Boosting the Electrochemical Performance of Fe-Based Layered Double Perovskite Cathodes by Zn2+ Doping for Solid Oxide Fuel Cells

Advancing Solid Oxide Fuel Cell Performance: Enhanced Electrochemical Properties of Pr1-xCaxBaFe2O5+δ Nanofiber Cathodes via Ca Doping

The double perovskite oxide PrBaFe2O5+δ has great potential as a cathode material for solid oxide fuel cells (SOFCs). However, the electrochemical characteristics of Fe-based double perovskites are relatively inferior. To improve its electrochemical performance, Ca is investigated to partially replace Pr, forming Pr1-xCaxBaFe2O5+δ (PCBFx, x = 0.0-0.3) by an electrospinning technique. The PCBFx nanofibers exhibited a crystalline structure characterized by orthorhombic symmetry and space group P4/mmm. Furthermore, these PCBFx nanofibers displayed exceptional chemical compatibility with the Sm0.2Ce0.8O1.95 (SDC) electrolyte when sintered at a temperature of 900 °C for 5 h. The X-ray photoelectron spectroscopy (XPS) analysis reveals a progressive increase in the Fe4+ concentration as the Ca doping level rises. The polarization resistances (Rp) of the PCBF00, PCBF01, PCBF02, and PCBF03 nanofiber cathodes were 0.103, 0.079, 0.056, and 0.048 Ω cm2 at 750 °C. In the meantime, doping Ca increases the peak power density of the single cell by 46%, from 762.80 (PCBF00) to 1114.85 (PCBF03) mW cm-2 at 750 °C. The results demonstrate that PCBF03 double perovskite nanofibers exhibit great potential as cathode materials for SOFCs.

A-Site Engineering of the High-Entropy Perovskite Pr0.4La0.4Ba0.4Sr0.4Ca0.4Fe2O5+δ Cathode for Intermediate-Temperature SOFCs

Mixed-oxygen ionic and electronic conduction is crucial for the cathode materials of solid oxide fuel cells, ensuring high efficiency and low-temperature operation. However, the electronic and oxygen ionic conductivity of traditional Fe-based layered perovskite cathode materials is low, resulting in insufficient oxygen reduction reactivity. Herein, a type of high-entropy perovskite oxide consisting of five equimolar metals, Pr0.4La0.4Ba0.4Sr0.4Ca0.4Fe2O5+δ (PLBSCF), a high-performance cobalt-free cathode derived from the PrBaFe2O5+δ (PBF), is proposed. Such A-site engineering could not only increase the oxygen vacancy concentration of PLBSCF but also give higher conductivity than PBF, thus significantly reducing the polarization impedance of the symmetric cell to only 0.052 Ω·cm2 at 750 °C. The good output performance of a single cell is also realized. The peak power density of the single cell with PLBSCF-Ce0.9Gd0.1O2-δ (GDC) as the cathode at 750 °C was 0.853 W·cm-2. Additionally, the single cell with the PLBSCF cathode exhibits a good durable performance of 100 h at 750 °C. Combining the distribution of relaxation time analysis, it can be seen that the enhancement of the oxygen reduction reaction is due to the reduction of intermediate-frequency and low-frequency resistance, indicating an improvement in the charge transfer process and adsorption/dissociation process of molecular oxygen.

Synergistically engineered in-situ self-assembled heterostructure composite nanofiber cathode with superior oxygen reduction reaction catalysis for solid oxide fuel cells

The engineering and exploration of cathode materials to achieve superior oxygen reduction catalytic activity and resistance to CO2 are crucial for enhancing the performance of solid oxide fuel cells (SOFCs). Herein, a novel heterostructure composite nanofiber cathode comprised of PrBa0.5Sr0.5Co2O5+δ and Ce0.8Pr0.2O1.9 (PBSC-CPO-ES) was prepared for the first time through a synergistic approach involving in-situ self-assembly and electrostatic spinning techniques. PBSC-CPO-ES exhibits exceptionally high oxygen reduction catalytic activity and CO2 resistance, which is attributed to its unique nanofiber microstructure and abundant presence of heterointerfaces, significantly accelerating the charge transfer process, surface exchange and bulk diffusion of oxygen. The introduction of CPO not only effectively reduces the thermal expansion of PBSC but also changes the characteristics of oxygen ion transport anisotropy in layered perovskite materials, forming three-dimensional oxygen ion transport pathways. At 750 °C, the single cell employing the PBSC-CPO-ES heterostructure nanofiber attains an impressive peak power density of 1363 mW cm-2. This represents a notable 60.7 % improvement in comparison to the single-phase PBSC powder. Moreover, PBSC-CPO-ES exhibits excellent CO2 tolerance and performance recovery after CO2 exposure. This work provides new perspectives to the design and advancement of future high-performance and high-stability SOFC cathode materials.

Exploring the potential of SrTi0.7Fe0.3O3 perovskite/Chitosan nanosheets for the development of a label-free electrochemical sensing assay for determination of naproxen in human plasma samples

Naproxen is a nonsteroidal anti-inflammatory drug used to treat nonrheumatic inflammation, migraine, and gout. Therefore, the determination of naproxen in pharmaceutical and biological samples is of particular importance. In the present work, SrTi0.7Fe0.3O3 perovskite/Chitosan nanosheets were used to modify the surface of a glassy carbon electrode (GCE) for highly sensitive determination of naproxen. To ensure the successful synthesis of the perovskite nanosheets, morphological studies including scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were carried out. The electrochemical investigations of naproxen on the modified surface of GCE were investigated and the limit of detection (LOD) and limit of quantification (LOQ) were acquired 0.50 and 1.67 μM, respectively. Additionally, the linear range (LR) of 1.99-130.84 μM was obtained for the oxidation of naproxen. The obtained results have been proved that the mentioned method is simple, sensitive, and specific with a short analysis time. The dominant analytical features of the designed sensor are possessing a low detection limit, excellent stability, repeatability, and high selectivity in the presence of naproxen. For investigation of the applicability of the designed assay in real sample analysis, human plasma samples have been examined and a recovery index was acquired 95%.

Ca-Doping Cobalt-Free Double Perovskite Oxide as a Cathode Material for Intermediate-Temperature Solid Oxide Fuel Cell

Mixed oxygen ion and electron-conducting materials are viable cathodes for solid oxide fuel cells due to their excellent oxygen transport kinetics and mixed electrical conductivity, which ensure highly efficient operation at low and medium temperatures. However, iron-based double perovskite oxides usually exhibit poor electrocatalytic activity due to low electron and oxygen ion conductivity. In this paper, Ca is doped in PrBaFe2O5+δ A-site to improve the electrochemical performance of PrBaFe2O5+δ. Results show that replacing Pr with Ca does not change the crystal structure, and the Ca doping effectively increases the adsorbed oxygen content and accelerates the migration and diffusion rate of O2- to the electrolyte|cathode interface. The polarization resistance of the symmetric cell PC0.15BF|CGO|PC0.15BF is 0.033 Ω·cm2 at 800 °C, which is about 56% lower than that of PBF, confirming the enhancement of the mixed conduction of oxygen ions and electrons. In addition, the anode-supported single cell has a peak power density of 512 mW·cm-2 at 800 °C.

Advancements in Perovskite-Based Cathode Materials for Solid Oxide Fuel Cells: A Comprehensive Review

The high-temperature solid oxide fuel cells (SOFCs) are the most efficient and green conversion technology for electricity generation from hydrogen-based fuel as compared to conventional thermal power plants. Many efforts have been made to reduce the high operating temperature (>800 °C) to intermediate/low operating temperature (400 °C Collapse

Key Words

• Ruddlesden-Popper phase
• Solid oxide fuel cell
• double perovskite
• electrochemical activity
• polarization resistance
• thermal expansion coefficient

Collapse

MESH Headings Collapse

Grants Collapse

Affiliation(s)

Ayesha Samreen Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan
Muhammad Sudais Ali Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan
Muhammad Huzaifa Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan
Nasir Ali Research Center for Sensing Materials and Devices, Zhejiang Labs, Yuhang District, Nanhu, China
Bilal Hassan Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan
Fazl Ullah Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan
Shahid Ali Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan
Nor Anisa Arifin Materials Engineering and Testing Group, TNB Research Sdn Bhd, No.1, Kawasan Institusi Penyelidikan, Jln Ayer Hitam, 43000, Kajang, Selangor, Malaysia

Collapse

Fe-based double perovskite with Zn doping for enhanced electrochemical performance as intermediate-temperature solid oxide fuel cell cathode material

This study aims to investigate the implications of transition-metal Zn doping at the B-site on the crystal structure, average thermal expansion coefficient (TEC), electrocatalytic activity, and electrochemical performance of LaBaFe2O5+δ by preparing LaBaFe2-xZnxO5+δ (x = 0, 0.05, 0.1, 0.15, 0.2, LBFZx). The X-ray diffraction (XRD) results show that Zn2+ doping does not change the crystal structure, the unit cell volume increases, and the lattice expands. The X-ray photoelectron spectroscopy (XPS) and mineral titration results show that the oxygen vacancy concentration and Fe4+ content gradually increase with the increase in doping amount. TEC decreases with the increase in Zn2+ doping amount, and the TEC of LBFZ0.2 is 11.4 × 10-6 K-1 at 30-750 °C. The conductivity has the best value of 103 S cm-1 at the doping amount of x = 0.1. The scanning electron microscopy (SEM) images demonstrate that the electrolyte CGO(Gd0.1Ce0.9O1.95) becomes denser after high-temperature calcination, and the cathode material is well attached to the electrolyte. The electrochemical impedance analysis shows that Zn2+ doping at the B-site can reduce the (Rp) polarization resistance, and the Rp value of the symmetric cell with LaBaFe1.8Zn0.2O5+δ as cathode at 800 °C is 0.014 Ω cm2. The peak power density (PPD) value of the anode-supported single cell is 453 mW cm-2, which shows excellent electrochemical performance.

BaLa5V2O3N7: a novel anti-perovskite oxynitride for electrode applications

The exploration of transition metal oxynitrides has garnered significant interest due to their intriguing property diversity. Herein, we present a promising new transition metal oxynitride BaLa5V2O3N7, which features an anti-perovskite structure type. This unique structural configuration endows the material with remarkable conductivity, particularly at low temperatures, paving the way for the material to be used in a wide range of technological applications.

Cobalt-Free Double Perovskite Oxide as a Promising Cathode for Solid Oxide Fuel Cells

Double perovskite oxide PrBaFe₂O_5+δ is a potential cathode material for intermediate-temperature solid oxide fuel cells. To improve its electrochemical performance, the trivalent element Ga is investigated to partially replace Fe, forming PrBaFe_2-xGa_xO_5+δ (PBFGx, x = 0.05, 0.1, and 0.15). The doping effects on physicochemical properties and electrochemical properties are analyzed regarding the phase structures, element valence states, amount of oxygen vacancies, content of oxygen species, oxygen surface exchange coefficients (k_chem), electrochemical polarization resistance, and single-cell performance. Specifically, PBFG0.1 exhibits improved k_chem, such as a 19% improvement from 4.09 × 10^-4 to 4.86 × 10^-4 cm s^-1 at 750 °C, due to the increased concentration of reactive oxygen species and oxygen vacancies. Consequently, the interfacial polarization resistance is decreased by 28% from 0.057 to 0.041 Ω cm² at 800 °C. The subreaction steps of the oxygen reduction reaction in the PBFG0.1 cathode are further investigated, which suggests that the oxygen dissociation process is greatly enhanced by doping Ga. Meanwhile, doping Ga increases the peak power density of the anode-supported single cell by 36% from 629 to 856 mW cm^-2 at 800 °C. The single cell with the PBFG0.1 cathode also exhibits good stability in 100 h of long-term operation at 750 °C.

Zirconia- and ceria-based electrolytes for fuel cell applications: critical advancements toward sustainable and clean energy production

Solid oxide fuel cells (SOFCs) are emerging as energy conversion devices for large-scale electrical power generation because of their high energy conversion efficiency, excellent ability to minimize air pollution, and high fuel flexibility. In this context, this critical review has focussed on the recent advancements in developing a suitable electrolyte for SOFCs which has been required for the commercialization of SOFC technology after emphasizing the literature from the prior studies. In particular, the significant developments in the field of solid oxide electrolytes for SOFCs, particularly zirconia- and ceria-based electrolytes, have been highlighted as important advancements toward the production of sustainable and clean energy. It has been reported that among various electrolyte materials, zirconia-based electrolytes have the potential to be utilized as the electrolyte in SOFC because of their high thermal stability, non-reducing nature, and high mechanical strength, along with acceptable oxygen ion conductivity. However, some studies have proved that the zirconia-based electrolytes are not suitable for low and intermediate-temperature working conditions because of their poor ionic conductivity to below 850 °C. On the other hand, ceria-based electrolytes are being investigated at a rapid pace as electrolytes for intermediate and low-temperature SOFCs due to their higher oxygen ion conductivity with good electrode compatibility, especially at lower temperatures than stabilized zirconia. In addition, the most emerging advancements in electrolyte materials have demonstrated that the intermediate temperature SOFCs as next-generation energy conversion technology have great potential for innumerable prospective applications.

Restrictions of nitric oxide electrocatalytic decomposition over perovskite cathode in presence of oxygen: Oxygen surface exchange and diffusion

Nitric oxide (NO) abatement from engine exhaust is of great significance to alleviate air pollution and haze. Compared with the traditional selective catalytic reduction (SCR) technology, electrocatalytic decomposition of NO simplifies the reductant supply system and therefore avoids secondary pollution. In this study, typical perovskite La_0.6Sr_0.4Co_xFe_1-xO_3-δ (LSCF) infiltrated by different dosages of nano ceria Ce_0.9Gd_0.1O_1.9 (GDC) was used as composite cathodes, in order to explore the critical factors to restrain NO conversion in excess of O₂. The results show that electron as reactive species transfers among NO, ABO₃-type cathode and oxygen vacancy. The maximum of NO removal efficiency can reach 96.27 % in absence of O₂ and up to 80.55 % in presence of 1% O₂ in case of LSCF infiltrated by moderate dosages LSCF-GDC(2), which is superior to those of LSCF, LSCF-GDC(4) and LSM-GDC(nano) composite cathode. Compared to oxygen storage capacity (OSC) caused by the infiltration of nano ceria, higher surface oxygen exchange coefficient (k_δ) and chemical diffusion coefficient (D^chem) lead to the significant decrease in polarization resistance (Rp), and consequently to the enhancement of NO removal in presence of O₂. No matter what kind of oxygen deriving from oxygen reduction reaction (ORR) and NO reduction reaction (NORR), GDC infiltration into LSCF improves oxygen transport property and however, the property of cathode in ORR is dominant over in NORR in presence of O₂. Moderate GDC loading has the highest oxygen transport kinetics, and oxygen surface exchange is faster than chemical diffusion, due to lower activation energy. Over loading of GDC with greater ohmic resistance (Rs) inversely influences the NO removal.

Structural Features and Defect Equilibrium in Cubic PrBa1−xSrxFe2O6−δ

The structure, oxygen non-stoichiometry, and defect equilibrium in perovskite-type PrBa_1−xSr_xFe₂O_6−δ (x = 0, 0.25, 0.50) synthesized at 1350 °C were studied. For all compositions, X-ray diffraction testifies to the formation of a cubic structure (S.G. Pm3¯m), but an electron diffraction study reveals additional diffuse satellites around each Bragg spot, indicating the primary incommensurate modulation with wave vectors about ±0.43a*. The results were interpreted as a sign of the short-order in both A-cation and anion sublattices in the areas of a few nanometers in size, and of an intermediate state before the formation of an ordered superstructure. An increase in oxygen deficiency was found to promote the ordering, whereas partial substitution of barium by strontium caused the opposite effect. The oxygen content in oxides as a function of oxygen partial pressure and temperature was measured by coulometric titration, and the data were used for the modeling of defect equilibrium in oxides. The simulation results implied oxygen vacancy ordering in PrBa_1−xSr_xFe₂O_6−δ that is in agreement with the electron diffraction study. Besides oxidation and charge disproportionation reactions, the reactions of oxygen vacancy distribution between non-equivalent anion positions, and their trapping in clusters with Pr³⁺ ions were taken into account by the model. It was demonstrated that an increase in the strontium content in Pr_0.5Ba_0.5−xSr_xFeO_3−δ suppressed ordering of oxygen vacancies, increased the binding energy of oxygen ions in the oxides, and resulted in an increase in the concentration of p-type carriers.

Promoted Performance of Layered Perovskite PrBaFe2O5+δ Cathode for Protonic Ceramic Fuel Cells by Zn Doping

Proton-conducting solid–oxide fuel cell (H-SOFC) is an alternative promising low-temperature electrochemical cell for renewable energy, but the performance is insufficient because of the low activity of cathode materials at low temperatures. A layered perovskite oxide PrBaFe1.9Zn0.1O5+δ (PBFZ) was synthesized and investigated as a promising cathode material for low-temperature H-SOFC. Here, the partial substitution of Fe by Zn further enhances the electrical conductivity and thermal compatibility of PrBaFe2O5+δ (PBF). The PBFZ exhibits improved conductivity in the air at intermediate temperatures and good chemical compatibility with electrolytes. The oxygen vacancy formed at the PBFZ lattice due to Zn doping enhances proton defects, resulting in an improved performance by extending the catalytic sites to the whole cathode area. A single cell with a Ni-BZCY anode, PBFZ cathode, and BaZr0.7Ce0.2Y0.1O3-δ (BZCY) electrolyte membrane was successfully fabricated and tested at 550–700 °C. The maximum power density and Rp were enhanced to 513 mW·cm−2 and 0.3 Ω·cm2 at 700 °C, respectively, due to Zn doping.

Sr Substituted La2−xSrxNi0.8Co0.2O4+δ (0 ≤ x ≤ 0.8): Impact on Oxygen Stoichiometry and Electrochemical Properties

Lanthanide nickelate Ln2NiO4+δ (Ln = La, Pr, or Nd) based mixed ionic and electronic conducting (MIEC) materials have drawn significant attention as an alternative oxygen electrode for solid oxide cells (SOCs). These nickelates show very high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values and hence exhibit good electrocatalytic activity. Earlier reported results show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) leads to an enhancement in the transport and electrochemical properties of the material. Herein, we perform the substitution at A-site with Sr, i.e., La2−xSrxNi0.8Co0.2O4+δ, in order to further investigate the structural, physicochemical, and electrochemical properties. The structural characterization of the synthesized powders reveals a decrease in the lattice parameters as well as lattice volume with increasing Sr content. Furthermore, a decrease in the oxygen over stoichiometry is also observed with Sr substitution. The electrochemical measurements are performed with the symmetrical half-cells using impedance spectroscopy in the 700–900 °C temperature range. The total polarization resistance of the cell is increased with Sr substitution. The electrode reaction mechanism is also studied by recording the impedance spectra under different oxygen partial pressures. Finally, the kinetic parameters are investigated by analyzing the impedance spectra under polarization. A decrease in exchange current density (i0) is observed with increasing Sr content.

An Effective Strategy to Enhance the Electrocatalytic Activity of Ruddlesden−Popper Oxides Sr3Fe2O7−δ Electrodes for Solid Oxide Fuel Cells

The target of this work is to develop advanced electrode materials with excellent performance compared to conventional cathodes. Cobalt-free Ruddlesden−Popper oxides Sr3Fe2−xCuxO7−δ (SFCx, x = 0, 0.1, 0.2) were successfully synthesized and assessed as cathode materials for solid oxide fuel cells (SOFCs). Herein, a Cu-doping strategy is shown to increase the electrical conductivity and improve the electrochemical performance of the pristine Sr3Fe2O7−δ. Among all the cathode materials, the Sr3Fe1.9Cu0.1O7−δ (SFC10) cathode exhibits the best electrocatalytic activity for oxygen reduction reaction (ORR). The polarization resistance is 0.11 Ω cm2 and the peak power density of the single-cell with an SFC10 cathode reaches 955 mW cm−2 at 700 °C, a measurement comparable to cobalt-based electrodes. The excellent performance is owed to favorable oxygen surface exchange capabilities and larger oxygen vacancy concentrations at elevated temperatures. Moreover, the electrochemical impedance spectra and distribution of relaxation time results indicate that the charge transfer process at the triple-phase boundary is the rate-limiting step for ORR on the electrode. This work provides an effective strategy for designing novel cathode electrocatalysts for SOFCs.

Defect engineering of oxide perovskites for catalysis and energy storage: synthesis of chemistry and materials science

Oxide perovskites have emerged as an important class of materials with important applications in many technological areas, particularly thermocatalysis, electrocatalysis, photocatalysis, and energy storage. However, their implementation faces numerous challenges that are familiar to the chemist and materials scientist. The present work surveys the state-of-the-art by integrating these two viewpoints, focusing on the critical role that defect engineering plays in the design, fabrication, modification, and application of these materials. An extensive review of experimental and simulation studies of the synthesis and performance of oxide perovskites and devices containing these materials is coupled with exposition of the fundamental and applied aspects of defect equilibria. The aim of this approach is to elucidate how these issues can be integrated in order to shed light on the interpretation of the data and what trajectories are suggested by them. This critical examination has revealed a number of areas in which the review can provide a greater understanding. These include considerations of (1) the nature and formation of solid solutions, (2) site filling and stoichiometry, (3) the rationale for the design of defective oxide perovskites, and (4) the complex mechanisms of charge compensation and charge transfer. The review concludes with some proposed strategies to address the challenges in the future development of oxide perovskites and their applications.

Building Ruddlesden-Popper and Single Perovskite Nanocomposites: A New Strategy to Develop High-Performance Cathode for Protonic Ceramic Fuel Cells

Here a new strategy is unveiled to develop superior cathodes for protonic ceramic fuel cells (PCFCs) by the formation of Ruddlesden-Popper (RP)-single perovskite (SP) nanocomposites. Materials with the nominal compositions of LaSr_x Co_1.5 Fe_1.5 O_{10- δ} (LSCFx, x = 2.0, 2.5, 2.6, 2.7, 2.8, and 3.0) are designed specifically. RP-SP nanocomposites (x = 2.5, 2.6, 2.7, and 2.8), SP oxide (x = 2.0), and RP oxide (x = 3.0) are obtained through a facile one-pot synthesis. A synergy is created between RP and SP in the nanocomposites, resulting in more favorable oxygen reduction activity compared to pure RP and SP oxides. More importantly, such synergy effectively enhances the proton conductivity of nanocomposites, consequently significantly improving the cathodic performance of PCFCs. Specifically, the area-specific resistance of LSCF2.7 is only 40% of LSCF2.0 on BaZr_0.1 Ce_0.7 Y_0.2 O_{3- δ} (BZCY172) electrolyte at 600 °C. Additionally, such synergy brings about a reduced thermal expansion coefficient of the nanocomposite, making it better compatible with BZCY172 electrolyte. Therefore, an anode-supported PCFC with LSCF2.7 cathode and BZCY172 electrolyte brings an attractive peak power output of 391 mW cm^-2 and excellent durability at 600 °C.

Enhanced Electrochemical Performance of the Fe-Based Layered Perovskite Oxygen Electrode for Reversible Solid Oxide Cells

Reversible solid oxide cells (RSOCs) present a conceivable potential for addressing energy storage and conversion issues through realizing efficient cycles between fuels and electricity based on the reversible operation of the fuel cell (FC) mode and electrolysis cell (EC) mode. Reliable electrode materials with high electrochemical catalytic activity and sufficient durability are imperatively desired to stretch the talents of RSOCs. Herein, oxygen vacancy engineering is successfully implemented on the Fe-based layered perovskite by introducing Zr⁴⁺, which is demonstrated to greatly improve the pristine intrinsic performance, and a novel efficient and durable oxygen electrode material is synthesized. The substitution of Zr at the Fe site of PrBaFe₂O_5+δ (PBF) enables enlarging the lattice free volume and generating more oxygen vacancies. Simultaneously, the target material delivers more rapid oxygen surface exchange coefficients and bulk diffusion coefficients. The performance of both the FC mode and EC mode is greatly enhanced, exhibiting an FC peak power density (PPD) of 1.26 W cm^-2 and an electrolysis current density of 2.21 A cm^-2 of single button cells at 700 °C, respectively. The reversible operation is carried out for 70 h under representative conditions, that is, in air and 50% H₂O + 50% H₂ fuel. Eventually, the optimized material (PBFZr), mixed with Gd_0.1Ce_0.9O₂, is applied as the composite oxygen electrode for the reversible tubular cell and presents excellent performance, achieving 4W and 5.8 A at 750 °C and the corresponding PPDs of 140 and 200 mW cm^-2 at 700 and 750 °C, respectively. The enhanced performance verifies that PBFZr is a promising oxygen electrode material for the tubular RSOCs.

Pr-Doping Motivating the Phase Transformation of the BaFeO3-δ Perovskite as a High-Performance Solid Oxide Fuel Cell Cathode

Intermediate temperature solid oxide fuel cells (IT-SOFCs) have been extensively studied due to high efficiency, cleanliness, and fuel flexibility. To develop highly active and stable IT-SOFCs for the practical application, preparing an efficient cathode is necessary to address the challenges such as poor catalytic activity and CO2 poisoning. Herein, an efficient optimized strategy for designing a high-performance cathode is demonstrated. By motivating the phase transformation of BaFeO3-δ perovskites, achieved by doping Pr at the B site, remarkably enhanced electrochemical activity and CO2 resistance are thus achieved. The appropriate content of Pr substitution at Fe sites increases the oxygen vacancy concentration of the material, promotes the reaction on the oxygen electrode, and shows excellent electrochemical performance and efficient catalytic activity. The improved reaction kinetics of the BaFe0.95Pr0.05O3-δ (BFP05) cathode is also reflected by a lower electrochemical impedance value (0.061 Ω·cm2 at 750 °C) and activation energy, which is attributed to high surface oxygen exchange and chemical bulk diffusion. The single cells with the BFP05 cathode achieve a peak power density of 798.7 mW·cm-2 at 750 °C and a stability over 50 h with no observed performance degradation in CO2-containing gas. In conclusion, these results represent a promising optimized strategy in developing electrode materials of IT-SOFCs.

Insights in to the Electrochemical Activity of Fe-Based Perovskite Cathodes toward Oxygen Reduction Reaction for Solid Oxide Fuel Cells

The development of novel oxygen reduction electrodes with superior electrocatalytic activity and CO2 durability is a major challenge for solid oxide fuel cells (SOFCs). Here, novel cobalt-free perovskite oxides, BaFe1−xYxO3−δ (x = 0.05, 0.10, and 0.15) denoted as BFY05, BFY10, and BFY15, are intensively evaluated as oxygen reduction electrode candidate for solid oxide fuel cells. These materials have been synthesized and the electrocatalytic activity for oxygen reduction reaction (ORR) has been investigated systematically. The BFY10 cathode exhibits the best electrocatalytic performance with a lowest polarization resistance of 0.057 Ω cm2 at 700 °C. Meanwhile, the single cells with the BFY05, BFY10 and BFY15 cathodes deliver the peak power densities of 0.73, 1.1, and 0.89 W cm−2 at 700 °C, respectively. Furthermore, electrochemical impedance spectra (EIS) are analyzed by means of distribution of relaxation time (DRT). The results indicate that the oxygen adsorption-dissociation process is determined to be the rate-limiting step at the electrode interface. In addition, the single cell with the BFY10 cathode exhibits a good long-term stability at 700 °C under an output voltage of 0.5 V for 120 h.