Silver incorporation into cathodes for solid oxide fuel cells operating at intermediate temperature

Silver (Ag) at 0.1–2.0 wt% was incorporated into cathodes for solid oxide fuel cells as a catalyst for oxygen reduction. A novel processing route for Ag incorporation ensuring a very homogeneous Ag ion distribution is presented. From the results of X-ray powder diffraction it can be concluded that the La_0.65Sr_0.3MnO_3– perovskite phase is already formed at 900 °C. The solubility of Ag in the crystal lattice in this type of perovskite was below 1 wt%. The electrochemical tests of these materials show that there is only a slight catalytic effect of Ag. Scanning electron microscopy reveals a low mechanical contact of the cathode grains to the electrolyte due to the low cathode sintering temperature that was chosen.     

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.     

On the history of solid electrolyte fuel cells

The path to the discovery of galvanic solid electrolyte gas cells (J.-M. Gaugain 1853) and to the first industrially produced solid electrolyte gas cells (Nernst lamps 1897) is described. The development of the fundamentals of solid electrolyte fuel cells started with the work of Haber 1905, Schottky 1935, Baur 1937 and Wagner 1943. Extensive work in the field of solid oxide fuel cells (SOFCs) was done in the fifties by Peters and Möbius. After 1960, a rapidly growing number of scientists worked on the different problems of SOFCs, and by 1970 the basis was established on which the broad technologically orientated development of SOFCs proceeds today.     

Study of transition metal oxide doped LaGaO3 as electrode materials for LSGM-based solid oxide fuel cells

Transition metal oxide doped lanthanum gallates, La_0.9Sr_0.1Ga_0.8M_0.2O₃ (where M=Co, Mn, Cr, Fe, or V), are studied as mixed ionic-electronic conductors (MIECs) for electrode applications. The electrochemical properties of these materials in air and in H₂ are characterized using impedance spectroscopy, open cell voltage measurement, and gas permeation measurement. Three single cells based on La_0.9Sr_0.1Ga_0.8 Mg_0.2O₃ (LSGM) electrolyte (1.13 to 1.65 mm thick) but with different electrode materials are studied under identical conditions to characterize the effectiveness of the lanthanum gallate-based MIECs for electrode applications. At 800 °C, a single cell using La_0.9Sr_0.1- Ga_0.8Co_0.2O₃ as the cathode and La_0.9Sr_0.1Ga_0.8Mn_0.2O₃ as the anode shows a maximum power density of 88 mW/cm², which is better than that of a cell using Pt as both electrodes (20 mW/cm²) and that of a cell using La_0.6Sr_0.4CoO₃ (LSC) as the cathode and CeO₂-Ni as the anode (61 mW/cm²) under identical conditions. The performance of LSGM-based fuel cells with MIEC electrodes may be further improved by reducing the electrolyte thickness and by optimizing the microstructures of the electrodes through processing. Received: 9 January 1998 / Accepted: 1 May 1998     

以椰壳生物质炭为燃料的直接炭固体氧化物燃料电池

通过热裂解制得椰壳炭,表征了其结构和组成,并将其用于电解质为钇稳定化氧化锆（YSZ）、电极材料为银和钆掺杂氧化铈（Ag-GDC）的固体氧化物燃料电池（SOFC）的燃料,对所构成的直接炭固体氧化物燃料电池（DC-SOFC）的性能进行了测试研究。结果表明,所制得的椰壳炭颗粒粒径在微米级别,具有介孔结构,而且椰壳炭中含有K、Ca等元素,可用作Boudouard反应催化剂。当使用椰壳炭作为DC-SOFC燃料时,在800 ℃下电池最大功率密度为255 mW/cm²;负载Fe催化剂后,最大功率密度提升为274 mW/cm²。以0.5 A/cm²的恒电流放电,0.5 g负载Fe椰壳炭燃料电池能够连续工作17.6 h,燃料利用率为39%,表明椰壳炭作为DC-SOFC燃料具有优异的性能和潜力。     

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.     

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La _x Sr _y MnO₃ cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.Dedicated to Professor Dr. rer. nat. Hubertus Nickel on the occasion of his 65th birthday     

A 3D fibrous cathode with high interconnectivity for solid oxide fuel cells

A three-dimensional (3D) fibrous cathode of solid oxide fuel cell was fabricated by using eggshell membranes (ESMs) as the template. This cathode possesses high porosity and interconnectivity, and low polarization resistance. A single fuel cell with the 3D fibrous Sm_0.5Sr_0.5CoO₃/Ce_0.8Sm_0.2O_1.9 cathode shows significantly improved performances at low operating temperatures (500–600 °C) as compared with the cell prepared with the ESM-templated cluster cathode in our previous study.     

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.     

固体氧化物直接碳燃料电池阳极反应过程分析

以氧化钇稳定的氧化锆(YSZ)为电解质组装成直接碳燃料电池(DCFC),分别以活性炭(AC)、石墨(G)、神府半焦(SC)作为DCFC燃料,研究了碳燃料的特性、电池操作温度以及阳极反应气氛等对DCFC阳极反应过程的影响。结果表明,三种碳燃料在空气、CO₂气氛中氧化反应活性顺序为AC > SC > G,当三种碳材料作为DCFC燃料时,活性炭作为燃料的DCFC性能最好,半焦燃料次之,石墨作为燃料的DCFC性能最差,而且燃料反应活性与其表面含氧官能团、孔隙结构有关;DCFC的阳极反应过程存在碳燃料直接氧化为CO₂、CO₂与C反应转化为CO,以及CO氧化为CO₂等。     

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.     

通过溅射与退火制备的用于固体氧化物燃料电池的氧化钆掺杂氧化铈电解质隔层

采用溅射或溅射与退火相结合的方法制备了一系列氧化钆掺杂的氧化铈（GDC）隔层,并考察了其对固体氧化燃料电池性能的影响. 结果表明,200 ℃下溅射获得了立方结构氧化钆掺杂的氧化铈均匀薄膜,在900-1100 ℃范围内的退火处理使得GDC薄膜致密,从而有效阻止了氧化钇掺杂的氧化锆电解质与阴极材料之间的反应,大幅度提高了电池的电化学性能.     

Effect of pretreatments on the anode structure of solid oxide fuel cells

An important objective in the development of solid oxide fuel cell (SOFC) is to produce thin stabilized zirconia electrolytes that are supported upon the nickel–zirconia composite anode. Although this will reduce some of the problems associated with SOFCs by permitting lower temperature operation, this design may encounter problems during start- up. The first step in a start-up involves the reduction of nickel oxide in the anode to metallic nickel and increase of three-phase boundary will be beneficial for further reaction. In this study, two pretreatment methods are investigated for their effects on the performances of SOFC. Performances of the SOFCs are influenced by the pretreatment conditions, which included exposure of the cells to dilute H₂/O₂ either under open-circuit or closed-circuit conditions before their performance studies. By carrying out the methods, the pretreatment using the closed circuit is found to attain much higher performances effectively and efficiently. Accompanying with SEM and element analysis, increase of three-phase boundary is considered to give rise to changes in the anode microstructure, leading to activation of the anode. Mechanisms of NiO in anode reducing to Ni and porous structure via different pretreatments and their effects on the anode microstructure are proposed.     

LaNi0.6Fe0.4O3 as a cathode contact material for solid oxide fuel cells

In solid oxide fuel cells (SOFCs) the interconnects electrically link air and fuel electrodes on either side to produce a practical electrical power output. The long-term stability of intermediate temperature (650–800 °C) SOFC operation strongly depends on the composition of the ferritic steel interconnection material and the steel/ceramic interface. During high-temperature operation the Cr-containing ferritic steel forms an oxide scale at its surface, thereby causing high ohmic electrical contact resistance when connected to the surface of an electronically conducting ceramic cathode material. In the long run, the vaporization of Cr species from these oxide scales also affects the cathode activity, eventually leading to cell deterioration. One way of overcoming the problem is to incorporate another electronically conducting ceramic compliant layer, commonly known as the contact layer, between the cathode and metallic interconnect. In this contribution, LaNi_0.6Fe_0.4O₃ was tested as a cathode contact material. Its performance at 800 °C in the form of a ~50 μm thick film applied on two ferritic steel compositions was examined. After 600 h of testing, contact resistances of 60 and 160 mΩ cm² were obtained. The different values are explained by the variation in steel composition.     

Protective coatings based on Mn-Co spinel for current collectors of solid oxide fuel cells

The method of electrostatic spray pyrolysis was designed to apply protective coatings based on Mn-Co spinel to ferrite stainless steels (Crofer22APU and 08Kh18T1). The comparative thermogravimetric (TG) studies of ferrite stainless steels with and without protective coatings were carried out. The electrochemical characteristics of protective coatings exposed to long current loading were studied. The formation processes of Cr₂O₃ oxide films were studied at the contact of ferrite stainless steel with La_0.8Sr_0.2MnO₃ ionic and electronic conductor. The coatings of Mn-Co spinel were shown not preventing formation of continuous oxide film on the stainless steel surface.     

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   

Ln_2MO_4 cathode materials for solid oxide fuel cells

One of the major challenges to develop intermediate temperature solid oxide fuel cells is finding a novel cathode material, which can meet the following requirements: (1) high electronic conductivity; (2) chemical compatibility with the electrolyte; (3) a matched thermal expansion coefficient (TEC); (4) stability in a wide range of oxygen partial pressure; and (5) high catalytic activity for the oxygen reduction reaction (ORR). In this short review, a survey of these requirements for K2NiF4-type material wi...     

Development of an O-ring from NR/EPDM filled silica/CB hybrid filler for use in a solid oxide fuel cell testing system

This research presents the effects of oxygen pressure and ambient temperatures on the crack behavior of O-rings from a semi-EV of NR/EPDM rubber with silica/CB filler, exposed to the inlet flow and outflow oxygen pressure in a Solid Oxide Fuel Cell (SOFC) environment. Blends of NR/EPDM were prepared with various ratios of silica/CB filler at 00/60, 10/50, 20/40, 30/30, 40/20, 50/10, and 60/00 phr. The fabricated O-ring complied with the standard for O-rings (TIS 2728-2559), with a minimum hardness of 65–75 Shore A, minimum tensile strength of 9 MPa, minimum elongation at break of 200%, and a minimum 100% modulus of 2.7 MPa. The mechanical properties of the compounds were tested, and the appropriate compound was chosen to make the O-rings to test in SOFC. The crack morphology of the fabricated O-rings was investigated and compared with a commercial O-ring after testing in the SOFC. As a result, the compound with silica/CB of 40:20 ratio provided the optimum mechanical properties, and passed the criteria standard of TIS 2728-2559. The mechanical properties of the prepared and commercial O-rings were similar (P-value of commercial with 60/00 = 0.273, 50/10 = 0.273, 40/20 = 0.144, 30/30 = 0.465, 20/40 = 0.465, 10/50 = 1.000 and 00/60 = 0.273; all > 0.05) and and both could still be continued to be used in SOFC despite some inner cracks after 24 h. The price of the prepared O-ring is cheaper than the commercial O-rings due to the low price of NR used in its formulation. Therefore, a prepared O-ring can be used in a SOFC, or other applications due to their mechanical properties and their reasonable price.     

Activation of a single-chamber solid oxide fuel cell by a simple catalyst-assisted in-situ process

Initialization is a critical processing step that has thus far limited the application of the single-chamber solid oxide fuel cell (SC-SOFC). In-situ initialization of a SC-SOFC with a nickel-based anode by methane–air mixtures was investigated. Porous Ru–CeO₂ was used as a catalyst layer over a Ni-ScSZ cermet anode. Catalytic testing demonstrated Ru–CeO₂ had high activity for methane oxidation. The Ru in the catalyst layer catalyzed the formation of syngas, which successfully reduced the nickel oxide to metallic nickel in the anode. Single cells with a La_0.8Sr_0.2MnO₃ (LSM) cathode, initialized by this in-situ reduction method, delivered peak power densities of 205 and 327 mW cm⁻² at 800 °C and 850 °C, respectively. Such performances were better than those of the cell without the Ru–CeO₂ catalyst layer that was initialized by an ex-situ reduction method were.