| Traditional solid oxide fuel cells need to obtain ideal performance at higher temperatures(>700℃),which brings a series of unavoidable problems,such as increased material cost,poor system stability and long start-stop time.However,the decrease in temperature can have many adverse effects on the performance of fuel cells driven by thermal activation,such as a surge in polarization resistance and significant performance degradation.In fact,the continuous thinning of the electrolyte will reduce the mechanical strength of the cell and adversely affect the system,so it has become an inevitable trend to study new low-temperature electrolytes.Strontium titanate(SrTiO3)is a typical perovskite compound with the advantages of high dielectric constant,low dielectric loss,good thermal and chemical stability,and has attracted the attention of related scholars in recent years.In this paper,three different electrolyte materials based on SrTiO3 were prepared.The effects of composition ratio and test temperature on the microstructure and cell performance of composite electrolyte materials were studied,and the mechanism of ion conduction enhancement was discussed.The main research contents and results are as follows:(1)In this paper,TiO2-SrTiO3 composite electrolyte material was prepared by hydrothermal reaction method.The characterization results showed that the hydrothermal reaction was good,and sufficient contact interface was formed between TiO2 and SrTiO3 without chemical reaction.It can be seen from the I-V-P curve that the performance of pure TiO2 is low,while the maximum power density of pure SrTiO3 is 559 mW/cm2.The best performance(OCV=1.08V,MPD=951 mW/cm2)is achieved when the molar ratio of 6TiO2-4SrTiO3 is 6TiO2-4SrTiO3,and the power density increases by 70.1%.However,the continuous increase of TiO2 content is not conducive to the improvement of cell performance;In addition,the activation energy required for proton transport in 6TiO2-4SrTiO3 cell is 0.23 eV,which is significantly lower than that of traditional oxygen ion conductor.Finally,the theoretical model of core-shell TiO2-SrTiO3 heterosystem was constructed based on the principle of energy band alignment,and the space charge region and built-in electric field were constructed.When the electrolyte was in the fuel cell atmosphere,protons were firmly bound near the contact interface by the built-in electric field force,thus enhancing proton transport.(2)In this paper,Mn doped SrTiO3(Mn-SrTiO3)electrolyte materials were prepared by solid-state reaction method.The characterization results show that different proportion of Mn2+ doping does not change the crystal structure of SrTiO3.It can be seen from the I-V-P curve that with the increase of doping concentration,the performance of the cell first increases,and the best performance is obtained at 10%molar doping ratio(OCV=1.08 V,MPD=809 mW/cm2).Compared with pure SrTiO3 cell,the maximum power density is increased by 44.7%,but there is a threshold for Mn2+ doping concentration,beyond which it will no longer promote;In addition,the activation energy required for proton transport in 10%Mn SrTiO3 cell is 0.43 eV,which reflects the conduction characteristics of proton conductor;Finally,electron paramagnetic resonance(EPR)confirmed that the oxygen vacancy concentration in Mn-SrTiO3 was higher than that of undoped SrTiO3,which provided more effective channels for proton transport,confirming the characterization and analysis results of XPS.(3)In this paper,Fe/Co/Ni co-doped SrTiO3(Fe/Co/Ni-SrTiO3)electrolyte materials were also prepared by solid-state reaction method.The characterization results showed that different proportions of Fe3+/Co2+/Ni2+ co-doping did not change the crystal structure of SrTiO3.It can be seen from the I-V-P curve that with the increase of doping concentration,the cell performance first increases and then decreases,and the best performance appears at 10%molar doping ratio(OCV=1.03 V,MPD=884 mW/cm2),and the maximum power density increases by 58.1%compared with that without doping.In addition,the activation energy required for proton transport in 10%Fe/Co/Ni-SrTiO3 cell is 0.39 eV,which is lower than that of conventional oxygen ion conductors;Finally,XPS characterization results are used to illustrate that the oxygen vacancy concentration in Fe/Co/Ni-SrTiO3 material is significantly improved,which is attributed to the efficient construction of high-entropy system,which increases the disorder of the system. |
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