Syngas production at intermediate temperature through H2O and CO2 electrolysis with a Cu-based solid oxide electrolyzer cell

Solid Oxide Electrolyzer Cells (SOECs) are promising energy devices for the production of syngas (H₂/CO) by H₂O and/or CO₂ electrolysis. Here we developed a Cu–Ce_0.9Gd_0.1O_2−δ/Ce_0.8Gd_0.2O_2−δ/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ-Ce_0.8Gd_0.2O_2−δ cell and performed H₂O and CO₂ electrolysis experiments in the intermediate temperature range (600°C–700 °C). As a baseline, the cell was first tested in fuel cell operation mode; the sample shows a maximum power density peak of 104 mW cm⁻² at 700 °C under pure hydrogen and air. H₂O electrolysis testing revealed a steady production of hydrogen with a Faraday's efficiency of 32% at 700 °C at an imposed current density of −78 mA cm⁻². CO production was observed during CO₂ electrolysis but higher cell voltages were required. A lower efficiency of about 4% was obtained at 700 °C at an imposed current density of −660 mA cm⁻². These results confirm that syngas production is feasible by water and carbon dioxide electrolysis but further improvements from both the manufacturing and the electrocatalytic aspects are needed to reach higher yields and efficiencies.     

Evaluation of layered perovskites YBa1−xSrxCo2O5+δ as cathodes for intermediate-temperature solid oxide fuel cells

This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa_1−xSr_xCo₂O_5+δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The high oxygen nonstoichiometry, δ = 0.18–0.43 at 700 °C, indicates the large oxygen vacancy concentrations in oxides. The electrical conductivity is improved due to the greater amount of electronic holes originated from the increased interstitial oxygen, and the conductivities of all samples are above 100 S cm⁻¹ at 400–700 °C in air. The results demonstrate the promising performance of YBa_1−xSr_xCo₂O_5+δ cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21–0.59 Ω cm² at 700 °C. The lowest ASR, 0.44 Ω cm², and the cathodic overpotential, −40 mV at a current density of −136 mA cm⁻², are obtained in YBaCo₂O_5+δ cathode at 650 °C. The dependence of polarization resistance on oxygen partial pressure suggests that the charge transfer process is the rate-limiting step for oxygen reduction reaction in YBaCo₂O_5+δ cathode.     

Biogas reforming for hydrogen production over mesoporous Ni2xCe1−xO2 catalysts

Biogas reforming for hydrogen production over mesoporous Ni_2xCe_1−xO₂ catalysts were proposed in this study. Mesoporous Ni_2xCe_1−xO₂ (x = 0.05, 0.13, 0.2) was prepared by a reverse precipitation method. The effects of nickel content were investigated in physicochemical properties and catalytic activities. All of the catalysts were reduced with 10% H₂/Ar at 600 °C before reactions, the reduced catalysts were found to be active for both dry and steam reforming of methane (CH₄:CO₂:H₂O = 3:1:2) to produce hydrogen and syngas. The studies were firstly carried out by temperature program reaction from 400 °C to 900 °C to verify the activity of temperature dependency. The long-term stability analysis was also studied at 700 °C for 24 h. Commercial catalyst (R67) was also employed for a comparative purpose.     

Electrode properties of Co-doped Ca2Fe2O5 as new cathode materials for intermediate-temperature SOFCs

Brownmillerite oxide Ca₂Fe_2−xCo_xO₅ (x = 0.2, 0.4, 0.6) was characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. Ca₂Fe_2−xCo_xO₅ has no reaction with Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte at 1100 °C for 10 h in air. The thermal expansion coefficient (TEC) of Ca₂Fe_2−xCo_xO₅ increased with increasing Co content, and the TEC value was compatible with SDC. The electrode properties of Ca₂Fe_2−xCo_xO₅ were studied under various temperatures and oxygen partial pressures. The polarization resistance (R_p) of Ca₂Fe_2−xCo_xO₅ with x = 0.2, 0.4 and 0.6 are 0.23, 0.48 and 1.05 Ω cm² at 700 °C in air, respectively. The rate-limiting step for oxygen reduction reaction was the charge transfer process. Ca₂Fe_1.8Co_0.2O₅ cathode exhibits the lowest overpotential of about 50 mV at a current density of 70 mA cm⁻² at 700 °C in air.     

La0.6Sr0.4Co0.8Ni0.2O3−δ hollow fiber membrane reactor: Integrated oxygen separation – CO2 reforming of methane reaction for hydrogen production

An integrated reactor system which combines oxygen permeable La_0.6Sr_0.4Co_0.8Ni_0.2O_3−δ (LSCN) perovskite ceramic hollow fiber membrane with Ni based catalyst has been successfully developed to produce hydrogen through oxy-CO₂ reforming of methane (OCRM). Dense La_0.6Sr_0.4Co_0.8Ni_0.2O_3−δ hollow fiber membrane was prepared using phase inversion-sintering method. OCRM reaction was tested from 650 °C to 800 °C with a quartz reactor packed with 0.5 g Ni/Al₂O₃ catalyst around the LSCN hollow fiber membrane. CH₄ and CO₂ were used as reactants and air as the oxygen source was fed through the bore side of the hollow fiber membrane. In order to gauge the effectiveness of this membrane reactor system, air flow was closed at 800 °C and dry reforming of methane (DRM) was tested for comparison. The results show that the oxygen fluxes of LSCN membrane swept by helium are nearly 3 times less than those swept by OCRM reactants. With increasing temperature and oxygen supply, methane conversion in the OCRM reactor reaches 100%, but CO₂ conversion decreases from 87% to 72% due to the competition reaction with POM. CO selectivity is as high as nearly 100% at reaction temperatures of 700 °C–800 °C while H₂ selectivity reaches a maximum of 88% at 700 °C. At 800 °C, when air supply was closed and DRM was conducted for comparison, CO selectivity decreased to 91%, resulting in carbon deposition which was around 4 times more than those obtained under OCRM reaction and H₂/CO ratio decreased from 0.93 to 0.74, showing better carbon resistance and higher H₂ selectivity of the Ni-based catalyst over the integrated oxygen separation-OCRM reaction across the LSCN hollow fiber membrane reactor.     

Synthesis, characterization and evaluation of PrBaCo2−xFexO5+δ as cathodes for intermediate-temperature solid oxide fuel cells

Iron doped layered structured perovskites, PrBaCo_2−xFe_xO_5+δ (x = 0, 0.5, 1.0, 1.5 and 2.0), are evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of dopant content are investigated on their structural and electrochemical properties including crystalline structure, oxygen nonstoichiometry, stability in presence of CO₂, compatibility with electrolytes, thermal expansion coefficient, electrical conductivity, and cathodic interfacial polarization resistance. The lattice parameter and oxygen nonstoichiometry content, δ, at room temperature increase, whereas the conductivity, thermal expansion coefficient, and cathodic performance decrease with increasing iron content, x. PrBaCo_2−xFe_xO_5+δ exhibit excellent stability at 700 °C in atmosphere consisting of 3% CO₂ and 97% air, show good chemical compatibility with doped ceria electrolytes at 1000 °C, but react readily with yttria-stabilized zirconia at 700 °C. Even with a Co-free PrBaFe₂O_5+δ as the electrode, a symmetrical cell demonstrates area specific resistance of 0.18 Ω cm² at 700 °C with samaria-doped ceria electrolyte. The resistance is lower than those for typical Co-free electrodes reported in the literatures, suggesting that PrBaCo_2−xFe_xO_5+δ are potential promising cathode materials for IT-SOFCs.     

Preparation and electrochemical properties of strontium doped Pr2NiO4 cathode materials for intermediate-temperature solid oxide fuel cells

Pr_2−xSr_xNiO₄ (PSNO, x = 0.3, 0.5 and 0.8) cathode materials for intermediate-temperature solid oxide fuel cell (IT-SOFC) were synthesized by a glycine-nitrate process using Pr₆O₁₁, Ni(NO₃)₂·6H₂O and SrCO₃ powders as raw materials. Phase structure of the synthesized powders was characterized by X-ray diffraction analysis (XRD). Microstructure of the sintered PSNO samples was observed and thermal expansion coefficient (TEC) and electrical conductivity were investigated. Electrochemical impedance spectroscopy (EIS) measurement of the PSNO materials on Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte was carried out, and single cells based on the PSNO cathodes were also assembled and their performances were tested. The results show that the synthesized PSNO powders have pure K₂NiF₄-type structure and the PSNO materials are chemically stable with Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte. The sintered PSNO samples have porous and fine microstructure with pore size smaller than 1 μm. Average thermal expansion coefficient of the PSNO materials is about 12–13 × 10⁻⁶ K⁻¹ at 200–800 °C and the electrical conductivity is in the range of 70–120 Scm⁻¹ at 800 °C. Area specific resistance (ASR) of the Pr_2−xSr_xNiO₄ materials on SCO electrolyte is 0.407 Ωcm², 0.126 Ωcm² and 0.112 Ωcm² for x = 0.3, 0.5 and 0.8 at 800 °C, respectively. Maximum open circuit voltage (OCV) and power density of the single NiO-SCO/SCO/PSNO cells are 0.75 V and 298 mWcm⁻² at 700 °C, respectively, which indicates that Pr_2−xSr_xNiO₄ may be a potential cathode material for IT-SOFC.     

New SrMo1−xCrxO3−δ perovskites as anodes in solid-oxide fuel cells

Oxides of composition SrMo_1−xCr_xO_3−δ (x = 0.1, 0.2) have been prepared, characterized and tested as anode materials in single solid-oxide fuel cells, yielding output powers higher than 700 mW cm⁻² at 850 °C with pure H₂ as a fuel. All the materials are suggested to present mixed ionic–electronic conductivity (MIEC) from neutron powder diffraction (NPD) experiments, complemented with transport measurements; the presence of a Mo⁴⁺/Mo⁵⁺ mixed valence at room temperature, combined with a huge metal-like electronic conductivity, as high as 340 S cm⁻¹ at T = 50 °C for x = 0.1, could make these oxides good materials for solid-oxide fuel cells. The magnitude of the electronic conductivity decreases with increasing Cr-doping content. The reversibility of the reduction–oxidation between the oxidized Sr(Mo,Cr)O_4−δ scheelite and the reduced Sr(Mo,Cr)O₃ perovskite phases was studied by thermogravimetric analysis, which exhibit the required cyclability for fuel cells. An adequate thermal expansion coefficient, without abrupt changes, and a chemical compatibility with electrolytes make these oxides good candidates for anodes in intermediate-temperature SOFC (IT-SOFCs).     

Preparation and characterization of new cobalt-free cathode Pr0.5Sr0.5Fe0.8Cu0.2O3−δ for IT-SOFC

A new cobalt-free perovskite oxide Pr_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ (PSFC) has been synthesized and evaluated as cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The chemical compatibility of PSFC with Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte has be proven by XRD, and its electrical conductivity reaches the maximum value of 264.1 S cm⁻¹ at 475 °C. Symmetrical cells with the configuration of PSFC/SDC/PSFC are used for the impedance study and the polarization resistance (Rp) of PSFC cathode is as low as 0.050 Ω cm² at 700 °C. Single cells, consisting of Ni–YSZ/YSZ/SDC/PSFC structure, are assembled and tested from 550 °C to 800 °C with wet hydrogen (∼3% H₂O) as fuel and static air as oxidant. A maximum power density of 1077 mW cm⁻² is obtained at 800 °C. All the results suggest that the cobalt-free perovskite oxide PSFC is a very promising cathode material for application in IT-SOFC.     

Electrochemical performance of La2Cu1−xCoxO4 cathode materials for intermediate-temperature SOFCs

K₂NiF₄-type structure oxides La₂Cu_1−xCo_xO₄ (x = 0.1, 0.2, 0.3) are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The materials are characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. The results show that no reaction occurs between La₂Cu_1−xCo_xO₄ electrode and Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte at 1000 °C. The electrode forms good contact with the electrolyte after sintering at 800 °C for 4 h in air. The electrode properties of La₂Cu_1−xCo_xO₄ are studied under various temperatures and oxygen partial pressures. The optimum composition of La₂Cu_0.8Co_0.2O₄ results in 0.51 Ω cm² polarization resistance (R_p) at 700 °C in air. The rate limiting step for oxygen reduction reaction (ORR) is the charge transfer process. La₂Cu_0.8Co_0.2O₄ cathode exhibits the lowest overpotential of about 50 mV at a current density of 48 mA cm⁻² at 700 °C in air.     

Fibrous mixed conducting cathode with embedded ionic conducting particles for solid oxide fuel cells

The Sm_0.5Sr_0.5CoO_3−δ (SSC) fibers with embedded nano-Sm_0.2Ce_0.8O_1.9 (SDC) particles are fabricated by electrospinning process using commercial SDC nanopowders and an SSC precursor gel containing polyvinyl alcohol (PVA) and aqueous metal nitrate. After calcination at 800 °C, fibers with diameters ranged between 300 and 500 nm and well-developed SSC cubic-perovskite structure and SDC fluorite are successfully obtained. The calculated crystallite sizes of SSC and SDC are 20.78 and 45.35 nm, respectively. Over whole measured temperature ranges during the symmetrical cell test, the fiber composite cathode exhibits much lower polarization resistance than conventional powder composite cathodes. The polarization resistances are estimated to 0.06 and 1.23 Ω cm² for the fiber composites and 0.15 and 2.10 Ω cm² for the powder composites at 700 and 550 °C, respectively. The single cell with the fiber composite cathode shows much higher performances; its maximum power density is 380.5 mW cm⁻² at 550 °C and higher than 1278 mW cm⁻² at 700 °C.     

Preparation and characterization of Ce1−x(Gd0.5Pr0.5)xO2 electrolyte for IT-SOFCs

The Ce_1−x(Gd_0.5Pr_0.5)_xO₂ (x = 0–0.24) compositions were synthesized through the sol–gel process followed by low temperature combustion. X-ray diffraction data analysis showed that all the samples exhibit a cubic structure with single phase. The lattice parameter was calculated by rietveld refinement of XRD patterns. Dense ceramics were prepared by sintering the pellets at 1300 °C. The relative density of the samples was over 98%. The surface morphology was studied by Scanning electron microscopy (SEM). Chemical composition was analyzed by Energy dispersive spectroscopy (EDX). A.C. impedance spectroscopy measurements were carried out to study the grain, grain boundary and total ionic conductivity of co-doped ceria samples in the temperature range 150–700 °C. The Ce_0.84(Gd_0.5Pr_0.5)_0.16O₂ composition showed highest grain ionic conductivity i.e., 1.059 × 10⁻² S/cm at 500 °C which is 11.5% higher than the Ce_0.9Gd_0.1O₂ (with an activation energy 0.62 eV). At intermediate temperatures, the Ce_1−x(Gd_0.5Pr_0.5)_xO₂ materials were found to be ionic in nature.     

Electrochemical behavior of Ba0.5Sr0.5Co0.2−xZnxFe0.8O3−δ (x = 0-0.2) perovskite oxides for the cathode of solid oxide fuel cells

Zinc-doped barium strontium cobalt ferrite (Ba_0.5Sr_0.5Co_0.2−xZn_xFe_0.8O_3−δ (BSCZF), x = 0, 0.05, 0.1, 0.15, 0.2) powders with various proportions of zinc were prepared using the ethylenediamine tetraacetic acid (EDTA)-citrate method with repeated ball-milling and calcining. They were then evaluated as cathode materials for solid oxide fuel cells at intermediate temperatures (IT-SOFCs) using XRD, H₂-TPR, SEM, and electrochemical tests. By varying the zinc doping (x) from zero to 0.2 (as a substitution for cobalt which ranged from zero to 100%), it was found that the lowest doping of 0.05 (BSCZF05) resulted in the highest electrical conductivity of 30.7 S cm⁻¹ at 500 °C. The polarization resistances of BSCZF05 sintered at 950 °C were 0.15 Ω cm², 0.28 Ω cm² and 0.59 Ω cm² at 700 °C, 650 °C and 600 °C, respectively. The resistance decreased further by about 30% when Sm_0.2Ce_0.8O_2−δ (SDC) electrolyte particles were incorporated and the sintering temperature was increased to 1000 °C. Compared to BSCF without zinc, BSCZF experienced the lowest decrease in electrochemical properties when the sintering temperature was increased from 950 °C to 1000 °C. This decrease was due to an increase in thermal stability and a minimization in the loss of some cobalt cations without a decrease in the electrical conductivity. Using a composite cathode of BSCZF05 and 30 wt.% of SDC, button cells composed of an Ni-SDC support with a 30 μm dense SDC membrane exhibited a maximum power density of 605 mW cm⁻² at 700 °C.     

Investigation of cobalt-free cathode material Sm0.5Sr0.5Fe0.8Cu0.2O3−δ for intermediate temperature solid oxide fuel cell

A cobalt-free cubic perovskite oxide Sm_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ (SSFCu) was investigated as a novel cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficient (TEC) of SSFCu was close to that of Sm_0.2Ce_0.8O_1.9(SDC) electrolyte and the electrical conductivity of SSFCu sample reached 72–82 S cm⁻¹ in the commonly operated temperatures of IT-SOFCs (400–600 °C). Symmetrical electrochemical cell with the configuration of SSFCu/SDC/SSFCu was applied for the impedance study and area specific resistance (ASR) of SSFCu cathode material was as low as 0.085 Ω cm² at 700 °C. Laboratory-sized tri-layer cells of NiO-SDC/SDC/SSFCu were operated from 450 to 700 °C with humidified hydrogen (∼3% H₂O) as fuel and the static air as oxidant. A maximum power density of 808 mW cm² was obtained at 700 °C for the single cell.     

Ceria interlayer-free Ba0.5Sr0.5Co0.8Fe0.2O3−δ–Sc0.1Zr0.9O1.95 composite cathode on zirconia based electrolyte for intermediate temperature solid oxide fuel cells

We synthesized Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) powders with a primary particle size of 20 nm using a Pechini type method. By using nanocrystalline BSCF powders, we were able to fabricate a ceria interlayer-free nanoporous cathode on a scandia stabilized zirconia (ScSZ) electrolyte at low temperatures. Cathodes sintered below 750 °C lacked sufficient mechanical adhesion to the electrolyte, while electrode was well adhered to the electrolyte when fired at 800 °C. The symmetrical BSCF-ScSZ|yttria stabilized zirconia (YSZ)|BSCF-ScSZ half-cell that we generated had an exceptionally low polarization resistance of 0.06 Ω·cm² at 700 °C. The maximum power density of the BSCF-ScSZ|ScSZ|Ni-ScSZ unit cell was over 1 W cm⁻² at 700 °C. We investigated the durability of the BSCF-ScSZ composite cathode by 30 thermo-cycles performed by varying the temperature from 200 to 700 °C. The polarization resistance after the test remained low at less than 0.08 Ω·cm².     

Hydrogen production aided by new (1−x)SrTi0.5Fe0.5O3–δ–xCe0.8(Sm0.8Sr0.2)0.2O2–δ (MIEC) composite membranes

In the present work, composite materials of the type (1–x)SrTi_0.5Fe_0.5O_3–δ–xCe_0.8(Sm_0.8Sr_0.2)_0.2O_2–δ (with х = 0, 0.25, 0.5, 0.75 and 1) are obtained by the two step solid state technique. Their transport properties are investigated in terms of their usage as mixed ionic-electronic conducting (MIEC) membrane materials for hydrogen production. It is found that, in reducing conditions the composites are characterized by mixed conductivity, which level is controlled by the electrical properties of the prevailing phase. Moreover, at 900 °C and pO₂ = 10⁻¹⁸ atm, total conductivity, ambipolar conductivity and oxygen permeability of composites dramatically grow (each of about 500%), when the fluorite component content x increases from 0 to 1. High-conducting and strengthened material 0.5SrTi_0.5Fe_0.5O_3–δ–0.5Ce_0.8(Sm_0.8Sr_0.2)_0.2O_2–δ is chosen for making tube shaped membranes using the tape rolling method, which are successfully applied for hydrogen production in laboratory scale. The hydrogen flux reached 0.176 ml cm⁻² min⁻¹ for x = 1, T = 900 °C and emf = 10 mV.     

Preparation and electrochemical performance of Pr2Ni0.6Cu0.4O4 cathode materials for intermediate-temperature solid oxide fuel cells

Cathode material Pr₂Ni_0.6Cu_0.4O₄ (PNCO) for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is synthesized by a glycine-nitrate process using Pr₆O₁₁, NiO, and CuO powders as raw materials. X-ray diffraction analysis reveals that nanosized Pr₂Ni_0.6Cu_0.4O₄ powders with K₂NiF₄-type structure can be obtained from calcining the precursors at 1000 °C for 3 h. Scanning electron microscopy shows that the sintered PNCO samples have porous microstructure with a porosity of more than 30% and grain size smaller than 2 μm. A maximum conductivity of 130 S cm⁻¹ is obtained from the PNCO samples sintered at 1050 °C. A single fuel cell based on the PNCO cathode with 30 μm Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte film and a 1 mm NiO-SCO anode support is constructed. The ohmic resistance of the single Ni-SCO/SCO/PNCO cell is 0.08 Ω cm² and the area specific resistance (ASR) value is 0.19 Ω cm² at 800 °C. Cell performance was also tested using humidified hydrogen (3% H₂O) as fuel and air as oxidant. The single cell shows an open circuit voltage of 0.82 V and 0.75 V at 700 °C and 800 °C, respectively. Maximum power density is 238 mW cm⁻² and 308 mW cm⁻² at 700 °C and 800 °C, respectively. The preliminary tests have shown that Pr₂Ni_1−xCu_xO₄materials can be a good candidate for cathode materials of IT-SOFCs.     

Preparation and characterization of Ba0.5Sr0.5Fe0.9Ni0.1O3−δ–Sm0.2Ce0.8O1.9 compose cathode for proton-conducting solid oxide fuel cells

A cobalt-free Ba_0.5Sr_0.5Fe_0.9Ni_0.1O_3−δ–Sm_0.2Ce_0.8O_1.9 (BSFN–SDC) composite was employed as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs) using BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) as the electrolyte. The chemical compatibility between BSFN and SDC was evaluated. The XRD results showed that BSFN was chemically compatible with SDC after co-fired at 1100 °C for 5 h. The thermal expansion coefficient (TEC) of BSFN–SDC, which showed a reasonably reduced value (16.08 × 10⁻⁶ K⁻¹), was effectively decreased due to Ce_0.8Sm_0.2O_1.9 (SDC) added. A single cell of Ni–BZCY/Ni–BZCY/BZCY/BSFN–SDC with a 25-μm-thick BZCY electrolyte membrane exhibited excellent power densities as high as 361.8 mW cm⁻² at 700 °C with a low polarization resistance of 0.174 Ω cm². The excellent performance implied that the cobalt-free BSFN–SDC composite was a promising alternative cathode for H-SOFCs.     

Cobalt-doped BaZrO3: A single phase air electrode material for reversible solid oxide cells

BaZr_1−xCo_xO_3−δ (BZC-x, x = 0.1, 0.2, 0.3, 0.4, 0.5) are prepared and identified as single phase air electrode materials for reversible solid oxide cells. BZC-x shows a typical perovskite structure with x ≤ 0.4, and slight BaCoO₃ second phase is observed with x = 0.5. Conductivity measurements suggest that BZC-x is an oxygen ion and electron mixed conductor in dry oxygen atmosphere. The electronic conductivity of BZC-x increases when increasing Co content in BZC-x specimen, while the ionic conductivity reduces. For BaZr_0.6Co_0.4O_3−δ, the electronic and ionic conductivity are 5.24 S cm⁻¹ and 1.20 × 10⁻³ S cm⁻¹, respectively, measured at 700 °C in dry oxygen. With BZC-0.4 as a single phase air electrode, the discharging and electrolysis current densities of a single cell are 299 mA cm⁻² (at 0.7 V) and −935 mA cm⁻² (at 1.5 V), respectively, measured at 700 °C. The polarization resistance of cells using this new air electrode is only 0.19 Ω cm², approximately 65% lower than that using a traditional Sm_0.5Sr_0.5CoO_3−δ/BaCe_0.5Zr_0.3Y_0.2O_3−δ composite air electrode.     

SmBa0.5Sr0.5Cu2O5+δ and SmBa0.5Sr0.5CuFeO5+δ layered perovskite oxides as cathodes for IT-SOFCs

Novel Cobalt-free layered perovskite oxides SmBa_0.5Sr_0.5Cu₂O_5+δ (SBSCO) and SmBa_0.5Sr_0.5CuFeO_5+δ (SBSCFO) were investigated as cathode materials for intermediate-temperature solid fuel cells (IT-SOFCs). The thermal expansion coefficients (TEC) of SBSCO and SBSCFO were 14.1 × 10⁻⁶/°C and 14.9 × 10⁻⁶/°C in 50 °C–800 °C, which were more compatible with electrolyte than cobalt-based cathodes. When A′-site is partially substituted by Sr, the conductivity of SBSCO and SBSCFO had been improved. The max electrical conductivity of SBSCO was 277.7 S cm⁻¹, about one order of magnitude higher than SmBaCu₂O_5+δ. Polarization resistance of SBSCO is 0.25 Ω cm² at 650 °C, which is twice lower than that of SmBaCu₂O_5+δ (SBCO). This implies SBSCO has higher activity for oxygen reduction than SBCO. Preliminary results indicate that SBSCO are promising as cathodes for IT-SOFCs.