.Infiltrated with 5uL BaO catalyst and sintered at 900 ℃ showed 0.04 Ωcm2 after 100 hours testing,which is the lowest and stable Rp.In order to improve the effect of the catalyst,performance of nickel and cobalt based perovskite catalyst were studied on the base of alkali metal oxide catalyst.The nickel based perovskite alkali metal oxide catalyst was infiltrated on LSCF cathode and was taken the long-term(100 hours)testing.The results showed that,testing of CaNiO3 catalyst showed that Rp can be stable during the long-term testing in air.The Rp can be reduced after infiltrated SrNiO3 catalyst.While Rp was lowest when 15 uL SrNiO3 catalyst infiltrated.The BaNiO3 catalyst receives lowest Rp and maintained stable after long-term(100 hours)testing.Rp was the best when infiltrated 5uL.For the cobalt based perovskite alkali metal oxide catalyst,SrCoO3 catalysts reduced and maintained stable Rp.Especially in low temperature(600-500 ℃),the more infiltrated the lower Rp shown.The average Ea of the BaCoO3 infiltrated LSCF cathode in symmetrical cells was only 1.13eV,of which the electrical performance showed the best(Rp=0.03 Qcm2 and Ea=1.11eV)at the 900℃ sintering temperature and 5 uL infiltrated amount.In the anti-Cr testing,the optimized BaO and BCO(BaCoO3)catalysts were selected.The experimental results showed that both BaO and BCO catalysts can effectively reduce Rp and maintain long-term stability.After testing the contents of different elements on the cathode surface of bare LSCF,BaO and BCO catalyst infiltrated LSCF,it showed that the Cr content on the cathode surface can be reduced from 12.75wt.%(bare LSCF)to 2.75wt.%by BCO catalyst infiltrated,which proved that BCO catalyst has excellent anti-Cr performance.For the anti-carbon deposition under CO2 environment,trivalent/tetravalent Co was used in the BCO catalyst to remove the carbon deposited on the cathode surface of LSCF to achieve the effect of anti-CO2.When kept in 1%and 3%CO2 environment for 100 hour,the impedance can be held steady at 0.05 Ω cm2 and 0.12 Ω cm2.We can conclude from Oxygen partial pressure testing by DRT figure that BCO catalyst infiltrated symmetrical cells shows the lowest transfer resistance and diffusion resistance compared with the bare LSCF and BaO catalyst infiltrated Rp.In the ECR testing,it was proved that at 750℃,the k coefficients of bare LSCF,BaO and BCO catalyst infiltrated were 3.21×10-4cm/s,8.88×10-4cm/s and 12.2×10-4cm/s,respectively.It showed that both of catalysts can accelerate the oxygen exchange process on the surface of LSCF,while BCO catalyst showed the best performance.Raman testing shows that BCO nano-particles have extraordinary oxygen absorption ability,and there were a large number of oxygen vacuums on the LSCF cathode surface.The modification of BCO catalyst was conducive to the adsorption and desorption of reactive oxygen species,thus improving the excellent catalytic activity of electrochemical properties and maintaining good stability of cathode materials.Catalytic reforming of anodic fuels is one of the key steps in the development of multicomponent anodic fuels in SOFC.The six-tank continuous reforming catalyst can supply the SOFC anode with high flow rate,constant pressure and current.This anodic fuel is environmentally friendly and renewable.This paper aims to improve the electrical performance of SOFCs by reducing ohmic impedance of electrolytes and infiltrating cathode with catalyst to reduce polarization impedance and maintain stability.It provides new ideas and methods for exploring high-performance SOFC. |
