BSCF Cathode Research Articles

Performance Investigation of Dual Layer Yttria-Stabilized Zirconia–Samaria-Doped Ceria Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells

The performance of yttria-stabilized zirconia (YSZ)–samaria-doped ceria (SDC) dual layer electrolyte anode-supported solid oxide fuel cell (AS-SOFC) was investigated. Tape-casting, lamination, and co-sintering of the NiO–YSZ anode followed by wet powder spraying of the SDC buffer layer and BSCF cathode was proposed for fabrication of these cells as an effective means of reducing the number of sintering stages required. The AS-SOFC showed a significant fuel cell performance of ∼1.9 W cm−2 at 800 °C. The fuel cell performance varies significantly with the sintering temperature of the SDC buffer layer. An optimal buffer layer sintering temperature of 1350 °C occurs due to a balance between the YSZ–SDC contact and densification at low sintering temperature and reactions between YSZ and SDC at high sintering temperatures. At high sintering temperatures, the reactions between YSZ and SDC have a detrimental effect on the fuel cell performance resulting in no power at a sintering temperature of 1500 °C.

Comparative study of La0.6Sr0.4Co0.2Fe0.8O3, Ba0.5Sr0.5Co0.2Fe0.8O3 and Sm0.5Sr0.5Co0.2Fe0.8O3 cathodes and the effect of Sm0.2Ce0.8O2 block layer in solid oxide fuel cells

In the pursuit for solid oxide fuel cell (SOFC) cathode materials which can perform better at 800 °C, perovskite structure materials La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), Ba0.5Sr0.5Co0.2Fe0.8O3 (BSCF), and Sm0.5Sr0.5Co0.2Fe0.8O3 (SSCF) are studied. Their electrochemical performance as the cathodes is compared by electrochemical impedance spectroscopy (EIS) at 800 °C for 100 h through an AISI 441 interconnect/cathode/yttria-stabilized zirconia (YSZ) electrolyte half-cell structure. SSCF cathode has the smallest polarization resistance and is the most desired cathode at 800 °C while BSCF cathode has the largest one. SrCrO4 phase forms on the LSCF and SSCF cathodes near the interconnect, but not on the BSCF cathode. With the spin coating of ∼3 μm thick Sm0.2Ce0.8O2 (SDC) block layer on the YSZ electrolyte, the polarization resistances of the three cathode materials all decrease. The SDC layer can effectively decrease the mismatch of the thermal expansion coefficients (TECs) between BSCF and YSZ.

Prevention of Reaction between (Ba,Sr)(Co,Fe)O3 Cathodes and Yttria-stabilized Zirconica Electrolytes for Intermediate-temperature Solid Oxide Fuel Cells

Perovskite (Ba,Sr)(Co,Fe)O3 (BSCF) cathodes are highly electrochemically active in the oxygen reduction process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, the phase of perovskite zirconate is formed between the BSCF cathode and yttria-stabilized zirconia (YSZ) electrolyte, which increased the cathode polarization resistance. In the present work, the (Ba,Sr)ZrO3 formation was not prevented by the insertion of a porous gadolinia-doped ceria (GDC) interlayer between the cathode and the electrolyte, when the BSCF cathode was sintered at 1100°C. Energy dispersive X-ray spectroscopy showed that the product of (Ba,Sr)ZrO3 formed between BSCF and YSZ was thicker than that of SrZrO3 formed between a conventional (La,Sr)(Co,Fe)O3 (LSCF) and YSZ. When a BSCF cathode was sintered at 900°C, no (Ba,Sr)ZrO3 formation was observed between the cathode and the electrolyte. The maximum power density at 650°C was improved from 7.5 to 740mW/cm2 by decreasing the sintering temperature of BSCF cathode from 1100°C to 900°C. Distribution of relaxation times (DRT) analysis showed that the polarization resistance of the oxygen exchange process in the BSCF cathode sintered at 900°C was lower than that in the LSCF cathode. The sintering temperature is important for obtaining high-performance BSCF cathodes for IT-SOFCs.

Composite cathode materials Ag-Ba0.5Sr0.5Co0.8Fe0.2O3 for solid oxide fuel cells

Silver-Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathodes were prepared in two ways. In the first method, Ag-BSCF composite powder was prepared in ethanol solution, where Ag nanoparticles serving as a component in the preparation of Ag-BSCF composite cathodes had been previously obtained via one-step synthesis in absolute ethanol using a neutral polymer (polyvinylpyrrolidone). To the best of our knowledge, this is the first study to use a Ag sol obtained by the above method for preparation of Ag-BSCF composite powder. Then, a paste containing this powder was screen-printed on a Sm0.2Ce0.8O1.9 electrolyte and sintered at 1,000 °C. In the second technique, an aqueous solution of AgNO3 was added to a previously sintered BSCF cathode, which was then sintered again at 800 °C. The oxygen reduction reaction at the quasi-point BSCF cathode on the Sm0.2Ce0.8O1.9 electrolyte was tested by electrochemical impedance spectroscopy at different oxygen concentrations in three electrode setup. The continuous decrease of polarization resistance was observed under polarization −0.5 V at 600 °C. The comparative studies of both obtained composite Ag-BSCF materials were performed in hydrogen-oxygen IT-SOFC involving samaria-doped ceria as an electrolyte and Ni-Gd0.2Ce0.8O1.9 anode. In both cases, the addition of silver to the cathode caused an increase in current and power density compared with an IT-SOFC built with the same components but involving a monophase BSFC cathode material.

Comparison of chromium poisoning among solid oxide fuel cell cathode materials

Chromium poisoning phenomena of solid oxide fuel cells (SOFCs) were investigated using (La0.8Sr0.2)0.98MnO3 (LSM), Pr0.8Sr0.2MnO3 (PrSM), Nd0.8Sr0.2MnO3 (NdSM), and Br0.5Sr0.5Co0.8Fe0.2O3 (BSCF) for the cathode materials and yttria-stabilized zirconia (YSZ) as the electrolyte material at 700°C under constant cathode polarization conditions. Deposition of chromium increased with increasing cathode polarization similarly for the four cathodes, although position of the deposition was different for the BSCF cathode. Chromium deposited near the cathode/electrolyte interface for the LSM cathode, the PrSM cathode and the NdSM cathode. Chromium deposition on the surface of the zirconia electrolyte was observed for the PrSM cathode and the NdSM cathode as previously observed in the LSM cathode. Oxygen deficiency in the deposited chromium on the surface of the zirconia electrolyte was also observed, thus the reaction mechanism of chromium vapor with the oxygen vacancy induced by cathode polarization was supported. The oxygen vacancy on the surface of the zirconia electrolyte seemed to be generated via metal oxides such as manganese oxide or neodymium oxide segregated from the cathode materials. Chromium deposited on the surface of the BSCF cathode. Cathode polarization seems to increase reactivity of BSCF and enhance trapping of chromium vapor near the cathode surface.

High performance La0.8Sr0.2MnO3-coated Ba0.5Sr0.5Co0.8Fe0.2O3 cathode prepared by a novel solid-solution method for intermediate temperature solid oxide fuel cells

La0.8Sr0.2MnO3 (LSM)-coated Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) composite powder (LSM-BSCF) was synthesized by a novel solid-solution method and investigated electrochemically as a cathode material for intermediate temperature solid oxide fuel cells. The cathode combined the merits of LSM and BSCF cathodes through an extended triple phase boundary and stabilized microstructure and demonstrated a polarization resistance between 0.61 and 0.09 Ω cm2 at 600 to 750 °C. Compared with high performance cathodes prepared by solution impregnation, this LSM-BSCF cathode greatly improved performance stability.

A highly active and long-term stable La-doped BaxSr1−xCo1−yFeyO3−δ cathode for solid-oxide fuel cells

Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF)-based perovskite oxides have attracted much attention as cathode materials with novel catalytic properties in intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The phase stability of these materials, however, is one of the huge obstacles for the commercialization of IT-SOFCs. Here, we examine the long-term stability and the electrochemical properties of La-doped BSCF (BLSCF) in which Ba was partially substituted with La to enhance the phase stability without losing the catalytic activity. From symmetric cell measurements, the initial electrode impedance of BLSCF was found to be 0.04 Ω cm2 in air at 973 K; it remained nearly constant even after 800 h, in contrast to BSCF without La doping. It was further demonstrated that a large tubular cell consisting of a BLSCF cathode exhibited a high maximum power density of 0.52 W cm−2 and impressive long-term stability at 973 K. Free-energy calculations using density functional theory and XRD experiments for these cathodes showed that the addition of La into BSCF cathode makes the cubic structure of the cathode stable and the phase transition into the hexagonal phase is prohibited. The excellent electrochemical activity of BSCF based cathode is maintained over 950 h in a large tubular cell.

Crystal Structure and Ionic Conductivity Study of Ni- Doped BSCF Cathode for Low Temperature SOFCS

Crystal Structure and Ionic Conductivity Study of Ni- Doped BSCF Cathode for Low Temperature SOFCS

Strontium and iron-doped barium cobaltite prepared by solution combustion synthesis: exploring a mixed-fuel approach for tailored intermediate temperature solid oxide fuel cell cathode materials

Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) powders were prepared by solution combustion synthesis using single and double fuels. The effect of the fuel mixture on the main properties of this well-known solid oxide fuel cell cathode material with high oxygen ion and electronic conduction was investigated in detail. Results showed that the fuel mixture significantly affected the area-specific resistance of the BSCF cathode materials, by controlling the oxygen deficiency and stabilizing the Co2+ oxidation state. It was demonstrated that high fuel-to-metal cations molar ratios and high reducing power of the combustion fuel mixture are mainly responsible for the decreasing of the area-specific resistance of BSCF cathode materials. Moreover, a new metastable monoclinic phase with Ba0.5Sr0.5CO3 composition was discovered in the as-burned BSCF powders, enlarging the existing information on the BSCF phase formation mechanism.

Ag decorated (Ba,Sr)(Co,Fe)O3 cathodes for solid oxide fuel cells prepared by electroless silver deposition

We reported nano-structured Ag modified Ba0.5Sr0.5Co0.6Fe0.4O3−δ (Ag@BSCF) cathode for solid oxide fuel cells (SOFCs) that is prepared by vacuum assisted electroless deposition technique. We show that the concentration of Ag can be easily adjusted by tuning the deposition time without altering the perovskite structure of the pristine BSCF. The effect of Ag loading on the electrochemical performance of the material has been systematically studied by varying the Ag loading and the working condition (oxygen partial pressure). An optimized electrode performance is observed with an Ag loading of ∼2 wt%. We demonstrate that the presence of Ag significantly reduces the electrode ohmic resistance and enhances the catalytic O2 reduction performance of the BSCF cathode.

Carbonates formed during BSCF preparation and their effects on performance of SOFCs with BSCF cathode

Series of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) samples have been prepared by modified citrate-nitrate combustion method from the precursor solutions with different pH values and citrate/metal ion ratios. The XRD results reveal that BSCF oxide free of impurity phases can be obtained from a precursor solution with a suitable pH value and a suitable C/M value, whereas CO2-TPD profiles show that there are minor carbonates species present in all BSCF samples, but the amount of these carbonates varies with the pH and C/M values of precursor solutions. The current density–voltage characteristics indicate that carbonates in the BSCF samples reduce the cell performance. The electrochemical impedance spectra (EIS) show that carbonates in BSCF lead to increases in ohmic and polarization resistances. High performance is achieved on the cell with a cathode using a pure BSCF calcined under O2 flow at 900 °C.

High performance tubular solid oxide fuel cells with BSCF cathode

Compared with planar SOFCs, tubular SOFCs have the advantages of facile sealing and easy scale up. In this study, a tubular anode-supported thin-film YSZ electrolyte SOFC was successfully fabricated by extrusion of the anode substrate in combination with wet powder spraying of the electrolyte layer. The fuel cell performance was tested by applying either hydrogen or methane as the fuel and ambient air as the cathode atmosphere. Peak power densities of 432 and 145 mW cm−2 were achieved respectively at 800 and 600 °C for a cell with conventional LSM and silver wire as the cathode and the current collector. The performance was further improved by adopting BSCF cathode with an SDC buffer layer. EIS demonstrated the large electrode polarization resistance is the main source of cell resistance, while the contact resistance is also not negligible. The performance of the cell directly operating on methane fuel was also investigated. A special operation mode by alternatively operating on methane and hydrogen fuels was adopted, which can effectively increase the cell operational stability.

Performance and Stability of Zn-Doped BSCF Cathode for IT-SOFCs

not Available.

Effect of enhanced reaction area in double layered Ba0.5Sr0.5Co0.8Fe0.2O3–δ cathode for intermediate temperature solid oxide fuel cells

To optimize the microstructure of cathode for IT-SOFCs, double layered Ba0.5Sr0.5Co0.8Fe0.2O3–δ was fabricated and its performances were evaluated. Two types of symmetric cell with BSCF cathodes were prepared on Ce0.8G0.2O1.9 electrolyte pellets using a single continuous process, electrostatic slurry spray deposition. Single layered BSCF cathode was fabricated with a porous layer only, while double layered one was fabricated with a porous layer over a thin dense layer. The polarization resistances at 500°C and the activation energy of double layered BSCF were about 61% and 22% lower than single layered BSCF, respectively. The exchange current density of double layered BSCF was also higher than that of single layered BSCF, suggesting that the larger active area of double layered BSCF cathode is effective in the increase of oxygen reduction reaction rates.

Evaluation of (Ba0.5Sr0.5)0.85Gd0.15Co0.8Fe0.2O3−δ cathode for intermediate temperature solid oxide fuel cell

A perovskite-type (Ba0.5Sr0.5)0.85Gd0.15Co0.8Fe0.2O3−δ (BSGCF) oxide has been investigated as the cathode of intermediate temperature solid oxide fuel cells (IT-SOFCs). Coulometric titration, thermogravimetry analysis, thermal expansion and four-probe DC resistance measurements indicate that the introduction of Gd3+ ions into the A-site of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) leads to the increase in both oxygen nonstoichiometry at room temperature and electrical conductivity. For example, the conductivity of BSGCF is 148Scm−1 at 507°C, over 4 times as large as that of BSCF. Furthermore, the electrochemical activity toward the oxygen reduction reaction is also enhanced by the Gd doping. Impedance spectra conducted on symmetrical half cells show that the interfacial polarization resistance of the BSGCF cathode is 0.171Ωcm2 at 600°C, smaller than 0.297Ωcm2 of the BSCF cathode. A Ni/Sm0.2Ce0.8O1.9 anode-supported single cell based on the BSGCF cathode exhibits a peak power density of 551mWcm−2 at 600°C.

Cathode materials for La 0.995Ca 0.005NbO 4 proton ceramic electrolyte

The study presents the chemical and mechanical compatibility of the proton conducting electrolyte La 0.995Ca 0.005NbO 4 (LCNO) with the LSM, LSCM and BSCF cathodes and the electrochemical performance of symmetrical cells based on LCNO. After annealing at high temperature the electrolyte-cathode mixtures in air and wet air, the obtained products were analyzed by X-ray powder diffraction (XRPD). The microstructure of the cathode and electrolyte materials and the interfaces were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The results show that LSCM cathode is chemically and mechanically stable with the LCNO electrolyte although the BSCF cathode reacts with it. Cation diffusion was observed between LSM cathode and LCNO electrolyte after the heat treatment of their mixture at T = 1150 °C. The electrochemical study performed on symmetrical cells revealed that the LSCM cathode presents the lowest value of area specific resistance (ASR) compared to the ones of the LSM and BSCF cathodes: ASR LSCM = 35 Ω cm 2; ASR LSM = 57 Ω cm 2; ASR BSCF = 416 Ω cm 2 (in humidified air at 750 °C). Finally, a CER–CER approach was used in order to minimize the polarisation resistance of the LSM cathode by mixing LSM and LCNO in different volumetric ratios. The lowest value of ASR for LSM-based composite cathode was obtained by adding 50 vol.% of LCNO to LSM cathode (ASR LSM/LCNO = 22 Ω cm 2 in humidified air at 750 °C).

Performance of Ba<sub>0.5</sub>Sr<sub>0.5</sub>Co<sub>0.8</sub>Fe<sub>0.2</sub>O<sub>3-δ</sub>-Ag Composite Cathode Materials for IT-SOFCs

°Abstract. In order to develop new cathodes for reduced temperature SOFCs, Ba0.5Sr0.5Co0.8Fe0.2O3-δ-Ag composite cathode was investigated in intermediate-temperature Solid Oxide Fuel Cells (IT-SOFCs). The XRD results suggested that no chemical reactions between BSCF and Ag in the composite cathode were found. The resistance measurements showed that the addition of Ag into BSCF improved electrical conductivity of pure BSCF, and the improved conductivity resulted in attractive cathode performance. In addition, electrochemical impedance spectra exhibited the better performance of BSCF-Ag composite cathodes than pure BSCF, e.g., the polarization resistance value of BSCF-Ag was only 0.36Ω cm2 at 650°C, which was nearly 80% lower than that of BSCF electrode. Polarization curves showed the overpotential decreased with the addition of Ag. The current density value of BSCF-Ag was 0.88Acm-2 under –120mV, about five times of that BSCF measured at 650°C. As a summary, compared to a pure BSCF cathode, it was found that adding Ag in the cathode enhanced the BSCF performance significantly.

Preparation and characteristics of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ cathodes for IT-SOFCs by electrostatic slurry spray deposition

To solve the interfacial peeling-off problem of cathode materials Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF), electrostatic slurry spray deposition (ESSD) was applied. The BSCF cathode was deposited on a CGO pellet by ESSD and the electrochemical performance of the BSCF cathode is investigated at various temperatures (650–800 °C) and oxygen partial pressures (0.15–0.8 atm). Microstructural observation showed that the BSCF/CGO half cell exhibited good adhesion between cathode and electrolyte layers without any cracks for peeling-off problem. The polarization resistance was estimated to 1.78 Ω cm 2 at 650 °C and the average activation energy was 118.8 kJ mol −1. The dependence of polarization resistances on Po 2 shows that the rate-determining step of the oxygen reduction reaction in the prepared BSCF cathode is the charge transfer between electrolyte and electrode.

Characterization and Electrochemical Performance of Composite BSCF Cathode for Intermediate-temperature Solid Oxide Fuel Cell

Characterization and Electrochemical Performance of Composite BSCF Cathode for Intermediate-temperature Solid Oxide Fuel Cell

Significant impact of the current collection material and method on the performance of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ electrodes in solid oxide fuel cells

The effects of the current collection material and method on the performance of SOFCs with Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF) cathodes are investigated. Ag paste and LaCoO 3 (LC) oxide are studied as current collection materials, and five different current collecting techniques are attempted. Cell performances are evaluated using a current-voltage test and electrochemical impedance spectra (EIS) based on two types of anode-supported fuel cells, i.e., NiO + SDC|SDC|BSCF and NiO + YSZ|YSZ|SDC|BSCF. The cell with diluted Ag paste as the current collector exhibits the highest peak power density, nearly 16 times that of a similar cell without current collector. The electrochemical characteristics of the BSCF cathode with different current collectors are further determined by EIS at 600 °C using symmetrical cells. The cell with diluted Ag paste as the current collector displays the lowest ohmic resistance (1.4 Ω cm 2) and polarization resistance (0.1 Ω cm 2). Meanwhile, the surface conductivities of various current collectors are measured by a four-probe DC conductivity technique. The surface conductivity of diluted Ag paste is 2–3 orders of magnitude higher than that of LC or BSCF. The outstanding surface conductivity of silver may reduce the contact resistance at the current collector/electrode interface and, thus, contributes to better electrode performance.