BSCF Perovskite Research Articles

Oxygen transport kinetics of BSCF-based high entropy perovskite membranes

Three high entropy BSCF perovskite membranes were designed by doping various cations into A- and/or B-sites to improve the oxygen permeation stability at 700–800 °C. The membrane with the highest mixed entropy (ΔSmix), i.e. HEBSCF-AB, can be operated stably at 750 and 800 °C, but unstable at 700 °C. To understand the degradation mechanism, the oxygen transport kinetics of the three high entropy perovskite materials were analyzed using the permeation model established by our group. An easy and feasible strategy was proposed to improve the stability of oxygen permeation. We find that the doping site has a significant influence on the bulk diffusion resistance of the membranes but has a weak effect on the interfacial exchange resistances. The continuous attenuation of HEBSCF-AB membrane at 700 °C is mainly caused by the increase of interfacial exchange resistance of the sweeping side, revealing the HEBSCF-AB oxide is not a stable catalyst for the oxygen evolution reaction when it is coated on the HEBSCF-AB membrane surfaces. By coating Sm0.5Sr0.5CoO3-δ (SSC) as the porous layer on the HEBSCF-AB surfaces for oxygen activation, the oxygen permeation flux at 700 °C becomes stable. ​It confirms that the simple approach is effective to improve the permeation stability and the high entropy strategy works well to restrain the phase transition of materials.

Reduced impedance in dual substituted strontium cobaltite nanoparticles for renewable energy applications

Sr1−xBaxCo1−xFexO3−δ (BSCF) nanoparticles were successfully synthesized with three modified wet chemical techniques; composite mediated hydrothermal method (CMHM), without water and surfactants (WOWS) sol-gel and co-precipitation methods. The probable electrical conduction mechanism of synthesized BSCF was explored via complex impedance analysis. Various physicochemical characterization techniques were employed to study the dependence of structure, homogeneity, physical parameters and electrical properties of BSCF on synthesis procedures. X-ray Diffraction (XRD) confirmed the formation of cubic BSCF perovskite structure. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated the presence of the fingerprint region of perovskite (ABO3−δ) structure. Scanning Electron Microscopy (SEM) images revealed uniformly diffused, micro porous and agglomerated morphology. Differential Thermal Analysis (DTA) and Thermogravimetry (TGA) verified the formation of intermediate metal carbonates that were decomposed to the final product. Nyquist plots against frequency (20 Hz–3 MHz) revealed single semi-circular arcs. The arc showed significant grain boundary contribution to total electrical conduction behaviour of BSCF material synthesized by CMHM and co-precipitation methods. Modulus analysis showed the Debye type conductivity relaxation in CMHM synthesized material. The AC conductivity graphs followed Jonscher’s power law. Temperature dependent (RT to 600 °C; 10 kHz) impedances showed decreasing trend that was an indication of thermally activated conduction process. A Correlation was established among structural and electrical conduction properties. Hydrothermally synthesized BSCF samples exhibited minimum impedances and maximum AC conductivity, which makes them a potential candidate for cathode material in (IT-SOFCs) applications.

Carbonation passivation layer of scandium loaded BSCF perovskite

Abstract This work investigates the improved CO 2 stability of the partial substitution of scandium (Sc) in the B-site of perovskite ceramic materials thus forming a compound also containing barium (Ba), strontium (Sr), cobalt (Co) and iron (Fe) as Ba 0.5 Sr 0.5 (Co 0.8 Fe 0.2 ) 1−x Sc x O 3-δ . The concentration of Sc in the B-site was varied between 0 and 40 mol%. It was found that perovskite cubic structure was maintained by the substitution with Sc. Further, the cubic cell lattice parameter increased as a function of Sc. However, XRD parameters showed that not all Sc was fully incorporated into the crystal structure of the perovskite, as Sc 2 O 3 phase was also detected. Exposure of as-prepared powders to CO 2 gases resulted in the carbonation reactions occurring at temperatures about 100 °C below those observed for unstable pure BSCF (i.e. no Sc) perovskite. This was attributed to the catalytic effect of Sc, which promoted the carbonation reaction of BSCF-Sc. Subsequently, discs were prepared and exposed to CO 2 gases at 800 °C. The analysis of the discs’ surface showed that the perovskite cubic structure retained 96% of its original values upon CO 2 exposure for the samples loaded with 40 mol% Sc, which then reduced to 32% to samples containing 5 mol% Sc. These results proved to be counterintuitive, as Sc promoted the carbonation reaction at lower temperatures for powders, though enhanced the stability of disc exposed to CO 2 atmosphere. Further analyses of the discs by scanning electron microscopy revealed images containing a rich carbon layer, as a passivation carbonation layer, which protected the remainder of the bulk perovskite structure in the disc.

Synthesis and Characterization of Ba0.5Sr0.5NixCo0.8‐xFe0.2O3‐δ (x=0 and 0.2) Perovskites as Electro‐catalysts for Methanol Oxidation in Alkaline Media

AbstractIn this study, the perovskite‐type oxides Ba0.5Sr0.5Ni0.2Co0.6Fe0.2O3‐δ (BSNCF) with different B‐site transition metal elements were investigated as a new catalyst for methanol oxidation. They were prepared by the partial substitution of cobalt by nickel in Ba0.5Sr0.5Co0.8Fe0.2O3‐δ (BSCF) sample. Both materials prepared using a combined citrate/EDTA complexing method and their catalytic activitiesfor methanol oxidation were comparativelystudied using cyclic‐voltammetry (CV) and chronoamperometry (CA) in alkaline media at room temperature. Structural, textural, morphological and redox properties of the synthesized solids were investigated by several physicochemical methods such as XRD, FTIR, LRS, SEM‐EDX, BET and H2‐TPR. The as‐prepared materials were obtained with high purity and high crystallinity. The partial substitution of cobalt by nickel in BSCF perovskite changes the structure of the solid which pass from cubic structure to a mixture of cubic and hexagonal forms. This change is accompanied by an increase in BET surface area and a decrease in crystalline size. For the electro‐catalysis measurements, results demonstrated that partially substituting of Co by Ni in BSCF structure enhance the electro‐catalytical activity towards the oxidation of methanol under alkaline conditions, making it an electro‐catalyst candidate for practical utilization in DMFCs.

Phase separation in BSCF perovskite under elevated oxygen pressures ranging from 1 to 50 bar

The influence of elevated oxygen pressure (from 1 to 50bar) on phase separation in Ba0.5Sr0.5Co0.8Fe0.2O3−δ(BSCF) cubic perovskite was investigated in the range of 300to 1300K. X-ray diffraction and thermogravimetric analysis revealed two separation processes occurring in the high temperature (HT), ~1043K, and low temperature (LT), ~713K, ranges. Increasing oxygen pressure shifts slightly the LT phase separation to lower temperature, but has a rather minor effect on the volume fraction growth of the secondary phase. Phase transformation in the HT range is a slow process and the degree of decomposition is strongly influenced by the cooling rate from higher temperatures. On the contrary, the LT separation is relatively fast and is essentially independent of the cooling rate. The BSCF ceramics thermally treated at p(O2)=50bar was analyzed by different electron microscopy techniques. The structures of separation products were identified as trigonal Ba3Co10O17-like lamellae and 2H-hexagonal Ba0.5±xSr0.5±xCoO3−δ perovskite, respectively.

Enhanced Oxygen Permeation Behavior of Ba0.5Sr0.5Co0.8Fe0.2O3−δ Membranes in a CO2-Containing Atmosphere with a Sm0.2Ce0.8O1.9 Functional Shell

The deployment of clean energy technologies has faced an uphill battle to reduce the cost. Ion-conducting membranes for cost-effective oxygen production help to overcome this bottleneck. The existing high-performance perovskite membrane, such as Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), is featured with a short running life as a result of the low material stability; surface decoration with a robust ion-conducting layer is one of the important strategies for improvement. To this purpose, in this work, an ultrathin dense Sm0.2Ce0.8O1.9 (SDC) with approximate 100 nm thickness has been successfully coated on the BSCF perovskite membrane surface for highly efficient oxygen production. In comparison to the pristine BSCF membrane, this new modified structure offers the enhanced performance of oxygen flux as a result of the better surface-exchange kinetics. Most importantly, the long-term oxygen permeation test under a CO2 atmosphere shows that the SDC-shell-protected BSCF membrane has improved stability comparable to the...

Synthesis of BSCF perovskites using a microwave-assisted combustion method

Ba0.5Sr0.5Co0.8Fe0.2O3−Δ (BSCF) perovskite-type oxide was synthesized using a microwave-assisted combustion method. Following about 10min of exposure to microwave, the combustion reaction was self-ignited and it produced a porous powder. For comparison, BSCF perovskite powders were also synthesized by conventional heating. Two different fuel types were used in the two heating methods. The crystalline BSCF powders were characterized using scanning calorimetry and thermogravimetry (DSC/TG), X-ray diffraction (XRD), BET surface area measurement, scanning electron microscopy (SEM), and dilatometric analysis. The microwave heating method resulted in a powder with nanometric crystallites, submicrometric particles, and a specific surface area of 9.93m2/g, which corresponds to a BET diameter of approximately 100nm. The dilatometric analysis showed that the microwave-synthesized BSCF powder has the maximum sintering rate at 970°C, but the sintering process initiates at lower temperatures.

SrNb0.1Co0.7Fe0.2O3−δ Perovskite as a Next‐Generation Electrocatalyst for Oxygen Evolution in Alkaline Solution

AbstractThe perovskite SrNb0.1Co0.7Fe0.2O3−δ (SNCF) is a promising OER electrocatalyst for the oxygen evolution reaction (OER), with remarkable activity and stability in alkaline solutions. This catalyst exhibits a higher intrinsic OER activity, a smaller Tafel slope and better stability than the state‐of‐the‐art precious‐metal IrO2 catalyst and the well‐known BSCF perovskite. The mass activity and stability are further improved by ball milling. Several factors including the optimized eg orbital filling, good ionic and charge transfer abilities, as well as high OH− adsorption and O2 desorption capabilities possibly contribute to the excellent OER activity.

SrNb(0.1)Co(0.7)Fe(0.2)O(3-δ) perovskite as a next-generation electrocatalyst for oxygen evolution in alkaline solution.

The perovskite SrNb0.1 Co0.7 Fe0.2 O3-δ (SNCF) is a promising OER electrocatalyst for the oxygen evolution reaction (OER), with remarkable activity and stability in alkaline solutions. This catalyst exhibits a higher intrinsic OER activity, a smaller Tafel slope and better stability than the state-of-the-art precious-metal IrO2 catalyst and the well-known BSCF perovskite. The mass activity and stability are further improved by ball milling. Several factors including the optimized eg orbital filling, good ionic and charge transfer abilities, as well as high OH(-) adsorption and O2 desorption capabilities possibly contribute to the excellent OER activity.

Interaction of hexavalent chromium and BSCF perovskite in water solutions

In this study, interaction of BSCF perovskite and hexavalent chromium in the aqueous solution was followed to provide additional useful insight in chemistry and behavior of this material. Adsorption experiments were carried out systematically by batch experiments to investigate the influence of contact time, temperature and initial concentration of metal ions. The adsorption data obtained were described by the Freundlich and Langmuir adsorption isotherm model. Thermodynamic study of hexavalent chromium adsorption on BSCF perovskite showed that the spontaneous adsorption process will be favored at higher temperatures (from 343 K) depending on the chromium concentration in water. .

New high temperature sealing technique and permeability data for hollow fiber BSCF perovskite membranes

Oxygen permeation through BSCF perovskite hollow fiber membranes has been investigated in a laboratory scale reactor in a temperature range of 850–1000°C at atmospheric pressure. An experimental study was conducted with particular focus on a new sealing technique which was found to provide fully gas-tight conditions with a 100% success rate for the 6 membranes reported in this work (and for 15 membranes in total). An overview of experimental tests on other sealants proposed in the literature is given. A new method for checking the sealing is suggested that allows detecting the possible leakages in all the parts of the membrane module. A loose-end reactor with a shell-and-tube layout is presented which allows accurate measurements of both gas leakages (if any) and product gas composition in a wide range of operating conditions (flow rates on both the permeate and feed side, O2 feed partial pressure, temperature). Permeation fluxes were studied for BSCF membranes with different thicknesses (0.2 and 0.5mm) using He as sweep gas. The O2 flux increased with both increasing the O2 driving force (i.e., the O2 partial pressure difference through the dense ceramic layer) and the reactor temperature. Long term tests (600h) have been carried out proving the high stability of both the membranes used and the newly proposed sealing technique. The presence of both O2 bulk diffusion and surface exchange resistance is suggested to limit the permeation rate of the ceramic hollow fibers for the range of wall thicknesses investigated. Finally, LSCF capillaries have also been successfully sealed allowing to extend the use of the proposed gas tight sealing system to different compositions of hollow fibers perovskite membranes.

In Situ Tetraethoxysilane‐Templated Porous Ba0.5Sr0.5Co0.8Fe0.2O3−δ Perovskite for the Oxygen Evolution Reaction

AbstractThe perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is one of the best catalysts for the oxygen evolution reaction (OER), which is critical to many energy‐storage applications. However, the catalytic activity of BSCF perovskites is constrained by a low specific surface area (0.5 m2 g−1). We report here, for the first time, a facile, in situ template method using tetraethoxysilane (TEOS) to synthesize porous BSCF with surface areas of up to 32.1 m2 g−1, which to our knowledge is the highest reported surface area in a BSCF perovskite, and with excellent catalytic activity for the OER. For example, the BCSF prepared using a TEOS‐to‐BSCF ratio of 3.4 exhibited up to 35.2 A g−1 at 1.63 V versus a reversible hydrogen electrode (overpotential, η=0.4 V) and this current is 5.3 times that exhibited by nonporous BSCF (6.6 A g−1). The high activity of the porous BCSF is attributed to the additional catalytic surface sites available in the pores created by the in situ TEOS‐template method. The general application of this technique to produce porous perovskites is demonstrated in the synthesis of a second example, porous LaMnO3.

Investigation of Zr-doped BSCF perovskite membrane for oxygen separation in the intermediate temperature range

The series of (Ba0.5Sr0.5)(Co0.8Fe0.2)1−zZrzO3−δ (z=0, 0.01, 0.03, 0.05, 0.07, and 0.09) was synthesized by a sol–gel method. The materials with a zirconium content up to 3 mol% were found to be single phase. Further increase results in formation of a mixed (Ba,Sr)ZrO3 by-phase, which was found along the grain boundaries and in the grains. With increasing zirconium content the oxygen permeation flux decreases considerably. The effect of the zirconium substitution on the long-term phase stability was investigated by long-term oxygen permeation experiments and X-ray diffraction. A slight stabilization of the oxygen flux of (Ba0.5Sr0.5)(Co0.8Fe0.2)0.97Zr0.03O3−δ was found after 180 h at 1023 K. However, all compositions show a decrease in permeation flux with time, but the pure BSCF membrane exhibited the strongest drop after 180 h of operation. The decomposition products of the cubic perovskite phase were found to be a hexagonal Ba0.5±xSr0.5±xCoO3 and a rhombohedral Ba1−xSrxCo2−yFeyO5−δ.

Phase Stability and Permeation Behavior of a Dead-End Ba0.5Sr0.5Co0.8Fe0.2O3−δTube Membrane in High-Purity Oxygen Production

Phase stability and oxygen permeation behavior of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) dead-end tube membranes were investigated in long-term oxygen production at 950 and 750 °C. At 950 °C, the BSCF tube membranes exhibit good long-term phase stability and a stable oxygen permeation flux. However, at the intermediate temperature of 750 °C, both the oxygen permeation flux and the oxygen purity decrease continuously. This behavior is related to the formation of two secondary phases that are a hexagonal perovskite, Ba0.5±xSr0.5±xCoO3−δ, and a trigonal mixed oxide, Ba1–xSrxCo2–yFeyO5, that evolved in the ceramic membrane made of cubic BSCF perovskite during the dynamic flow of oxygen through it. Tensile stress as a result of phase formation causes the development of cracks in the membrane, which spoil the purity of the permeated oxygen. The partial degradation of cubic BSCF perovskite in the intermediate temperature range (750 °C) was more pronounced under the strongly oxidizing conditions on the oxygen supply (fe...

Effect of foreign oxides on the phase structure, sintering and transport properties of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ as ceramic membranes for oxygen separation

A series of foreign oxides including CuO, ZnO, NiO, Co 2O 3 and Al 2O 3 were investigated as sintering aids to facilitate the densification of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF) membranes for oxygen separation. The effects of these oxides on the phase structure, sintering behavior, electrical conductivity and oxygen permeability of BSCF oxide were systematically studied by X-ray diffraction (XRD), oxygen temperature-programmed desorption (O 2-TPD), environmental scanning electron microscopy (ESEM), four-probe direct current (DC) conductivity and gas permeation measurements. The results showed that reactions between the membrane material and the foreign oxides took place at elevated temperatures. These oxides displayed different sintering behaviors during the sintering process of BSCF perovskite, with obvious improvement demonstrated in the case of CuO, minimal effects observed from ZnO, Co 2O 3 and NiO samples, and suppressing effects from Al 2O 3. The electrical conductivity was clearly increased by introducing Co 2O 3 as a sintering aid, yielding a maximum value of 70 S cm −1 at 900 °C. The oxygen permeation fluxes of the membrane samples from BSCF + NiO (5 wt.%) and BSCF + ZnO (5 wt.%) are comparable to those of pristine BSCF membranes, whereas the fluxes decreased noticeably when the other foreign oxides were introduced.

Thermochemistry of brazing ceramics and metals in air

Abstract Reactive air brazing offers economically and technologically advantageous joining of ceramics to metals. Solid oxide fuel cells and membranes for oxyfuel combustion are recent fields of application. However, it remains a problem that strong metallurgical reactions between brazes and base materials occur. These reactions were analysed by differential scanning calorimetry tests to get a better understanding. Therefore, three braze alloys (Ag8Cu, Ag8Cu0.5Ti and Ag4Cu4Ni) and five base materials (alumina, 3YSZ partially stabilised zirconia, BSCF perovskite ceramic, X1CrTiLa22 and X15CrNiSi25-20) were investigated. The reaction peaks correlate with the formation of reaction layers, which were observed in metallographic analysis of brazed specimens. The results help to explain the reaction mechanisms and allow optimised selection of filler metals and brazing temperature.

Yttrium doped BSCF membranes for oxygen separation

This work investigates the partial substitution of yttrium in place of iron in BSCF to form Ba 0.5Sr 0.5Co 0.8Fe 0.2− x Y x O 3− δ , where x varied between 0 and 0.2. X-ray diffraction patterns showed the formation of a perovskite cubic phase structure up to x = 0.15, whilst the full substitution of yttrium ( x = 0.2) for iron resulted in a non-cubic crystal structure that did not exhibit oxygen permeation. The yttrium partial substitution in BSCFY discs (1.2 mm thick) delivered best results for x = 0.025, as oxygen fluxes reached 2.05 ml cm −2 min −1 at 900 °C, an increase of 160% as compared to a blank BSCF ( x = 0) membrane. This was attributed to the combined effect of the formation of a greater number of oxygen vacancies, together with improved ion mobility, associated with the beneficial yttrium substitution into the BSCF perovskite structure which stemmed from the crystal lattice expansion.

Synthesis of Ba<sub>0.5</sub>Sr<sub>0.5</sub>Co<sub>0.2</sub>Fe<sub>0.8</sub>O<sub>3</sub> (BSCF) Nanoceramic Cathode Powders by Sol-Gel Process for Solid Oxide Fuel Cell (SOFC) Application

The nano ceramic Ba0.5Sr0.5Co0.2Fe0.8O3 (BSCF) powders have been synthesized by Sol-Gel process using nitrate based chemicals for SOFC applications since these powders are considered to be more promising cathode materials for SOFC. Glycine was used as a chelant agent and ethylene glycol as a dispersant. The powders were calcined at 850℃/3 hr in the air using Thermolyne 47,900 furnace. These powders were characterized by employing SEM/EDS, XRD and TGA/DTA techniques. The SEM images BSCF powder indicate the presence of highly porous spherical particles with nano sizes. The XRD results shows the formation of BSCF perovskite phase at the calcination temperature of 850℃. From XRD line broadening technique, the average crystllite size of the BSCF powders were found to be around 9.15 - 11.83 nm and 13.63 - 17.47 nm for as prepared and after calcination at 850℃ respectively. The TGA plot shows that there is no weight loss after the temperature around 450℃ indicating completion of combustion.

Thermomechanical representation of the stored energy during plastic deformation

AbstractReactive air brazing offers economically and technologically advantageous joining of ceramics to metals. Solid oxide fuel cells and membranes for oxyfuel combustion are recent fields of application. However, it remains a problem that strong metallurgical reactions between brazes and base materials occur. These reactions were analysed by differential scanning calorimetry tests to get a better understanding. Therefore, three braze alloys (Ag8Cu, Ag8Cu0.5Ti and Ag4Cu4Ni) and five base materials (alumina, 3YSZ partially stabilised zirconia, BSCF perovskite ceramic, X1CrTiLa22 and X15CrNiSi25-20) were investigated. The reaction peaks correlate with the formation of reaction layers, which were observed in metallographic analysis of brazed specimens. The results help to explain the reaction mechanisms and allow optimised selection of filler metals and brazing temperature.

In situ templating synthesis of conic Ba0·5Sr0·5Co0·8Fe0·2O3−δ perovskite at elevated temperature

Conic Ba0·5Sr0·5Co0·8Fe0·2O3−δ (BSCF) functional composite oxide was synthesized via a simple in situ templating process. The treatment of the solid precursor with concentrated nitric acid resulted in the mismatch of ionic radius at A-site and B-site of the ABO3 perovskite, due to the oxidation of cobalt/iron ions, and the formation of Ba0·5Sr0·5(NO3)2 solid solution. Therefore, instead of the direct formation of BSCF oxide, an intermediate phase of Ba0·5Sr0·5CoO3 (BSC) in hexagonal lattice structure and with conic particle shape was preferentially formed during calcination at low temperature. BSCF perovskite was then produced by the in situ templating of BSC with iron diffusing into the BSC lattice during calcination at high temperature. Well-crystallized BSCF particles in conic shape were obtained by the calcination of the nitric acid treated precursor at 900°C.