Coated interconnects development for high temperature water vapour electrolysis: Study in anode atmosphere

High temperature water vapour electrolysis (HTE) is an efficient technology for hydrogen production. In this context, a commercial stainless steel, K41X (AISI 441), was chosen as interconnect. In a previous paper, the high temperature corrosion and the electrical conductivity were evaluated in both anode (O₂–H₂O) and cathode (H₂–H₂O) atmosphere at 800 °C. In O₂–H₂O atmosphere, the formation of a thin chromia protective layer was observed. Nevertheless, the ASR parameter measured was higher than the maximum accepted value. These results, in addition with chromium evaporation measurements, proved that the K41X alloy is not suitable for HTE interconnect application. In this study, two perovskite-type oxides La_0.8Sr_0.2MnO_3−δ and LaNi_0.6Fe_0.4O_3−δ were tested as coatings in O₂–H₂O atmosphere at 800 °C. Screen-printing and physical vapour deposition were used as coating processes. The high temperature corrosion resistance and the electrical conductivity were improved, especially with the LaNi_0.6Fe_0.4O_3−δ coating. Cr specie volatility was also reduced.     

Development of a novel type of composite cathode material for proton-conducting solid oxide fuel cells

A high-performance solid oxide fuel cell La_1−xSr_xMnO₃ (LSM) cathode/metallic interconnect contact material Ni_1−xCo_xO, added with the mixed ionic-electronic conducting Sm_0.2Ce_0.8O_2−δ (SDC), was proposed as a novel composite cathode for proton-conducting solid oxide fuel cells (H-SOFCs) with BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb) as the electrolyte. The X-ray diffraction (XRD) results indicated that the maximum doped ratio of Ni_1−xCo_xO was Ni_0.7Co_0.3O (NC3O), also shown that NC3O was chemically compatible with SDC at temperatures up to 1400 °C. The TEC of NC3O was also measured to check its thermal compatibility with other components. Laboratory-sized tri-layer cells of NiO–BZCYYb/BZCYYb/NC3O-SDC were fabricated and tested with humidified hydrogen (∼3% H₂O) as fuel and static air as oxidant, respectively. A maximum power density of 204 mW cm⁻² and a low interfacial polarization resistance Rp of 0.683 Ω cm² were achieved at 700 °C. The results have indicated that the NC3O-SDC composite is a simple, stable and cost-effective cathode material for H-SOFCs.     

Chemical compatibility and electrical contact between Ni–Cr–Mo alloy and LaCo0.6Ni0.4O3−δ in intermediate temperature solid oxide fuel cells

The contact resistance and chemical compatibility of LaCo_0.6Ni_0.4O_3−δ (LCN) coated Ni–Mo–Cr alloy are investigated at 750 °C in air for more than 530 h to simulate the contact situation of cathode/contact layer/interconnect in SOFC stacks. With La_0.72Sr_0.18MnO₃ (LSM) as the cathode, the area specific resistance (ASR) of LSM/LCN/Ni–Mo–Cr alloy assembly increases to a maximum of 240 mΩ cm² during the early stage of the test, and decreases after 55 h to a steady level of ∼220 mΩ cm² till the end of the test. The contribution of formed oxide scale on the alloy to the measured ASR is negligible, compared to that of big AgLaMo₂O₈ particles sporadically distributed in LCN matrix. AgLaMo₂O₈ is formed of evaporated Mo from the alloy, Ag from the testing lead and La from the LCN before the oxide scale on the alloy is well developed. This reaction is expected to cease once the oxide scale is fully established.     

La substituted Sr2MnO4 as a possible cathode material in SOFC

Sr_2−xLa_xMnO_4+δ (x = 0.4, 0.5, 0.6) oxides were studied as the cathode material for solid oxide fuel cells (SOFC). The reactivity tests indicated that no reaction occurred between Sr_2−xLa_xMnO_4+δ and CGO at annealing temperature of 1000 °C, and the electrode formed good contact with the electrolyte after being sintered at 1000 °C for 4 h. The total electrical conductivity, which has strong effect on the electrode properties, was determined in a temperature range from 100 to 800 °C. The maximum value of 5.7 S cm⁻¹ was found for the x = 0.6 phase at 800 °C in air. The cathode polarization and AC impedance results showed that Sr_1.4La_0.6MnO_4+δ exhibited the lowest cathode overpotential. The area specific resistance (ASR) was 0.39 Ω cm² at 800 °C in air. The charge transfer process is the rate-limiting step for oxygen reduction reaction on Sr_1.4La_0.6MnO_4+δ electrode.     

Investigation of La0.6Sr0.4Co1-xNixO3-δ (x=0, 0.2, 0.4, 0.6, 0.8) catalysts on solid oxide fuel cells anode for biogas dry reforming

The introduction of catalyst on anode of solid oxide fuel cell (SOFC) has been an effective way to alleviate the carbon deposition when utilizing biogas as the fuel. A series of La_0.6Sr_0.4Co_1-xNi_xO_3-δ (x = 0, 0.2, 0.4, 0.6, 0.8) oxides are synthesized by sol-gel method and used as catalysts precursors for biogas dry reforming. The phase structure of La_0.6Sr_0.4Co_1-xNi_xO_3-δ oxides before and after reduction are characterized by X-ray diffraction (XRD). The texture properties, carbon deposition, CH₄ and CO₂ conversion rate of La_0.6Sr_0.4Co_1-xNi_xO_3-δ catalysts are evaluated and compared. The peak power density of 739 mW cm^?2 is obtained by a commercial SOFC with La_0.6Sr_0.4Co_0.4Ni_0.6O_3-δ catalyst at 850 °C when using a mixture of CH₄: CO₂ = 2:1 as fuel. This shows a great improvement from the cell without catalyst for internal dry reforming, which is attributed to the formation of NiCo alloy active species after reduction in H₂ atmosphere. The results indicate the benefits of inhibiting the carbon deposition on Ni-based anode through introducing the La_0.6Sr_0.4Co_0.4Ni_0.6O_3-δ catalyst precursor. Additionally, the dry reforming technology will also help to convert part of the exhaust heat into chemical energy and improve the efficiency of SOFC system with biogas fuel.     

Electrochemical performance of Sr1.9La0.1Fe1.5Mo0.5O6-δ symmetric electrode for solid oxide fuel cells with carbon-based fuels

La-doped Sr_2-xLa_xFe_1.5Mo_0.5O_6-δ perovskite oxides are synthesized and used as a symmetric electrode to evaluate the effect of La on the crystal structure, conductivity, and catalytic activity for O₂ reduction and H₂ oxidation reaction. The electronic doping effect dominates the oversize effect in Sr_2-xLa_xFe_1.5Mo_0.5O_6-δ oxide, resulting in unit cell volume expansion and decreased conductivity in air. In addition, the introduction of La increases the chemical structural stability of Sr₂Fe_1.5Mo_0.5O_6-δ in reducing condition due to the higher La–O bond compared with Sr–O bond, leading to high catalytic activity for the H₂ oxidation reaction. At 800 °C, the R_p values of Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ symmetric cell in air and wet H₂ are as low as 0.075 and 0.21 Ω cm², respectively. Moreover, the peak power densities of 769, 561, 439, and 653 mW cm^?2 at 850 °C are obtained when wet H₂, CO, CH_4, and C₃H₈ are used as fuels on Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ/LSGM/Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ cell. The symmetric cell also shows excellent stability (>100 h) in wet H₂/air, implying Sr_1.9La_0.1Fe_1.5Mo_0.5O_6-δ oxide is a promising symmetric electrode material.     

Enhancing catalysis activity of La0.6Sr0.4Co0.8Fe0.2O3-δ cathode for solid oxide fuel cell by a facile and efficient impregnation process

The development of high performance electrocatalysts to promote oxygen reduction reaction (ORR) and to prolong the durability of cathodes of solid oxide fuel cell is essential at intermediate or low temperatures. Here, we report a facile and efficient spray impregnation strategy in enhancing catalytic activity of La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ (LSCF) due to the introduction of a multitude of homogeneous nanoparticles. With a highly active surface abundance in B-site cations, the modified LSCF cathode manifests an area-specific resistance (ASR) of ∼0.140 Ω cm², only a fifth of that for a pristine LSCF cathode (∼0.764 Ω cm²) at 600 °C, and anode-supported fuel cells with the decorated LSCF cathode show markedly improved peak power densities (∼0.94 W cm⁻² at 700 °C). Furthermore, the ORR kinetics of the modified LSCF cathode can be further enhanced by impregnating Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O solution again. X-ray photoelectron spectroscopy analysis indicates that the homogeneous nanoparticles alter the distribution of Sr_surface and O_surface. It is found that ‘Co’ decoration can effectively alleviate the surface aggregation of Sr and ‘Co’ and ‘Ni’ decoration play a pivotal role in the reactivation of electrode surface.     

Efficient dual layer interconnect coating for high temperature electrochemical devices

Effects of novel dual layer coatings Co₃O₄/La_0.85Sr_0.15MnO_3−δ on high temperature oxidation behaviour of candidate steels for interconnects are studied at 1123 K in flowing simulated ambient air (air + 1% H₂O) and oxygen. Four alloys are investigated: Crofer 22 APU, Crofer 22 H, E-Brite and AL 29-4C. The reaction kinetics is followed by measuring the mass increase of the samples over time. The oxide scale microstructure and chemical composition are investigated by scanning electron microscopy/energy dispersive spectroscopy. The kinetic data follow the parabolic rate law. It is found that the oxidation reaction is limited by outward Cr³⁺ diffusion in the chromia scale. The coating effectively reduces the oxidation rate. Reactions and cation inter-diffusion between the coating and the oxide scale are observed. Long term effects of these interactions are discussed and practical implications for interconnect electrochemical performance are suggested.     

Electrochemical performance of La0.65Sr0.35MnO3 oxygen electrode with alternately infiltrated Sm0.5Sr0.5CoO3-δ and Sm0.2Ce0.8O1.9 nanoparticles for reversible solid oxide cells

La_1-xSr_xMnO₃ is a well-known oxygen electrode for reversible solid oxide cells (RSOCs). However, its poor ionic conductivity limits its performance in redox reaction. In this study, we selected Sm_0.5Sr_0.5CoO_3-δ (SSC) as catalyst and Sm_0.2Ce_0.8O_1.9 (SDC) as ionic conductor and sintering inhibitor to co-modify the La_0.65Sr_0.35MnO₃ (LSM) oxygen electrode through an alternate infiltration method. The infiltration sequence of SSC and SDC showed an influence on the morphology and performance of LSM oxygen electrode, and the influence was gradually weakened with the increasing infiltration time. The polarization resistance of the alternately infiltrated LSM-SSC/SDC electrode was 0.08 Ω cm² at 800 °C in air, which was 3.36% of the LSM electrode (2.38 Ω cm²). The Ni-YSZ/YSZ/LSM-SSC/SDC single cell attained a maximum power density of 1205 mW cm^?2 in SOFC mode at 800 °C, which was 8.73 times more than the cell with LSM electrode. The current density achieved 1620 mA .cm^?2 under 1.5 V at 800 °C in SOEC mode and the H₂ generation rate was 3.47 times of the LSM oxygen electrode.     

Sr1−xPrxCo0.95Sn0.05O3−δ ceramic as a cathode material for intermediate-temperature solid oxide fuel cells

In this study, the physical properties of the Sr_1−xPr_xCo_0.95Sn_0.05O_3−δ ceramics were measured and their potential for use as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs) was evaluated. A cubic phase was retained in all of the Sr_1−xPr_xCo_0.95Sn_0.05O_3−δ ceramics. Analysis of the temperature-dependent conductivity found the SrCo_0.95Sn_0.05O_3−δ and Sr_0.9Pr_0.1Co_0.95Sn_0.05O_3−δ ceramics exhibiting semiconductor-like behavior below 550 °C and metal-like behavior above the same temperature. The Sr_0.8Pr_0.2Co_0.95Sn_0.05O_3−δ and Sr_0.7Pr_0.3Co_0.95Sn_0.05O_3−δ ceramics, however, reported a metal-like conductivity in the whole temperature range. The electrical conductivities of the Sr_0.8Pr_0.2Co_0.95Sn_0.05O_3−δ ceramic at 500 °C and 700 °C read respectively 1250 S/cm and 680 S/cm, both of which were superior than those in most of the common perovskites. Single cells with a structure of NiO–Sm_0.2Ce_0.8O_2−δ (SDC)/SDC/Sr_0.8Pr_0.2Co_0.95Sn_0.05O_3−δ-SDC were built and characterized. Addition of SDC in Sr_0.8Pr_0.2Co_0.95Sn_0.05O_3−δ emerged to be a crucial factor reducing the ohmic resistance (R₀) and polarization resistance (R_P) of the cell by facilitating a better adhesion to and electrical contact with the electrolyte layer. The R₀ and R_P of the cell read respectively 0.068 Ω cm² and 0.0571 Ω cm² at 700 °C and 0.298 Ω cm² and 1.310 Ω cm² at 550 °C. With no microstructure optimization and hermetic sealing of the cells, maximum power density (MPD) and open circuit voltage (OCV) reached respectively 0.872 W/cm² and 0.77 V at 700 °C and 0.482 W/cm² and 0.86 V at 550 °C. It is evident that Sr_1−xPr_xCo_0.95Sn_0.05O_3−δ is a promising cathode material for IT-SOFCs.     

Co-free La0.6Sr0.4Fe0.9Nb0.1O3-δ symmetric electrode for hydrogen and carbon monoxide solid oxide fuel cell

Co-free La_0.6Sr_0.4FeO_3-δ (LSFNb₀) and La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ (LSFNb_0.1) perovskite oxides were prepared by a standard solid-state reaction method. The structural stability and electrochemical performance of La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ as both cathode and anode were studied. Nb dopant in LSFNb₀ significantly enhances the structural and chemical stability in anode condition. At 800 °C, the polarization resistances (Rp) of LSFNb_0.1 symmetric electrode based on YSZ electrolyte are 0.5 and 0.05 Ω cm² in H₂ and air, respectively. The peak power densities of LSFNb_0.1 based on LSGM electrolyte-supported SSOFCs are 934 and 707 mW cm⁻² at 850 °C in H₂ (3% H₂O) and dry CO, respectively. Moreover, the symmetric cell exhibits reasonable stability in both H₂ and CO fuel, suggesting that La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ may be a potential symmetric electrode material for hydrogen and carbon monoxide SOFCs.     

Investigating the electrochemical performance of Nd1-xSrxCo0.8Fe0.2O3−δ (0 ≤ x ≤ 0.85) as cathodes for intermediate temperature solid oxide fuel cells

Perovskite-type structure oxides with the nominal chemical composition Nd_1-xSr_xCo_0.8Fe_0.2O_3−δ (0 ≤ x ≤ 0.85) (NSCF) were synthesized by solid-state method to investigate the effect of Sr-doping on the crystal structure and electrochemical performance in the intermediate temperature range of 600 °C–750 °C. The electrical conductivity of the sintered NSCF pellets was found to be in the range of 300–1000 S cm⁻¹. All the NSCF compositions showed a transition from semiconducting to metallic behavior with an increase in temperature. NSCF showed reactivity with the La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The electrochemical performance was tested by preparing the symmetrical cells with the configuration 70 wt% NSCF +30 wt% LSGM using LSGM electrolyte in the temperature range of 650–800 °C. AC-impedance results showed a decrease in polarization resistance (Rp) of the cathode with increase in Sr-doping due to increase in electrical conductivity. Among the samples studied, composite electrode of Nd_0.3Sr_0.7Co_0.8Fe_0.2O_3−δ – LSGM showed the lowest area specific resistance (ASR) of 0.1 Ω cm² at 750 °C in air. It was chosen to investigate the effect of pO₂ on the electrochemical performance of the cathode to determine the rate determining step (RDS) in oxygen reduction reaction (ORR). Dissociation of molecular oxygen into oxygen atoms seems to be the RDS in the ORR.     

Optimization of Sr content in layered SmBa1–xSrxCo2O5+δ perovskite cathodes for intermediate-temperature solid oxide fuel cells

Cation ordered perovskites have been recognized as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This study focuses on the effects of Sr substitution on crystal characteristics, electrical properties, and electrochemical performance of SmBa_1−xSr_xCo₂O_5+δ (x = 0, 0.25, 0.5, 0.75, and 1.0) as an IT-SOFC cathode material. The electrical conductivity improves with increasing Sr content due to the greater amount of electronic holes originated from the increased interstitial oxygen. The area specific resistances (ASRs) of SmBa_1−xSr_xCo₂O_5+δ decrease with Sr content up to x = 0.75 and increase abruptly for x = 1. For x = 0.75, the lowest ASR value, 0.138 Ω cm², and the highest single cell performance, 1.039 W cm⁻² at 600 °C, are obtained. These results indicate that SmBa_1−xSr_xCo₂O_5+δ is optimized at x = 0.75 in terms of obtaining the best performance for IT-SOFCs.     

Electrocatalytic activity of perovskite La1−xSrxMnO3 towards hydrogen peroxide reduction in alkaline medium

Perovskite-type series of compounds La_1−xSr_xMnO₃ are synthesized by a sol-gel method using Chitosan as the gelling agent. Their catalytic activity for hydrogen peroxide electroreduction in 3.0 mol dm⁻³ KOH at room temperature is evaluated by means of cyclic voltammetry and chronoamperometry. Effects of annealing temperature and the ratio of La to Sr of La_1−xSr_xMnO₃ on their catalytic performance are investigated. Among this series of compounds, La_0.4Sr_0.6MnO₃ calcined at 650 °C exhibits the highest activity, which is comparable with Co₃O₄. An aluminum-hydrogen peroxide semi-fuel cell using La_0.4Sr_0.6MnO₃ as cathode catalyst achieves a peak power density of 170 mW cm⁻² at 170 mA cm⁻² and 1.0 V running on 0.6 mol dm⁻³ H₂O₂.     

CuxCo3-xO4-δ (0≤x≤1) coatings for solid oxide fuel cell interconnect applications

In order to obtain the solid oxide fuel cell (SOFC) interconnect coatings with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion, a series of Cu_xCo_3-xO_4-δ (x = 0, 0.5, 0.8, and 1.0) coatings are prepared by supersonic spraying via subsequent sintering. The chemical composition, lattice and morphological structures, electrical properties, and thermal expansion are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), area-specific resistance (ASR), and coefficient of thermal expansion (CTE) measurements. The experimental results show that the formation of CuCo₂O₄ is a reversible and incomplete reaction at the elevated temperature, and the coexistence of CuO, Co₃O₄, and CuCo₂O₄ is inevitable in the coatings. The concentration of the chemicals mentioned above is highly related to the coatings’ Cu:Co molar ratio. The correlation between the chemical composition and the properties is comprehensively studied in this research. The Cu_xCo_3-xO_4-δ coatings exhibit good electrical conductivity when 0 ≤ x ≤ 0.8, satisfactory protectiveness when 0.5 ≤ x ≤ 1.0, and fitting CTE with remarkable robustness through the quick heating-cooling cycles when 0.8 ≤ x ≤ 1.0. In general, Cu_0.8Co_2.2O_4-δ can be an appropriate candidate to meet the advancing interconnect coating demands with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion properties.     

Thin films of La0.7Sr0.3MnO3−δ dip-coated on Fe–Cr alloys for SOFC metallic interconnect

La_0.7Sr_0.3MnO_3−δ (LSM) porous films were deposited on different ferritic stainless steels (SS) (430: Cr-16.0%; 439: Cr-16.6%; 444: Cr-17.4%) by sol–gel/dip-coating process. The structure, morphology and composition profiles of investigated assemblies were examined using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The area specific resistance (ASR) was measured during long term oxidation in air at 800 °C for 200 h by DC measurements. ASR values lower than 10 mΩ cm² were recorded after 200 h for LSM-coated SS439 and SS444. This is likely to be due to the high Cr content and to Nb, Ti and Mo elements used to stabilize the stainless steel against oxidation. This paper shows that LSM coatings provide an enhanced stability of the alloy at high temperature and the formation of an interfacial Cr–Mn spinel layer hinders the oxide scale growth.     

Easy sintering of silver doped lanthanum strontium manganite current collector for solid oxide fuel cells

A new system, (La_0.8Sr_0.2)_1−xAg_xMnO_3+δ (LSAM, x ≤ 0.2), is developed as current collector for solid oxide fuel cell (SOFC). LSAM is prepared by a modified sol-gel method and presents a single phase. The shrinkage temperature reduces from 1150 °C to 800 °C with an addition of 15 mol% Ag to La_0.8Sr_0.2MnO_3+δ (LSM20). The contact resistance between the current collector and the cathode is measured, and the influence of Ag content on the contact resistance is investigated. The result shows that the contact resistance using (La_0.8Sr_0.2)_0.85Ag_0.15MnO_3+δ (LSAM15) as current collector is about 12 mΩ cm² at 750 °C, which is close to the value using expensive Pt paste as current collector. This new system is a promising current collecting material for the practical application of SOFC.     

In-situ exsolved FeRu alloy nanoparticles on Ruddlesden-Popper oxides for direct hydrocarbon fuel solid oxide fuel cells

FeRu alloy (FRA) nanoparticles surface decorated Ruddlesden-Popper type layer perovskite PrSrFe_1-xRu_xO_4+δ (RP-PSFeRu) was prepared by in-situ reduction of the cubic (Pr_0.5Sr_0.5)_0.9Fe_0.9Ru_0.1O_3-δ (P–PSFeRu) in H₂ at 800 °C. When used as the SOFC anode material, it has excellent catalytic activity for H₂ and hydrocarbon fuels. The La_0.8Sr_0.2Ga_0.83Mg_0.17O_3-δ electrolyte supported SOFC single cell with RP-PSFeRu-FRA-GDC composite anode can deliver a maximum power density of 0.75 and 0.50 W cm⁻² in wet H₂ and C₃H₈ at 800 °C, respectively. Furthermore, the single cell shows a stability outputs at a constant current load of 0.5 A cm⁻² in wet H₂ and 0.15 A cm⁻² in wet C₃H₈ fuels, indicating an exceptional stability and cooking resistance.     

Enhanced H2 production by using La5.5WO11.25-δ-La0.8Sr0.2FeO3-δ mixed oxygen ion-proton-electron triple-conducting membrane

Although lanthanum tungstates (Ln_nWO_12-δ) show superior CO₂-tolerance compared to the traditional perovskite-type oxides, their hydrogen permeation fluxes are not competitive. Herein, a mixed oxygen ion-proton-electron triple-conducting membrane with a nominal composition of La_5.5WO_11.25-δ-La_0.8Sr_0.2FeO_3-δ (LWO-LSF) was developed for H₂ production. The triple-conducting membrane is composed of a LWO phase with proton conductivity and a LSF phase with mixed oxygen ion-electron conductivities. In the LWO-LSF membrane, proton (H⁺) permeation and oxygen ion (O²⁻) counter-permeation property was simultaneously displayed. The improved H₂ production can be ascribed to (1) hydrogen permeated as H⁺ through LWO phase, and (2) hydrogen produced from water splitting that is enhanced by O²⁻ counter-permeation through LSF phase. A higher H₂ flux of 0.15 mL min⁻¹ cm⁻² was achieved at 900 °C using LWO-LSF triple-conducting membrane, compared with the conventional proton-electron conducting membranes LWO or La_5.5WO_11.25-δ-La_0.8Sr_0.2CrO_3-δ (LWO-LSC). Furthermore, the constant H₂ fluxes in various atmospheres indicated the good stability of LWO-LSF membrane in simulated raw hydrogen.     

Evaluation of layered perovskites YBa1−xSrxCo2O5+δ as cathodes for intermediate-temperature solid oxide fuel cells

This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa_1−xSr_xCo₂O_5+δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The high oxygen nonstoichiometry, δ = 0.18–0.43 at 700 °C, indicates the large oxygen vacancy concentrations in oxides. The electrical conductivity is improved due to the greater amount of electronic holes originated from the increased interstitial oxygen, and the conductivities of all samples are above 100 S cm⁻¹ at 400–700 °C in air. The results demonstrate the promising performance of YBa_1−xSr_xCo₂O_5+δ cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21–0.59 Ω cm² at 700 °C. The lowest ASR, 0.44 Ω cm², and the cathodic overpotential, −40 mV at a current density of −136 mA cm⁻², are obtained in YBaCo₂O_5+δ cathode at 650 °C. The dependence of polarization resistance on oxygen partial pressure suggests that the charge transfer process is the rate-limiting step for oxygen reduction reaction in YBaCo₂O_5+δ cathode.