Synthesis and evaluation of (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF)–Y0.08Zr0.92O1.96 (YSZ)–Gd0.1Ce0.9O2−δ (GDC) dual composite SOFC cathodes for high performance and durability

This paper investigates a (La_0.6Sr_0.4)(Co_0.2Fe_0.8)O₃ (LSCF)–Y_0.16Zr_0.92O_1.96 (YSZ)–Gd_0.1Ce_0.9O_2−δ (GDC) dual composite cathode to achieve better cathodic performance compared to an LSM/GDC–YSZ dual composite cathode developed in previous research. To synthesize the structures of the LSCF/GDC–YSZ and LSCF/YSZ–GDC dual composite cathodes, nano-porous composite cathodes containing LSCF, YSZ, and GDC were prepared by a two-step polymerizable complex (PC) method which prevents the formation of YSZ–GDC solid solution. At 800 °C, the electrode polarization resistance of the LSCF/YSZ–GDC dual composite cathode showed to be significantly lower (0.075 Ω cm²) compared to that of a commercial LSCF–GDC cathode (0.195 Ω cm²), a synthesized LSCF/GDC–YSZ dual composite cathode (0.138 Ω cm²), and an LSM/GDC–YSZ dual composite cathode (0.266 Ω cm²) respectively. Moreover, the Ni–YSZ anode-supported single cell containing the LSCF/YSZ–GDC dual composite cathode achieved a maximum power density of 1.24 W/cm² and showed excellent durability without degradation under a load of 1.0 A/cm² over 570 h of operation at 800 °C.     

Enhanced and stable strontium and cobalt free A-site deficient La1-xNi0.6Fe0.4O3 (x=0, 0.02, 0.04, 0.06, 0.08) cathodes for intermediate temperature solid oxide fuel cells

Perovskite oxides with cobalt and strontium element exhibit severe degradation during the operation for the solid oxide fuel cells (SOFC). Here, we report stable non-cobalt and non-strontium La_1-xNi_0.6Fe_0.4O₃ perovskite cathodes with improved oxygen reduction reaction (ORR) activity. A-site deficient La_1-xNi_0.6Fe_0.4O₃ cathodes within 8 at.% all exhibit the invariable phase structure with LaNi_0.6Fe_0.4O₃ (LNF), and the matched thermal expansion coefficient with that of the (Ce_0.90Gd_0.10)O_1.95 (GDC) electrolyte. The polarization resistance of the La_0.94Ni_0.6Fe_0.4O₃ (LNF94) cathode is 0.61 Ω cm² at 750 °C in air, which is 1/5 of the LaNi_0.6Fe_0.4O₃ (2.78 Ω cm²). The peak power density of the corresponding single cell with LNF94 cathode is 0.37 W cm⁻² at 750 °C, which is 2.36 times higher than that of the single cell with LNF cathode (0.11 W cm⁻²). We further study the long-term stability of LNF and LNF94 cathodes, the polarization resistance of the LNF94 electrode slightly fluctuates around 0.18 Ω cm² during 50 h operation at 800 °C, while the polarization resistance of the LNF increases by about 15%. This work highlights the A-site deficient LNF as an effective and stable non-cobalt and non-strontium cathode for the intermediate temperature solid oxide fuel cells.     

Ni–YSZ-supported tubular solid oxide fuel cells with GDC interlayer between YSZ electrolyte and LSCF cathode

Highly sinterable gadolinia doped ceria (GDC) powders are prepared by carbonate coprecipitation and applied to the GDC interlayer in Ni–YSZ (yttria stabilized zirconia)-supported tubular solid oxide fuel cell in order to prevent the reaction between YSZ electrolyte and LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ) cathode materials. The formation of highly resistive phase at the YSZ/LSCF interface was effectively blocked by the low-temperature densification of GDC interlayer using carbonate-derived active GDC powders and the suppression of Sr diffusion toward YSZ electrolyte via GDC interlayer by tuning the heat-treatment temperature for cathode fabrication. The power density of the cell with the configuration of Ni–YSZ/YSZ/GDC/LSCF–GDC/LSCF was as high as 906 mW cm⁻², which was 2.0 times higher than that (455 mW cm⁻²) of the cell with the configuration of Ni–YSZ/YSZ/LSM(La_0.8Sr_0.2MnO_3−δ)–YSZ/LSM at 750 °C.     

Development of LSCF–GDC composite cathodes for low-temperature solid oxide fuel cells with thin film GDC electrolyte

La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) powder was prepared by glycine–nitrate combustion method. The electrochemical properties of porous LSCF cathodes and LSCF–Gd_0.1Ce_0.9O_1.95 (GDC) composite cathodes were evaluated at intermediate/low temperatures of 500–700 °C. The polarization resistance of pure LSCF cathode sintered at 975 °C for 2 h was 1.20 Ω cm² at 600 °C. The good performance of pure LSCF cathode is attributed to its unique microstructure—small grain size, high porosity and large surface area. The addition of GDC to LSCF cathode further reduced the polarization resistance. The lowest polarization resistance of 0.17 Ω cm² was achieved at 600 °C for LSCF–GDC (40:60 wt%) composite cathode. An anode-supported solid oxide fuel cell (SOFC) was prepared using LSCF–GDC (40:60 wt%) composite as cathode, GDC film (49-μm-thick) as electrolyte, and Ni–GDC (65:35 wt%) as anode. The total electrode polarization resistance was 0.27 Ω cm² at 600 °C, which implies that LSCF–GDC (40:60 wt%) composite cathode used in the anode-supported SOFC had a polarization resistance lower than 0.27 Ω cm² at 600 °C. The cell generated good performance with the maximum power density of 562, 422, 257 and 139 mW/cm² at 650, 600, 550 and 500 °C, respectively.     

Characterization of electrical properties of GDC doped A-site deficient LSCF based composite cathode using impedance spectroscopy

The composite cathode consisting of A-site deficient perosvkite material La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ (L58SCF) and Ce_0.8Gd_0.2O_2−δ (GDC) on YSZ electrolyte is studied for potential applications in intermediate/low-temperature solid oxide fuel cells (SOFCs). Impedance spectroscopy measurements are performed in air over the temperature range of 600–800 °C under open circuit potential. The results show that the addition of 40 wt.% GDC to L58SCF (L58SCF–GDC40) results in the lower polarization resistance (0.07 Ω cm² at 800 °C, 0.11 Ω cm² at 750 °C and 0.22 Ω cm² at 700 °C) than other composite cathodes and its activation energy values calculated for the low- and high-frequency arcs are 0.86 and 1.10 eV, respectively. The composite cathode exhibit high exchange current density and low charge-transfer resistance.     

Low temperature processed composite cathodes for Solid-oxide fuel Cells

Low temperature processed composite cathodes for solid-state fuel cell (SOFC) have been developed, consisting of La_0.6Sr_0.4Ti_0.1Fe_0.9O₃ and Ag, as low as 800 °C process temperature. Using micro-tubular design, the performances of the cathodes have been investigated at the operating temperatures of 650 and 700 °C. The cell consists of NiO-Y stabilized zirconia (YSZ) as an anode (support tube), Sc stabilized zirconia (ScSZ) as an electrolyte, Gd doped ceria (GDC) for an inter-layer between the electrolyte and the cathodes. The single performance has varied depending upon the types of cathodes, and the composite cathode with 50 wt% La_0.6Sr_0.4Ti_0.1Fe_0.9O₃ and 50 wt% Ag has shown comparable performance to the cell with standard LSCF-GDC cathode.     

Development of LSM-based cathodes for solid oxide fuel cells based on YSZ films

In an attempt to achieve desirable cell performance, the effects of La_0.7Sr_0.3MnO₃ (LSM)-based cathodes on the anode-supported solid oxide fuel cells (SOFCs) were investigated in the present study. Three types of cathodes were fabricated on the anode-supported yttria-stabilized zirconia (YSZ) thin films to constitute several single cells, i.e., pure LSM cathode, LSM/YSZ composite by solid mixing, LSM/Sm_0.2Ce_0.8O_1.9 (SDC) composite by the ion-impregnation process. Among the three single cells, the highest cell output performance 1.25 W cm⁻² at 800 °C, was achieved by the cell using LSM/SDC cathode when the cathode was exposed to the stationary air. Whereas, the most considerable cell performance of 2.32 W cm⁻² was derived from the cell with LSM/YSZ cathode, using 100 ml min⁻¹ oxygen flow as the oxidant. At reduced temperatures down to 700 °C, the LSM/SDC cathode was the most suitable cathode for zirconia-based electrolyte SOFC in the present study. The variation in the cell performances was attributed to the mutual effects between the gas diffusing rate and three-phase boundary length of the cathode.     

(La0.74Bi0.10Sr0.16)MnO3−δ–(Bi2O3)0.7(Er2O3)0.3 composite cathodes for intermediate temperature solid oxide fuel cells

(La_0.74Bi_0.10Sr_0.16)MnO_3−δ (LBSM)–(Bi₂O₃)_0.7(Er₂O₃)_0.3(ESB) composite cathodes were fabricated for intermediate-temperature solid oxide fuel cells with Sc-stabilized zirconia as the electrolyte. The performance of these cathodes was investigated at temperatures below 750 °C by AC impedance spectroscopy and the results indicated that LBSM–ESB had a better performance than traditional composite electrodes such as LSM–GDC and LSM–YSZ. At 750 °C, the lowest interfacial polarization resistance was only 0.11 Ω cm² for the LBSM–ESB cathode, 0.49 Ω cm² for the LSM–GDC cathode, and 1.31 Ω cm² for the LSM–YSZ cathode. The performance of the cathode was improved gradually by increasing the ESB content, and the performance was optimal when the amounts of LBSM and ESB were equal in composite cathodes. This study shows that the sintering temperature of the cathode affected performance, and the optimum sintering temperature for LBSM–ESB was 900 °C.     

Electrochemical characteristics of an La0.6Sr0.4Co0.2Fe0.8O3–La0.8Sr0.2MnO3 multi-layer composite cathode for intermediate-temperature solid oxide fuel cells

An La_0.6Sr_0.4Co_0.2Fe_0.8O₃–La_0.8Sr_0.2MnO₃ (LSCF–LSM) multi-layer composite cathode for solid oxide fuel cells (SOFCs) was prepared on an yttria-stabilized zirconia (YSZ) electrolyte by the screen-printing technique. Its cathodic polarization curves and electrochemical impedance spectra were measured and the results were compared with those for a conventional LSM/LSM–YSZ cathode. While the LSCF–LSM multi-layer composite cathode exhibited a cathodic overpotential lower than 0.13 V at 750 °C at a current density of 0.4 A cm⁻², the overpotential for the conventional LSM–YSZ cathode was about 0.2 V. The electrochemical impedance spectra revealed a better electrochemical performance of the LSCF–LSM multi-layer composite cathode than that of the conventional LSM/LSM–YSZ cathode; e.g., the polarization resistance value of the multi-layer composite cathode was 0.25 Ω cm² at 800 °C, nearly 40% lower than that of LSM/LSM–YSZ at the same temperature. In addition, an encouraging output power from an YSZ-supported cell using an LSCF–LSM multi-layer composite cathode was obtained.     

Effects of Gd0.8Ce0.2O1.9−δ coating with different thickness on electrochemical performance and long-term stability of La0.8Sr0.2Co0.2Fe0.8O3-δ cathode in SOFCs

The commercialization of Solid oxide fuel cells (SOFCs) has always been limited by the poor catalytic activity and the severe degradation of cathode in the intermediate and low operating temperature. Here we report a Gd_0.8Ce_0.2O_1.9?δ (GDC) coated La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ (LSCF) composite cathode material, which can significantly improve the electrochemical performance and durability of LSCF cathode. The effects of different GDC coating thickness on the electrochemical performance and long-term working stability of LSCF cathode are investigated, and the optimal coating thickness is established. The polarization impedance of GDC coated LSCF (LSCF@GDC) cathode with 9 nm of GDC coating is 0.08 Ω cm² at 800 °C, which is only one quarter of that of the raw LSCF cathode, and the degradation rate of constant current polarization with 100 mA cm^?2 is only 0.42%/100 h at 700 °C, which is far less than that of the raw LSCF cathode. The X-ray photoelectron spectroscopy (XPS) results show that the degree of Sr segregation decreases with the increase of the thickness of the coated GDC layer. The potential LSCF@GDC composite material is expected to increase the operability of SOFCs and accelerate its commercialization.     

Palladium and ceria infiltrated La0.8Sr0.2Co0.5Fe0.5O3−δ cathodes of solid oxide fuel cells

La_0.8Sr_0.2Co_0.5Fe_0.5O_3−δ (LSCF) cathodes infiltrated with electrocatalytically active Pd and (Gd,Ce)O₂ (GDC) nanoparticles are investigated as high performance cathodes for the O₂ reduction reaction in intermediate temperature solid oxide fuel cells (IT-SOFCs). Incorporation of nano-sized Pd and GDC particles significantly reduces the electrode area specific resistance (ASR) as compared to the pure LSCF cathode; ASR is 0.1 Ω cm² for the reaction on a LSCF cathode infiltrated with 1.2 mg cm⁻² Pd and 0.06 Ω cm² on a LSCF cathode infiltrated with 1.5 mg cm⁻² GDC at 750 °C, which are all significantly smaller than 0.22 Ω cm² obtained for the reaction on a conventional LSCF cathode. The activation energy of GDC- and Pd-impregnated LSCF cathodes is 157 and 176 kJ mol⁻¹, respectively. The GDC-infiltrated LSCF cathode has a lower activation energy and higher electrocatalytic activity for the O₂ reduction reaction, showing promising potential for applications in IT-SOFCs.     

La(Ni,Fe)O3 as a cathode material with high tolerance to chromium poisoning for solid oxide fuel cells

A novel cathode material, La(Ni_0.4Fe_0.6)O₃ (LNF), is synthesized by a solid-state reaction for applications in solid oxide fuel cells (SOFCs). The electrochemical performance of the LNF cathode is investigated for the oxygen reduction reaction at 900 °C in the presence of a Fe–Cr alloy interconnect, and compared with (La,Sr)MnO₃ (LSM) cathodes. Under these conditions, the LNF electrode has a more stable electrochemical activity than that of the LSM electrode. There is no deposition of chromium species on the electrode surface or at the LNF electrode|yttria-stabilized zirconia (YSZ) electrolyte interface after passage of 200 mA cm⁻² for 20 h at 900 °C. By contrast, a significant amount of chromium species is preferentially deposited at the LSM|YSZ interface regions for the LSM electrode. The results demonstrate that the LNF electrode has high tolerance to chromium poisoning, and is, therefore, promising as a SOFC cathode when using chromia-forming alloy interconnects.     

Low-temperature preparation of dense (Gd,Ce)O2−δ–Gd2O3 composite buffer layer by aerosol deposition for YSZ electrolyte-based SOFC

The (Gd_0.1Ce_0.9)O_2−δ (GDC)–Gd₂O₃ composite buffer layer was fabricated on yttria stabilized zirconia (YSZ) electrolyte by aerosol deposition for usage as diffusion barrier layer between YSZ and (La_0.6Sr_0.4)(Co_0.2Fe_0.8)O_3−δ (LSCF)–GDC composite cathode. The deposited composite buffer layer was quite dense in nature and effectively prevented the formation of SrZrO₃ and La₂Zr₂O₇ interlayer with low conductivity at the interfaces. The cell's I–V performance was enhanced with an increase in the GDC content in the composite buffer layer. The cell containing composite buffer layer showed maximum power density of up to 1.74 W/cm² at 750 °C, which was ∼30% higher than that of the cell containing GDC buffer layer prepared using conventional process.     

Enhanced performance of a single-chamber solid oxide fuel cell with an SDC-impregnated cathode

The electrochemical performance of anode-supported single-chamber solid oxide fuel cells (SC-SOFCs) with and without SDC-impregnated cathodes was compared in a diluted methane–oxygen mixture. These cells were made of conventional materials including yttrium-stabilized zirconia (YSZ) thin film, a Ni + YSZ anode and a La_0.7Sr_0.3MnO₃ (LSM) cathode. Our results showed that the cell performance was greatly enhanced with the SDC-impregnated LSM cathode. At a furnace temperature of 750 °C, the maximum power density was as high as 404 mW cm⁻² for a CH₄ to O₂ ratio of 2:1, which was 4.0 times higher than the cell with a pure LSM cathode (100 mW cm⁻²). The overall polarization resistance of the impregnated cell was 1.6 Ω cm², which was much smaller than that of the non-impregnated one (4.2 Ω cm²). The impregnation introduced SDC nanoparticles greatly extended the electrochemical active zone and hence greatly improved the cell performance.     

Solid oxide fuel cell cathodes prepared by infiltration of LaNi0.6Fe0.4O3 and La0.91Sr0.09Ni0.6Fe0.4O3 in porous yttria-stabilized zirconia

SOFC composite electrodes of yttria-stabilized zirconia (YSZ) and either LaNi_0.6Fe_0.4O₃ (LNF) or La_0.91Sr_0.09Ni_0.6Fe_0.4O₃ (LSNF) were prepared by infiltration to a loading of 40 wt% of the perovskite into porous YSZ using aqueous solutions of the nitrate salts. XRD measurements indicated that the perovskite structures were formed following calcination at 850 °C, at which temperature the LNF and LSNF form small particles that coat the YSZ pores. Heating to 1100 °C causes the particles to form a dense film over the YSZ but caused no solid-state reaction. Calcination of an LNF-YSZ composite to 1200 °C led to an expansion of the LNF lattice, suggesting introduction of Zr(IV) into the perovskite; further heating to 1300 °C caused the formation of La₂Zr₂O₇. For 850 °C calcination, the electrode performance of both LNF-YSZ and LSNF-YSZ composites was similar to that reported for composites of YSZ and La_0.8Sr_0.2FeO₃ (LSF), with a current-independent impedance of approximately 0.1 Ω cm² at 700 °C in air. For 1100 °C calcination, both LNF-YSZ and LSNF-YSZ composites exhibited impedances that decreased strongly under both anodic and cathodic polarization. The implications of these results for preparing electrodes based on LNF and LSNF are discussed.     

LaNi0.6Fe0.4O3-Ce0.8Sm0.2O1.9-Ag composite cathode for intermediate temperature solid oxide fuel cells

LaNi_0.6Fe_0.4O₃ (LNF), LNF-Sm_0.2Ce_0.8O_1.9 (SDC), and LNF-SDC-Ag cathodes on SDC electrolytes were investigated at intermediate temperatures using AC impedance spectroscopy. Results show that adding 50 wt.% SDC into LNF yields a significant low area specific resistance (ASR) which was found to be 0.92 Ω cm² at 700 °C. Infiltrating 0.3 mg/cm² Ag into LNF-50 wt.% SDC can improve the electronic conductivity and oxygen exchange reaction activity, and thereby remarkably decrease the ASRs. The ASR value of the LNF-SDC-Ag cathode is as low as 0.18 Ω cm² at 700 °C, and 0.46 Ω cm² at 650 °C. The long-term test shows that the LNF-SDC-Ag cathode may be a promising candidate for solid oxide fuel cells operating at temperatures lower than 650 °C.     

Perovskite-related intergrowth cathode materials with thin YSZ electrolytes for intermediate temperature solid oxide fuel cells

The electrochemical performances of solid oxide fuel cells with thin yttria-stabilized zirconia (YSZ) electrolytes and YSZ/Ni anodes were studied with two intergrowth oxides cathodes (Sr_2.7La_0.3Fe_1.4Co_0.6O_7−δ and LaSr₃Fe_1.5Co_1.5O_10−δ) and the results compared to a related perovskite cathode (La_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ). It was found that cells produced with LaSr₃Fe_1.5Co_1.5O_10−δ exhibited peak power densities close to 0.75 W cm⁻², despite the relatively modest electrical conductivity of this compound. In contrast, cells produced with Sr_2.7La_0.3Fe_1.4Co_0.6O_7−δ and La_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathodes both exhibited peak power densities of less than 0.4 W cm⁻². The greater performance for the cells produced with LaSr₃Fe_1.5Co_1.5O_10−δ may be attributed to a higher catalytic activity for this compound or to an improved adhesion of the cathode to the interlayer/electrolyte.     

Synthesis and electrochemical characterization of La0.6Sr0.4Co0.2Fe0.8O3–δ / Ce0.9Gd0.1O1.95 co-electrospun nanofiber cathodes for intermediate-temperature solid oxide fuel cells

Synthesis and electrochemical characterization of composite cathodes, formed from a mixture of La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) and Ce_0.9Gd_0.1O_1.95 (GDC) nanofibers, is reported. The electrodes are obtained by simultaneous electrospinning of the two precursor solutions, using apparatus equipped with two spinnerets working in parallel. Results of electrochemical testing carried out through electrochemical impedance spectroscopy (EIS) are presented and discussed. The results suggest that the electrochemical reaction takes place in an electrode region close to the electrode/current collector interface and that the oxygen ions then flow along the ionic conducting path of the GDC fibers. At 650 °C, the polarization resistance is R_p = 5.6 Ω cm^?2, in line with literature values reported for other IT-SOFC cathodes.     

Performance stability of impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ–Y2O3 stabilized ZrO2 cathodes of intermediate temperature solid oxide fuel cells

The stability of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ impregnated Y₂O₃ stabilized ZrO₂ (LSCF–YSZ) cathodes was investigated under the condition of open circuit or current polarization at 750 °C in air. The electrochemical measurement and the microstructure characteristic show that the flattening of LSCF particles has great contribution to the increase of resistance of LSCF–YSZ cathodes after 500 h heat treatment at 750 °C. Microstructure coarsening and the damage of well-connected porous structure are main reasons of the performance degradation for LSCF–YSZ cathodes testing at 200 mA cm⁻² and 750 °C in air. Higher current density of 500 mA cm⁻² applying on cathodes accelerates degradation processes. X-ray photoelectron spectroscopy (XPS) shows that Sr concentration on the cathode surface decreases after current polarization, which plays a main role in performance activation processes observed at the beginning stage. The enhancement of cobalt activity in LSCF lattice by current polarization increases the conductivity and decreases the stability of LSCF–YSZ cathodes.     

Reactive Spray Deposition Technology - An one-step deposition technique for Solid Oxide Fuel Cell barrier layers

In order to reduce the cost of the manufacturing of Solid Oxide Fuel Cells (SOFC), and to enable metal supported cell fabrication, a new fabrication method called Reactive Spray Deposition Technology (RSDT) for direct deposition of the material onto ceramic or metal support for low temperature SOFC is currently being developed. The present work describes the effect on the performance of a SOFC when a Gd_0.2Ce_0.8O_1.9 (GDC) layer has been introduced as diffusion barrier layer between the yttria stabilized zirconia (YSZ) electrolyte and the La_0.6Sr_0.4CoO_3−δ (LSC) cathode. The dense, thin and fully crystalline GDC films were directly applied by RSDT, without any post-deposition heating or sintering step. The quality of the film and performance of the cell prepared by RSDT was compared to a GDC blocking layer deposited by screen printing (SP) and then sintered. The observed ohmic resistance of the ASC with a GDC layer deposited by RSDT is 0.24 Ω cm², which is close to the expected theoretical value of 0.17 Ω cm² for a 5-μm thick 8 mol% yttria YSZ (8YSZ) electrolyte at 873 K.