A Performance Study of Solid Oxide Fuel Cells With BaZr0.1Ce0.7Y0.2O3–δ Electrolyte Developed by Spray‐Modified Pressing Method

Fuel cells with BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY) proton‐conducting electrolyte is fabricated using spray‐modified pressing method. In the present study the spray‐modified pressing technology is developed to prepare thin electrolyte layers on porous Ni‐BZCY anode supports. SEM data show the BZCY electrolyte film is uniform and dense, well‐bonded with the anode substrate. An anode‐supported fuel cell with BZCY electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ (BSCF) cathode is characterized from 600 to 700 °C using hydrogen as fuel and ambient air as oxidant. Maximum power density of 536 mW cm^–2 along with a 1.01 V OCV at 700 °C is obtained. Impedance spectra show that Ohmic resistances contribute minor parts to the total ones, for instance, only ~23% when operating at 600 °C. The results demonstrate that spray‐modified pressing technology offers a simple and effective way to fabricate quality electrolyte film suitable to operate in intermediate temperature.     

Preparation of BaZr0.1Ce0.7Y0.2O3–δ Based Solid Oxide Fuel Cells with Anode Functional Layers by Tape Casting

Solid oxide fuel cells (SOFCs) based on the proton conducting BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY) electrolyte were prepared and tested in 500–700 °C using humidified H₂ as fuel (100 cm³ min^–1 with 3% H₂O) and dry O₂ (50 cm³ min^–1) as oxidant. Thin NiO‐BZCY anode functional layers (AFL) with 0, 5, 10 and 15 wt.% carbon pore former were inserted between the NiO‐BZCY anode and BZCY electrolyte to enhance the cell performance. The anode/AFL/BZCY half cells were prepared by tape casting and co‐sintering (1,300 °C/8 h), while the Sm_0.5Sr_0.5CoO_3–δ (SSC) cathodes were prepared by thermal spray deposition. Well adhered planar SOFCs were obtained and the test results indicated that the SOFC with an AFL containing 10 wt.% pore former content showed the best performance: area specific resistance as low as 0.39 Ω cm² and peak power density as high as 0.863 W cm^–2 were obtained at 700 °C. High open circuit voltages ranging from 1.00 to 1.12 V in 700–500 °C also indicated negligible leakage of fuel gas through the electrolyte.     

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.     

Flame Spray Synthesis of BaZr0.8Y0.2O3–δ Electrolyte Nanopowders for Intermediate Temperature Proton Conducting Fuel Cells

Flame Spray Synthesis (FSS) technique has been used for the preparation of BaZr_0.8Y_0.2O_3–δ (BZY20) nanoprecursors. The nanoprecursors were composed of a perovskite phase mixed with doped Zirconia and barium nitrate. Pure phase powder could be obtained after calcining the precursors at 1,200 °C. Both nanoprecursors and pure phase powder were then sintered at 1,600 °C to obtain dense specimen. AC impedance spectroscopy performed on the sintered samples allowed correlation of the electrical properties of the samples to their microstructures. The sintered nanoprecursors compared with the sintered pure phase powders showed enhanced grain growth associated with higher grain boundary conductivity. The influence of the reactive sintering on the enhanced grain growth and electrical properties in the nanoprecursors is discussed. The high total proton conductivity measured (7.7·10⁻³ S cm⁻¹ at 450 °C) promotes FSS as an effective powder synthesis method for the preparation of BZY20 electrolyte material for proton conducting fuel cells operating in the intermediate temperature range.     

Optimisation and Evaluation of La0.6Sr0.4CoO3 – δ Cathode for Intermediate Temperature Solid Oxide Fuel Cells

In this work, La_0.6Sr_0.4CoO_{3 – δ}/Ce_{1 – x}Gd_xO_{2 – δ} (LSC/GDC) composite cathodes are investigated for SOFC application at intermediate temperatures, especially below 700 °C. The symmetrical cells are prepared by spraying LSC/GDC composite cathodes on a GDC tape, and the lowest polarisation resistance (R_p) of 0.11 Ω cm² at 700 °C is obtained for the cathode containing 30 wt.‐% GDC. For the application on YSZ electrolyte, symmetrical LSC cathodes are fabricated on a YSZ tape coated on a GDC interlayer. The impact of the sintering temperature on the microstructure and electrochemical properties is investigated. The optimum temperature is determined to be 950 °C; the corresponding R_p of 0.24 Ω cm² at 600 °C and 0.06 Ω cm² at 700 °C are achieved, respectively. An YSZ‐based anode‐supported solid oxide fuel cell is fabricated by employing LSC/GDC composite cathode sintered at 950 °C. The cell with an active electrode area of 4 × 4 cm² exhibits the maximum power density of 0.42 W cm^–2 at 650 °C and 0.54 W cm^–2 at 700 °C. More than 300 h operating at 650 °C is carried out for an estimate of performance and degradation of a single cell. Despite a decline at the beginning, the stable performance during the later term suggests a potential application.     

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).     

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.     

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.%.     

Flame Spray Synthesis of Nanoscale La0.6Sr0.4Co0.2Fe0.8O3–δ and Ba0.5Sr0.5Co0.8Fe0.2O3–δ as Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells

Electrochemical performance and degradation was analysed by conductivity measurements as well as thermogravimetric analysis (TGA) under different atmospheres. CO₂ was identified as a critical parameter in terms of carbonate formation from Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ and causes a strong increase in the material resistivity, whereas La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ is unaffected. The oxygen exchange kinetic of both compositions is affected by CO₂ containing atmospheres.     

Performance of Cobalt‐free La0.6Sr0.4Fe0.9Ni0.1O3–δ Cathode Material for Intermediate Temperature Solid Oxide Fuel Cells

A series of cobalt‐free perovskite‐type cathode materials La_0.6Sr_0.4Fe_1–xNi_xO_3–δ (0 ≤ x ≤ 0.15) for intermediate temperature solid oxide fuel cells (IT‐SOFCs) are prepared by a citric‐nitrate process. The conductivities of the cathode materials are measured as functions of temperature (300–800 °C) in air by AC impedance method, and the La_0.6Sr_0.4Fe_0.9Ni_0.1O_3–δ (LSFN10) has the highest conductivity to be 160 S cm^–1 at 400 °C. A single IT‐SOFC based on LSFN10 cathode, BaZr_0.1Ce_0.7Y_0.2O_3–δ electrolyte membrane and Ni–BaZr_0.1Ce_0.7Y_0.2O_3–δ anode substrate was fabricated by a simple spin‐coating process, and the performances of the cell using hydrogen as fuel and air as the oxidant were researched by electrochemical methods at 600–700 °C. The maximum power densities of the cell are 405 mW cm^–2 at 700 °C, 238 mW cm^–2 at 650 °C, and 140 mW cm^–2 at 600 °C, respectively. The results indicate that the LSFN10 is a promising cathode material for proton conducting IT‐SOFCs.     

Fabrication of Solid Oxide Fuel Cells with a Thin (La0.9Sr0.1)0.98(Ga0.8Mg0.2)O3–δ Electrolyte on a Sr0.8La0.2TiO3 Support

This paper describes Sr_0.8La_0.2TiO₃ (SLT)‐supported solid oxide fuel cells with a thin (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3–δ (LSGM) electrolyte and porous LSGM anode functional layer (AFL). Optimized processing for the SLT support bisque firing, LSGM electrolyte layer co‐firing, and LSGM AFL colloidal composition is presented. Cells without a functional layer yielded a power density of 228 mW cm^–2 at 650 °C, while cells with a porous LSGM functional layer yielded a power density of 434 mW cm^–2 at 650 °C. Cells with an AFL yielded a higher open circuit voltage, possibly due to reduced Ti diffusion into the electrolyte. Infiltration produced Ni nanoparticles within the support and AFL, which proved crucial for the electrochemical activity of the anode. Power densities increased with increasing Ni loadings, reaching 514 mW cm^–2 at 650 °C for 5.1 vol.% Ni loading. Electrochemical impedance spectroscopy analysis indicated that the cell resistance was dominated by the cathode and electrolyte resistance with the anode resistance being relatively small.     

Design of BaZr0.8Y0.2O3–δ Protonic Conductor to Improve the Electrochemical Performance in Intermediate Temperature Solid Oxide Fuel Cells (IT‐SOFCs)

BaZr_0.8Y_0.2O_3–δ, (BZY), a protonic conductor candidate as an electrolyte for intermediate temperature (500–700 °C) solid oxide fuel cells (IT‐SOFCs), was prepared using a sol–gel technique to control stoichiometry and microstructural properties. Several synthetic parameters were investigated: the metal cation precursors were dissolved in two solvents (water and ethylene glycol), and different molar ratios of citric acid with respect to the total metal content were used. A single phase was obtained at a temperature as low as 1,100 °C. The powders were sintered between 1,450 and 1,600 °C. The phase composition of the resulting specimens was investigated using X‐ray diffraction (XRD) analysis. Microstructural characterisation was performed using field emission scanning electron microscopy (FE‐SEM). Chemical stability of the BZY oxide was evaluated upon exposure to CO₂ for 3 h at 900 °C, and BZY showed no degradation in the testing conditions. Fuel cell polarisation curves on symmetric Pt/BZY/Pt cells of different thicknesses were measured at 500–700 °C. Improvements in the electrochemical performance were obtained using alternative materials for electrodes, such as NiO‐BZY cermet and LSCF (La_0.8Sr_0.2Co_0.8Fe_0.2O₃), and reducing the thickness of the BZY electrolyte, reaching a maximum value of power density of 7.0 mW cm^–2 at 700 °C.