Novel cobalt-free Pr2Ni1-xNbxO4 (x = 0, 0.05, 0.10, and 0.15) perovskite as the cathode material for IT-SOFC

The cobalt-free cathode materials with high activity is critical to the commercial application of medium temperature solid oxide fuel cells (IT-SOFC). Herein, a series of cobalt-free Nb-doped Pr₂Ni_1-xNb_xO₄ (x = 0, 0.05, 0.10, and 0.15) perovskite oxides were successfully prepared, and the effects of Nb-doping on the structure, thermal stability and electrochemical properties of the cathode material are studied in detail. The Pr₂Ni_1-xNb_xO₄ exhibits a K₂NiF₄ type structure with Fmmm space group. The Nb⁵⁺ cations that doped into Pr₂NiO₄ replaces the Ni site, which increases the surface oxygen content, then effectively eliminates the phase transition of Pr₂NiO₄ and significantly improves the ORR catalytic activity. The Pr₂Ni_0.9Nb_0.1O₄ was found to occupy the lowest polarization resistance of 0.057 Ω cm², and the peak power density of single cells supported by the electrolyte is 0.576 W cm^?2 at 700 °C, which has good long-term stability.     

常压液相法一步合成铌掺杂二氧化钛

采用四氯化钛为钛源,常压下在离子液体（1-乙基-3-甲基咪唑四氟化硼酸盐）中一步合成掺杂铌的二氧化钛粉末。采用X射线衍射、扫描电子显微镜、紫外–可见漫反射光谱对产物的结晶、掺杂、表面形貌进行表征,并测试了掺杂量的改变对光吸收性及表观介电常数的影响。结果表明：制备的掺杂TiO2粉末为锐钛矿晶型且结晶完善;Nb5＋掺杂使粉末光吸收带边发生蓝移;掺杂后粉末的介电常数增大,当掺杂Nb量为5%（摩尔分数）时表观介电常数达到最高值。     

基于AZO/Ag/AZO透明导电薄膜的染料敏化太阳电池研究

采用化学气相沉积和直流溅射沉积方法成功制备了与基体附着力高的不同Pt厚度的Pt/碳纳米管(CNT)膜层。通过扫描电子显微镜(SEM)和能谱分析(EDS)分别对薄膜厚度和表面形貌以及膜层中Pt的含量进行了研究;通过电化学阻抗谱和循环伏安曲线分别对Pt和Pt/CNT对电极的光电催化性进行了研究。结果表明:CNT与基体具有良好的接触性,并且随Pt沉积时间的增加,Pt在CNT薄膜中的含量增加,染料敏化太阳电池(DSSC)的光电转化效率随Pt厚度的增加而增加;与单纯的Pt对电极相比,Pt/CNT对电极具有更高的活性比表面,更低的电子迁移电阻以及更高的还原电流密度;以Pt(80 nm)/CNT为对电极的DSSC具有最高的光电转化效率8.54%;另外,与Pt(80 nm)对电极相比,以Pt(40 nm)/CNT为对电极制备的DSSC具有更高的光电转化效率,因此,该新型对电极结构可大大节省贵金属Pt的用量,在DSSC的应用中具有很大的潜力。     

Transparent conducting Nb-doped anatase TiO2 (TNO) thin films sputtered from various oxide targets

Transparent conducting Nb-doped anatase TiO₂ (TNO) epitaxial films were sputtered from TiO₂-, Ti₂O₃-, and Ti-based targets at various oxygen partial pressures (Po₂). Using the TiO₂- and Ti₂O₃-based targets, highly conductive films showing a resistivity (ρ) of ~ 3 × 10^− 4 Ω cm could be formed without postdeposition treatment. In the case of the TNO films formed from the Ti-based target, reductive annealing had to be carried out at a temperature of 600 °C to achieve similar resistivity values. Thus, the use of oxide targets is preferable to obtain as-grown transparent conducting TNO films. In particular, the Ti₂O₃-based target is practically advantageous, because it offers a wide range of optimal Po₂ values at which ρ values of the order of 10^− 4 Ω cm are achievable.     

Metal-semiconductor transition in Nb-doped ZnO thin films prepared by pulsed laser deposition

The structural, electrical and optical properties of Nb-doped ZnO films were investigated with different Nb contents (0, 0.15, 0.31, 0.46, 0.62, and 0.94 at.%) in this article. The film with 0.46 at.% Nb content showed the lowest resistivity of 8.95 × 10^− 4 Ω cm and high transmittance about 80% with high c-axis orientation. The undoped ZnO film showed a semiconducting behavior. And Nb-doped ZnO films showed a metal-semiconductor transition (MST), which was connected with localization of degenerate electrons. The films showed metallic conductivity at temperatures closer to the ambient temperature and semiconducting behavior at lower temperatures. It was noted that the NZO films with much lower Nb concentration of 0.15 at.% presented MST compared with other transparent conducting oxides films.     

原位热压合成Nb掺杂Al2O3/TiAl复合材料

利用Al-Ti-TiO2-Nb2O5体系的放热反应,原位热压合成了Nb掺杂Al2O3/TiAl复合材料.借助DTA结合XRD探讨了Al-Ti-TiO2-Nb2O5体系的反应过程,并采用XRD、OM和SEM研究了复合材料的物相组成及显微结构.结果表明:Al熔化的同时,体系发生了Al和Nb2O5的铝热反应,生成了NbO2和Nb等中间产物,并放出了较多热量,这些热量促使Ti和Al较早化合生成TiAl3,随即引发Al和TiO2较早的还原反应,进而促使材料在较低温度下致密烧结;产物由γ-TiAl、α2-Ti3Al、Al2O3和NbAl3相构成,Al2O3颗粒分布于基体交界处,存在一定的团聚;Nb2O5的引入,对基体γ-TiAl相和α2-Ti3Al相的的分布有一定的影响,使得基体晶粒细化,较好地改善了材料的力学性能.     

Sol-Gel processing of Nb-doped Pb(Zr,Ti)O3 thin films for ferroelectric memory applications

The ferroelectric properties of Nb-doped PZT thin films prepared by a sol-gel method were evaluated relative to memory device application requirements. Within the range of 0 to 4 mol %, Nb-doping of PZT compositions near the morphotropic phase boundary region (i.e. PZT 53/47) enhanced overall ferroelectric properties by reducing the te-tragonal distortion of the unit cell. A 4 mol % Nb-doped PZT 53/47 thin film (0.26 μm) had a coercivity of 8 V/ μm, a remanence ratio of 0.54, a switchable polarization of 45 μC/cm², and a specific resistivity of 3 x 10⁹ Ω-cm. Nb-doping levels in excess of 5 mol had a detrimental effect on the resulting thin film ferroelectric properties. X-ray diffraction (XRD) analysis of highly doped films showed development of a significant PbO phase accompanied by diffraction line broadening of the perovskite phase. As such, it was postulated that the creation of excessive lead vacancies in the PNZT lattice resulted in PbO accumulation at the grain boundaries which impeded grain growth, and hence, adversely affected ferroelectric switching performance. The fatigue performance of the sol-gel derived thin film capacitor system was a function of switching voltage. At switching fields sufficient to saturate the polarization, the endurance of the thin film capacitor was greater than 10⁹ cycles. Cycling with lower fields reduced endurance values, but in all cases, the switchable polarization decreased linearly with the logarithm of cycles. Nb-doping did not have a significant effect on the fatigue performance.     

Suppression of Sr surface segregation in La0.8Sr0.2Co0.2Fe0.8O3-δ via Nb doping in B-site

Sr surface segregation has been one of the main reasons for the cathode performance degradation during the long-term operation of solid oxide fuel cells (SOFC). Investigation on Sr segregation mechanism and proposing strategies on suppressing the Sr surface segregation are significant for SOFC development. In this paper, La_0.8Sr_0.2Co_0.2Fe_0.8-xNb_xO_3-δ (LSCFNb, x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) are prepared via sol-gel method. The electrochemical performance and long-term stability are tested through electrochemical impedance spectroscopy (EIS) and constant current polarization. The results show that the long-term stability of LSCFNb cathodes are strongly affected by Nb content. Combining the results of ICP and XPS, it's revealed that the Sr surface segregation can be effectively suppressed with the increase of Nb content. The LSCFNb cathodes gain the optimal electrochemical performance when x = 0.04, with minimum polarization resistance of 0.27 Ω cm² at 750 °C and oxygen reduction reaction activation energy of 1.54 eV. After cathodic polarization for 144 h, the polarization resistance and activation energy of LSCFNb4 cathode increase slightly, revealing it a promising cathode material for SOFC research.     

Effects of reductive annealing on insulating polycrystalline thin films of Nb-doped anatase TiO2: recovery of high conductivity

We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb-doped TiO₂ (TNO). The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 ℃. Reduced free carrier absorption in the insulating TNO films indicated carrier compensation due to excess oxygen. With H₂-annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers.     

Photoelectrochemical Performance of Nb-doped TiO2 Nanoparticles Fabricated by Hydrothermal Treatment of Titanate Nanotubes in Niobium Oxalate Aqueous Solution

Nb-doped TiO2 nanoparticles were prepared by hydrothermal treatment of titanate nanotubes in niobium oxalate aqueous solution.The effect of Nb doping and rutile content on the photoelectrochemical performance based on TiO2 powder electrodes was investigated.The results show that Nb-doped TiO2 with a small amount of rutile exhibits the enhanced photoelectric conversion efficiency for dye-sensitized solar cell.The highest photoelectric conversion efficiency of 8.53%is obtained for 1%Nb—TiO2 containing a small amount of rutile.When a small amount of rutile contained in 2%Nb—TiO2,a higher photoelectric conversion efficiency of8.77%is achieved.