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.     

Performances of SmBaCoCuO5+δ–Ce0.9Gd0.1O1.95 composite cathodes for intermediate-temperature solid oxide fuel cells

SmBaCoCuO_5+δ–xCe_0.9Gd_0.1O_1.95 (SBCCO–xGDC, x = 10, 30, 50, 60, wt%) composite cathodes have been investigated for their potential utilization in intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion behavior shows that the thermal expansion coefficient (TEC) values of SBCCO cathode decrease with GDC addition. The TEC of SBCCO–50GDC cathode is 13.1 × 10⁻⁶ K⁻¹ from 30 to 850 °C in air. By means of DC polarization and AC impedance spectroscopy, the electrochemical performance of SBCCO–xGDC composite cathodes on GDC electrolyte is examined. Results indicate that the proper addition of GDC could improve the performance of SBCCO cathode. The optimum content of GDC in the composite cathodes is 50 wt% with the polarization resistance (R_p) of 0.040 Ω cm² at 800 °C. An electrolyte-supported single-cell configuration of SBCCO–50GDC/GDC/Ni–GDC attains a maximum power density of 628 mW cm⁻² at 800 °C. Preliminary results indicate that SBCCO–50GDC is especially promising as a cathode for IT-SOFCs.     

Effect of B2O3–Bi2O3–PbO frit on the performance of LaBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The effects of B₂O₃–Bi₂O₃–PbO (BBP) frit on the electrochemical performance, electrical conductivity, and thermal expansion of LaBaCo₂O_5+δ (LBCO) cathode were investigated. BBP frit was found to be effective in lowering the sintering temperature of LBCO cathode by about 200 °C and in improving its electrochemical performance within the intermediate-temperature range of 600–800 °C. LBCO with 5 wt.% BBP frit cathode based on Sm_0.2Ce_0.8O_1.9 electrolyte showed the best electrochemical performance, i.e., the lowest area-specific resistance (ASR) and cathodic overpotential. The ASR values were about 64.1%, 66.1%, and 74.5% lower than those of LBCO at 700, 750, and 800 °C, respectively. The cathodic overpotential decreased from 51.0 mV for LBCO to 8.2 mV at a current density of 0.2 A cm⁻² at 700 °C. The electrical conductivity of LBCO with 5 wt.% BBP frit was about 320–330 S cm⁻¹ at 600–800 °C in air.     

Synthesis, characterization and evaluation of PrBaCo2−xFexO5+δ as cathodes for intermediate-temperature solid oxide fuel cells

Iron doped layered structured perovskites, PrBaCo_2−xFe_xO_5+δ (x = 0, 0.5, 1.0, 1.5 and 2.0), are evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of dopant content are investigated on their structural and electrochemical properties including crystalline structure, oxygen nonstoichiometry, stability in presence of CO₂, compatibility with electrolytes, thermal expansion coefficient, electrical conductivity, and cathodic interfacial polarization resistance. The lattice parameter and oxygen nonstoichiometry content, δ, at room temperature increase, whereas the conductivity, thermal expansion coefficient, and cathodic performance decrease with increasing iron content, x. PrBaCo_2−xFe_xO_5+δ exhibit excellent stability at 700 °C in atmosphere consisting of 3% CO₂ and 97% air, show good chemical compatibility with doped ceria electrolytes at 1000 °C, but react readily with yttria-stabilized zirconia at 700 °C. Even with a Co-free PrBaFe₂O_5+δ as the electrode, a symmetrical cell demonstrates area specific resistance of 0.18 Ω cm² at 700 °C with samaria-doped ceria electrolyte. The resistance is lower than those for typical Co-free electrodes reported in the literatures, suggesting that PrBaCo_2−xFe_xO_5+δ are potential promising cathode materials for IT-SOFCs.     

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.     

Novel SrCo1−yNbyO3−δ cathodes for intermediate-temperature solid oxide fuel cells

Perovskite oxides SrCo_1−yNb_yO_3−δ (SCNy, y = 0.00-0.20) are investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. Compared to the undoped SrCoO_3−δ, the Nb doping significantly improves the thermal stability and enhances the electrical conductivity of the SCNy oxides. The cubic phase of the SCNy oxides with high thermal stability can be totally obtained when the Nb doping content y ≥ 0.10. Among the investigated compositions, the SrCo_0.9Nb_0.1O_3−δ oxide exhibits the highest electrical conductivity of 461-145 S cm⁻¹ over the temperature range of 300-800 °C in air. The SCNy cathode has a good chemical compatibility with the LSGM electrolyte for temperatures up to 1050 °C for 5 h. The area specific resistances of SCNy with y = 0.10, 0.15 and 0.20 cathodes on LSGM electrolyte are 0.083, 0.099 and 0.110 Ω cm² at 700 °C, respectively. At y = 0.10, 0.15 and 0.20, the maximum power densities of a single-cell with SCNy cathodes on 300-μm thick LSGM electrolyte achieve 675, 642 and 625 mW cm⁻² at 800 °C, respectively. These results indicate that SCNy perovskite oxides with cubic phase are potential cathode materials for application in IT-SOFCs.     

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.     

Mn1.5Co1.5O4−δ infiltrated yttria stabilized zirconia composite cathodes for intermediate-temperature solid oxide fuel cells

The composite cathodes of yttria stabilized zirconia (YSZ) and Mn_1.5Co_1.5O₄ (MCO) are prepared by infiltration of the MCO oxides into porous YSZ backbones using aqueous solutions of the corresponding nitrate salts. Calcinations at 850 °C promote the formation of the MCO spinel oxide and yield nano-scale catalyst coatings on the YSZ pore walls. Impedance measurements on the symmetric MCO–YSZ cathode fuel cells show that the lowest polarization resistance in air at 800 °C is 0.43 Ω cm² for the MCO impregnated YSZ composite at the MCO volume loading of 13.5%. Analysis of the impedance spectra suggest that the oxygen reduction kinetics is probably limited by double ionization of the adsorbed oxygen atoms or charge transfer at the triple-phase boundaries. Furthermore, introducing the oxide ion conductor of samarium-doped ceria as a second component in the coated catalysts yields much lower polarization resistances, e.g., 0.15 Ω cm² at 800 °C.     

Characterization of SmBaCoFeO5+δ−Ce0.9Gd0.1O1.95 composite cathodes for intermediate-temperature solid oxide fuel cells

The performance of SmBaCoFeO_5+δ (SBCF)–xCe_0.9Gd_0.1O_1.95 (GDC) (x = 0, 10, 30, 50, 60, wt%) composite cathodes has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion coefficient (TEC) and electrochemical property measurements are employed to study the materials. The XRD results prove that there is no serious reaction between SBCF and GDC oxides even at 1000 °C. The thermal expansion behavior shows that the TEC value of SBCF cathode decreases greatly with GDC addition. The addition of GDC to SBCF cathode further reduces the polarization resistance. The lowest polarization resistance of 0.036 Ω cm² is achieved at 800 °C for SBCF–50GDC composite cathode. An electrolyte-supported fuel cell is prepared using SBCF–50GDC as cathode and NiO–GDC (65:35 by weight) as anode. The cell generates good performance with the maximum power density of 691 mW cm⁻², 503 mW cm⁻² and 337 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively. Preliminary results indicate that SBCF–50GDC is especially promising as a cathode for IT-SOFCs.     

Characterization of cation-ordered perovskite oxide LaBaCo2O5+δ as cathode of intermediate-temperature solid oxide fuel cells

A-site cation-ordered perovskite oxide LaBaCo₂O_5+δ (LBCO) was synthesized and evaluated as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs). LBCO was structurally stable when calcined at 850 °C in air but transformed into cation-disordered structure at 1050 °C. LBCO showed chemical compatibility with Gd_0.1Ce_0.9O_1.95 (GDC) electrolyte at 850 °C and 1000 °C in air. Conductivity of LBCO firstly increased slightly with higher temperature to a maximum of 470 S cm⁻¹ at ∼250 °C and then decreased gradually with further increase in temperature. Electrochemical impedance spectra of the LBCO/GDC/LBCO symmetric cell were measured, and electrode reaction mechanism for the LBCO cathode was analyzed. The electrode polarization resistance of LBCO was mainly contributed by oxygen ionic transfer across the cathode/electrolyte interface and oxygen atom diffusion-electronic charge transfer process. Low area-specific resistances with values ranging from 0.15 Ω cm² at 650 °C to 0.0086 Ω cm² at 800 °C were obtained. These results have demonstrated that the A-site cation-ordered perovskite oxide LBCO is a promising cathode material for IT-SOFCs.     

Oxygen reduction mechanism of NdBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells under cathodic polarization

The oxygen reduction reaction mechanism of NdBaCo₂O_5+δ cathode for intermediate-temperature solid oxide fuel cells was investigated by the electrochemical impedance spectroscopy under cathodic polarization. The Nyquist diagrams showed the different changes with the applied cathodic voltage at three temperature ranges: at 500 and 550 °C, at 600 °C, at 650 and 700 °C, which might be related to the changes in the charge transfer and/or oxygen diffusion processes including O₂ adsorption/desorption. Besides, the diffusion process was more easily affected by the increase of applied cathodic voltages than the charge transfer process, which was ascribed to the low activation energy of the diffusion process.     

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.     

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.     

High-performance PrBaCo2O5+δ-Ce0.8Sm0.2O1.9 composite cathodes for intermediate temperature solid oxide fuel cell

PrBaCo₂O_5+δ-Ce_0.8Sm_0.2O_1.9 (PBCO-SDC) composite material are prepared and characterized as cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction result proves that there are no obvious reaction between the PBCO and SDC after calcination at 1100 °C for 3 h. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures shows that the addition of SDC to PBCO improved remarkably the electrochemical performance of a PBCO cathode, and that a PBCO-30SDC cathode exhibits the best electrochemical performance in the PBCO-xSDC system. The total interfacial resistances R_p is the smallest when the content of SDC is 30 wt%, where the value is 0.035 Ω cm² at 750 °C, 0.072 Ω cm² at 700 °C, and 0.148 Ω cm² at 650 °C, much lower than the corresponding interfacial resistance for pure PBCO. The maximum power density of an anode-supported single cell with PBCO-30SDC cathode, Ni-SDC anode, and dense thin SDC/LSGM (La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ)/SDC tri-layer electrolyte are 364, 521 and 741 mW cm⁻² at 700, 750 and 800 °C, respectively.     

Self-assembled Fe-doped PrBaCo2O5+δ composite cathodes with disorder transition region for intermediate-temperature solid oxide fuel cells

PrBa(Co_1-xFe_x)₂O_5+δ polymorphs (0.1 < x < 0.4, denoted as PBCF-x with Fe-doping level x) are reported and dual phase of cubic phase Pr_0.5Ba_0.5Co_1−xFe_xO_3−δ and tetragonal phase PrBa(Co_1-xFe_x)₂O_5+δ are co-produced through an common sol–gel method. The co-generation of the dual-phases leads to the formation of abundant hetero-interfaces between the neighboring crystal phases and the synergic effect demonstrates remarkably high oxygen adsorption and dissociation ability in the air. The density functional theory (DFT) calculation establishes that the existence of hetero-interfaces promotes oxygen reduction reaction activity (ORR) which is crucial to improve cathode performance of proton-conducing solid oxide fuel cells (H–SOFCs). Moreover, an outstanding electrochemical performance is obtained for the single cell with a PBCF03 cathode and the research demonstrates that a self-assemble dual phase cathode can be an effective approach for developing high-performing H–SOFCs.     

SrCo1−yTiyO3−δ as potential cathode materials for intermediate-temperature solid oxide fuel cells

The perovskites SrCo_1−yTi_yO_3−δ (SCTy, y = 0.00-0.20) are synthesized and assessed as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. SCTy composites with y ≥ 0.05 adopt a cubic perovskite structure with thermal stability between 30 °C and 1000 °C in air. Substitution of Ti significantly enhances the electrical conductivity of the SCTy composites relative to the undoped SrCoO_3−δ. The highest electrical conductivity of the sample with y = 0.05 varied from 430 S cm⁻¹ to 160 S cm⁻¹ between 300 °C to 800 °C in air. The area-specific resistances of the SCTy cathodes on the LSGM electrolyte gradually increase from 0.084 Ω cm² at y = 0.05 to 0.091 Ω cm² at y = 0.20 with increasing Ti content at 750 °C. Single-cells that used SCTy cathodes with y = 0.05, 0.10, 0.15, and 0.20 on a 300 μm-thick LSGM electrolyte achieve peak power densities of 793, 608, 525, and 425 mW cm⁻² at 800 °C, respectively. These novel SCTy cubic perovskites demonstrate considerable potential for application in IT-SOFC cathodes.     

Chemical compatibility, thermal expansion matches and electrochemical performance of SrCo0.8Fe0.2O3−δ-La0.45Ce0.55O2−δ composite cathodes for intermediate-temperature solid oxide fuel cells

The chemical compatibility, thermal expansion and electrochemical property measurements of the SrCo_0.8Fe_0.2O_3−δ (SCF)-La_0.45Ce_0.55O_2−δ (LDC) composite cathodes for solid oxide fuel cells (SOFCs) were investigated by X-ray diffraction (XRD), thermal expansion coefficients (TECs) and cathodic polarization measurements together with electrochemical impedance spectroscopy (EIS). The results indicated that LDC had good chemical compatibility with SCF and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM), and the addition of LDC to SCF markedly reduced the polarization resistance. When the content of LDC reached 50 wt%, the SCF50 cathode showed the best electrochemical performance, with a cathodic overpotential of 0.1 V at the current density of 1102.0 mA cm⁻², together with a polarization resistance of 0.149 Ω cm² at 800 °C. The improved electrochemical performance was attributed to the expansion of the electrochemical reaction region into the electrode, and offering an easier path for the oxygen ion transport. Furthermore, the SCF-LDC composite cathodes match better with the LSGM electrolyte.     

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.     

Nanosized Ce0.8Sm0.2O1.9 infiltrated GdBaCo2O5+δ cathodes for intermediate-temperature solid oxide fuel cells

In this paper, Ce_0.8Sm_0.2O_1.9 (SDC) nanoparticles modified GdBaCo₂O_5+δ (GBCO) cathodes were fabricated by an infiltration technique and evaluated for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Good chemical compatibility between GBCO and infiltrated SDC was confirmed by X-ray diffraction (XRD) characterization. SDC nanoparticles (∼40 nm) formed continuous ionic-conducting phase on porous GBCO backbone, which contributed to significantly improved electro-catalytic property. At 600 °C, the composite cathode with 3.3 mg cm⁻² SDC loading exhibited encouragingly low R_p value of 0.1 Ω cm², which was much lower than 0.43 Ω cm² of pure-GBCO cathode. As revealed by PO₂ dependence of impedance spectra, the oxygen reduction reaction was mainly limited by charge-transfer processes. Furthermore, a stable operation of 80 h was obtained at 600 °C. Our study implies that infiltrated GBCO cathode is very attractive for application in IT-SOFC cathode.     

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.