Preparation And Application Of Hafnium Series Proton Conductor

High temperature proton conductor is a kind of solid electrolyte material that can conduct proton,and one of its main uses is as a dense ceramic membrane for hydrogen separation.Among them,the hafnium series proton conductor is a relatively novel material,which is worthy of further study.The sintering properties,electrical conductivity and chemical stability of several hafnium series proton conductor materials were systematically studied.And the hydrogen permeation membrane was prepared to hydrogen separation test.La₂Ce₂-xHf_xO₇ proton conductors were prepared by high temperature solid phase method to study the effects of Hf doping on the phase composition,morphology,hardness and electrical properties of La₂Ce₂O7.The results show that the sintering properties gradually improve,and hardness of the sample increase,but the conductivities decrease with Hf doping amount increasing.The conductivity in hydrogen atmosphere is higher than that in air.At 700℃,the conductivity of the La₂Ce_1.9Hf_0.1O₇ sample in humid hydrogen is 4.86×10-3 S·cm^-1,which is higher than 3.66×10-3 S·cm^-1 in humid air.A solid solubility limit exist of Hf doping in La₂Ce₂O7,which is between 0.4～0.45.The La_2-xM_xHf₂O_7-δ（M=Ca,Sr,Ba;x=0,0.025,0.05,0.1）series proton conductors by doping alkaline earth elements in La site were prepared by high temperature solid phase method.The results show that doping increases the conductivity of La2Hf2O7.The performance of Ca-doped samples is best among the three doping elements.Among the La2-xCaxHf2O7-δ series materials,the sample with x=0.05 ratio has the best sintering condition and the highest conductivity.The conductivity in humid air is 2.86×10-3 S·cm^-1 at 700℃.The La_1.95Ca_0.05Hf₂O_7-δ sample has good chemical stability under H₂O,H₂,CO₂ and H₂S atmospheres.The hydrogen permeability is measured by an external short circuit method,and the 1.25 mm thick La_1.95Ca_0.05Hf₂O_7-δ hydrogen permeable membrane has the hydrogen permeation fluxes of 0.1497 mL·min-1·cm^-2 at 900℃ and 70%H₂/He.The hydrogen permeation fluxes become larger after the introduction of steam on feed gas side or sweep gas side.The hydrogen permeation fluxes decrease by 2.9%and 2.7%after introduce 3%CO₂ or 300 ppmH₂S on feed gas side,but it gradually return to the initial value after the CO₂ or H₂S is stopped.The BaZr_0.6Hf_0.2Y_0.2O₃-δ-La0.9Sr0.1CrO3-δ two-phase proton-electron mixed conductors with different mass ratios（8:2,7:3,6:4）were prepared.The results show that the sample is a dense ceramic composed of evenly distributed two phases.The two-phase mixed conductor has good chemical stability under H₂O,H₂,CO₂,H₂S atmosphere.When the ratio of BaZr_0.6Hf_0.2Y_0.2O₃-δ-La0.9Sr0.1CrO3-δ is 7:3,the sample has the highest hydrogen permeation fluxes.At 900℃ and 60%H₂/He,the hydrogen permeation fluxes of the 1.23 mm thick hydrogen permeable membrane is 0.2068 mL·min-1·cm^-2.The hydrogen permeation fluxes become larger after the introduction of steam on feed gas side or sweep gas side,but there is no significant change in the hydrogen permeation fluxes after introduce 3%CO₂ or 300 ppmH₂S on feed gas side.Hafnium series proton conductor will certainly occupy a position in the field of hydrogen permeable membranes due to their stability.Figure 37;Table 7;Reference 95...