A potential interconnect material for solid oxide fuel cells: Nd0.75Ca0.25Cr0.98O3−δ

Chromium-deficient Nd_0.75Ca_0.25Cr_1−xO_3−δ (0.02 ≤ x ≤ 0.06) oxides are synthesized and assessed as a novel ceramic interconnect for solid oxide fuel cells (SOFCs). At room temperature, all the samples present single perovskite phase after sintering at 1600 °C for 10 h in air. Cr-deficiency significantly improves the electrical conductivity of Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides. No structural transformation occurs in the Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides in the temperature range studied. Among all the samples, the Nd_0.75Ca_0.25Cr_0.98O_3−δ sample with a relative density of 96.3% exhibits the best electrical conductivity of 39.0 and 1.6 S cm⁻¹ at 850 °C in air and hydrogen, respectively. The thermal expansion coefficient of Nd_0.75Ca_0.25Cr_0.98O_3−δ sample is 9.29 × 10⁻⁶ K⁻¹ in the temperature range from 30 to 1000 °C in air, which is close to that of 8 mol% yttria stabilized zirconia electrolyte (10.3 × 10⁻⁶ K⁻¹) and other cell components. The results indicate that Nd_0.75Ca_0.25Cr_0.98O_3−δ is a potential interconnect material for SOFCs.     

Effect of polytetrafluoroethylene-treatment and microporous layer-coating on the electrical conductivity of gas diffusion layers used in proton exchange membrane fuel cells

The purpose of this study is to investigate the effect of ploytetrafluoroethylene (PTFE)-treatment and microporous layer (MPL)-coating on the electrical conductivity of gas diffusion layers (GDLs), as used in proton exchange membrane fuel cells (PEMFCs). The results show that, for PTFE-treated GDLs, the electrical conductivity in orthogonal in-plane directions is almost invariant with the PTFE loading. On the other hand, the in-plane conductivity of the MPL-coated GDL SGL 10BE (50% PTFE) was found to be higher than that of the counterpart SGL 10BC (25% PTFE) and this was explained by the presence of more conductive carbon particles in the MPL of SGL 10BE. Further, the conductivity of each GDL sample was measured in two perpendicular in-plane directions in order to investigate the in-plane anisotropy. The results show that the electrical conductivity of the GDL sample in one direction is different to that in the other direction by a factor of about two. The contact resistance, the main factor affecting the through-plane conductivity, of PTFE-treated GDLs shows a different trend to the corresponding in-plane conductivity, namely it increases as the PTFE loading increases. On the other hand, the contact resistance of the MPL-coated GDL SGL 10BE (50% PTFE) was found to be lower than that of the counterpart SGL 10BC (25% PTFE) and again this was explained by the presence of more conductive carbon particles in the MPL of SGL 10BE. Also, it was noted that the MPL coating appears to have a positive effect in reducing the contact resistance between the GDL and the bipolar plate. This is most likely due to the compressibility of the MPL layers that allows them to fill in the ‘gaps’ that exist in the surface of the bipolar plates and therefore establishes a good contact between the latter plates and the GDLs. Finally, good curve fitting of the contact resistance as a function of the clamping pressure has been achieved.     

Double-perovskites A2FeMoO6−δ (A = Ca, Sr, Ba) as anodes for solid oxide fuel cells

Double-perovskites A₂FeMoO_6−δ (A = Ca, Sr, Ba) have been investigated as potential anode materials for solid oxide fuel cells (SOFCs). At room temperature, A₂FeMoO_6−δ compounds crystallize in monoclinic, tetragonal, and cubic structures for A = Ca, Sr, and Ba, respectively. A weak peak observed at around 880 cm⁻¹ in the Raman spectra can be attributed to traces of AMoO₄. XPS has confirmed the coexistence of Fe²⁺-Mo⁶⁺ and Fe³⁺-Mo⁵⁺ electronic configurations. Moreover, a systematic shift from Fe^2+/3+-Mo^6+/5+ to Fe²⁺-Mo⁶⁺ configuration is seen with increasing A-site cation size. A₂FeMoO_6−δ samples display distinct electrical properties in H₂, which can be attributed to different degrees of degeneracy of the Fe²⁺-Mo⁶⁺ and Fe³⁺-Mo⁵⁺ configurations. Ca₂FeMoO_6−δ is unstable in a nitrogen atmosphere, while Sr₂FeMoO_6−δ and Ba₂FeMoO_6−δ are stable up to 1200 °C. The thermal expansion coefficients of Sr₂FeMoO_6−δ and Ba₂FeMoO_6−δ are very close to that of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM). The performances of cells with 300 μm thick LSGM electrolyte, double-perovskite SmBaCo₂O_5+x cathodes, and A₂FeMoO_6−δ anodes follow the sequence Ca₂FeMoO_6−δ < Ba₂FeMoO_6−δ < Sr₂FeMoO_6−δ. The maximum power densities of a cell with an Sr₂FeMoO_6−δ anode reach 831 mW cm⁻² in dry H₂ and 735 mW cm⁻² in commercial city gas at 850 °C, respectively.     

Effect of Gd and Yb co-doping on structure and electrical conductivity of the Sm2Zr2O7 pyrochlore

SmYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 1.0) ceramics were pressureless-sintered at 1973 K for 10 h in air. The relative density, structure and electrical conductivity of SmYb_1−xGd_xZr₂O₇ ceramics were investigated by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance spectroscopy measurements. SmYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 0.5) ceramics exhibit a defect fluorite-type structure, while SmYb_1−xGd_xZr₂O₇ (0.7 ≤ x ≤ 1.0) ceramics have a pyrochlore-type structure. The measured values of the electrical conductivities obey the Arrhenius relation. The grain conductivity of each composition in SmYb_1−xGd_xZr₂O₇ ceramics increases with increasing temperature from 723 to 1173 K. The grain conductivity of SmYb_1−xGd_xZr₂O₇ ceramics gradually increases with increasing gadolinium content at identical temperature levels. An increase of about one order of magnitude in grain conductivity is found at all temperature levels when the gadolinium content increases from 0.5 to 0.7. SmYb_1−xGd_xZr₂O₇ ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 2.69 × 10⁻² S cm⁻¹ at 1173 K for SmGdZr₂O₇ ceramic.     

CNTs nanostructuring effect on the properties of graphite composite bipolar plate

Intent of present investigation is to improve the properties of graphite–polymer composite bipolar plate by nanostructuring. This involves the incorporation of different vol.% of multiwall carbon nanotubes (MWNTs) in graphite–polymer composite bipolar plate. It has been found that by inclusion of 1 vol.% of MWNTs in graphite composite plate, the electrical and thermal conductivity of nanocomposite increased by 100%. The thermal conductivity of nanocomposite plate increases from 1 W/m K to 13 W/m K in through-plane and in-plane from 25 W/m K to 50 W/m K at 1 vol.% of MWNTs. This significant enhancement is due to the orientation of MWNTs in all the directions of composite, positive synergistic effect of MWNTs and heat transfer along the axis directions. However, bending strength of nanocomposite increases by 25% and maximum augmentation is in case of 1 vol.% of MWNTs. The improvement in conductivity of nanocomposite plate is due to an increase in the electron transfer ability within the composite plate which influences the I–V performance of ultimate fuel cell. These observations confirm that the optimal content of MWNTs is 1 vol.%, in graphite–polymer composite.     

Characterization of photoelectrochemical cells for water splitting by electrochemical impedance spectroscopy

The photocurrent-voltage characteristic of a photoelectrochemical cell for solar hydrogen production via water splitting, using undoped-hematite as photoanode, was obtained. Photoelectrochemical characteristics of the cell were also investigated by electrochemical impedance spectroscopy. Both techniques were carried out in the dark and under illumination. The analysis of the frequency spectra for the real and imaginary parts of the complex impedance allowed obtaining equivalent electrical analogs for the PEC cell operating in the dark and under 1 sun simulated illumination. Additionally, different electrode configurations were used (two and three-electrode arrangements). The two-electrode configuration allowed the study of the overall charge transfer phenomena occurring at the semiconductor, within the electrolyte and at the counter-electrode side of the cell, whereas the three-electrode configuration gave more detailed information concerning the double charged layer at the semiconductor/electrolyte interface.     

选择分块SVM电容层析成像改进方法

针对SVM在处理具有样本集规模大的ECT系统数据时,存在ECT图像重建的成像精度不高和速度慢的问题,采用了选择分块支持向量机CSSVM算法。将ECT系统样本数据构成列数固定的样本矩阵,每个样本作为样本矩阵的行,66个电容值和66个敏感度值作为矩阵的列。该算法将大样本矩阵按照某一成像单元进行选择性分块,并形成多个小样本矩阵,再分别采用SVM算法进行训练和预测,将各个成像单元组合成像。数值实验证明,使用CSSVM新算法比单独使用SVM算法重建图像具有更高的分类准确率和更短的成像时间。     

Chebyshev神经网络在ECT图像重建中的研究与应用

针对目前电容层析成像系统图像重建分辨率不高,精确度低的问题,提出了一种新的采用Chebyshev神经网络对电容层析成像系统进行图像重建的方法。该神经网络不仅扩大了网络辨识模型的能力与学习适应性,而且算法简单,学习收敛速度快,有线性、非线性逼近精度高等优异特性。通过对封闭管道的气固两相流进行数据检测,并采用改进后的神经网络算法进行图像重建,实验结果证明该方法能明显改善成像质量,进而证明了该方法的有效性。     

电容层析成像系统传感器仿真研究

ECT技术是多相流检测领域中的一项新技术,主要用于识别一个封闭管道内两相流/多相流系统中各个相成分分布问题。采用一种新的方法,通过电磁场有限元仿真软件COMSOL,对电容层析成像系统进行图像重建与仿真研究。构建了ECT的不同电极模型,分别对四种典型流型进行了图像重建;通过对离散介质场域的仿真研究,分析了电极数目、屏蔽罩、径向电极对重建图像质量的影响;对气液固三相流进行了图像重建,获得了满意的重建结果。     

Ｐｅｃｈｉｎｉ法制备Ｂｉ２Ｓｒ２ＣａＣｕ２Ｏ８＋δ粉体的工艺优化及表征

以硝酸盐为原料,乙二胺四乙酸（ＥＤＴＡ）为络合剂,乙烯乙二醇为交联剂,利用Ｐｅｃｈｉｎｉ法制备了名义组分为Ｂｉ_２Ｓｒ_２ＣａＣｕ_２Ｏ_８＋δ（Ｂｉ－２２１２）超导粉体。通过Ｘ射线衍射（ＸＲＤ）、标准四引线法等手段,研究了络合剂、交联剂用量及油浴温度、时间对超导粉体物相、结晶性及电学性能的影响。实验结果表明：不同凝胶化条件制备的超导粉体,均保持较高的相纯度;但工艺参数的改变对Ｂｉ－２２１２粉体的结晶性与电学性能影响显著,其临界转变温度Ｔ_ｃ,０相差７．３Ｋ。