Characteristics of LaCo0.4Ni0.6-xCuxO3-δ ceramics as a cathode material for intermediate-temperature solid oxide fuel cells

In this study, the effects of Cu-ion substitution on the densification, microstructure, and physical properties of LaCo_0.4Ni_0.6-xCu_xO_3-δ ceramics were investigated. The results indicate that doping with Cu ions not only enhances the densification but also promotes the grain growth of LaCo_0.4Ni_0.6-xCu_xO_3-δ ceramics. The Cu substitution at x ≤ 0.2 can suppress the formation of La₄Ni₃O₁₀, while the excess Cu triggers the formation of La₂CuO_4.032 phase. The p-type conduction of LaCo_0.4Ni_0.6O_3-δ ceramic was significantly raised by Cu substitution because the acceptor doping ($\begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill C{u}_{Ni}^{\text{'}}\hfill \end{array}\hfill \end{array}\hfill \end{array}\hfill \end{array}$) triggered the formation of hole carriers; this effect was maximized in the case of LaCo_0.4Ni_0.4Cu_0.2O_3-δ composition (1480 S cm^?1 at 500 °C). Thermogravimetric data revealed a slight weight increase of 0.29% for LaCo_0.4Ni_0.4Cu_0.2O_3-δ compact up to 871 °C; this is due to the incorporation of oxygen that creates metal vacancies and additional $\begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill h^{?}\hfill \end{array}\hfill \end{array}\hfill \end{array}\hfill \end{array}\hfill \end{array}$carriers, partially compensating the conductivity loss due to the spin-disorder scattering. As the temperature of the LaCo_0.4Ni_0.4Cu_0.2O_3-δ compacts rose above 871 °C, significant weight loss with temperature was observed because of the release of lattice oxygen to the ambient air as a result of Co (IV) thermal reduction accompanied by the formation of oxygen vacancies. A solid oxide fuel cell (SOFC) single cell with Sm_0.2Ce_0.8O_2-δ (electrolyte) and LaCo_0.4Ni_0.4Cu_0.2O_3-δ (cathode) was built and characterized. The Ohmic (0.256 Ω cm²) and polarization (0.434 Ω cm²) resistances of the single cell at 700 °C were determined; and the maximum power density was 0.535 W cm^?2. These results show that LaCo_0.4Ni_0.4Cu_0.2O_3-δ is a very promising cathode material for SOFC applications.     

Electrochemical performance of La2NiO4+δ cathode for intermediate-temperature solid oxide fuel cells

The application of the La₂NiO_4+δ (LNO), one of the Ruddlesden–Popper series materials, as a cathode material for intermediate temperature solid oxide fuel cells is investigated in detail. LNO is synthesized via a complex method using ethylenediaminetetraacetic acid (EDTA) and citric acid. The effect of the calcination temperature of the LNO powder and the sintering temperature of the LNO cathode layer on the anode-supported cell, Ni–YSZ/YSZ/GDC/LNO, is characterized in view of the charge transfer resistance and the mass transfer resistance. Charge transfer resistance was not significantly affected by calcination and sintering temperature when the sintering temperature was not lower than the calcination temperature. Mass transfer resistance was primarily governed by the sintering temperature. The unit cell with the LNO cathode sintered at 1100 °C with 900 °C-calcined powder presented the lowest polarization resistance for all the measured temperatures and exhibited the highest fuel cell performances, with values of 1.25, 0.815, 0.485, and 0.263 W cm⁻² for temperatures of 800, 750, 700, and 650 °C, respectively.     

Evaluation of GdBaCuCo0.5Fe0.5O5+δ as cathode material for intermediate temperature solid oxide fuel cells

The GdBaCuCo_0.5Fe_0.5O_5+δ (GBCCF) layered perovskite oxide was evaluated as novel cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). Its electrical conductivity was 9–13 S cm^?1 at 650–800 °C in air. The average thermal expansion coefficient (TEC) of GBCCF was 14.4 × 10^?6 K^?1, which was close to that of the typical electrolyte material. The cathode polarization resistance of GBCCF was 0.650 Ω cm² at 750 °C and it decreases to 0.118 Ω cm² when Ce_0.9Gd_0.1O_1.95 (GDC) was added to form a GBCCF–GDC composite cathode. Preliminary results indicated that layered perovskite GBCCF was a promising alternative cathode material for IT-SOFCs.     

Effect of Fe doping on the performance of suspension plasma-sprayed PrBa0.5Sr0.5Co2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

PrBa_0.5Sr_0.5Co_2–xFe_xO_5+δ (PBSCF) (X = 0, 0.3, 0.4, and 0.5) is investigated as cathode material for intermediate-temperature solid oxide fuel cells. Suspension plasma spraying is used as a low cost and large-scale manufacturing process to prepare PBSCF cathodes. Fe substitution effects on the crystal structure and electrochemical performance are characterized. All plasma-sprayed PBSCF cathodes exhibit a pure and stable cubic structure. The suspension plasma-sprayed PBSCF deposits show a porous and fine structure, and the microstructures are insensitive to Fe substitution. Subsequent to Fe doping, the polarization resistance of PBSCF cathodes rapidly decreases for increasing Fe substitution concentration from 0 to 0.4. Further increase of the Fe doping concentration increases the cathode polarization instead. At 600 and 700 °C, a 20% Fe-doped (x = 0.4) PBSCF cathode exhibits remarkably low area-specific polarization resistances (R_p) of 0.074 Ω cm² and 0.012 Ω cm², respectively. Moreover, the R_p of all cathodes remains almost identical after isothermal annealing at 600 °C for 300 h. Furthermore, the thermally-sprayed porous metal-supported cell assembled with the optimal PBSCF cathode shows excellent performance with peak power densities of 0.37, 0.8, and 1.35 W cm⁻² at 500, 600, and 700 °C, respectively.     

Effect of GDC addition method on the properties of LSM–YSZ composite cathode support for solid oxide fuel cells

Equal amounts of Gd_0.1Ce_0.9O_2−δ (GDC) were added to La_0.65Sr_0.3MnO_3−δ/(Y₂O₃)_0.08(ZrO₂)_0.92 (LSM/YSZ) powder either by physical mixing or by sol–gel process, to produce a porous cathode support for solid oxide fuel cells (SOFCs). The effect of the GDC mixing method was analyzed in view of sinterability, thermal expansion coefficient, microstructure, porosity, and electrical conductivity of the LSM/YSZ composite. GDC infiltrated LSM/YSZ (G-LY) composite showed a highly porous microstructure when compared with mechanically mixed LSM/YSZ (LY) and LSM/YSZ/GDC (LYG) composites. The cathode support composites were used to fabricate the button SOFCs by slurry coating of YSZ electrolyte and a nickel/YSZ anode functional layer, followed by co-firing at 1250 °C. The G-LY composite cathode-supported SOFC showed maximum power densities of 215, 316, and 396 mW cm⁻² at 750, 800, and 850 °C, respectively, using dry hydrogen as fuel. Results showed that the GDC deposition by sol–gel process on LSM/YSZ powder before sintering is a promising technique for producing porous cathode support for the SOFCs.     

SrCo1−xSbxO3−δ cathode materials prepared by Pechini method for solid oxide fuel cell applications

In this study, SrCo_1?ySb_yO_3?δ powders were prepared by a modified Pechini method. According to the study results, the cubic Pm3m phase of the SrCo_1?ySb_yO_3?δ ceramics was obtained as 10% of cobalt ions were substituted by antimony ions. Doping of Sb³⁺ ions appeared both to stabilize the Pm3m phase of the SrCo_1?ySb_yO_3?δ ceramics and to enhance densification and retard grain growth. The coefficient of thermal expansion of the SrCo_1?xSb_xO_3?δ ceramics increased with the content of the antimony ions, ranging from 10.17 to 15.37 ppm/°C at temperatures lower than the inflection point (ranging from 450 °C to 550 °C) and from 22.16 to 29.29 ppm/°C at higher temperatures. For the SrCo_0.98Sb_0.02O_3?δ ceramic, electrical conductivity reached a maximum of 507 S/cm at 450 °C. The ohmic and polarization resistances of the single cell with the pure SrCo_0.98Sb_0.02O_3?δ cathode at 700 °C read respectively 0.298 Ω cm² and 0.560 Ω cm². The single cell with the SrCo_0.98Sb_0.02O_3?δ-SDC composite cathode appeared to reduce the impedances with the R₀ and R_P at 700 °C reading respectively 0.109 Ω cm² and 0.127 Ω cm². Without microstructure optimization and measured at 700 °C, the single cells with the pure SrCo_0.98Sb_0.02O_3?δ cathode and the SrCo_0.98Sb_0.02O_3?δ-SDC composite cathode, demonstrated maximum power densities of 0.100 W/cm² and 0.487 W/cm². Apparently, SrCo_1?ySb_yO_3?δ is a potential cathode for use in IT-SOFCs.     

Lowering the co-sintering temperature of cathode–electrolyte bilayers for micro-tubular solid oxide fuel cells

To prevent undesirable reactions between the cathode and electrolyte materials in cathode-supported solid oxide fuel cells (SOFCs), the co-sintering temperature of these two layers must be lowered. In the present work, we employed different strategies to lower the co-sintering temperature of cathode–electrolyte bilayers for micro-tubular SOFCs by increasing the cathode sintering shrinkage and adding sintering aids to the electrolyte. Strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ) were used as the cathode and electrolyte materials, respectively. To facilitate densification of the electrolyte layer by controlling the shrinkage of the cathode support, the particle size of the LSM powder was reduced by high-energy ball milling and different amounts of micro-crystalline cellulose pore former were used. Sintering aids, namely NiO and Fe₂O₃, were also added to the YSZ electrolyte to further improve its low-temperature sintering. Our results indicate that with the improvement in the cathode support shrinkage and use of the small amounts of sintering aids, the cathode–electrolyte co-sintering temperature can be reduced to 1250–1300 °C. It was also observed that the presence of the sintering aids helps to reduce the reactivity between the LSM cathode and YSZ electrolyte.     

Characteristics of Cu and Mo-doped Ca3Co4O9−δ cathode materials for use in solid oxide fuel cells

In this study, Cu and Mo ions were doped in Ca₃Co₄O_9−δ to improve the electrical conductivity and electrochemical behavior of Ca₃Co₄O_9−δ ceramic and the performance of a solid oxide fuel cell (SOFC) single cell based on NiO-SDC/SDC/doped Ca₃Co₄O_9−δ-SDC were examined. Cu substitution in the monoclinic Ca₃Co₄O_9−δ ceramic effectively enhanced the densification, slightly increased the grain size, and triggered the formation of some Ca₃Co₂O₆; however, no second phase was found in porous Mo-doped Ca₃Co₄O_9−δ ceramics even when the sintering temperature reached 1050 °C. Substitution of Cu ions caused slight increase in the Co³⁺ and Co⁴⁺ contents and decrease in the Co²⁺ content; however, doping with Mo ions showed the opposite trend. Doping the Ca₃Co₄O_9−δ ceramic with a small amount of Cu or Mo increased its electrical conductivity. The maximum electrical conductivity measured was 218.8 S cm⁻¹ for the Ca₃Co_3.9Cu_0.1O_9−δ ceramic at 800 °C. The Ca₃Co_3.9Cu_0.1O_9−δ ceramic with a coefficient of thermal expansion coefficient of 12.1×10⁻⁶ K⁻¹ was chosen as the cathode to build SOFC single cells consisting of a 20 μm SDC electrolyte layer. Without optimizing the microstructure of the cathode or hermetically sealing the cell against the gas, a power density of 0.367 Wcm⁻² at 750 °C was achieved, demonstrating that Cu-doped Ca₃Co₄O_9−δ can be used as a potential cathode material for IT-SOFCs.     

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.     

Effect of Bi2O3 on the electrochemical performance of LaBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The LaBaCo₂O_5+δ−x wt.% Bi₂O₃ (LBCO-xBi₂O₃, x=10, 20, 30, and 40) were prepared as composite cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) via the conventional mechanical mixing method. The effect of Bi₂O₃ on polarization resistance, overpotential, and long-term stability of the LBCO cathode was investigated. An effective sintering aid for LBCO cathode, Bi₂O₃ not only lowers its sintering temperature by ~200 °C, but also improves the electrochemical performance within the intermediate temperature range of 600–800 °C. Electrochemical impedance spectroscopy measurements showed that the addition of 20 wt% Bi₂O₃ to LBCO exhibited the lowest area-specific resistance of 0.020 Ω cm² at 800 °C in air, which was about a seventh of that of the LBCO cathode at the same condition. At a current density of 0.2 A cm⁻², the cathodic overpotential of LBCO-20Bi₂O₃ was about 12.6 mV at 700 °C, while the corresponding value for LBCO was 51.0 mV. Compared to B₂O₃–Bi₂O₃–PbO frit, the addition of Bi₂O₃ significantly improved the long-term stability of cathode. Therefore, LBCO-20Bi₂O₃ can be a promising cathode for IT-SOFCs.     

Characterization of Ba0.5Sr0.5M1−xFexO3−δ (M = Co and Cu) perovskite oxide cathode materials for intermediate temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_1?xFe_xO_3?δ (x = 0.2, 0.6, and 0.8) and Ba_0.5Sr_0.5Cu_1?xFe_xO_3?δ (x = 0.6 and 0.8) perovskite oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. All the samples synthesized by a citrate–EDTA complexing method were single-phase cubic perovskite solid solutions. Then, the thermal expansion coefficient, electrical conductivities, the oxygen vacancy concentrations, the polarization resistances (R_p), and the power densities were measured. An increase in the Co content resulted in a decrease in the polarization resistance, the electrical conductivities at low temperatures, and the inflection point of the thermal expansion coefficient, but it led to an increase in the electrical conductivities at high temperatures, the oxygen vacancy concentrations, and the maximum power densities. The Cu-based system has similar behavior to the Co-based system; yet, in terms of the electrical conductivities, high Cu content gave a better result than low content for the entire range of temperatures.     

The effect of nickel doping on the microstructure and conductivity of Ca(Ti,Al)O3–δ for solid oxide fuel cells

The ABO₃ type perovskite oxide-based ceramic membranes are one of the most important classes of materials for high-temperature solid oxide fuel cell applications. The acceptor-doped calcium titanate (CaTiO₃) perovskite has attracted considerable attention as an oxide ion-conducting membrane due to its potentially high ionic conductivity and excellent stability. Nonetheless, the ionic conductivity of the material must still be improved. Following the strategy of the substitution of dopants on the B-site, the current work is focused on exploring the effect of Al and Ni additions on electrical properties, by studying the nominal compositions CaTi_0.7Al_0.3–xNi_xO_3−δ (x = 0, 0.1, 0.2 and 0.3). The materials were synthesized by the sol–gel method and studied as a function of phase composition, microstructure, and electrical properties. The results demonstrate an increase of both total and specific grain boundary conductivity with increasing Ni content, while predominant p-type behavior is shown under oxygen-rich atmosphere.     

Synthesis and characterisation of MnGaxCr2−xO4 (0.1≤x≤1) spinels as potential electrode support materials for intermediate-temperature solid oxide fuel cells

MnGa_xCr_2−xO₄ (MGCO, x=0.1, 0.2, 0.4, 0.8, 1) oxides are synthesised using a citric acid nitrate combustion method. The influence of Ga substitution on the structure, electrical conductivity and electrochemical performance are systematically investigated. The chemical and thermal compatibility of MGCO materials with yttrium-stabilised zirconia (YSZ) are also studied. All the samples exhibit a single phase spinel structure. Thermal expansion coefficients (TECs) of the MGCO oxides are in the range of 9–12×10⁻⁶ K⁻¹, indicating a good thermal match with the YSZ electrolyte. No chemical reactions are detected between MGCO materials and YSZ, indicating their good chemical compatibility with YSZ. The magnitude of electrical conductivity of all the obtained samples is in the order of about 10⁻³ S cm⁻¹at 800 °C measured in air. The polarisation resistance reaches a value as low as 5.2 Ω cm² for x=0.4 at 800 °C. The preliminary results demonstrate that MGCO materials could be used as electrode support materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs).     

Carbon-tolerance effects of Sm0.2Ce0.8O2−δ modified Ni/YSZ anode for solid oxide fuel cells under methane fuel conditions

Samarium-doped ceria (SDC) is coated onto a Ni/yttria-stabilized zirconia (Ni/YSZ) anode for the direct use of methane in solid-oxide fuel cells. Porous SDC thin layer is applied to the anode using the sol–gel coating method. The experiment was performed in H₂ and CH₄ conditions at 800 °C. The cell performance was improved by approximately 20 % in H₂ conditions by the SDC coating, due to the high ionic conductivity, the mixed ionic and electronic conductive property of the SDC, and the increased triple phase boundary area by the SDC coating in the anode. Carbon was hardly deposited in the SDC-coated Ni/YSZ anode. The cell performance of the SDC-coated Ni/YSZ anode did not show any significant degradation for up to 90 h under 0.1 A cm^?2 at 800 °C. The porous thin SDC coating on the Ni/YSZ anode provided the electrochemical oxidation of CH₄ over the whole anode, and minimized the carbon deposition by electrochemical carbon oxidation.     

Highly electrocatalytic activity Ruddlesden−Popper type electrode materials for solid oxide fuel cells

To promote the viability of commercial solid oxide fuel cell (SOFC), developing novel oxygen electrodes with high electrochemical activity is essential. Herein, a series Ruddlesden-Popper oxides, Sr_3?xLa_xFe₂O_7?δ (SLFx), are successfully synthesized and evaluated as potential cathode materials for SOFC. The oxygen desorption behavior, electrochemical activity and oxygen reduction reaction (ORR) kinetics of the SLFx cathodes are systematically discussed. The Sr_2.9La_0.1Fe₂O_7?δ (SLF10) cathode exhibits highest oxygen vacancy concentration and excellent electrocatalytic performance, as evidenced by a low polarization resistance of 0.14 Ω cm² and high maximum power density of 0.77 W cm^?2 at 700 °C. From electrochemical impedance spectra and distribution of relaxation times analysis, the oxygen adsorption/desorption process is the rate-limiting step toward ORR at the cathode interface. Furthermore, SLF10 shows considerable polarization overpotentials in both SOFC and solid oxide electrolysis cell (SOEC) modes, indicating that SLF10 is a promising bifunctional electrode for electrocatalytic oxygen reaction.     

Compaction pressure effect on microstructure and electrochemical performance of GdBaCo2O5+δ cathode for IT-SOFCs

In order to optimize the morphology of starting powder, raw GBCO powder synthesized via solid state reaction was repeatedly compacted by uniaxial die pressing at two apparent compaction pressures of 500 and 1000 MPa. The particle size distribution curves and SEM images indicated that, with increasing compaction pressure and number of compaction times, the larger particles in the powder were gradually broken apart and the particle size became small and uniform. Then the effect of pressing treatment for the starting GBCO particles on the microstructure and performance of sintered cathode was studied. The results demonstrated that, after being sintered under the same conditions, the cathode prepared from the treated GBCO particles showed a finer microstructure compared with that prepared from the raw GBCO particles. In addition, optimizing the morphology of the starting GBCO powder by pressing treatment could improved the cathode performance and made the polarization resistance of final cathode reduce from 1.33 Ω cm² to 0.40 Ω cm² at 600 °C.     

Evaluation of A-site deficient Sr1−xSc0.175Nb0.025Co0.8O3−δ (x=0, 0.02, 0.05 and 0.1) perovskite cathodes for intermediate-temperature solid oxide fuel cells

This work strives to improve the performance of SrSc_0.175Nb_0.025Co_0.8O_3−δ (SSNC) cathode by introducing A-site cation deficiency up to 10 mol%. Three different Sr-deficient compositions, i.e., Sr_1−xSc_0.175Nb_0.025Co_0.8O_3−δ (S_1−xSNC, x=0.02, 0.05 and 0.1) including the non-deficient analogue, SSNC are prepared. Powder X-ray diffraction patterns indicate that the original cubic perovskite structure is retained. The thermal expansion coefficient between 50 °C and 900 °C increases progressively with increasing Sr deficiency, consistent with the “β-oxygen” release profiles trend. The electrical conductivities for SSNC, S_0.98SNC, S_0.95SNC and S_0.9SNC show a maximum-type profile against increasing temperature, i.e., semiconducting behavior followed by metallic behavior. Despite the consistent increase in the oxygen non-stoichiometry with increasing Sr deficiency, the oxygen reduction reaction performance increases in the order of SSNC, S_0.9SNC, S_0.98SNC and S_0.95SNC. That the highest oxygen reduction reaction (ORR) performance is demonstrated by S_0.95SNC indicates the trade-off between the increase in the concentration of oxygen vacancies and the formation of the phase impurities. At 650 °C, S_0.95SNC shows an area specific resistance of 0.017 Ω cm² (from symmetric cell test) and a peak power density of 1263 mW cm⁻² (from single fuel cell test on a Ni-Sm_0.2Ce_0.8O_1.9 (SDC) anode supported SDC electrolyte).     

Rational design of the self-assembled BaCo1-xZrxO3-δ (x = 0.8–0.2) nanocomposites as the promising low/intermediate-temperature solid oxide fuel cell cathodes

Assembling multiple perovskites with complementary properties is a promising strategy to achieve high-performance cathodes for low/intermediate-temperature solid oxide fuel cell (LT/IT-SOFC). In this work, self-assembling perovskites of cubic BaZr_0.82Co_0.18O_3-δ (cub-BZC) and hexagonal BaCo_0.96Zr_0.04O_2.6+δ (12H-BC) at the nanoscale can be realized in novel designed nanocomposites with nominal composition of BaCo_1-xZr_xO_3-δ (x = 0.8–0.2), which can possess congenital compatibility, improved thermal expansion coefficients and electrical conductivity. The relative contents of cubic and hexagonal phases are significantly correlated with the zirconium content (x). Therein, BaCo_1-xZr_xO_3-δ nanocomposites exhibit relatively low content differences among perovskite phases when x = 0.4 (cubic/hexagonal = 62:38) and x = 0.2 (hexagonal/cubic = 69:31) nanocomposites, which can form more extensive heterointerfaces for promoting oxygen adsorption, dissociation and reduction reaction. When further applied as cathode, the cell with BaCo_1-xZr_xO_3-δ nanocomposites achieve 2265–598 mW cm^?2 (800–600 °C) when x = 0.2 as a promising IT-SOFC cathode, and 315?148 mW cm^?2 (550–500 °C) when x = 0.4 as a promising LT-SOFC cathode.     

Evaluation of Fe and Mn co-doped layered perovskite PrBaCo2/3Fe2/3Mn1/2O5+δ as a novel cathode for intermediate-temperature solid-oxide fuel cell

A B-site cation-deficient double-perovskite oxide, PrBaCo_2/3Fe_2/3Mn_1/2O_5+δ (PBCFM2), was successfully synthesized by a sol-gel method and systematically investigated as an efficient cathode for IT-SOFC. The PBCFM2 exhibits good thermally stability and broad chemical compatibility at high temperature. Appropriate substitution of Mn and Fe for Co dramatically decreases the thermal expansion coefficient (TEC) from 21.5 × 10^–6 K^–1 for PrBaCo₂O_5+δ to 17.8 × 10^–6 K^–1 to PBCFM2 at a temperature range of 30–1000 °C. The temperature dependence of conductivity of the PBCFM2 was tested from 300 °C to 850 °C and then confirmed using the p-type small-polaron transport mode. The maximum conductivity value was 72 S cm^–1 at 600 °C. When using 300 µm of Sm_0.2Ce_0.8O_1.9 (SDC) as an electrolyte, the area specific resistance (ASR) and peak power density values were 0.028 Ω cm² and 588 mV cm^–2 at 800 °C, respectively. The activity and performance of the PBCFM2 cathode are further improved by impregnation with nano-sized SDC particles. The composite cathode with two times impregnation provided the optimal nano-scale SDC loading and microstructure where the ASR and peak power densities were 0.023 Ω cm² and 621 mV cm^–2 at 800 °C, respectively. Our preliminary results lead us to propose that PBCFM and its composite cathodes are good candidate cathodes for IT-SOFC.     

Barium-doped Pr2Ni0.6Cu0.4O4+δ with triple conducting characteristics as cathode for intermediate temperature proton conducting solid oxide fuel cell

Proton conducting solid oxide fuel cell (H-SOFC) is an emerging energy conversion device, with lower activation energy and higher energy utilization efficiency. However, the deficiency of highly active cathode materials still remains a major challenge for the development of H-SOFC. Therefore, in this work, K₂NiF₄-type cathode materials Pr_2-xBaNi_0.6Cu_0.4O_4+δ (x=0, 0.1, 0.2, 0.3), single-phase triple-conducting (e^-/O^2-/H⁺) oxides, are prepared for intermediate temperature H-SOFCs and exhibit good oxygen reduction reaction activity. The investigation demonstrates that doping Ba into Pr_2-xBaNi_0.6Cu_0.4O_4+δ can increase its electrochemical performance through enhancing electrical conductivity, oxygen vacancy concentration and proton conductivity. EIS tests are carried at 750℃ and the minimum polarization impedances are obtained when x=0.2, which are 0.068 Ω·cm² in air and 1.336 Ω·cm² in wet argon, respectively. The peak power density of the cell with Pr_1.8Ba_0.2Ni_0.6Cu_0.4O_4+δ cathode is 298 mW·cm^-2 at 750℃ in air with humidified hydrogen as fuel. Based on the above results, Ba-doped Pr_2-xBaNi_0.6Cu_0.4O_4+δ can be a good candidate material for SOFC cathode applications.