Barium-doped Sr2Fe1.5Mo0.5O6-δ perovskite anode materials for protonic ceramic fuel cells for ethane conversion

Protonic ceramic ethane fuel cells fed by hydrocarbon fuels are demonstrated to be effective energy conversion devices. However, their practical application is impeded by a lack of anode materials combining excellent catalytic activity with good chemical stability and anti-carbon deposition properties. In this work, in which Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) double perovskite oxide is used as the matrix framework, catalytic activity toward H₂ and C₂H₆ oxidation is systematically investigated using Ba-doping. It is found that the concentration of the oxygen vacancy is gradually improved with increased Ba content to significantly enhance catalytic activity toward H₂ and C₂H₆ oxidation. From the series studied, Ba_0.6Sr_1.4Fe_1.5Mo_0.5O_6-δ exhibits the highest catalytic activity, while the power densities of the electrolyte-supported Ba_0.6SFM/BaCe_0.7Zr_0.1Y_0.2O_3-δ (BCZY)/La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF)-Sm_0.2Ce_0.8O_2-δ (SDC) single cell reach 205 and 138 mW cm^–2 at 750°C in H₂ and C₂H₆, respectively. The ethane conversion rate of the experimental cell is shown to reach 38.4%, while simultaneously maintaining ethylene selectivity at 95%. Furthermore, the single cell exhibits no significant attenuation during stable operation for 20 h, as well as demonstrating excellent anti-coking performance. The proposed results suggest that Ba_0.6Sr_1.4Fe_1.5Mo_0.5O_6-δ represents a promising anode material for efficient hydrocarbon-related electrochemical conversion to realize the coproduction of ethylene and power in protonic ceramic ethane fuel cells.     

Tuning Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode to high stability and activity via Ce-doping for ceramic fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) fuel-cell cathode stands out because of its ultrahigh ionic conductivity and excellent electrocatalytic activity, but it is still very subject to instability. Here, a new strategy of Ce doping is proposed to boost the stability and activity of the BSCF cathode. A one-pot combustion method is employed to synthesize (Ba_0.5Sr_0.5)_1–xCe_xCo_0.8Fe_0.2O_3-δ (x=0–0.2) cathodes. Both BSCF and (Ba_0.5Sr_0.5)_0.9Ce_0.1Co_0.8Fe_0.2O_3-δ have a cubic perovskite structure. (Ba_0.5Sr_0.5)_0.8Ce_0.2Co_0.8Fe_0.2O_3-δ shows two phases of cubic perovskite and fluorite ceria. Proper Ce doping can boost the electrical conductivity of BSCF, and can dramatically reduce the polarization resistance of BSCF cathode. Ce doping significantly improved BSCF cathode long-term stability by 160 h. Moreover, ten-percent Ce doping in BSCF highly improves single-cell output performance from 516.33 mW cm^?2 to 629.75 mW cm^?2 at 750 °C. The results reveal that Ce doping as a potential strategy for enhancing the stability and activity of BSCF cathode is promising.     

Improving performance of proton ceramic electrolysis cell perovskite anode by Zn doping

As an important renewable energy, hydrogen energy becomes an important part of the future energy system. Proton ceramic electrolysis cell (PCEC) enables the efficient, clean, large-scale preparation of hydrogen, which is a new type of energy conversion device, attracting the attention of many researchers. Sr₂Fe_1.4Zn_0.1Mo_0.5O_6-δ (SFZM) anode materials were developed to investigate the effect of B-site doping of Zn on the electrochemical properties of the Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) materials. The results reveal that the doping of Zn increases the concentration of oxygen vacancies and improves the electrocatalytic activity, which in turn improves the performance of the material. A current density of 408 mA cm⁻² has been achieved at 1.3 V when the SFZM-based single cell was operated in an electrolysis mode (50% H₂O in air) at 600 °C, higher than SFM-based single cells (286 mA cm⁻² at 1.3 V). In addition, the SFZM-based single cell exhibited good durability in a stability test at an electrolysis current density of 408 mA cm⁻². This work confirms that SFZM is a promising material for proton ceramic electrolysis cell anode.     

La0.5Sr0.5Fe0.9Mo0.1O3-δ-CeO2 anode catalyst for Co-Producing electricity and ethylene from ethane in proton-conducting solid oxide fuel cells

A La_0.5Sr_0.5Fe_0.9Mo_0.1O_3-δ-CeO₂ (LSFM-CeO₂) composite was prepared by impregnating CeO₂ into porous La_0.5Sr_0.5Fe_0.9Mo_0.1O_3-δ perovskite and was used as an anode material for proton-conducting solid oxide fuel cells (SOFCs). The maximum power densities of the BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) electrolyte-supported single cell with LSFM-CeO₂ as the anode reached 291 mW cm^?2 and 190 mW cm^?2 in hydrogen and ethane fuel at 750 °C, respectively, which are significantly higher than those of a single cell with only LSFM as the anode. Additionally, the ethylene selectivity and ethylene yield from ethane for the fuel cell at 750 °C were as high as 93.4% and 37.1%, respectively. The single cell also showed negligible degradation in performance and no carbon deposition during continuous operation for 22 h under an ethane fuel atmosphere. The improved electrochemical performance due to the impregnation of CeO₂ can be a result of enhanced electronic and ionic conductivity, abundant active sites, and a broad three-phase interface in the resultant composite anode. The LSFM-CeO₂ composite is believed to be a promising anode material for proton-conducting SOFCs for co-producing electricity and high-value chemicals from hydrocarbon fuels.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ cathode prepared by the citrate-EDTA complexing method

This study reports the successful preparation of single-phase perovskite (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ (x = 0-0.2) by the citrate-EDTA complexing method. The crystal structure, thermal gravity analysis, coefficient of thermal expansion, electrical conductivity, and electrochemical performance of (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The lattice parameter a of (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ decreases as the amount of Mn doping increases. The coefficients of thermal expansion of the samples are in the range of 21.6-25.9 × 10⁻⁶ K⁻¹ and show an abnormal expansion at around 400 °C associated with the loss of lattice oxygen. The electrical conductivity of the (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ samples decreases as the amount of Mn-doping increases. The electrical conductivity of the samples reaches a maximum value at around 400 °C and then decreases as the temperature increases. The charge transfer resistance, diffusion resistance and total resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2Fe_0.8Mn_0.15O_3-δ-Ce_0.8Sm_0.2O_1.9 composite cathode electrode at 800 °C are 0.11 Ω cm², 0.24 Ω cm² and 0.35 Ω cm², respectively.     

Performance of XSCoF (X = Ba, La and Sm) and LSCrX′ (X′ = Mn, Fe and Al) perovskite-structure materials on LSGM electrolyte for IT-SOFC

X_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (X = Ba, La and Sm) and La0.75Sr0.25Cr0.5X^′0.5O3−δ (X′ = Mn, Fe and Al) mixed ionic-electronic conducting perovskite-based oxides have been tested as SOFC electrode materials on La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) electrolytes under different atmospheres (air, oxygen, argon and dry and wet 5% H₂/Ar) and the area-specific resistances (ASR) were compared. Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCoF) possesses the lowest ASR values in air (0.04 Ω cm² at 1073 K) whilst La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM) possesses the lowest ASR values in wet 5% H₂/Ar (0.28 Ω cm² at 1073 K). In addition, fuel cell tests were carried out using wet 5% H₂/Ar as fuel and air as oxidant. The maximum power density (∼123 mW cm⁻²) at 1073 K was reached with the electrolyte-supported system BSCoF/LSGM/LSCrM (∼1.5 mm electrolyte thickness). Furthermore, LSCrX′ materials were used simultaneously as cathode and anode in fuel cell tests and the symmetric system LSCrM/LSGM/LSCrM (∼1.5 mm electrolyte thickness) reached a maximum power density of ∼54 mW cm⁻² at 1073 K.     

Ca and Pr substitution promoted the cell performance in LnSr3Fe3O10-δ cathode for solid oxide fuel cells

The substitution of Ca for Sr in the LnSr_3-xCa_xFe₃O_10-δ (x = 0–1.5, Ln = La, Pr, and Sm), Ruddlesden-Popper (RP) intergrowth structure was investigated to determine how the physical and electrochemical properties of this potential cathode material in solid oxide fuel cells (SOFCs) are impacted. A small amount of Ca incorporated into the structure reduced the thermal expansion coefficient, improved the electrical conductivity, and increased power density by up to 30% of a La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte-supported single cell. The microstructure and oxygen permeability of the materials were independent of Ca substitution. A phase transformation of LaSr_3-xCa_xFe₃O_10-δ to perovskite was observed when the Ca composition of x > 1.0. Among the substitution of Pr and Sm for La in LaSr_2.7Ca_0.3Fe₃O_10-δ, only PrSr_2.7Ca_0.3Fe₃O_10-δ was pure with no phase transformation found. The co-substitution of Pr and Ca promoted the reduction of Fe, enhanced the oxygen permeation and active surface, and diminished the contact resistance at the cathode-electrolyte interlayer. The co-substitution of Ca and Pr delivered good electrochemical performance of approximately 354 mWcm⁻² at 800 °C on a 0.3 mm thick La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte-supported cell and the lowest area specific resistance (ASR).     

Ba and Gd Doping Effect in (BaxSr1–x)0.95Gd0.05Co0.8Fe0.2O3–δ (x = 0.1–0.9) Cathode on the Phase Structure and Electrochemical Performance

In this study, Ba_xSr_1–xCo_0.8Fe_0.2O_3–δ (BSCF) doped with trace of Gd were studied for phase structures and properties about thermal expansion, electrical conductivity, and electrocatalytic activity. The solution range of barium in Ba_xSr_1–xCo_0.8Fe_0.2O_3–δ can be extended to 0.1 ≤ x ≤ 0.7 after the introduction of small amount of Gd³⁺ ions (only for 5%) into the Ba/Sr‐site. The calculation results of the crystal structure and the crystal lattice energy show that the ratio of Ba/Sr and doping of Gd³⁺ lead to increase the lattice parameter and the Co/Fe ionic average valence state in B‐site. Moreover, the ratio of Ba/Sr and doping of Gd³⁺ were found to have significant impacts on the high‐temperature physical properties and electrochemical characteristics. All oxides exhibited decreases in the thermal expansion coefficient (TEC) and electrical conductivity with increasing Ba/Sr ratio. Barium insertion was found to change the area‐specific resistance (ASR) of porous (not dense) cathodes. An ASR values of 0.048, 0.072, 0.064, 0.121, and 0.059 Ω cm² under air condition were observed at 650 °C for BSGCF with x = 0.1, 0.2, 0.3, 0.5, and 0.7, respectively.     

Compositional modification of Sr2TiCoO6 double perovskites by Mo and La for high temperature thermoelectric applications

Double perovskites (A₂B^/B^//O₆) are an interesting family of materials, which are amenable to compositional modification. Recently double perovskites have shown promising thermoelectric properties especially at high temperature. In this report, we investigated the combination of two different cubic double perovskites with similar lattice constant but one (Sr₂TiCoO₆) showing good Seebeck coefficient and the other (Sr₂TiMoO₆) with high electrical conductivity. Dense ceramic samples of Sr₂TiCo_0.5Mo_0.5O₆ and La_0.2Sr_1.8TiCo_0.5Mo_0.5O₆ were synthesized by solid state reaction method. Rietveld refinement of XRD data confirmed the cubic structure with Pm$\overline{3}$m space group in these ceramics. Doping of Mo in Sr₂TiCoO₆ helped in increasing its conductivity; however Seebeck coefficient showed the n-type behavior unlike the p-type conductivity observed in Sr₂TiCoO₆ ceramics. Aliovalent doping of La in Sr₂TiCo_0.5Mo_0.5O₆ further increased its conductivity and Seebeck coefficient demonstrated temperature driven p-type to n-type conduction switching behavior. Conductivity mechanism of these ceramics was found to be governed by small polaron hopping model. Temperature driven p-n switching observed in the thermopower (S) measurement of La_0.2Sr_1.8TiCo_0.5Mo_0.5O₆ was further explained by an analytical model.     

Electrochemical Properties of La0.5Sr0.5Co0.8M0.2O3–δ (M=Mn,Fe, Ni,Cu) Perovskite Cathodes for IT‐SOFCs

The electrochemical properties of La_0.5Sr_0.5Co_0.8M_0.2O_3–δ (M=Mn, Fe, Ni, Cu) cathodes are investigated with chemical bulk diffusion coefficients (D_chem) and polarization resistances. The electrochemical performance of long‐term testing for La_0.5Sr_0.5Co_0.8Cu_0.2O_3–δ cathode was carried out to investigate its electrochemical stability. In this work, an anode‐supported single cell with a thick‐film SDC electrolyte (30 μm), a Ni‐SDC cermet anode (1 mm), and a La_0.5Sr_0.5Co_0.8Cu_0.2O_3–δ cathode (10 μm) reaches a maximum peak power density of 983 mW/cm² at 700°C. Obviously, Cu substitution for B‐site of La_0.5Sr_0.5CoO_3–δ cathode reduced thermal expansion coefficient (TEC) value and enhanced oxygen bulk diffusion and electrochemical properties. La_0.5Sr_0.5Co_0.8Cu_0.2O_3–δ is a promising cathode material for intermediate temperature solid oxide fuel cells (IT‐SOFC).     

A redox−reversible perovskite electrode for CeO2− and LaGaO3−based symmetric solid oxide fuel cells

Perovskite oxide SrFe_0.9Mo_0.1O_3?δ (SFM) was evaluated as the electrode for symmetric solid oxide fuel cells (S–SOFCs) with Sm_0.2Ce_0.8O_2?δ (SDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3?δ (LSGM) electrolytes. Under reducing conditions at 800 °C, the SFM was reduced to be a multi-phase composite consisting of the single perovskite phase, Ruddlesden–Popper (RP) layered perovskite phase, and Fe⁰ phase. After reoxidation at 800 °C in air, this multi?phase system was again transformed into the parent perovskite phase again, indicating good redox reversibility of the SFM. At 700 °C, polarisation resistances of the SFM used as the cathodes on the LSGM and SDC electrolytes were 0.28 and 0.14 Ω cm², respectively, in air. Using H₂ as a fuel, the LSGM and SDC supported S–SOFCs with the SFM symmetric electrodes showed the peak power outputs of 253 and 269 mW cm^?2, respectively, at 700 °C. Finally, the good long-term stability and redox-cycling stability of the S–SOFCs further demonstrate the potential of the SFM as the symmetric electrode.     

Synthesis and Characterization of Oxyanion‐Doped Cobalt Containing Perovskites

In this paper, we report the incorporation of borate, silicate and phosphate into La_0.6Sr_0.4Co_0.8Fe_0.2O_3–δ (LSCF) and Sr_0.9Y_0.1CoO_3–δ (SYC) cathode materials for solid oxide fuel cells (SOFCs). In the former, an increase in the electronic conductivity was observed, which can be correlated with electron doping due to the oxyanion doping favoring the introduction of oxide ion vacancies. The highest conductivity was observed for La_0.6Sr_0.4Co_0.76Fe_0.19B_0.05O_3–δ, 1190 S cm^–1 at 700 °C, in comparison with 431 S cm^–1 for undoped La_0.6Sr_0.4Co_0.8Fe_0.2O_3–δ at the same temperature. For Sr_0.9Y_0.1CoO_3–δ series the conductivity suffers a decrease on doping, attributed to any effect of electron doping being outweighed by the effect of partial disruption of the electronic conduction pathways by the oxyanion. Composites of these cathode materials with 50% CGO10 were examined on dense CGO10 pellets and the area‐specific resistances (ASR) in symmetrical cells were determined. The ASR values, at 800 °C, were 0.20, 0.08 and 0.11 Ω cm² for La_0.6Sr_0.4Co_0.8Fe_0.2O_3–δ, La_0.6Sr_0.4Co_0.76Fe_0.19B_0.05O_3–δ and La_0.6Sr_0.4Co_0.78Fe_0.195Si_0.025O_3–δ, respectively. For the SYC materials, the oxyanion‐doped compositions also showed an improvement in the ASR values with respect to the parent compounds, despite the lower electronic conductivity in these cases. This observation may be due to an increase in ionic conductivity due to oxyanion incorporation leading to the formation of oxide ion vacancies. In addition, the stability of these systems towards CO₂ was studied. For La_0.6Sr_0.4Co_0.8(1–x)Fe_0.2(1–x)M_xO_3–δ series, all compositions showed no evidence for reactivity with CO₂ between RT and 1000 °C. On the other hand, for the Sr_0.9Y_0.1Co_1–xM_xO_3–δ series, some reactivity was observed, although the CO₂ stability was shown to be improved on oxyanion doping. Thus, these results show that oxyanion doping can have a beneficial effect on the performance of perovskite cobaltite cathode materials.     

A Performance Study of Solid Oxide Fuel Cells With BaZr0.1Ce0.7Y0.2O3–δ Electrolyte Developed by Spray‐Modified Pressing Method

Fuel cells with BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY) proton‐conducting electrolyte is fabricated using spray‐modified pressing method. In the present study the spray‐modified pressing technology is developed to prepare thin electrolyte layers on porous Ni‐BZCY anode supports. SEM data show the BZCY electrolyte film is uniform and dense, well‐bonded with the anode substrate. An anode‐supported fuel cell with BZCY electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ (BSCF) cathode is characterized from 600 to 700 °C using hydrogen as fuel and ambient air as oxidant. Maximum power density of 536 mW cm^–2 along with a 1.01 V OCV at 700 °C is obtained. Impedance spectra show that Ohmic resistances contribute minor parts to the total ones, for instance, only ~23% when operating at 600 °C. The results demonstrate that spray‐modified pressing technology offers a simple and effective way to fabricate quality electrolyte film suitable to operate in intermediate temperature.     

Sr2Fe1.5Mo0.5O6–δ – Zr0.84Y0.16O2–δ Materials as Oxygen Electrodes for Solid Oxide Electrolysis Cells

The high‐temperature solid oxide electrolysis cell (SOEC) is one of the most promising devices for hydrogen mass production. To make SOEC suitable from an economical point of view, each component of the SOEC has to be optimized. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on an alternative oxygen electrode of Zr_0.84Y_0.16O_2–δ‐Sr₂Fe_1.5Mo_0.5O_6–δ (YSZ‐SFM). YSZ‐SFM composite oxygen electrodes were fabricated by impregnating the YSZ matrix with SFM, and the ion‐impregnated YSZ‐SFM composite oxygen electrodes showed excellent performance. For a voltage of 1.2 V, the electrolysis current was 223 mA cm⁻², 327 mA cm⁻² and 310 mA cm⁻² at 750 °C for the YSZ‐SFM10, YSZ‐SFM20, and YSZ‐SFM30 oxygen electrode, respectively. A hydrogen production rate as high as 11.46 NL h⁻¹ has been achieved for the SOEC with the YSZ‐SFM20 electrode at 750 °C. The results demonstrate that YSZ‐SFM fabricated by impregnating the YSZ matrix with SFM is a promising composite electrode for the SOEC.     

Enhancing oxygen permeation via multiple types of oxygen transport paths in hepta‐bore perovskite hollow fibers

The multiple types of efficient oxygen transport paths were demonstrated in high‐mechanical‐strength hepta‐bore Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ hollow fiber membranes. These types of paths play a prominent role in enhancing oxygen permeation fluxes (17.6 mL min^?1 cm^?2 at 1223 K) which greatly transcend the performance of state‐of‐the‐art Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ hollow fiber membranes, showing a good commercialization prospect. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4273–4277, 2017     

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

A perovskite-type (Ba_0.5Sr_0.5)_0.85Gd_0.15Co_0.8Fe_0.2O_3?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 Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF) leads to the increase in both oxygen nonstoichiometry at room temperature and electrical conductivity. For example, the conductivity of BSGCF is 148 S cm^?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 0.171 Ω cm² at 600 °C, smaller than 0.297 Ω cm² of the BSCF cathode. A Ni/Sm_0.2Ce_0.8O_1.9 anode-supported single cell based on the BSGCF cathode exhibits a peak power density of 551 mW cm^?2 at 600 °C.     

Development of Single Chamber Solid Oxide Fuel Cells (SCFC)

Single Chamber Solid Oxide Fuel Cells (SCFC) have been prepared using an electrolyte as support (Ce_0.9Gd_0.1O_1.95 named GDC). Anode (Ni‐GDC) and different cathodes (Sm_0.5Sr_0.5CoO₃ (SSC), Ba_0.5Sr_0.5Co_0.2Fe_0.8O₃ (BSCF) and La_0.8Sr_0.2MnO₃ (LSM)) were placed on the same side of the electrolyte. All the electrodes were deposited using screen‐printing technology. A gold collector was also deposited on the cathode to decrease the over‐potential. The different materials and fuel cell devices were tested under propane/air mixture, after a preliminary treatment under hydrogen to reduce the as‐deposited nickel oxide anode. The results show that SSC and BSCF cathodes are not stable in these conditions, leading to a very low open circuit voltage (OCV) of 150 mV. Although LSM material is not the more adequate cathode regarding its high catalytic activity towards hydrocarbon conversion, it has a better chemical stability than SSC and BSCF. Ni‐GDC‐LSM SCFC devices were elaborated and tested; an OCV of nearly 750 mV could be obtained with maximum power densities around 20 mW cm^–2 at 620 °C, under air–propane mixture with C₃H₈/O₂ ratio equal to 0.53.     

Assessment of cobalt–free ferrite–based perovskite Ln0.5Sr0.5Fe0.9Mo0.1O3–δ (Ln = lanthanide) as cathodes for IT-SOFCs

Cobalt–free perovskites Ln_0.5Sr_0.5Fe_0.9Mo_0.1O_3–δ (Ln = lanthanide; LnSFM) were prepared via a sol–gel process. Pure rhombohedral phases were still not obtained for the samples (Ln = Sm and Gd) even sintered at 1300 °C. Thus, only the LaSFM, PrSFM and NdSFM compositions were assessed as IT–SOFC cathodes in terms of their thermal, electrical and electrochemical properties. Thermal expansion of the LnSFM was well compatible with that of Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. Both conductivity and electrochemical performances of the LnSFM followed the same sequence of La > Nd > Pr. For the LaSFM, NdSFM and PrSFM cathodes, peak conductivities reached 73, 63 and 59 S·cm^–1 at 650 °C; polarization resistances attained 0.211, 0.446 and 0.469 Ω·cm² at 700 °C; peak power densities of the LnSFM cells with 300–μm–thick SDC electrolyte achieved 269, 261 and 233 mW·cm^–2 at 700 °C without cell degradation for operating 100 h. By comprehensive comparison, the LaSFM is assessed as a preferred cobalt–free ceramic cathode for IT–SOFC.     

The effect of Fe2+ state in electrical property variations of Sn‐doped hematite powders

The structural, electrical, and chemical properties of Sn‐doped Fe₂O₃ powders were investigated. Various quantities of Sn‐doped Fe₂O₃ powders were synthesized using solid‐state reactions. Rietveld analysis for the powders that were doped below 2% revealed a phase‐pure Sn‐doped Fe₂O₃ structure (i.e., identical to Fe₂O₃ structure). Alternatively, the analysis for the powders that were doped more than 3% exhibited secondary phase. The unit cell volume and electrical conductivity of the phase‐pure samples increased with an increase in the doping concentration. X‐ray photoelectron spectroscopy measurements showed an increased Fe²⁺ state with the increase in Sn doping concentration. Therefore, the improved electrical conductivity and unit cell volume with the increase in doping concentration of the phase‐pure powders might be related to the increased Fe²⁺ state.     

In situ growth of LaSr(Fe,Mo)O4 ceramic anodes with exsolved Fe–Ni nanoparticles for SOFCs: Electrochemical performance and stability in H2, CO,and syngas

Fe–Ni nanoparticle–decorated LaSr(Fe,Mo)O₄ Ruddlesden–Popper (R–P) perovskite anodes, named R–LSFMNx, were prepared in situ by reducing perovskites La_0.5Sr_0.5Fe_0.9Mo_0.1–xNi_xO_3–δ (LSFMNx; x = 0.03–0.07) under SOFC anode operating conditions. Electrolyte–supported single cells with a configuration of R–LSFMNx|La_0.9Sr_0.1Ga_0.8Mg_0.2O_3–δ (LSGM)|Ba_0.5Sr_0.5Co_0.9Nb_0.1O_3–δ were used to evaluate the electrochemical performances and redox/long–term stability of the R–LSFMNx anodes fuelled by H₂, CO, and simulated syngases (x% H₂/CO; x = 50–10). EIS analyses indicated that the increased Ni level in the exsolved Fe–Ni nanocatalysts significantly promotes fuel diffusion/adsorption/dissociation, which plays a rate–limiting role in the anode fuel oxidation. Furthermore, the incremental Ni in Fe–Ni alloy also enhances the anode redox/long–term stability and carbon resistance/tolerance, and the R–LSFMN0.07 anode, i.e., Ni level in Fe–Ni alloy attaining ～14 mol.%, displays the optimal stability and carbon resistance/tolerance. Finally, the potential of the R–LSFMN0.07 anode for direct utilization of syngas was demonstrated by the characterization of the electrochemical performance and stability based on the R–LSFMN0.07 anode cell.