Anode Material For Solid Oxide Fuel Cells Research Articles

Effects of Manganese Oxides on the Activity and Stability of Ni-Ce0.8Sm0.2O1.9 Anode for Solid Oxide Fuel Cells with Methanol As the Fuel

Solid oxide fuel cells (SOFCs) are one of the most promising devices for the direct conversion of chemical energy in fuels into electric power[1]. The Ni-based cermet has been considered as the most promising anode material for SOFCs due to its high catalytic activity, sufficient electrical conductivity and low cost[2]. However, Ni-based anodes face a severe problem of carbon deposition when fueled with hydrocarbons[2]. In this work, Ni-MnOx-Ce0.8Sm0.2O1.9 (SDC) is synthesized with a hydrothermal method and investigated as the anode material of an SOFC fed with methanol. The lowest anodic polarization resistance is obtained when the molar ratio of Mn to Ni is 0.05:0.95. The single cell with that anode and SDC-carbonate composite electrolyte exhibits a maximum power density of 722 mW cm-2 at 700 oC (Fig. 1). The high catalytic activity is attributed to the transfer of electrons from Ni to Mn and the increase of the content of the lattice oxygen in the anode. Mn also increases the resistance to carbon deposition of the anode due to the high lattice oxygen content and the redox cycle of the Mn species. The stability of the single cell is enhanced with the increase of the content of Mn in the anode. Fig.1 I–V and I-P curves of the fuel cells with various anodes at 700 °C with methanol as fuel. References A. Sin, E. Kopnin, Y. Dubitsky, et al., Journal of Power Sources, 2007, 164: 300–305.Z. Wang, W. Weng, K. Cheng, et al., Journal of Power Sources, 2008, 179: 541-546.S. Alayoglu, K. An, G. Melaet, et al., The Journal of Physical Chemistry C, 2013,117: 26608-26616. Figure 1

Exceptionally High Performance Anode Material Based on Lattice Structure Decorated Double Perovskite Sr2FeMo2/3Mg1/3O6−δ for Solid Oxide Fuel Cells

AbstractA novel double perovskite Sr2FeMo2/3Mg1/3O6−δ is prepared and characterized as an anode material for solid oxide fuel cells (SOFCs). X‐ray diffraction refinement reveals that Mg and Mo cations locate separately in two different B sites (B and B′ in A2BB′O6) while Fe occupies both B and B′ sites, forming the lattice structure with the form of Sr2(Mg1/3Fe2/3)(Mo2/3Fe1/3)O6−δ. The inactive element Mg doping not only endows the material with excellent redox structural stability but also triggers the creation of antisite defects in the crystal lattice, which provide the material with excellent electrochemical activity. The anode performance of Sr2FeMo2/3Mg1/3O6−δ is characterized in an La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte supported cell with La0.58Sr0.4Fe0.8Co0.2O3−δ cathode. A peak power density of 531, 803, 1038, and 1316 mW cm−2 at 750, 800, 850, and 900 °C, respectively, is achieved in humidified H2. The Sr2FeMo2/3Mg1/3O6−δ shows suitable thermal expansion coefficient (16.9(2) × 10−6 K−1), high electrical conductivity, and good tolerance to carbon deposition and sulfur poisoning. First‐principle computations demonstrate that the presence of FeBOFeB′ bonds can promote the easy formation and fast migration of oxygen vacancies in the lattice, which are the key to affecting the anode reaction kinetics. The excellent overall performance of Sr2FeMo2/3Mg1/3O6−δ compound makes it a promising anode material for SOFCs.

Archiving high-performance solid oxide fuel cells with titanate anode in sulfur- and carbon-containing fuels

Yttria doped strontium titanate (Y0.07Sr0.89TiO3, YST) material is synthesized using a conventional combustion method as anode for solid oxide fuel cells (SOFCs) in sulfur- and hydrocarbon-containing fuels. The YST perovskite exhibits good stability and chemical compatibility with yttria stabilized zirconia (YSZ) electrolyte in 0.5% H2S-containing fuel at high temperatures. Moreover, the YST shows high electrical conductivity of 35 S cm−1 at 900 °C and the cell with this anode achieves a maximum power density of 200, 162 and 70 mW cm−2 when the anode is fed by 0.5% H2S-containing hydrogen, syngas and methane fuels, respectively. More importantly, the cell shows negligible degradation in the sulfur-, carbon- and hydrocarbon-containing fuels. Thus, YST holds the promise as anode material for SOFCs, especially in high concentration sulfur-, carbon- and hydrocarbon-containing fuels.

Sulphur tolerance of Au-modified Ni/GDC during catalytic methane steam reforming

Au doping and high calcination temperatures improve the sulphur tolerance of Ni/GDC, a potential SOFC anode.

Niobium Doped Lanthanum Strontium Ferrite as A Redox‐Stable and Sulfur‐Tolerant Anode for Solid Oxide Fuel Cells

The Nb-doped lanthanum strontium ferrite perovskite oxide La0.8 Sr0.2 Fe0.9 Nb0.1 O3-δ (LSFNb) is evaluated as an anode material in a solid oxide fuel cell (SOFC). The effects of Nb partial substitution in the crystal structure, the electrical conductivity, and the valence of Fe ions are studied. LSFNb exhibits good structural stability in a severe reducing atmosphere at 800 °C, suggesting that high-valent Nb can effectively promote the stability of the lattice structure. The concentration of Fe2+ increases after Nb doping, as confirmed by X-ray photoelectron spectroscopy. The maximum power density of a thick Sc-stabilized zirconia (ScSZ) electrolyte-supported single cell reached 241.6 mW cm-2 at 800 °C with H2 as fuel. The cell exhibited excellent stability for 100 h continuous operation without detectable degeneration. Scanning electron microscopy clearly revealed exsolution on the LSFNb surface after operation. Meanwhile, LSFNb particles agglomerated significantly during long-term stability testing. Impedance spectra suggested that both the LSFNb anode and the (La0.75 Sr0.25 )0.95 MnO3-δ /ScSZ cathode underwent an activation process during long-term testing, through which the charge transfer ability increased significantly. Meanwhile, low-frequency resistance (RL ) mainly attributed to the anode (80 %) significantly increased, probably due to the agglomeration of LSFNb particles. The LSFNb anode exhibits excellent anti-sulfuring poisoning ability and redox stability. These results demonstrate that LSFNb is a promising anode material for SOFCs.

Alternative SOFC Anode Materials with Ion– and Electron–Conducting Backbones for Higher Fuel Utilization

Introduction Solid oxide fuel cells (SOFC) have a great potential to generate electricity with a high efficiency. Currently, Ni-YSZ cermet is widely used as the SOFC anode material. As anode Ni can be oxidized under a high fuel utilization, however, SOFC fuel cannot be fully used [1]. In this study, we analyze alternative anode materials composed of ionic conducting GDC (Ce0.9Gd0.1O2) and electronic conducting LST (Sr0.9La0.1TiO3), both of which act as stable ion- and electron-conducting frameworks, respectively, and Ni acts only as an electrocatalyst, as described in Figure 1. In addition, Rh, despite Ni, is also impregnated for higher fuel utilization. Experimental Electrolyte-supported cells with ScSZ (10 mol% Sc2O3 - 1 mol% CeO2 - 89 mol% ZrO2) plate (20 mmφ×0.2 mmt) were used in this study. Mixture of LST and GDC (50:50 in volume) was used for the anode and was sintered at 1300oC for 3h. Mixture of (La0.8Sr0.2)0.98MnO3 (LSM) and ScSZ with a weight ratio of 50:50 was used for the cathode. In order to further improve the anodic performance, Ni and GDC were impregnated into the porous LST-GDC composite anode. Electrode area was 8×8 mm2 and Pt mesh was used as the current collector. Cell performance such as I-V characteristics, anodic overvoltage, and anode-side ohmic loss were measured at 800oC by feeding humidified fuel. This Ni-GDC co-impregnated anode was evaluated through the I-V measurements, FESEM analysis, and Red-Ox cycling tests [2]. Moreover, in order to investigate the stability for the operation under high fuel utilization in the downstream of practical SOFC systems, the long-term durability test (fuel: 95%-humidified H2, constant current density: 0.2 A cm-2) was conducted. In addition, the Rh-GDC co-impregnated anode performance was investigated for higher fuel utilization. Results and discussion The Ni-GDC co-impregnated anode (Ni:GDC = 1:5 in volume) showed comparable performance to the conventional Ni-ScSZ anode, as shown in Figure 2. The Ni loading was 0.167 mg-Ni/cm2 and the I-V performances were investigated using 3%-humidified H2 fuel. This anode was more stable against redox cycling than the conventional anode. The FIB-SEM micrograph of the Ni-GDC co-impregnated anode is shown in Figure 3, showing that catalytic Ni nanoparticles were supported on the LST-GDC composite frameworks in a highly dispersed manner, which could prevent Ni agglomeration. Although the Ni-GDC co-impregnated anode was stable against the redox cycling and its performance was comparable to the conventional one, it deteriorated in the durability test at high fuel utilization. Ni particles were oxidized to lose their catalytic activity because the initial anode voltage of the co-impregnated anodes was lower (< 0.701 V [3]) under the heavily-humidified hydrogen fuel. On the other hand, Rh-GDC co-impregnated (0.232 mg-Rh/cm2, Rh:GDC = 1:5 in volume) anode was stable against this durability test because Rh is a stable catalyst even under high oxygen partial pressure. Consequently, these anodes could be promising alternative anodes for high fuel utilization operation of SOFCs.

Synthesis of Mo-doped CeO2 by the Combustion Method for Carbon-Air Fuel Cells Applications: Study of Composition, Crystalline Structure and Mechanical Properties

The electrochemical oxidation of carbonaceous fuels in solid oxide fuel cells (SOFCs) appears as a promising alternative for energy generation, considering the high chemical to electrical energy conversion efficiencies of these systems [1]. However, carbonaceous fuels usually contain a significant amount of sulfur, which can poison SOFCs anode materials such as nickel-yttria stabilized zirconia (Ni-YSZ) composites [2,3], which in addition suffers from carbon deposition [2,4]. For this reason, it is necessary to develop alternative materials to be used in carbon-air fuel cells (CAFCs) applications. In this respect, ceria (CeO2) appears as a material of interest for fabrication of CAFCs anodes due to its catalytic activity in the oxidation of carbonaceous fuels and its good tolerance to sulfur poisoning [5]. However, ceria-based materials present low electronic conductivity for SOFCs applications, thus it needs to be improved by doping ceria with other metal oxides, such as molybdenum trioxide (MoO3) which shows similar catalytic and stability properties than ceria [6-9]. Recently, ball milling followed by solid-state reaction processes has been reported in the literature as a method for the synthesis of Mo-doped ceria (CMO) nanoparticles (Ce0.9Mo0.1O2+δ) for SOFCs applications [10]. However, this method is associated with contamination of the products and low synthesis rates. Therefore, this research project proposes the combustion method as an alternative to produce these CMO nanoparticles. As-prepared powders and calcined powders (700 °C / 2 hours in air) were characterized by XRD, TEM, UV-visible spectrophotometry, EDS, XPS and TGA. Figure 1a shows the XRD pattern of as-prepared and calcined powders. These results together with TEM analysis (Figures 1b and 1c) show that CMO nanoparticles crystallize in the fluorite-type structure, similarly to its CeO2 parent, and have an average size of 14 nm. It was not detected MoO3 signals or any secondary phase in these XRD patterns. To determine the effect of molybdenum as a dopant, the lattice parameter was calculated using Rietveld refinement and compared with that for pure ceria. The results obtained (see Table 1) show that the lattice parameter of the CMO nanoparticles synthesized present a different lattice parameter from pure ceria, which evidences the presence of a dopant in the matrix of ceria. UV-visible spectrophotometry analysis (Figure 2a) confirm this result by showing a shift of the absorbance spectra towards higher wavelength values which can be related to a change in the electronic structure of ceria. The presence of molybdenum in the CMO nanoparticles was evidenced as well by EDS and XPS analysis (Figure 2b and Figure 2c), the last of which showed a Mo 3d double peak which indicates the presence of Mo6+. Finally, the thermal stability of the synthesized material was confirmed by TGA under a nitrogen atmosphere at 950 °C (Figure 3). Currently, dense pellets made from CMO nanoparticles are being produced by pressing and calcination for mechanical strength (elasticity modulus, micro-hardness and fracture toughness) and electrical-ionic conductivity (electrochemical impedance spectroscopy) tests. The density of the pellets obtained was 6.954 g cm-3, which is similar to the value reported in [10]. Acknowledgments. The authors thank the Chilean Government for a CONICYT studentship for IDA. References. [1] S. Giddey et al. (2012) Prog. Energy Combust. Sci., 38(3) 360-399.[2] T.M. Gür et al. (2010) J. Power Sources, 195(4) 1085-1090. [3] S.P. Jiang and S.H. Chan (2004) J. Mater. Sci., 39(14) 4405-4439. [4] I.F. Elbaba and P.T. Williams (2014) Energy Fuels, 28(3) 2104-2113.[5] G.K. Reddy et al. (2011) J. Catal., 282(2) 258-269. [6] H. Tu et al. (2008) J. Fuel Cell Sci. Technol., 5(3) 31203. [7] H. Lv et al. (2007) Solid State Ion., 177(39-40) 3467-3472. [8] O. Marin-Flores et al. (2010) Appl. Catal. B – Environ., 98(3-4) 186-192.[9] J.A. Rodriguez and J. Hrbek (1999) Acc. Chem. Res., 32(9) 719-728. [10] Q. Li and V. Thangadurai (2009) Fuel Cells, 9(5) 684-698. Figure 1

Density functional theory study for the enhanced sulfur tolerance of Ni catalysts by surface alloying

Sulfur compounds in fuels deactivate the surface of anode materials in solid oxide fuel cells (SOFCs), which adversely affect the long-term durability. To solve this issue, it is important to design new SOFC anode materials with high sulfur tolerance. Unfortunately, it is difficult to completely replace the traditional Ni anode owing to its outstanding reactivity with low cost. As an alternative, alloying Ni with transition metals is a practical strategy to enhance the sulfur resistance while taking advantage of Ni metal. Therefore, in this study, we examined the effects of transition metal (Cu, Rh, Pd, Ag, Pt, and Au) doping into a Ni catalyst on not only the adsorption of H2S, HS, S, and H but also H2S decomposition using density functional theory (DFT) calculations. The dopant metals were selected rationally by considering the stability of the Ni-based binary alloys. The interactions between sulfur atoms produced by H2S dissociation and the surface are weakened by the dopant metals at the topmost layer. In addition, the findings show that H2S dissociation can be suppressed by doping transition metals. It turns out that these effects are maximized in the Au-doped Ni catalyst. Our DFT results will provide useful insights into the design of sulfur-tolerant SOFC anode materials.

High conductive and long-term phase stable anode materials for SOFCs: A 2 FeMoO 6 (A = Ca, Sr, Ba)

Abstract In this work, the mixed oxide-ion/electron conductor (MIEC) double-perovskite compounds A 2 FeMoO 6 (AFMO, A = Ca, Sr, Ba) are investigated as anode materials for O 2− -ion conducting solid-oxide fuel cells (SOFCs). Several advantages are outlined here; 1) under H 2 atmosphere, the conductivities of Ba 2 FeMoO 6 (BFMO), Sr 2 FeMoO 6 (SFMO) and Ca 2 FeMoO 6 (CFMO) reach as high as 243, 302 and 561 S cm −1 , respectively, which can be comparable with the commercial NiO-electrolyte anode; 2) excellent structure and phase stability at high temperature and in H 2 atmosphere; 3) matched thermodynamic compatibility (such as TECs) with electrolyte materials; 4) fast oxidization for fuel with O 2− ions accepted by oxygen vacancies from the electrolyte. Moreover, with H 2 as fuel gas, the cell power output, cell's long-term stabilities and the structural parameter are also been examined to evaluate the AFMO anode.

Alternative SOFC Anode Materials with Ion– and Electron–Conducting Backbones for Higher Fuel Utilization

Redox-stable anodes are developed for zirconia-based electrolyte-supported solid oxide fuel cells (SOFCs) operating at high fuel utilization, as an alternative to the Ni yttrium-stabilized-zirconia (YSZ) cermet. Gadolinium-doped ceria (GDC, Ce0.9Gd0.1O2) is utilized as a mixed ionic electronic conductor (MIEC), and combined with lanthanum‐doped strontium titanate (LST, Sr0.9La0.1TiO3) as an electronic conductor. Catalyst nanoparticles (either Ni or Rh) are incorporated via impregnation. The electrochemical characteristics of SOFC single cells using these anodes are characterized in humidified H2 at 800°C. The stability against redox cycling and under high fuel utilization is analyzed and discussed.

Improve Activity and Stability of Ni-Ce0.8Sm0.2O1.9 As the Anode of a Methanol Fuelled Solid Oxide Fuel Cell

Solid oxide fuel cells (SOFCs) are electrochemical devices those convert chemical energy in fuels directly into electricity. Compared with H2, commercial hydrocarbon fuels can be safely stored and are more readily available, which could reduce the overall operation cost. Therefore, direct electrochemical oxidation of hydrocarbons into electricity using SOFCs is appealing. However, there are many operational problems those still need to be solved. The typical NiO-YSZ anode material has excellent catalytic properties for fuel oxidation and good electrical conductivity, while it experiences serious carbon deposition with hydrocarbons as fuels. Therefore, there is a need for developing new kinds of carbon resistant SOFC anode materials for the utilization of hydrocarbon fuels. In this work, Mo is utilized to modify the Ni-Ce0.8Sm0.2O1.9 (SDC) anode. The NiO-MoO3-SDC anode materials are prepared by impregnation technique, which are reduced to SDC and Ni-Mo alloy phases in H2 atmosphere. SOFCs with Ni-Mo-SDC composite anodes are fabricated and tested with methanol as fuel. The addition of Mo into Ni–SDC anode effectively improves performance and stability of the single cell at 700 oC. The anode with a mole ratio of Mo to Ni of 0.03:1 (Ni-3Mo-SDC) exhibits the lowest polarization resistance. The cell with that anode and SDC-carbonate composite electrolyte exhibits a maximum power density of 680 mW cm-2 at 700 oC. The stability of the cell is enhanced with the increase of the content of Mo in the anode. In order to further improve the cell performance and stability, rare earth elements (La, Pr and Sm) are introduced into Ni-3Mo-SDC. The effects of La, Pr and Sm addition on the catalytic activity for methanol pyrolysis and coking resistance of the Ni-3Mo-SDC anode are examined. The electrochemical performance of the SOFC is enhanced with introducing La and Sm into the anode. The cell with La addition in the anode shows a maximum power density of 765 mW cm-2 at 700 oC with methanol as fuel. The addition of La, Pr and Sm into Ni-3Mo-SDC anode improves the stability of the cell, which is mainly attributed to the decreased amount of carbon deposition with a high graphitization degree.

In-Situ Investigation on the Crystal and Microstructure Change of Nickel Interacted with Methane at High Temperatures

The solid oxide fuel cell (SOFC) is a novel electricity generation technology which converts the chemical energy of fuels into electrical power, with high efficiency and low pollution. One of the superiors of SOFCs over other kinds of fuel cell is that carbon-containing fuels can be directly used, leading to much lower operation cost. Nickel cermet is the most commonly used anode material for SOFCs. However, nickel promotes carbon deposition reaction, which results in significant performance degradation, when carbon-containing fuels are used. While there have been quite a few studies on replacing nickel with other materials in the anode of SOFCs operated with carbon-containing fuels, none of the alternatives can surpass nickel for practical application. Meanwhile, there are some evidences showing that carbon can be used as a fuel for SOFCs (the so-called direct carbon solid oxide fuel cells, DC-SOFCs), suggesting that carbon itself is not the cause of deactivation of Ni-based anode exposed to carbon-containing fuels in SOFCs. It is the interaction between nickel and carbon-containing gas that destroys the structure of nickel bulk, resulting in pulverization of the anode. Some previous researches have shown that carbon fiber may grow when transition metals, including nickel, are exposed to carbon-containing gases. The crystal lattice and microstructure changes were assumed but rarely verified by direct experimental evidences. In this report, we present our recent work of in situ investigation on the crystal lattice and microstructure changes of nickel-based bulk interacted with methane at high temperatures. In situ thermal expansion measurements are carried out, using a thermal dilatometer, on Ni-YSZ bulk samples exposed to methane at temperatures of 650 and 800°C, respectively. The samples for the thermal dilatation measurements are of cylindrical shape with relatively thin wall. In situ XRD characterizations are carried out on Ni-YSZ powder, which also exposed to methane at 650 and 800°C, respectively. The thermal dilatation measurement results show that the Ni-YSZ bulk expands when it is exposed to methane at both 650 and 800°C. The expansion leads to the bulk broken or destroyed. At 800°C, the time it takes, from the moment of nickel exposed to methane to that when it is destroyed, is 14 minutes, which is 4 times shorter than that it takes at 650°C, 70 minutes. Room temperature TEM measurements show that carbon deposits on nickel interacted with methane at 800°C is in the form of encapsulation while that of 650°C is carbon fiber. The in situ XRD characterizations show that when nickel is exposed to methane, its crystal lattice parameter increases, both in the situations of 650 and 800°C. At the beginning of nickel exposed to methane (i.e., 10 minutes) at 650°C, its crystal lattice parameter increases. However, the increased parameter reduces almost back to the initial value after a while (i.e., 20 minutes). In the situation of nickel exposed to methane at 800°C, its lattice parameter increases to maximum in 10 minutes and the value is stable in the following time. The above experimental results are analyzed and discussed in detail in the report.

Alternative SOFC Anode Materials with Ion- and Electron-Conducting Backbones for Higher Fuel Utilization

Introduction &Solid oxide fuel cells (SOFC) have a great potential to generate electricity with a high efficiency. Currently, Ni-YSZ cermet is widely used as the SOFC anode material. As anode Ni can be oxidized under a high fuel utilization, however, SOFC fuel can not be fully used. In this study, we analyzed alternative anode materials composed of GDC (Ce0.9Gd0.1O2; ionic conductor), LST (Sr0.9La0.1TiO3; electronic conductor), both of which act as stable ion- and electron-conducting frameworks, respectively, and Ni acts only as an electrocatalyst, as described in Fig. 1. Experimental &Electrolyte-supported cells with ScSZ (10 mol % Sc2O3-1 mol % CeO2-89 mol % ZrO2) plate (20 mmφ×&0.2 mmt) were used in this study. Mixture of LST and GDC (1 : 1 ; vol. %) was used for the anode and was sintered at 1300 oC for 3 h. Mixture of (La0.8Sr0.2)0.98MnO3 (LSM) and ScSZ with a weight ratio of 1:1 was used for the cathode. In order to further improve the anodic performance, Ni nanoparticles were impregnated into the porous LST-GDC composite anode. Electrode area was 8×&8 mm2 and Pt mesh was used as the current collector. Cell performance such as I-V characteristics, anodic overvoltage, and anode-side ohmic loss were measured at 800 oCby feeding humidified fuel. The amount of the catalytic Ni loading was optimized through the I-V measurements, FESEM analysis, and Red-Ox cycling tests. Results and discussion &The optimized amount of Ni loading was difficult to be judged only from the I-V measurements and the SEM figures because there were no obvious difference in the anode performance of the cells impregnated more than 0.0833mg-Ni/cm2. Then, Red-Ox cycling tests were conducted according to the procedure shown in Fig. 2, in order to investigate the stable distribution in which Ni catalytic particles are difficult to aggregate. As a result, the best Ni loading in this study was 0.0833mg-Ni/cm2for which anode voltage degradation was only 2% after 50 Red-Ox cycles, whereas that of Ni-ScSZ, conventional Ni-cermet anode was more than 20%. The STEM-EDX micrographs of the optimized anode are shown in Fig. 3, showing that catalytic Ni nanoparticles were supported on the LST-GDC composite frameworks in highly dispersed manner. Anode degradation mechanisms during cycle durability test suggested from these results are shown in Fig. 4. In the conventional Ni-cermet anodes, Ni grains increase in size with Red-Ox cycling and then its electron conducting framework is broken which deteriorates cell performance. On the other hand, in the best impregnated Ni-cermet anodes, Ni nanoparticles loaded on the LST –GDC composite anodes are difficult to aggregate during Red-Ox cycling. Consequently, the stable electrode frameworks exhibit negligible degradation.

Characteristics of SrxY1-XTiyNi1-YO3-d anode in Humidified Methane Fuel for Intermediate-Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are a promising alternative energy conversion device because of high energy efficiency and fuel flexibility. Nickel/yttria-stabilized zirconia (Ni/YSZ) cermet has been widely used as an anode material in SOFCs. The Ni/YSZ anode, however, may not be appropriated for direct use of commercial hydrocarbon fuels because of carbon deposition and sulfur poisoning on the Ni phase. In this study, yttrium and nickel co-doped strontium titanium oxide SrxY1-xTiyNi1-yO3-δ (SYTN) was investigated as an alternative anode material for SOFCs. To improve the ionic conductivity of the Sr0.92Y0.08TiO3-δ (SYT) anode, Ti4+ at the B-site was substituted to Ni2+, leading to introduction of oxygen vacancies in the SYT. The stability of the SYTN anode at high temperatures and reducing atmospheric conditions was as good as the SYT anode. The SYTN exhibits excellent phase stability during the cell fabrication processes, SOFC operation, and good electrical conductivity at 700~900 oC in methane. The SYTN anode was compatible with YSZ at the SOFC operating condition. The electrochemical reactions of the SYT anode in both hydrogen and methane were limited by relatively slow reactions, such as non-charged processes including oxygen surface exchange and solid surface diffusion. To improve such poor electrochemical activities, the surface of the SYTN anode was modified by the SDC coating. The polarization resistance and the cell performance in hydrogen and methane were significantly improved by the SDC modification. The SDC-coated SYT anode cell was successfully operated with methane for more than 300 hours without any degradation of the cell performance.

Electrochemical Property of Ni-Ba(Zr,Y)O3 Anode for Direct Ammonia-Fueled SOFC

Hydrogen carriers have attracted much attention as alternative fuels to hydrogen. This is because the hydrogen fuel has technological difficulties in transportation and storage, which impedes the wide application. Among various hydrogen carriers, ammonia is one of the promising candidates because of various advantages such as ease in liquefaction, high energy density, large hydrogen content, and zero emission of CO2during reforming or decomposition. In addition, the infrastructure for ammonia utilization has been established because ammonia has been used as a fertilizer and commodity chemicals worldwide. In the case of solid oxide fuel cells (SOFCs) directly supplied with ammonia fuel, ammonia decomposes into hydrogen and nitrogen on the anode and subsequently hydrogen is electrochemically oxidized. Therefore, the anode materials for ammonia-fueled SOFCs need to be active for the electrochemical hydrogen oxidation as well as the catalytic ammonia decomposition. The mixture of nickel and Ba(Ce,Y)O3−δ (BCY), which is one of the promising proton conductors, has been already reported as a highly active catalyst for ammonia decomposition[1].In this study, then, the activity tests for ammonia decomposition were performed for various nickel catalysts supported on proton conductors. Ammonia decomposition proceeded at lower temperature over Ni−proton conductor cermets compared with the conventional anode of Ni−yttria-stabilized zirconia (YSZ) cermet. Ammonia decomposed completely over Ni−proton conductor cermets at ca. 600ºC, while a complete ammonia decomposition was accomplished over Ni−YSZ at higher temperature. In particular, the Ni−Ba(Zr,Y)O3−δ (BZY) catalyst exhibited superior activity. In order to evaluate the anode performance of ammonia-fueled SOFC, a single anode-supported cell composed of Ni−BZY|BZY|Pt was fabricated. Electrochemical measurements were conducted at 600−700ºC by using ammonia or hydrogen as a fuel and oxygen as an oxidant. The partial pressure and flow rate of hydrogen in the hydrogen-containing fuel gas were controlled to be the same as those after the complete decomposition of ammonia in the ammonia-containing one. At each temperature, the open circuit voltages (OCVs) under both fuel gas flows were almost the same. From this result, it can be tentatively concluded that ammonia was oxidized via the two-step reaction on the anode as mentioned above. At 700ºC, the current density at the terminal voltage of 0.5 V under hydrogen and ammonia fuel conditions were 280 mA cm−2 and 250 mA cm−2, respectively. The difference in performance between ammonia and hydrogen-containing fuels was small. Consequently, the Ni−BZY catalyst is a promising anode for ammonia-fueled SOFCs. [1] J. Yang, A.F.S. Molouk, T. Okanishi, H. Muroyama, T. Matsui, K. Eguchi. ACS Appl. Mater. Inter., 7, 7406 (2015).

The Effect of B-Cation Disordered Structure on the Electrocatalytic and Electrochemical Performance of A2CrMoO6 (A= Ca, Sr, Ba)

As a kind of promising candidate of anode material for solid oxide fuel cell (SOFC), A2BB'O6-δ type double perovskites such as Sr2MnMoO6, Sr2MgMoO6, Sr2NiMoO6, Sr2FeMoO6, etc. have exhibited excellent catalytic activity, redox stability and other promising behaviors in high temperatures. Therefore oxide anodes has become a promising anode for SOFC instead of cermet anodes. Magnetic materials A2CrMoO6-δ (A=Ca, Sr, Ba) (ACM oxide) was first found having a lower magnetic susceptibility and lower negative magnetoresistance than that of Sr 2 FeMoO6 due to the effect of B-cation disorder on electronic and magnetic properties. In this work, we would focus on the researchabout effect of B-cation disorder on electrocatalytic and electrochemical behaviors. B-site disordered double perovskite ACM oxide was synthesized by solid-state reaction under reducing atmosphere. Then it was refined to acquire the lattice parameters and characterized to investigate the comprehensive behaviors and properties of ACM oxide, such as electrical, catalysis and electrochemical behaviors. H2-TPR (temperature programmed reduction) analysis were conducted using a TP-5076 TPD/TPR dynamic adsorption instrument to investigate the catalytic activity and reversibility. Herein, the H2 consumption temperature corresponds to the catalytic activity area, and the H2 consumption (amount) refers to the extent of catalysis (See Figure). On the one hand, the material showing the lowest H2 consumption temperature has is easier to work as a catalysis under lower temperatures. On the other hand, the material displaying the lowest H2 consumption peak can play a part as catalysis with fewer H2. The H2-TPR results demonstrated ACM anode was catalytically activated for hydrogen which is the very fuel gas when a SOFC is operating in working temperature. The reduction temperatures gradually go up with the atomic radius, and H2-consumption saw a considerable growth in the same order so that BCM oxide is endowed with the highest catalytic activity, followed by SCM and CCM oxides. To study the stability and the reversibility of the anode samples, multiple runs of H2-TPR are needed. The results display that ACM oxide is relatively stable after multiple run of H2-TPR as well meaning the catalytic activity of ACM anode is steady and can be repeated multiple times. Obviously, the sample without peak shift is more stable. By comparison with BCM and SCM anodes, SCM anode possesses a stronger repeatability and more powerful reversibility.As for the average thermal expansion coefficient (TEC) of SCM anode is 12.7×10-6 K-1 between 30 and 1000℃ in 5%H2/95%Ar matching the value of electrolyte La0.9Sr0.1Ga0.8Mg0.2O2.85 （LSGM） (∼12.5×10-6 K-1) , as well as the excellent chemical compatibility with LSGM we use LSGM as electrolyte in cell assembly. Then the symmetrical cells equipped with each anode as electrode and supported by electrolyte were fabricated and tested under reduction atmosphere within the operating temperature. Symmetrical cells impedance analysis would be operated under hydrogen atmosphere. Therefore, the polarization resistance of the symmetrical cells can be used to analyse the electrochemical performance. Finally, we'll analyse the effect of the B-cation disorder of structrue on the electrocatalytic and electrochemical properties combining the results of refined structure of ACM oxide.Given the above superior electrocatalytic and electrochemical properties of ACM anode materials, we recommend them as a series of promising anode materials for SOFC. Figure 1

A Study on Degradation of Ni-YSZ Anode Materials in Terms of Redox Stability for Solid Oxide Fuel Cells

▪ Introduction Solid oxide fuel cells (SOFCs) have lately attracted considerable attention as the source of new energy considering environmental pollution and exhaustion of underground resources. Nickel-yttria stabilized zirconia (Ni-YSZ) cermet has been used as an anode material for SOFCs for more than 20 years. Although Ni-YSZ has various advantages such as high catalytic activity for H2 oxidation and methane reforming, stability in reducing atmosphere, high electrical conductivity, it exhibits various types of degradations such as poor redox stability, sulfur poisoning, carbon deposition. Ni-YSZ anode still suffers from exposure to oxidizing condition caused by sudden interruption of fuel or sealing problem like leakage. When exposed in oxidizing atmosphere, Ni-YSZ experiences significant volume change due to the oxidation of Ni to NiO, which causes internal cracks and consequent destruction of the cell. In this study, the redox stability of Ni-YSZ cermet according to various conditions such as porosity, pore size distribution, and composition has been studied systematically. ▪ Experimental NiO-YSZ composite powders have been prepared by mixing of commercial NiO (High purity chemicals, 99.97%), 8YSZ (TZ-8YS: 8 mol% Y2O3-stabilized ZrO2, 99.9% Tosoh, Japan) and PMMA as a pore former. The NiO-YSZ bulk samples were fabricated by the typical die compaction method and sintering at 1450 °C for 4 h in air. The sintered NiO-YSZ samples were reduced at 800 °C for 3 h in H2 in order to make Ni-YSZ. The phase change was confirmed by the X-ray diffraction (XRD). The morphology of Ni-YSZ was investigated by scanning electron microscopy (SEM). Degree of oxidation (D.o.O) of Ni was calculated from thermogravimetric analysis (TGA) data. The amount of volume change of Ni powders during oxidation was measured using a helium pycnometer. The both porosity and pore size distribution of Ni-YSZ bulk samples were analyzed with mercury porosimeter. The linear length change of Ni-YZ during oxidation was measured using dilatometer. ▪ Results and Discussion If we know both temperature and time of exposure in oxidizing atmosphere, we can predict the D.o.O of Ni at a certain condition using the D.o.O equation obtained from TGA data. The percentage weight gain per specific surface area can explain the oxidation kinetics of the Ni-YSZ anode supports, which obeys a multi-stage parabolic law expressed by Kp. Kp can be expressed by Kp1 and Kp2. Kp1 and Kp2 correspond to fast oxidation reaction at early oxidation stage and slow oxidation reaction at the next oxidation stage, respectively. The volume change of Ni-YSZ caused by oxidation can be the result of two competing factors: expansion caused by NiO formation and shrinkage caused by continuous sintering of both Ni and NiO. Ni-YSZ cermet with high porosity showed higher tolerance to the cumulative length change due to providing the more relaxation space.

High Performance Anode Material for Solid Oxide Fuel Cells: Ni Exsolution on a-Site Deficient La0.4Sr0.4Sc0.9Ni0.1O3

Highly efficient and environment-friendly devices for energy transformation are in urgent demand for the sustainable production of power. Solid oxide fuel cells (SOFCs) are among the most efficient systems that can convert chemical energy directly into electricity. Currently, Ni/yttria-stabilized ZrO2 (YSZ) is the state-of-the-art SOFC anode material (or the cathode material of solid oxide electrolysis cells), due to its relatively high mechanical strength, high performance, and low cost. However, the Ni/YSZ anode still has several limitations including Ni agglomeration at high temperature, sulfur poison, and carbon coking. While perovskite-type materials have been used as SOFC anodes to overcome many of these challenges, their catalytic activity is typically poor. Recently, exsolution of catalytic nanoparticles on the surface of perovskites has drawn great research interest because of the potential enhancement in electrochemical activity. Irvine and collaborators have shown that A-site deficient perovskites allow easier and more controllable exsolution, and several materials capable of growing nanoparticles in-situ have been developed. However, the catalytic activity delivered by A-site deficient perovskites with exsolved nanoparticles is still not comparable to that of state-of-the-art SOFC anode materials. There are still many opportunities for materials development and improvement, since most of the recent studies have focused on La0.5Sr0.5TiO3 or NbTiO4 related materials. Perovskites based on other non-easily-reducible metals may be used to deliver even better activity. In this work, we report a novel Sc-based A-site deficient perovskite La0.4Sr0.4Sc0.9Ni0.1O3-δ (LSSN), synthesized as an anode material for solid oxide fuel cells. LSSN is reduced in hydrogen at 900 oC for 15 hours to form a highly active and stable anode. Spherical Ni nanoparticles (~100 nm in diameter) with well-defined boundaries are exsolved on the surface after reduction. the reduced LSSN (rLSSN) show high electrochemical catalytic activity, with the area specific resistances as low as 0.055 Ω cm2 at 800 °C in humid H2. Our work introduces a new anode material with potential to enhance electrochemical catalytic activity and suggests a new series of A-site deficient perovskites for SOFC anodes.

Double Perovskite Ba2FeMoO6-D As Fuel Electrode for Protonic-Ceramic Membranes

In this paper, we present development of a novel Ba2FeMoO6- δ ceramic electrode for use with proton-conducting ceramic membranes. The membranes are based on barium cerate-zirconate materials, such as BaCexZr0.9-xY0.1O3-d (BCZY) [1, 2]. Such ceramic hydrogen-separation membranes have a wide range of industrial applications, including fuel cells for electricity generation, electrolyzers for energy storage, and membrane reactors for fuels upgrading. A number of these applications require development of a high-performance electrode for use in high-temperature reducing atmospheres containing hydrogen and / or methane gases. Such conditions present a number of unique challenges. Sluggish catalytic and charge-transfer chemistries between the gases, the electrode, and the membrane can result in high activation polarization losses and poor electrochemical performance. Additionally, the high methane concentration can cause performance degradation due to deleterious carbon-deposit formation on the electrode surface. Finally, the stability and adherence of the electrode and membrane materials bring fabrication and synthesis challenges. Ceramic oxides are considered to be good candidates to serve as such electrodes. Some oxides developed for solid-oxide fuel cells (SOFCs) are found to be chemically stable and electrically conductive in reducing conditions. The high resistance against carbon deposition (coking), good mechanical compatibility with protonic ceramic membrane, and strong endurance to particle coarsening enable ceramic oxides to be developed as potential electrode in this application. Layered double perovskites (Ba,Sr)2MMoO6-δ (M=Fe, Mg, Ni, Co, etc) have been recently developed as anode materials for direct hydrocarbon SOFCs [3]. These oxides show high conductivity of ~ 100 S/cm and low area-specific resistance (ASR) of 0.45 ohm cm2 in H2 at 700 ºC. Such characteristics make these layered double perovskites well matched with the protonic-ceramic membranes. In this work, we investigate the use of Ba2FeMoO6-δ (BFMO) for use as an electrode with a BCZY proton-conducting ceramic membrane. The performance of this layered double perovskite is evaluated through analysis of the phase structure, chemical stability and compatibility, coking propensity, and area-specific resistance. Ceramic-processing parameters are developed to promote reasonable adhesion between the BFMO electrode and the BCZY membrane. Reasonable adhesion is obtained with composite ceramic 5:1 BFMO:BCZY. Without any current collector applied on the surface of electrode, the preliminary results show that the composite BFMO electrode is very stable in H2, with an ASR as low as ~10 ohm cm2 in moist H2 at 700 ºC. The effect of synthesis technique on particle size and electrochemical performance are also being explored. Far smaller particle sizes are obtained through Pechini synthesis in comparison to solid-state reaction. This leads to lower area-specific resistance, as shown in Figure 1. Citations: S. Babiniec, S. Ricote, N.P. Sullivan, “Characterization of ionic transport through BaCe0.2Zr0.7Y0.1O3-d membranes in galvanic and electrolytic operation,” International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2015.05.162 40 (2015) 9278-9286. S. Babiniec, S. Ricote, N.P. Sullivan, “Infiltrated lanthanum nickelate cathodes for use with BaCe0.2Zr0.7Y0.1O3-d proton conducting electrolytes,” Journal of the Electrochemical Society 161 : 6 (2014) F717-F723. Qin Zhang, Tao Wei, Yun-Hui Huang, “Electrochemical performance of double-perovskite Ba2MMoO6 (M = Fe, Co, Mn, Ni) anode materials for solid oxide fuel cells,” Journal of Power Sources 198 (2012) 59–65. Figure 1

Electrochemical Performance and Stability of Perovskite Structured Anode Materials for Intermediate Temperature-Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are highly promising energy conversion devices that can directly convert chemical energy in a fuel to electrical energy. Because they have numerous advantages, such as high conversion efficiency, low pollutant output, and great fuel flexibility, SOFCs have been considered as next-generation clean energy generators.Currently the state of the art anode material for SOFCs is Ni-YSZ cermet. This materials show excellent catalytic activity and stability for the H2 oxidation of hydrogen fuel at SOFC operation conditions. However, Ni-YSZ based anode cermets have a number of drawbacks in system where hydrocarbon fuel is used, such as carbon deposition and sulfur poisoning. In addition, Ni-based anodes suffer from instability upon redox cycling due to the volume expansion of the anode by the Ni oxidation to NiO. This drawbacks of Ni-YSZ cermet significantly may reduces the SOFC lifetime.To overcome these drawbacks of Ni-YSZ based anode, we investigate Ni-free ceramic oxide material as alternative anodes. Developments of Ni-free anode, such as ceria, titanate and lanthanum chromite-based oxides, are required to meet various properties such as high electrochemical performances, tolerance to formation of carbon coking, thermal and redox stability. Among these materials, perovskite-structured materials have been explored to replace Ni-based cermet for SOFCs because they have high tolerance against the carbon deposition and sulfur poisoning with good electrocatalytic performances. In this work, hence we investigate the performance and durability of Ni-free ceramic-based anode during redox cycles of IT-SOFCs. In addition, various transition metals are doped to cramic-based oxide materials to improve electrocatalytic activity, thus resulting in improving the SOFC performance. After the durability testing of SOFCs, electrochemical properties and physicochemical properties of Ni-free ceramic anode cells are investigate by using various analytic techniques such as EIS, SEM, TEM, and XRD.