Suchergebnisse

Cathode activation polarisation is one of the main contributions to the losses of a Solid Oxide Fuel Cell. To reduce this loss we use a pulsed laser to modify the surface of yttria stabilized zirconia (YSZ) electrolytes to make a corrugated micro-patterning in the mesoscale. The beam of the laser source, 5 ns pulse width and emitting at λ = 532 nm (green region), is computer-controlled to engrave the selected micro-pattern on the electrolyte surface. Several laser scanning procedures and geometries have been tested. Finally, we engrave a square array with 28 μm of lattice parameter and 7 μm in depth on YSZ plates. With these plates we prepare LSM-YSZ/YSZ/LSM-YSZ symmetrical cells (LSM: La1-xSrxMnO3) and determine their activation polarisation by Electrochemical Impedance Spectroscopy (EIS). To get good electrode-electrolyte contact after sintering it is necessary to use pressure-assisted sintering with low loads (about 5 kPa), which do not modify the electrode microstructure. The decrease in polarisation with respect to an unprocessed cell is about 30%. EIS analysis confirms that the reason for this decrease is an improvement in the activation processes at the electrode-electrolyte interface. ; This work was funded by the MAT2015-68078-R project, which is financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder Program of the European Union. ; Peer reviewed

By laser machining we have prepared thin and self-supported yttria stabilized zirconia (YSZ) electrolytes that can be used in electrolyte-supported solid oxide fuel cells for reducing the operation temperature. The membranes, which are supported by thicker areas of the same material, have an active area of ∼20 μm in thickness and up to 8 mm in diameter. Buckling limits the maximum size of the thin areas to below 1 mm, the overall effective active area being formed by multiple thin areas bounded by ribs. Electron Backscattering Diffraction experiments determined that there are not significant strains inside the membranes and that the heat-affected zone is confined to a shallow layer of ∼1–2 μm. The bending strength of the membranes decreases by ∼26% as a result of the surface microcracking produced by the laser machining. The membranes have a roughness of ∼2.5 μm and are coated by a layer of nanoparticles produced by the laser ablation. This coating and small roughness is not detrimental for the cathodic polarization of the cells. Conversely, the cathode polarization resistance decreases ∼5% in the 650–850 °C temperature range. ; This study was funded by the MAT2015-68078-R financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder Program of the European Union. ; Peer reviewed

Self-supporting thin Yttria Stabilized Zirconia (YSZ) ceramics electrolytes have been prepared by laser machining. They are carved from a sintered YSZ plate to shape a 20 µm thick and 8 mm in diameter central region, surrounded by an unprocessed 150 µm thick supporting zone. Scanning Electron Microscopy (SEM) and Electron BackScattering Diffraction (EBSD) studies confirmed that the strains produced by the laser processing are small and limited to only one or two layers of YSZ grains (~5 µm). SEM and Transmission Electron Microscopy (TEM) have been also used to characterize the surface of the membrane. It is corrugated and coated with YSZ nanoparticles as a result of the laser plasma deposition. Electrochemical characterization by Impedance Spectroscopy (EIS) showed that this surface morphology improves the electrical performance of the membrane slightly but clearly, reducing the cathode polarization resistance by about 5% in the 650-850 ºC range. ; This study was funded by the MAT2012-30763 project, which is financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder program of the European Union. ; Peer Reviewed

Liquid-Assisted Pulsed Laser Ablation (LA-PLA) is a promising top-down method to directly synthesize colloidal dispersions of nanoparticles in a eco-friendly manner. However, the role of LA-PLA synthesis parameters is not yet fully agreed. This work seeks to optimize the production of nanoscale zero-valent iron (nZVI) particles suitable for biomedical or environmental applications using nanosecond LA-PLA on iron targets with different ablation media, laser and target scanning parameters. The use of alcohols as solvents produces iron-iron oxide core-shell nanoparticles with amorphous cores, except for a small crystalline fraction corresponding to the biggest core sizes. Decreasing carbon chain length and complexity leads to a thinning of the carbonaceous material coatings and an increase of the colloidal stability and the nanoparticle productivity. Moreover, a decrease of solvent density and surface tension allows obtaining reduced sizes and polydispersity values. Among, laser and scanning parameters, the pulse accumulation per spot displayed a clear effect in boosting size and productivity. As main outcome, aqueous dispersions with suitable colloidal properties are obtained, either by transferring to water of optimized nZVI particles produced in ethanol, or by direct formation of nZVI particles and in situ coating with hydrophilic molecules in aqueous solutions of these molecules ; This research has been funded by the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER [research projects MAT2015-67354R, MAT2014-53961-R, and MAT2017- 86826-R] and by the Aragón government (DGA) [grant for consolidated group PLATON E31_17R]. OBM thanks the financial support from the "Ramón y Cajal Program" [research project RYC2010-07332] of the Spanish Ministry of Economy and Competitiveness (MINECO) and the H2020 Action H2020-MSCA-IF-2014_ST [grant 656908-NIMBLIS] of the Executive Agency for Research Manages of EU Commission

This is an Open Access article distributed under the terms of the Creative Commons Attribution License. ; Laser ablation of selected coordination complexes can lead to the production of metal-carbon hybrid materials, whose composition and structure can be tailored by suitably choosing the chemical composition of the irradiated targets. This 'laser chemistry' approach, initially applied by our group to the synthesis of P-containing nanostructured carbon foams (NCFs) from triphenylphosphine-based Au and Cu compounds, is broadened in this study to the production of other metal-NCFs and P-free NCFs. Thus, our results show that P-free coordination compounds and commercial organic precursors can act as efficient carbon source for the growth of NCFs. Physicochemical characterization reveals that NCFs are low-density mesoporous materials with relatively low specific surface areas and thermally stable in air up to around 600°C. Moreover, NCFs disperse well in a variety of solvents and can be successfully chemically processed to enable their handling and provide NCF-containing biocomposite fibers by a wet-chemical spinning process. These promising results may open new and interesting avenues toward the use of NCFs for technological applications. ; This work has been supported by the regional Government of Aragón (Spain, Project PI119/09, and E101 and T87 Research Groups funding) and the Spanish Government and Feder funds through grant MAT2010-19837-C06-06. This work has been funded in part by the European Commission through projects LIFE11/ENV/ES 560 and grant agreement no. 280658. ; Peer Reviewed