Nanostructured anodes for solid oxide fuel cells

Solid oxide fuel cells (SOFC) have much promise as efficient devices for the direct conversion of the energy stored in chemical fuels into electricity. The development of highly robust SOFC that can operate on a range of fuels, however, requires improvements in the electrodes, especially the anode, where nanoscale engineering of the structure is required in order to maximize the number of sites where the electrochemical reactions take place. In this article we review the approaches that are currently being used to improve anode performance and microstructure with a focus on new materials and synthesis techniques.     

Discovery and characterization of novel oxide anodes for solid oxide fuel cells

The search for alternative anode materials for solid oxide fuel cells (SOFCs) has been reviewed in the light of structure, stability, conductivity, chemical and thermal compatibility with electrolyte YSZ. In this review, we have presented the advantages and disadvantages of the traditional Ni-YSZ anode for SOFCs. The development of alternative anode for SOFCs with fluorite, rutile, tungsten bronze, pyrochlore, perovskite and spinel structures has been reviewed and discussed in detail. Among the reported materials systems, materials with perovskite structure are promising particularly where two ions with complimentary function are present on the B-site at high concentration. We have recently found a good redox stable anode (La(0.75)Sr(0.25))(1-x)Cr(0.5)Mn(0.5)O(3) (0 相似文献   

LSM-YSZ nano-composite cathode with YSZ interlayer for solid oxide fuel cells

Low temperature prepared(La_(0.8)Sr_(0.2))_(0.9)MnO_3-δ-Y_(0.15)Zr_(0.85)O_(1.93)(LSM-YSZ) nano-composite cathode has high three-phase boundary(TPB) density and shows higher oxygen reduction reaction(ORR) activity than traditional LSM-YSZ cathode at reduced temperatures. But the weak connection between cathode and electrolyte due to low sintering temperature restrains the performance of LSM-YSZ nano-composite cathode. A YSZ interlayer, consisted of nanoparticles smaller than 10 nm, is introduced by spinning coating hydrolyzed YSZ sol solution on electrolyte and sintering at 800 °C. The thickness of the interlayer is about 150 nm. The YSZ interlayer intimately adheres to the electrolyte and shows obvious agglomeration with LSM-YSZ nano-composite cathode. The power densities of the cell with interlayer are 0.83, 0.46 and 0.21 W/cm~2 under 0.7 V at 800, 700 and 600 °C, respectively, which are 36%, 48% and 50% improved than that of original cell. The interlayer introduction slightly increases the ohmic resistance but significantly decreases the polarization resistance. The depressed high frequency arcs of impedance spectra suggest that the oxygen incorporation kinetics are enhanced at the boundary of YSZ interlayer and LSM-YSZ nanocomposite cathode, contributing to improved electrochemical performance of the cell with interlayer.     

Practical solid oxide fuel cells with anodes derived from self-assembled mesoporous-NiO-YSZ

Solid oxide fuel cells comprised of an anode made from sintered and reduced mesoporous-NiO-YSZ are shown to provide stable current and power densities at the operating temperature of 800 degrees C and show better performance than cells with anode cermets made from mechanical mixtures of NiO and YSZ, attributable to the unique anode microstructure.     

Aqueous electrophoretic deposition of YSZ electrolyte layers for solid oxide fuel cells

A 6-μm-thick, dense, and uniform yttria-stabilized zirconia (YSZ) thin-film electrolyte for solid oxide fuel cell was able to be formed, via aqueous electrophoretic deposition, onto a porous Ni-YSZ cermet anode, which was made via attrition mill, pressure casting, and pressureless sintering. Nonconductive yet suitably porous substrates could be used for electrophoretic deposition, with the help of an auxiliary electrode. Ni/YSZ cermet presintered at 1,200 °C and reduced at 700 °C, on the other hand, behaved like a metal electrode and required no more the use of such an auxiliary electrode. It was also found that the deposition rate increased with increasing current density and with decreasing NH₄-polyacrylate concentration.     

Formation of NiO/YSZ functional anode layers of solid oxide fuel cells by magnetron sputtering

The decrease in the polarization resistance of the anode of solid-oxide fuel cells (SOFCs) due to the formation of an additional NiO/(ZrO₂ + 10 mol % Y₂O₃) (YSZ) functional layer was studied. NiO/YSZ films with different NiO contents were deposited by reactive magnetron sputtering of Ni and Zr–Y targets. The elemental and phase composition of the films was adjusted by regulating oxygen flow rate during the sputtering. The resulting films were studied by scanning electron microscopy and X-ray diffractometry. Comparative tests of planar SOFCs with a NiO/YSZ anode support, NiO/YSZ functional nanostructured anode layer, YSZ electrolyte, and La_0.6Sr_0.4Co_0.2Fe_0.8O₃/Ce_0.9Gd_0.1O₂ (LSCF/CGO) cathode were performed. It was shown that the formation of a NiO/YSZ functional nanostructured anode leads to a 15–25% increase in the maximum power density of fuel cells in the working temperature range 500–800°C. The NiO/YSZ nanostructured anode layers lead not only to a reduction of the polarization resistance of the anode, but also to the formation of denser electrolyte films during subsequent magnetron sputtering of electrolyte.     

不同含钴阴极在YSZ薄膜电解质固体氧化物燃料电池中的性能

固体氧化物燃料电池阴极材料的阻抗对固体氧化物燃料电池的性能有较大影响.我们通过XRD、对称电池以及单电池性能测试等方法比较系统地研究了4种最为常用的含钴阴极材料直接用于钇稳定化氧化锆（YSZ）电解质薄膜与通过引入SDC夹层后用于YSZ电解质薄膜后的性能.我们发现,不同的含钴阴极材料与YSZ材料之间都不同程度地发生相反应,在应用于YSZ电解质薄膜上时,相反应大大降低了含钴阴极材料的性能,在使用了SDC夹层后,单电池的功率输出显著提高.     

Preparation of YSZ thin films for intermediate temperature solid oxide fuel cells by dip-coating method

By studying the effects of different solvents, dispersants and solid loading amount on the suspension stability from sedimentation and viscosity experiments, a simple, effective and highly stable YSZ particle suspension based on MEK/EtOH was developed for dip-coating anode supported electrolyte films for intermediate temperature solid oxide fuel cells (IT-SOFCs). The morphologies of the prepared YSZ thin films from different dip-coating times were studied by scanning electron microscopy (SEM), and a film with a thickness of 16 μm by twice dip-coating was determined to be homogeneous, crack-free and well adherent to the anode substrate. The single cell assembled with this film presents an open-circuit voltage (OCV) of 1.01 V, and a maximum power density of 262 mW cm⁻² under H₂ as the fuel at 800 °C.     

An octane-fueled low temperature solid oxide fuel cell with Ru-free anodes

A Ru-free anode was developed for the direct utilization of iso-octane in low temperature solid oxide fuel cells (SOFCs). The anode was consisted of a Ni framework and a nano-sized oxygen–ion conductor, samaria-doped ceria (SDC), which was coated onto the inner surface of the framework via an ion impregnation process. Compared with the cells based on conventional Ni–SDC anodes, single cells with the SDC-coated Ni anodes exhibited improved stability and enhanced electrochemical activity. Peak power density of 400 mW cm⁻² was achieved at 600 °C, and power generation was relatively stable over 260 h when iso-octane–air mixture was directly used as the fuel. The performance is comparable with those obtained using ceria-Ru as an internal reforming catalyst.     

Intermediate temperature solid oxide fuel cells

High temperature solid oxide fuel cells (SOFCs), typified by developers such as Siemens Westinghouse and Rolls-Royce, operate in the temperature region of 850-1000 degrees C. For such systems, very high efficiencies can be achieved from integration with gas turbines for large-scale stationary applications. However, high temperature operation means that the components of the stack need to be predominantly ceramic and high temperature metal alloys are needed for many balance-of-plant components. For smaller scale applications, where integration with a heat engine is not appropriate, there is a trend to move to lower temperatures of operation, into the so-called intermediate temperature (IT) range of 500-750 degrees C. This expands the choice of materials and stack geometries that can be used, offering reduced system cost and, in principle, reducing the corrosion rate of stack and system components.This review introduces the IT-SOFC and explains the advantages of operation in this temperature regime. The main advances made in materials chemistry that have made IT operation possible are described and some of the engineering issues and the new opportunities that reduced temperature operation affords are discussed.This tutorial review examines the advances being made in materials and engineering that are allowing solid oxide fuel cells to operate at lower temperature. The challenges and advantages of operating in the so-called 'intermediate temperature' range of 500-750 degrees C are discussed and the opportunities for applications not traditionally associated with solid oxide fuel cells are highlighted. This article serves as an introduction for scientists and engineers interested in intermediate temperature solid oxide fuel cells and the challenges and opportunities of reduced temperature operation.     

Comparison of characteristics of solid oxide fuel cells with YSZ and CGO film solid electrolytes formed using magnetron sputtering technique

The work describes the methods of manufacturing single cells of solid oxide fuel cell (SOFC) with thin–film YSZ and CGO electrolytes and also with the bilayer YSZ/CGO electrolyte. Formation of YSZ and CGO films on the supporting NiO–YSZ anode of SOFC was carried out using the combined electron–ionic–plasma deposition technique. The microstructure and phase composition of the formed coatings are studied and also comparative analysis of electrochemical characteristics of single fuel cells with different electrolytes is performed. It is shown that the maximum power density of 1.35 W/cm² at the temperature of 800°C is obtained for the cell with bilayer YSZ/CGO electrolyte. However, the highest performance at lower working temperatures (650–700°C) is characteristic for the fuel cell with single–layer CGO electrolyte; its power density is 600–650 mW/cm².     

Effects of exit-stream mixtures of the steam reforming on the intermediate-temperature solid oxide fuel cells with nickel-based anodes

Journal of Solid State Electrochemistry - Hydrocarbon fuel attracts attention due to its abundant source and low cost. However, carbon deposition damages solid oxide fuel cells (SOFC), especially...     

Chlorine contaminants poisoning of solid oxide fuel cells

Investigation has been conducted on the poisoning effect of various contaminants containing chlorine at ppm level (<10 ppm) on the performance of Ni-YSZ anode-supported solid oxide fuel cells. The results indicate that cell performance drops by exposure to 1 ppm Cl₂(g) at 750 °C, whereas the introduction of Cl₂(g) with concentration higher than 5 ppm causes only a slight degradation at 850 °C. The presence of 2–6 ppm CH₃Cl(g) and C₂H₃Cl(g) can also induce measurable cell performance decline at 750 and 850 °C and this deterioration cannot be completely removed after switching to pure fuel at 850 °C. No performance loss is found when the cell is operated in fuel containing 1–8 ppm HCl(g) at 750 and 850 °C. It is thus concluded that chlorine in the form of Cl₂(g) yields the largest poisoning effect at 750 °C, while the degradation rate caused by addition of C₂H₃Cl(g) increases with the increase of operation temperature. Agglomerations at anodic region are observed in the samples after poisoning test by Cl₂(g), CH₃Cl(g), and C₂H₃Cl(g), but the anode microstructure is uniform for the sample exposed to HCl(g) for poisoning test.     

LSM-infiltrated LSCF cathodes for solid oxide fuel cells

Mixed ionic-electronic conductors in the family of La_xSr_1–xCo_yFe_1–yO_3–δ have been widely studied as cathode materials for solid oxide fuel cells (SOFCs). However, the long-term stability was a concern. Here we report our findings on the effect of a thin film coating of La_0.85Sr_0.15MnO_3–δ (LSM) on the performance of a porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) cathode. When the thicknesses of the LSM coatings are appropriate, an LSM-coated LSCF electrode showed better stability and lower polarization (or higher activity) than the blank LSCF cathode without LSM infiltration. An anode-supported cell with an LSM-infiltrated LSCF cathode demonstrated at 825 °C a peak power density of ～1.07 W/cm², about 24% higher than that of the same cell without LSM infiltration (～0.86 W/cm²). Further, the LSM coating enhanced the stability of the electrode; there was little degradation in performance for the cell with an LSM-infiltrated LSCF cathode during 100 h operation.     

Calcium-containing cathodic material for solid oxide fuel cells

Using the citrate sol-gel method, a new complex oxide Ca_0.75Y_0.25Co_0.15Mn_0.85O_2.92 is synthesized. It is shown that this compound is crystallized in the rhombically distorted version of perovskite structure (a = 0.53397(8), b = 0.7470(1), c = 0.52810(6) nm). The phase is characterized by a low coefficient of thermal expansion (CTE) (13.8 ppm K^?1) and high electric conductivity (135 S/cm at 900°C). The chemical reaction between Ca_0.75Y_0.25Co_0.15Mn_0.85O_2.92 and the YSZ and GDC electrolyte materials is studied. The material is highly reactive and reacts with YSZ and GDC at 900°C and 1070°C, respectively. It is concluded that Ca_0.75Y_0.25Co_0.15Mn_0.85O_2.92 is a promising cathodic material for solid oxide fuel cells, provided a reliable protection SDC sublayer is formed between the cathode and the YSZ membrane.     

Modeling of electrochemical processes in solid oxide fuel cells

A mathematical model of electrochemical processes in a solid oxide fuel cell is presented. A procedure for the calculation of the current—voltage characteristic (CVC) taking into account the influence of the reagent concentration, pressure, and temperature is considered. The problem of calculation of the electromotive force (emf) and thermodynamic efficiency was studied in detail. The influence of the presence of carbon dioxide and water vapor in the anode gas on the emf and thermodynamic efficiency is analyzed. The method of measuring the CVC in an experiment at a constant fuel rate is briefly considered. The results of application of the calculation model are compared with the experimental data.     

High-performance bilayered electrolyte intermediate temperature solid oxide fuel cells

The ESB/GDC bilayer electrolyte concept has been proved to improve open circuit voltage and reduce the effective area specific resistance of SOFCs utilizing a conventional single-layer GDC electrolyte. However, high performance from such bilayer cells had not yet been demonstrated. The main obstacles toward this end have been fabrication of anode-supported thin-film electrolytes and the reactivity of ESB with conventional cathodes. Recently, an ESB-compatible low area specific resistance cathode was developed: microstructurally optimized Bi₂Ru₂O₇-ESB composites. In addition, we recently developed a novel anode functional layer which can significantly enhance the performance of SOFC utilizing GDC electrolytes. This study combines these recent achievements in SOFC studies and shows that exceptionally high performance of SOFC is possible using ESB/GDC bilayer electrolytes and Bi₂Ru₂O₇-ESB composite cathodes. The result confirms that the bilayer electrolyte and the Bi₂Ru₂O₇-ESB cathode can increase the open circuit potential and reduce the total area specific resistance. The maximum power density of the bilayered SOFC was improved to 1.95 W cm^?2 with 0.079 Ω cm² total cell area specific resistance at 650 °C. This is the highest power yet achieved in the IT range and we believe redefines the expectation level for maximum power under IT-SOFC operating conditions.     

X-ray absorption spectroscopic studies on solid oxide fuel cells and proton-conducting ceramic fuel cells

X-ray absorption spectroscopy (XAS) is one of the best techniques to obtain the information on the electronic and local structures of materials. In the last few decades, XAS becomes a common analytical technique for the investigation of solid oxide fuel cells and proton-conducting ceramic fuel cells. In particular, operando and/or advanced XAS measurements can be recently available with the increased accessibility of synchrotron radiation. In this article, recent trends of solid oxide fuel cell and proton-conducting ceramic fuel cell researches using XAS are overviewed.     

Micro-tubular solid oxide fuel cells fabricated by phase-inversion method

A novel structured micro-tubular solid oxide fuel cell (MT-SOFC) has been fabricated by combining a phase-inversion, dip-coating and high temperature co-sintering process with impregnation of the electrode catalyst into a porous electrode matrix. The asymmetric porous anode made by phase-inversion is divided into two different layers, a thick fuel delivery layer with large finger-like pores and a thin function layer with small finger-like pores. The MT-SOFC demonstrates maximum power densities of 0.44, 0.54, 0.65 and 0.78 W/cm² at 650, 700, 750 and 800 °C, respectively with H₂–15%H₂O as fuel and ambient air as oxidant. Combining the power output with the quick start-up behavior, novel structured MT-SOFC offers a potential solution for rapid start-up high performance power devices.