Neodymium-deficient nickelate oxide Nd1.95NiO4+δ as cathode material for anode-supported intermediate temperature solid oxide fuel cells

The neodymium-deficient nickelate Nd_1.95NiO_4+δ, mixed conducting K₂NiF₄-type oxide, was evaluated as cathode for solid oxide fuel cells. The electrochemical properties were investigated on planar Ni–YSZ anode-supported SOFC based on co-tape casted and co-fired HTceramix^® cells. Using a layer of strontium doped lanthanum cobaltite as current collector, a current density of 1.31 A cm⁻² (at 0.70 V) was obtained at 800 °C using hydrogen fuel with small single cells, after optimizing the cathode sintering temperature. Impedance spectroscopy measurements were performed; the different resistive contributions and the values of the corresponding equivalent capacities are discussed.     

Electrochemical evaluation of La2NiO4+δ as a cathode material for intermediate temperature solid oxide fuel cells

La₂NiO_4+δ powders were synthesized using a polyaminocarboxylate complex precursor method. La₂NiO_4+δ electrodes were prepared on Ce_0.8Sm_0.2O_1.9 (SDC) substrates using a screen-printing technique. The microstructure feature and electrocatalytic activity of the electrodes were investigated with respect to the calcination temperature of the starting powders and sintering temperature of the electrodes. The effects of microstructure features on the electrochemical properties of La₂NiO_4+δ electrodes have been inspected. Moreover, the electrochemical performance of the La₂NiO_4+δ cathode has been evaluated based on a Ni-SDC anode supported single cell. The single cell showed a modified electrochemical performance compared with the literature results, attaining a maximum power density of 295 mW cm⁻² at 800 °C. For the single cell, applying an Au layer onto the La₂NiO_4+δ cathode led to an evident reduction of ohmic resistance and a substantial enhancement of the maximum power density to 464 mW cm⁻².     

Nd1.8Sr0.2NiO4−δ:Ce0.9Gd0.1O2−δ composite cathode for intermediate temperature solid oxide fuel cells

The (100 − x)Nd_1.8Sr_0.2NiO_4−δ:(x)Ce_0.9Gd_0.1O_2−δ (x = 00, 10, 20, 30, 40 and 50 vol%) composites are obtained by ball milling requisite mixture at 200 rotations per minute for 2 h under acetone followed by sintering at 1000 °C for 4 h. The increase in concentration of Ce_0.9Gd_0.1O_2−δ in composite reduces the crystallite size of host Nd_1.8Sr_0.2NiO_4−δ from 378 ± 0.7 to 210 ± 0.8 nm. The dc (electronic) conductivity of composite decreases moderately with an increase in Ce_0.9Gd_0.1O_2−δ content in composite up to 30 vol%, and it decreases abruptly, thereafter at x > 30. A minimum polarization resistance value of 0.24 Ω cm² (at 700 °C) is obtained for a (70)Nd_1.8Sr_0.2NiO_4−δ:(30)Ce_0.9Gd_0.1O_2−δ composite cathode, and this value is attributed to the optimal dispersion of Ce_0.9Gd_0.1O_2−δ into Nd_1.8Sr_0.2CuO_4−δ matrix. The oxygen partial pressure dependent polarization resistance study suggests that the charge transfer and the non-charge transfer oxygen adsorption–desorption along with diffusion are the major rate limiting steps of overall oxygen reduction reaction process.     

A potential interconnect material for solid oxide fuel cells: Nd0.75Ca0.25Cr0.98O3−δ

Chromium-deficient Nd_0.75Ca_0.25Cr_1−xO_3−δ (0.02 ≤ x ≤ 0.06) oxides are synthesized and assessed as a novel ceramic interconnect for solid oxide fuel cells (SOFCs). At room temperature, all the samples present single perovskite phase after sintering at 1600 °C for 10 h in air. Cr-deficiency significantly improves the electrical conductivity of Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides. No structural transformation occurs in the Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides in the temperature range studied. Among all the samples, the Nd_0.75Ca_0.25Cr_0.98O_3−δ sample with a relative density of 96.3% exhibits the best electrical conductivity of 39.0 and 1.6 S cm⁻¹ at 850 °C in air and hydrogen, respectively. The thermal expansion coefficient of Nd_0.75Ca_0.25Cr_0.98O_3−δ sample is 9.29 × 10⁻⁶ K⁻¹ in the temperature range from 30 to 1000 °C in air, which is close to that of 8 mol% yttria stabilized zirconia electrolyte (10.3 × 10⁻⁶ K⁻¹) and other cell components. The results indicate that Nd_0.75Ca_0.25Cr_0.98O_3−δ is a potential interconnect material for SOFCs.     

Preparation and characterization of Nd2−xSrxCoO4+δ cathodes for intermediate-temperature solid oxide fuel cell

K₂NiF₄-type structural Nd_2−xSr_xCoO_4+δ (x = 0.8, 1.0, 1.2) was synthesized and evaluated as cathodes for intermediate-temperature solid oxide fuel cell (IT-SOFC). The crystal structure, thermal expansion, electrical conductivity and electrochemical properties were investigated by X-ray diffraction, dilatometry, DC four-probe method, AC impedance and polarization techniques. It is found that the electrochemical properties were remarkably improved with the increasing of Sr in the experiment range. Nd_0.8Sr_1.2CoO_4+δ showed the highest electrical conductivity of 212 S cm⁻¹ at 800 °C, the lowest polarization resistance and cathodic overpotential, 0.40 Ωcm² at 700 °C and 35.6 mV at a current density of 0.1 A cm⁻² at 700 °C, respectively. The chemical compatibility experiment revealed that Nd_0.8Sr_1.2CoO_4+δ cathode was chemically stable with the SDC electrolyte. The thermal expansion coefficient also increased with the Sr content.     

A novel cobalt-free layered GdBaFe2O5+δ cathode for proton conducting solid oxide fuel cells

While cobalt-containing perovskite-type cathode materials facilitate the activation of oxygen reduction, they also suffer from problems like poor chemical stability in CO₂ and high thermal expansion coefficients. In this research, a cobalt-free layered GdBaFe₂O_5+δ (GBF) perovskite was developed as a cathode material for protonic ceramic membrane fuel cells (PCMFCs) based on proton conducting electrolyte of stable BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7). The button cells of Ni-BZCY7|BZCY7|GBF were fabricated and characterized using complex impedance technique from 600 to 700 °C. An open-circuit potential of 1.007 V, maximum power density of 417 mW cm⁻², and a low electrode polarization resistance of 0.18 Ω cm² were achieved at 700 °C. The results indicate that layered GBF perovskite is a good candidate for cobalt-free cathode material, while the developed Ni-BZCY7|BZCY7|GBF cell is a promising functional material system for solid oxide fuel cells.     

La2NiO4+δ potential cathode material on La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for intermediate temperature solid oxide fuel cell

La₂NiO_4+δ, a mixed ionic-electronic conducting oxide with K₂NiF₄ type structure, has been studied as cathode material with La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) electrolyte for intermediate solid oxide fuel cells (IT-SOFCs). XRD results reveal excellent chemical compatibility between the La₂NiO_4+δ sample and LSGM electrolyte.A single cell (0.22 cm² active area) was fabricated with La₂NiO_4+δ as cathode, Ni-Sm_0.2Ce_0.8O_1.9 (2:1; w/w) as anode and LSGM as electrolyte. A thin buffer layer of Sm_0.2Ce_0.8O_1.9 (SDC) between anode and electrolyte was used to avoid possible interfacial reactions. The cell was tested under humidified H₂ and stationary air as fuel and oxidant, respectively. The electrochemical behaviour was evaluated by means of current-voltage curves and impedance spectroscopy. Microstructure and morphology of the cell components were analysed by SEM-EDX after testing.The maximum power densities were 160, 226, and 322 mW cm⁻² at 750, 800 and 850 °C, respectively with total polarisation resistances of 0.77, 0.48 and 0.31 Ω cm² at these temperatures. Cell performance remained stable when a current density of 448 mA cm⁻² was demanded for 144 h at 800 °C, causing no apparent degradation in the cell. The performance of this material may be further improved by reducing the electrolyte thickness and optimisation of the electrode microstructure.     

Characterization and evaluation of NdBaCo2O5+δ cathode for proton-conducting solid oxide fuel cells

The layered perovskite structure oxide NdBaCo₂O_5+δ (NBCO) with rapid oxygen ion diffusion and surface exchange kinetics was synthesized by auto ignition process and initially examined as a cathode for proton-conducting fuel cells (H-SOFCs). The single cell, consisting of NdBaCo₂O_5+δ (NBCO)/BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY)/NiO–BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) structure, was assembled and tested from 650 to 700 °C with humidified hydrogen (∼3% H₂O) as the fuel and air as the oxidant. A maximum power density of 438 mW cm⁻² at 700 °C was obtained for the single cell and electrochemical performance of the cell was studied.     

Double-perovskites YBaCo2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskites YBaCo_2−xFe_xO_5+δ (YBCF, x = 0.0, 0.2, 0.4 and 0.6) are synthesized with a solid-state reaction and are assessed as potential cathode materials for utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs) on the La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMC) electrolyte. The YBCF materials exhibit chemical compatibility with the LSGMC electrolyte up to a temperature of 950 °C. The conductivity of the YBCF samples decreases with increasing Fe content, and the maximum conductivity of YBCF is 315 S cm⁻¹ at 325 °C for the x = 0.0 sample. A semiconductor-metal transition is observed at about 300-400 °C. The thermal expansion coefficient of the YBCF samples increases from 16.3 to 18.0 × 10⁻⁶ K⁻¹ in air at temperatures between 30 and 900 °C with increase in Fe content. The area-specific resistances of YBCF cathodes at x = 0.0, 0.2 and 0.4 on the LSGMC electrolyte are 0.11, 0.13 and 0.15 Ω cm² at a temperature of 700 °C, respectively. The maximum power densities of the single cells fabricated with the LSGMC electrolyte, Ce_0.8Sm_0.2O_1.9 (SDC) interlayer, NiO/SDC anode and YBCF cathodes at x = 0.0, 0.2 and 0.4 reach 873, 768 and 706 mW cm⁻², respectively. This study suggests that the double-perovskites YBCF (0 ≤ x ≤ 0.4) can be potential candidates for utilization as IT-SOFC cathodes.     

Characterization and electrochemical performances of Ba2−xSrxFeO4+δ as a novel cathode material for intermediate-temperature solid oxide fuel cells

Novel cathode materials, Ba_2−xSr_xFeO_4+δ (x = 0.5, 0.6, 0.7, 0.8, 1.0), for intermediate-temperature solid oxide fuel cells on a samaria-doped ceria (SDC) electrolyte were prepared by the glycine–nitrate route and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric (TG) analysis, electrochemical impedance spectroscopy and steady-state polarization measurement. SEM results showed that the electrode formed a good contact with the SDC electrolyte after sintering at 1000 °C for 2 h. The value of δ in Ba_1.0Sr_1.0FeO_4+δ materials was calculated from the TG results. The electrochemical impedance spectra revealed that Ba_2−xSr_xFeO_4+δ had a better electrochemical performance than that of Ln₂NiO₄ (Ln = La, Pr, Nd, Sm). In the Ba_2−xSr_xFeO_4+δ (x = 0.5, 0.6, 0.7, 0.8, 1.0) family, the composition Ba_1.0Sr_1.0FeO_4+δ exhibited the best electrochemical activity for oxygen reduction. The polarization resistance of Ba_1.0Sr_1.0FeO_4+δ on SDC electrolyte was 1.11 Ω cm² at 700 °C, which was less than half that reported for Ln₂NiO₄ at the same temperature.     

Novel layered perovskite oxide PrBaCuCoO5+δ as a potential cathode for intermediate-temperature solid oxide fuel cells

A novel layered perovskite oxide PrBaCuCoO_5+δ (PBCCO) is employed as a potential cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Thermal expansion and electrochemical performance on samarium-doped ceria (SDC) electrolyte are evaluated. The thermal expansion coefficient (TEC) of PrBaCuCoO_5+δ (PBCCO) is close to that of SDC electrolyte and electrical conductivity of PrBaCuCoO_5+δ (PBCCO) reaches the general required value of cathode material. Symmetrical electrochemical cell with the configuration of PrBaCuCoO_5+δ (PBCCO)/SDC/PrBaCuCoO_5+δ (PBCCO) applied for the impedance studies, the area specific resistance of PrBaCuCoO_5+δ (PBCCO) cathode is as low as 0.047 Ω cm² at 700 °C. A maximum power density of 791 mW cm⁻² is obtained at 700 °C for the single cell consisting of PrBaCuCoO_5+δ (PBCCO)/SDC/NiO-SDC. Preliminary results indicate that PrBaCuCoO_5+δ (PBCCO) is especially promising as a cathode for IT-SOFCs.     

Sr0.92Y0.08TiO3−δ/Sm0.2Ce0.8O2−δ anode for solid oxide fuel cells running on methane

Yttria-doped strontium titanium oxide (Sr_0.92Y_0.08TiO_3−δ; SYT) was investigated as an alternative anode material for solid oxide fuel cells (SOFCs). The SYT synthesized by the Pechini method exhibits excellent phase stability during the cell fabrication processes and SOFC operation and good electrical conductivity (about 0.85 S/cm, porosity 30%) in reducing atmosphere. The performance of SYT anode is characterized by slow electrochemical reactions except for the gas-phase diffusion reactions. The cell performance with the SYT anode running on methane fuel was improved about 5 times by SDC film coating, which increased the number of reaction sites and also accelerated electrochemical reaction kinetics of the anode. In addition, the SDC-coated SYT anode cell was stably operated for 900 h with methane. These results show that the SDC-coated SYT anode can be a promising anode material for high temperature SOFCs running directly on hydrocarbon fuels.     

Sr2Fe1.5Mo0.5O6−δ as a regenerative anode for solid oxide fuel cells

Sr₂Fe_1.5Mo_0.5O_6−δ (SFM) was prepared using a microwave-assisted combustion synthesis method. Rietveld refinement of powder X-ray diffraction data reveals that SFM crystallizes in the simple cubic perovskite structure with iron and molybdenum disordered on the B-site. No structure transition was observed by variable temperature powder X-ray diffraction measurements in the temperature range of 25-800 °C. XPS results show that the iron and molybdenum valences change with an increase in temperature, where the mixed oxidation states of both iron and molybdenum are believed to be responsible for the increase in the electrical conductivity with increasing temperature. SFM exhibits excellent redox stability and has been used as both anode and cathode for solid oxide fuel cells. Presence of sulfur species in the fuel or direct utilization of hydrocarbon fuel can result in loss of activity, however, as shown in this paper, the anode performance can be regenerated from sulfur poisoning or coking by treating the anode in an oxidizing atmosphere. Thus, SFM can be used as a regenerating anode for direct oxidation of sulfur-containing hydrocarbon fuels.     

Cobalt-free Sr0.7Y0.3CuO2+δ as a cathode for intermediate-temperature solid oxide fuel cell

Cobalt-free oxide Sr_0.7Y_0.3CuO_2+δ (SYCu) with one-dimensional structure has been investigated as potential cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. The crystal structure, chemical compatibility, thermal expansion and electrochemical performance were examined by X-ray diffraction technique, electrochemical workstation and thermal dilatometer. One-dimensional structure Sr_1−xY_xCuO_2+δ and Sr_2−xY_xCuO_3+δ phases appeared as the main parts after calcination above 900 °C. The copper based oxide SYCu showed a thermal expansion coefficient (TEC) about 11.1 × 10⁻⁶/°C at 25–800 °C, exhibiting good physical compatibility with samarium doped cerium (SDC) electrolyte. High electro-catalytic performance was obtained for SYCu cathode in a symmetrical cell with a polarization resistance (R_p) of 0.029 Ω cm² and an overpotential of 4.9 mV at 100 mA/cm² at 800 °C, showing great promising use as cathode materials for IT-SOFCs. In addition, the polarization resistance of SYCu cathode remain constant after operation at 800 °C for 100 h, showing excellent long-term stability at operation temperature.     

Scandium-doped PrBaCo2−xScxO6−δ oxides as cathode material for intermediate-temperature solid oxide fuel cells

Scandium-doped PrBaCo_2−xSc_xO_6−δ(PBCS-x, x = 0.00–1.00) oxides have been evaluated as cathode materials of intermediate-temperature solid oxide fuel cells (IT-SOFCs) with respect to phase structure, oxygen content, thermal expansion behavior and electrical and electrochemical properties. The XRD results have demonstrated a phase transition in PBCS-x due to Sc³⁺ doping from tetragonal double-layered perovskite structure at x = 0.00–0.20, bi-phase mixtures at x = 0.30–0.40, to cubic perovskite structure at x = 0.50–0.90. The oxygen contents (6-δ) and average valences of cobalt ions in PBCS-x decrease with the higher Sc³⁺ content and increasing temperatures in air. Sc³⁺ doping has also led to decreased thermal expansion coefficients, lowered electrical conductivities and enhanced electrochemical reaction activities for PBCS-x characterized by decreased area-specific resistances (ASRs) and smaller reaction activation energies. Among the studied samples, the PBCS-0.50 oxide with Sc³⁺-doping content of x = 0.50 exhibits the best electrochemical performance on Ce_0.9Gd_0.1O_1.95 electrolyte. Its ASR values range from 0.123 Ω cm² at 600 °C to 0.022 Ω cm² at 750 °C, which are much lower than the related cathode materials. These results have demonstrated that the PBCS-0.50 oxide is a promising cathode material for IT-SOFCs.     

Novel layered perovskite GdBaCoFeO5+δ as a potential cathode for proton-conducting solid oxide fuel cells

While cobalt-containing perovskite-type cathode materials facilitate the activation of oxygen reduction, they also suffer from problems like poor chemical stability in CO₂, high thermal expansion coefficients, etc. Partial B site substitution with Fe element is expected to be able to mitigate these problems while keeping high catalyst performance. In this paper, a layered perovskite GdBaCoFeO_5+δ (GBCF) was developed as a cathode material for protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolyte of stable BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7). The button cells of Ni-BZCY7|BZCY7|GBCF were fabricated and tested from 600 to 700 °C with humidified H₂ (∼3% H₂O) as a fuel and ambient oxygen as oxidant. An open-circuit potential of 1.002 V, maximum power density of 482 mW cm⁻², and a low electrode polarization resistance of 0.11 Ωcm² were achieved at 700 °C. The experimental results indicated that the layered perovskite GBCF is a good candidate for cathode material, while the developed Ni-BZCY7|BZCY7|GBCF cell is a promising functional material system for intermediate temperature solid oxide fuel cells.     

La0.9−xCaxCe0.1CrO3−δ as potential anode materials for solid oxide fuel cells

LaCrO₃ doped with calcium and cerium on the A-site in the series of La_0.9−xCa_xCe_0.1CrO_3−δ (LCCC3060, LCCC4050, LCCC5040, LCCC6030 corresponding to x = 0.6, 0.5, 0.4, and 0.3 respectively), is synthesized by a sol–gel combustion method and evaluated as anode material for solid oxide fuel cells (SOFCs). Relatively higher Ca-doping on La in LaCrO₃ is found to improve both electronic and ionic conductivity. LCCC compositions have demonstrated good chemical stability in reducing atmospheres. Evaluation of the LCCC material as anode in symmetrical cell configuration shows that the highest Ca-doping composition results in the lowest activation energy and the lowest polarization resistance. La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM) electrolyte-supported single cells with LCCC3060 as the anode and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) as the cathode show that LCCC3060 can be a potential anode material for H₂, but not for CH₄.     

Effect of DC current polarization on the electrochemical behaviour of La2NiO4+δ and La3Ni2O7+δ-based systems

The electrode performance of La₂NiO₄ and La₃Ni₂O₇ as cathode materials for solid oxide fuel cells (SOFC) was analyzed. The study was focused on the electrode polarization resistance of the interfaces formed by the cathodes with Ce_0.8Sm_0.2O_2−δ + 2%Co electrolyte. The study was extended to cathodes based on La₂NiO₄-Ce_0.8Sm_0.2O_2−δ composite and Pt to analyze the effect of changing the electronic and/or ionic transport properties on the electrode interface resistance. The electrode performance was studied in open circuit conditions and with DC current polarization. Important differences in the performance of the pure cathode materials were obtained as function of DC current flux. However, in La₂NiO₄-Ce_0.8Sm_0.2O_2−δ composite the DC current flux produces minor changes in the electrode polarization resistance. The aging process also affects the OCV electrode performance of cathodes based on Pt and pure ceramics, whereas the effect is practically invaluable in La₂NiO₄-Ce_0.8Sm_0.2O_2−δ composite. The electrode performance is higher for the composite cathode compared to pure ceramic electrodes for OCV or for low values of DC polarization. However, the important decrease in the interface resistance obtained for high values of DC current flux for La₂NiO₄ and La₃Ni₂O₇ cathodes increases their electrode performances to values close to those obtained in La₂NiO₄-Ce_0.8Sm_0.2O_2−δ composite. This retains the cathode overpotential with values as low as 140 mV at 750 °C for values of current load of 530 mA cm⁻² for both pure and composite La₂NiO₄-based cathodes. The low cathode overpotential allows to estimate values of power density between 300 and 350 mW cm⁻² at 750 °C for La₂NiO₄, La₃Ni₂O₇ and La₂NiO₄-Ce_0.8Sm_0.2O_2−δ composite, operating with Ce_0.8Sm_0.2O_2−δ + 2%Co electrolyte, with 300 μm in thickness, and a Ni-Ce_0.8Sm_0.2O_2−δ cermet anode with H₂ as fuel.     

LaCo0.6Ni0.4O3−δ as cathode contact material for intermediate temperature solid oxide fuel cells

LaCo_0.6Ni_0.4O_3−δ (LCN64) was prepared through the polymeric steric entrapment precursor route with Polyvinyl alcohol (PVA) as the entrapment agent and was evaluated as a contact material between the metallic interconnect and the cathode in planar intermediate temperature solid oxide fuel cell stacks (IT-SOFC). The ratio of PVA to metal nitrates and the calcination temperature of the precursor were optimized for the process. The electrical conductivity and thermal expansion coefficient (TEC) of the synthesized LCN64 and its chemical compatibility with SUS 430 were also characterized. The results indicate that 1:4 is a proper ratio of PVA to metal nitrates for process control and safety management; and calcination of the precursor at temperatures above 650 °C leads to formation of single perovskite phase LCN64. The conductivity of fully sintered LCN64 is above 1150 S cm⁻¹ in the temperature range between 100 °C and 800 °C, which is higher than those of conventional contact materials La_1−xSr_xMnO₃ (LSM) and LaNi_yFe_1−yO₃ (LNF). The average TEC is 17.22 × 10⁻⁶ K⁻¹ at temperatures below 900 °C, which is higher than those of the metallic interconnect and cell components. Mn and Cr elements contained in SUS 430 migrated into the porous LCN64 layer at 800 °C without chemically forming resistive phases.     

Microstructure and reactivity effects on the performance of Nd2NiO4+δ oxygen electrode on Ce0.9Gd0.1O1.95 electrolyte

The effect of electrode microstructure on the electrochemical behavior of symmetrical Nd₂NiO_4+δ/Ce_0.9Gd_0.1O_1.95/Nd₂NiO_4+δ cells was studied by Electrochemical Impedance Spectroscopy as a function of temperature (500 < T < 750 °C) and oxygen partial pressure (10⁻⁴ < pO₂ < 1 atm). Nd₂NiO_4+δ powders were synthesized by Solid State Reaction, HMTA and Citrates. The samples observed by Scanning Electron Microscopy presented very different microstructures. Three characteristic processes were distinguished at high, medium and low frequency. High frequency contribution was attributed to oxygen ion transfer electrode/electrolyte. Medium frequency contribution was related to oxygen interstitial bulk diffusion and oxygen incorporation in those cases in which the surface of small particles is affected by chemical reactivity with the electrolyte. The low frequency contribution was attributed to dissociative adsorption for electrodes with small particle sizes and high porosity, and a co-limited process of adsorption and gas diffusion for an electrode with dense microstructure and low porosity.