Synthesis And Characterization Of Apatite-type Lanthanum Silicate/germanate Electrolyte

With the progress of the society,the energy problem is paid more and more attention.Solid fuel cell as a kind of green energy with low cost,high efficiency and friendly environment as attracted the attention of experts and scholars in related fields.Solid fuel cell is composed of electrolyte material,cathode,anode,connector and sealing material.The electrolyte material,as the core part of the battery,plays a major role in the transfer and isolation of oxygen ions.During the working state,the electrolyte will be exposed to oxidizing and reducing gases,and the operating temperature is moderate.Therefore,the electrolyte material must meet the requirements of high ionic conductivity,compactness and good stability and other relevant conditions.Therefore,in this paper,the apatite electrolyte material can achieve high ionic conductivity under the conditions of appropriate temperature and compactness.We first prepared apatite-type Mg-doped lanthanum germanium electrolyte La₁₀Ge_6-xMg_xO_27-x?LGM,0?x?0.4?,found that Mg could doping on Ge and Si site.In order to improve the electrical conductivity,we also prepared La_9.33Si_6-xGe_xO₂₆?LSGO,0?x?6?and La_9.33(Si_1/3Ge_2/3)_6-xMg_xO_26+x?LSGM,0?x?0.7?,studied Mg doping on Si/Ge site.Firstly,we prepared La₁₀Ge_6-xMg_xO_27-x?LGM,0?x?0.4?,powder material by molten salt method,tested and discussed the lattice structure,morphology and electrical properties of its series of materials,and confirmed the threshold and optimal value of Mg doping on Ge site.The experimental results show that:when 0?x?0.3,the sample conductivity increases with the increase of Mg content,because of the radius of Mg²⁺is greater than Ge⁴⁺.After substitution,it expand lattice and enlarges the oxygen ion conduction channel,lead to improving the conductivity.When x?0.4,the conductivity decreases,which is caused by the lattice shrinkage by the reason of excessive doping.when x=0.3,has the maximum oxygen ion conductivity,the value of 0.95×10^-2S·cm^-1 at 850oC,indicate threshold and optimal value of Mg doping on Ge site is x=0.4 and x=0.3.Secondly,we also prepared La_9.33Si_6-xGe_xO₂₆?LSGO,0?x?6?series powder materials by molten salt method,and tested and discussed their lattice structure,morphology and electrical properties,and also determined the threshold and optimal value of Si doping on Ge.The experimental results show that:when 0?x?4,Si⁴⁺was replace by Ge⁴⁺,the lattice expands and the conductivity increases by the reason of radius of Ge⁴⁺is larger thanSi⁴⁺,when x?5,the conductivity begins to decline.when x=4,has the maximum oxygen ion conductivity,the optimal value of Si doping on Ge of 2.5×10^-2S·cm^-1 at 800?.In order to prepare better materials,we finally prepared La_9.33(Si_1/3Ge_2/3)_6-xMg_xO_26+x?LSGM,0?x?0.7?,series powder materials.By the same analysis,the threshold and optimal value of Mg doping on Si/Ge were determined.The experimental results show that:when 0?x?0.5,Si⁴⁺/Ge⁴⁺was replace,the lattice expands and the conductivity increases by the reason of radius of Mg²⁺is larger than Si⁴⁺/Ge⁴⁺,when x?0.6,the lattice became shrinkage.The threshold and optimal value of Mg doping on Si/Ge is x=0.6 and x=0.5,it has the maximum oxygen ion conductivity of 3.2?10^-2S·cm^-1 at 850?.To assess its potential as a SOFC electrolyte material and to consider the overall performance of the electrolyte,we constructed SOFC single cells using La_9.33(Si_1/3Ge_2/3)_5.9Mg_0.1O_26.1,La_9.33(Si_1/3Ge_2/3)_5.5Mg_0.5O_26.5,La_9.33(Si_1/3Ge_2/3)_5.3Mg_0.7O_26.7electrolyte.Thus,as a kind of potential electrolyte material,development prospect is very considerable.