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.     

Compatibility and conductivity of La2Ni1−xFexO4+δ and LaNi0·6Fe0·4O3−δ with GDC electrolyte

Abstract

The compatibilities and conductivities of K₂NiF₄ typed La₂Ni_0·9Fe_0·1O_4+δ (L₂NF91) and LaNi_0·6Fe_0·4O_3?δ (LNF64) perovskites, promising cathode materials for solid oxide fuel cell, with Gd_0·1Ce_0·9O_1·95 (GDC) electrolyte were investigated. L₂NF91 and LNF64 were synthesised using citrate and modified citrate methods with the calcination temperature of 1000°C for 5 h. The single phased oxides with the average particle sizes of L₂NF91 and LNF64 ～0·2 μm were obtained. The thermal expansion coefficients of L₂NF91 and LNF64 were 12·7×10^?6 and 13·2×10^?6 K^?1 respectively. The mixtures of cathode materials and the electrolytes were heated between 800 and 1200°C to observe the formation of secondary phases at the operation temperatures of solid oxide fuel cell. The X-ray diffraction and scanning electron microscopy–energy dispersive X-ray results indicated that L₂NF91 and LNF64 had good chemical compatibility with GDC from room temperature up to 900°C. Both L₂NF91 and LNF64 showed higher conductivities when in contact with GDC electrolyte than with Zr_0·92Y_0·08O_1·96 electrolyte.     

Study of the efficiency of composite LaNi0.6Fe0.4O3-based cathodes in intermediate-temperature anode-supported SOFCs

The paper focuses on the performance comparison of LaNi_0.6Fe_0.4O_3-δ (LNF) composite cathodes comprising Ce_0.8Sm_0.2O_1.9 (SDC) and Bi_1.5Y_0.5O₃ (YDB) electrolytes and La_0.6Sr_0.4Fe_0.8Co_0.2O_3-δ (LSFC)-SDC cathodes in anode-supported SOFCs with YSZ/GDC electrolyte films obtained by magnetron sputtering. Cathodes with LNF-SDC and LNF-YDB functional layers and the LNF-YDB-CuO oxide collector show a sufficient thermo-mechanical compatibility with the electrolyte. The performance of the anode-supported SOFC with the LNF-YDB/LNF-YDB-CuO cathode, reaches 650 and 1050 mW/cm² at 700 and 800 °C, respectively, which is significantly higher than that obtained in other works for anode-supported cells with LNF cathodes. The initial total polarization resistance of the NiO-YSZ/YSZ/GDC/LNF-YDB/LNF-YDB-CuO cell, is 0.53 Ω cm², which is lower than the initial resistance of the similar anode-supported cell with the LNF-SDC/LNF-YDB-CuO cathode (1.35 Ω cm²) and LSFC-SDC cathode with LNF-YDB-CuO (1.71 Ω cm²) and La_0.6Sr_0.4CoO₃ (1.17 Ω cm²) collectors. The most probable reason for the LNF-YDB electrode aging is the growth of Bi-containing particles. Experimental results show that LNF-based composite cathodes are competitive with cobalt-containing cathodes and can be promising for anode-supported SOFCs with decreased operating temperature, that allows extending the material choice for both functional and collector cathode layers.     

Influence of cathode polarization on the chromium deposition near the cathode/electrolyte interface of SOFC

Chromium poisoning phenomena were compared among three SOFC cathodes using (La_0.8Sr_0.2)_0.98MnO₃ (LSM), La_0.6Sr_0.4Fe_0.8Co_0.2O₃ (LSCF) and LaNi_0.6Fe_0.4O₃ (LNF) at 700 °C by changing cathode polarization (0–400 mV). Chromium vapor deposited near the electrolyte for LSM and LNF, and the amount of the deposition increased with increasing cathode polarization. In the case of LSCF, chromium deposited near the cathode surface under smaller cathode polarization (≤200 mV). Under larger cathode polarization (≥300 mV), however, chromium deposition near the cathode/electrolyte interface similarly increased for the three cathodes. Cathode polarization facilitated the chromium deposition and there seemed to be no correlation with the current density. Microscopic distribution of the deposited chromium, which was located on the surface of LSM, LSCF, LNF grains, and also on the surface of zirconia and ceria, seemed to correspond to the distribution of oxygen vacancy by cathode polarization at the electrode reaction sites. Chromium deposition on the zirconia surface seemed to be assisted by metal oxides segregated from the cathode material, which can conduct electron required for generating oxygen vacancy continuously. Oxygen deficiency on the surface of the deposited chromium was confirmed and interdiffusion of chromium and zirconium caused by cathode polarization was also suggested.     

Chemical compatibility and electrochemical property of intermediate-temperature SOFC cathodes under Cr poisoning condition

We have investigated the relationship between the chemical compatibility and electrochemical properties of La_0.6Sr_0.4Fe_0.8Co_0.2O₃ (LSCF), LaNi_0.6Fe_0.4O₃ (LNF), and La_0.8Sr_0.2MnO₃ (LSM) as a cathode against the Cr poisoning condition. Powder mixtures of LSCF–Cr₂O₃, LSM–Cr₂O₃, and LNF–Cr₂O₃ were heated at 1073 K and analyzed by X-ray powder diffraction with the Rietveld refinement. It was found that LNF powder was less reactive with Cr₂O₃ than LSCF and LSM powder from the viewpoint of the consumption of Cr₂O₃ in the mixtures. From electrochemical measurement, it was found that the cathodic overvoltage was almost unchanged for cells with LNF cathode, either in the presence or absence of a Cr-containing alloy. On the other hand, the cells with LSCF and LSM cathode in the presence of the alloy exhibited a steep increase in the overvoltage curve. These results show that LNF cathode is more stable against Cr poisoning than the other two cathodes. Therefore, we expect LNF to be a long-life cathode with high stability against Cr poisoning in solid oxide fuel cell because of the low reactivity of LNF with Cr₂O₃.     

Performance of intermediate temperature (600–800 °C) solid oxide fuel cell based on Sr and Mg doped lanthanum-gallate electrolyte

The solid electrolyte chosen for this investigation was La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSGM). To select appropriate electrode materials from a group of possible candidate materials, AC complex impedance spectroscopy studies were conducted between 600 and 800 °C on symmetrical cells that employed the LSGM electrolyte. Based on the results of the investigation, LSGM electrolyte supported solid oxide fuel cells (SOFCs) were fabricated with La_0.6Sr_0.4Co_0.8Fe_0.2O₃–La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSCF–LSGM) composite cathode and nickel–Ce_0.6La_0.4O₂ (Ni–LDC) composite anode having a barrier layer of Ce_0.6La_0.4O₂ (LDC) between the LSGM electrolyte and the Ni–LDC anode. Electrical performances of these cells were determined and the electrode polarization behavior as a function of cell current was modeled between 600 and 800 °C.     

Performance and optimization of perovskite-type La1·4Ca0·6CoMnO5+δ cathode for intermediate-temperature solid oxide fuel cells

There has been a considerable interest in improving electrocatalytical activity of doped lanthanum manganite and thermal stability of cobaltite cathodes. In the current work, a perovskite-type oxide La_1·4Ca_0·6CoMnO_5+δ (LCCM), as a combination of manganite and cobaltite perovskites, is developed as a potential cathode for intermediate-temperature solid oxide fuel cells. The LCCM has a monoclinic structure and highly structural stability at RT-900 °C. The LCCM exhibits good chemical compatibility and relatively matched thermal expansion coefficient with the La_0·9Sr_0.1Ga_0.8Mg_0·2O_3–δ (LSGM) and Sm_0.2Ce_0·8O_1.9 (SDC) electrolytes up to 1000 °C. The mixed valence states of Co^2+/3+ and Mn^3+/4+ coexist in the LCCM. The LCCM exhibits a typical p-type semiconducting behavior, and the sample sintered at 1300 °C possesses the highest conductivity of 223 S cm⁻¹ at 800 °C. The maximum power density of NiO-SDC/SDC/LSGM/LCCM single cell is 445 mW cm⁻² at 800 °C. The electrochemical performance, thermal expansion behavior and stability of LCCM are further improved by adding appropriate amounts of SDC. The LCCM-30 wt% SDC composite cathode shows the best electrochemical performance: the area specific resistance is decreased by 68% at 800 °C, and the maximum power density is increased by 22%.     

Fabrication of a quasi-symmetrical solid oxide fuel cell using a modified tape casting/screen-printing/infiltrating combined technique

To develop the symmetrical electrode materials for solid oxide fuel cells (SOFCs) and to explore the facile cell fabrication technique are both meaningful and of great significance. Here a bi-functional hybrid material LaNi_0.82Fe_0.18O₃ (LNF)/NiO was synthesized by a one-pot citrate method and further used as the quasi-symmetrical electrode catalysts for solid oxide fuel cells (SOFCs). LNF and Ni (reduced NiO) functioned as the cathode/anode catalysts. The La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSGM) based asymmetrical tri-layered substrates were fabricated by a screen-printing assisted co-firing technique. The polarization resistances (Rp) of the infiltrated anode at 700, 650, 600 and 550 °C were only 0.08, 0.12, 0.18 and 0.3 Ω cm², respectively. Comparably, the Rp of the infiltrated cathode were much larger, e.g., 0.18, 0.35, 0.875 and 2.55 Ω cm² at 700, 650, 600 and 550 °C, respectively. Encouragingly, these cathode Rp values were largely reduced when discharge due to an activation process. The LNF and NiO reversibly formed and decomposed during the oxidation and reduction processes, suggesting that the LNF/NiO hybrid is a potential quasi-symmetrical SOFC electrode material. When using H₂ as fuel and air as oxidant, the maximum power densities of the single cell at 650, 600 and 550 °C were as high as 928, 580 and 329 mW cm^?2, respectively.     

Electrochemical performance of novel NGCO-LSCF composite cathode for intermediate temperature solid oxide fuel cells

In this study, a co-dopant CGO was synthesized to produce more efficient cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Neodymium (Nd) was doped into CGO in four different weight ratios in the formula Nd_xGd_0.15Ce_0.85-xO_2-δ (NGCO); the selected percentages for x were 1%, 3%, 5% and 7%. XRD patterns showed pure phase for all synthesized compositions and good compatibility at high temperature under static air with the most common ceramic cathode material in IT-SOFC (La_0·60Sr_0·40Co_0·20Fe_0·80O_2-ä, LSCF). Impedance spectroscopic characterization of symmetrical cells of the composite NGCO-LSCF at different temperatures (650–800 °C in steps of 50 °C) and a frequency range of 0.1–1 MHz in synthetic air revealed interesting results. The lowest polarization resistance (R_p) was achieved for Nd_0.05Gd_0.15Ce_0·80O_2-δ (0.06 Ω cm² at 800 °C, 0.17 Ω cm² at 750 °C, 0.31 Ω cm² at 700 °C, and 0.59 Ω cm² at 650 °C). The expected decrease in R_p was not observed for the sample with higher Nd content (7% Nd). Thus, it can be said that there is a distinction between the compositions Nd_0.05Gd_0.15Ce_0·80O_2-δ and Nd_0.07Gd_0.15Ce_0·78O_2-δ; the co-doping of Nd in NGCO incremented the oxygen ion diffusion path, thereby optimization in the triple phase boundary (TPB) sites was obtained. Furthermore, SEM and TGA measurements were conducted to clarify the reasons of such improvements. This work showed that an NGCO-LSCF composite can be considered as a potential candidate for cathode material for future IT-SOFC applications.     

Mn-rich SmBaCo0.5Mn1.5O5+δ double perovskite cathode material for SOFCs

SmBaCo_0.5Mn_1.5O_5+δ oxide with Sm-Ba cation-ordered perovskite-type structure is synthesized and examined in relation to whole RBaCo_0.5Mn_1.5O_5+δ series (R: selected rare earth elements). Presence of Sm and 3:1 ratio of Mn to Co allows to balance physicochemical properties of the composition, with moderate thermal expansion coefficient value of 18.70(1)·10⁻⁶ K⁻¹ in 300–900 °C range, high concentration of disordered oxygen vacancies in 600–900 °C range (δ = 0.16 at 900 °C), and good transport properties with electrical conductivity reaching 33 S cm⁻¹ at 900 °C in air. Consequently, the compound enables to manufacture catalytically-active cathode, with good electrochemical performance measured for the electrolyte-supported laboratory-scale solid oxide fuel cell with Ni-Gd_1.9Ce_0.1O_2-δ|La_0.4Ce_0.6O_2-δ|La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ|SmBaCo_0.5Mn_1.5O_5+δ configuration, for which 1060 mW cm⁻² power density is observed at 900 °C. Furthermore, the tested symmetrical SmBaCo_0.5Mn_1.5O_5+δ|La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ|SmBaCo_0.5Mn_1.5O_5+δ cell delivers 377 mW cm⁻² power density at 850 °C, which is a promising result.     

Exploring MnCr2O4–Gd0.1Ce0.9O2-δ as a composite electrode material for solid oxide fuel cell

Symmetrical solid oxide fuel cell (SOFC) adopting the same material at both electrodes is potentially capable of promoting thermomechanical compatibility between near components and lowering stack costs. In this paper, MnCr₂O₄–Gd_0.1Ce_0.9O_2-δ (MCO-GDC) composite electrodes prepared by co-infiltration method for symmetrical electrolyte supported and anode supported solid oxide fuel cells are evaluated at a temperature range of 650–800 °C in wet (3% H₂O) hydrogen and air atmospheres. Without any alkaline earth elements and cobalt, the co-infiltrated MCO-GDC composite electrode shows excellent activity for oxygen reduction reaction but mediocre activity for hydrogen oxidation reaction. With MCO-GDC as the cathode, the Ni-YSZ (Y₂O₃ stabilized ZrO₂) anode supported asymmetrical cell demonstrates a peak power density of 665 mW cm⁻² at 800 °C. The above results suggest MCO-GDC is a promising candidate cathode material for solid oxide fuel cells.     

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.     

Modifying the cathodes of intermediate-temperature solid oxide fuel cells with a Ce0.8Sm0.2O2 sol–gel coating

To increase the performance of solid oxide fuel cells operated at intermediate temperatures (<700 °C), we used the electronic conductor La_0.8Sr_0.2MnO₃ (LSM) and the mixed conductor La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) to modify the cathode in the electrode microstructure. For both cathode materials, we employed a Sm_0.2Ce_0.8O₂ (SDC) buffer layer as a diffusion barrier on the yttria-stabilized zirconia (YSZ) electrolyte to prevent the interlayer formation of SrZrO₃ and La₂Zr₂O₇, which have a poor ionic conductivity. These interfacial reaction products were formed only minimally at the electrolyte–cathode interlayer after sintering the SDC layer at high temperature; in addition, the degree of cathode polarization also decreased. Moreover to extend the triple phase boundary and improve cell performance at intermediate temperatures, we used sol–gel methods to coat an SDC layer on the cathode pore walls. The cathode resistance of the LSCF cathode cell featuring SDC modification reached as low as 0.11 Ω cm² in air when measured at 700 °C. The maximum power densities of the cells featuring the modified LSCF and LSM cathodes were 369 and 271 mW/cm², respectively, when using O₂ as the oxidant and H₂ as the fuel.     

Tailoring La2-XAXNi1-YBYO4+δ cathode performance by simultaneous A and B doping for IT-SOFC

The present work focuses on the study of different Ruddlesden-Popper based cathode materials for Solid Oxide Fuel Cells at Intermediate Temperature (IT-SOFC). The partial substitution of La and Ni by Pr and Co, respectively, were studied in the La_2-XPr_XNi_1-YCo_YO_4+δ system, with the purpose of enhancing their mixed ionic-electronic conductivity and the electrocatalytic activity for the O₂-reduction while the crystal structure was preserved. All synthesized compounds were characterized by electrochemical impedance spectroscopy (EIS), DC conductivity measurements, X-Ray diffraction (XRD), iodometric titration and scanning electron microscopy (SEM). XRD analyses by Rietveld refinement revealed the influence of the ionic radius on the crystalline phase for the different dopants, i.e., variation of the cell parameters and M−O bond lengths. The substitution in both La and Ni sites improves La₂NiO_4+δ electrochemical properties as IT-SOFC cathode, since higher conductivity and lower polarization resistance were obtained. Finally, La_1.5Pr_0.5Ni_0.8Co_0.2O_4+δ cathode exhibited the lowest electrode polarization resistance and activation energy values in the temperature range of 450–900 °C. La_1.5Pr_0.5Ni_0.8Co_0.2O_4+δ was applied on an anode supported cell and a maximum power density of ~400 mW cm⁻² was obtained at 700 °C using pure hydrogen and air.     

A facial and effective way to prepare high-performance hetero-structured composite cathode for intermediate temperature solid oxide fuel cells

A hetero-structured composite porous cathode has been prepared by mixing 90 wt% single-phase perovskite (SP¹) La_0·6Sr_0·4Co_0·2Fe_0·8O_3-δ (LSCF113²) and 10 wt% Ruddlesden-Popper layered perovskite (RP³) LaSrCo_0·2Fe_0·8O_4-δ (LSCF214⁴) nano-powders. The powders were separately synthesized by wet chemical coprecipitation (CP⁵) method, and subsequently mixed by ball-milling to obtain the composite CP-LSCF214-113 cathode with RP/SP hetero-interface. The hetero-interface has been confirmed by XRD and TEM. The polarization impedance (R_p) of symmetrical cell with the composite cathode achieved 0.024 and 0.147 Ω cm² at 800 and 700 °C, decreasing 65% and 72% of the cathode impedance of CP-LSCF113, respectively. An anode supported SOFC with the CP-LSCF214-113 composite cathode achieved maximum power density of 1.02 W cm^?2 at 800 °C. The CP-LSCF214-113 based single cell also showed acceptable stability similar to CP-LSCF113 based cell over 100 h at 700 °C. Moreover, the CP-LSCF214-113 effectively inhibits the coarsening of grains and the growth of RP phase. The solid state reaction (SSR⁶) method was used for comparison. Our results revealed that the CP method combined with ball-milling and subsequent calcining is an effective way to construct RP/SP hetero-interface in porous cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs).     

Development and testing of anode-supported solid oxide fuel cells with slurry-coated electrolyte and cathode

A laboratory setup was designed and put into operation for the development of solid oxide fuel cells (SOFCs). The whole project consisted of the preparation of the component materials: anode, cathode and electrolyte, and the buildup of a hydrogen leaking-free sample chamber with platinum leads and current collectors for measuring the electrochemical properties of single SOFCs. Several anode-supported single SOFCs of the type (ZrO₂:Y₂O₃ + NiO) thick anode/(ZrO₂:Y₂O₃) thin electrolyte/(La_0.65Sr_0.35MnO₃ + ZrO₂:Y₂O₃) thin cathode have been prepared and tested at 700 and 800 °C after in situ H₂ anode reduction. The main results show that the slurry-coating method resulted in single-cells with good reproducibility and reasonable performance, suggesting that this method can be considered for fabrication of SOFCs.     

SOFC cathode material of La1.2Sr0.8CoO4±δ with a fibrous morphology: Preparation and electrochemical performance

Using soluble salts as metal-ion sources and polyacrylonitrile (PAN) as a polymer matrix, La_1.2Sr_0.8CoO_4±δ cathode material with a fibrous morphology is prepared by electrostatic spinning, and microstructural characteristic of this material is investigated by field-emission scanning microscopy and X-ray diffraction. Electrochemical performance of the material in solid-oxide fuel cells is then tested. The results demonstrate that phase-pure La_1.2Sr_0.8CoO_4±δ fibrils with tetragonal structure can be prepared from fresh silky precursors using electrospinning after annealing at high temperature. Compared to the conventional cathode material that possesses a plain granular structure, La_1.2Sr_0.8CoO_4±δ fibrils exhibit superior electrochemical performance. At a temperature of 800 °C, the area specific resistance with this fibrous cathode is as low as 0.043 Ω cm², and maximum power density with the corresponding single-cell is 716 mW cm^?2, demonstrating the fast electrode kinetics in the O₂ reduction reaction. Comparatively, the area specific resistance with the plain cathode is 0.062 Ω cm², and the maximum power density with the corresponding single-cell is only 642 mW cm^?2. Under a constant voltage load of 0.6 V at a fixed temperature of 750 °C, the power output from a single-cell with the fiber-structured cathode maintains between 615 mW cm^?2 and 585 mW cm^?2 even after 15 h of running time, showing a slower fading rate and a more stable electrochemical performance than the plain cathode.     

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.     

Electrochemical performance and distribution of relaxation times analysis of tungsten stabilized La0·5Sr0·5Fe0·9W0·1O3-δ electrode for symmetric solid oxide fuel cells

W-doped La_0·5Sr_0·5Fe_0·9W_0·1O_3-δ (LSFW) was prepared and evaluated as a symmetric electrode for solid oxide fuel cells (SSOFCs). Phase and structural stability of LSFW under both reducing and oxidizing atmospheres was studied. The oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) mechanisms were investigated by using electrochemical impedance spectra (EIS) and distribution of relaxation times (DRT). Electrode polarization resistance (R_p) of LSFW are 0.08 and 0.16 Ω cm² in air and wet hydrogen at 800 °C, respectively. DRT results indicate that the rate-limiting step of LSFW at 800 °C in cathodic conditions and anodic conditions are related to oxygen diffusion and hydrogen adsorption/diffusion, respectively. A La_0·8Sr_0.2Ga_0.8Mg_0·2O_3-δ (LSGM) electrolyte-supported single cell using LSFW electrodes shows a maximum power density of 617.3 mW cm⁻² at 800 °C with considerable stability and reversibility, which enables LSFW a promising SOFCs symmetric electrode material.     

A high-performance cobalt-free Ruddlesden-Popper phase cathode La1·2Sr0·8Ni0·6Fe0·4O4+δ for low temperature proton-conducting solid oxide fuel cells

Ruddlesden-Popper typological (R-P type) layered material La₂NiO₄ is known for the excellent ionic conductivity and fast oxygen kinetics, but limited by its electronic conductivity as a single-phase cathode for low-temperature proton-conducting solid oxide fuel cells (LT H-SOFC). Cobalt-doping can improve the electro-catalytic capability, accompanied with an increased thermal expansion coefficient (TEC), which would lead to the delamination at the cathode/electrolyte interface. In this assignment, strontium and iron co-doped R-P phase cathode La_1·2Sr_0·8Ni_0·6Fe_0·4O_4+δ (LSNF), exhibiting fine oxygen conduction, sufficient electronic conductivity and compatible TEC with the electrolyte, is investigated thoroughly. The single cell with LSNF cathode based on BaZr_0·1Ce_0·7Y_0·2O_3-δ (BZCY) electrolyte achieves a maximum power density (MPD) of 781 mW cm⁻² with the low interfacial polarization resistance (R_p) of 0.078 Ω cm² at 700 °C. Interestingly, the single cell can also possess an eximious power output of 138.5 mW cm⁻² at relatively low temperature of 500 °C. Moreover, the excellent long-term stability with no observable performance degradation for almost 100 h at 600 °C could also indicate that the single-phase R-P layered material LSNF is a preeminent cathode candidate for LT H-SOFC.