Effect of Sr and Al or Fe co-doping on the sinterability and conductivity of lanthanum silicate oxyapatite electrolytes for solid oxide fuel cells

The effect of co-doping of Sr and Al or Fe on the microstructure, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites is investigated in detail at 300–800 °C by the electrochemical impedance spectroscopy. The oxide-ion conductivity is 1.46 × 10⁻² S cm⁻¹ for La_9.5Sr_0.5Si_5.5Fe_0.5O_26.5 (LSSFO) and 1.34 × 10⁻² S cm⁻¹ at 800 °C for La_9.5Sr_0.5Si_5.5Al_0.5O_26.5 (LSSAO), respectively, which is one order of magnitude higher than 6.16 × 10⁻³ S cm⁻¹ measured on La_9.67Si₆O_26.5 (LSO) oxyapatite under the identical test conditions. The grain bulk and grain boundary resistances of co-doped oxyapatite are significantly smaller than that of LSO oxyapatite, and decrease significantly with the increase of the sintering temperature. LSSFO and LSSAO also show significantly higher density as compared to that of LSO. The results indicate that co-doping of Sr and Al or Fe significantly improves the densification, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites.     

Study on BaCo0.7Fe0.2Nb0.1O3−δ—SDC composite cathodes for intermediate temperature solid oxide fuel cell

BaCo_0.7Fe_0.2Nb_0.1O_3−δ(BCFN)/Ce_0.8Sm_0.2O_1.9(SDC) composite material was prepared and characterized as cathode for intermediate temperature solid oxide fuel cells. The X-ray diffraction result proved that there was no obvious reaction between the BCFN and SDC after calcination at 1000 °C for 10 h. AC impedance spectra based on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ(LSGM) electrolyte measured at intermediate temperatures showed that a cathode with 30 wt% SDC exhibited the best electrochemical performance among the electrodes studied. The interfacial resistance value for BCFN/30SDC was as low as 0.0104, 0.017, 0.029, and 0.062 Ω cm² at 800, 750, 700 and 650 °C, respectively. The maximum power density of a single cell with BCFN/30SDC cathode, Ni_0.9Cu_0.1-SDC anode, and LSGM/SDC electrolyte was 209.7, 298.2, 407.1, 543.4 and 697.9 mW cm⁻² at 600, 650, 700, 750 and 800 °C.     

Performance and degradation of La0.8Sr0.2Ga0.85Mg0.15O3−δ electrolyte-supported cells in single-chamber configuration

Electrolyte-supported cells were made of a La_0.8Sr_0.2Ga_0.85Mg_0.15O_3−δ (LSGM2015) electrolyte (200 μm thickness) prepared by ethylene glycol complex solution synthesis, isostatic pressing and sintered at 1400 °C, a Ni-SDC anode, a Sm_0.2Ce_0.8O_3−δ (SDC) buffer-layer between anode and electrolyte, and a La_0.5Sr_0.5CoO_3−δ-SDC cathode. The cells were tested in single-chamber configuration using methane–air mixtures. The results of X-ray diffraction and SEM-EDS showed a single-phase in the electrolyte and conductivities (∼0.01 S cm⁻¹ at 650 °C) close to the typical values. Good cell power densities of 215 and 102 mW cm⁻² were achieved under CH₄/O₂ = 1.4 of at 800 and 650 °C, respectively. However, the cell stability tests indicated that the operating temperature strongly influenced on the cell performance after 100 h. While no significant change in the power density was observed working at 650 °C, a clear performance degradation was evidenced at 800 °C. SEM-EDS revealed an appreciable degradation of the electrolyte and both the electrodes.     

La0.6Sr0.4Fe0.8Cu0.2O3−δ perovskite oxide as cathode for IT-SOFC

A La_0.6Sr_0.4Fe_0.8Cu_0.2O_3−δ (LSFCu) perovskite was investigated as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFC). The LSFCu material exhibited chemical compatibility with the Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte up to a temperature of 1100 °C. The electrical conductivity of the sintered sample was measured as a function of temperature from 100 to 800 °C. The highest conductivity of about 238 S cm⁻¹ was observed for LSFCu. The average thermal-expansion coefficient (TEC) of LSFCu was 14.6 × 10⁻⁶ K⁻¹, close to that of typical CeO₂ electrolyte material. The investigation of electrical properties indicated that the LSFCu cathode had lower interfacial polarization resistance of 0.070 Ω cm² at 800 °C and 0.138 Ω cm² at 750 °C in air. An electrolyte-supported single cell with 300 μm thick SDC electrolyte and LSFCu as cathode shows peak power densities of 530 mW cm⁻² at 800 °C.     

A comparative study of Sm0.5Sr0.5MO3−δ (M = Co and Mn) as oxygen reduction electrodes for solid oxide fuel cells

Sm_0.5Sr_0.5MO_3−δ (M = Co and Mn) materials are synthesized, and their properties and performance as cathodes for solid oxide fuel cells (SOFCs) on Sm_0.2Ce_0.8O_1.9 (SDC) and Y_0.16Zr_0.92O_2.08 (YSZ) electrolytes are comparatively studied. The phase structure, thermal expansion behavior, oxygen mobility, oxygen vacancy concentration and electrical conductivity of the oxides are systematically investigated. Sm_0.5Sr_0.5CoO_3−δ (SSC) has a much larger oxygen vacancy concentration, electrical conductivity and TEC than Sm_0.5Sr_0.5MnO_3−δ (SSM). A powder reaction demonstrates that SSM is more chemically compatible with the YSZ electrolyte than SSC, while both are compatible with the SDC electrolyte. EIS results indicate that the performances of SSC and SSM electrodes depend on the electrolyte that they are deposited on. SSC is suitable for the SDC electrolyte, while SSM is preferred for the YSZ electrolyte. A peak power density as high as 690 mW cm⁻² at 600 °C is observed for a thin-film SDC electrolyte with SSC cathode, while a similar cell with YSZ electrolyte performs poorly. However, SSM performs well on YSZ electrolyte at an operation temperature of higher than 700 °C, and a fuel cell with SSM cathode and a thin-film YSZ electrolyte delivers a peak power density of ∼590 mW cm⁻² at 800 °C. The poor performances of SSM cathode on both YSZ and SDC electrolytes are obtained at a temperature of lower than 650 °C.     

Pr0.5Ba0.5Co0.7Fe0.25Nb0.05O3-δ as air electrode for solid oxide steam electrolysis cells

Pr_0.5Ba_0.5Co_0.7Fe_0.25Nb_0.05O_3-δ (PBCFN) is synthesized and evaluated as air electrode for solid oxide steam electrolysis cells (SOECs). X-ray diffraction and TEM analysis show that PBCFN has a pure tetragonal perovskite structure with a lattice fringe spacing of 0.39 nm for the (110) planes. When the applied voltage is set at 1.3 V, a relatively high electrolysis current density of 470 mA cm² at 800 °C is achieved for electrolyte-supported electrolysis cells with the cell configuration of Sr₂Fe_1.5Mo_0.5O₆ (SFM)–Sm_0.2Ce_0.8O₂ (SDC)/La_0.8Sr_0.2Ga_0.87Mg_0.13O₃ (LSGM)/SDC–PBCFN. In addition, there is no obvious performance degradation during the short-term stability test of the above cells at a constant electrolysis voltage of 1.3 V, indicating that PBCFN is a promising air electrode for SOECs.     

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 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.     

High-performance PrBaCo2O5+δ-Ce0.8Sm0.2O1.9 composite cathodes for intermediate temperature solid oxide fuel cell

PrBaCo₂O_5+δ-Ce_0.8Sm_0.2O_1.9 (PBCO-SDC) composite material are prepared and characterized as cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction result proves that there are no obvious reaction between the PBCO and SDC after calcination at 1100 °C for 3 h. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures shows that the addition of SDC to PBCO improved remarkably the electrochemical performance of a PBCO cathode, and that a PBCO-30SDC cathode exhibits the best electrochemical performance in the PBCO-xSDC system. The total interfacial resistances R_p is the smallest when the content of SDC is 30 wt%, where the value is 0.035 Ω cm² at 750 °C, 0.072 Ω cm² at 700 °C, and 0.148 Ω cm² at 650 °C, much lower than the corresponding interfacial resistance for pure PBCO. The maximum power density of an anode-supported single cell with PBCO-30SDC cathode, Ni-SDC anode, and dense thin SDC/LSGM (La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ)/SDC tri-layer electrolyte are 364, 521 and 741 mW cm⁻² at 700, 750 and 800 °C, respectively.     

Ba0.9Co0.5Fe0.4Nb0.1O3−δ as novel oxygen electrode for solid oxide electrolysis cells

A novel perovskite oxide Ba_0.9Co_0.5Fe_0.4Nb_0.1O_3−δ (BCFN) was prepared and characterized as oxygen electrode for solid oxide electrolysis cells (SOECs) using La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM) as electrolyte. Symmetrical half-cell study shows that the polarization resistance of BCFN is only 0.08 Ω cm² at 750 °C in air. Electrochemical impedance spectra and voltage-current curves of the electrolysis cell with the configuration of BCFN|LSGM|La_0.4Ce_0.6O_2−x|Ni-Ce_0.9Gd_0.1O_1.95 were measured as a function of operating temperature and steam concentrations to characterize the electrolysis cell performances. Under an applied electrolysis voltage of 1.5 V, the maximum consumed current density increased from 0.835 A cm⁻² at 700 °C to 3.237 A cm⁻² at 850 °C with 40 vol.% absolute humidity (AH), and the hydrogen generation rate of the cell can be up to 1352 mL cm⁻² h⁻¹ with 40 vol.% AH at 850 °C. Further, the electrolysis cell has showed very stable performance during a 200 h short-term electrolysis testing, indicating that BCFN can be a very promising candidate for the oxygen electrode of SOECs using LSGM electrolyte.     

Thermal inkjet printing of thin-film electrolytes and buffering layers for solid oxide fuel cells with improved performance

In this study, we report the facile fabrication of thin-film yttria-stabilized zirconia (YSZ) electrolytes and Sm_0.2Ce_0.8O_1.9 (SDC) buffering layers for solid oxide fuel cells (SOFCs) using a thermal inkjet printing technique. Stable YSZ and SDC inks with solids contents as high as 20 and 10 wt.%, respectively, were first prepared. One single printing typically resulted in an YSZ membrane with thickness of approximately 1.5 μm, and membranes with thicknesses varied from 1.5 to 7.5 μm were fabricated with multiple sequential printing. An as-fabricated cell with a La_0.8Sr_0.2MnO₃ (LSM) cathode delivered a peak power density (PPD) of 860 mW cm⁻² at 800 °C. The SDC layer prepared using the inkjet printing method exhibited enclosed pores and a rough surface, which was, however, ideal for its application as a buffering layer. A cell with a dense 7.5-μm-thick YSZ layer, a 2-μm-thick SDC buffering layer and a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) cathode was fabricated; this cell delivered a PPD of 1040 mW cm⁻² at 750 °C and a high open circuit voltage (OCV) of approximately 1.10 V. The described technique provides a facile method for the fabrication of electrolytes for SOFCs with precise thickness control.     

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.     

Characterization of nanosized Ce0.8Sm0.2O1.9-infiltrated Sm0.5Sr0.5Co0.8Cu0.2O3−δ cathodes for solid oxide fuel cells

This study investigates the microstructure and electrochemical properties of Sm_0.5Sr_0.5Co_0.8Cu_0.2O_3−δ (SSC-Cu) cathode infiltrated with Ce_0.8Sm_0.2O_1.9 (SDC). The newly formed nanosized electrolyte material on the cathode surface, leading the increase in electrochemical performances is mainly attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the electrochemical sites for oxygen reduction reaction. Based on the experiment results, the 0.4 M SDC infiltration reveals the lowest cathode polarization resistance (R_P), the cathode polarization resistances (R_p) are 0.117, 0.033, and 0.011 Ω cm² at 650, 750, and 850 °C, and the highest peak power density, are 439, 659, and 532 mW cm⁻² at 600, 700, and 800 °C, respectively. The cathode performance in SOFCs can be significantly improved by infiltrating nanoparticles of SDC into an SSC-Cu porous backbone. This study reveals that the infiltration approach may apply in SOFCs to improve their electrochemical properties.     

Cobalt and molybdenum co-doped Ca2Fe2O5 cathode for solid oxide fuel cell

Recently, Brownmillerite oxides Ca₂Fe_2-xM_xO₅ (0 ≤ x ≤ 0.2) (M = transition metal such as Co, Mo), have been drawing attention as they possess mixed ionic and electronic conductivity. Fe site of parent Ca₂Fe₂O₅ (CFO) structure is partially substituted by Co and/or Mo as well as CoMo co-doping and tested as cathodes in SOFC. Physical characterizations such as X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and Brunauer–Emmett–Teller (BET) have been carried out to assess the phase formation, microstructure, presence of constituent elements, particle size, and surface area of the cathode, respectively. The Co doped CFO cathodes have better percolation, large surface area, and extended triple phase boundary. Further, the doped CFO cathodes exhibited chemical compatibility with other cell components during fabrication and cell testing as evident from SEM micrographs. The Ca₂Fe_2-xM_xO₅ (0 ≤ x ≤ 0.2) oxides show a semiconductor behaviour having sufficient electrical conductivity values in the SOFCs operating temperature 600–800 °C range. The best electrical conductivity, 0.47 S/cm at 800 °C and the corresponding activation energy of 0.17 eV is exhibited by Ca₂Fe_1.8Co_0.2O₅ (CFCO), whereas Ca₂Fe_1.8Mo_0.2O₅ (CFMO) and Ca₂Fe_1.8Mo_0.1Co_0.1O₅ (CFMCO) cathode shows electrical conductivity 0.11 S/cm and 0.15 S/cm at 800 °C, respectively. CFMO performed better with SDC than YSZ electrolyte between 600 and 700 °C although the lowest area specific resistance (ASR) of 1.28 Ω cm² at 800 °C is observed for CFMO with YSZ electrolyte. Similarly, CFMCO provided low ASR at lower temperature with SDC than that with YSZ electrolyte but exhibited lowest ASR of 0.41 Ω cm² at 800 °C with YSZ. The CFCO cathode shows lower ASR with YSZ than that with SDC for all the temperature and provided lowest value of ASR 0.21 Ω cm² at 800 °C. CFCO cathode has been tested in 900 μm thick electrolyte (SDC/YSZ) supported solid oxide fuel cell (SOFC) CFCO-SDC/SDC/NiO-SDC and CFCO-YSZ/YSZ/NiO-YSZ provided maximum power densities of 171 and 506 mW/cm² (i-R corrected) at 800 °C, respectively.     

Sm0.5Sr0.5Co0.4Ni0.6O3−δ–Sm0.2Ce0.8O1.9 as a potential cathode for intermediate-temperature solid oxide fuel cells

The mixed ionic and electronic conductors (MIECs) of Sm_0.5Sr_0.5Co_0.4Ni_0.6O_3−δ (SSCN)–Sm_0.2Ce_0.8O_1.9 (SDC) were investigated for potential application as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on an SDC electrolyte. Electrochemical impedance spectroscopy (EIS) technique was performed over the temperature range of 600–850 °C to determine the cathode polarization resistance which is represented by area specific resistance (ASR). To investigate the ORR mechanism, the impedance diagram for 70SSCN–30SDC was measured under applied cathodic voltage from E = 0.0 to E = −0.3 V. It indicated that the charge transfer dominated the rate-determining step at the temperature of 600 °C; whereas the diffusion or dissociative adsorption of oxygen dominated the rate-determining step at the temperature of 800 °C. In this study, the exchange current density (i₀) for oxygen reduction reaction (ORR) was determined from the EIS data. The i₀ value of 70SSCN–30SDC/SDC was 187.6 mA cm⁻² which is larger than the i₀ value of 160 mA cm⁻² for traditional cathode/electrolyte, i.e. LSM/YSZ at 800 °C, indicating that the 70SSCN–30SDC composite cathode with a high catalytically active surface area could provide the oxygen reduction reaction areas not only at the triple-phase boundaries but also in the whole composite cathode.     

PrBa0.5Sr0.5Co2O5+x as cathode material based on LSGM and GDC electrolyte for intermediate-temperature solid oxide fuel cells

PrBa_0.5Sr_0.5Co₂O_5+x (PBSC) oxides have been evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ce_0.9Gd_0.1O_1.95 (GDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolytes. XRD results show that PBSC cathode is chemically compatible with the intermediate-temperature electrolyte materials GDC and LSGM. The maximum electrical conductivity is 1522 S cm⁻¹ at 100 °C and its value is higher than 581 S cm⁻¹ over the whole temperature range investigated. Microstructures show that the contact between PBSC and LSGM is better than that between PBSC and GDC. The area-specific resistances (ASRs) of PBSC cathode on GDC and LSGM electrolytes are 0.048 and 0.027 Ωcm² at 800 °C, respectively. The electrolyte-supported (thickness of electrolyte is 300 μm) fuel cells generate good performance with the maximum power densities of 617 mW cm⁻² on GDC electrolyte and 1021 mW cm⁻² on LSGM electrolyte at 800 °C. All results demonstrate that PBSC oxide is a very promising cathode material for application in IT-SOFCs and this cathode based on LSGM electrolyte obtained better performance than on GDC electrolyte.     

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.     

A high performance BaZr0.1Ce0.7Y0.2O3-δ-based solid oxide fuel cell with a cobalt-free Ba0.5Sr0.5FeO3-δ–Ce0.8Sm0.2O2-δ composite cathode

A cobalt-free Ba_0.5Sr_0.5FeO_3-δ–Ce_0.8Sm_0.2O_2-δ (BSF–SDC) composite is employed as a cathode for an anode-supported 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 BSF and SDC is evaluated. The XRD results show that BSF is chemically compatible with SDC after co-fired at 1000 °C for 6 h. A single cell with a 20-μm-thick BZCY electrolyte membrane exhibits excellent power densities as high as 792 and 696 mW cm⁻² at 750 and 700 °C, respectively. To the best of our knowledge, this is the highest performance reported in literature up to now for BZCY-based single cells with cobalt-free cathode materials. Extremely low polarization resistances of 0.030 and 0.044 Ωcm² are achieved at 750 and 700 °C respectively. The excellent performance implies that the cobalt-free BSF–SDC composite is a promising alternative cathode for H-SOFCs. Resistances of the tested cell are investigated under open circuit conditions at different operating temperatures by impedance spectroscopy.     

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.     

Low-temperature solid oxide fuel cells with novel La0.6Sr0.4Co0.8Cu0.2O3−δ perovskite cathode and functional graded anode

The perovskite La_0.6Sr_0.4Co_0.8Cu_0.2O_3−δ (LSCCu) oxide is synthesized by a modified Pechini method and examined as a novel cathode material for low-temperature solid oxide fuel cells (LT-SOFCs) based upon functional graded anode. The perovskite LSCCu exhibits excellent ionic and electronic conductivities in the intermediate-to-low-temperature range (400-800 °C). Thin Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte and NiO-SDC anode functional layer are prepared over macroporous anode substrates composed of NiO-SDC by a one-step dry-pressing/co-firing process. A single cell with 20 μm thick SDC electrolyte on a porous anode support and LSCCu-SDC cathode shows peak power densities of only 583.2 mW cm⁻² at 650 °C and 309.4 mW cm⁻² for 550 °C. While a cell with 20 μm thick SDC electrolyte and an anode functional layer on the macroporous anode substrate shows peak power densities of 867.3 and 490.3 mW cm⁻² at 650 and 550 °C, respectively. The dramatic improvement of cell performance is attributed to the much improved anode microstructure that is confirmed by both SEM observation and impedance spectroscopy. The results indicate that LSCCu is a very promising cathode material for LT-SOFCs and the one-step dry-pressing/co-firing process is a suitable technique to fabricate high performance SOFCs.