Composite cathodes based on Sm0.5Sr0.5CoO3−δ with porous Gd-doped ceria barrier layers for solid oxide fuel cells

Cobaltite-based perovskites based on Sm_0.5Sr_0.5CoO_3−δ (SSC) are attractive as a cathode material with a barrier layer for solid oxide fuel cells (SOFC) due to their high electrochemical activity and electrical conductivity. SSC, synthesized by a complex method, is used as a cathode material in a composite cathode with Gd-doped ceria (GDC). A porous GDC layer is fabricated as a barrier to resist reactions of SSC with yttria-stabilized zirconia (YSZ). The effects of the ratio of SSC on GDC in composite cathodes and the thickness of the GDC barrier are characterized in this study. An SOFC with an SSC7–GDC3 composite cathode on a 4 μm GDC layer at 0.8 V yields the highest fuel cell performance: 1.24 W cm⁻² and 0.61 W cm⁻² at 780 °C and 680 °C, respectively. Impedance analysis indicates that the ohmic resistances are more dependent upon the GDC barrier thickness than the cathode composition. The polarization resistances at 780 °C and 730 °C exhibit similar values, but with decreasing temperature, the polarization resistances change dramatically according to the composition and barrier thickness. The ohmic and polarization resistances show different trends in different temperature ranges, due to the different charge transfer mechanisms of SSC and GDC within those temperature ranges. To obtain higher fuel cell performance, the addition of GDC into the porous SSC is effective, and the compositions of the composite cathode as well as the thickness of the barrier layer need to be optimized.     

High-performance NdSrCo2O5+δ–Ce0.8Gd0.2O2-δ composite cathodes for electrolyte-supported microtubular solid oxide fuel cells

NdSrCo₂O_5+δ (NSCO) is a perovskite with an electrical conductivity of 1551.3 S cm⁻¹ at 500 °C and 921.7 S cm⁻¹ at 800 °C and has a metal-like temperature dependence. This perovskite is used as the cathode material for Ce_0.8Gd_0.2O_2-δ (GDC)-supported microtubular solid oxide fuel cells (MT-SOFCs). The MT-SOFCs fabricated in this study consist of a bilayer anode, comprising a NiO–GDC composite layer and a NiO layer, and a NSCO–GDC composite cathode. Three cell designs with different outer tube diameters, GDC thicknesses, and NSCO/GDC ratios are designed. The MT-SOFC with an outer tube diameter of 1.86 mm, an electrolyte thickness of 180 μm, and a 5NSCO–5GDC composite cathode presents the best performance. The flexural strength of the aforementioned cell is 177 MPa, which is sufficient to confer mechanical integrity to the cell. Moreover, the ohmic and polarization resistance values of the cell are 0.22 and 0.09 Ω cm² at 700 °C, respectively, and 0.15 and 0.03 Ω cm² at 800 °C, respectively. These results indicate that the NSCO-GDC composite exhibits high electrochemical activity. The maximum power densities of the cell at 700 and 800 °C are 0.46 and 0.67 W cm⁻², respectively, exceeding those of existing electrolyte-supported MT-SOFCs with similar electrolyte thicknesses.     

Preparation of 3D structure high performance Ba0·5Sr0·5Fe0·8Cu0·2O3-δ nanofiber SOFC cathode material by low-temperature calcination method

The electrospinning and sol-gel methods are used to prepare a Ba_0·5Sr_0·5Fe_0·8Cu_0·2O_3-δ (BSFC) cathode material with good chemical compatibility with the traditional electrolyte Ce_0.8Gd_0.2O_2?δ (GDC). Systematic experiments are performed to investigate the effect of sintering temperature on BSFC fibers microstructure, morphology and electrochemical properties. The results show that the three dimensional (3D) BSFC-F800 prepared by the low-temperature calcination method (800 °C) has a well-organized porous structure and larger specific surface area and porosity. In addition, the fibers are connected to each other to form a continuous electrode path, which provides an uninterrupted channel for charge transmission, and the low-temperature calcination can efficiently reduce the surface Sr segregation and increase ORR activity. At 700 °C, the 3D nanofiber cathode material BSFC-F800 has lower area specific resistance (ASR = 0.128 Ω cm²) and higher peak power density (PPD = 0.51 W cm^?2). The voltage decay rate in the 100 h long-term stability test is only 0.0342% h^?1.     

Effects of Gd0.8Ce0.2O1.9−δ coating with different thickness on electrochemical performance and long-term stability of La0.8Sr0.2Co0.2Fe0.8O3-δ cathode in SOFCs

The commercialization of Solid oxide fuel cells (SOFCs) has always been limited by the poor catalytic activity and the severe degradation of cathode in the intermediate and low operating temperature. Here we report a Gd_0.8Ce_0.2O_1.9?δ (GDC) coated La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ (LSCF) composite cathode material, which can significantly improve the electrochemical performance and durability of LSCF cathode. The effects of different GDC coating thickness on the electrochemical performance and long-term working stability of LSCF cathode are investigated, and the optimal coating thickness is established. The polarization impedance of GDC coated LSCF (LSCF@GDC) cathode with 9 nm of GDC coating is 0.08 Ω cm² at 800 °C, which is only one quarter of that of the raw LSCF cathode, and the degradation rate of constant current polarization with 100 mA cm^?2 is only 0.42%/100 h at 700 °C, which is far less than that of the raw LSCF cathode. The X-ray photoelectron spectroscopy (XPS) results show that the degree of Sr segregation decreases with the increase of the thickness of the coated GDC layer. The potential LSCF@GDC composite material is expected to increase the operability of SOFCs and accelerate its commercialization.     

Enhanced and stable strontium and cobalt free A-site deficient La1-xNi0.6Fe0.4O3 (x=0, 0.02, 0.04, 0.06, 0.08) cathodes for intermediate temperature solid oxide fuel cells

Perovskite oxides with cobalt and strontium element exhibit severe degradation during the operation for the solid oxide fuel cells (SOFC). Here, we report stable non-cobalt and non-strontium La_1-xNi_0.6Fe_0.4O₃ perovskite cathodes with improved oxygen reduction reaction (ORR) activity. A-site deficient La_1-xNi_0.6Fe_0.4O₃ cathodes within 8 at.% all exhibit the invariable phase structure with LaNi_0.6Fe_0.4O₃ (LNF), and the matched thermal expansion coefficient with that of the (Ce_0.90Gd_0.10)O_1.95 (GDC) electrolyte. The polarization resistance of the La_0.94Ni_0.6Fe_0.4O₃ (LNF94) cathode is 0.61 Ω cm² at 750 °C in air, which is 1/5 of the LaNi_0.6Fe_0.4O₃ (2.78 Ω cm²). The peak power density of the corresponding single cell with LNF94 cathode is 0.37 W cm⁻² at 750 °C, which is 2.36 times higher than that of the single cell with LNF cathode (0.11 W cm⁻²). We further study the long-term stability of LNF and LNF94 cathodes, the polarization resistance of the LNF94 electrode slightly fluctuates around 0.18 Ω cm² during 50 h operation at 800 °C, while the polarization resistance of the LNF increases by about 15%. This work highlights the A-site deficient LNF as an effective and stable non-cobalt and non-strontium cathode for the intermediate temperature solid oxide fuel cells.     

A promising Bi-doped La0.8Sr0.2Ni0.2Fe0.8O3-δ oxygen electrode for reversible solid oxide cells

Reversible solid oxide cells (RSOCs) are clean and effective electrochemical conversion devices that require highly active electrodes and stable electrochemical performance for the practical application. Herein, we investigate a series of La_0.8-xBi_xSr_0.2Ni_0.2Fe_0.8O_3-δ (LBSNF-x, x = 0.0, 0.05, 0.1, 0.15) oxides as the potential oxygen electrode material for RSOCs. The properties of electrical conductivity, thermal expansion coefficient, and chemical compatibility with the Ce_0.9Gd_0.1O_1.95 (GDC) barrier layer of LBSNF-x oxides are evaluated. When LBSNF-0.1 and GDC forms a composite oxygen electrode with the ratio of 7:3, it shows the lowest polarization resistance with fastest oxygen reduction reaction activity in the symmetrical cell test. Then the cell with the configuration of Ni-YSZ/YSZ/GDC/LBSNF-0.1-GDC was prepared and evaluated both in fuel cell (FC) and electrolysis cell (EC) mode. The maximum power density of 824 mW cm⁻² is obtained at 800 °C in FC mode, and current density of 1.20 A cm⁻² is achieved under 50% steam content at 1.3 V in EC mode. Additionally, the cell exhibits good stability both in FC and EC mode after 80 h test at 700 °C. The results of this work provide a strong support for application of the LBSNF-0.1-GDC oxygen electrode for reversible solid oxide cells.     

Application of La0.3Sr0.7Fe0.7Ti0.3O3-δ/GDC electrolyte in LT-SOFC

Recently semiconductor-ionic electrolytes have capture much attentions for its promising application in low temperature solid oxide fuel cells. In this paper, semiconductor La_0.3Sr_0.7Fe_0.7Ti_0.3O_3-δ (LSTF) and ionic Ce_0.9Gd_0.1O_2-δ (GDC) composites are investigated. The new composite consisting of LSTF and GDC are used as ionic-semiconductor electrolytes for LT-SOFC. It was found that when the ratio of LSTF to GDC was 5:5, the performance of the fuel cell is the best. The open circuit voltage is 0.92 V, and the power density is 654 mW cm^?2 at 600 °C. Its electrical performance is much higher than that of traditional SOFC at low temperature. The energy band of different semiconductor is discussed by using optical equipment.     

Low-temperature preparation of dense (Gd,Ce)O2−δ–Gd2O3 composite buffer layer by aerosol deposition for YSZ electrolyte-based SOFC

The (Gd_0.1Ce_0.9)O_2−δ (GDC)–Gd₂O₃ composite buffer layer was fabricated on yttria stabilized zirconia (YSZ) electrolyte by aerosol deposition for usage as diffusion barrier layer between YSZ and (La_0.6Sr_0.4)(Co_0.2Fe_0.8)O_3−δ (LSCF)–GDC composite cathode. The deposited composite buffer layer was quite dense in nature and effectively prevented the formation of SrZrO₃ and La₂Zr₂O₇ interlayer with low conductivity at the interfaces. The cell's I–V performance was enhanced with an increase in the GDC content in the composite buffer layer. The cell containing composite buffer layer showed maximum power density of up to 1.74 W/cm² at 750 °C, which was ∼30% higher than that of the cell containing GDC buffer layer prepared using conventional process.     

Intriguing electrochemistry in low-temperature single layer ceramic fuel cells based on CuFe2O4

A composite of CuFe₂O₄ and Gd-Sm co-doped CeO₂ is studied for a single layer ceramic fuel cell application. In order to optimize the cell performance, the effects of sintering temperatures (600 °C, 700 °C, 800 °C, 900 °C and 1000 °C) were investigated for the fabrication of the cells. It was found that the cells sintered at 700 °C outperformed other cells with a maximum peak power density of 344 mW/cm² at 550 °C. The electrochemical impedance spectroscopy analysis on the best cell revealed significant ohmic losses (0.399 Ω cm²) and polarization losses (0.174 Ω cm²) in the cell. The HR-TEM and SEM gave microstructural information of the cell. The HT-XRD spectra showed the crystal structures in different sintering temperatures. The cell performance was stable and the composite material did not degrade during an 8 h stability test under open-circuit condition. This study opens up new avenues for the exploration of this nanocomposite material for the low temperature single component ceramic fuel cell research.     

High-performing electrolyte-supported symmetrical solid oxide electrolysis cells operating under steam electrolysis and co-electrolysis modes

Symmetrical solid oxide cells (s-SOC) present several advantages compared to typical configuration, as a reduction of sintering steps or a better thermomechanical compatibility between the electrodes and the electrolyte. Different mixed ionic-electronic conductors (MIEC) have been reported as suitable candidates for symmetrical configuration, allowing operations under steam electrolysis (SOEC) or co-electrolysis (co-SOEC) without the use of reducing safe gas (typically employed in SoA nickel based cells). In the present study, Sr₂Fe_1.5Mo_0.5O_6−δ (SFM) electrodes are deposited on both sides of YbScSZ tapes previously coated with a Ce_1-xGd_xO_1.9 (GDC) barrier layer grown by PLD. Electrode sintering temperature is optimized and fixed at 1200 °C by means of electrochemical impedance spectroscopy (EIS) measurements in symmetrical atmosphere. The cell is then characterized at 900 °C in SOEC and co-SOEC modes without the use of any safe gas obtaining high current densities of 1.4 and 1.1 A cm⁻² at 1.3 V respectively. Short-term reversibility is finally proven by switching the gas atmosphere between the cathode and anode sides while keeping the electrolysis conditions. Similar performances are obtained in both configurations.     

Ni–YSZ-supported tubular solid oxide fuel cells with GDC interlayer between YSZ electrolyte and LSCF cathode

Highly sinterable gadolinia doped ceria (GDC) powders are prepared by carbonate coprecipitation and applied to the GDC interlayer in Ni–YSZ (yttria stabilized zirconia)-supported tubular solid oxide fuel cell in order to prevent the reaction between YSZ electrolyte and LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ) cathode materials. The formation of highly resistive phase at the YSZ/LSCF interface was effectively blocked by the low-temperature densification of GDC interlayer using carbonate-derived active GDC powders and the suppression of Sr diffusion toward YSZ electrolyte via GDC interlayer by tuning the heat-treatment temperature for cathode fabrication. The power density of the cell with the configuration of Ni–YSZ/YSZ/GDC/LSCF–GDC/LSCF was as high as 906 mW cm⁻², which was 2.0 times higher than that (455 mW cm⁻²) of the cell with the configuration of Ni–YSZ/YSZ/LSM(La_0.8Sr_0.2MnO_3−δ)–YSZ/LSM at 750 °C.     

Interface channels accelerating ion transport through alkaline earth metal carbonate - Gd0.1Ce0.9O1.95 heterostructure

Designing the interface proton channel between different phases to accelerate the proton ion transport is an effective way to realize the high proton conduction for the low-temperature ceramic fuel cell (CFC). Cerium based materials coated with molten carbonate has been widely demonstrated for high performance CFCs. Here, we prepared alkaline earth metal carbonate - Gd_0.1Ce_0.9O_1.95 (GDC) heterostructure composites in various compositions by precipitation method using NH₄HCO₃ and NaHCO₃ as the deposit. The samples prepared using NH₄HCO₃ as the electrolyte, the cell can deliver an even higher power output of 811 mW cm⁻². The results are much higher than that reported in the literature for the GDC electrolyte fuel cells. The ion conduction on the interface between GDC and solid carbonate particles is proposed. The ionic conductivity is determined to be 0.13 S cm⁻¹ at 500 °C; while GDC as reported in literature is 0.005 S cm⁻¹ at the same temperature. This proposed solid carbonate-GDC heterostructure method has succeeded in enhancing ionic conductivity and the CFC performance, which presents a new way to develop high proton conducting materials and advanced ceramic fuel cells at low temperatures (<550 °C).     

Effect of unsintered gadolinium-doped ceria buffer layer on performance of metal-supported solid oxide fuel cells using unsintered barium strontium cobalt ferrite cathode

In this study, a Gd_0.1Ce_0.9O_1.95 (GDC) buffer layer and a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) cathode, fabricated without pre-sintering, are investigated (unsintered GDC and unsintered BSCF). The effect of the unsintered GDC buffer layer, including the thickness of the layer, on the performance of solid oxide fuel cells (SOFCs) using an unsintered BSCF cathode is studied. The maximum power density of the metal-supported SOFC using an unsintered BSCF cathode without a buffer layer is 0.81 W cm⁻², which is measured after 2 h of operation (97% H₂ and 3% H₂O at the anode and ambient air at the cathode), and it significantly decreases to 0.63 W cm⁻² after 50 h. At a relatively low temperature of 800 °C, SrZrO₃ and BaZrO₃, arising from interaction between BSCF and yttria-stabilized zirconia (YSZ), are detected after 50 h. Introducing a GDC interlayer between the cathode and electrolyte significantly increases the durability of the cell performance, supporting over 1000 h of cell usage with an unsintered GDC buffer layer. Comparable performance is obtained from the anode-supported cell when using an unsintered BSCF cathode with an unsintered GDC buffer layer (0.75 W cm⁻²) and sintered GDC buffer layer (0.82 W cm⁻²). When a sintered BSCF cathode is used, however, the performance increases to 1.23 W cm⁻². The adhesion between the BSCF cathode and the cell can be enhanced by an unsintered GDC buffer layer, but an increase in the layer thickness (1-6 μm) increases the area specific resistance (ASR) of the cell, and the overly thick buffer layer causes delamination of the BSCF cathode. Finally, the maximum power densities of the metal-supported SOFC using an unsintered BSCF cathode and unsintered GDC buffer layer are 0.78, 0.64, 0.45 and 0.31 W cm⁻² at 850, 800, 750 and 700 °C, respectively.     

Distribution of relaxation times analysis and interfacial effects of LSCF fired at different temperatures

This paper describes the effects of (La_0.60Sr_0.40)_0.95Co_0.20Fe_0.80O_3-x (LSCF) firing temperature on the electrochemical performance and the chemical interactions at the interface of Gd-doped ceria (GDC) barrier layer and yttria-stabilized zirconia (YSZ) electrolyte for commercial cells. Initial scanning electron microscopy (SEM) analysis indicate that the optimal cathode porosity is obtained at a firing temperature of 1100 °C; however, the peak power is not observed at the same firing temperature. At 750 °C and using humidified hydrogen, the peak power densities are found to be 0.607, 0.959, 1.41, and 0.842 W/cm² for a cathode firing temperature of 900, 1000, 1050, and 1100 °C, respectively. The power density data indicate an increasing trend in performance as the firing temperature increases; however, the electrochemical performance drops drastically at a firing temperature of 1100 °C. Using impedance spectroscopy (IS) and distribution of relaxation times (DRT) analysis, it is determined that the decrease in cell performance is mostly due to a slower charge transfer process. This is further confirmed using high resolution SEM/EDS and STEM/EDS analysis which show that Sr is present at the GDC/YSZ interface with the highest concentration at 1100 °C. This indicates that an insulating layer of strontium zirconate (possibly SrZrO₃) has formed and is mostly responsible for low cell performance. In addition, STEM/EDS analysis shows that Zr and Ce have interdiffused with each other as well. It is further shown that more Zr (in addition to interdiffusion) has moved into the barrier layer in order to react with Sr to form the strontium zirconate.     

Kinetics of oxygen reaction in porous La0.6Sr0.4Co0.2Fe0.8O3–δ-Ce0.8Gd0.2O1.9 composite electrodes for solid oxide cells

Kinetics of oxygen reaction in porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ-Ce_0.8Gd_0.2O_1.9 (LSCF-GDC) electrodes are systematically studied. Normally, there are two pathways of oxygen reaction in porous LSCF: in reaction region with oxygen exchanging at electrode/air interface, and around electrode/electrolyte interface with oxygen exchanging at electrode/electrolyte/air triple-phase boundary (TPB). GDC in porous LSCF-GDC accelerates oxygen transport and oxygen gas diffusion during oxygen reaction. In addition, because the formation of LSCF/GDC interface increases the length of TPB and affects the geometry of reaction region, oxygen reaction in LSCF-GDC tends to proceed in the TPB pathway. The performance and oxygen reactions of LSCF-GDC are evaluated at 650 °C and 850 °C. Oxygen reaction in LSCF-GDC is suppressed by CO₂, but increasing GDC content is able to improve the CO₂ tolerance of electrode. Though the performance reduction by H₂O is unobvious, H₂O can aggravate CO₂ degradation at low temperature.     

Fabrication of anode-supported thin BCZY electrolyte protonic fuel cells using NiO sintering aid

A thin and fully dense BaCe_0.6Zr_0.2Y_0.2O_3-δ (BCZY) electrolyte for the use of anode-supported protonic fuel cells has been successfully prepared by spin coating using NiO sintering aid. The effects of NiO addition on the electrolyte microstructures and fuel cell performances are also investigated. An appropriate NiO addition has a significant positive contribution to the densification and grain growth of thin BCZY electrolytes. However, too much NiO addition gives rise to NiO aggregation in BCZY electrolyte and deteriorates the cell performance. The enhanced sintering mechanism can be mainly attributed to the oxygen vacancies generated from the NiO decomposition and bulk diffusion of Ni into BCZY perovskites. The fuel cell with a BCZY-3%NiO electrolyte exhibits the highest maximum power density of ~106.6 mW/cm² at 800 °C among all fuel cells in this study. The electrochemical impedance characteristics of thin BCZY electrolyte fuel cells are further discussed under open circuit conditions.     

Electrochemical performance of a Ni0.8Co0.15Al0.05LiO2 cathode for a low temperature solid oxide fuel cell

The electrochemical performance of the Ni_0.8Co_0.15Al_0.05LiO₂ (NCAL) cathode was investigated by comparing it with the traditional La_0.4Sr_0.6Co_0.2Fe_0.8O_3-δ (LSCF) and LSCF/Ce_0.9Gd_0.1O_2-δ (GDC) cathodes with a GDC electrolyte-supported solid oxide fuel cell (SOFC). It is found that the electrochemical performance of the cells with the NCAL and NCAL/GDC cathode is better than that of the cells with the LSCF and LSCF/GDC cathode at 550 °C. The results of the electrochemical performance tests of the cells with different NCAL/GDC mass ratios (10/0, 9/1, 8/2, 7/3 and 6/4) show that the NCAL/GDC composite cathode with the mass ratio of 8/2 has the best electrochemical performance. XRD results show that when the sintering temperature is higher than 700 °C, the NCAL/GDC composite will undergo chemical reactions and generate new phases, reducing the performance of the composite cathode. XPS results show that a small amount of Li₂CO₃ was formed on the surface of NCAL during cathode preparation, forming a special interface between NCAL, Li₂CO₃ and GDC. At the NCAL-Li₂CO₃/GDC interfaces, due to the migration and aggregation of Li⁺ to the interface, a space charge region may be formed in which the Li⁺ enrichment may lead to the formation of the region with a high oxygen vacancy concentration. A very high oxygen vacancy concentration at the NCAL-Li₂CO₃/GDC interfaces will provide sufficient oxygen ion conductivity for oxygen reduction reaction (ORR) and reduce the activation energy of the reaction. NCAL will be a potential cathode material that can reduce the operating temperature of the traditional SOFC to 550 °C or lower.     

One-pot synthesis of Fe2O3/C by urea combustion method as an efficient electrocatalyst for oxygen evolution reaction

The hematite type Fe₂O₃/C catalyst for oxygen evolution reaction (OER) was prepared using a facile urea combustion method. The Fe₂O₃/C electrode showed excellent electrocatalytic ability towards OER in alkaline medium. The phase and morphology of the product were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The sintering temperature is 600 °C, and the calcination time is 3 h, which is the best preparation process condition. The particles were irregular spherical with the size of 10–30 nm and dispersed uniformly. The current density of the Fe₂O₃/C electrode was 147 mA cm⁻² at 0.6 V (vs. HgO/Hg) in 6 mol L⁻¹ KOH electrolyte at room temperature.     

Modifying the cathodes of intermediate-temperature solid oxide fuel cells with a Ce0.8Sm0.2O2 sol–gel coating

To increase the performance of solid oxide fuel cells operated at intermediate temperatures (<700 °C), we used the electronic conductor La_0.8Sr_0.2MnO₃ (LSM) and the mixed conductor La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) to modify the cathode in the electrode microstructure. For both cathode materials, we employed a Sm_0.2Ce_0.8O₂ (SDC) buffer layer as a diffusion barrier on the yttria-stabilized zirconia (YSZ) electrolyte to prevent the interlayer formation of SrZrO₃ and La₂Zr₂O₇, which have a poor ionic conductivity. These interfacial reaction products were formed only minimally at the electrolyte–cathode interlayer after sintering the SDC layer at high temperature; in addition, the degree of cathode polarization also decreased. Moreover to extend the triple phase boundary and improve cell performance at intermediate temperatures, we used sol–gel methods to coat an SDC layer on the cathode pore walls. The cathode resistance of the LSCF cathode cell featuring SDC modification reached as low as 0.11 Ω cm² in air when measured at 700 °C. The maximum power densities of the cells featuring the modified LSCF and LSM cathodes were 369 and 271 mW/cm², respectively, when using O₂ as the oxidant and H₂ as the fuel.     

Reactivity of pulverized coals during combustion catalyzed by CeO2 and Fe2O3

Effects of CeO₂ and Fe₂O₃ on combustion reactivity of several fuels, including three ranks of coals, graphite and anthracite chars, were investigated using thermo-gravimetric analyzer. The results indicated that the combustion reactivity of all the samples except lignite was improved with CeO₂ or Fe₂O₃ addition. It was interesting to note that the ignition temperatures of anthracite were decreased by 50 °C and 53 °C, respectively, with CeO₂ and Fe₂O₃ addition and that its combustion rates were increased to 15.4%/min and 12.2%/min. Ignition temperatures of lignite with CeO₂ and Fe₂O₃ addition were 250 °C and 226 °C, and the combustion rates were 12.8% and 19.3%/min, respectively. When compared with those of lignite without catalysts, no obvious catalytic effects of the two catalysts on its combustion reactivity were revealed. The results from the combustion of the three rank pulverized coals catalyzed by CeO₂ and Fe₂O₃ indicated significant effects of the two catalysts on fixed carbon combustion. And it was found that the higher the fuel rank, the better the catalytic effect. The results of combustion from two kinds of anthracite chars showed obvious effects of anthracite pyrolysis catalyzed by CeO₂ and Fe₂O₃ on its combustion reactivity.