Coal syngas reactivity over Ni-added LSCF–GDC anode of solid oxide fuel cells

Coal syngases of various CO/H₂ ratios were used as the fuel over anode of solid oxide fuel cells. Anode materials of La_0.58Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF)–gadolinia-doped ceria (GDC) composites and Ni-added LSCF–GDC were tested. The maximum power density of CO is higher than that of H₂ and increases as the CO concentration in the CO + H₂ mixture increases. As the LSCF content in the LSCF–GDC composites increases, the H₂ reactivity increases but the CO reactivity decreases. The maximum power density of Ni-added LSCF–GDC is highest but the steady-state current density of LSCF–GDC can be higher than that of Ni-added LSCF–GDC via an induction period of activation.     

A comprehensive three-dimensional modeling of an internal reforming planar solid oxide fuel cell with different interconnect designs

Development of low-emission or zero-emission power generation systems is one of the most important subjects humanity is dealing with. Among different under development technologies and energy systems, a solid oxide fuel cell (SOFC) is an efficient and low-emission energy conversion device that is passing its research and development career. The current study aims to investigate a hydrocarbon fueled anode-supported planar-type SOFC due to simpler geometry, higher power density, and low overpotentials. In this study, electric performance of a SOFC with different interconnect designs under different operating conditions, such as operating voltage, channel inlet temperature, pre-reforming rate of methane, and inlet fuel and air velocity, has been investigated by use of a three-dimensional model considering complicated systems of equations: species mass conservation, first law of thermodynamics, conservation of momentum, and non-linear electrochemical models including multi-specious diffusion. It has been concluded that at a given voltage, inlet temperature, inlet air and fuel velocity, and pre-reforming rate, wider gas channels help to more uniform distribution and better penetration of reactant gases. Therefore, considering low-concentration polarization as an object, narrow ribs are preferred over wide ribs. By increasing the rate of the electrochemical reaction, the current and power density and subsequently the temperature difference increase but the fuel consumption in all cases has almost a decreasing trend. Also, it has been found that increasing inlet air velocity has little effect on current and power density but because of more cooling effect, it reduces the temperature difference and fuel consumption coefficient. On the other hand, increasing the inlet temperature has no meaningful effect on the temperature difference along the channels.

     

YSZ传导膜H_2S固体氧化物燃料电池

研究了Y2O3稳定的ZrO2(YSZ)氧离子传导膜H2S固体氧化物燃料电池性能。掺杂NiS、电解质、Ag粉和淀粉制备了双金属复合MoS2阳极催化剂,掺杂电解质、Ag粉和淀粉制备了复合NiO阴极催化剂,用扫描电镜对YSZ和膜电极组装(MEA)进行了表征,比较了不同电极催化剂的性能和极化过程,考察了不同温度对电池性能的影响。结果表明,双金属复合MoS2/NiS阳极催化剂在H2S环境下比Pt和单金属MoS2催化剂稳定,复合NiO阴极催化剂比Pt性能好,在电极催化剂中加入Ag可显著提高电极的导电性;与Pt电极相比,复合MoS2阳极和复合NiO阴极催化剂的过电位较小,阳极的极化比阴极侧小;温度升高,电池的电流密度与功率密度增加,电化学性能变好。在750℃、800℃、850℃和900℃及101.13 kPa时,结构为H2S、(复合MoS2阳极催化剂)/YSZ氧离子传导膜/(复合NiO阴极催化剂)、空气的燃料电池最大功率密度分别为30 mW/cm2、70 mW/cm2、155 mW/cm2及295 mW/cm2、最大电流密度分别为120 mA/cm2、240 mA/cm2、560 mA/cm2和890 mA/cm2。     

Symmetrical solid oxide fuel cell with strontium ferrite-molybdenum electrodes

The work contains the results of studies of a promising composite material of Sr₂Fe_1.5Mo_0.5O₆ + Ce_0.8Sm_0.2O_1.9 for electrodes of symmetrical solid oxide fuel cells. It is shown that conductivity of the composite at 800°C is about 10 and 15 S/cm, for air and humid hydrogen, respectively, and polarization resistance of the electrodes in contact with the electrolyte based on doped lanthanum gallate under the same conditions is about 0.26 and 0.12 Ohm cm². Tests of a symmetrical fuel cell with a planar design and the supporting gallate electrolyte with the thickness of 300 μm show that the cell can develop the power of about 0.5 W/cm² at 800°C when air is supplied to the cathode and humid hydrogen is supplied to the anode. Analysis of polarization losses shows that the polarization of the oxygen electrode considerably exceeds the polarization of the anode.     

EPMA of interfaces applied to the solid oxide fuel cell

Chemical interactions at the phase boundaries of materials applied for the solid oxide fuel cell (SOFC) have been studied by EPMA. The chemical reactivity at the interface of La_y-xSr_xMnO₃/ZrO₂-Y₂O₃ is dependent on the stoichiometry (y) and the Sr content (x) of the perovskite. Typical reaction products (zirconates) and a diffusion zone in the ZrO₂–Y₂O₃ have been observed. The extension of cation release (Mn) is related to the increasing chemical activity of Mn oxide in the perovskite by the Sr substitution for La. The wettability of the metal/oxide interface in the anode cermet (Ni/ZrO₂–Y₂O₃) has been found to be influenced by chemical reactions resulting from the applied reducing atmosphere with high carbon activity. The disintegration of ZrO₂–Y₂O₃ in contact with molten Ni or Ni-Ti and Ni-Cr alloys leads to the redeposition of Y₂O₃-enriched oxides and also to Zr-rich intermetallic compounds and eutectics.     

固体氧化物燃料电池直接以焦炭为燃料的电性能

直接碳固体氧化物燃料电池（DC-SOFC）是一种潜在的固体碳燃料高效率、低污染发电技术。本研究报道了将工业焦炭直接用作管式DC-SOFC燃料的研究。制备了电极材料为Ag-GDC （钆掺杂氧化铈）的YSZ （钇稳定化氧化锆）电解质支撑型管式固体氧化物燃料电池（SOFC）。采用拉曼光谱、扫描电镜和X射线能谱仪对焦炭燃料进行了性质表征。结果表明,焦炭燃料呈微米级的颗粒状,并含有大量对Boudouard反应有利的缺陷结构。电池以纯焦炭为燃料在850℃取得的最大功率密度为149mW/cm²,在碳燃料表面负载能提高Boudouard反应速率的Fe催化剂后,最大功率密度提高至217mW/cm²。通过电化学测试和尾气表征,分析了恒电流放电过程中电池的性能衰减机制。测试结果证明了将焦炭直接用作全固态DC-SOFC的燃料产生电能的可行性。     

Quantitative three-dimensional microstructure of a solid oxide fuel cell cathode

Solid oxide fuel cells (SOFCs) are being actively developed world wide for clean and efficient electrical generation from fuels such as natural gas, hydrogen, coal, and gasoline. The cathode in state of the art SOFCs is typically a porous composite of electronically-conducting La_1?xSr_xMnO₃ (LSM) and ionically-conducting Y₂O₃-stabilized ZrO₂ (YSZ) that facilitates the critical oxygen reduction reaction. Here we describe the three-dimensional characterization and quantification of key structural parameters from an LSM-YSZ cathode, using imaging and volume reconstruction based on focused ion beam – scanning electron microscopy. LSM-YSZ-pore three-phase boundaries (TPBs) were identified. Approximately 1/3 of the TPBs were found to be electrochemically inactive, as they were on isolated LSM particles, yielding an active TPB density of 4.9 μm^?2. Cathode electrochemical modeling, which included a measured YSZ tortuosity of 3.4, yielded an effective TPB resistance of ≈2.5 × 10⁵ Ω cm at 800 °C.     

Prediction of infiltrated solid oxide fuel cell cathode polarization resistance

The polarization resistance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF)-infiltrated Ce_0.9Gd_0.1O_1.95 cathodes was quantitatively explained using a simple model where the resistance scaled directly with the LSCF surface area, as estimated from cross-sectional fracture surfaces. The Tanner, Fung, Virkar composite cathode model was also applied and showed that ionic transport in these 25-μm-thick cathodes was not a significant limitation at 600 °C, but became more limiting at 700 °C. Calculated polarization resistances were within ～40% (without fitting parameters) of reported values.     

EPMA of interfaces applied to the solid oxide fuel cell

Chemical interactions at the phase boundaries of materials applied for the solid oxide fuel cell (SOFC) have been studied by EPMA. The chemical reactivity at the interface of La(y-x)Sr(x)MnO(3)/ZrO(2)-Y(2)O(3) is dependent on the stoichiometry (y) and the Sr content (x) of the perovskite. Typical reaction products (zirconates) and a diffusion zone in the ZrO(2)-Y(2)O(3) have been observed. The extension of cation release (Mn) is related to the increasing chemical activity of Mn oxide in the perovskite by the Sr substitution for La. The wettability of the metal/oxide interface in the anode cermet (Ni/ZrO(2)-Y(2)O(3)) has been found to be influenced by chemical reactions resulting from the applied reducing atmosphere with high carbon activity. The disintegration of ZrO(2)-Y(2)O(3) in contact with molten Ni or Ni-Ti and Ni-Cr alloys leads to the redeposition of Y(2)O(3)-enriched oxides and also to Zr-rich intermetallic compounds and eutectics.     

A direct-methane solid oxide fuel cell with a double-layer anode

A tubular anode-supported solid oxide fuel cell with a double-layer anode for the direct conversion of CH₄ has been prepared and operated at 800 °C successfully. The double-layer anode was composed of NiO–YSZ and CoO–NiO–SDC acting as supporting layer and active reforming layer, respectively. At 800 °C, a maximum power density of 350 mW cm⁻² was obtained with CH₄ as fuel and air as oxidant. The time-dependent impedance spectra of the tubular cell were examined and discussed. No carbon deposition was observed on the surface of the anode when the cell was operated at a constant current density of 250 mA cm⁻².     

Structure-designed gadolinia doped ceria interlayer for solid oxide fuel cell

A bi-structured gadolinia doped ceria (GDC) interlayer, which has a dense layer combining tightly with yttria-stabilized zirconia (YSZ) film and a porous layer with rough surface for contacting closely with the cathode, is prepared from a two-step sputtering process. Compared to the cell with a dense GDC interlayer, the single cell with the bi-structured GDC interlayer depicts greatly reduced ohmic and polarization resistances and increased electrochemical performance.     

Effects of low hydrocarbons on the solid oxide fuel cell anode

In this work, the effects of ethylene on the solid oxide fuel cell (SOFC) anode were investigated both for an SOFC single cell and an SOFC stack. Two fuels were used to observe the effects that low hydrocarbons (over C1-hydrocarbons) in the reformate gas stream have on the SOFC anode. Methane or ethylene was supplied to the electrolyte-supported SOFC anode. Using ethylene as a fuel, catastrophic degradation of SOFC performance was observed due to ethylene-induced carbon deposition onto the SOFC anode. Thus, a new methodology, termed “post-reforming,” is introduced for the removal of low hydrocarbons (over C1-hydrocarbons) from the reformate gas stream. The CGO-Ru catalyst was selected as the post-reforming catalyst because of its high selectivity for removing low hydrocarbons (over C1-hydrocarbons) and for its long-term stability. The diesel reformer and post-reformer were continuously operated for ∼250 h in coupled-operation mode. The reforming performance was not degraded, and low hydrocarbons (over C1-hydrocarbons) in the diesel reformate were completely removed.     

High-temperature Raman spectroscopy of solid oxide fuel cell materials and processes

Chemical and material processes occurring in high temperature environments are difficult to quantify due to a lack of experimental methods that can probe directly the species present. In this letter, Raman spectroscopy is shown to be capable of identifying in-situ and noninvasively changes in material properties as well as the formation and disappearance of molecular species on surfaces at temperatures of 715 degrees C. The material, yttria-stabilized zirconia or YSZ, and the molecular species, Ni/NiO and nanocrystalline graphite, factor prominently in the chemistry of solid oxide fuel cells (SOFCs). Experiments demonstrate the ability of Raman spectroscopy to follow reversible oxidation/reduction kinetics of Ni/NiO as well as the rate of carbon disappearance when graphite, formed in-situ, is exposed to a weakly oxidizing atmosphere. In addition, the Raman active phonon mode of YSZ shows a temperature dependent shift that correlates closely with the expansion of the lattice parameter, thus providing a convenient internal diagnostic for identifying thermal gradients in high temperature systems. These findings provide direct insight into processes likely to occur in operational SOFCs and motivate the use of in-situ Raman spectroscopy to follow chemical processes in these high-temperature, electrochemically active environments.     

Crystallization kinetics of basalt-based glass-ceramics for solid oxide fuel cell application

Journal of Thermal Analysis and Calorimetry - Solid oxide fuel cell (SOFC) is a very efficient and clean source of energy. The glass and glass-ceramics are the most suitable and compatible sealing...     

Direct oxidation of sulfur-containing fuels in a solid oxide fuel cell

Solid-oxide fuel cells with Cu-ceria anodes are shown to provide stable power generation through the direct oxidation of hydrocarbon fuels having sulfur levels similar to that in gasoline and can be regenerated by steam after being poisoned with higher sulfur levels.     

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。     

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.     

薄膜型中温固体氧化物燃料电池 (SOFC)研制及性能考察

用一种廉价的湿化学方法 ,在Ni_YSZ阳极基膜上制备出致密的YttriaStabilizedZirconia(YSZ)薄膜 .薄膜的厚度约为 10 μm ,致密均匀 ,无裂纹等缺陷 .以Ni_YSZ阳极基膜 ,YSZ薄膜和锶掺杂锰酸镧阴极 (LSM )组装的SOFC单电池 ,在 80 0℃下功率密度达 0 1W /cm2 .研究分析表明 ,YSZ薄膜的IR降 (包括电极 /YSZ薄膜的接触电阻 )较小 ,不是影响电池性能的主要因素 ,大的阳极过电位是影响电池性能的主要因素 .     

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.