中温固体氧化物燃料电池优势和挑战的简要评述

燃料电池是一种将燃料的化学能直接转化为电能的电化学发电装置. 在各种类型的燃料电池中,固体氧化物燃料电池（SOFC）在600~800 ^oC的中温区运行,因此与质子交换膜燃料电池等低温燃料电池相比,它的燃料选择范围更广,具有更广泛的应用前景. 然而,SOFC的商业应用面临着两大挑战：成本和稳定性. 这两种挑战与阳极、阴极、电解质、连接体和密封材料等组件的加工、制备、性能、化学和微结构稳定性密切相关. 电池堆的导管连接材料也需要经过仔细地筛选,以最大限度地降低有毒害的挥发性成分,从而确保电池结构的稳定和完整. 本文旨在简要评述SOFC的材料和组分的研究现状,并提出展望. 本文也对新一代SOFC技术面临的机遇和挑战进行了探讨.     

In-situ construction of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoarrays on La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3-δ</Subscript> electrodes for intermediate temperature solid oxide fuel cells

Novel NiCo₂O₄ nanoarrays have been in-situ grown on a La_0.8Sr_0.2MnO_3-δ(LSM) cathode through a hydrothermal method, which presents the enhanced electrochemical performances of the LSM cathode for the intermediate temperature solid oxide fuel cells. XRD and SEM have been used to characterize phase structure and morphology of NiCo₂O₄ nanoarrays. The LSM cathode, modified by the NiCo₂O₄ nanoarrays, exhibits excellent electrochemical performances compared with the bare LSM cathode. The maximum peak power density of single cell, based on the NiCo₂O₄ nanoarrays modified the LSM cathode, reaches 957 mW cm^?2 at 800 °C, which is almost two times higher than that for the cell based on the bare LSM cathode.     

Characteristics of the La0.6Sr0.4Fe0.8Co0.2O3 − δ electrode in contact with the lanthanum gallate-based electrolyte

Lowering the working temperature of solid oxide fuel cells (SOFCs) is the main trend in their development, which requires selection of materials for electrolyte and electrodes. A highly conducting lanthanum gallate-based electrolyte is a promising material for creating medium-temperature SOFCs. The electrochemical characteristics of the La_0.6Sr_0.4Fe_0.8Co_0.2O_{3 ? δ} cathode that contacted with the La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 electrolyte subject to electrode formation temperatures have been investigated. It was found that at optimum bake-on temperatures of 1200–1250°C, the cathode polarization resistance at 800°C was ～0.08 Ohm cm², which is comparable to the world’s best achievements.     

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.     

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.     

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.     

An Aurivillius Oxide Based Cathode with Excellent CO2 Tolerance for Intermediate‐Temperature Solid Oxide Fuel Cells

The Aurivillius oxide Bi₂Sr₂Nb₂MnO_12?δ (BSNM) was used as a cobalt‐free cathode for intermediate‐temperature solid oxide fuel cells (IT‐SOFCs). To the best of our knowledge, the BSNM oxide is the only alkaline‐earth‐containing cathode material with complete CO₂ tolerance that has been reported thus far. BSNM not only shows favorable activity in the oxygen reduction reaction (ORR) at intermediate temperatures but also exhibits a low thermal expansion coefficient, excellent structural stability, and good chemical compatibility with the electrolyte. These features highlight the potential of the new BSNM material as a highly promising cathode material for IT‐SOFCs.     

A novel multistep dip-coating method for the fabrication of anode-supported microtubular solid oxide fuel cells

A novel multistep dip-coating method was developed and successfully applied to the fabrication of anode-supported microtubular solid oxide fuel cells (SOFCs) using carbon rods as combustible cores. The fabricated microtubular SOFCs consisted of Ni-yttria-stabilized zirconia (YSZ), YSZ, strontium-doped lanthanum manganite (LSM)–YSZ, and LSM as the anode, electrolyte, cathode, and cathode current collector materials, respectively. To investigate the role of anode porosity on cell performance, two types of anode supports were prepared: one without a pore former and the other with a 10 wt.% graphite pore former. The microstructural features of the microtubular SOFCs were examined using scanning electron microscope images whereas the electrochemical performance was characterized by electrochemical impedance spectroscopy measurements as well as I–V characteristic curves. The results showed that the method used is a simple and low-cost alternative to conventional methods for the fabrication of microtubular SOFCs. We found that the anode porosity played an important role in improving the overall performance of the microtubular SOFC by reducing the concentration polarization.     

Synthesis and characterization of PrBaCo2 − x Ni x O5 + δ cathodes for intermediate temperature SOFCs

Nickel-substituted layered perovskite PrBaCo_{2 ? x} Ni _x O_{5 + δ} (PBCN) powders with various proportions of nickel (x?=?0, 0.1, 0.2, and 0.3, abbreviated as PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively) are investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) based on the yttria-stabilized zirconia (YSZ) electrolyte. It is found that PBCN-1 has the highest electrical conductivity of 1,397 S cm^?1 at 400 °C. Substitution of Co by Ni decreases the thermal expansion coefficient (TEC) clearly. The average TEC at the temperature range of 35–900 °C decreases from 22.8?×?10^?6 K^?1 for PBCN-0 to 18.9?×?10^?6 K^?1 for PBCN-3. The polarization resistances of PBCN samples on YSZ electrolyte at 800 °C are 0.053, 0.048, 0.052, and 0.042 Ω cm² for PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively. The single fuel cell with the configuration of PBCN-3/YSZ/Pt delivers the highest power densities of 100, 185, 360, 495, and 660 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively.     

(La0.8Sr0.2)0.9MnO3–Gd0.2Ce0.8O1.9 composite cathodes prepared from (Gd, Ce)(NO3) x -modified (La0.8Sr0.2)0.9MnO3 for intermediate-temperature solid oxide fuel cells

Development of high performance cathodes with low polarization resistance is critical to the success of solid oxide fuel cell (SOFC) development and commercialization. In this paper, (La_0.8Sr_0.2)_0.9MnO₃ (LSM)–Gd_0.2Ce_0.8O_1.9(GDC) composite powder (LSM ~70 wt%, GDC ~30 wt%) was prepared through modification of LSM powder by Gd_0.2Ce_0.8(NO₃) _x solution impregnation, followed by calcination. The electrode polarization resistance of the LSM–GDC cathode prepared from the composite powder was ~0.60 Ω cm² at 750 °C, which is ~13 times lower than that of pure LSM cathode (~8.19 Ω cm² at 750 °C) on YSZ electrolyte substrates. The electrode polarization resistance of the LSM–GDC composite cathode at 700 °C under 500 mA/cm² was ~0.42 Ω cm², which is close to that of pure LSM cathode at 850 °C. Gd_0.2Ce_0.8(NO₃) _x solution impregnation modification not only inhibits the growth of LSM grains during sintering but also increases the triple-phase-boundary (TPB) area through introducing ionic conducting phase (Gd,Ce)O_2-δ, leading to the significant reduction of electrode polarization resistance of LSM cathode.     

Cathode infiltration with enhanced catalytic activity and durability for intermediate-temperature solid oxide fuel cells

To lower the operation temperature and increase the durability of solid oxide fuel cells(SOFCs), increasing attentions have been paid on developing cathode materials with good oxygen reduction reaction(ORR)activity at intermediate-temperature(IT, 500–750 °C) range. However, most cathode materials exhibit poor catalytic activity, or they thermally mismatch with SOFC electrolytes and undergo severe degeneration. Infiltrating catalysts on existing backbone materials has been proved to be an efficie...     

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.     

Options for adjustment of microstructure and conductivity of cathodic substrates of La(Sr)MnO<Subscript>3</Subscript>

The electrodes of solid-oxide fuel cells (SOFCs) must be characterized by high conductivity to decrease ohmic losses and sufficient porosity to provide high gas diffusion rate. In the cases, when the SOFC electrodes are substrates, they must be synthesized at the temperature above the temperature of formation of their solid-electrolyte coating. Herewith, manufacturing of supporting electrodes with the required micro-structure is rather complicated. The present paper studies the effect of the method of manufacturing of the initial La_0.6Sr_0.4MnO₃ (LSM) powders, their degree of dispersion, introduction of sintering additives and pore agents on their microstructure, conductivity, and possibility of adjusting the temperature of SOFC cathodic substrate formation at which the required characteristics are reached. It is shown that sintering of cathodic substrates to the relative density of 65–70% can be carried out at the temperatures from 1050 to 1350–1400°C, which would allow obtaining electrolyte films of powders with different sintering ability on such substrates. The average pore size in cathodic substrates can be varied in the range of 0.4 to 2.5 μm by using the initial LSM powder with different dispersion degree and by employing graphite as a pore agent. At 900°C, conductivity of cathodic substrates of LSM grows at an increase in their relative density from 50% to 70% approximately from 50 to 100 S/cm and weakly depends on the dispersion degree of the initial powders.     

Electrode performance and X-ray absorption spectroscopy of La0.8Sr0.2Mn1−x Cu x O3 (0 ≤ x ≤ 0.2)–GDC composite cathodes for SOFCs

Electrochemical properties of composite cathodes consisting of La_0.8Sr_0.2Mn_1?x Cu _x O₃ (LSMCu, 0?≤?x?≤?0.2) and Ce_0.8Gd_0.2O_2?x (GDC) were determined by impedance spectroscopy, and conduction mechanism for the composite cathodes was investigated by a near-edge X-ray absorption fine-structure analysis (NEXAFS). LSMCu–GDC cathodes showed lower polarization resistance (R _p) than LSM–GDC up to 750 °C, whereas they exhibited better performance at higher temperature (≥800 °C). The best performance was achieved with the LSMCu10–GDC cathode: 0.27 and 0.08?Ω cm² at 800 °C and 850 °C, respectively. NEXAFS and refinement results confirmed that Cu doping caused the oxidation of Mn³⁺ to Mn⁴⁺ and lattice contraction. This additional Mn⁴⁺ can lead to the formation of oxygen vacancies when Mn⁴⁺ is converted to Mn³⁺ at relatively high temperatures (above 600 °C). This in turn contributes to improved oxygen ion transport in LSM. The LSMCu–GDC composite cathode can thus be considered a suitable potential cathode for SOFC applications.     

Fabrication and performance test of solid oxide fuel cells with screen-printed yttria-stabilized zirconia electrolyte membranes

Yttria-stabilized zirconia (YSZ) membranes were deposited onto porous NiO–YSZ anode supports by screen printing. Combined with La_0.7Sr_0.3MnO₃–YSZ composite cathode, the prepared anode-supported solid oxide fuel cells (SOFCs) were electrochemically tested. A typical SOFC with a 30-μm-thick YSZ electrolyte membrane gave the maximum power densities (MPDs) of 0.26, 0.53, 0.78, and 1.03 W/cm² at 650, 700, 800, and 850 °C, respectively, using hydrogen as fuel and stationary air as oxidant. Replacement of stationary air with pure oxygen flow exerted a significant positive effect on the MPDs of the cell. Using 100- and 200-ml/min oxygen as oxidants, the MPDs of the cell were enhanced 35.3% and 68.6%, respectively. Polarization analysis indicated that, at the MPD points, the electrode polarization resistances accounted for 80% of the cell total resistances.

     

Barium carbonate nanoparticle as high temperature oxygen reduction catalyst for solid oxide fuel cell

BaCO₃ nanoparticles are demonstrated as outstanding electrocatalysts to enhance the high temperature oxygen reduction reaction (ORR) in solid oxide fuel cells (SOFCs). BaCO₃ nanoparticles are formed from thermal decomposition of barium acetate, Ba(Ac)₂ infiltrated to porous cathode skeleton and shows good chemical compatibility with cathode materials. BaCO₃ nanoparticles can greatly reduce the area specific resistance (ASR) of typical SOFC cathode materials, including La_0.8Sr_0.2FeO_3 -δ (LSF), La_0.6Sr_0.4Co_0.2Fe_0.8O_3 -δ (LSCF) and La_0.8Sr_0.2MnO_3 -δ (LSM). For example at 700 °C, ASR for LSF on yttria-stabilized zirconia (YSZ) electrolyte decreases from 2.95 Ω cm² to 0.77 Ω cm² when 12.9 wt.% BaCO₃ nanoparticles are deposited on the surface of the porous LSF electrode. Impedance spectra analysis shows that the decrease in ASR mainly comes from the reduction of the low frequency resistance. Furthermore, BaCO₃ nanoparticles are found to greatly enhance the oxygen chemical exchange coefficient. Most importantly, it has been found that the catalytic activity of BaCO₃ nanoparticles is even higher than those of the precious metals such as Pd, Rh, Pt and Ag, infiltrated into LSF, LSCF and LSM electrodes supported on YSZ electrolytes.     

固-溶法制备中温固体氧化物燃料电池高性能La0.8Sr0.2MnO3-Ba0.5Sr0.5Co0.8Fe0.2O3阴极

研究了新型固溶法合成La_0.8Sr_0.2MnO₃（LSM）包覆Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃（BSCF）复合粉体（LSM-BSCF）,并探讨了其作为中温固体氧化物燃料电池阴极材料的电化学性能。LSM-BSCF阴极结合了LSM和BSCF阴极的优点,不仅增大了三相界面,而且稳定了微观结构。当温度为600-750℃时,其极化阻抗为0.61-0.09 Ω·cm²。与溶液注入法制备的高性能电极相比,极大地提高了性能稳定性。     

Cathode materials for solid oxide fuel cells: a review

The composition and microstructure of cathode materials has a large impact on the performance of solid oxide fuel cells (SOFCs). Rational design of materials composition through controlled oxygen nonstoichiometry and defect aspects can enhance the ionic and electronic conductivities as well as the catalytic properties for oxygen reduction in the cathode. Cell performance can be further improved through microstructure optimization to extend the triple-phase boundaries. A major degradation mechanism in SOFCs is poisoning of the cathode by chromium species when chromium-containing alloys are used as the interconnect material. This article reviews recent developments in SOFC cathodes with a principal emphasis on the choice of materials. In addition, the reaction mechanism of oxygen reduction is also addressed. The development of Cr-tolerant cathodes for intermediate temperature solid oxide fuel cells, and a possible mechanism of Cr deposition at cathodes are briefly reviewed as well. Finally, this review will be concluded with some perspectives on the future of research directions in this area.     

Fabrication and performance test of solid oxide fuel cells with screen-printed yttria-stabilized zirconia electrolyte membranes

Yttria-stabilized zirconia (YSZ) membranes were deposited onto porous NiO?CYSZ anode supports by screen printing. Combined with La_0.7Sr_0.3MnO₃?CYSZ composite cathode, the prepared anode-supported solid oxide fuel cells (SOFCs) were electrochemically tested. A typical SOFC with a 30-??m-thick YSZ electrolyte membrane gave the maximum power densities (MPDs) of 0.26, 0.53, 0.78, and 1.03?W/cm² at 650, 700, 800, and 850?°C, respectively, using hydrogen as fuel and stationary air as oxidant. Replacement of stationary air with pure oxygen flow exerted a significant positive effect on the MPDs of the cell. Using 100- and 200-ml/min oxygen as oxidants, the MPDs of the cell were enhanced 35.3% and 68.6%, respectively. Polarization analysis indicated that, at the MPD points, the electrode polarization resistances accounted for 80% of the cell total resistances.     

Preparation and characterization of ceria-Based electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFC)

Solid-oxide fuel cells (SOFCs) can be used for clean, efficient and environment-friendly energy conversion with a variety of fuels at high temperature (1273 K). The high temperature operation accelerates unwanted reactions and creates materials challenges; so, intermediate-temperature SOFCs (IT-SOFCs) have been developed. Reduction of the operating temperature (between 873–1073 K) requires solid electrolyte materials with higher conductivities. In this study, partially substituted ceria as solid electrolyte is experimented systematically for use in solid oxide fuel cells operating below 1073 K (intermediate temperature range). Nine compositions namely, CeO₂, Ce_0.95Gd_0.05O_2-δ (CGO9505), Ce_0.90Gd_0.10O_2-δ (CGO9010), Ce_0.85Gd_0.15O_2-δ (CGO8515), Ce_0.80Gd_0.20O_2-δ (CGO8020), Ce_0.95Sm_0.05O_2-δ (SDC9505), Ce_0.90Sm_0.10O_2-δ (SDC9010), Ce_0.85Sm_0.15O_2-δ (SDC8515) and Ce_0.80Sm_0.20O_2-δ (SDC8020) were synthesized by Glycine Nitrate (GN) combustion technique and investigated. The physical properties and the other relevant features of the data obtained are analyzed with a view to use these alternate electrolyte materials in IT-SOFC.