Oxygen transport membranes made of Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ (BSCF) were manufactured by tape casting and co-firing. The disk-shaped membranes consisted of a top gastight layer (70μm thick) and a ...porous substrate (830μm thick) with 34% open porosity. The variation of the permeation operation conditions allowed (i) the identification of the different limitations steps in the permeation process, i.e., bulk oxygen ion diffusion, catalytic surface exchange and gas phase diffusion in the membrane compartments and porous substrate, and (ii) the ultimate optimization of the oxygen flux. The variables considered in the systematic permeation study included the inlet gas flow rate of the sweep and air feed, the temperature and the nature of the oxygen feed gas (air or pure oxygen). Moreover, the influence of the deposition of a catalytic activation layer (17μm thick) made of BSCF on top of the thin gastight layer was investigated. As a result of this parametric study, unpreceded oxygen flux values were achieved, i.e., a maximum flux of 67.7ml(STP)min⁻¹cm⁻² was obtained at 1000°C using pure oxygen as the feed and argon as the sweep, while a flux of 12.2ml(STP)min⁻¹cm⁻² at 1000°C was obtained when air was used as the feed.
One of the most promising materials for oxygen separation amongst ceramic oxygen transport membranes (OTMs) is La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) due to its relatively high oxygen permeability combined ...with high stability. In this work, asymmetric thin-film LSCF membranes supported over a porous LSCF support were manufactured by inverse sequential tape casting. Moreover, surface activation was accomplished by depositing a porous LSCF activation layer in order to promote oxygen evolution reaction, i.e. O2− to O2 oxidation, in the permeate membrane side. In this case, the porous layer allows the surface area available for oxygen activation to be enlarged. Both the manufacturing of the asymmetric thin-film membranes and the surface activation are described in detail. A thorough study of the oxygen permeation is presented for disk-shaped 30µm thick LSCF-supported membranes considering the following operating parameters: temperature (1000–600°C), sweep flow rate (300–750mlmin−1 argon) and oxygen partial pressure in the feed (0.21–1atm). High permeation fluxes were achieved, e.g., 11.87mlmin−1cm−2 at 1000°C and 300mlmin−1 argon sweep when using pure oxygen as feed. A change in the apparent activation energy at about 850ºC was related to a reversible structural change in the perovskite symmetry (cubic↔rhombohedral), as revealed by XRD measurements. Furthermore, the application of an activation layer allowed the permeation process to be improved, especially at low temperatures, i.e. below 800°C. Specifically, an improvement of up to about 300% at 600°C is observed upon application of the activation layer. The activated membrane reached a flux of 13.3mlmin−1cm−2 at 1000°C under an O2/Ar gradient. Additional permeation tests using CO2-rich sweep gas demonstrated the good stability and performance of these LSCF asymmetric membranes at 900 and 1000ºC.
A 30µm dense LSCF membrane has been deposited on a porous support by means of inverse sequential tape casting, this has permitted the achievement of an O2 flux of 11.87mlmin−1cm−2 at 1000°C. Furthermore, the application of an activation layer allowed improving the permeation process, especially at low temperatures, obtaining an improvement of ca. 300% at 600°C with respect to the bare membrane. Display omitted
•Asymmetric membranes made of LSCF were prepared by inverse tape casting.•Concentration polarization in the porous support (air feed) limits the permeation.•High sweep flow rates allowed gas concentration limitations to be minimized.•Catalytic activation improves notably (~300%) the O2 flux, especially at 750–600°C.•A peak flux of 13.3mlmin−1cm−2 is reached at 1000°C for the activated membrane using O2 as feed.
The overall permeation rate through asymmetric oxygen transport membranes is significantly governed by the porous support. Therefore, the microstructuring of the support's pore structure is essential ...to achieving the highest performances. Freeze casting is already proven to obtain hierarchical porous structures with low tortuosity, which potentially enhances the oxygen flux of oxygen transport membranes. Although a performance improvement has been reported, such improvement is not self-evident. There has yet to be a detailed comparison of the achieved microstructures in order to identify the relevant microstructural parameters. Asymmetric membranes from Ba0.5Sr0.5(Co0.8Fe0.2)0.97Zr0.03O3-δ consisting of a surface-activated 20 µm membrane layer with tape- or freeze-cast supports that have identical pore volume and layer thickness were manufactured, characterized, and compared by means of oxygen flux measurements. They were also microstructurally investigated via computed X-Ray tomography and flow simulation experiments. In the air/Ar gradient, the freeze-cast support membrane performs below the tape-cast-supported membrane. In particular, the transition zone close to the membrane, which is caused by the freezing process, significantly constrains the diffusivity and permeability of the support, and therefore leads to concentration polarizations. At temperatures below 800 °C, surface exchange kinetics at the membrane-support interface become rate-limiting.
•Membrane manufacturing by tape- and freeze-casting with controlled microstructure.•Membrane oxygen permeation performance analyzed.•Detailed microstructure analysis by computed X-ray tomography additionally to SEM.•Tape cast membrane oxygen permeation better than the freeze cast membrane.•Analysis of the support microstructure's influence on the gas transport.
Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is widely known as a promising candidate material for oxygen transport membranes (OTMs). In order to maximize the oxygen permeation through such a membrane, the ...membrane layer should be as thin as possible, which requires a porous support. Because of the expansion behavior of BSCF, porous supports of the same material were developed to avoid failure due to mismatches in the thermal expansion coefficients. For the purpose of minimizing concentration polarization in the support pores, the microstructure of these support-layers has been optimized. For that reason supports with a porosity of up to 41% were developed. Membrane curvature caused by different shrinkage rates during co-firing could be minimized by the use of corn starch as pore former. By increasing the support porosity from 26% to 41%, the oxygen permeation of a supported 20μm membrane in an air–argon gradient at 800°C was increased by 50%. Compared to a disc membrane of 0.9mm thickness the permeation enhancement is 90%.
► Supported 20μm membrane layers manufactured by sequential tape casting. ► Support porosity optimized (porosity >40%). ► Adjusting sintering behavior of supports by pore former leads to low deflection. ► Support still limits oxygen transport while using air as feed gas. ► Oxygen permeation rates up to 29mlcm−2min−1 at 900°C achieved.
Photochemical upconversion based on triplet-triplet annihilation (TTA-UC) is employed to enhance the short-circuit currents generated by two varieties of thin-film solar cells, a hydrogenated ...amorphous silicon (a-Si:H) solar cell and a dye-sensitized solar cell (DSC). TTA-UC is exploited to harvest transmitted sub-bandgap photons, combine their energies and re-radiate upconverted photons back towards the solar cells. In the present study we employ a dual-emitter TTA-UC system which allows for significantly improved UC quantum yields as compared to the previously used single-emitter TTA systems. In doing so we achieve record photo-current enhancement values for both the a-Si:H device and the DSC, surpassing 10
−3
mA cm
−2
sun
−2
for the first time for a TTA-UC system and marking a record for upconversion-enhanced solar cells in general. We discuss pertinent challenges of the TTA-UC technology which need to be addressed in order to achieve its viable device application.
A dual-emitter upconvertor is applied to thin-film solar cells for the first time, generating record figures of merit.
•First realization of planar, asymmetric membrane components for 4-end operation.•Design of the membrane component supported by FEM and CFD simulations.•Flexible process chain for the production of ...membrane components developed.•Fabrication of defect free membrane components by scalable processes.
Membrane-based oxy-combustion is a promising technology for energy efficient combustion of carbon-containing fuels with the simultaneous opportunity to capture CO2 from the resulting exhaust gas. However, oxy-combustion conditions result in special demands on the design of the ceramic membrane components due to the high pressure and temperature applied. Therefore, we have developed a planar membrane design for 4-end operation using asymmetric membranes of La0.6Sr0.4Co0.2Fe0.8O3−δ. FEM and CFD simulations have been performed in order to develop an internal channel structure that allows withstanding pressures of 5 bar on the feed side while achieving the desired O2 concentrations of 27% in the sweep gas, i.e. CO2, and an oxygen recovery rate from the feed gas of 86% at the same time.
Due to the symmetric design of the membrane components, they are scalable and adaptable in size. This design has been realized in a process chain from powder to the final component consisting of thin 20 µm Membrane layer, support with 38% porosity, an inner channelled architecture and a thin (3–5 µm) porous activation layer. Particular emphasis was laid on scalable manufacturing processes in order to ensure transferability to industrial scale. The process chain is also applicable to other membrane materials suitable for any application of interest. Finally, the reproducible processing was successfully demonstrated by the fabrication of membrane components in lengths of 100 mm and widths of 70 mm.
Accurate prediction of future wind speed is important for wind energy integration into the power grid. Wind speeds are usually measured and predicted at lower heights, while modern wind turbines have ...hub heights of about 80-120 m. As per understanding, this is first attempt to analyze predictability of wind speed with height. To achieve this, wind data was collected using Laser Illuminated Detection and Ranging (LiDAR) system at 10 m, 20 m, 40 m, 90 m, 120 m, 200 m, 250 m and 300 m heights. The collected data is used for training and testing an Artificial Neural Network (ANN) for hourly wind speed prediction for each of the future 12 hours, using 48 previous hourly values. Careful analyses of short term wind speed prediction at different heights and future hours show that wind speed is predicted more accurately at higher heights. For example, the mean absolute percent error decreases from 0.25 to 0.12 corresponding to heights 10 to 300 m, respectively for the 6th future hour prediction, an improvement of around 50%. The performance of ANN method is compared with hybrid genetic algorithm and ANN method namely GANN. Results showed that GANN outperformed ANN for most of the heights for prediction of wind speed at the future 6th hour. Results are also confirmed on another data set and other methods.
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