Electrochemical Properties And Applications Of High Temperature Proton Conductors With Perovskite Structure

Hydrogen is an important chemical raw material due to its high energy density,no pollutant emissions during combustion,and it has received widespread attention.However,when hydrogen is produced industrially,many by-products are produced,so hydrogen needs to be separated and purified.Mixed conducing hydrogen separation membranes have attracted wide attention because of its simple equipment and high separation efficiency.Among proton conductors,the doped BaCeO₃ materials have the highest proton conductivity,but their stability is too poor for practical application.In order to improve the stability of the materials,Y and Ta elements were used co-dope the BaCeO₃,and the performance of Ni-BaCe_0.7Y_0.3-xTa_xO_3-?proton-electron mixed conducting hydrogen separation membranes was studied.On the contrary,the doped BaZrO₃ material has good stability,but low electrical conductivity and poor sintering activity.In this thesis,Ni,Pr,and Y elements were co-doped into BaZrO₃ and the electrochemical properties were studied.BaCe_0.7Y_0.3-xTa_xO_3-??x=0,0.05,0.1?proton conductor powders were prepared by liquid phase method.Because of the relatively high electronegativity of Ta,Ta doping can improve the stability of BaCe_0.7Y_0.3-xTa_xO_3-?powders in boiling water and CO₂atmospheres.However,Ta doping also makes the conductivity of the BaCe_0.7Y_0.3-xTa_xO_3-?decrease with the increase of Ta content.Under wet N₂ atmosphere,at 600?,the activation energy of BaCe_0.7Y_0.25Ta_0.05O_3-?conductivity decreases from 61.53 kJ/mol to20.22 kJ/mol.The appearance of the inflection point of the conductivity curve may be due to the change of the main conduction form of the material.Ni-BaCe_0.7Y_0.3-xTa_x O_3-?cermet hydrogen separation membranes were prepared with Ni as the electronic conductive phase,and their hydrogen permeation fluxes decreas with the increase of the doping amount of Ta.In wet 3%CO₂-and 10%CO₂-containing atmospheres,the hydrogen permeation flux of Ni-BaCe_0.7Y_0.2Ta_0.1O_3-?remains basically unchanged,while the hydrogen permeation fluxes of Ni-BaCe_0.7Y_0.25Ta_0.05O_3-?and Ni-BaCe_0.7Y_0.3O_3-?gradually increase.All samples react with CO₂ to produce non-conductive oxides,which obstructs the proton transmission.However,due to the more serious reaction between the BaCe_0.7Y_0.25Ta_0.05O_3-?and BaCe_0.7Y_0.3O_3-?membranes and CO₂,the generated non-conductive products are not dense,leading to a reduction in the effective thickness of the sample.BaZr_0.76-xY_0.2Pr_x Ni_0.04O_3-??x=0,0.05,0.1?ceramic powders were prepared by sol-gel method,and their sintering activity,electrical conductivity and hydrogen permeability were analyzed.In addition to the role of Ni in the sintering process of samples,the Pr element with larger ion size increases the free lattice volume of the system,then increasing the mobility of cations and the growth rate of grains.Therefore,the sintering performance of BaZr_0.76-xY_0.2Pr_xNi_0.04O_3-?increases with the increase of Pr doping amount.In different atmospheres,the conductivity of BaZr_0.76-xY_0.2Pr_xNi_0.04O_3-?decreases with the increase of Pr content.However,under the atmosphere of 20%H₂+80%N₂,when the temperature is higher than 750?,the conductivity of BaZr_0.66Pr_0.1Y_0.2Ni_0.04O_3-?is higher than that of BaZr_0.71Pr_0.05Y_0.2Ni_0.04O_3-?,which causes the hydrogen penetration flux of BaZr_0.66Pr_0.1Y_0.2Ni_0.04O_3-?is higher than that of BaZr_0.71Pr_0.05Y_0.2Ni_0.04O_3-?.