Investigation on silver electric adhesive doped with Al2O3 ceramic particles for sealing planar solid oxide fuel cell

The silver electric adhesive doped with Al₂O₃ ceramic particles is used as sealing material for planar solid oxide fuel cell (SOFC). The sealing temperature of this sealing material is 600 °C with the heating rate of 2 °C min⁻¹, and the minimal leak rate ranges from 0.030 sccm cm⁻¹ to 0.040 sccm cm⁻¹. When doping 15 mass% Al₂O₃ ceramic particles into this sealing material, the thermal expansion coefficient of this material decreases from 20 ppm K⁻¹ to 15 ppm K⁻¹, which improves the thermal matching performance and the long-term stability of the material significantly. When using the gradient sealing method with the pure silver electric adhesive and the silver electric adhesive doped with Al₂O₃ ceramic particles to seal the interface of Ni-YSZ/SUS430 in the simulating cell, the minimal leak rate of 0.035 sccm cm⁻¹ is obtained for the cell. Furthermore, the simulating cell sealed with the compound silver electric adhesive presents good heat-resistant impact ability. Therefore, this compound sealing technique is a very promising sealing method for SOFC.     

A first principle study of SO3 decomposition on silver nano-clusters: Implications toward hydrogen production

In this work, based on first principles density functional theory, we have investigated the interaction of SO₃ molecule on three different substrates; (i) clean Al₂O₃ surface (0001) (ii) an isolated Ag₆ cluster and (iii) Ag₆ clusters deposited on the Al₂O₃ surface. All calculations were carried out using the plane wave based pseudopotential method under the framework of density functional theory. For the clean Al₂O₃ surface, the SO₃ molecule was adsorbed in parallel orientation on the surface resulting in an elongation of the S–O bond from 1.44 to 1.52 Å with interaction energy of 1.67 eV. In contrast, the interaction of SO₃ with Ag₆ was found to be weak with 0.4 eV interaction energy and 1.47 Å as the largest S–O bond length. Remarkably, when SO₃ molecule interacted with Ag₆ cluster deposited on the Al₂O₃ support, the binding was found to be higher than both Al₂O₃ and Ag₆ clusters in their isolated state. In particular, upon adsorption of SO₃ on Ag₆/@Al₂O₃, the S–O bond length was found to increases from 1.44 to 1.64 Å and the interaction energy was estimated to be 2.00 eV. As the bond elongation bears the signature of bond weakening, a comparison of the above three results clearly suggests that the dissociation barrier of S–O bond on the Ag₆@Al₂O₃ support will be significantly lower than that on the isolated Ag₆ or Al₂O₃ surface. The nature of chemical interaction of SO₃ on these three systems has been discussed based on the electronic density of states analysis.     

Effects of silver particles on the photovoltaic properties of dye-sensitized TiO2 thin films

To evaluate the possibility of using the plasmon resonance effect to enhance the efficiency of photochemical cells, cis-(SCN)₂Bis(2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) dye-sensitized cells were used to measure the photoresponse of TiO₂ film electrodes before and after deposition of Ag particles. The deposited Ag particles created a film with Ag islands. We found that the photoresponse in the visible region increased as the mass-equivalent Ag-island film thickness, t_Ag, increased to 3.3 nm, but decreased when t_Ag was further increased to 6 nm. On the other hand, compared with bare TiO₂ films, the photoresponse in the UV region decreased for any level of Ag islands. These results suggest that under proper conditions, enhancement of the optical absorption of the dye by the Ag plasmon resonance effect contributes to the photocurrent, and indicates the possibility of improving the energy conversion efficiency of photoelectrochemical cells with Ag-island films.     

Influence of microstructure on the hydrogen permeation of alumina coatings

In this work, the influence of microstructure on the hydrogen permeation property of alumina coatings was investigated. The different microstructures were obtained by annealing coatings at 700 °C or 900 °C. The permeation measurements showed that the 700 °C annealed coating exhibited lower hydrogen permeability than the 900 °C annealed coating. The 700 °C annealed coating was amorphous alumina. While, the 900 °C annealed coating had the spinel MnCr₂O₄ phase and γ-alumina. This spinel MnCr₂O₄ formed a network on the coating surface compared with the fine and smooth surface of the 700 °C annealed coating. The MnCr₂O₄ network in the 900 °C annealed coating formed short-cut for hydrogen diffusion, and thus resulted in high permeability. Furthermore, apparent delamination of coating was illustrated on the 900 °C annealed coating after the permeation test, and this was another reason for the high permeability of coating.     

Glycerol steam reforming over Ni catalysts supported on ceria and ceria-promoted alumina

In this paper glycerol steam reforming over Ni catalysts supported on bare CeO₂ and Al₂O₃, and CeO₂-promoted Al₂O₃ to produce H₂ was studied. The catalytic activity results for the NiAl5Ce and NiAl10Ce catalysts showed that the incorporation of low ceria loadings enhances the activity of the NiAl catalyst prepared using a similar composition to the commercial Ni/Al₂O₃ catalysts. The catalyst surface characterization revealed that the good behaviour of the NiAl5Ce and the NiAl10Ce catalysts depends on the stabilization of Ni° particles which is promoted by the formation of nickel–ceria interactions. The increase of ceria content reduced the capacity of the NiAl20Ce catalyst to convert intermediate oxygenated hydrocarbons into H₂.     

Combustion synthesis of alumina with possible CO-GENERATION of power

Aluminum-water combustion method has been advocated to produce hydrogen and synthesize ceramic materials with high purity. In the present study, aluminum-water combustion was employed to synthesize alumina, along with possible co-generation of power. The exhaust gases from aluminum-water combustion comprises of 70% (by mole basis) of hydrogen. This hydrogen gas was burnt with excess air, around an A/F ratio of 16:1 to produce large mass flow rate of gases at temperatures around 1873 K. These gases could be further used to run a turbine for generating power. The possible power generation for this method was estimated to be 6.37 MW per kg of aluminum. The purity and the fraction of alumina in the residue of aluminum-water combustion was mainly influenced by oxidizer to fuel (O/F) ratio. The stoichiometric O/F ratio of 1 resulted in 94% pure α-alumina at all pressures, which was confirmed by X-Ray diffraction (XRD) analysis.     

A comparative study of the optical properties of nickel pigmented alumina films of different thicknesses exposed to elevated temperature and humidity

Commercial solar absorbers of nickel pigmented anodized aluminium are composed of an inner nickel pigmented sublayer of about 0.3 μm thickness and a 0.4–0.5 μm thick top layer of plain alumina. Thermal emittance can be reduced from 0.17 to 0.12 if the top layer is made thinner, to be about 0.1 μm. The solar absorptance is 0.96 as for the thicker coating. In this study degradation is analysed for samples with thin or thick alumina top layer after exposure to elevated temperature, 300–500°C, or humidity. The results from these tests show that a thinner aluminium oxide top layer has the same durability as a thicker top layer. The implication of making commercial nickel pigmented anodized aluminium with an oxide half as thick as today is a reduction of the anodization time to about half the time and lower manufacturing costs.     

Hydrogen adsorption on palladium dimer decorated graphene: A bonding study

We report a density-functional theory study of dihydrogen adsorption on a graphene sheet functionalized with palladium dimers considering different adsorption sites on the carbon surface and both molecular and dissociative Pd₂H₂ coordination structures. Our results show that a (PdH)₂ ring without an H–H bond and not dissociative Pd₂(H₂) complexes are stable adsorbed systems with more elongated Pd−Pd and Pd–H bonds compared to the unsupported configurations caused by C–Pd interactions. In contrast, individual Pd atoms supported on graphene react with H₂ to form only a Pd(H₂) complex with a relaxed but not dissociated H–H bond. We also performed the Mulliken analysis to study the bonding mechanism during the adsorption process. In most cases, we found donor-acceptor C−Pd and Pd−H interactions in which C 2p, Pd 5s, and H 1s orbitals played an important role. We also found that the adsorption of a second Pd atom close to a PdH₂ system destabilizes the H−H bond. In this work we contribute to shed more light on the relation between Pd clustering and the possibility of hydrogen storage in graphene-based materials.     

Optical properties of alumina ceramics as a substrate of thin film solar cells

For full understanding of the optical properties of alumina ceramics which are used as a substrate of thin film c-Si solar cells, we carried out computer simulations of diffuse reflectance and measurements of angle-resolved reflectance. As the result of the computer simulations, we obtained a theoretical expression for the reflectance properties of alumina ceramics with flat surface. The expression can be applied for the measured reflectance of alumina ceramics with rough surface when an effect of surface condition was taken into account.     

Effect of Green synthesized silver oxide nanoparticle on biological hydrogen production

Investigation of the effect of different nanoparticles on dark fermentation is very popular nowadays. Among the nanoparticle production methods, the use of nanoparticles produced by the green synthesis method, which is more environmentally friendly, is important for a sustainable environment. This study investigated the effect of green synthesized silver oxide nanoparticles on bio-hydrogen yield. Nanoparticle synthesis was carried out by using Chlorella sp. microalgae as a reducing agent. SEM, EDX and UV–Visible spectrum analyzes were performed for the characterization of the synthesized nanoparticles. The synthesized silver nanoparticles have a uniform structure and an average particle size of 85 nm. Hydrogen production performance by Clostridium sp. was evaluated using different ratios of produced nanoparticles (100–600 μg/L). The addition of 400 μg/L nanoparticles increased the production of dark fermentative bio-hydrogen by 17% compared to the control group. The highest hydrogen yield was 2.44 mol H₂/mol glucose.     

Thermal analysis of nanostructured alumina stabilized zirconia coating on exhaust manifold

Rapid rise in pollution has increased the number of automobiles usage worldwide. The exhaust manifold is an important part in the automobile since it acts as a passage for the transport of exhaust gases from the combustion chamber to the atmosphere. It is a sensitive component since it handles high-temperature exhaust gases. Continuous exposure of high-temperature exhaust gas may cause thermal stress which decreases the life of the exhaust manifold. Cast iron or steel is the most common material used for exhaust manifold. The present study deals with the improvement of material properties of exhaust manifold. In order to optimize the cast iron properties such as thermal conductivity and corrosion resistance, a zirconia-based nanocomposite coating such as alumina stabilized Zirconia (ASZ) can be coated on both sides of the exhaust manifold, instead of replacing the whole material. By coating nano structured ASZ, the amount of heat flow from exhaust gases to the exhaust manifold is decreased, thereby reducing the thermal fatigue. The method of coating can be achieved by radio frequency Magnetron sputtering technique. A steady-state thermal analysis is performed by simulation approach using ANSYS R17.2 to validate the output in the numerical approach. The results obtained shows that ASZ nanocomposite coating acts as an efficient thermal barrier coating for the exhaust manifold thus increasing its reliability.     

Substrate to substrate aluminized bonding of 10 cm round silicon substrates for application in solar photovoltaics

Large area silicon solar cells with screen printed contacts have been realized for the first time on 10 cm diameter, p-type, Cz silicon wafers which were bonded to silicon substrates by alloying of a suitably thick screen printed layer of Al on them. In cells made on 300 μm thick wafers without texturization, antireflection coating and passivation of the front surface, the values of the open-circuit voltage (V_oc), the short-circuit current density (J_sc), curve factor (CF) and the efficiency (η) were found to be in the range 572–579 mV, 16–19.2 mA cm⁻², 0.53–0.61 and 5.5–5.89%, respectively, under simulated tungsten halogen light of 100 mW cm⁻² intensity. Using thinner wafers and having optical confinement, surface passivation and effective back surface field, the cell performance would be substantially improved. In fact, an efficiency close to 18% (AM1.5) would be realizable with this approach. Another attractive feature of this approach is that a low-cost silicon substrate could be used at the bottom that would act as support for the thin top surface without disadvantage to the cell performance. In this paper only the principle has been demonstrated experimentally. Possible improvements have been shown by computer simulation.     

Effect of silver nano-fluid on pulsating heat pipe thermal performance

This paper presents preliminary experimental results on using copper tube having internal and external diameter with 2.4 mm and 3 mm, respectively, to carry out the experimental pulsating heat pipe. The working fluids include the silver nano-fluid water solution and pure water.In order to study and measure the efficiency, we compare with 20 nm silver nano-fluid at different concentration (100 ppm and 450 ppm) and various filled ratio (20%, 40%, 60%, 80%, respectively), also applying with different heating power (5 W, 15 W, 25 W, 35 W, 45 W, 55 W, 65 W, 75 W, 85 W, respectively). According to the experimental result in the midterm value (i.e. 40%, 60%) of filled ratio shows better. In the majority 60% of efficiency is considered much better. The heat dissipation effect is analogous in sensible heat exchange, 60% has more liquid slugs that will turn and carry more sensible heat, so in 60% of filled ratio, heat dissipation result is better than 40%, and the best filled fluid is 100 ppm in silver nano-fluid.Finally, we observed through the measurement comparison in thermal performance with pure water. When the heating power is 85 W, the average temperature difference and the thermal resistance of evaporator and condenser are decreased by 7.79 °C and 0.092 °C/W, respectively.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

Steam reforming of acetic acid for hydrogen production over attapulgite and alumina supported Ni catalysts: Impacts of properties of supports on catalytic behaviors

In this study, the potential of attapulgite (ATTP) as the support of nickel catalysts for steam reforming of acetic acid to produce hydrogen were evaluated. Ni/Al₂O₃ was prepared and evaluated for comparison. The results showed that ATTP had a much lower specific surface area and a lower thermal stability than alumina. Nevertheless, the interaction between nickel and ATTP was much weaker than that of nickel with alumina. As a result, the Ni/ATTP catalyst had superior activity than the Ni/Al₂O₃ catalyst, especially at low nickel loading. Ni/Al₂O₃ was more stable than Ni/ATTP. The fibrous coke, which was probably catalytic coke, formed over Ni/Al₂O₃ did not cause the rapid deactivation of the catalyst, while the amorphous coke formed over Ni/ATTP catalyst, which was probably the polymeric coke, rapidly deactivated the catalyst. The coke species contained COOH, CO, aliphatic structure and aromatic ring structures. In addition, the effects of these two carriers on the steam reforming mechanism were investigated by the in-situ DRIFTS.     

Preparation of Ni-based egg-shell-type catalyst on cylinder-shaped alumina pellets and its application for hydrogen production via steam methane reforming

Nickel-based ‘egg-shell-type’ catalysts were prepared using cylinder-shaped alumina pellets as supports. In the egg-shell-type catalysts, nickel was selectively located in the outer region of the alumina pellets. Ethylene glycol or 1-octanol were used as hydrophobic solvents to retard internal penetration of the alumina pellets by the nickel nitrate solution. Without hydrophobic solvent, a ‘homo-type’ catalyst with even nickel distribution inside the alumina pellets was achieved. Cross-sectional images and SEM-EDS analysis of the cylinder-shaped alumina pellets showed that nickel concentration in the egg-shell-type catalyst was higher in the outer region and decreased towards the inner region of the alumina pellets. The egg-shell-type nickel distribution was maintained after subsequent magnesium impregnation and calcination processes. X-ray diffraction patterns and temperature programmed reduction profiles showed that the only difference between homo-type and egg-shell type catalysts, when their nickel loading was the same, was the nickel distribution inside pellets; and this was shown to cause significant difference in their catalytic activity in the steam methane reforming (SMR) reaction. For the homo-type catalyst, nickel loading of 3.5 wt% was insufficient for the SMR reaction, as metallic nickel particles were evenly distributed through the entire alumina pellet. However, nickel loading of 3.5 wt% was sufficient for the egg-shell-type catalyst, because active sites with metallic nickel particles were concentrated in the outer region of the pellets. These experimental results confirmed that the egg-shell-type nickel distribution is a favorable design for an SMR reaction catalyst.     

Biogas reforming over bimetallic PdNi catalysts supported on phosphorus-modified alumina

A series of bimetallic PdNi catalysts supported on alumina modified with different amounts of phosphorus (0.5-5 wt%) were prepared. The effect of phosphorus content on the structure, surface properties and catalytic behavior of supported PdNi catalysts in biogas reforming was studied. The physicochemical properties of the samples were characterized by using different techniques: N₂ adsorption-desorption isotherms, X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (TPD), thermogravimetric and differential thermal analysis (TG/DTA) and scanning transmission electron microscopy (STEM). The catalytic properties of the catalysts were evaluated in the reaction of reforming of methane with CO₂. It was shown that increasing the P content (≥1 wt%) leads to agglomeration of the metal Ni particles, as well as to increase of the total acidity of the catalysts. Within bimetallic system, the PdNi catalyst with 0.5 wt% phosphorus showed the best performance and stability caused by the presence of highly dispersed nickel particles on the catalyst surface due to the strong interaction between supported species and alumina.     

A study of bonding and failure mechanisms in fuel pellets from different biomass resources

Pelletization of biomass reduces its handling costs, and results in a fuel with a greater structural homogeneity. The aim of the present work was to study the strength and integrity of pellets and relate them to the quality and mechanisms of inter-particular adhesion bonding. The raw materials used were: beech, spruce and straw, representing the most common biomass types used for fuel pellet production, i.e. hardwoods, softwoods and grasses, respectively. The results showed that the compression strengths of the pellets were in general higher for pellets produced at higher temperatures, and much higher for wood pellets than for straw pellets. Scanning electron microscopy of the beech pellets fracture surfaces, pressed at higher temperatures, showed areas of cohesive failure, indicating high energy failure mechanisms, likely due to lignin flow and inter-diffusion between adjacent wood particles. These were absent in both spruce and straw pellets. Infrared spectroscopy of the fracture surfaces of the straw pellets indicated high concentrations of hydrophobic extractives, that were most likely responsible for their low compression strength, due to presence of a chemical weak boundary layer, limiting the adhesion mechanism to van der Waals forces. Electron micrographs indicating interfacial failure mechanisms support these findings. Infrared spectra of the fracture surface of wood pellets, pressed at elevated temperatures, showed no signs of hydrophobic extractives. It has been shown that both temperature and chemical composition, i.e. the presence of hydrophobic extractives, have a significant influence on the bonding quality between biomass particles during the pelletizing process.     

Hydrogenation of plasma-excited nitrogen over an alumina catalyst for ammonia synthesis

Ammonia (NH₃) is a potential hydrogen carrier as alternative fuel and feedstock for hydrogen production. In this study, plasma synthesis of NH₃ was conducted in a packed-bed dielectric barrier discharge (DBD) reactor using Al₂O₃ as the catalyst. In order to explore the mechanism of hydrogenation of plasma-excited nitrogen for NH₃ synthesis, the whole NH₃ synthesis process was divided into three steps including N₂ activation, hydrogenation of plasma-excited N(a), and desorption of NH₃(a) from catalyst. The effects of reaction conditions on the three steps and corresponding NH₃ production were examined. Results showed that more plasma-excited nitrogen species were formed through N₂ activation at higher N₂ flow rate, discharge time and discharge power for N₂ activation. Hydrogenation of plasma-excited N(a) to form NH₃(a) was improved by more discharge time at the second step. Higher discharge temperature for N(a) hydrogenation favored NH₃(a) desorption from catalyst and increased NH₃ production at the second step, with the total NH₃ yield slightly changed. In addition, one-step NH₃ synthesis in plasma was investigated and compared with the three-step process. The results will provide reference for catalyst and reactor design in plasma synthesis of ammonia.