Anode performance of Mn-doped ceria–ScSZ for solid oxide fuel cell

The 70 wt.% Mn-doped CeO₂ (MDC)-30 wt.% Scandia-stabilized zirconia (ScSZ) composites are evaluated as anode materials for solid oxide fuel cells (SOFCs) in terms of chemical compatibility, thermal expansion coefficient, electrical conductivity, and fuel cell performance in H₂ and CH₄. The conductivity of MDC10 (10 mol.% Mn-doping), MDC20, and CeO₂ are 4.12, 2.70, and 1.94 S cm⁻¹ in H₂ at 900 °C. With 10 mol.% Mn-doping, the fuel cells performances improve from 166 to 318 mW cm⁻² in H₂ at 900 °C. The cell with MDC10–ScSZ anode exhibits a better performance than the one with MDC20–ScSZ in CH₄, the maximum power density increases from 179 to 262 mW cm⁻². Electrochemical impedance spectra indicate that the Mn doping into CeO₂ can reduce the ohmic and polarization resistance, thus leading to a higher performance. The results demonstrate the potential ability of MDC10–ScSZ composite to be used as SOFCs anode.     

Development of novel LSM/GDC composite and electrochemical characterization of LSM/GDC based cathode-supported direct carbon fuel cells

(La_0.8Sr_0.2)_0.95MnO_3?δ (LSM)–Gd_0.1Ce_0.9O_2?δ (gadolinium-doped ceria, GDC) composite cathode material was developed and characterized in terms of chemical stability, sintering behaviour, electrical conductivity, mechanical strength and microstructures to assess its feasibility as cathode support applications in cathode-supported fuel cell configurations. The sintering inhibition effect of LSM, in the presence of GDC, was observed and clearly demonstrated. The mechanical characterization of developed composites revealed that fracture behaviour is directly affected by pore size distribution. The Weibull strength distribution showed that for bimodal pore size distribution, two different fracture rates were present. Furthermore, the contiguity of LSM and GDC grains was calculated with image analysis, and correlation of microstructural features with mechanical and electrical properties was established. Subsequently, an LSM/GDC-based cathode-supported direct carbon fuel cell (DCFC) with Ni/ScSZ (scandia-stabilised zirconia) anode was successfully fabricated via slurry coating and co-firing techniques. The microstructures of electrodes and electrolyte layers were observed to confirm the desired morphology after co-sintering, and a single cell was electrochemically characterized in solid oxide fuel cell (SOFC) and DCFC mode with ambient air as oxidant. The higher values of open-circuit voltage indicated that the electrolyte layer prepared by vacuum slurry coating is dense enough. The corresponding peak power densities at 850 °C were 450 and 225 mW cm^?2 in SOFC and DCFC mode, respectively. Electrochemical impedance spectroscopy was carried out to observe electrode polarization and ohmic resistance.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Influence of organo-clay on electrical and mechanical properties of PP/MWCNT/OC nanocomposites

The electrical, thermal and mechanical properties of nanocomposites, based on polypropylene (PP) filled by multi-walled carbon nanotubes (MWCNTs) and organo-clay (OC), were studied with the purpose of finding out the effect of OC on the microstructure of MWCNTs dispersion and PP/MWCNT/OC composites. It was found that addition of organo-clay nanoparticles improved nanotube dispersion and enhanced electrical properties of PP/MWCNT nanocomposites. Addition of organo-clay (MWCNT/OC ratio was 1/1) reduced the percolation threshold of PP/MWCNT nanocomposites from ?_c = 0.95 vol.% to ?_c = 0.68 vol.% of carbon nanotubes, while the level of conductivity became 2–4 orders of magnitude higher. The DSC and DMA analyses have shown that the influence of organo-clay on the thermal and mechanical properties of material was not significant in composites with both fillers as compared to PP/OC. Such an effect can be caused by stronger interaction of OC with carbon nanotubes than with polymer matrix.     

Conductivity of CaF2-MgO composites

Conductivity of CaF₂-(20, 30, 40 vol %) MgO composites was measured as dependent on the temperature and MgO dispersion degree using a standard four-probe dc method. It is shown that the conductivity of composites grows at an increase in the MgO dispersion degree and volume fraction and achieves its maximum at 30 vol % MgO. It is found that the conductivity of CaF₂-30 vol % MgO nanocomposite is higher by two orders of magnitude as compared to pure CaF₂.     

Composite electrode materials for solid oxide fuel cells with the protonic electrolyte of La<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>ScO<Subscript>3 – δ</Subscript>

Heterogeneous systems based on the proton–conducting oxide of La_0.95Sr_0.05ScO_{3 – δ} with Cu, Fe, Ni, Pd, La_0.9Sr_0.1MnO_{3 – δ} considered as potential materials of solid oxide fuel cell (SOFC) electrodes are synthesized. Chemical interaction between individual components of composite materials is studied, dependences of thermal and chemical expansion of the electrolyte and composites are obtained, conductivity of electrodes is measured under the conditions of SOFC operation.     

Fabrication of membrane–electrode assemblies for solid-oxide fuel cells by joint sintering of electrodes at high temperature

The results on optimizing the procedure of preparation of the electrode system within membrane–electrode assemblies (MEA) of solid-oxide fuel cells (SOFC) by joint sintering of electrodes at the enhanced temperature close to that of anode sintering are presented. The MEA are prepared based on membranes of the anionic conductor Hionic^TM (Fuel Cell Materials, USA); the cathode is formed based on cation–deficient lanthanum-strontium manganite (La_0.8Sr_0.2)_0.95MnO₃ with addition of activated carbon for optimizing its microstructure; the anode is formed on the basis of cermet NiO/10Sc1CeSZ (89 mol % ZrO₂, 10 mol % Sc₂O₃, 1 mol % CeO₂). The results of electrochemical testing of model MEA are also shown.     

Performance of cathode-supported SOFC with Ni0.5Cu0.5–CGO anode operated in humidified hydrogen and in low-concentration dry methane

A Ni_0.5Cu_0.5–CGO (Ce_0.8Gd_0.2O_1.9) anode in a LSM ((La_0.75Sr_0.25)_0.95MnO_3?δ )–CGO cathode-supported SOFC is tested in humidified H₂ (3% H₂O) and in low concentration of dry methane, respectively. After co-sintering at 1,300?°C, it was found that the A-site-deficient LSM effectively hindered the formation of La₂Zr₂O₇ or SrZrO₃. The OCVs of the cell are as high as 1.132, 1.14, and 1.147?V in humidified H₂ and 1.314, 1.269, and 1.2?V in 14.8% of dry methane at 850, 800 and 750?°C, respectively, indicating that the ScSZ electrolyte film prepared by the present method is dense enough. The corresponding peak power densities are 0.396, 0.287, and 0.19?W?cm^?2 in humidified H₂ and 0.249, 0.164, and 0.096?W?cm^?2 in 14.8% of dry methane at 850, 800, and 750?°C, respectively. The prepared cathode-supported SOFC with NiCu–CGO bimetallic anode shows long-term stability when dry methane is used as fuel.     

High performance cathode-supported SOFC with perovskite anode operating in weakly humidified hydrogen and methane

A high performance cathode-supported solid oxide fuel cell (SOFC), suitable for operating in weakly humidified hydrogen and methane, has been developed. The SOFC is essentially made up by a YSZ/LSM composite supporting cathode, a thin YSZ film electrolyte, and a GDC-impregnated La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) anode. A gas tight thin YSZ film (∼27 μm) was formed during the co-sintering of cathode/electrolyte bi-layer at 1200 °C. The cathode-supported SOFC developed in this study showed encouraging performance with maximum power density of 0.182, 0.419, 0.628 and 0.818 W cm⁻² in air/3% H₂O–97% H₂ (and 0.06, 0.158, 0.221 and 0.352 W cm⁻² in air/3% H₂O–97% CH₄) at 750, 800, 850 and 900 °C, respectively. Such performance is close to that of the cathode-supported cell (0.42 W cm⁻² vs. 0.455 W cm⁻² in humidified H₂ at 800 °C) developed by Yamahara et al. [Solid State Ionics 176 (2005) 451–456] with a Co-infiltrated supporting LSM-YSZ cathode, a (Sc₂O₃)_0.1(Y₂O₃)_0.01(ZrO₂)_0.89 (SYSZ) electrolyte of 15 μm in thickness and a SYSZ/Ni anode, indicating that the performance of the GDC-impregnated LSCM anode is comparable to that made of Ni cermet while stable in weakly humidified methane fuel.     

Composite materials based on fluoropolymers and oxyfluoride glasses

It was shown that molded specimens of polymer composite materials can be obtained by an extrusion method by melt blending of Fluoroplast F-2 MB (modified poly(vinylidene difluoride)) and oxyfluoride glasses of the composition 3B₂O₃ (40SnF₂–30SnO–30P₂O₅). The compositions of the observed phases of the composites were determined. Conclusions were made on the incompatibility of the components, their dispersion distribution, and strong adhesion interaction. Data on the nano level of the blending of the components were obtained. The elongation and Brinell hardness were measured in the composites with various (0–50 vol %) oxyfluoride contents. It was concluded that it is possible to produce composites based on fluorinated hydrocarbon and fluoroxide polymers.     

Preparation of MB<Subscript>2</Subscript>/SiC and MB<Subscript>2</Subscript>/SiC-MC (M = Zr or Hf) powder composites which are promising materials for design of ultra-high-temperature ceramics

This survey shows the prospects of studies targeted at preparing MB₂/SiC and MB₂/SiC-MC (M = Zr or Hf) nanosized composite powders for use in the manufacture of ultra-high-temperature ceramics (UHTCs) and antioxidant protective coatings on C_f/C and C_f/SiC composites. The survey considers the specifics of various preparation methods, including sol-gel technology or precipitation followed by borothermic/ carbothermic reduction, self-propagating high-temperature synthesis (SHS), specifically variants combined with mechanochemical activation or spark plasma sintering (SPS), chemical modification of ZrB₂(HfB₂) powders with polycarbosilane followed by pyrolysis, and dispersion of appropriate ceramics with the stabilization of the slurry. The elemental and phase compositions, particle sizes, microstructures, and some other characteristics of the products reported in the related literature are summarized.     

Preparation and characterization of alumina-doped powders for the design of multi-phasic nano-microcomposites

The composite powders 90 vol.% Al₂O₃–5 vol.% YAG–5 vol.% ZrO₂ were produced by doping commercial alumina powders with zirconium and yttrium chloride aqueous solutions. Both a nanocrystalline transition alumina and a pure α-phase powder were used as starting materials. The obtained materials were characterized by DTA-TG, XRD and dilatometric analyses and compared to the respective biphasic systems developed by the same procedure. Pressureless sintering at 1500 °C for 3 h was able to consolidate the doped powders in fully dense bodies, characterized by a very fine and homogeneous dispersion of the second phases into the micronic alumina matrix.     

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.     

Improvement of Ni/SDC anode by alkaline earth metal oxide addition for direct methane–solid oxide fuel cells

The anodic performances of Ni/CeO₂–Sm₂O₃(Ni/SDC) modified by the addition of alkaline earth metal oxides (MgO, CaO, and SrO) were investigated for direct oxidation of CH₄ in solid oxide fuel cells (SOFCs). Although the initial power density of cell with Ni/SDC anode modified by the addition of CaO was slightly lower than that of cell with Ni/SDC, the former anode exhibited an excellent stability compared to the latter one. Such a high stability of Ni–CaO/SDC anode may come from the inhibition of carbon deposition in addition to the retained ionic conductivity of anode.     

阳极负载型SOFC阳极基底厚度对性能的影响

制备不同厚度阳极负载型YSZ薄膜固体氧化物燃料电池 ,并对电池的极化、放电性能进行了测试 .结果表明 ,电池的性能明显受阳极性能的影响 ,阳极过电位大的原因之一是受多孔阳极气体扩散的影响 .降低阳极基底的厚度 ,阳极过电位明显减小 ,电池性能明显提高 .当阳极基底厚度为 0 .5mm时 ,在 80 0℃工作温度下 ,电池的功率密度达到 0 .1 9W·cm- 2 ,较之阳极厚度为 1 .0mm的电池性能提高近 1 .5倍 (0 .1 3W·cm- 2 ) .     

Thermal expansion, gas permeability, and conductivity of Ni-YSZ anodes produced by different techniques

The supported Ni-YSZ (50 wt.% Ni?+?50 wt.% Zr_0.84Y_0.16O_1.92) anodes were produced of powders, obtained by the ceramic method, combustion synthesis, deposition of nickel oxide onto the YSZ ceramics, and deposition of 28 wt.% of nickel oxide onto the 39 wt.% NiO?+?61 wt.% YSZ powders. The influence of the NiO-YSZ powder production technique, the amount of pore former and sintering temperature on the porosity, gas permeability, thermal expansion, and anode conductivity were studied. The porosity of anodes made of powders obtained by the ceramic method is always lower than the porosity of the anodes made of powders produced by combustion synthesis under otherwise equal conditions. The anode electrical conductivity greatly depends on the powder production techniques, while the anode thermal expansion is only slightly influenced by them.     

Scandia-stabilized zirconia-impregnated (La,Sr)MnO3 cathode for tubular solid oxide fuel cells

We have studied the properties of a LSM-ScSZ composite cathode fabricated by a two-step process including dip-coating LSM framework and ion-impregnating ScSZ, for using with anode-supported tubular solid oxide fuel cells. A preliminary examination of the single tubular cell, consisting of a Ni-YSZ anode support tube, a Ni-ScSZ anode functional layer, a ScSZ electrolyte film, and a LSM-ScSZ cathode fabricated by ion-impregnating, has been carried out, and an improved performance was obtained. The polarization resistance of the cathode side clearly decreased for impregnating the electronic conducting phase (LSM) with the ionic conducting phase (ScSZ). And the single cell with the impregnated cathode generated a maximum power density of 433 mW cm⁻² at 850 °C, when operating with humidified hydrogen.     

Mechanochemical activation of aluminum. 4. Kinetics of mechanochemical synthesis of aluminum carbide

The kinetics of mechanochemical synthesis of aluminum carbide Al₄C₃ from elements was studied with X-ray diffraction analysis, low-temperature argon adsorption, laser granulometry, chemical analysis, X-ray photoelectron spectroscopy, and electron scanning microscopy. The conversion was presented as a function of energy consumption (dose) upon the mechanical treatment of mixtures of aluminum and graphite powders with the composition Al-15 wt % C and Al-30 wt % C. A multistage mechanism of the mechanochemical reaction was revealed, and the following stages were separated and characterized: (i) independent grinding and mixing of reagents, (ii) formation of molecular-dense Al/C composites based on nanosized aluminum particles, (iii) chemical interaction of components with the formation of interatomic Al-C bonds, and (iv) crystallization of Al₄C₃ carbide. The formation of amorphous nuclei of aluminum carbide occurs on the contact surface of aluminum nanoparticles with carbon.     

A New Method of Synthesis of Nanosized Boehmite (AlOOH) Powders with a Low Impurity Content

A new method of synthesis of nanosized aluminum oxyhydroxide (AlOOH, boehmite) powders has been suggested through a hydrothermal treatment of nanosized γ-Al₂O₃ powder in water and a 1.5 wt % HCl solution at different temperatures. It has been found that hydrothermal treatment in a 1.5 wt % HCl solution leads to the purification of the starting material; different treatment durations allow one to obtain boehmite particles of different shape. It has been demonstrated that a nanosized boehmite powder is obtained upon the hydrothermal treatment of a nanosized γ-Al₂O₃ in water above 80°С. The nanosized boehmite powders synthesized at different temperatures have been studied by various methods.     

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.