Optimizing La1-xSrxFeO3-δ electrodes for symmetrical reversible solid oxide cells

Reversible solid oxide cells (RSOCs) are prone to material thermal property mismatching problems between electrodes and electrolyte, which greatly reduces their energy efficiency and causes irreversible performance degradation. One solution is to develop symmetrical RSOCs (SRSOCs) employing identical electrode materials to effectively address thermal property mismatching related issues and also simplify the manufacturing process. Herein, La_1-xSr_xFeO_3-δ (x = 0–0.20) perovskites are developed and applied as both fuel and air electrode materials for SRSOCs for the first time. The impact of Sr substitution for La on the crystal structures, conductivities and electrochemical performance of LaFeO₃ oxides is systematically investigated. It is found, after doping with Sr, overall properties of the LaFeO₃ oxides show an obvious improvement, especially for the sample of La_0·9Sr_0·1FeO_3-δ (LSF9010). The peak power density of SRSOCs featuring LSF9010 can stand at 0.575 W cm⁻² at 800 °C under the solid oxide fuel cell (SOFC) working model. Under solid oxide electrolysis cell (SOEC) model, the current density stands at 0.84 A cm⁻² at 800 °C and 1.5 V. More importantly, the La_0·9Sr_0·1FeO_3-δ symmetrical cell can operate steadily for 128 h under SOFC mode and 25 h under SOFC-SOEC cycle mode, respectively, with almost no performance degradation found. The outcomes of the current study show that the developed LSF9010 may be used as an outstanding multifunctional electrode material in SRSOCs.     

Highly stable La0.5Sr0.5Fe0.9Mo0.1O3-δ electrode for reversible symmetric solid oxide cells

Reversible solid oxide cells (RSOCs) using identical material as both fuel electrode and air electrode have received extensive attentions due to their simplified fabrication process, increased compatibility between electrolyte and electrode. In this work, Molybdenum doped La_0.5Sr_0.5Fe_0.9Mo_0.1O_3-δ (LSFMo) symmetric electrode based on RSOCs is firstly designed and synthesized via sol-gel method. The effect of Molybdenum substitution at Fe-site on crystal structure, chemical stability, conductivity and electrochemical performance of La_0.5Sr_0.5FeO_3-δ oxide is thoroughly investigated. The structural stability of La_0.5Sr_0.5FeO_3-δ (LSF) in reducing condition is significantly enhanced after the incorporation of Mo^5+/6+ and the conductivity in 5% H₂ for LSFMo is ~7 times higher than that of undoped LSF. In addition, the polarization resistance value at 850 °C based on LSFMo/LSGM/LSFMo is 0.08 and 0.09 Ω cm² in air and wet H₂, respectively. At 850 °C and 20%H₂O–H₂, a peak power density of 640 mW cm⁻² is obtained in fuel cell mode, while a current density of −1000 mA cm⁻² is attained at 1.3 V in electrolysis mode. Finally, the symmetric cell exhibits an excellent cycling reversible operation in both SOFCs mode and SOECs mode without detectable degradation.     

La1-xSrxFeO3 perovskite-type oxides for chemical-looping steam methane reforming: Identification of the surface elements and redox cyclic performance

We report a family of perovskite-type oxides La_1-xSr_xFeO₃ (x = 0.1, 0.3, 0.5, 0.7, 1.0) prepared by combustion method as effective redox catalysts for methane partial oxidation and thermochemical water splitting in a cyclic redox scheme. The effect of Sr-doping on the characterizations and properties of these perovskite-type oxides were studied by means of X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). All the as-prepared and regenerated samples with various Sr substitutions exhibited pure crystalline perovskite structure. The oxygen carrying capacity of the La_1-xSr_xFeO₃ perovskites was improved by doping Sr into the La-site. Besides, Sr-substitution has obvious effects on the valences of the Fe cations in the B-site and the oxygen species distribution of the La_1-xSr_xFeO₃ perovskites. We recommend La_0.7Sr_0.3FeO₃ as the optimal oxygen carrier in the series because it gives the maximum O_la/O_ad (O_la and O_ad stand for lattice oxygen and adsorbed oxygen species, respectively.) ratio of 3.64:1, which can be regarded as a criterion for the reactivity and selectivity of partial oxidation of methane into syngas of the oxygen carriers. Up to 80% CH₄ conversion in the methane partial oxidation step and 96% of H₂ concentration in the water splitting step were achieved in ten successive redox tests conducted in a fixed bed reactor at 850 °C with La_0.7Sr_0.3FeO₃ as a redox catalyst. The electronic properties of the original LaFeO₃ cell and its lattice substituted by Sr were calculated based on the density functional theory method. Electronic structure analysis demonstrates that doping of Sr makes LaFeO₃ more electric conductive and its electron is prone to be excited. This is in agreement with the test results that La_0.7Sr_0.3FeO₃ exhibited better performance in chemical looping reactions.     

Electrochemical performance of La0.65Sr0.35MnO3 oxygen electrode with alternately infiltrated Sm0.5Sr0.5CoO3-δ and Sm0.2Ce0.8O1.9 nanoparticles for reversible solid oxide cells

La_1-xSr_xMnO₃ is a well-known oxygen electrode for reversible solid oxide cells (RSOCs). However, its poor ionic conductivity limits its performance in redox reaction. In this study, we selected Sm_0.5Sr_0.5CoO_3-δ (SSC) as catalyst and Sm_0.2Ce_0.8O_1.9 (SDC) as ionic conductor and sintering inhibitor to co-modify the La_0.65Sr_0.35MnO₃ (LSM) oxygen electrode through an alternate infiltration method. The infiltration sequence of SSC and SDC showed an influence on the morphology and performance of LSM oxygen electrode, and the influence was gradually weakened with the increasing infiltration time. The polarization resistance of the alternately infiltrated LSM-SSC/SDC electrode was 0.08 Ω cm² at 800 °C in air, which was 3.36% of the LSM electrode (2.38 Ω cm²). The Ni-YSZ/YSZ/LSM-SSC/SDC single cell attained a maximum power density of 1205 mW cm^?2 in SOFC mode at 800 °C, which was 8.73 times more than the cell with LSM electrode. The current density achieved 1620 mA .cm^?2 under 1.5 V at 800 °C in SOEC mode and the H₂ generation rate was 3.47 times of the LSM oxygen electrode.     

Mn-rich SmBaCo0.5Mn1.5O5+δ double perovskite cathode material for SOFCs

SmBaCo_0.5Mn_1.5O_5+δ oxide with Sm-Ba cation-ordered perovskite-type structure is synthesized and examined in relation to whole RBaCo_0.5Mn_1.5O_5+δ series (R: selected rare earth elements). Presence of Sm and 3:1 ratio of Mn to Co allows to balance physicochemical properties of the composition, with moderate thermal expansion coefficient value of 18.70(1)·10⁻⁶ K⁻¹ in 300–900 °C range, high concentration of disordered oxygen vacancies in 600–900 °C range (δ = 0.16 at 900 °C), and good transport properties with electrical conductivity reaching 33 S cm⁻¹ at 900 °C in air. Consequently, the compound enables to manufacture catalytically-active cathode, with good electrochemical performance measured for the electrolyte-supported laboratory-scale solid oxide fuel cell with Ni-Gd_1.9Ce_0.1O_2-δ|La_0.4Ce_0.6O_2-δ|La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ|SmBaCo_0.5Mn_1.5O_5+δ configuration, for which 1060 mW cm⁻² power density is observed at 900 °C. Furthermore, the tested symmetrical SmBaCo_0.5Mn_1.5O_5+δ|La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ|SmBaCo_0.5Mn_1.5O_5+δ cell delivers 377 mW cm⁻² power density at 850 °C, which is a promising result.     

Novel nanocomposite membranes based on PBI and doped-perovskite nanoparticles as a strategy for improving PEMFC performance at high temperatures

In this work, Sr²⁺ dopant effects of Ba_0.9Sr_0.1TiO₃ and La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles on increasing proton conductivity, fuel cell performance, and mechanical and thermal stability of polybenzimidazole-based nanocomposite membranes were studied. The Sr²⁺ dopant creates cation vacancies in Ba_0.9Sr_0.1TiO₃ doped-perovskite nanoparticles and oxygen vacancies in La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles. The oxygen vacancies, which decrease columbic repulsion between protons and positive ions, have a more important role than the cation vacancies. They provide high surface area and high interfacial interaction between La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles, phosphoric acid, and polybenzimidazole for proton transfer and increase the proton conductivity of the nanocomposite membranes. In addition, the results of relative humidity effects showed that the ordered arrangement of oxygen vacancies of the La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles creates a specific pathway in the nanocomposite membranes for increasing proton transfer in the presence of relative humidity. Furtheremore, at phosphoric acid doping level of 13 mol phosphoric acid per monomer unit, proton conductivity of the nanocomposite membranes containing 8 wt.% La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles was obtained as 126 mS cm^-1 at 180°C and 6% relative humidity. The nanocomposite membrane showed the best performance and the power density of 0.62 W cm^-2 at 180°C and 0.5 V.     

Factors governing surface exchange kinetics in undoped and strontium/iron co-substituted La2NiO4+δ

Surface oxygen exchange in the La₂NiO_4+δ and La_1.5Sr_0.5Ni_1-yFe_yO_4+δ (y = 0.3, 0.4) oxides is analyzed using the data on oxygen permeability through the membranes with different thicknesses measured under various oxygen partial pressure P(O₂) gradients in the 800–1000 °C range. The increase in P(O₂) gradient induced surface limitations in La₂NiO_4+δ leading to a predominant role of surface exchange in the overall oxygen flux. The origin of surface exchange limitations in La₂NiO_4+δ is ascribed to a relatively fast decrease in oxygen excess and Ni³⁺ concentration with P(O₂) reduction compared to La_1.5Sr_0.5Ni_0.7Fe_0.3O_4+δ and La_1.5Sr_0.5Ni_0.6Fe_0.4O_4+δ, which retained an oxygen excess. Faster surface exchange kinetics for La_1.5Sr_0.5Ni_0.6Fe_0.4O_4+δ in comparison with that for La_1.5Sr_0.5Ni_0.7Fe_0.3O_4+δ is interpreted on the basis of surface microstructure obtained by electron backscatter diffraction (EBSD). It is suggested that the observed changes in size, shape and crystallographic orientation of grains in La_1.5Sr_0.5Ni_0.6Fe_0.4O_4+δ (compared to La_1.5Sr_0.5Ni_0.7Fe_0.3O_4+δ) could result in a higher amount of 3d-metal cations in surface layers of the oxide.     

Investigation of La0.6Sr0.4Co1-xNixO3-δ (x=0, 0.2, 0.4, 0.6, 0.8) catalysts on solid oxide fuel cells anode for biogas dry reforming

The introduction of catalyst on anode of solid oxide fuel cell (SOFC) has been an effective way to alleviate the carbon deposition when utilizing biogas as the fuel. A series of La_0.6Sr_0.4Co_1-xNi_xO_3-δ (x = 0, 0.2, 0.4, 0.6, 0.8) oxides are synthesized by sol-gel method and used as catalysts precursors for biogas dry reforming. The phase structure of La_0.6Sr_0.4Co_1-xNi_xO_3-δ oxides before and after reduction are characterized by X-ray diffraction (XRD). The texture properties, carbon deposition, CH₄ and CO₂ conversion rate of La_0.6Sr_0.4Co_1-xNi_xO_3-δ catalysts are evaluated and compared. The peak power density of 739 mW cm^?2 is obtained by a commercial SOFC with La_0.6Sr_0.4Co_0.4Ni_0.6O_3-δ catalyst at 850 °C when using a mixture of CH₄: CO₂ = 2:1 as fuel. This shows a great improvement from the cell without catalyst for internal dry reforming, which is attributed to the formation of NiCo alloy active species after reduction in H₂ atmosphere. The results indicate the benefits of inhibiting the carbon deposition on Ni-based anode through introducing the La_0.6Sr_0.4Co_0.4Ni_0.6O_3-δ catalyst precursor. Additionally, the dry reforming technology will also help to convert part of the exhaust heat into chemical energy and improve the efficiency of SOFC system with biogas fuel.     

Electrochemical performance of Sr1.9La0.1Fe1.5Mo0.5O6-δ symmetric electrode for solid oxide fuel cells with carbon-based fuels

La-doped Sr_2-xLa_xFe_1.5Mo_0.5O_6-δ perovskite oxides are synthesized and used as a symmetric electrode to evaluate the effect of La on the crystal structure, conductivity, and catalytic activity for O₂ reduction and H₂ oxidation reaction. The electronic doping effect dominates the oversize effect in Sr_2-xLa_xFe_1.5Mo_0.5O_6-δ oxide, resulting in unit cell volume expansion and decreased conductivity in air. In addition, the introduction of La increases the chemical structural stability of Sr₂Fe_1.5Mo_0.5O_6-δ in reducing condition due to the higher La–O bond compared with Sr–O bond, leading to high catalytic activity for the H₂ oxidation reaction. At 800 °C, the R_p values of Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ symmetric cell in air and wet H₂ are as low as 0.075 and 0.21 Ω cm², respectively. Moreover, the peak power densities of 769, 561, 439, and 653 mW cm^?2 at 850 °C are obtained when wet H₂, CO, CH_4, and C₃H₈ are used as fuels on Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ/LSGM/Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ cell. The symmetric cell also shows excellent stability (>100 h) in wet H₂/air, implying Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ oxide is a promising symmetric electrode material.     

Coking resistant Ni–La0.8Sr0.2FeO3 composite anode improves the stability of syngas-fueled SOFC

An improved SOFC anode with excellent stability against carbon deposition with syngas as fuel is reported. The anode material is Ni–La_0.8Sr_0.2FeO₃ (LSF) composite synthesized by anhydrous impregnation. After reduction in wet H₂ (3% H₂O), the material partially decomposes to SrLaFeO₄ and exsolved Fe. The exsolved Fe forms Ni–Fe alloy with impregnated Ni. The particle size of Ni–Fe alloy is about 20–50 nm. The Ni–Fe alloy nanoparticles disperse on the surface of the La_0.8Sr_0.2FeO₃ and SrLaFeO₄ oxides. The increase of Ni content promotes the exsolution of Fe and increases the reaction sites of Ni–Fe alloy. With the increase of the Ni content, the electrical conductivity and catalytic activity are enhanced, which improves the electrochemical performance of the single cell. The cell with 10 mol.% Ni impregnated Ni-LSF as anode achieves a maximum power density of 550 mW cm^?2 at 700 °C fueled with syngas. The strong interaction of the nano-sized Ni–Fe alloy with the La_xSr_yFeO_z (La_0.8Sr_0.2FeO₃ or SrLaFeO₄) oxide substrate efficiently suppresses carbon deposition with high graphitization degree. Besides, the SrLaFeO₄ phase which can accommodate interstitial oxygen facilitates the removal of the deposited carbon.     

Preparation of Pr2NiO4+δ-La0.6Sr0.4CoO3-δ as a high-performance cathode material for SOFC by an impregnation method

As a Ruddlesden-Popper (RP) phase solid oxide fuel cell (SOFC) cathode material, Pr₂NiO_4+δ (PNO) is a critical challenge for SOFC commercialization due to the lack of oxygen vacancies and insufficient redox reaction (ORR) activity. In this paper, various concentrations of La_0.6Sr_0.4CoO_3-δ (LSC) nanoparticles are coated on the surface of PNO by an impregnation method, and the ORR kinetics of PNO is found to be improved by constructing a composite cathode with heterointerfaces. The formation of the heterointerface effectively enhances the transfer of interstitial oxygen in the PNO and the oxygen vacancies in LSC, which can promote the conduction of O^2? in the cathode and thus improves the ORR activity of the material. When the impregnation concentration of LSC reached C_LSC = 0.2 mol L^?1, the ORR activity can reach the highest level. At 700 °C, the area-specific resistance of PNO-LSC reaches 0.024 Ω cm², which is 83.4% lower than that of PNO (0.145 Ω cm²). And the peak power density of PNO-LSC reaches 0.618 W cm^?2, which is 1.89 times larger than that of PNO (0.327 W cm^?2). Therefore, the construction of composite cathodes with heterointerfaces via impregnation provides an alternative strategy for enhancing the ORR activity of the cathode materials in SOFC.     

Co-free La0.6Sr0.4Fe0.9Nb0.1O3-δ symmetric electrode for hydrogen and carbon monoxide solid oxide fuel cell

Co-free La_0.6Sr_0.4FeO_3-δ (LSFNb₀) and La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ (LSFNb_0.1) perovskite oxides were prepared by a standard solid-state reaction method. The structural stability and electrochemical performance of La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ as both cathode and anode were studied. Nb dopant in LSFNb₀ significantly enhances the structural and chemical stability in anode condition. At 800 °C, the polarization resistances (Rp) of LSFNb_0.1 symmetric electrode based on YSZ electrolyte are 0.5 and 0.05 Ω cm² in H₂ and air, respectively. The peak power densities of LSFNb_0.1 based on LSGM electrolyte-supported SSOFCs are 934 and 707 mW cm⁻² at 850 °C in H₂ (3% H₂O) and dry CO, respectively. Moreover, the symmetric cell exhibits reasonable stability in both H₂ and CO fuel, suggesting that La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ may be a potential symmetric electrode material for hydrogen and carbon monoxide SOFCs.     

Ni-doped A-site-deficient La0.7Sr0.3Cr0.5Mn0.5O3-δ perovskite as anode of direct carbon solid oxide fuel cells

A Ni-doped A-site-deficient La_0.7Sr_0.3Cr_0.5Mn_0.5O_3-δ perovskite (N-LSCM) was synthesized and systematically characterized towards the application as the anode electrode for direct carbon solid oxide fuel cells (DC-SOFCs). The microstructure and electrochemical properties of N-LSCM under the operation conditions of DC-SOFCs have been evaluated. An in-situ exsolution of Ni nanoparticles on the N-LSCM perovskite matrix is found, revealing a maximum power density of 153 mW cm⁻² for the corresponding DC-SOFC at 850 °C, compared to 114 mW cm⁻² of the cell with stoichiometric LSCM. The introduction of Ni nanoparticles exsolution and A-site deficient is believed to boost the formation of highly mobile oxygen vacancies and electrochemical catalytic activity, and further improves the output performance of the DC-SOFC. It thus promises as a suitable anode candidate for DC-SOFCs with whole-solid-state configuration.     

Tuning oxygen vacancy of the Ba0·95La0·05FeO3−δ perovskite toward enhanced cathode activity for protonic ceramic fuel cells

Innovation of highly active cathode is of great significance to the development of protonic ceramic fuel cells (PCFCs). Herein, tailoring oxygen vacancies in Zn-doped Ba_0·95La_0·05FeO_3?δ (BLFZ) perovskite is proved to be beneficial for promoting the formation of proton defects. Hydration ability of the triple conducting BLFZ perovskites is confirmed by electrical conductivity relaxation (ECR). The results demonstrate that BLFZ exhibits a proton surface exchange coefficient of 1.34 × 10^?3 cm s^?1 at 600 °C, which greatly extends active sites from the electrolyte/cathode interface to the entire electrode. Mechanism and process elementary steps of the oxygen reduction reaction (ORR) of BLFZ-BaCe_0.7Zr_0·1Y_0.1Yb_0.1O_3?δ (BCZYYb) are detailedly studied. It is found that the rate-determining step of ORR is surface dissociative adsorption of oxygen on BLFZ-BCZYYb cathode. A maximum power density of 673 mW cm^?2 at 700 °C is achieved and BLFZ-BCZYYb based single-cell shows no obvious degradation at 600 °C for 200 h. The good performance is ascribed to the rapid proton diffusion of BLFZ-BCZYYb composite electrode by regulating the oxygen vacancies.     

High-performance fluorine-doped cobalt-free oxide as a potential cathode material for solid oxide fuel cells

The potential utilization of the cobalt-free fluorine-doped LaBa_0.5Sr_0.5Fe₂O_5.875-δF_0.125 oxide as a solid oxide fuel cell (SOFC) cathode candidate is investigated and assessed. The polarization resistance of the LaBa_0.5Sr_0.5Fe₂O_5.875-δF_0.125 cathode is 0.089 Ω cm² at 750 °C, and meanwhile, a larger power density of the electrolyte-supported single cell with the LaBa_0.5Sr_0.5Fe₂O_5.875-δF_0.125 cathode is 511 mWcm^?2. In addition, the electrode still possesses a better stability after 120 h operation. Combining with the oxygen reduction kinetics research and the corresponding distribution of relaxation time analysis, rate-determining steps are further defined. Current research results indicate that the LaBa_0.5Sr_0.5Fe₂O_5.875-δF_0.125 sample is an attractive cathode for SOFCs.     

Characterization of La0.5Sr0.5Co0.5Ti0.5O3−δ as symmetrical electrode material for intermediate-temperature solid-oxide fuel cells

La_0.5Sr_0.5Co_0.5Ti_0.5O_3−δ perovskite oxide has been prepared as polycrystalline powder, characterized and tested as cathode and anode material for solid-oxide fuel cells. The oxidized material is suggested to present mixed ionic-electronic conductivity (MIEC) from “in-situ” neutron powder diffraction (NPD) experiments, complemented with transport measurements; the presence of a sufficiently high oxygen deficiency, with large displacement factors for oxygen atoms suggest a large lability and mobility combined with a semiconductor-like behaviour with a maximum conductivity of 29 S cm⁻¹ at T = 850 °C. A complete reversibility towards reduction–oxidation processes has been observed, where the reduced Pm-3m perovskite with La_0.5Sr_0.5Co_0.5Ti_0.5O_2.64 composition has been obtained by topotactical oxygen removal without abrupt changes in the thermal expansion. The oxidized material shows good performance working as a cathode with LSGM electrolyte, yielding output power densities close to 500 mW/cm² at 850 °C. At intermediate temperatures (800 °C) it may be used as a cathode or as an anode, yielding power densities of 220 and 170 mW/cm², respectively. When used simultaneously as cathode and anode a maximum power density of 110 mW/cm² was obtained. Therefore, we propose the La_0.5Sr_0.5Co_0.5Ti_0.5O_3−δ composition as a promising candidate for symmetrical electrode in intermediate-temperature SOFC.     

Novel La0.7Sr0.3FeO3 − δ/(La0.5Sr0.5)2CoO4 + δ composite hollow fiber membrane for O2 separation with high CO2 resistance

Recently, the reported Perovskite/Ruddlesden‐Popper composite with significant improvement of oxygen surface kinetics has been adopted into gas separation process. Here, we report a novel La_0.7Sr_0.3FeO_{3 ? δ}/(La_0.5Sr_0.5)₂CoO_{4 + δ} (LSF‐LSC) composite hollow fiber membrane (HFM), which was characterized by X‐ray diffraction (XRD), scanning electron microscope (SEM), and thermal expansion test, etc. The O₂ permeation test results indicated that, under sweeping gas of pure He (100 mL min^?1), the composite HFM exhibited the superior O₂ permeability (0.72 mL min^?1 cm^?2) at the temperature of 950^°C with respect to the single La_0.7Sr_0.3FeO_{3 ? δ} (LSF) membrane, acid‐etched membrane, and (La_0.5Sr_0.5)₂CoO_{4 + δ} (LSC)‐coated membrane. Moreover, the composite membrane exhibited high CO₂ tolerance as well as phase stability. The generation of hetero‐interface between Ruddlesden‐Popper phase and perovskite phase could be responsible for the improvement of the oxygen transportation over the fabricated composite membrane.     

Enhanced methane electrooxidation by ceria and nickel oxide impregnated perovskite anodes in solid oxide fuel cells

A key challenge preventing the full utilization of the electrochemical work potentials of hydrocarbon fuels in solid oxide fuel cells (SOFCs) is the prevalence of partial hydrocarbon electrooxidation at the anode and the resultant catalytic deactivation by coking. CeO₂–NiO impregnated La_0.3Sr_0.5TiO_3-δ (LST_A-) anodes solve both issues. These anodes exhibit 2-fold increase in the exchange current density (i_o) for CH₄ electrooxidation compared to CeO₂ impregnated NiO-YSZ (yttria-stabilized-zirconia) anodes. The presence of metal support interactions between Ni–CeO_2-δ along with the oxygen vacancies in LST_A- and CeO_2-δ enabled fast oxidation of carbon species and resulted in reduced coking. The uses of this anode in an electrolyte supported full cell configuration yielded a maximum power density of 490 mW cm⁻² in CH₄ at 1173 K.     

Enhanced H2 production by using La5.5WO11.25-δ-La0.8Sr0.2FeO3-δ mixed oxygen ion-proton-electron triple-conducting membrane

Although lanthanum tungstates (Ln_nWO_12-δ) show superior CO₂-tolerance compared to the traditional perovskite-type oxides, their hydrogen permeation fluxes are not competitive. Herein, a mixed oxygen ion-proton-electron triple-conducting membrane with a nominal composition of La_5.5WO_11.25-δ-La_0.8Sr_0.2FeO_3-δ (LWO-LSF) was developed for H₂ production. The triple-conducting membrane is composed of a LWO phase with proton conductivity and a LSF phase with mixed oxygen ion-electron conductivities. In the LWO-LSF membrane, proton (H⁺) permeation and oxygen ion (O²⁻) counter-permeation property was simultaneously displayed. The improved H₂ production can be ascribed to (1) hydrogen permeated as H⁺ through LWO phase, and (2) hydrogen produced from water splitting that is enhanced by O²⁻ counter-permeation through LSF phase. A higher H₂ flux of 0.15 mL min⁻¹ cm⁻² was achieved at 900 °C using LWO-LSF triple-conducting membrane, compared with the conventional proton-electron conducting membranes LWO or La_5.5WO_11.25-δ-La_0.8Sr_0.2CrO_3-δ (LWO-LSC). Furthermore, the constant H₂ fluxes in various atmospheres indicated the good stability of LWO-LSF membrane in simulated raw hydrogen.     

Co-precipitation synthesis of SOFC electrode materials

A series of four compounds (LaMnO₃, La_0.70Sr_0.30MnO_3−δ, La_0.80Sr_0.20FeO_3−δ and La_0.75Sr_0.25Cr_0.50Mn_0.50O_3−δ) of interest as electrode materials in intermediate temperature solid oxide fuel cells have been prepared using a carbonate co-precipitation route in aqueous medium. LaMnO₃, La_0.70Sr_0.30MnO_3−δ, and La_0.75Sr_0.25Cr_0.50Mn_0.50O_3−δ have been obtained as a pure phase, while La_0.80Sr_0.20FeO_3−δ retained an impurity phase; fine microstructures with sub-micron sized particles can be obtained in all cases at the proper calcinations temperature, except for LaMnO₃. The precipitation yield of the single metal ions have been experimentally determined in the mother liquors and in the final powders; the results have been evaluated also in comparison with expected yields calculated from thermodynamics of the precipitation process using the software Medusa. pH higher than 7.5 are suggested to avoid ion losses for all cations. Structural and microstructural properties and TPO/TPR behaviour suggest that materials prepared via co-precipitation, especially LSCM, could be suited as electrode materials in solid oxide fuel cells.