Nanoparticles formed on oxide surfaces are of key importance in many fields such as catalysis and renewable energy. Here, we control B-site exsolution via lattice strain to achieve a high degree of ...exsolution of nanoparticles in perovskite thin films: more than 1100 particles μm
with a particle size as small as ~5 nm can be achieved via strain control. Compressive-strained films show a larger number of exsolved particles as compared with tensile-strained films. Moreover, the strain-enhanced in situ growth of nanoparticles offers high thermal stability and coking resistance, a low reduction temperature (550 °C), rapid release of particles, and wide tunability. The mechanism of lattice strain-enhanced exsolution is illuminated by thermodynamic and kinetic aspects, emphasizing the unique role of the misfit-strain relaxation energy. This study provides critical insights not only into the design of new forms of nanostructures but also to applications ranging from catalysis, energy conversion/storage, nano-composites, nano-magnetism, to nano-optics.
Perovskite oxides have potential for use as alternative anode materials in solid oxide fuel cells (SOFCs) due to stability in anode atmosphere; donor-doped SrTiO3 (e.g., La0.2Sr0.8TiO3−δ) is a good ...candidate for this purpose. Electro-catalytic nanoparticles can be produced in oxide anodes by the ex-solution method, e.g., by incorporating Ni into a perovskite oxide in air, then reducing the oxide in H2 atmosphere. In this study, we varied the temperature (1100, 1250 °C) and atmosphere (air, H2) of La0.2Sr0.8Ti0.9Ni0.1O3−δ (LSTN) anode firing to control the degree of Ni ex-solution and microstructure. LSTN fired at 1250 °C in H2 showed the best anodic performance for scandia-stabilized zirconia (ScSZ) electrolyte-supported cells in H2 and CH4 fuels due to the favorable microstructure and Ni ex-solution.
•Firing conditions (temp, Po2) of La0.2Sr0.8Ti0.9Ni0.1O3−δ (LSTN) anodes were tested.•The degree of Ni ex-solution and microstructure of LSTN was optimized.•LSTN anode showed very stable performance in H2 and in CH4.•Performance may be improved by mixing with electrolyte.
Metallic bi-layer of porous Ni and porous stainless steel (STS) is utilized as a support for micro-solid oxide fuel cells (SOFCs) using a thin-film layer of electrolyte. Tape-casting and ...screen-printing processes are employed to fabricate a thick ( similar to 250 mu m) STS-layer covered with a thin ( similar to 20 mu m) nano-porous Ni layer. Successful deposition of a nearly pore-free electrolyte layer by the pulsed laser deposition (PLD) method is demonstrated by the high open-circuit-voltage (OCV) value of a single cell. The Ohmic resistance of the micro-SOFC deposited on a porous Ni/STS-support is stable and it shows similar to 28 mW cm-2 after operation for similar to 112 h at 450 degree C. The use of a porous Ni/STS bi-layer as a support for micro-SOFCs is successfully demonstrated.
Gd-doped ceria (GDC, Ce0.86Gd0.14O2−δ) films are deposited on conductive substrates by RF-magnetron sputtering and their across-plane electrical conductivities (perpendicular to film plane) are ...measured as a function of temperature (300≤T≤400°C) and oxygen partial pressure (Po2) to assess the feasibility of their use as an electrolyte in miniaturized solid oxide fuel cells (micro-SOFCs). The films deposited at relatively high T=500°C, deposited on either dense or porous substrate, show columnar grains with diameter 200nm. The magnitude of conductivities in air is similar to those of pellet-form GDC. However, the electronic conductivities of GDC films in low Po2 are higher than that of pellet.
•GDC films were deposited by RF-sputter on dense or porous conductive substrate.•Ionic and electronic conductivities were measured in across-plane mode.•Grain and grain boundary resistances were not distinguishable in impedance spectra.•Ionic conductivities of films were slightly higher than that of the pellet.•Electronic conductivity was increased due possibly to small grains or columns.
A novel thick-film electrolyte-supported cell is constructed to separate cathodic (fuel electrode) from anodic (air electrode) polarization resistance Rp under high electrolysis current in a solid ...oxide electrolysis cell (SOEC). Rp of the SOEC are measured in various fuel humilities (40, 60, 80% H2O + balance H2) at temperature of 650–800 °C and also compared those of a solid oxide fuel cell (SOFC). Anodic Rp of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) is ∼3 times larger than cathodic Rp of Ni-YSZ (yttria-stabilized zirconia) composite at all temperatures tested, so anodic polarization is the limiting factor of electrolysis performance. Degradation of polarization resistance also occurs mostly at the anode under electrolysis current (−800 mA/cm2).
•A new design of a solid oxide cell to separate electrode polarization resistance.•Polarization of anode and cathode is compared with humidities (40–80% H2O).•Polarization of anode is dominant at all temperature (650–800 °C) and humidities.•Air electrode (anode) degraded during electrolysis.
We report design, fabrication method, and fast thermal-cycling ability of solid oxide fuel cells (SOFCs) that use stainless steel (STS) as a support, and a new 3-phase anode. La and Ni co-doped ...SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3-d, LSTN), replaces some of the Ni in conventional Ni-yttria stabilized zirconia (YSZ) anode; the resultant LSTN-YSZ-Ni 3-phase-composite anode is tested as a new reduction (or decomposition)-resistant anode of STS-supported SOFCs that can be co-fired with STS. A multi-layered cell with YSZ electrolyte (thickness ∼5 μm), composite anode, STS-cermet contact-layer, and STS support is designed, then fabricated by tape casting, lamination, and co-firing at 1250 °C in reducing atmosphere. The maximum power density (MPD) is 325 mW cm−2 at 650 °C; this is one of the highest among STS-supported cells fabricated by co-firing. The cell also shows stable open-circuit voltage and Ohmic resistance during 100 rapid thermal cycles between 170 and 600 °C. STS support minimizes stress and avoids cracking of electrolyte during rapid thermal cycling. The excellent MPD and stability during thermal cycles, and promising characteristics of SOFC as a power source for vehicle or mobile devices that requires rapid thermal cycles, are attributed to the new design of the cell with new anode structure.
•A solid oxide fuel cell using new cell components is designed and fabricated.•A new 3-phase anode is co-fired with stainless steel support.•The cell shows excellent stability during fast heating and cooling thermal cycles.•High power density is maintained before and after thermal cycles.•The cell is a candidate as a power source for vehicle or mobile devices.
A thin metal (NiFe)-supported SOFC is fabricated by tape casting and co-sintering, and its mechanical flexibility is tested. A single cell, composed of ∼120 μm-thick NiFe-support, ∼30 μm-thick Ni-YSZ ...(yttria-stabilized zirconia) anode, and ∼15 μm-thick YSZ electrolyte, shows a good mechanical flexibility. With the use of a thin metal (NiFe) support, the degree of bending for the metal-supported cell is much larger than that for the anode- or electrolyte-supported SOFCs as the displacement shows under the mechanical load. The rupture of the cell is also largely prevented due to its flexibility. A thin NiFe-supported cell that operated at 800 °C with a LSCF (La0.6Sr0.4Co0.2Fe0.8O3−δ) cathode shows a power density of ∼430 mW cm−2. This type of cell is promising as a mobile or portable power generator because it is light weight and highly resistant to mechanical shocks.
•A thin NiFe-supported SOFC is fabricated by tape casting and co-firing process.•The cell with a LSCF cathode shows a power density of ∼430 mW cm−2 at 800 °C.•Good mechanical flexibility of the cell is demonstrated by 3-point bending test.
A new diffusion barrier layer (DBL) is proposed for solid oxide fuel cells (SOFCs) supported on stainless-steel where DBL prevents inter-diffusion of atoms between anode and stainless steel (STS) ...support during fabrication and operation of STS-supported SOFCs. Half cells consisting of dense yttria-stabilized zirconia (YSZ) electrolyte, porous Ni-YSZ anode layer, and ferritic STS support, with or without Y0.08Sr0.88TiO3–CeO2 (YST-CeO2) composite DBL, are prepared by tape casting and co-firing at 1250 and 1350 °C, respectively, in reducing (H2) atmosphere. The porous YST-CeO2 layer (t ∼ 60 μm) blocks inter-diffusion of Fe and Ni, and captures the evaporated Cr during cell fabrication (1350 °C). The cell with DBL and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode achieved a maximum power density of ∼220 mW cm−2 which is stable at 700 °C. In order to further improve the power performance, Ni coarsening in anode during co-firing must be prevented or alternative anode which is resistive to coarsening is suggested. This study demonstrates that the new YST-CeO2 layer is a promising as a DBL for stainless-steel-supported SOFCs fabricated with co-firing process.
•STS-supported SOFC with YSZ and Ni-YSZ is tape-casted and co-fired at 1350 °C.•Y0.08Sr0.88TiO3–CeO2 composite is tested as a new diffusion barrier layer (DBL).•The cell with DBL shows peak power density ∼220 mW cm−2 and maintains it at 700 °C.
To clarify the role of milling process on polarization resistance of Ni/GDC cermet anodes for low temperature solid oxide fuel cell (LT-SOFC), an anode with the structure of NiO/Ce0.8Gd0.2O2−δ ...(NiO/GDC20) was prepared via two different milling processes, including conventional ball-milling (CBM) and high energy ball-milling (HEBM). NiO/GDC20 anode composites were fabricated by screen-printing of the milled powders on the dense sintered GDC electrolyte substrate. By employing electrochemical impedance spectroscopy analysis, the effect of the milling process intensity on the LT-SOFC anode performance was examined using a symmetric Ni–GDC20/GDC20/Pt electrolyte-supported cell at 400–600°C. Microstructural studies of NiO/GDC composite powders showed effectiveness of HEBM method on disintegration of CBM aggregates. HEBM powder with much finer particle size showed smaller crystallites than the CBM powder, which led to a finer-grained uniformly-distributed Ni/GDC anode microstructure. In comparison with the anode prepared by CBM powder, the resulted cermet anode showed further GDC lattice expansion, lower anodic polarization resistance, and also decreased activation energy for hydrogen oxidation reaction. Detailed anode impedance analysis showed dominant role of the charge transfer process and rate determining step of dissociation/adsorption/diffusion in hydrogen-oxidation reaction of both Ni/GDC anodes. In addition, evaluation of activation energy showed enhancement of the charge transfer and dissociation/adsorption/diffusion steps with finer-grained microstructure. It is found that the refinement of microstructure has a significant role on the anode polarization resistance and related electrochemical processes.
This study evaluates the effect of donor-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3-δ, LSTN) coating on chromia growth on the surface of porous stainless steel (STS). During subsequent exposure to wet H2 ...atmosphere at 800 °C, the porous STS oxidizes, and its Ohmic resistance increases slowly for 300 h to an area-specific resistance (ASR) ∼2.5 mΩ cm2, but at a much slower rate does uncoated STS and to a much lower ASR than that of uncoated STS (∼17.9 mΩ cm2). The estimated parabolic rate constant indicates that the porous LSTN-coated STS may be used at temperature <680 °C for ∼10 y.
•The oxidation of porous stainless steel (STS) is examined in wet H2 atmosphere.•Porous STS can be used as a support in metal-supported solid oxide fuel cells.•La and Ni co-doped SrTiO3 (LSTN) is suggested as a protective coating for STS.•The LSTN coating strongly reduces the oxidation rate of porous STS.•The coated STS has the resistance of 2.5 mΩ cm2 after 300 h in humid H2 at 800 °C.
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