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

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

Effect of Fe Doping on Layered GdBa0.5Sr0.5Co2O5+δ Perovskite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Layered perovskite cathode materials have received considerable attention for intermediate temperature solid oxide fuel cells (IT‐SOFCs) because of their fast oxygen ion diffusion through pore channels and high catalytic activity toward the oxygen reduction reaction (ORR) at low temperatures. In this study, we have investigated the effects of Fe substitution for the Co site on electrical and electrochemical properties of a layered perovskite, GdBa_0.5Sr_0.5Co_2?xFe_xO_5+δ (x = 0, 0.5, and 1.0), as a cathode material for IT‐SOFCs. Furthermore, electrochemical properties of GdBa_0.5Sr_0.5CoFeO_5+δ–yGDC (y = 0, 20, 40, and 50 wt%) cathodes were evaluated to determine the optimized cell performance. At a given temperature, the electrical conductivity and the area‐specific resistances (ASRs) of GdBa_0.5Sr_0.5Co_2?x Fe_xO_5+δ decrease with Fe content. The lowest ASR of 0.067 Ω·cm² was obtained at 873 K for the GdBa_0.5Sr_0.5CoFeO_5+δ. The GdBa_0.5Sr_0.5CoFeO_5 + δ composite with 40 wt% GDC was identified as an optimum cathode material, showing the highest maximum power density (1.31 W/cm²) at 873 K, and other samples also showed high power density over 1.00 W/cm².     

Application of sonochemical processing to LSC(La0.6Sr0.4CoO3)/SDC(Sm2O3-doped CeO2) composite cathodes for solid oxide fuel cells involving CeO2-based electrolytes

Nanocrystalline Sm₂O₃-Doped CeO₂ (SDC) powders were synthesized in a single- and two-phase material system by using sonochemical processing with high-frequency agitation. The synthesized SDC nanocrystalline powders were used to coat the mixed-conducting La_0.6Sr_0.4CoO₃ (LSC) cathode materials. The combined synthesis processing allows the artificial coating of the LSC materials with the ionic-conducting SDC electrolyte. The electrochemical polarizations of the SDC/LSC composites are characterized using a geometrically constricted contact between the ionic probe and the SDC/LSC composites. The lowest cathode polarization was obtained for the LSC (85 wt%)/SDC (15 wt%). The lowest electrode polarization is believed to result from the high density of the triple-phase boundaries when the constituent phases are interconnected in a 3-dimensional manner.     

Fabrication and Performance of Solid Oxide Fuel Cells with La0.2Sr0.7TiO3–δ as Anode Support and La2NiO4+δ as Cathode

A novel fabrication process for solid oxide fuel cells (SOFCs) with La_0.2Sr_0.7TiO_3–δ (LST_A–) as anode support and La₂NiO_4+δ (LNO) as cathode material, which avoids complicated impregnation process, is designed and investigated. The LST_A– anode‐supported half cells are reduced at 1,200 °C in hydrogen atmosphere. Subsequently, the LNO cathode is sintered on the YSZ electrolyte at 1,200 °C in nitrogen atmosphere and then annealed in situ at 850 °C in air. The results of XRD analysis and electrical conductivity measurement indicate that the structure and electrochemical characteristics of LNO appear similar before and after the sintering processes of the cathode. By using La_0.6Sr_0.4CoO_3–δ (LSC) as current collector, the cell with LNO cathode sintered in nitrogen atmosphere exhibits the power density at 0.7 V of 235 mW cm⁻² at 800 °C. The ohmic resistance (R_S) and polarization resistance (R_P) are 0.373 and 0.452 Ω cm², respectively. Compared to that of the cell with the LNO cathode sintered in air, the sintering processes of the cell with the LNO cathode sintered in nitrogen atmosphere can result in better electrochemical performance of the cell mainly due to the decrease in R_S. The microstructures of the cells reveal a good adhesion between each layer.     

Electrochemical Performance of PrBaCo2O5+δ and Sm0.5Sr0.5CoO3−δ Infiltrated Ce0.9Gd0.1O1.95 Cathodes

Cathodes with PrBaCo₂O_5+δ (PBC) and Sm_0.5Sr_0.5CoO_3−δ (SSC) infiltrated on Ce_0.9Gd_0.1O_1.95 (CGO) backbones are prepared using metal nitrates as precursors and ethanol as wetting agent. Electrochemical impedance spectra (EIS) are measured from cathode/CGO/cathode symmetrical cells in 400–650 °C under humidified air. The results indicate that interfacial area specific resistance (ASR) value decreases and then increases with infiltrate loading and minimum values occur at 50 wt.% loading (relative to sum of infiltrate and backbone) for both PBC and SSC infiltrates. ASR values of PBC infiltrated cathodes are lower than that of corresponding SSC infiltrated cathodes in general, and in particular ASR values as low as 1.36 × 10⁻² and 2.27 × 10⁻² Ω cm² are obtained at 650 °C in air for 50 wt.% PBC and 50 wt.% SSC infiltrated cathodes, respectively. Conductivity values of CGO electrolyte increase with infiltrate loading and agree with the reported values when the loading reaches 50 wt.%.     

Co‐synthesis of Sm0.5Sr0.5CoO3‐Sm0.2Ce0.8O1.9 Composite Cathode with Enhanced Electrochemical Property for Intermediate Temperature SOFCs

A 70 wt.% Sm_0.5Sr_0.5CoO₃ – 30 wt.% Sm_0.2Ce_0.8O_1.9 (SSC–SDC73) composite cathode was co‐synthesized by a facile one‐step sol–gel method, which showed lower polarization resistance and overpotential than those of physically mixed SSC–SDC73 cathode. The polarization resistance of co‐synthesized SSC–SDC73 cathode at 800 °C was as low as 0.03 Ω cm² in air. Scanning electron microscopy (SEM) images showed that the enhanced electrochemical property was mainly attributed to the smaller grains and good dispersion of SSC and SDC phases within the composite cathode, leading to an increase in three‐phase boundary length. The dependence of polarization resistance with oxygen partial pressure indicated that the rate‐limiting step for oxygen reduction reaction was the dissociation of molecular oxygen to atomic oxygen process. An anode supported fuel cell with a co‐synthesized SSC–SDC73 cathode exhibited a peak power density of 924 mW cm⁻² at 800 °C. Our results suggested that co‐synthesized composite was a promising cathode for intermediate temperature solid oxide fuel cells (IT‐SOFCs).     

Characterization of La0.6Sr0.4Co0.2Fe0.8O3–δ + La2NiO4+δ Composite Cathode Materials for Solid Oxide Fuel Cells

The structure, electrical conduction, thermal expansion and electrochemical properties of the La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ + La₂NiO_4+δ (LSCF‐LNO) composite cathodes were investigated with regard to the volume fraction of the LNO composition. No chemical reaction product between the two constituent phases was found for the composite cathodes sintered at 1,400 °C for 10 h within the sensitivity of the XRD. Compared to the performance of the LSCF cathode, the LNO composition in the composite cathode plays a role in deteriorating both electrical conductivity and electrochemical properties, however, improving the thermal expansion properties. The trade‐off between electrical conducting and thermal expansion classifies the composite cathode containing 30 volume percent (vol.%) LNO as the optimum composition. For characterizing cathode performance in a single cell, a slurry spin coating technique was employed to prepare a porous cathode layer as well as a YSZ/Ce_0.8Sm_0.2O_3–δ (SDC) electrolyte. The optimum conditions for fabricating the YSZ/SDC electrolyte were investigated. The resulting single cell with 70 vol.% LSCF‐30 vol.%LNO (LSCF‐LNO30) cathode shows a power density of 497 mW cm^–2 at 800 °C, which is lower than that of the cell with a LSCF cathode, but still within the limits acceptable for practical applications.     

High permittivitty (La0.5Sr0.5)CoO3-δ-La(Co0.5Ti0.5)O3-δ ceramic composites for next generation MIM capacitors

Dielectrics with low capacitance loss and high relative permittivity are of high demand in metal-insulator-metal (MIM) capacitor that offers higher level of miniaturization, flexibility and performance. In order to achieve high relative permittivity, developing ceramics with metallic inclusions, has been suggested as a working strategy. But such materials may have high leakage currents and often lack thermal stability. With the objective for MIM applications, a series of (1-x)La(Co_0.5Ti_0.5)O_3-δ-x(La_0.5Sr_0.5)CoO_3-δ ceramics [x?=?0.0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 1] were developed. The crystal structure analysis was performed for La(Co_0.5Ti_0.5)O_3-δ, (La_0.5Sr_0.5)CoO_3-δ and 0.5La(Co_0.5Ti_0.5)O_3-δ-0.5(La_0.5Sr_0.5)CoO_3-δ using X-pert High Score Plus. The composite with x?=?0.5 in (1-x)La(Co_0.5Ti_0.5)O_3-δ-x(La_0.5Sr_0.5)CoO₃-_δ showed a maximum relative permittivity of 4920 with promising ac electrical resistivity (～202?Ω-cm). The thermal, electrical and dielectric properties together suggest that the composition 0.5La(Co_0.5Ti_0.5)O_3-δ-0.5(La_0.5Sr_0.5)CoO₃-_δ is suitable for MIM capacitors in DRAM and RF devices.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2CoO3−δ cathode for intermediate-temperature solid oxide fuel cell

This study reports the successful preparation of a single-phase cubic (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ perovskite by the citrate–EDTA complexing method. Its crystal structure, thermogravimetry, coefficient of thermal expansion, electric conductivity, and electrochemical performance were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Its coefficient of thermal expansion shows abnormal expansion at 300 °C, which is associated with the loss of lattice oxygen. The maximum conductivity of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ electrode is 689 S/cm at 300 °C. Above 300 °C, the electronic conductivity of (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ decreases due to the formation of oxygen vacancies. The charge-transfer resistance and gas phase diffusion resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ–Ce_0.8Sm_0.2O_1.9 composite cathode are 0.045 Ω cm² and 0.28 Ω cm², respectively, at 750 °C.     

Electrochemical studies on Sr doped LaMnO<Subscript>3</Subscript> and LaCoO<Subscript>3</Subscript> layers synthesised in a low-pressure plasma reactor equipped with a convergent nozzle

The aim of this work was to synthesise and deposit a perovskite (La_1-x Sr _x MnO₃ or La_1-x Sr _x CoO₃) cathode on an SOFC electrolyte (8% Yttria Stabilised Zirconia – YSZ). The recombination of atomic oxygen on Sr doped LaMnO₃ was performed in order to study the properties of perovskite for the adsorption of oxygen. The electrical resistance of the layers was measured as a function of the chemical composition. Impedance measurements on different samples were performed in order to analyse the electrochemical response of the cathode – electrolyte stack as a function of temperature and nature of the atmosphere. Moreover, the Faradaic impedance representing the electrochemical processes at the cathode – electrolyte interface was calculated from the global impedance in various conditions.     

A New Composite Material Ca3Co4O9+δ+La0.7Sr0.3CoO3 Developed for Intermediate‐Temperature SOFC Cathode

In this study, Ca₃Co₄O_9+δ (CCO) and La_0.7Sr_0.3CoO₃ (LSC) have been mixed as mass fraction by 1:1, to prepare novel two‐phase composites with high electrical conductivity and low thermal expansion coefficient (TEC), for potential application in intermediate‐temperature solid oxide fuel cells. The conductivity of the composite, Ca₃Co₄O_9+δ (50 wt.%) + La_0.7Sr_0.3CoO₃ (50 wt.%) (CCO‐LSC50), is improved to be three times that of single phase CCO material. And, the TEC of CCO‐LSC50 has been effectively improved to be 15.3 × 10^–6 °C^–1, about 20% lower than single phase LSC cathode, which ensures better chemical compatibility with adjacent electrolyte. As a result, compared with pure LSC and CCO cathodes, CCO‐LSC50 composite cathode improves the electrochemical performance, a percentage of 16 and 84%, respectively, according to the impedance spectra experiments. In addition, cathodic overpotential and oxygen reduction kinetics have also been researched to reveal what is driving the results. The microstructures and phases of cathodes were also compared and analyzed.     

Structure and thermal properties of La0.6Sr0.4Co0.2Fe0.8O3−δ-SDC carbonate composite cathodes for intermediate- to low-temperature solid oxide fuel cells

The structure and thermal properties of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ-SDC carbonate (LSCF-SDC carbonate) composite cathodes were investigated with respect to the calcination temperatures and the weight content of the samarium-doped ceria (SDC) carbonate electrolyte. The composite cathode powder has been prepared from La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ and SDC carbonate powders using the high-energy ball milling technique in air at room temperature. Different powder mixtures at 30 wt%, 40 wt% and 50 wt% of SDC carbonate were calcined at 750-900 °C. The findings indicated that the structure and thermal properties of the composite cathodes were responsive to the calcination temperature and the content of SDC carbonate. The absence of any new phases as confirmed via XRD analysis demonstrated the excellent compatibility between the cathode and electrolyte materials. The particle size of the composite cathode powder was ∼0.3-0.9 μm having a surface area of 4-15 m² g⁻¹. SEM investigation revealed the presence of large particles in the resultant powders resulting from the increased calcination temperature. The composite cathode containing 50 wt% SDC carbonate was found to exhibit the best thermal expansion compatibility with the electrolyte.     

Pr0.6Sr0.4CoO3−δ electrocatalyst for solid oxide fuel cell cathode introduced via infiltration

Effects of infiltrated Pr_0.6Sr_0.4CoO_3−δ (PSCo) electrocatalyst on SOFC cathode performance have been studied. Nano-sized particulate catalysts, deposited on surfaces of a composite cathode of Sm₂O₃ doped CeO₂ (SDC) and La_1−xSr_xCo_1−yFe_yO_3−δ (LSCF), are assumed to effectively widen active sites, or triple phase boundaries, for the oxygen reduction reaction. Area specific resistance of commercially available cells has been decreased by 36–40% with the addition of 23 wt% PSCo electrocatalyst on cathode. Analysis of the impedance spectra demonstrates that PSCo electrocatalyst plays a significant role in dissociation of oxygen molecules and adsorption of oxygen atoms into the cathode. A total of 200 h operation of the cells demonstrated that catalytic activity of PSCo has not been significantly degraded. Simultaneous operations of multiple cells using a parallel-cell testing system have made it possible to compare the performance of several cells with high reliability.     

Characterization of Sr1–xDyxCoO3–δ (x = 0.1, 0.2, 0.3) Cathode Materials for IT‐SOFCs

The cobaltate perovskites Sr_1–xDy_xCoO_3–δ (SDCO, x = 0.1, 0.2, 0.3) materials were synthesized and evaluated as cathode for La_0.8Sr_0.2Ga_0.8Mg_0.2O_3–δ solid electrolyte supported intermediate‐temperature‐solid oxide fuel cells (IT‐SOFCs). The crystal structure of Sr_0.9Dy_0.1CoO_3–δ was defined in the cubic Pm–3m space group (No. 221), Sr_0.8Dy_0.2CoO_3–δ and Sr_0.7Dy_0.3CoO_3–δ had a tetragonal I4/mmm structure. The electrical conductivities were all higher than 100 S cm^–1 in the temperature of 170–800 °C. The polarization resistance (R_p) and its activation energy (E_a) increased with increasing x. SEM analysis confirmed the porous microstructure of the SDCO cathodes and good LSGM|LDC|SDCO adherence. Sr_0.9Dy_0.1CoO_3–δ exhibited the best cathode characteristics with a maximum test‐cell power density of 841 mW cm^–2, being a high potential candidate of cathode material for IT‐SOFCs.     

Performance evaluation of Sm0.5Sr0.5CoO3−δ fibers with embedded Sm0.2Ce0.8O1.9 particles as a solid oxide fuel cell composite cathode

Sm_0.2Ce_0.8O_1.9 (SDC)–embedded Sm_0.5Sr_0.5CoO_3?δ (SSC) composite fibers were successfully fabricated by electrospinning using commercial SDC nanopowders and an SSC precursor gel containing polyvinyl alcohol (PVA) and hydrated metal nitrate. After calcination of the composite fibers at 800 °C, the fibers of 300 ± 80 nm in diameter with a well-developed SSC cubic-perovskite structure and fluorite SDC were successfully obtained. An anode-supported single cell composed of NiO–Gd_0.2Ce_0.8O_1.9 (GDC)/GDC/SSC–SDC fibers was fabricated, and its electrochemical performance was evaluated. The maximum power densities were 1250 and 360 mW/cm² at 700 and 550 °C, respectively, which we ascribe to the excellent properties of the SSC fibers with embedded SDC particles such as a highly porous and continuous structure promoting mass transport and a charge transfer reaction.     

Enhanced electrochemical properties of Bi-layer La0.5Sr0.5CoO3−δ cathode prepared by a hybrid method

Bi-layer La_0.5Sr_0.5CoO_3−δ (LSCO) cathodes are processed by a hybrid method that combines a seed layer prepared by a pulsed laser deposition (PLD) technique and a conventional cathode layer (∼7 μm in thickness) by a screen printing method. By inserting the PLD seed layer with the thickness of ∼500 nm or less, robust cathode films with desired microstructure and excellent adhesion properties with the underlying electrolyte layer, are successfully fabricated. The area specific resistance (ASR) of the hybrid cathode layers decreases about 5 times compared with that of the single layer cathode films prepared by the conventional screen printing method. The hybrid approach provides a cost-effective way to fabricate thick cathode films with significantly enhanced electrochemical properties for solid oxide fuel cells (SOFCs).     

Effects of Particle Size on Electromagnetic and Microwave Absorption Properties of La0.7Sr0.3MnO3±δ‐Epoxy Composite

La_0.7Sr_0.3MnO_3±δ powders were fabricated by solid‐state reaction method at 1473 K for 4 h. The precursors were prepared by ball‐milling raw materials for 3, 6, 9, and 12 h, respectively. The crystal structures, particle size, and morphologies of precursors and prepared La_0.7Sr_0.3MnO_3±δ were characterized by XRD, laser particle size analyzer and SEM, respectively. It is found that La_0.7Sr_0.3MnO_3±δ possessed large particle size by ball‐milling raw materials for a long time. Results indicated that La_0.7Sr_0.3MnO_3±δ, synthesized by ball‐milling raw materials for 3 h, exhibited the optimal microwave absorption properties. The maximum reflection loss was ?28.8 dB, and the ?6 dB absorption bandwidth was 5.80 GHz.     

Characterization of Ba0.5Sr0.5Co0.7In0.1Fe0.2O3−δ as the Cathode Material for Proton‐conducting SOFCs

Ba_0.5Sr_0.5Co_0.7In_0.1Fe_0.2O_3−δ powders are successfully synthesized as the cathode materials for proton‐conducting solid oxide fuel cells (SOFCs). The prepared cells consisting of the structure of a BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7)‐NiO anode substrate, a BZCY7 electrolyte membrane and a cathode layer, are measured from 600 to 700 °C with humidified hydrogen (ca. 3% H₂O) as the fuel. The electrochemical results show that the cell exhibits a high power density which could obtain an open‐circuit potential of 0.986 V and a maximum power density of 400.84 mW cm⁻² at 700 °C. The polarization resistance measured at the open‐circuit condition is only 0.15 Ω cm² at 700 °C.     

Sm0.5Sr0.5CoO3–Sm0.2Ce0.8O1.9 Composite Oxygen Electrodes for Solid Oxide Electrolysis Cells

In this paper, a series of Sm_0.5Sr_0.5CoO₃–Sm_0.2Ce_0.8O_1.9 (SSC–SDC) composite with different ratios were prepared and characterized as oxygen electrodes for solid oxide electrolysis cells (SOECs). Yttria‐stabilized zirconia (YSZ) was selected as the electrolyte with a SDC barrier layer to avoid detrimental solid state interaction between SSC and YSZ. At 850 °C, the impedance spectra showed that the optimum SDC content in the composite electrode was found to be about 30 wt.%, which showed a much lower area specific resistance of 0.03 Ω cm². The electrochemical performances of a Ni–YSZ hydrogen electrode supported YSZ membrane SOEC with the SSC–SDC73 oxygen electrode were also measured at 750–850 °C. The hydrogen production rate calculated from the Faraday's law was 327 mL cm^–2 h^–1 at 850 °C at an electrolysis voltage of 1.3 V with a steam concentration of ∼40%, which indicated that the SSC–SDC73 was a promising oxygen electrode candidate for high temperature electrolysis cells.     

Rational modification of traditional La0.5Sr0.5(Fe/Mn)O3 cathodes for proton-conducting solid oxide fuel cells: Inspiration from nature

By screening a series of La_0.5Sr_0.5MnO_3-δ (LSM)-La_0.5Sr_0.5FeO_3-δ (LSF) solid solutions using first-principles calculations, an optimal solid solution of LSM and LSF was chosen as the cathode for proton-conducting solid oxide fuel cells (H–SOFCs). In terms of oxygen vacancy formation energy, O₂ adsorption energy, bond length of adsorbed O₂, and O p-band center, La_0.5Sr_0.5Mn_0.875Fe_0.125O₃ (LSMF125) and La_0.5Sr_0.5Mn₂₅Fe_0.75O₃ (LSMF75) exhibited superior properties. Subsequent experimental investigations revealed that the H–SOFC with the LSMF75 cathode performed better than the cell with the LSMF125 cathode. The structure analysis revealed that LSMF75 has both Mn and Fe cations on its surface, similar to the designs of several naturally occurring enzymes, hence the increased cathode activity. By improving the LSMF75 cathode further, the cell utilizing the LSMF75 cathode attained a peak power density of 1238 mW cm^-2 at 700 °C, which was much greater than that of the cells using the LSM or LSF cathodes, illustrating the benefits of using the LSM-LSF solid solution. Additionally, the good chemical stability of the LSMF75 cathode was maintained, allowing for 150 h of stable operation under operational conditions.