Double Perovskite Cathodes Research Articles

Lithium doping enhanced ORR kinetics and CO2 tolerance of iron-based double perovskite cathode for solid oxide fuel cells

Fe-based double perovskites exhibit significant potential as cathode materials for solid oxide fuel cells (SOFCs) owing to their affordability, moderate thermal expansion, and impressive stability. Nevertheless, their practical utility has been constrained by their comparatively lower oxygen reduction reaction (ORR) catalytic activity. In this study, for the first time, lithium (Li) was employed as a dopant to improve the ORR activity of the Fe-based double perovskite PrBaFe2O5+δ (PBFO). The results indicated that the ratios of Fe3+/Fe2+ and Oads/Olat were effectively tuned by incorporating Li at Ba-sites of PBFO. Consequently, the adsorption and dissociation of oxygen, along with the charge transfer processes were regulated significantly, resulting in an increase in ORR kinetics and improved CO2 resistance. At 800 °C, PrBa0.9Li0.1Fe2O5+δ (PBLFO) demonstrated an Rp of 0.072 Ω cm², which was decreased by 43.3% compared to PBFO. Simultaneously, the maximum power density of PBLFO-based full cell was improved by 23.3%, reaching 670 mW cm−2. These findings suggest that Li-doping holds great potential for improving the performance of Fe-based SOFC cathodes, thereby contributing to the advancement of clean and sustainable energy technologies.

Review on Fe-based double perovskite cathode materials for solid oxide fuel cells

As a clean and efficient energy conversion device, solid oxide fuel cells have been garnering attention due to their environmentally friendly and fuel adaptability. Consequently, they have become one of the current research directions of new energy. The cathode, as the electrochemical reaction site of an oxidation atmosphere in solid oxide fuel cells, plays a key role in determining the output performance. In recent years, the development of double perovskite cathode materials with mixed ionic and electronic conductors has made significant progress in intermediate-temperature (600-800 °C) fuel cells. These materials have the potential to deliver higher power densities and improved stability, making them promising candidates for future fuel cell applications. The Fe-based double perovskite structure cathode material has gained extensive attention due to its adjustable crystal structure and performance, as it has A(A’) or B(B’) positions in its AA’BB’O6 structure. This material has several advantages, such as high oxygen catalytic activity, low thermal expansion coefficient, and compatibility with the thermal expansion of the electrolyte. An increasing number of researchers have been exploring the performance reaction mechanism of double perovskite by modifying and adjusting its material microstructure, crystal structure, and electronic structure. In this paper, the research progress of LnBaFe2O5 and Sr2Fe2-xMoxO6 double perovskite cathode materials is reviewed to highlight the effects of various modification methods developed on electrochemical performance of these materials. Furthermore, the potential future research directions of double perovskite cathode materials are prospected.

An acidity-regulated double perovskite cathode for efficient and durable power generation of intermediate-temperature solid oxide fuel cells

This work reports a double perovskite oxide EuBa0.5Sr0.5Co2−xFexO5+δ (EBSCFx, x = 0.5, 1, and 1.5) as cathode for IT-SOFC. Specifically, the cell using EBSCF1.0 cathode delivers excellent performance with a PPD of 1.50 W cm−2 at 650 °C.

High entropy double perovskite cathodes with enhanced activity and operational stability for solid oxide fuel cells

Rare-earth site high entropy double perovskite oxides with different molar ratios have been evaluated as the cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFC). The effect of configuration entropy on crystal structure, electrical conductivity, electrochemical performance and stability are investigated. Our results reveal that the activity of all high entropy oxides show enhanced electrochemical activity. Among them, the equimolar one (HEO) exhibits the highest activity with a low polarization resistance of 0.05 Ω cm2 at 700 °C. Moreover, it exhibits excellent stability in the CO2-containing atmosphere. The enhanced activity and operational stability can be attributed to reduced surface Ba segregation and the formation of active and robust BaCoO3-δ nanoparticles on HEO surface, rather than BaCO3 and Co3O4 phases. This work indicates that configurational entropy engineering is very effective for rational surface composition regulation.

Implications of Cation Interdiffusion between Double Perovskite Cathode and Proton-Conducting Electrolyte for Performance of Solid Oxide Fuel Cells

Chemical compatibility and cation interdiffusion between the double perovskite cobaltites RBaCo2O6−δ (R = Gd, Pr) and proton-conducting electrolyte BaZr0.8Y0.2O3−δ were studied. Chemical interaction was found to occur already at 1100 °C as a result of the partial dissolution of RBaCo2O6−δ (R = Gd, Pr) in BaZr0.8Y0.2O3−δ. Analysis of the element distribution along the cross sections of diffusion couples RBaCo2O6−δ(R = Gd, Pr)|BaZr0.8Y0.2O3−δ showed strong interdiffusion of cations, with cobalt being the most mobile one. Its diffusion depth in the electrolyte reaches up to several hundreds of micrometers. The addition of NiO as a sintering aid to BaZr0.8Y0.2O3−δ promotes cation diffusion especially through the grain boundary mechanism, increasing the diffusion depth of Co. The possible implications of cation interdiffusion on the performance of proton-conducting SOFCs are discussed based on the results obtained.

Structural, particle size distribution, and electrochemical behavior of double perovskite oxide doped Ce0.8Sm0.2O1.9 for intermediate temperature solid oxide fuel cells

Double perovskite SmBa0.5Sr0.5Co2O5+δ(70%)+Ce0.8Sm0.2O1.9(30%) as SBSC70+SDC30 cathode was fabricated using solid-state reaction technique and investigated as cathode material for solid oxide fuel cells operating at intermediate temperature (IT-SOFC). This work aims to determine the effect of SDC electrolyte doping into double perovskite cathodes on SOFC performance. LS-POP carried out particle size distribution analysis, and the equipment operates on a light source (HE-Ne laser) basis. XRD was used to determine the structure of the cathode powder, and SEM was used to analyze the microstructure morphology. Symmetrical cells were tested using a potentiostat Voltalab PGZ 301. The distribution of particle size for the SBSC70+SDC30 cathode was in the range of 1.41-2.03 µm. The polarization resistance (Rp) value of SBSC70+SDC30 cathode decreases with increasing temperature from 1.22 cm2 at 600°C to 0.21 cm2 at 800°C. The SBSC70+SDC30 activation energy (Ea) for Rp was 117. 3 kJ mol−1. From the overall results, double perovskite SBSC70+SDC30 cathode has potential as a cathode of medium temperature SOFC cells.

Enhanced Compatibility and Activity of High-entropy Double Perovskite Cathode Material for IT-SOFC

Enhanced Compatibility and Activity of High-entropy Double Perovskite Cathode Material for IT-SOFC

High-entropy approach to double perovskite cathode materials for solid oxide fuel cells: Is multicomponent occupancy in (La,Pr,Nd,Sm,Gd)BaCo2O5+δ affecting physicochemical and electrocatalytic properties?

High-entropy (La,Pr,Nd,Sm,Gd)BaCo2O5+δ double perovskite-type oxide having an equimolar, high-entropy, A-site-layered arrangement of cations is synthesized for the first time. A modified Pechini method, followed by calcination and sintering at 1,100°C helps in obtaining a single-phase, homogenous material with tetragonal I4/mmm symmetry. In situ X-ray diffraction and dilatometric studies show excellent phase stability up to 1,100°C in air, with the average thermal expansion coefficient of 23.7∙10–6 K−1 within the 25–1,100°C range. Total electrical conductivity of the metallic character exceeds 1,600 S cm−1 at room temperature. Equilibrated oxygen content at room temperature is determined as 5.69. The cathodic polarization resistance of the (La,Pr,Nd,Sm,Gd)BaCo2O5+δ layers, manufactured on the La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM) solid electrolyte of proved inertness, is as low as 0.037 Ω cm2 at 900°C, and 0.175 Ω cm2 at 750°C. The determined value of the power density in the LSGM-based, electrolyte-supported (thickness ca. 200 μm) fuel cell reaches 857 mW cm−2. These results indicate possible applicability of the developed cathode material for solid oxide fuel cells, making it also one of the best-performing high-entropy air electrodes reported until now. However, the determined physiochemical characteristics of the material indicate a relatively limited influence of the high-entropy A-site arrangement in comparison to the conventional analogs, including the synthesized Nd0.88Sm0.12Co2O5+δ composition, characterized by the same effective radius of the lanthanide cations.

Novel CO2-tolerant Co-based double perovskite cathode for intermediate temperature solid oxide fuel cells

For the commercial application of solid oxide fuel cells (SOFCs), CO2-tolerant cathode materials with high electrochemical activity are required. Here, we discuss the performance of double perovskite Pr0.2Sr1.8CoTiO6−δ (P02STC) as a potential cathode material for SOFCs. P02STC has a cubic structure and keeps lattice structure stable in the CO2 atmosphere. The average thermal expansion coefficient is 17.8 × 10–6 K–1 at 30–900 °C in air. The P02STC cathode exhibits good electrochemical performance with a low polarization resistance of 0.080 Ωcm2 at 700 °C. The P02STC cathode shows good structure stability, electrochemical performance stability, and excellent tolerance to CO2 poisoning for the symmetrical cells based on the 350 h stability test in air and the 150 h stability test in O2 containing 5%CO2 at 700 °C. The electrolyte-supported single cell with a P02STC cathode shows a maximum power density of 677 mW cm− 2 at 800 °C. The single cell operates stably for 250 h at a constant current of 0.3 A/cm2 without obvious degrading performance. According to all of the experimental results, the P02STC sample might be a promising candidate cathode for SOFCs.

Probing Zr Substituting Effects on the Oxygen Reduction Reaction of Fe-Based Double Perovskite Cathodes for Solid Oxide Fuel Cells

Probing Zr Substituting Effects on the Oxygen Reduction Reaction of Fe-Based Double Perovskite Cathodes for Solid Oxide Fuel Cells

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

Mixed oxygen ionic and electronic conduction is a vital function for cathode materials of solid oxide fuel cells (SOFCs), ensuring high efficiency and low-temperature operation. However, Fe-based layered double perovskites, as a classical family of mixed oxygen ionic and electronic conducting (MIEC) oxides, are generally inactive toward the oxygen reduction reaction due to their intrinsic low electronic and oxygen-ion conductivity. Herein, Zn doping is presented as a novel pathway to improve the electrochemical performance of Fe-based layered double perovskite oxides in SOFC applications. The results demonstrate that the incorporation of Zn ions at Fe sites of the PrBaFe2O5+δ (PBF) lattice simultaneously regulates the concentration of holes and oxygen vacancies. Consequently, the oxygen surface exchange coefficient and oxygen-ion bulk diffusion coefficient of Zn-doped PBF are significantly tuned. The enhanced mixed oxygen ionic and electronic conduction is further confirmed by a lower polarization resistance of 0.0615 and 0.231 Ω·cm2 for PrBaFe1.9Zn0.1O5+δ (PBFZ0.1) and PBF, respectively, which is measured using symmetric cells at 750 °C. Moreover, the PBFZ0.1-based single cell demonstrates the highest output performance among the reported Fe-based layered double perovskite cathodes, rendering a peak power density of 1.06 W·cm-2 at 750 °C and outstanding stability over 240 h at 700 °C. The current work provides a highly effective strategy for designing cathode materials for next-generation SOFCs.

Enhancing the oxygen reduction activity of PrBaCo2O5+δ double perovskite cathode by tailoring the calcination temperatures

In this study, the oxygen reduction activity of PrBaCo2O5+δ (PBC) double perovskite is remarkably enhanced by rationally tuning the calcination temperatures of the cathode precursor for solid oxide fuel cells (SOFCs). Effects of the calcination temperatures on the phase structure, microstructure, surface area and oxygen reduction reaction (ORR) activity of PBC cathode is systematically investigated. The cathode with optimized calcination temperature (900 °C, PBC-900) shows excellent activity and stability for ORR at 600 °C in terms of area specific resistances (ASRs). A distinctive low ASR of 0.068 Ω cm2 is obtained at 600 °C for PBC-900, which is 92.6%, 34.6% and 15.0% lower than PBC-800, PBC-1000 and PBC-1100, respectively. After operating for 250 h in air at 600 °C, the ASR value of PBC-900 is not significantly reduced. Furthermore, a single cell with PBC-900 cathode delivers attractive peak power density of 1.60 W cm−2 at 600 °C. The present study suggests that the ORR activity of PBC cathode can be greatly boosted by rationally tailoring the calcination temperatures, which may bring new avenue for the design of highly active cathodes for SOFCs.

Study of a Promising Co-Doped Double Perovskite Cathode Material for IT-SOFCs

Based on the high catalytic activity and mixed ionic and electronic conductivity, double layered perovskites have been recognized as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). A recent study has outlined that the synergic effect of co-doping high valence cations (Nb5+ and Ta5+) on a simple perovskite (SrCo1.8Ta0.1Nb0.1O5+δ) has created an optimal balance of oxygen vacancies, ionic mobility and surface electron transfer which results with a drop of the ASR and a promising power density of the fuel cell. In this study, a co-doped double layered perovskite, LnBa0.5Sr0.5Co1.8Ta0.1Nb0.1O5+δ (Ln = Sm and Pr), was evaluated as IT-SOFC cathode material. The properties of the materials were analyzed with yttria stabilized zirconia and gadolinium-doped ceria electrolytes. As result, the Ta-Nb co-doped materials exhibits excellent chemical compatibility with typical electrolyte material and good electrochemical performance over 100 hours, making them as a promising cathode material for applications in IT-SOFCs.

Heterostructured simple perovskite nanorod-decorated double perovskite cathode for solid oxide fuel cells: Highly catalytic activity, stability and CO2-durability for oxygen reduction reaction

Apart from conventional composite materials, in situ exsolution for constructing the heterostructure is one of the most effective strategies to design the high-performance electro-catalysts. Herein we report a novel heterostructured simple perovskite nanorod-decorated A site-deficient double perovskite PrBa0.94Co2O5+δ (SPN-A-PBC) cathode, synthesized by an in situ exsolving process from A site-deficient double perovskite PrBa0.94Co2O5+δ (A-PBC). The results demonstrate a highly electro-catalytic activity of the SPN-A-PBC cathode toward oxygen reduction reaction (ORR) for intermediate-temperature solid oxide fuel cells (IT-SOFCs), achieving a very low and stable polarization resistance of ˜0.025 Ω cm2 at 700 °C in air. The anode-supported single cell with this heterostructured cathode delivers a maximum power density of 1.1 W cm−2 at 700 °C and a superior steady operation over 120 h at a loading voltage of 0.6 V. Furthermore, the SPN-A-PBC electrode exhibits a good tolerance to CO2. When tested in air with 6 vol% CO2 at 700 °C, the SPN-A-PBC electrode still maintains a stable polarization resistance of ˜0.078 Ω cm2. The unique catalytic activity of the SPN-A-PBC cathode for ORR may be attributed to extended active sites, abundant interface defects, enhanced redox property and oxygen mobility. The fast ORR kinetics and excellent durability in air with CO2 highlight the potential of SPN-A-PBC as a potential functional material in the energy conversion devices.

New reduced-temperature ceramic fuel cells with dual-ion conducting electrolyte and triple-conducting double perovskite cathode

New reduced-temperature ceramic fuel cells with dual-ion conducting electrolyte and triple conducting double perovskite cathode.

Effect of Cation Ordering on the Performance and Chemical Stability of Layered Double Perovskite Cathodes.

The effect of A-site cation ordering on the cathode performance and chemical stability of A-site cation ordered LaBaCo2O5+δ and disordered La0.5Ba0.5CoO3−δ materials are reported. Symmetric half-cells with a proton-conducting BaZr0.9Y0.1O3−δ electrolyte were prepared by ceramic processing, and good chemical compatibility of the materials was demonstrated. Both A-site ordered LaBaCo2O5+δ and A-site disordered La0.5Ba0.5CoO3−δ yield excellent cathode performance with Area Specific Resistances as low as 7.4 and 11.5 Ω·cm2 at 400 °C and 0.16 and 0.32 Ω·cm2 at 600 °C in 3% humidified synthetic air respectively. The oxygen vacancy concentration, electrical conductivity, basicity of cations and crystal structure were evaluated to rationalize the electrochemical performance of the two materials. The combination of high-basicity elements and high electrical conductivity as well as sufficient oxygen vacancy concentration explains the excellent performance of both LaBaCo2O5+δ and La0.5Ba0.5CoO3−δ materials at high temperatures. At lower temperatures, oxygen-deficiency in both materials is greatly reduced, leading to decreased performance despite the high basicity and electrical conductivity. A-site cation ordering leads to a higher oxygen vacancy concentration, which explains the better performance of LaBaCo2O5+δ. Finally, the more pronounced oxygen deficiency of the cation ordered polymorph and the lower chemical stability at reducing conditions were confirmed by coulometric titration.

Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

18O and 2H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCo2O5+δ (PBCO) in flowing air containing 200 mbar of 2H216O. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity (~1.3 × 10−11 cm2s−1) at this temperature and that the presence of water (2H216O), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of ~3. The 2H distribution, as inferred from the 2H216O− SIMS signal, shows an apparent depth profile which could be interpreted as 2H diffusion. However, examination of the 3-D distribution of the signal shows it to be nonhomogeneous and probably related to the presence of hydrated layers in the interior walls of pores and is not due to proton diffusion. This suggests that PBCO acts mainly as an oxygen ion mixed conductor when used in PCFC devices, although the presence of a small amount of protonic conductivity cannot be discounted in these materials.

Novel Gradient-Porosity Structure Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

A-site cation ordered double perovskite cathode, especially LnBaCo2O5+δ series, have drawn great interests due to their faster oxygen ion diffusion and higher electrical conductivity[1-3].As a promising SOFC cathode with highest oxygen diffussion coefficient (D*) among the mixed ionic and electronic conductor (MIEC)[4], PrBaCo2O5+ δ exhibits great oxygen reduction reaction(ORR) catalytic activity and electrochemical performance[5] .Here we proposed a gradient-porosity PrBaCo2O5+ δ SOFC cathode. The top-layer of the cathode was highly porous while the sub-layer much denser. Gases’ adsorption plays important roles in ORR process, thus pores’ distribution has great influence on cathode’s performance[6]. Higher porosity means more ORR active regions but less ions paths, and vice versa. There is a trade-off between gases path and ions path. And gradient-porosity cathode aiming at increasing gases adsorption region at gas-contacted surface of cathode about 3-5um depth, at the meantime ensure ions’ fast transfer by enlarge cathode-electrolyte contacted regions. This targeted modification will enhanced cathode’s ORR activity and can be adopted in SOFC’s practical application. [1] Q. Zhou, T. He, Y. Ji, J. Power Sources, 185,754-758 (2008) .[2] A. Chang, S.J. Skinner, J.A. Kilner, Solid State Ion, 177,2009-2011 (2006) .[3] S. Choi, S. Yoo, J. Kim, S. Park, A. Jun, S. Sengodan, J. Kim, J. Shin, H.Y. Jeong, Y. Choi, Sci. Rep, 3 (2013).[4] A. Tarancón, M. Burriel, J. Santiso, S.J. Skinner, J.A. Kilner, J. Mater. Chem, 20,3799-3813 (2010) .[5] D. Chen, R. Ran, K. Zhang, J. Wang, Z. Shao, J. Power Sources, 188,96-105 (2009) .[6] S. Skinner, J. Kilner, Solid State Ion, 135,709-712 (2000) .

Improved electrochemical performance and thermal expansion compatibility of LnBaCoFeO5+δ–Sm0.2Ce0.8O1.9 (Ln[dbnd]Pr and Nd) composite cathodes for IT-SOFCs

To improve electrochemical performance and thermal expansion compatibility of LnBaCoFeO5+δ (P(N)BCF; LnPr and Nd) double perovskite cathodes, P(N)BCF–xCe0.8Sm0.2O1.9 (P(N)BCF–xSDC; x = 20–50 wt%) composites were developed as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). P(N)BCF materials exhibited good chemical compatibility with SDC at 1150 °C for 5 h. Electrical conductivity and thermal expansion coefficient (TEC) of the P(N)BCF–xSDC composite cathodes decreased with increasing SDC content. The introduction of SDC into P(N)BCF improved the electrochemical performance of P(N)BCF–xSDC composite cathodes. The P(N)BCF–xSDC composite cathodes containing 40 wt% and 30 wt% SDC displayed the best electrochemical performance: the area specific resistances were 0.037 and 0.046 Ω cm2 at 800 °C; the maximum power densities achieved 960 and 891 mW cm−2 at 800 °C for PBCF–40SDC and NBCF–30SDC composite cathodes, respectively. These results suggested that the introduction of SDC into P(N)BCF cathodes was very effective in reducing the TEC and improving the electrochemical performance, making the PBCF–40SDC and NBCF–30SDC composites more suitable as IT-SOFC cathodes.

A-site calcium-doped Pr1−xCaxBaCo2O5+δ double perovskites as cathodes for intermediate-temperature solid oxide fuel cells

The LnBaCo2O5+δ (Ln = rare earth) double perovskite cathodes possess superior electrochemical performance in intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, high thermal expansion coefficients (TECs) and material costs are major challenges to their widespread applications. In this paper, a novel A-site Ca doping strategy that can suppress the spin-state transition of Co3+ is proposed to reduce the TECs and material costs of Pr1−xCaxBaCo2O5+δ (x = 0.1–0.4; PCBCO). Substitution of Ca for Pr effectively reduces the TEC from 22.2 × 10−6 K−1 at x = 0.1 to 19.1 × 10−6 K−1 at x = 0.3 between 100 and 800 °C. PCBCO exhibits good chemical compatibility with the Sm0.2Ce0.8O1.9 (SDC) electrolyte. The area-specific resistances of PCBCO cathodes with x = 0.1, 0.2, and 0.3 are 0.081, 0.082, and 0.089 Ω cm2, respectively, at 700 °C on the SDC electrolyte. The maximum power densities of a single cell on a 0.3 mm-thick SDC electrolyte reach 646.5, 636.8, and 620.6 mW cm−2 at 800 °C for cathodes with x = 0.1, 0.2, and 0.3, respectively. The PCBCO double perovskites exhibit excellent chemical compatibility and electrochemical performance while reducing the TECs and material costs; thus, these double perovskites are promising cathode materials for applications in IT-SOFCs.