Integration of Spin‐Coated Nanoparticulate‐Based La0.6Sr0.4CoO3–δ Cathodes into Micro‐Solid Oxide Fuel Cell Membranes

Thin cathodes for micro‐solid oxide fuel cells (micro‐SOFCs) are fabricated by spin‐coating a suspension of La_0.6Sr_0.4CoO_3–δ (LSC) nanoparticulates obtained by salt‐assisted spray pyrolysis. The resulting 250 nm thin LSC layers exhibit a three‐dimensional porous microstructure with a grain size of around 45 nm and can be integrated onto free‐standing 3 mol.% yttria‐stabilized‐zirconia (3YSZ) electrolyte membranes with high survival rates. Weakly buckled micro‐SOFC membranes enable a homogeneous distribution of the LSC dispersion on the electrolyte, whereas the steep slopes of strongly buckled membranes do not allow for a perfect LSC coverage. A micro‐SOFC membrane consisting of an LSC cathode on a weakly buckled 3YSZ electrolyte and a sputtered Pt anode has an open‐circuit voltage of 1.05 V and delivers a maximum power density of 12 mW cm^–2 at 500 °C.     

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.     

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.     

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 and Characterization of Anode‐Supported Low‐Temperature SOFC Based on Gd‐Doped Ceria Electrolyte

Large‐size, 9.5 cm × 9.5 cm, Ni‐Gd_0.1Ce_0.9O_1.95 (Ni‐GDC) anode‐supported solid oxide fuel cell (SOFC) has been successfully fabricated with NiO‐GDC anode substrate prepared by tape casting method and thin‐film GDC electrolyte fabricated by screen‐printing method. Influence of the sintering shrinkage behavior of NiO‐GDC anode substrate on the densification of thin GDC electrolyte film and on the flatness of the co‐sintered electrolyte/anode bi‐layer was studied. The increase in the pore‐former content in the anode substrate improved the densification of GDC electrolyte film. Pre‐sintering temperature of the anode substrate was optimized to obtain a homogeneous electrolyte film, significantly reducing the mismatch between the electrolyte and anode substrate and improving the electrolyte quality. Dense GDC electrolyte film and flat electrolyte/anode bi‐layer can be fabricated by adding 10 wt.% of pore‐former into the composite anode and pre‐sintering it at 1,100 °C for 2 h. Composite cathode, La_0.6Sr_0.4Fe_0.8Co_0.2O₃, and GDC (LSCF‐GDC), was screen‐printed on the as‐prepared electrolyte surface and sintered to form a complete single cell. The maximum power density of the single cell reached 497 mW cm^–2 at 600 °C and 953 mW cm^–2 at 650 °C with hydrogen as fuel and air as oxidant.     

Fabrication of BaZr0.1Ce0.7Y0.2O3 – δ ‐Based Proton‐Conducting Solid Oxide Fuel Cells Co‐Fired at 1,150 °C

Dense proton‐conducting BaZr_0.1Ce_0.7Y_0.2O_{3 – δ} (BZCY) electrolyte membranes were successfully fabricated on NiO–BZCY anode substrates at a low temperature of 1,150 °C via a combined co‐press and co‐firing process. To fabricate full cells, the LaSr₃Co_1.5Fe_1.5O_{10 – δ}–BZCY composite cathode layer was fixed to the electrolyte membrane by two means of one‐step co‐firing and two‐step co‐firing, respectively. The SEM results revealed that the cathode layer bonded more closely to the electrolyte membrane via the one‐step co‐firing process. Correspondingly, determined from the electrochemical impedance spectroscopy measured under open current conditions, the electrode polarisation and Ohmic resistances of the one‐step co‐fired cell were dramatically lower than the other one for its excellent interface adhesion. With humidified hydrogen (2% H₂O) as the fuel and static air as the oxidant, the maximum power density of the one‐step co‐fired single cell achieved 328 mW cm^–2 at 700 °C, showing a much better performance than that of the two‐step co‐fired single cell, which was 264 mW cm^–2 at 700 °C.     

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.     

Electrophoretic Deposition of Zirconia Thin Film on Nonconducting Substrate for Solid Oxide Fuel Cell Application

Electrophoretic deposition (EPD) of 8 mol% yttria‐stabilized zirconia (YSZ) electrolyte thin film has been carried out onto nonconducting porous NiO‐YSZ cermet anode substrate using a fugitive and electrically conducting polymer interlayer for solid oxide fuel cell (SOFC) application. Such polymer interlayer burnt out during the high‐temperature sintering process (1400°C for 6 h) leaving behind a well adhered, dense, and uniform ceramic YSZ electrolyte film on the top of the porous anode substrate. The EPD kinetics have been studied in depth. It is found that homogeneous and uniform film could be obtained onto the polymer‐coated substrate at an applied voltage of 15 V for 1 min. After the half‐cell (anode + electrolyte) is co‐fired at 1400°C, a suitable cathode composition (La_0.65Sr_0.3MnO₃) thick film paste is screen printed on the top of the sintered YSZ electrolyte. A second stage of sintering of such cathode thick film at 1100°C for 2 h finally yield a single cell SOFC. Such single cell produced a power output of 0.91 W/cm² at 0.7 V when measured at 800°C using hydrogen and oxygen as fuel and oxidant, respectively.     

Fabrication and Operation of Tubular Segmented‐In‐Series (SIS) Solid Oxide Fuel Cells (SOFC)

A tubular segmented‐in‐series (SIS) solid oxide fuel cell (SOFC) sub module for intermediate temperature (700–800 °C) operation was fabricated and operated in this study. For this purpose, we fabricated porous ceramic supports of 3 YSZ through an extrusion process and analyzed the basic properties of the ceramic support, such as visible microstructure, porosity, and mechanical strength, respectively. After that, we fabricated a tubular SIS SOFC single cell by using dip coating and vacuum slurry coating method in the case of electrode and electrolyte, and obtained at 800 °C a performance of about 400 mW cm^–2. To make a sub module for tubular SIS SOFC, ten tubular SIS SOFC single cells with an effective electrode area of 1.1 cm² were coated onto the surface of the prepared ceramic support and were connected in series by using Ag + glass interconnect between each single cell. The ten‐cell sub module of tubular SIS SOFC showed in 3% humidified H₂ and air at 800 °C a maximum power of ca. 390 mW cm^–2.     

Development and Fabrication of a New Concept Planar‐tubular Solid Oxide Fuel Cell (PT‐SOFC)

The paper reports a new concept of planar‐tubular solid oxide fuel cell (PT‐SOFC). Emphasis is on the fabrication of the required complex configuration of Ni‐yttria‐stabilised zirconia (YSZ) porous anode support by tert‐butyl alcohol (TBA) based gelcasting, particularly the effects of solid loading, amounts of monomers and dispersant on the rheological behaviour of suspension, the shrinkage of a wet gelcast green body upon drying, and the properties of final sample after sintering at 1350 °C and reduction from NiO‐YSZ to Ni‐YSZ. The results show that the gelcasting is a powerful method for preparation of the required complex configuration anode support. The anode support resulted from an optimised suspension with the solid loading of 25 vol% has uniform microstructure with 37% porosity, bending strength of 44 MPa and conductivity of 300 S cm^—1 at 700 °C, meeting the requirements for an anode support of SOFC. Based on the as‐prepared anode support, PT‐SOFC single cell of Ni‐YSZ/YSZ/LSCF has been fabricated by slurry coating and co‐sintering technique. The cell peak power density reaches 63, 106 and 141 mW cm^—2 at 700, 750 and 800 °C, respectively, using hydrogen as fuel and ambient air as oxidant.     

Electrochemical Performance of a Ni and YSZ Composite Synthesised by Ultrasonic Spray Pyrolysis as an Anode for SOFCs

The electrochemical performance of an anode material for a solid oxide fuel cell (SOFC) depends highly on microstructure in addition to composition. In this study, a NiO–yttria‐stabilised zirconia (NiO–YSZ) composite with a highly dispersed microstructure and large pore volume/surface area has been synthesised by ultrasonic spray pyrolysis (USP) and its electrochemical characteristics has been investigated. For comparison, the electrochemical performance of a conventional NiO–YSZ is also evaluated. The power density of the zirconia electrolyte‐supported SOFC with the synthesised anode is ∼392 mW cm^–2 at 900 °C and that of the SOFC with the conventional NiO–YSZ anode is ∼315 mW cm^–2. The improvement is ∼24%. This result demonstrates that the synthesised NiO–YSZ is a potential alternative anode material for SOFCs fabricated with a zirconia solid electrolyte.     

Microstructure and Polarization Studies on Interlayer Free La0.65Sr0.3Co0.2Fe0.8O3–δ Cathodes Fabricated on Yttria Stabilized Zirconia by Solution Precursor Plasma Spraying

Nano‐structured cathodes of La_0.65Sr_0.3Co_0.2Fe_0.8O_3–δ (LSCF) are fabricated by solution precursor plasma spraying (SPPS) on yttria stabilized zirconia (YSZ) electrolytes (LSCF‐SPPS‐YSZ). Phase pure LSCF is obtained at all plasma power. Performances of LSCF‐SPPS‐YSZ cathodes are compared with conventionally prepared LSCF cathodes on YSZ (LSCF‐C‐YSZ) and gadolinium doped ceria (GDC) (LSCF‐C‐GDC) electrolytes. High R_p is observed in the LSCF‐C‐YSZ (∼42 Ohm cm² at 700 °C) followed by LSCF‐C‐GDC (R_p ∼ 1.5 Ohm cm² at 700 °C) cathodes. Performance of the LSCF‐SPPS‐YSZ cathodes (R_p ∼ 0.1 Ohm cm² at 700 °C) is found to be even superior to the performance of LSCF‐C‐GDC cathodes. High performance in LSCF‐SPPS‐YSZ cathodes is attributed to its nano‐structure and absence of any interfacial insulating phase which may be attributed to the low temperature at the interaction point of LSCF and YSZ and low interaction time between LSCF and YSZ during SPPS process. In the time scale of 100 h, no change in the polarization resistances is observed at 750 °C. Based on the literature and from the present studies it can be stated that SOFC with YSZ electrolyte and LSCF‐SPPS‐YSZ cathode can be operated at 750 °C for a longer duration of time and good performance can probably be achieved.     

Oxygen Dissociation and Interfacial Transfer Rate on Performance of SOFCs with Metal‐Added (LaSr)(CoFe)O3‐(Ce,Gd)O2 – δ Cathodes

A solid oxide fuel cell (SOFC) unit is constructed with Ni‐Ce_0.9Gd_0.1O_{2 – δ} (GDC) as the anode, yttria‐stabilised zirconia (YSZ) as the electrolyte and Pt, Ag or Cu‐added La_0.58Sr_0.4Co_0.2Fe_0.8O_{3 – δ} (LSCF)–GDC as the cathode. The current–voltage measurements are performed at 800 °C. Cu addition leads to best SOFC performance. LSCF–GDC–Cu is better than LSCF–GDC and much better than GDC as the material of the cathode interlayer. Cu content of 2 wt.‐% leads to best SOFC performance. A cathode functional layer calcined at 800 °C is better than that calcined at higher temperature. Metal addition increases the O₂ dissociation reactivity but results in an interfacial resistance for O transfer. A balance between the rates of O₂ dissociation and interfacial O transfer is needed for best SOFC performance.     

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.     

Bi1.4Er0.6O3‐(La0.74Bi0.10Sr0.16) MnO3‐δ Cathodes Fabricated By Ion‐impregnating Method For IT‐SOFCs

Bi_1.4Er_0.6O₃‐(La_0.74Bi_0.10Sr_0.16)MnO_3‐δ (ESB‐LBSM) composite cathodes were fabricated by impregnating the ionic conducting ESB matrix with the LBSM electronic conducting materials. The ion‐impregnated ESB‐LBSM cathodes were beneficial for the O₂ reduction reactions, and the performance of these cathodes was investigated at temperatures below 700 °C by AC impedance spectroscopy and the results indicated that the ion‐impregnated ESB‐LBSM system had an excellent performance. At 700 °C, the lowest cathode polarisation resistance (R_p) was only 0.07 Ω cm² for the ion‐impregnated ESB‐LBSM system. For the performance testing of single cells, the maximum power density was 1.0 W cm^–2 at 700 °C for a cell with the ESB‐LBSM cathode. The results demonstrated that the unique combination of the ESB ionic conducting matrix with electronic conducting LBSM materials was a valid method to improve the cathode performance, and the ion‐impregnated ESB‐LBSM was a promising composite cathode material for the intermediate‐temperature solid oxide fuel cells.     

Gadolinia Doped Ceria Thin Films Prepared by Aerosol Assisted Chemical Vapor Deposition and Applications in Intermediate‐Temperature Solid Oxide Fuel Cells

Furthermore, deposition at such low temperatures is promising for processing of thin film assemblies. The preparation of bi‐layer electrolytes of yttria stabilized zirconia and gadolinia doped ceria thin films by aerosol assisted chemical vapor deposition is demonstrated. Gadolinia doped ceria films as thin as 150 nm are applied as barrier layers between yttria stabilized zirconia electrolyte and La_0.6Sr_0.4CoO_3–δ cathode in anode supported solid oxide fuel cells. High power densities above 850 mW cm^–2 at 650 °C are only obtained with these barrier layers, indicating that the GDC thin films effectively inhibit the formation of unwanted interface reactions.     

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.     

Sr2Fe1.5Mo0.5O6–δ – Zr0.84Y0.16O2–δ Materials as Oxygen Electrodes for Solid Oxide Electrolysis Cells

The high‐temperature solid oxide electrolysis cell (SOEC) is one of the most promising devices for hydrogen mass production. To make SOEC suitable from an economical point of view, each component of the SOEC has to be optimized. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on an alternative oxygen electrode of Zr_0.84Y_0.16O_2–δ‐Sr₂Fe_1.5Mo_0.5O_6–δ (YSZ‐SFM). YSZ‐SFM composite oxygen electrodes were fabricated by impregnating the YSZ matrix with SFM, and the ion‐impregnated YSZ‐SFM composite oxygen electrodes showed excellent performance. For a voltage of 1.2 V, the electrolysis current was 223 mA cm⁻², 327 mA cm⁻² and 310 mA cm⁻² at 750 °C for the YSZ‐SFM10, YSZ‐SFM20, and YSZ‐SFM30 oxygen electrode, respectively. A hydrogen production rate as high as 11.46 NL h⁻¹ has been achieved for the SOEC with the YSZ‐SFM20 electrode at 750 °C. The results demonstrate that YSZ‐SFM fabricated by impregnating the YSZ matrix with SFM is a promising composite electrode for the SOEC.     

Performance of IT‐SOFC with Ce0.9Gd0.1O1.95 Functional Layer at the Interface of Ce0.9Gd0.1O1.95 Electrolyte and Ni‐Ce0.9Gd0.1O1.95 Anode

In this paper we present results for a high power density IT‐SOFC and a method for dispersing nanosized Ce_0.9Gd_0.1O_1.95 (GDC) particles at the GDC electrolyte and Ni‐GDC anode interface. Dispersed nanosized particles were deposited to form an anode functional layer (AFL). Anode supports were prepared by tape casting of large micron‐sized NiO powder and sub micron‐sized GDC powder without pore former. For the cathode a La_0.6Sr_0.4Co_0.2Fe_0.8O_{3 – δ} (LSCF)‐GDC composite was used. Without an AFL the open circuit potential (OCP) and the maximum power density were 0.677 V and 407 mW cm^–2, respectively, at 650 °C using 30 sccm of hydrogen and air flow‐rate. With an AFL the OCP and the maximum power density increased to 0.796 V and 994 mW cm^–2, respectively, at the same temperature. Two point probe impedance measurements revealed that the AFL fabricated by the proposed method not only increased the OCP but also reduced the electrode polarisation by 68%. The effect of gas flow‐rate is also present in this paper. When hydrogen and air flow‐rate is increased to 90 sccm, the sample with AFL obtained 1.57 W cm^–2 at 650 °C.     

Long‐Term Stability Studies of Anode‐Supported Microtubular Solid Oxide Fuel Cells

A long‐term stability study of an anode‐supported NiO/YSZ‐YSZ‐LSM/YSZ microtubular cell was performed, under low fuel utilization conditions, using pure humidified hydrogen as fuel at the anode side and air at the cathode side. A first galvanometric test was performed at 766 °C and 200 mA cm^–2, measuring a power output at 0.5 V of ∼250 mW cm^–2. During the test, some electrical contact breakdowns at the anode current collector caused sudden current shutdowns and start‐up events. In spite of this, the cell performance remains unchanged. After a period of 325 h, the cell temperature and the current density was raised to 873°C and 500 mA cm^–2, and the cell power output at 0.5 V was ∼600 mW cm^–2. Several partial reoxidation events due to disturbance in fuel supply occurred, but no apparent degradation was observed. On the contrary, a small increase in the cell output power of about 4%/1,000 h after 654 h under current load was obtained. The excellent cell aging behavior is discussed in connection to cell configuration. Finally, the experiment concluded when the cell suffered irreversible damage due to an accidental interruption of fuel supply, causing a full reoxidation of the anode support and cracking of the thin YSZ electrolyte.