Y-doped SrTiO3 based sulfur tolerant anode for solid oxide fuel cells

A solid oxide fuel cell (SOFC) anode with high sulfur tolerance was developed starting from a Y-doped SrTiO₃ (SYTO)-yttria stabilized zirconia (YSZ) porous electrode backbone, and infiltrated with nano-sized catalytic ceria and Ru. The size of the infiltrated particles on the SYTO-YSZ pore walls was 30–200 nm, and both infiltrated materials improved the performance of the SYTO-YSZ anode significantly. The infiltrated ceria covered most of the surface of the SYTO-YSZ pore walls, while Ru was dispersed as individual nano-particles. The performance and sulfur tolerance of a cathode supported cell with ceria- and Ru-infiltrated SYTO-YSZ anode was examined in humidified H₂ mixed with H₂S. The anode showed high sulfur tolerance in 10–40 ppm H₂S, and the cell exhibited a constant maximum power density 470 mW cm⁻² at 10 ppm H₂S, at 1073 K. At an applied current density 0.5 A cm⁻², the addition of 10 ppm H₂S to the H₂ fuel dropped the cell voltage slightly, from 0.79 to 0.78 V, but completely recovered quickly after the H₂S was stopped. The ceria- and Ru-infiltrated SYTO-YSZ anode showed much higher sulfur tolerance than conventional Ni-YSZ anodes.     

Electrophoretic deposition of (Mn,Co)3O4 spinel coating for solid oxide fuel cell interconnects

We discuss here our attempt to develop (Mn,Co)₃O₄ spinel coatings on the surface of Cr-containing steel through electrophoretic deposition (EPD) followed by reduced-atmosphere sintering for solid oxide fuel cell (SOFC) interconnect application. The effects of EPD voltages and sintering atmospheres on the microstructure, electrical conductivity and long-term stability of the coated interconnects are examined by means of scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and four-probe resistance techniques. For the spinel coatings generated using smaller voltage than 400 V, the interconnect surfaces exhibit good packing behavior and high conductivity. The reduced atmosphere during sintering has a beneficial impact on the minimizing chromia subscale formation and thus reducing the area specific resistance (ASR) of the coated interconnects. Moreover, it is interesting to note that a more stable long-term performance is achieved for the spinel coating sintered in H₂/H₂O atmosphere with thin chromia sub-scale and no Cr penetration. Based on the current results, EPD followed by reduced-atmosphere sintering is a fast and economic way to deposit (Mn,Co)₃O₄ coating for SOFC interconnect applications.     

Synthesis and dehydrogenation of LiCa(NH2)3(BH3)2

We report the synthesis of a new hydrogen storage material with a composition of LiCa(NH₂)₃(BH₃)₂. The theoretical hydrogen capacity of LiCa(NH₂)₃(BH₃)₂ is 9.85 wt.%. It can be prepared by ball milling the mixture of calcium amidoborane (Ca(NH₂BH₃)₂) and lithium amide (LiNH₂) in a molar ratio of 1:1. The experimental results show that this material starts to release hydrogen at a temperature as low as ca. 50 °C, which is ca. 70 °C lower than that of pure Ca(NH₂BH₃)₂ possibly resulting from the active interaction of NH₂⁻ in LiNH₂ with BH₃ in Ca(NH₂BH₃)₂. ca. 4.1 equiv. or 6.8 wt.% hydrogen can be released at 300 °C. The dehydrogenation is a mildly exothermic process forming stable nitride products.     

Electrochemical supercapacitor behavior of Ni3(Fe(CN)6)2(H2O) nanoparticles

Nanosized Ni₃(Fe(CN)₆)₂(H₂O) was prepared by a simple co-precipitation method. The electrochemical properties of the sample as the electrode material for supercapacitor were studied by cyclic voltammetry (CV), constant charge/discharge tests and electrochemical impedance spectroscopy (EIS). A specific capacitance of 574.7 F g⁻¹ was obtained at the current density of 0.2 A g⁻¹ in the potential range from 0.3 V to 0.6 V in 1 M KNO₃ electrolyte. Approximately 87.46% of specific discharge capacitance was remained at the current density of 1.4 A g⁻¹ after 1000 cycles.     

Rate-controlling species for the sintering of LiTi2(PO4)3

A series of Li deficient LiTi₂(PO₄)₃ samples were prepared and sintered and the density was measured to determine the rate-controlling species for sintering of LiTi₂(PO₄)₃. It was observed that as the Li content decreased the density decreased. This result suggests that oxygen does not control sintering. A comparison of the LiTi₂(PO₄)₃ sintering data to sintering and diffusion data in olivine, which exhibits a similar framework structure to LiTi₂(PO₄)₃, suggests that P is the species which controls sintering. This suggestion was confirmed by the density results of a Li excess LiTi₂(PO₄)₃ sample.     

Plasma spray synthesis of La10(SiO4)6O3 as a new electrolyte for intermediate temperature solid oxide fuel cells

The apatite-type lanthanum silicate films were successfully synthesized by modified atmosphere plasma spraying using lanthanum oxide and silicon oxide mixed powders and precalcined hypereutectic powders in the size range 1–3 μm and 5–8 μm, respectively, as starting feedstock materials. The films differed not only in microstructural scale, but also in the characteristic of the degree of film densification. A detail describing the evolution of microstructure has been discussed. A considerable improvement in densification of the La₁₀(SiO₄)₆O₃ electrolyte films has been observed.     

Nanoscale bismuth oxide impregnated (La,Sr)MnO3 cathodes for intermediate-temperature solid oxide fuel cells

Bismuth oxide based oxygen ion conductors are incorporated into (La,Sr)MnO₃ (LSM), the classical cathode material for solid oxide fuel cells (SOFC), to improve the cathode performance. Yttria-stabilized bismuth oxide (YSB) is taken as an example and is impregnated into a preformed porous LSM frame, forming a highly active cathode for intermediate-temperature SOFCs (IT-SOFCs) with doped ceria electrolytes. X-ray diffraction indicates that YSB is chemically compatible with LSM at intermediate temperatures below 800 °C. The impregnated YSB particles are nanosized and are deposited on the surface of the framework. Significant performance improvement is achieved by introducing nanosized YSB into the LSM electrodes. At 600 °C, the interfacial polarization resistance under open-circuit conditions for electrodes impregnated with 50% YSB is only 1.3% of the original value for a pure LSM electrode. The resistance is further reduced dramatically when current is passed through. In addition, the YSB impregnated LSM electrodes has the highest electrochemical performance among those based on LSM. Single cell with 25% of YSB impregnated LSM cathode generates maximum power density of 300 mW cm⁻² at 600 °C, indicating the promise of using LSM-based electrodes for IT-SOFC.     

Effect of milling methods on performance of Ni–Y2O3-stabilized ZrO2 anode for solid oxide fuel cell

A Ni–YSZ (Y₂O₃-stabilized ZrO₂) composite is commonly used as a solid oxide fuel cell anode. The composite powders are usually synthesized by mixing NiO and YSZ powders. The particle size and distribution of the two phases generally determine the performance of the anode. Two different milling methods are used to prepare the composite anode powders, namely, high-energy milling and ball-milling that reduce the particle size. The particle size and the Ni distribution of the two composite powders are examined. The effects of milling on the performance are evaluated by using both an electrolyte-supported, symmetric Ni–YSZ/YSZ/Ni–YSZ cell and an anode-supported, asymmetric cell. The performance is examined at 800 °C by impedance analysis and current-voltage measurements.     

Novel synthesis of LiFePO4-Li3V2(PO4)3 composite cathode material by aqueous precipitation and lithiation

LiFePO₄-Li₃V₂(PO₄)₃ composite cathode material is synthesized by aqueous precipitation of FeVO₄·xH₂O from Fe(NO₃)₃ and NH₄VO₃, following chemical reduction and lithiation with oxalic acid as the reducer and carbon source. Samples are characterized by XRD, SEM and TEM. XRD pattern of the compound synthesized at 700 °C indicates olivine-type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ are co-existed. TEM image exhibits that LiFePO₄-Li₃V₂(PO₄)₃ particles are encapsulated with a carbon shell 5-10 nm in thickness. The LiFePO₄-Li₃V₂(PO₄)₃ compound cathode shows good electrochemical performance, and its discharge capacity is about 139.1 at 0.1 C, 135.5 at 1 C and 116 mA h g⁻¹ at 3 C after 30 cycles.     

Electrical conductivity and structural stability of La-doped SrTiO3 with A-site deficiency as anode materials for solid oxide fuel cells

A-site-deficient (La_0.3Sr_0.7)_1−xTiO_3−δ materials were synthesized by conventional solid-state reaction. The A-site deficiency limit in (La_0.3Sr_0.7)_1−xTiO_3−δ was below 10 mol% in 5%H₂/Ar at 1500 °C. A-site deficiency level promoted the sintering process of (La_0.3Sr_0.7)_1−xTiO_3−δ. The ionic conductivity increased but the electronic conductivity decreased with increasing A-site deficiency level. The ionic conductivity of (La_0.3Sr_0.7)_0.93TiO_3−δ sample was as high as 0.2–1.6 × 10⁻² S/cm in 500–950 °C and 1.0 × 10⁻² S/cm at 800 °C, over twice of La_0.3Sr_0.7TiO_3−δ. Its electrical conductivity was in the range of 83–299 S/cm in 50–950 °C and 145 S/cm at 800 °C. A-site deficiency improved the thermal stability of (La_0.3Sr_0.7)_1−xTiO_3−δ and ensured the material with a stable electrical performance in different atmospheres.     

Electrical conduction behavior of La,Co co-doped SrTiO3 perovskite as anode material for solid oxide fuel cells

The effects of La- and Co-doping into SrTiO₃ perovskite oxides on their phase structure, electrical conductivity, ionic conductivity and oxygen vacancy concentration have been investigated. The solid solution limits of La in La_xSr_1 − xTiO_3 − δ and Co in La_0.3Sr_0.7Co_yTi_1 − yO_3 − δ are about 40 mol% and 7 mol%, respectively, at 1500 °C. The incorporation of La decreases the band gap and thus increases the electrical conductivity of SrTiO₃ remarkably. La_0.3Sr_0.7TiO_3 − δ shows an electrical conductivity of 247 S/cm at 700 °C. Co-doping into La_0.3Sr_0.7TiO_3 − δ increases the oxygen vacancy concentration and decreases the migration energy for oxygen ions, leading to a significant increase in ionic conductivity but at the expense of some electrical conductivity. The electrical and ionic conductivities of La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ are 63 S/cm and 6 × 10⁻³ S/cm, respectively, at 700 °C. Both La_0.3Sr_0.7TiO_3 − δ and La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ show relatively stable electrical conductivities under oxygen partial pressure of 10⁻¹⁴–10⁻¹⁹ atm at 800 °C. These properties make La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ a promising anode candidate for solid oxide fuel cells.     

MoO2 synthesized by reduction of MoO3 with ethanol vapor as an anode material with good rate capability for the lithium ion battery

MoO₂ synthesized through reduction of MoO₃ with ethanol vapor at 400 °C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Its electrochemical performance as an anode material for lithium ion battery was tested by cyclic voltammetry (CV) and capacity measurements. During the reduction process, the starting material (MoO₃) collapsed into nanoparticles (∼100 nm), on the nanoparticles remains a carbon layer from ethanol decomposition. Rate capacity and cycling performance of the as-prepared product is very satisfactory. It displays 318 mAh g⁻¹ in the initial charge process with capacity retention of 100% after 20 cycles in the range of 0.01–3.00 V vs. lithium metal at a current density of 5.0 mA cm⁻², and around 85% of the retrievable capacity is in the range of 1.00–2.00 V. This suggests the application of this type of MoO₂ as anode material in lithium ion batteries.     

Co-doped Sr2FeNbO6 as cathode materials for intermediate-temperature solid oxide fuel cells

Sr₂Fe_1−xCo_xNbO₆ (0.1 ≤ x ≤ 0.9) (SFCN) oxides with perovskite structure have been developed as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). These materials are synthesized via solid-state reaction and characterized by XRD, SEM, electrical conductivity, AC impedance spectroscopy and DC polarization measurements. The reactivity tests show that the Sr₂Fe_1−xCo_xNbO₆ electrodes are chemically compatible with the Zr_0.85Y_0.15O_1.925 (YSZ) and Ce_1.9Gd_0.1O_1.95 (CGO) electrolytes at 1200 °C, and the electrode forms a good contact with the electrolyte after sintering at 1200 °C for 12 h. The total electrical conductivity that has a considerable effect on the electrode properties is determined in a temperature range from 200 °C to 800 °C. The highest conductivity of 5.7 S cm⁻¹ is found for Sr₂Fe_0.1Co_0.9NbO₆ at 800 °C in air. The electrochemical performances of these cathode materials are studied using impedance spectroscopy at various temperatures and oxygen partial pressures. Two different kinds of reaction rate-limiting steps exist on the Sr₂Fe_0.1Co_0.9NbO₆ electrode, depending on the temperature. The Sr₂Fe_0.1Co_0.9NbO₆ electrode on CGO electrolyte exhibits a polarization resistance of 0.74 Ω cm² at 750 °C in air, which indicates that the Sr₂Fe_0.1Co_0.9NbO₆ electrode is a promising cathode material for IT-SOFCs.     

Characterization of infiltrated (La0.75Sr0.25)0.95MnO3 as oxygen electrode for solid oxide electrolysis cells

Porous strontium doped lanthanum manganite (LSM)-yttria-stabilized zirconia (YSZ) composite has been made by an impregnation method as oxygen electrodes for solid oxide electrolysis cells. X-ray diffraction and SEM results showed that LSM powders with well-crystallized perovskite phase uniformly distributed in the porous YSZ matrix. Impedance spectra and voltage-current density curves were measured as a function of absolute humidity at different temperatures to characterize the cell performance. The LSM infiltrated cell has an area specific resistance (ASR) of 0.20 Ω cm² at 900 °C at open circuit voltage with 50% absolute humidity (AH), which is relatively lower than that of the cell with LSM-YSZ oxygen electrode made by a conventionally mixing method. Electrolysis cell with LSM infiltrated oxygen electrode has demonstrated stable performance under electrolysis operation with 0.33 A/cm² and 50 vol.% AH at 800 °C.     

Li3V2(PO4)3 cathode material synthesized by chemical reduction and lithiation method

The monoclinic-type Li₃V₂(PO₄)₃ cathode material was synthesized via calcining amorphous Li₃V₂(PO₄)₃ obtained by chemical reduction and lithiation of V₂O₅ using oxalic acid as reducer and lithium carbonate as lithium source in alcohol solution. The amorphous Li₃V₂(PO₄)₃ precursor was characterized by using TG–DSC and XPS. The results showed that the V⁵⁺ was reduced to V³⁺ by oxalic acid at ambient temperature and pressure. The prepared Li₃V₂(PO₄)₃ was characterized by XRD and SEM. The results indicated the Li₃V₂(PO₄)₃ powder had good crystallinity and mesoporous morphology with an average diameter of about 30 nm. The pure Li₃V₂(PO₄)₃ exhibits a stable discharge capacity of 130.08 mAh g⁻¹ at 0.1 C (14 mA g⁻¹).     

Sr2Fe4/3Mo2/3O6 as anodes for solid oxide fuel cells

Sr₂Fe_4/3Mo_2/3O₆ has been synthesized by a combustion method in air. It shows a single cubic perovskite structure after being reduced in wet H₂ at 800 °C and demonstrates a metallic conducting behavior in reducing atmospheres at mediate temperatures. Its conductivity value at 800 °C in wet H₂ (3% H₂O) is about 16 S cm⁻¹. This material exhibits remarkable electrochemical activity and stability in H₂. Without a ceria interlayer, maximum power density (P_max) of 547 mW cm⁻² is achieved at 800 °C with wet H₂ (3% H₂O) as fuel and ambient air as oxidant in the single cell with the configuration of Sr₂Fe_4/3Mo_2/3O₆|La_0.8Sr_0.2Ga_0.83Mg_0.17O₃ (LSGM)| La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). The P_max even increases to 595 mW cm⁻² when the cell is operated at a constant current load at 800 °C for additional 15 h. This anode material also shows carbon resistance and sulfur tolerance. The P_max is about 130 mW cm⁻² in wet CH₄ (3% H₂O) and 472 mW cm⁻² in H₂ with 100 ppm H₂S. The cell performance can be effectively recovered after changing the fuel gas back to H₂.     

Use of La0.75Sr0.25Cr0.5Mn0.5O3 materials in composite anodes for direct ethanol solid oxide fuel cells

The perovskite system La_1−xSr_xCr_1−yM_yO_3−δ (M, Mn, Fe and V) has recently attracted much attention as a candidate material for the fabrication of solid oxide fuel cells (SOFCs) due to its stability in both H₂ and CH₄ atmospheres at temperatures up to 1000 °C. In this paper, we report the synthesis of La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) by solid-state reaction and its employment as an alternative anode material for anode-supported SOFCs. Because LSCM shows a greatly decreased electronic conductivity in a reducing atmosphere compared to that in air, we have fabricated Cu-LSCM-ScSZ (scandia-stabilized zirconia) composite anodes by tape-casting and a wet-impregnation method. Additionally, a composite structure (support anode, functional anode and electrolyte) structure with a layer of Cu-LSCM-YSZ (yttria-stabilized zirconia) on the supported anode surface has been manufactured by tape-casting and screen-printing. Single cells with these two kinds of anodes have been fabricated, and their performance characteristics using hydrogen and ethanol have been measured. In the operation period, no obvious carbon deposition was observed when these cells were operated on ethanol. These results demonstrate the stability of LSCM in an ethanol atmosphere and its potential utilization in anode-supported SOFCs.     

Preparation and characterization of nanocrystalline Ce0.8Sm0.2O1.9 for low temperature solid oxide fuel cells based on composite electrolyte

Nanocrystalline Ce_0.8Sm_0.2O_1.9 (SDC) has been synthesized by a combined EDTA–citrate complexing sol–gel process for low temperature solid oxide fuel cells (SOFCs) based on composite electrolyte. A range of techniques including X-ray diffraction (XRD), and electron microscopy (SEM and TEM) have been employed to characterize the SDC and the composite electrolyte. The influence of pH values and citric acid-to-metal ions ratios (C/M) on lattice constant, crystallite size and conductivity has been investigated. Composite electrolyte consisting of SDC derived from different synthesis conditions and binary carbonates (Li₂CO₃–Na₂CO₃) has been prepared and conduction mechanism is discussed. Water was observed on both anode and cathode side during the fuel cell operation, indicating the composite electrolyte is co-ionic conductor possessing H⁺ and O²⁻ conduction. The variation of composite electrolyte conductivity and fuel cell power output with different synthesis conditions was in accordance with that of the SDC originated from different precursors, demonstrating O²⁻ conduction is predominant in the conduction process. A maximum power density of 817 mW cm⁻² at 600 °C and 605 mW cm⁻² at 500 °C was achieved for fuel cell based on composite electrolyte.     

NiMn2O4 spinel as an alternative coating material for metallic interconnects of intermediate temperature solid oxide fuel cells

In an effort to improve the performance of SUS 430 alloy as a metallic interconnect material, a low cost and Cr-free spinel coating of NiMn₂O₄ is prepared on SUS 430 alloy substrate by the sol-gel method and evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. A oxide scale of 3-4 μm thick is formed during cyclic oxidation at 750 °C in air for 1000 h, consisting of an inner layer of doped Cr₂O₃ and an outer layer of doped NiMn₂O₄ and Mn₂O₃; and the growth of Cr₂O₃ and formation of MnCr₂O₄ are depressed. The oxidation kinetics obeys the parabolic law with a rate constant as low as 4.59 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹. The area specific resistance at temperatures between 600 and 800 °C is in the range of 6 and 17 mΩ cm². The above results indicate that NiMn₂O₄ is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells.