Novel cobalt-free cathode materials BaCexFe1−xO3−δ for proton-conducting solid oxide fuel cells

A series of cobalt-free and low cost BaCe_xFe_1−xO_3−δ (x = 0.15, 0.50, 0.85) materials are successful synthesized and used as the cathode materials for proton-conducting solid oxide fuel cells (SOFCs). The single cell, consisting of a BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BaCe_xFe_1−xO_3−δ cathode layer, is assembled and tested from 600 to 700 °C with humidified hydrogen (3% H₂O) as the fuel and the static air as the oxidant. Within all the cathode materials above, the cathode BaCe_0.5Fe_0.5O_3−δ shows the highest cell performance which could obtain an open-circuit potential of 0.99 V and a maximum power density of 395 mW cm⁻² at 700 °C. The results indicate that the Fe-doped barium cerates can be promising cathodes for proton-conducting SOFCs.     

On Ba0.5Sr0.5Co1−yFeyO3−δ (y = 0.1–0.9) oxides as cathode materials for La0.9Sr0.1Ga0.8Mg0.2O2.85 based IT-SOFCs

Ba_0.5Sr_0.5Co_1−yFe_yO_3−δ (y = 0.1–0.9) (BSCF) oxides have been evaluated as cathode materials for intermediate solid oxide fuel cells with La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) as electrolyte. The increase of iron content in BSCF materials results in an increase of the area-specific resistance (ASR), e.g. 0.04, 0.08 and 0.13 Ω cm² for compositions with y = 0.2, 0.4 and 0.6 respectively at 1073 K. The influence of iron content in BSCF oxides on the unit cell volume via high temperature X-ray diffraction, the overall electrical conductivity and the thermal expansion coefficient (TEC) has also been investigated. The lattice cell parameters for the BSCF series increase as a function of the temperature and exhibit a non-linear behaviour, with a sudden increase at around 673 K due to the loss of lattice oxygen, which in turn is caused by the reduction of Co⁴⁺ and Fe⁴⁺ to lower oxidation states. This was determined by O₂ temperature-programmed desorption and thermogravimetric analysis. Such oxygen non-stoichiometry results in a significant thermal expansion and conductivity change for all compositions at the same temperature.     

La1−xSrxMO3 (M = Mn, Fe) perovskites as materials for thermochemical hydrogen production in conventional and membrane reactors

La_1−xSr_xMO₃ (M = Mn, Fe) perovskites are investigated as potential redox materials for the thermochemical production of hydrogen. Thermogravimetric oxidation/reduction experiments indicated that the materials are able to lose and uptake oxygen reversibly from their lattice up to 5.5 wt.% for La_1−xSr_xMnO₃ with x = 1 and up to 1.7 wt.% for La_1−xSr_xFeO₃ with x = 0. Pulse reaction experiments indicated that the materials can be used as redox catalysts in a redox process where water is dissociated giving rise to the production of pure hydrogen during the oxidation step. The oxidation and reduction steps can be combined in a membrane reactor constructed from dense perovskite membranes towards a continuous and isothermal operation. The system is also able to operate on partial pressure-based desorption without the need of a carbon-containing reductant, so that a process towards hydrogen production, based only on renewable hydrogen source such as water, can be established. At steady state and 900 ^°C, 25 ± 7 cm³ (STP) H₂ m⁻² min⁻¹ is produced in purified state.     

First principles study on the oxygen reduction reaction of the La1–xSrxMnO3–δ coated Ba1–xSrxCo1–yFeyO3–δ cathode for solid oxide fuel cells

A core-shell structured composite cathode for solid oxide fuel cell with Ba_1–xSr_xCo_1–yFe_yO_3–δ (BSCF) as core while La_1–xSr_xMnO_3–δ (LSM) as shell (LSM@BSCF) has been designed to achieve dual optimization of high stability and electrochemical activity. The atomic structure, oxygen vacancy formation, oxygen adsorption and diffusion, and CO₂ adsorption properties of the core-shell interface have been studied by the first principles method. The calculated binding energies and interface energies suggest that the combination of La/Sr–O plane of LSM (100) surface and the Co/Fe–O plane of BSCF (100) surface is the most favourable composite structure. The formation energy of oxygen vacancy in LSM is 1.73 eV, and 0.06 eV in BSCF, thus the oxygen vacancy is easier to be formed in BSCF, which results in better oxygen ion conductivity of BSCF than LSM. The oxygen diffusion barrier from LSM to BSCF at the interface is determined to be 0.66 eV, indicating an easy oxygen ionic transport between the interface. CO₂ is hard to be adsorbed onto the LSM@BSCF surface. Thus, the introducing of LSM Shell can prevent the BSCF cathode from being poisoned by CO₂.     

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.     

Surface exchange and bulk diffusion properties of Ba0.5Sr0.5Co0.8Fe0.2O3−δ mixed conductor

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) is a mixed conducting oxide that shows high oxygen permeability to perform as a ceramic membrane and high electrochemical activity for oxygen reduction to perform as a cathode of solid oxide fuel cells. Both performances are closely related to the bulk and surface properties of the BSCF oxide. In this study, the chemical bulk diffusion coefficient (D_chem) and chemical surface exchange coefficient (k_chem) of BSCF at various temperatures and oxygen partial pressures are determined by an electrical conductivity relaxation (ECR) method. Both D_chem and k_chem are found to be dependent on pO₂ with positive effect. Ea of D_chem and k_chem are respectively 111 ± 5 and 110 ± 6 kJ mol⁻¹ between 600 and 800 °C. Oxygen-ion diffusion and tracer diffusion coefficients are estimated from D_chem and compared with the literature results. Ionic conductivities are further derived according to the Nernst-Einstein relation. The poisoning effect of CO₂ on the performances of BSCF is further investigated by the ECR method in combination with oxygen temperature-programmed desorption technique. The presence of CO₂ causes a substantial decrease in k_chem, however, the surface kinetics can be recovered by performing re-calcination in an oxidative atmosphere at 900 °C, agreeing well with literature reports.     

Structural and electrical properties of selected La1−xSrxCo0.2Fe0.8O3 and La0.6Sr0.4Co0.2Fe0.6Ni0.2O3 perovskite type oxides

In this paper, the structural and transport properties of selected La_1−xSr_xCo_0.2Fe_0.8O₃ (LSCF) perovskites and La_0.6Sr_0.4Co_0.2Fe_0.6Ni_0.2O₃ (LSCFN64262) perovskite are presented. Crystal structure of the samples was characterized by means of X-ray studies with Rietveld method analysis. DC electrical conductivity and thermoelectric power were measured at a wide temperature range (80–1200 K) in air. For La_0.2Sr_0.8Co_0.2Fe_0.8O₃ (LSCF2828) and La_0.4Sr_0.6Co_0.2Fe_0.8O₃ (LSCF4628) perovskites a maximum observed on electrical conductivity dependence on temperature exists at about 750 K. It can be associated with an appearance of oxygen vacancies and implies a mixed ionic-electronic transport. A growing amount of oxygen vacancies at higher temperatures causes a decrease in the electrical conductivity due to a recombination mechanism associated with lowering of the average valence of 3d metals. A similar characteristic was found for LSCFN64262 perovskite, which also exhibits a relatively high electrical conductivity.     

Intermediate temperature single-chamber methane fed SOFC based on Gd doped ceria electrolyte and La0.5Sr0.5CoO3−δ as cathode

Single-chamber fuel cells with electrodes supported on an electrolyte of gadolinium doped ceria Ce_1−xGd_xO_2−y with x = 0.2 (CGO) 200 μm thickness has been successfully prepared and characterized. The cells were fed directly with a mixture of methane and air. Doped ceria electrolyte supports were prepared from powders obtained by the acetyl-acetonate sol–gel related method. Inks prepared from mixtures of precursor powders of NiO and CGO with different particle sizes and compositions were prepared, analysed and used to obtain optimal porous anodes thick films. Cathodes based on La_0.5Sr_0.5CoO₃ perovskites (LSCO) were also prepared and deposited on the other side of the electrolyte by inks prepared with a mixture of powders of LSCO, CGO and AgO obtained also by sol–gel related techniques. Both electrodes were deposited by dip coating at different thicknesses (20–30 μm) using a commercial resin where the electrode powders were dispersed. Finally, electrical properties were determined in a single-chamber reactor where methane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Temperature, composition and flux rate values of the carrier gas were determinants for the optimization of the electrical properties of the fuel cells.     

Fe-substituted (La,Sr)TiO3 as potential electrodes for symmetrical fuel cells (SFCs)

In the work presented herein, the potential use of La₄Sr₈Ti_12−xFe_xO_38−δ (LSTF) materials as electrodes for a new concept of solid oxide fuel cells, symmetrical fuel cells (SFCs), is considered. Such fuel cells use simultaneously the same material as anode and cathode, which notably simplifies the assembly and further maintenance of the cells. Therefore, we search for materials showing high conductivity in a wide range of oxygen partial pressures in addition to certain degree of catalytic activity for the oxidation of the fuel and reduction of the oxidant, respectively. The preliminary electrochemical experiments performed reveal that the overall conductivity increases notably upon Fe substitution, being the main contribution electronic n-type. The fuel cell tests indicate that LSTF composites with YSZ and CeO₂ perform reasonably well under H₂ conditions, although the performance in methane is rather modest and require further optimisation.     

Synthesis and assessment of La0.8Sr0.2ScyMn1−yO3−δ as cathodes for solid-oxide fuel cells on scandium-stabilized zirconia electrolyte

Perovskite-type La_0.8Sr_0.2Sc_yMn_1−yO_3−δ oxides (LSSMy, y = 0.0–0.2) were synthesized and investigated as cathodes for solid-oxide fuel cells (SOFCs) containing a stabilized zirconia electrolyte. The introduction of Sc³⁺ into the B-site of La_0.8Sr_0.2MnO_3−δ (LSM) led to a decrease in the oxides’ thermal expansion coefficients and electrical conductivities. Among the various LSSMy oxides tested, LSSM0.05 possessed the smallest area-specific cathodic polarization resistance, as a result of the suppressive effect of Sc³⁺ on surface SrO segregation and the optimization of the concentration of surface oxygen vacancies. At 850 °C, it was only 0.094 Ω cm² after a current passage of 400 mA cm⁻² for 30 min, significantly lower than that of LSM (0.25 Ω cm²). An anode-supported cell with a LSSM0.05 cathode demonstrated a peak power density of 1300 mW cm⁻² at 850 °C. The corresponding value for the cell with LSM cathode was 450 mW cm⁻² under the same conditions. The LSSM0.05 oxide may potentially be a good cathode material for IT-SOFCs containing doped zirconia electrolytes.     

Characterization of Pr1−xSrxCo0.8Fe0.2O3−δ (0.2 ≤ x ≤ 0.6) cathode materials for intermediate-temperature solid oxide fuel cells

Cathode materials consisting of Pr_1−xSr_xCo_0.8Fe_0.2O_3−δ (x = 0.2–0.6) were prepared by the sol–gel process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The samples had an orthorhombic perovskite structure. The electrical conductivities were all higher than 279 S cm⁻¹. The highest conductivity, 1040 S cm⁻¹, was found at 300 °C for the composition x = 0.4. Symmetrical cathodes made of Pr_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (PSCF)–Ce_0.85Gd_0.15O_1.925 (50:50 by weight) composite powders were screen-printed on GDC electrolyte pellets. The area specific resistance value for the PSCF–GDC cathode was as low as 0.046 Ω cm² at 800 °C. The maximum power densities of a cell using the PSCF–GDC cathode were 520 mW cm⁻², 435 mW cm⁻² and 303 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively.     

Preparation and characterization of La1−xSrxNiyFe1−yO3−δ cathodes for low-temperature solid oxide fuel cells

Perovskite-type La_1−xSr_xNi_yFe_1−yO_3−δ (x = 0.3, 0.4, 0.5, 0.6, y = 0.2; x = 0.3, y = 0.2, 0.3, 0.4) oxides have been synthesized and employed as cathodes for low-temperature solid oxide fuel cells (SOFCs) with composite electrolyte. The segregation of La₂NiO_4±δ is observed to increase with the increasing Sr²⁺ incorporation content according to X-ray diffraction (XRD) results. The as-prepared powders appear porous foam-like agglomeration with particle size less than 1 μm. Maximum power densities yield as high as 725 mW cm⁻² and 671 mW cm⁻² at 600 °C for fuel cells with the LSNF4628 and LSNF7337 composite cathodes. The maximum power densities continuously increase with the increasing Sr²⁺ content in LSNF cathodes, which can be mainly ascribed to the possible charge compensating mechanism. The maximum power densities first increase with the Ni ion incorporation content up to y = 0.3 due to the increased oxygen vacancy, ionic conductivity and oxygen permeability. Further increase in Ni ion content results in a further lowering of fuel cell performance, which can be explained by the association of oxygen vacancies and divalent B-site cations in the cathode.     

La1−xSrxCoO3 (x = 0.1-0.5) as the cathode catalyst for a direct borohydride fuel cell

Direct borohydride fuel cells (DBFCs), with a series of perovskite-type oxides La_1−xSr_xCoO₃ (x = 0.1-0.5) as the cathode catalysts and a hydrogen storage alloy as the anode catalyst, are studied in this paper. The structures of the perovskite-type catalysts are mainly La_1−xSr_xCoO₃ (_x = 0.1-0.5) oxides phases. However, with the increase of strontium content, the intensities of the X-ray diffraction peaks of the impure phases La₂Sr₂O₅ and SrLaCoO₄ are gradually enhanced. Without using any precious metals or expensive ion exchange membranes, a maximum current density of 275 mA cm⁻² and a power density of 109 mW cm⁻² are obtained with the Sr content of x = 0.2 at 60 °C for this novel type of fuel cell.     

Sm0.2(Ce1−xTix)0.8O1.9 modified Ni-yttria-stabilized zirconia anode for direct methane fuel cell

Sm_0.2(Ce_1−xTi_x)_0.8O_1.9 (SCTx, x = 0-0.29) modified Ni-yttria-stabilized zirconia (YSZ) has been fabricated and evaluated as anode in solid oxide fuel cells for direct utilization of methane fuel. It has been found that both the amount of Ti-doping and the SCTx loading level in the anode have substantial effect on the electrochemical activity for methane oxidation. Optimal anode performance for methane oxidation has been obtained for Sm_0.2(Ce_0.83Ti_0.17)_0.8O_1.9 (SCT0.17) modified Ni-YSZ anode with SCT0.17 loading of about 241 mg cm⁻² resulted from four repeated impregnation cycles. When operating on humidified methane as fuel and ambient air as oxidant at 700 °C, single cells with the configuration of SCT0.17 modified Ni-YSZ anode, YSZ electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O₃-Sm_0.2Ce_0.8O_1.9 (LSCF-SDC) composite cathode show the polarization cell resistance of 0.63 Ω cm² under open circuit conditions and produce a peak power density of 383 mW cm⁻². It has been revealed that the coated Ti-doped SDC on Ni-YSZ anode not only effectively prevents the methane fuel from directly impacting on the Ni particles, but also enhances the kinetics of methane oxidation due to an improved oxygen storage capacity (OSC) and redox equilibrium of the anode surface, resulting in significant enhancement of the SCTx modified Ni-YSZ anode for direct methane oxidation.     

Thermal, electrical and electrochemical characteristics of Ba1−xSrxCo0.8Fe0.2O3−δ cathode material for intermediate temperature solid oxide fuel cells

Ba_1−xSr_xCo_0.8Fe_0.2O_3−δ (x = 0.3-0.9) perovskite oxides have been studied as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The structural characteristics, temperature dependent weight loss, thermal expansion, electrical conductivity, and electrochemical properties in combination with YSZ electrolyte together with an SDC buffer layer were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), dilatometry, DC four probe conductivity measurement and electrochemical impedance spectroscopy (EIS) techniques respectively. XRD study revealed the lattice parameter and unit cell volume decrease with increase in Sr⁺² content at the A-site. TEC and electrical conductivity were found to increase with increasing Sr⁺² content. Electrical conductivity was found to be dependent on the thermal history of the samples. Polarization resistance of the samples with SDC buffered YSZ electrolyte decreased with increasing Sr⁺² content which was ascribed to the higher conductivity with improved oxygen adsorption/desorption and oxygen ions diffusion processes. The intrinsic oxygen reduction reaction rate also increased with Sr⁺² content at the A-site. The exchange current for intrinsic oxygen reduction reaction at 700 °C was found to be 50.0 mA cm⁻² for Ba_0.3Sr_0.7Co_0.8Fe_0.2O_3−δ; a value which is about 50% higher than that for Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ, a widely studied cathode material. Therefore, the present composition may be a potential cathode material for IT-SOFC application.     

Experimental analysis of micro-tubular solid oxide fuel cell fed by hydrogen

This paper analyzes the thermodynamic and electrochemical performance of an anode supported micro-tubular solid oxide fuel cell (SOFC) fed by hydrogen. The micro-tubular SOFC used is anode supported, consisting of a NiO and Gd_0.2Ce_0.8O_2−x (GDC) cermet anode, thin GDC electrolyte, and a La_0.6Sr_0.4Co_0.2Fe_0.8O_3−y (LSCF) and GDC cermet cathode. The fabrication of the cells under investigation are described, and an analysis of the different procedures with emphasis of the innovations with respect to traditional techniques. Such micro-tubular cells were tested using a test stand consisting of: a vertical tubular furnace, an electrical load, a galvanostast, gas pipelines, temperature, pressure and flow meters. The tests on the micro-SOFC were performed using hydrogen, to determine the cell polarization. A parametric study is also presented with the scope to analyze the variations of the thermodynamic and electrochemical performances of the cell in function of its operating temperature and fuel flow.     

Property evaluation of Sm1‐xSrxFe0.7Cr0.3O3‐δ perovskites as cathodes for intermediate temperature solid oxide fuel cells

Perovskite‐type (ABO₃) complex oxides of Sm_1‐xSr_xFe_0.7Cr_0.3O_3‐δ (x = 0.5‐0.7) series were prepared by a glycine‐nitrate combustion process. The crystal structure, oxygen nonstoichiometry, electrical conducting, thermal expansion, and electrocatalytic properties of Sm_1‐xSr_xFe_0.7Cr_0.3O_3‐δ perovskites were inspected in view of their use as cathode materials for intermediate temperature solid oxide fuel cells (IT‐SOFCs). Changing the content of Sm³⁺ at the A‐site was demonstrated to be effective in tuning the structure and properties. The variation of the various properties with Sm³⁺ content was explained in relation to the corresponding evolution of the crystal structure and oxygen nonstoichiometry. Sm_0.3Sr_0.7Fe_0.7Cr_0.3O_3‐δ (x = 0.7) was determined to be the optimal composition in the Sm_1‐xSr_xFe_0.7Cr_0.3O_3‐δ series based on a trade‐off between the thermal expansion and electrocatalytic properties. Sm_0.3Sr_0.7Fe_0.7Cr_0.3O_3‐δ ceramic specimen exhibited an electrical conductivity of approximately 40 S·cm^?1 at 800°C and a thermal expansion coefficient of 14.1 × 10^?6 K^?1 averaged in the temperature range from 40°C to 1000°C. At 800°C in air, Sm_0.3Sr_0.7Fe_0.7Cr_0.3O_3‐δ electrode showed a cathodic polarization resistance of 0.19 Ω·cm², a cathodic overpotential of 30 mV at current density of 200 mA·cm^?2, and an exchange current density of 257 mA·cm^?2. It is suggested that Sm_0.3Sr_0.7Fe_0.7Cr_0.3O_3‐δ is a potential candidate material for cathode of IT‐SOFCs in light of its overall properties.     

Thermochemical two-step water splitting by ZrO2-supported NixFe3−xO4 for solar hydrogen production

A thermochemical two-step water-splitting cycle using a redox metal oxide was examined for Ni(II) ferrites or Ni_xFe_3−xO₄ (0  x  1) for the purpose of converting solar high-temperature heat to hydrogen. The Ni(II) ferrite was decomposed to Ni-doped wustite (Ni_yFe_1−yO) at 1400 °C under an inert atmosphere in the first thermal-reduction step of the cycle; it was then reoxidized with steam to generate hydrogen at 1000 °C in the second water-decomposition step. Although nondoped Fe₃O₄ powders formed a nonporous, dense mass of iron oxide by the fusion of FeO and its subsequent solidification after the thermal-reduction step, Ni(II)–ferrite powders were converted into a porous, soft mass after the step. This was probably because Ni doping in the FeO phase raised the melting point of wustite above 1400 °C. Supporting the Ni(II) ferrites on m-ZrO₂ (monoclinic zirconia) alleviated the high-temperature sintering of iron oxide; as a result, the supported ferrites exhibited greater reactivity and assisted the repeatability of the cyclic water splitting process as compared to the unsupported ferrites. The reactivity increased with the doping value x, and was maximum at x = 1.0 in the Ni_xFe_3−xO₄/m-ZrO₂ system.     

Electrical conduction behavior of La,Co co-doped SrTiO3 perovskite as anode material for solid oxide fuel cells

The effects of La- and Co-doping into SrTiO₃ perovskite oxides on their phase structure, electrical conductivity, ionic conductivity and oxygen vacancy concentration have been investigated. The solid solution limits of La in La_xSr_1 − xTiO_3 − δ and Co in La_0.3Sr_0.7Co_yTi_1 − yO_3 − δ are about 40 mol% and 7 mol%, respectively, at 1500 °C. The incorporation of La decreases the band gap and thus increases the electrical conductivity of SrTiO₃ remarkably. La_0.3Sr_0.7TiO_3 − δ shows an electrical conductivity of 247 S/cm at 700 °C. Co-doping into La_0.3Sr_0.7TiO_3 − δ increases the oxygen vacancy concentration and decreases the migration energy for oxygen ions, leading to a significant increase in ionic conductivity but at the expense of some electrical conductivity. The electrical and ionic conductivities of La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ are 63 S/cm and 6 × 10⁻³ S/cm, respectively, at 700 °C. Both La_0.3Sr_0.7TiO_3 − δ and La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ show relatively stable electrical conductivities under oxygen partial pressure of 10⁻¹⁴–10⁻¹⁹ atm at 800 °C. These properties make La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ a promising anode candidate for solid oxide fuel cells.     

Assessment of perovskite-type La0.8Sr0.2ScxMn1−xO3-δ oxides as anodes for intermediate-temperature solid oxide fuel cells using hydrocarbon fuels

Composites formed by the infiltration of 40 wt% La_0.8Sr_0.2Sc_xMn_1−xO_3-δ (LSSM) oxides (x = 0.1, 0.2, 0.3) into 65% porous yttria-stabilized zirconia (YSZ) are investigated as anode materials for intermediate-temperature solid oxide fuel cells for hydrocarbon oxidation. The oxygen non-stoichiometry and electrical conductivity of each LSSM-YSZ composite are determined by coulometric titration. As the concentration of Sc increases, the composites show higher phase stability and the electrical conductivity of LSSM is significantly affected by the Sc doping, the non-stoichiometric oxygen content, and oxygen partial pressure (p(O₂)). To achieve better electrochemical performance, it is necessary to add ceria-supported palladium catalyst for operation with humidified CH₄. Anode polarization resistance increases with Sc doping due to a decrease in electrical conductivity. An electrolyte-supported cell with a LSSM-YSZ composite anode delivers peak power densities of 395 and 340 mW cm⁻² at 923 K in humidified (3% H₂O) H₂ and CH₄, respectively, at a flow rate of 20 mL min⁻¹.