Ce_(1-x)Sc_xO_(2-x/2)固体电解质的微观结构及电性能研究

研究了Sc_2O_3掺杂CeO_2基电解质材料的微观形貌和电性能。采用溶胶凝胶法制备了Sc_2O_3掺杂CeO_2基电解质粉体, Sc_2O_3掺杂量分别为6%, 8%, 10%。采用单向压力法将电解质粉体压制为圆片状素坯,分别在1400, 1450, 1500℃下,空气中烧结制备电解质材料。研究分析了不同掺杂比例及不同烧结温度对电解质的相组成、微观形貌及电导率的影响。实验结果表明:低温下, Sc_2O_3能溶于CeO_2中形成固溶体,随着Sc_2O_3掺杂量由6%增加到10%(摩尔分数,下同),晶胞参数减小;高温烧结时溶于CeO_2中的Sc_2O_3会析出,且随着烧结温度的升高析出量增加;当Sc_2O_3掺杂量为8%、烧结温度为1500℃时,在750℃时Sc_2O_3掺杂CeO_2电解质电导率最大为8.78×10~(-3) S·cm~(-1),活化能为1.220 eV。     

中温固体氧化物燃料电池阴极材料Nd2-xSrxCuO4的制备与性能研究

采用固相法合成了类钙钛矿结构的中温固体氧化物燃料电池(IT-SOFC)阴极材料Nd2-xSrxCuO4(简称NSC,x=0.0～0.1).通过XRD和SEM对材料进行了表征.结果表明该阴极材料与电解质Ce0.9Gd0.1O1.9(CGO)在1 000℃烧结4 h后不发生化学反应,具有良好的化学相容性;且烧结后二者之间能形成良好的接触界面.利用交流阻抗谱研究了电极的性能.发现随着Sr掺杂量的增加,极化电阻逐渐减小,其中Nd1.93Sr0.07CuO4在空气中的极化电阻最小,750℃时仅为0.14 Ω·cm2.700℃时,电极反应的速率控制步骤为电极上发生的电荷转移过程.     

Ce0.8Gd0.2O1.9固体电解质膜的制备

以硝酸铈和氧化钆为前驱物,采用凝胶浇注工艺合成了钆掺杂氧化铈（Ce0.8Gd0.2O1.9,简称GDC）粉体。然后用流延工艺制备了GDC固体电解质薄膜,采用DTA－TG,XRD,TEM等方法研究了粉体的相形成,粒度等与合成工艺的关系,通过密度测定及显微组织观察等技术研究了流延生坯的烧结性能。借助交流阻抗谱仪对所制备的GDC电解质膜的电导率进行了测量。结果表明,采用本实验的凝胶浇注方法,在700℃温度下煅烧干凝胶,即可制备出纯度高,组成均匀,相结构完整,纳米粒度的GDC粉体。而且所得粉体具有较高的烧结活性,其流延生坯经1450℃烧结后的相对密度可达95％以上,所得GDC电解质膜在700℃空气中的氧离子电导率可达4.6S/m.     

中温固体氧化物燃料电池Pr1.2Sr0.8NiO4阴极材料的制备、结构和性能

以相应的氧化物粉末和盐为原料,通过甘氨酸-硝酸盐法合成出了中温固体氧化物燃料电池(IT-SOFC)Pr1.2Sr0.8NiO4(PSNO)阴极原料粉体,并制备出了烧结体试样.采用X射线衍射(XRD)分析对所合成粉体的相组成进行了分析,分别采用热膨胀仪和四端子法对PSNO烧结体试样的热膨胀系数和电导率进行了测定,同时对该阴极材料与Sm0.2Ce0.8O1.9(sco)电解质材料的电化学阻抗谱(EIS)进行了测试分析以SCO作电解质,分别以NiO/SCO和PSNO作阳极和阴极材料,制备出固体氧化物燃料单电池,并对其性能进行测试.实验结果表明,通过甘氨酸-硝酸盐法,在1050℃以上煅烧前驱体,可以获得具有K2NiF4结构的PSNO粉体.所制备的PSNO烧结体试样在200-800℃间的热膨胀系数约为12×10-6 K-1,在450℃下的电导率约为155 S· cm-1,在400-800℃,平均电导活化能为0.034 eV.电化学阻抗谱分析结果表明,在700 ℃下PSNO阴极和SCO电解质间的比表面阻抗(ASR)为0.37Ω·cm2,而Ni-SCO/SCO/PSNO单电池的比表面阻抗为0.61Ω·cm2;所制备的SOFC单电池在800℃下的输出功率为288 mW· cm-2,开路电压为0.75 V.本研究的初步结果表明PSNO 材料是一种综合性能较为优良的新型巾温固体氧化物燃料电池阴极材料.     

还原剂对低温燃烧合成Ce_(0.85)Sm_(0.15)O_(1.925)粉体性能的影响

低温燃烧合成法是新兴的制备纳米粉体的工艺,在制备固体氧化物电解质方面有着很好的应用前景。对低温燃烧合成工艺中不同还原剂对粉体性能的影响进行了研究。分别用甘氨酸和尿素作还原剂制备Ce0.85Sm0.15O1.925粉体,以固相法粉体为参照,通过红外光谱、XRD,SEM等检测方法,从粉体的掺杂效果和烧结活性两方面进行比较。结果发现:用甘氨酸作还原剂制备的Ce0.85Sm0.15O1.925粉掺杂效果良好,晶格常数为0.5431 nm;晶粒细小,平均晶粒尺寸为5.8 nm;烧结活性良好,在1200℃即可达到较高致密度,烧结体晶界洁净,晶粒尺寸均匀适中。     

EDTA-甘氨酸法制备SmBaCo2O5+δ阴极材料及其性能

采用EDTA-甘氨酸法(EGP)合成了中温固体氧化物燃料电池(IT-SOFC)的阴极材料SmBaCo2O5+δ(SBCO).通过热重-差热分析(TG-DTA),X射线衍射(XRD),透射电镜(TEM),扫描电镜(SEM),直流四极法及交流阻抗技术分析材料的性能.结果表明,初始粉体在850°C煅烧5 h形成钙钛矿结构单相.EGP制备的SBCO粉体颗粒细小、分散性好、粒径分布均匀,其与Sm0.2Ce0.8O1.9(SDC)电解质材料具有良好的高温化学相容性.SBCO的电导率在500-800°C时达到668-382 S cm-1.以SDC为电解质,SBCO为阴极制备对称半电池,其界面结合良好,颗粒连接充分,形成好的三相界面,具有高的阴极催化活性,750°C时阴极极化电阻为0.0688Ωcm2,远低于固相法(SSR)的值,活化能(Ea)为122.21 kJ mol-1.     

碱土金属双掺杂的Ce_(0.9)Ca_(0.1-x)Sr_xO_(1.9)中温固体电解质的性能与应用

以固相反应方法合成了碱土 (Ca ,Sr)双掺杂的氧化铈基固溶体材料Ce0 .9Ca0 .1 -xSrxO1 .9(x =0 ,0 0 4,0 0 5 ,0 0 6 ,0 1)。结构研究表明 :碱土双掺杂的CeO2 呈立方萤石结构。利用阻抗谱研究了材料的离子导电性 ,发现碱土双掺杂有利于提高材料离子导电率 ,掺杂两种碱土金属离子的等效半径接近临界离子半径时导电率最高。将此系列材料作为电解质进行了燃料电池试验 ,发现电池的输出功率高于YSZ电解质及碱土单掺杂氧化铈 ,且电池输出开路电压亦高于单掺杂的情况。     

水热合成纳米氧化锡粉体的烧结性能

采用水热合成法合成得到了高纯度氧化锡基纳米粉体材料，以XRD、BET、TEM等手段对合成得到的粉体进行了表征，粉体的晶粒尺寸大小为10～20 nm，分散性能良好。采用无压烧结技术对粉体进行了烧结研究。结果表明，氧化锡粉体粒径的减小提高了粉体烧结活性，烧结助剂Ni离子的加入大大促进了SnO₂的烧结，当Ni离子掺杂为1at%时，SnO₂陶瓷的烧结相对密度最高可达98.6%。     

LaGaO3基固体氧化物燃料电池阳极材料Ce1-xTmxO2-δ（Tm=Cu,Mn,Fe）研究

以研究与Sr,Mg掺杂LaGaO3(LSGM)电解质匹配的阳极材料为出发点,系统研究了Ce1-xTmxO2-δ(Tm=Cu,Mn,Fe)固溶体的晶体结构、热化学稳定性、电化学性能和单电池发电实验。柠檬酸法合成的Ce1-xTmxO2-δ化合物在x<0.2时均为单相材料,与LSGM电解质有良好的热化学相容性。采用交流阻抗法研究了阳极材料的电化学性能,金属元素掺杂可以显著地改善CeO2电化学性能,Fe元素掺杂阳极材料极化电阻最小,随着元素掺杂量的增加以及氢气增湿,极化电阻减小。采用电解质支撑结构单电池进行发电实验,在800℃时,以Ce0.8Fe0.2O2-δ作为阳极的单电池最高功率密度可达98 mW.cm-2,表明该材料作为IT-SOFC的阳极材料具有一定的可行性,有望成为适合LSGM电解质的阳极材料。     

合成方法对纳米Ce-Zr-Al高温稳定性及储氧性能的影响

采用柠檬酸溶胶凝胶、溶胶辅助共沉淀和溶胶共沉淀3种方法合成了不同Al掺杂的纳米CexZr1-xO2与Al2O3的复合体Ce-Zr-Al.用XRD、BET和H2-TPR表征了纳米Ce-Zr-Al复合体的抗烧结性与储氧性能,与未掺杂的铈锆固溶体相比,Al掺杂的纳米铈锆复合体的抗烧结性与储氧性能均有显著改善,柠檬酸溶胶凝胶法的最佳掺杂量为5倍Al(Al与CexZr1-xO2摩尔比),溶胶辅助共沉淀法最佳掺杂量为10倍Al,溶胶共沉淀法最佳掺杂量为5倍Al,其中,柠檬酸溶胶凝胶法合成的Ce-Zr-Al纳米复合物储氧量最高,为717.5 μmol/g-CeO2,占理论储氧量(即储氧效率)的49.3％.     

CO2 Reduction by Hydrogen Pre-Reduced Acceptor-Doped Ceria

The reactivity of H₂ pre-reduced acceptor-doped ceria materials Gd_0.10Ce_0.90O_2-δ (GDC10) and Sm_0.15Ce_0.85O_2-δ (SDC15) was tested with respect to the reduction of CO₂ to CO in the context of the reverse water-gas shift reaction. It was demonstrated that not only oxygen vacancies, but also dissolved hydrogen is a reactive species for the reduction of CO₂. Dissolved hydrogen must be considered upon discussion of the mechanism of the reverse water-gas shift reaction on ceria-derived materials apart from oxygen vacancies and formates. The reduction of CO₂ is preceded by the formation of carbonate species of different thermal stability and reactivity. The stability of these carbonates was directly demonstrated by in situ infrared spectroscopy and revealed the largely reversible nature of CO₂ ad- and desorption. In comparison to pre-reduced samples, decreased carbonate coverage is obtained after oxidative treatments of GDC10 and SDC15. No significant effect of the sample treatment (O₂ oxidation or H₂ reduction) on the surface carbonate stability was noticed. Mono-dentate carbonates and carboxylates appear to be more easily formed on pre-reduced (i. e. defective) samples. Ce⁴⁺ reduction to Ce³⁺ (by H₂) and re-oxidation to Ce⁴⁺ (by CO₂) on GDC10/SDC15 were directly monitored by infrared spectroscopic analysis of a distinct, IR-active electronic transition of Ce³⁺. These results show the complex interplay of oxygen vacancy/dissolved hydrogen reactivity and surface chemical aspects in acceptor-doped ceria materials.     

Synthesis of barium and strontium carbonate crystals with unusual morphologies using an organic additive

In this paper, strontium carbonate (SrCO₃) and barium carbonate (BaCO₃) crystals were synthesized in the presence of an organic additive-hexamethylenetetramine (HMT) using two CO₂ sources. Scanning electron microscopy and X-ray powder diffractometry were used to characterize the products. The results showed that the morphologies of orthorhombic strontianite SrCO₃ transformed from branch-like to flower-like, and to capsicum-like at last, while the morphologies of BaCO₃ change from fiber-like to branchlike, and to rod-like finally with an increase of the molar ratio HMT/Sr²⁺ and HMT/Ba²⁺ from 0.2 to 10 using ammonium carbonate as CO₂ source. When using diethyl carbonate instead of ammonium carbonate as CO₂ source, SrCO₃ flowers aggregated by rods and BaCO₃ shuttles were formed. The possible formation mechanisms of SrCO₃ and BaCO₃ crystals obtained in different conditions were also discussed.     

Preparation of Barium Titanate Nanopowder through Thermal Decomposition of Peroxide Precursor and Its Formation Mechanism

H₂TiO₃ was dissolved in the mixture of hydrogen formed peroxide and ammonia under the pH range of 8–10 with a transparent yellow solution formed. When an equivalent mole of Ba²⁺ solution was added into the yellow solution, the precipitate produced was the peroxide precursor of barium titanate. The cubic nanopowder of barium titanate was obtained when the precipitate was washed, stoved, and then calcined at 600°C for 1 h. The peroxide precursor of barium titanate and barium titanate nanopowder prepared were characterized to be BaTi(H₂O₂)₂O₃ by TGA‐DTA, XRD, TEM, SEM, and XREDS. The peroxide precursor of barium titanate was determined to be BaTi(H₂O₂)₂O₃. The particle size of the barium titanate nanopowder, the calcined product of BaTi(H₂O₂)₂O₃, was in the range of 20–40 nm. A formation mechanism of the barium titanate nanopowder through thermal decomposition of its peroxide precursor was proposed and then validated.     

Ru-Catalyzed Hydrogenolysis of Chiral Allylic and Propargylic Cyclic Carbonates: Synthesis of Optically Active (E)-Allylic and Allenic Alcohols

RuH₂(PPh₃)₄-catalyzed reductive cleavage reactions of chiral allylic cyclic carbonates with ammonium formate afforded optically active (E)-allylic alcohols with excellent regioselectivity. Alternatively, hydrogenolysis of propargylic cyclic carbonates in the presence of RuH₂(PPh₃)₄ catalyst afforded allenic alcohols as a sole products.     

Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films

Double-scale composite lead zirconate titanate Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from both the pure sol and the composite suspension on Pt/Al₂O₃ substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL⁻¹. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction (XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and ≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films deposited on Pt/Al₂O₃ substrates was evaluated.     

Catalysis over zinc-incorporated berlinite (ZnAlPO4) of the methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to form dimethylhexane-1,6-dicarbamate

Background  

The alkoxycarbonylation of diamines with dialkyl carbonates presents promising route for the synthesis of dicarbamates, one that is potentially 'greener' owing to the lack of a reliance on phosgene. While a few homogeneous catalysts have been reported, no heterogeneous catalyst could be found in the literature for use in the synthesis of dicarbamates from diamines and dialkyl carbonates. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO₄) and zinc-incorporated berlinite (ZnAlPO₄) as heterogeneous catalysts in the production of dimethylhexane-1,6-dicarbamate from 1,6-hexanediamine (HDA) and dimethyl carbonate (DMC). The catalysts were characterized by means of XRD, FT-IR and XPS. Various influencing factors, such as the HDA/DMC molar ratio, reaction temperature, reaction time, and ZnAlPO₄/HDA ratio, were investigated systematically.     

Utilisation of CO2 as “Structure Modifier” of Inorganic Solids

Utilisation of CO₂ as a chemical reagent is challenging, due to the molecule's inherent chemical stability. However, CO₂ reacts promptly at high temperature (∼1000 °C) with alkaline-earth oxides to form carbonates and such reactions are used towards capture and re-utilisation. In this work, this concept is extended and CO₂ is utilised as a reagent to modify the crystal structure of mixed-metal inorganic solids. Modification of the crystal structure is a “tool” used by materials scientists to tailor the physical property of solids. CO₂ gas was reacted with several isostructural mixed-metal oxides Sr₂CuO₃, Sr_1.8Ba_0.2CuO₃ and Ba₂PdO₃. These oxides are carefully selected to show anion vacancies in their crystal structure, to act as host sites for CO₂ molecules, leading to the formation of carbonate anions, (CO₃)²⁻. The corresponding oxide carbonates were formed successfully and the favourable formation of SrCO₃ as secondary phase was minimised via an innovative, yet simple synthetic procedure involving alternating of CO₂ and air. We also derived a simple model to predict the kinetics of the reactions for the cuprates, using first-principles density functional theory and assimilating the reaction to a gas-surface process.     

Carbon Dioxide Fixation with Dialkyltellurium(IV) Dihydroxides

Aqueous solutions of Me₂Te(OH)₂ and (CH₂)₄Te(OH)₂ readily absorb carbon dioxide giving rise to the formation of the dialkyltelluroxane carbonates (Me₂TeOTeMe₂CO₃)_n ( 1 ) and HO(CH₂)₄TeOTe(CH₂)₄CO₃Te(CH₂)₄OH·2H₂O ( 2 ·2H₂O), which were characterised by ¹³C MAS and ¹²⁵Te MAS NMR spectroscopy as well as X‐ray crystallography. The spatial arrangement of the tellurium atoms is defined by C₂O₂ donor sets in the primary coordination sphere and one or two secondary Te···O contacts, which involve coordination of the carbonate moieties. In turn, the different Te–O coordination modes render a lack of symmetry to the carbonate moieties, which show significantly different C–O bond lengths, an important feature when contemplating the C–O bond activation in carbonates. The structural and spectroscopic parameters of 1 and 2 are discussed in comparison with other heavy p‐block element carbonates. In solution, electrolytic dissociation of 1 and 2 takes place.     

(La0.8Sr0.2)0.9MnO3–Gd0.2Ce0.8O1.9 composite cathodes prepared from (Gd, Ce)(NO3) x -modified (La0.8Sr0.2)0.9MnO3 for intermediate-temperature solid oxide fuel cells

Development of high performance cathodes with low polarization resistance is critical to the success of solid oxide fuel cell (SOFC) development and commercialization. In this paper, (La_0.8Sr_0.2)_0.9MnO₃ (LSM)–Gd_0.2Ce_0.8O_1.9(GDC) composite powder (LSM ~70 wt%, GDC ~30 wt%) was prepared through modification of LSM powder by Gd_0.2Ce_0.8(NO₃) _x solution impregnation, followed by calcination. The electrode polarization resistance of the LSM–GDC cathode prepared from the composite powder was ~0.60 Ω cm² at 750 °C, which is ~13 times lower than that of pure LSM cathode (~8.19 Ω cm² at 750 °C) on YSZ electrolyte substrates. The electrode polarization resistance of the LSM–GDC composite cathode at 700 °C under 500 mA/cm² was ~0.42 Ω cm², which is close to that of pure LSM cathode at 850 °C. Gd_0.2Ce_0.8(NO₃) _x solution impregnation modification not only inhibits the growth of LSM grains during sintering but also increases the triple-phase-boundary (TPB) area through introducing ionic conducting phase (Gd,Ce)O_2-δ, leading to the significant reduction of electrode polarization resistance of LSM cathode.     

Microwave assisted low temperature synthesis of sodium zirconium phosphate (NaZr<Subscript>2</Subscript>P<Subscript>3</Subscript>O<Subscript>12</Subscript>)

Sodium zirconium phosphate [NaZr₂P₃O₁₂], a potential ceramic matrix for fixation of high level nuclear waste, was synthesized by heating the mixture of sodium carbonate [Na₂CO₃], zirconyl nitrate hydrate [ZrO(NO₃)₂·5H₂O] and ammonium dihydrogen phosphate [NH₄H₂PO₄] in air, in a resistance heated furnace and a microwave heating system respectively in the temperature range 450 to 650°C. The mixture heated for 1 h in a resistance furnace at 450°C yielded a poorly crystalline NaZr₂P₃O₁₂ [NZP]. Increasing the temperature to 650°C produced a highly crystalline product. The same mixture heated in a microwave oven at 450°C for 1 h however, yielded the most crystalline NZP.In an alternate method, the mixture of sodium dihydrogen phosphate (NaH₂PO₄), zirconium dioxide (ZrO₂) and diammonium hydrogen phosphate [(NH₄)₂HPO₄] heated in resistance furnace at 650°C for the same period did not react in air. It also did not yield the pure product at 450°C when heated in microwave assembly for 1 h.The authors thank the Board of Research in Nuclear Sciences (BRNS) of the Department of Atomic Energy (DAE) for the financial support for this work under the project No. 2000/37/19/BRNS/1959 dtd09-02-02.