Al2O3-based composite seal with 10 wt% Al powder addition (A10) possesses excellent plastic and mechanical performance under wide temperature range of solid oxide fuel cell. The thickening phenomenon of A10 seal between 250 degrees C-400 degrees C and 600 degrees C-750 degrees C is caused by the thermal expansion of organic additives and the volume expansion when solid-liquid Al react with oxygen to form Al2O3. The thickness change rate reaches the maximum which is about 5% at 300 degrees C and is about 4.46% at 650 degrees C. The Gibbs free energy for reaction between Al and Al2O3 in the temperature range of 523-1 023 K is all less than 0, which is proved by the fact that A10 exhibits excellent self-expansion and thermodynamic properties in the solid oxide fuel cell operating temperature.

In this study, the novel h-BN based ceramic seals are investigated for nitrogen oxide sensor. The alkaline-free glass (H4) exhibited good wettability on the Fe-16Cr alloy and yttria stabilization zirconia (YSZ) chip and the wetting rate obviously accelerated when the temperature exceeds 940 ℃. The shape parament Ɛ and wetting area of the H4 glass on the substrate of Fe-16Cr alloy and YSZ chip reach the maximum value at 900 °C that Ɛ was 1.46 and wetting area was 146.58 mm2 for Fe-16Cr alloy while Ɛ was 0.89 and wetting area was 165.99 mm2 for YSZ chip. In addition, the addition of 20 wt% H4 glass to hexagonal boron nitride (h-BN) formed BN-20 composite seal that can be effectively reduce the formation of substrate pores, microcracks and exhibited excellent chemical compatibility and stability, which shows that BN-20 seal is can be considered as a promising seal for nitrogen oxide sensors.

The long-term operation of solid oxide fuel cell stack critically depends on the joint strength between cells and interconnect alloy. In this work, 20 wt% YSZ (Y2O3 stabilized ZrO2) was added into different kinds of glass to form H1-20 and H4-20 composite seals. It was focused on the mechanical behavior between YSZ-glass composite seals and Fe-16Cr alloy under various thermal cycles by shear force testing and tensile force testing. The shear strength and the tensile strength between H4-20 seals and Fe-16Cr alloy were higher than that of H1-20. Two composite seals differed in characteristic temperature, viscosity, and crystalline phase with possible impacts on the joint strength. The interfacial composition between H1-20 and Fe-16Cr alloy was different from that of H420. Based on examination results, four possible fracture modes were proposed to illustrate the failure mechanism between composite seals and alloy.

Glass ceramic seals have been widely used in solid oxide fuel cell (SOFC). However, the sealing performance of seals is a big challenge for SOFC operating at high temperature. In this work, the gas tightness, chemical compatibility and thermal cycle stability of the glass-based seals with various proportions of YSZ and glass are evaluated and discussed. The study showed that when 20 wt% YSZ is added to H4 glass, the as-prepared glass ceramic seal (denoted as H4-20) exhibited extremely low leakage rate of 0.00171 sccm cm-1 under input pressure of 20.7 kPa and wide temperature range from 650 degrees C to 800 degrees C. In addition, the leakage rate of H4-20 glass ceramic seal below 0.004 sccm cm-1 was obtained after 10 thermal cycles at 750 degrees C. The SEM analysis indicated that the H4-20 glass ceramic seal could form well bonding interface between the interconnect/seal/ cell. The above results prove the possibility of the H4-20 glass ceramic seals to be considered for intermediate temperature SOFC application.

In this work, we introduced two-dimensional (2D) WSe2 with the lowest heat conductivity to enhance thermoelectric properties of the non-toxic and cost-effective SnTe. On one hand, the improved power factor can be attributed to the enhancement of Seebeck coefficient due to the decrease of low-energy carriers and minority carriers by the addition of WSe2-SnTe p-p-type heterojunction interface barriers. On the other hand, the thermal conductivity also decreased sharply by the heightened phonon scattering from the high-density stacking faults and multiscale hierarchical architectures. Ultimately, benefiting from the dual regulation effect of the introduction of 2D WSe2 on the electro-acoustic decoupling, an improved figure of merit (ZT) of 1.0 is achieved for the composition of SnTe + 6 wt% WSe2 at 873 K, which is enhanced by 134% in comparison with the pure SnTe sample. Moreover, the meaningful attempt represents an effective and feasible strategy for mixing SnTe with other compounds by the method of ball milling.

Al2O3 ceramic was added to a CaO-B2O3-Al2O3-SiO2 glass system to improve mechanical properties and thermal cycle stability in solid oxide fuel cell composite seals. The performance of glass-based seals with different Al2O3 content was evaluated, including the shear strength and leakage rate of the composite seals. The results showed that HA80 composite seal, with 20 wt% Al2O3, had excellent joint strength and gas tightness. HA80 had the highest shear strength among specimens, reaching 3.83 MPa after heat treatment at 750 degrees C. Gas tightness was greatly improved by using HA80 composite seals, with leakage rates from 0.0007 sccm/cm to 0.0011 sccm/cm corresponding to gas input pressures varying from 13.6 to 68 kPa. The leakage rates remained stable about 0.0022 sccm/cm at the highest gas input pressure (68 kPa) during twenty thermal cycles because of improved interfacial bonding between the composite seals and adjacent components. The 5-cell stack was assembled and achieved an open circuit voltage of 5.78 V and maximum power output of 354 W at 750 degrees C, demonstrating that HA80 composite seal was suitable for SOFC application.

The novel h-BN/glass compressive seals were investigated for use in solid oxide fuel cell. The glass was mixed with h-BN powders to obtain composite materials using tape casting technique. Leakage rates were measured below 0.012 sccm/cm under input gas pressure of 6.8 kPa. Seals containing 40% by weight glass showed excellent thermal cycle and long-term operation stability. The leakage rates were reduced by more than half after ten thermal cycles under different input gas pressure. Also, the leakage rates gradually decreased to 0.008 sccm/cm under input gas pressure of 20.4 kPa at 750 degrees C during 208 h, and then remained stable. These observations can be explained by liquid B2O3 films having gradually formed on the h-BN surface. Boron oxidation effectively improved bondage for both interface and interior particles. This phenomenon was interpreted by seals' microstructure analyses and transmission electron microscopy. Finally, an evolution model is proposed to explain the process. (C) 2020 Elsevier B.V. All rights reserved.

The crystallization behavior of glass-ceramic seals for solid oxide fuel cells (SOFC) applications was investigated using thermal analysis. Two kinds of glass-based seals H1-20 and H4-20 were formulated by adding 20 wt% YSZ (Y(2)O(3 )stabilized ZrO2) powder into two powdered glasses H1 and H4. The results showed that the two seals can inhibit uncontrolled deformation and maintain structure integrity at SOFC operation temperatures. The Avrami parameters (n) calculated for the seals H1-20 and H4-20 are 3.2 and 2.6, respectively, and the respective activation energies (E-c) of crystal growth calculated are 17.2 kJ/mol and 32.7 kj/mol. These crystallization kinetic parameters are consistent with the results of the phase transformation analyses for the two seals at 750 degrees C, suggesting that the thermal stability of the seal H4-20 was higher than that of the seal H1-20. Furthermore, the microstructure of the two seals were characterized using XRD and TEM, and the results suggest that the seal H4-20 is a promising candidate for long-term SOFC stack applications. (C) 2019 Published by Elsevier B.V.

In this work, a composite product of Mn-substituted SnTe, SnO2 nanoparticles, and MnTe-supersaturated precipitates has been fabricated by a simple in situ reaction between SnTe and MnO2 for the first time. Benefiting from the synergistic effect induced by the product of in situ reaction, a remarkable improvement in the thermoelectric performance has been achieved. On the one hand, Mn substitution in SnTe can effectively modify the band structure and enhance the electrical properties of SnTe; on the other hand, the thermal transport can also be dramatically suppressed by in situ reaction-derived multiscale phonon scattering by point defects, SnO2 nanoparticles, and supersaturated MnTe precipitates. Ultimately, a maximum ZT of similar to 1.5 at 873 K has been achieved in the SnTe + 10 mol % MnO2 sample, which increases by 224% in comparison with the pristine SnTe, representing one of the best results ever reported for SnTe-based thermoelectric materials.

Ceramic based compressive seal is regarded as an option for sealing the planar solid oxide fuel cell (SOFC) stack. However, during the practice of SOFC stack testing, the powder-based seals are found to have weakness in keeping mechanical integrity. In consideration of enhancing mechanical properties, ceramic fibers are added to the powder-based seals and the relationship between sealing performance and the content ratio of the ceramic fiber under different inlet gas pressure is investigated. The seal containing 20 wt% ceramic fiber (F20) is found to have the best sealing performance. The leakage rate can be maintained at about 0.01 sccm/cm at 750 degrees C during 10 thermal cycle testing. The interface between the seal and adjacent components exhibits good contact conditions and chemical compatibility which can effectively avoid the formation of interface leakage paths. Introducing the ceramic fiber reduces the tensile strength of the seal but enhances ductility and thus improves the reliability and structural integrity of the seal. The applicability of the F20 composite seal is verified in a SOFC 1-cell stack testing.

A 5-cell solid oxide fuel cell (SOFC) stack with external manifold structure is assembled and underwent a durability test with an output of 250 w for nearly 4400 h when current density and operating temperature are 355 mA/cm(2) and 750 degrees C. Cells used in the stack are anode-supported cells (ASC) with yttria-stabilized zirconia (YSZ) electrolytes, Ni/YSZ hydrogen electrodes, and YSZ based composite cathode. The dimension of the cell is 150 x 150 mm (active area: 130 x 130 mm). Ceramic-glass sealant is used in the stack to keep the gas tightness between cells, interconnects and manifolds. Pure hydrogen and dry air are used as fuel and oxidant respectively. The stack has a maximum output of 340 W at 562 mA/cm(2) current density at 750 degrees C. The stack shows a degradation of 1.5% per 1000 h during the test with 2 thermal cycles to room temperature. After the test, the stack was dissembled and examined. The relationship between microstructure changes of interfaces and degradation in the stack are discussed. The microstructure evolution of interfaces between electrode, contact material and current collector are unveiled and their relationship with the degradation is discussed.

A novel compressive boron nitride (h-BN) based seal has been developed for planar intermediate temperature solid oxide fuel cell (SOFC). It exhibited extremely low leakage rates and thermal cycling stability under simulated stack conditions. The h-BN based seal showed leakage rates of 0.01 sccm/cm under gas pressure of 6.8kPa in the temperature range of 650–800°C, and maintained similar leakage rates during 10 thermal cycles. The excellent sealing performance can be explained by oxidation of h-BN surface to form liquid B2O3 layers beyond the critical temperature of 700°C. Two of compliant B2O3 glass layers were observed on the surface of the h-BN to adjoin well cell and metallic interconnect. The sandwich structure with liquid B2O3 layer on two sides of the h-BN seal could not only enhance interfacial adherence but also eliminate the gas leakage paths at SOFC operation temperature. The applicability of the h-BN based seal has also been verified by single cell test.

The suitability of glass-based seal is evaluated for application in intermediate temperature solid oxide fuel cell (SOFC). Several glass-YSZ composite seals are investigated in temperature range from 650 degrees C to 800 degrees C. The leakage rates are obviously reduced with temperature increased. The seal containing 20 wt% YSZ exhibits excellent gas tightness and thermal cycle stability, obtaining the leakage rate of 0.005 sccm cm(-2) under input gas pressure of 6.8 kPa at 750 degrees C. Stable leakage rates can be maintained after ten thermal cycles, implying that YSZ addition suppresses crack propagation of the seals. It is also explained by both interfacial bondage and chemical compatibility examination. When large-area-cell is operated during five thermal cycling tests, its performance is found to be constant at 750 degrees C, all of cell tests achieving OCV of 1.2V and power density of 520 mW/cm(2). The above results demonstrate the possibility of using the H1-20 seals for SOFC application. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In 1-butyl-3-methylimidazolium trifluoromethanesulfonate ( [ Bmim] [ CF3 SO3 ] ) /propylene carbonate ( PC ) solution, the rate-determining step and catalytic mechanism of ionic liquid for CO2 electrochemical reduction on gold electrode were studied by cyclic voltammetry, electrochemical impedance spectroscopy and impedance simulation. Experimental results show that the rate-determining step for CO2 reduction is the formation of CO2- radical by one-electron transfer. Due to the catalytic effect of ionic liquid, the onset potential of CO2 reduction in [ Bmim] [ CF3 SO3 ]/PC shifts positively by 239 mV comparing to that occurred in tetrabutylammonium trifluoromethanesulfonate ( [ Bu-4 N [ CF3 SO3 ]) /PC catholyte. The catalytic mechanism of ionic liquid is proposed as follows; firstly, the cation of ionic liquid ( [ Bmim ] (+) ) adsorbed on the Au electrode and lead to the formation of ionic liquid film; then, CO2 in catholyte diffuses from the bulk solution to the surface of cathode. After transfer through the ionic liquid film adsorbed on the surface of Au electrode, CO2 is reduced to CO2- radical via single electron transfer. The generated CO2- radical further react with cation [ Bmim ] (+) and induce the formation of [ Bmim-CO2 ] (ad). Through this route, the activation energy of CO2 electrochemical reduction is reduced. Hence the overpotential of CO2 electrochemical reduction is reduced substantially.

Carbon dioxide (CO2) can be electrochemically reduced to useful products under mild condition. In recent years, increased attempts have been devoted to use ionic liquid (IL) as the solvents, electrolytes and catalysts for CO2 reduction. However, owing to the high viscosity of ILs, CO2 diffusion in ILs is restrained, lead to low current density of CO2 reduction. To overcome this problem, in present work, we used methanol as the organic solvent to dilute 1-Ethyl-3-Methylimidazolium BF4 ([EmiBF4), an commonly used IL in electrochemistry, the obtained [BmiBF4/methanol solution have many unique properties, such as low viscosity, high ionic conductivity, high CO2 solubility and low cost. The current density of CO2 reduction reached 14.2 mA/cm2 at-1.95V (vs SCE) on Ag electrode. Electrochemical reduction of CO2 in [BmiBF4/methanol solution provides a hopeful technique for CO2 recycling utilization and renewable electrical energy storage.

The electrochemical reduction of carbon dioxide (CO2) has been studied on various metal electrodes including main group and transition elements in aqueous solution. Of these electrodes, silver and gold are found to have catalytic activity for the conversion of CO2 to CO with considerably high Faradaic efficiencies. However, no work has been done to evaluate the electrocatalytical property of these two electrodes in the same electrochemical system under the same condition. In present work, we investicate the electrocatalytical property of Ag and Au electrodes in the same electrolysis cell and under the same condition. We found Au electrode exhibits higher current density and higher faradaic efficiency for CO formation than Ag electrode.