[Show abstract][Hide abstract] ABSTRACT: The effect of formulations and procedures to deposit thin active layers based on low surface area powders on complex geometry substrates (open-cell foams) was experimentally assessed. An acid-free liquid medium based on water, glycerol, and polyvinyl alcohol was used for powder dispersion, while a dip-coating technique was chosen for washcoat deposition on 30 PPI ceramic open-cell foams. The rheological behavior was explained on the bases of both porosity and actual powder density. It was proved that the use of multiple dippings fulfills flexibility requirements for washcoat load management. Multiple depositions with intermediate flash drying steps at 350 degrees C were carried out. Washcoat loads in the 2.5 to 22 wt. % range were obtained. Pore clogging was seldom observed in a limited extent in samples with high loading (>20 wt. %). Adhesion, evaluated by means of accelerated stress test in ultrasound bath, pointed out good results of all the deposited layers.
[Show abstract][Hide abstract] ABSTRACT: Nowadays, the cathode is the most studied component in Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFCs). Decreasing SOFCs operating temperature implies slow oxygen reduction kinetics and large polarization losses. Double perovskites with general formula REBaCo2O5+δ are promising mixed ionic-electronic conductors, offering a remarkable enhancement of the oxygen diffusivity and surface exchange respect to disordered perovskites. In this review, more than 250 compositions investigated in the literature were analyzed. The evaluation was performed in terms of electrical conductivity, Area Specific Resistance (ASR), chemical compatibility with electrolytes and Thermal Expansion Coefficient (TEC). The most promising materials have been identified as those bearing the mid-sized rare earths (Pr, Nd, Sm, Gd). Doping strategies have been analyzed: Sr doping on A site promotes higher electrical conductivity, but worsen ASR and TECs; B-site doping (Fe, Ni, Mn) helps lowering TECs, but is detrimental for the electrochemical properties. A promising boost of the electrochemical activity is obtained by simply introducing a slight Ba under-stoichiometry. Still, the high sensitivity of the electrochemical properties against slight changes in the stoichiometry hamper a conclusive comparison of all the investigated compounds. Opportunities for an improvement of double perovskite cathodes performance is tentatively foreseen in combining together the diverse effective doping strategies.
No preview · Article · Dec 2015 · Journal of Power Sources
[Show abstract][Hide abstract] ABSTRACT: free download until 25 Nov 2015 at:
Neodymium- and cobalt-based layered perovskite oxides with increasing Ba deficiency (NdBa1-xCo2O5+δ, x = 0.0 ÷ 0.2) are prepared via solid state firing. The chemical and electrochemical properties of these materials are characterized via XRD, SEM, TG-DTA, 4-probe conductivity measurement and EIS tests on symmetric cells. The maximum tolerated Ba deficiency is slightly below 10%. The compounds crystallize in an ordered layered structure with orthorhombic Pmmm (for x = 0 and 0.5) and tetragonal P4/mmm (for x = 0.10) crystal lattice. All the compounds show high total conductivity (between 400 and 600 S/cm at 700 °C). A remarkable tenfold decrease of the area specific resistance is observed at decreasing the Ba content from 0 to 10%, with the compound at 10% Ba deficiency reaching the best performance (0.1 Ω*cm2 at 700 °C). Detailed equivalent circuit analysis on EIS tests at varying temperature (550 to 700 °C) and O2 content (100% to 5% v/v) reveals that the limiting steps are the transport of oxygen ions within the cathodic phase and across the electrolyte interface at high frequency, and the formation of an oxygen ion at intermediate frequency. The effect of Ba on the electrochemical mechanism is associated with a promotion of the bulk diffusion steps at high frequency.
[Show abstract][Hide abstract] ABSTRACT: Two mineral clays of the montmorillonite group were tested as sorbents for the removal of Rare Earths (REs) from liquid solutions. Lanthanum and neodymium model solutions were used to perform uptake tests in order to: (a) verify the clays sorption capability, (b) investigate the sorption mechanisms and (c) optimize the experimental parameters, such as contact time and pH.
The desorption was also studied, in order to evaluate the feasibility of REs recovery from waters. The adsorption–desorption procedure with the optimized parameters was also tested on a leaching solution obtained by dissolution of a dismantled NdFeB magnet of a hard-disk.
The clays were fully characterized after REs adsorption and desorption by means of X-ray powder diffraction (XRPD) and X-ray photoelectron spectroscopy (XPS); the liquid phase was characterized via Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) analyses.
The experimental results show that both clays are able to capture and release La and Nd ions, with an ion exchange mechanism. The best total efficiency (capture ≈ 50%, release ≈ 70%) is obtained when the uptake and release processes are performed at pH = 5 and pH = 1 respectively; in real leached scrap solutions, the uptake is around 40% but release efficiency is strongly decreased passing from a mono-ion system to a real system (from 80% to 5%). Furthermore, a strong matrix effect is found, with the matrix largely affecting both the uptake and the release of neodymium.
No preview · Article · Oct 2015 · Waste Management
[Show abstract][Hide abstract] ABSTRACT: Two mineral clays of the montmorillonite group were tested as sorbents for the removal of Rare Earths
(REs) from liquid solutions. Lanthanum and neodymium model solutions were used to perform uptake
tests in order to: (a) verify the clays sorption capability, (b) investigate the sorption mechanisms and
(c) optimize the experimental parameters, such as contact time and pH.
The desorption was also studied, in order to evaluate the feasibility of REs recovery from waters. The
adsorption–desorption procedure with the optimized parameters was also tested on a leaching solution
obtained by dissolution of a dismantled NdFeB magnet of a hard-disk.
The clays were fully characterized after REs adsorption and desorption by means of X-ray powder
diffraction (XRPD) and X-ray photoelectron spectroscopy (XPS); the liquid phase was characterized via
Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) analyses.
The experimental results show that both clays are able to capture and release La and Nd ions, with an
ion exchange mechanism. The best total efficiency (capture � 50%, release � 70%) is obtained when the
uptake and release processes are performed at pH = 5 and pH = 1 respectively; in real leached scrap solutions, the uptake is around 40% but release efficiency is strongly decreased passing from a mono-ion system to a real system (from 80% to 5%). Furthermore, a strong matrix effect is found, with the matrix
largely affecting both the uptake and the release of neodymium.
No preview · Article · Sep 2015 · Waste Management
[Show abstract][Hide abstract] ABSTRACT: An acid-free formulation based on water, glycerol, and polyvinyl alcohol (PVA) was studied to disperse and stabilize, via steric-like interaction, low surface area cerium oxide powders. A dispersion route that implies a milling process and a proper ratio among the components was experienced. PVA was used as viscosity modulator, to enhance viscosity and system stability. Newtonian fluids, suitable for foams dip-coating, were obtained in the application shear range. Foams with different porosities (20, 30, and 40 pore per inch density) were coated. It was found that withdrawal velocity did not affect deposition: a constancy in coating load was obtained once rheology was fixed, while multiple dipping was effective to enhance load. An optimal flash drying temperature (350°C) was identified to consolidate the coated layer and to decompose the organic additives. Good loads, homogeneous coverage, and no pore clogging were obtained after calcination at 900°C. Even though acceptable weight losses were obtained, further investigations need to be accomplished to understand data scattering after adhesion tests. 2016
No preview · Article · Jul 2015 · Particulate Science And Technology
[Show abstract][Hide abstract] ABSTRACT: Gas diffusion medium (GDM) is a crucial component in proton exchange membrane fuel cells (PEMFCs). Being composed of a gas diffusion layer (GDL) with a micro-porous layer (MPL) coated onto it, it ensures a proper water management due to the highly hydrophobic materials employed in cell assembly. In current commercial applications, the desired water repellent behaviour is usually obtained by using polytetrafluoroethylene (PTFE). In this work, Fluorolink® P56 (Solvay Specialty Polymers, Milan, Italy), a commercially available, anionic, segmented high molecular weight polyfluorourethane with perfluoropolyether groups was extensively evaluated as an alternative to PTFE for micro-porous layer hydrophobization. A change in polymer used is desirable in order to simplify the production process, both in terms of ink formulation and thermal treatment, as well as to get a higher hydrophobicity and, consequently, more efficient water management. Innovative prepared samples were compared to a PTFE-based GDM, in order to assess differences both from morphological and from an electrochemical point of view.
[Show abstract][Hide abstract] ABSTRACT: Currently, Gas Diffusion Media for Polymer Electrolyte Membrane Fuel Cells are made hydrophobic by using mainly PTFE. In this work, PTFE was replaced with a less conventionally employed polymer (i.e. fluorinated ethylene propylene, FEP) and carbon nanotubes partially substituted carbon black in the formulation for preparing MPLs. Three inks with variable CNTs concentration were prepared. The presence of FEP allowed to decrease the treatment temperature (260 °C) with respect to the one necessary with GDMs based on PTFE (350 °C). Performances of the cells assembled with FEP-based samples were better than those obtained with conventional GDMs. GDM containing the highest amount of CNTs (10% wt) showed the best results in terms of output power density and cell efficiency. Durability of such a sample was also assessed. Both chemical and mechanical ad-hoc accelerated stress tests were developed. Such tests showed that the main degradation for MPL is due to mechanical stresses, which led to detachment of part of the micro-porous surface and this caused a dramatic mass transfer resistance increase which means a reduction of capability of managing water. Whereas, chemical AST did not show substantial changes in GDMs surface resulting in more restrained diffusion resistance increases.
No preview · Article · Jun 2015 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: In this paper the effect of the addition of carboxymethylcellulose (CMC) to microporous layers (MPLs) formulation is reported and the rheological, morphological and electrical properties of the so-obtained MPLs are assessed. Two different PTFE/carbon black ratios are considered, with and without CMC in the ink formulation. CMC addition results in a better homogeneity and stability of the inks. Moreover, the presence of CMC leads to a better shear thinning behaviour and to a general increase in viscosity that makes these slurries more appropriate for coating deposition via doctor blade technique. The presence of CMC in MPL formulation also affects the electrochemical performances in terms of I–V curves and impedance spectra. CMC-containing MPLs show the best performances in terms of generated power at high temperature (80 °C) and low cathodic relative humidity (RH 60 %). Ohmic resistances too, in presence of CMC, are lower than those exhibited by CMC-free MPLs.
[Show abstract][Hide abstract] ABSTRACT: A natural smectite mineral clay (STx-1b) was modified by intercalating different concentrations of Pentaethylenehexamine (PEHA) with the final aim of synthesizing new solid materials for the recovery of valuable metals, in particular Rare Earths (REs), from Waste Electrical and Electronic Equipment (WEEE). The modified clays were then contacted with a model solution of Lanthanum (chosen as representing element of REs family). Finally, release tests were performed on the different samples in order to verify the organo-clay capability not only to capture but also to recover metal ions. The results showed that the experimental procedure was appropriate to intercalate the polymer in the clay for every initial polymer concentration considered. Furthermore, the obtained organo-clays were effective in both uptake (efficiencies up to 99 %) and release processes (efficiency around 80 % contacting with acid solutions). The organo-clay system with polymer content of 0.4 mmolpolymer/gclay was selected as that of choice to guarantee the highest global process efficiency, ensuring a Lanthanum recovery of 80 %. The adsorbed and released metal ions were calculated by ICP-OES while the amounts of intercalated polymer were estimated by COD (Chemical Oxygen Demand) analysis of the residual amounts in solution and deduced by difference. All the solid materials were characterized by X-ray diffraction (XRD).
[Show abstract][Hide abstract] ABSTRACT: In this work, the development of acid-free stable oxide dispersions has been studied to obtain thin oxide layers onto substrates of complex geometry to obtain structured catalysts and reactors for process intensification. In particular, attention has been paid to syngas production in steam reforming process using CeO2-based oxides. For this purposes commercial cerium oxide (3 m2 g-1) was selected as model of low surface area catalyst precursor and dip-coating as deposition technique. Ceramic monoliths were used as structured supports (diameter 1 cm, length 1.5 cm). A slurry formulation, including the powder, glycerol, polyvinyl alcohol and distilled water allowed to obtain the proper rheological behavior and stability of the suspension. The addition of a relatively small PVA quantity changes dispersion properties, allowing to properly tune viscosity. Results were evaluated in terms of coating load and adhesion performance. Final coating loads of about 18 %wt. were obtained performing multiple depositions. A good homogeneity of the washcoat layers was found, accompanied by a quite good adhesion (6% wt of coating loss after ultrasound treatment).
[Show abstract][Hide abstract] ABSTRACT: press as: Pelosato R, et al. Electrical characterization of co-precipitated LaBaCo 2 O 5+δ and YBaCo 2 O 5+δ oxides. J Eur Ceram Soc (2014), Abstract REBaCo 2 O 5+δ layered perovskite oxides (RE = Rare Earth) are promising cathodes for IT-SOFCs. In this work, a simple co-precipitation synthesis in aqueous medium was applied to prepare LaBaCo 2 O 5+δ (LBC) and YBaCo 2 O 5+δ (YBC) cathodes. The chemical and electrochemical properties of both materials were characterized via XRD, SEM, TPO, TG–DTA, 4-probe conductivity measurement, and EIS tests on symmetric cells. The coprecipitation synthesis revealed a promising preparation route: the measured ASR values of both materials were well comparable with the literature ones. A kinetic investigation of the O 2 reduction process was performed on LBC (600–800 • C, 5–100% O 2 , v/v), whose results were analyzed with equivalent circuits. The main steps were identified (oxygen diffusion and charge transfer at high frequency, O 2 chemisorption at medium frequency), and their activation energy and reaction order were quantified. Aging tests (500 h time on stream, 500–800 • C) revealed quick deactivation for YBC and good stability for LBC.
Full-text · Article · Dec 2014 · Journal of the European Ceramic Society
[Show abstract][Hide abstract] ABSTRACT: Coating is the most widely used technique for the preparation of structured catalysts. This paper reviews the main methods reported in the open literature for depositing catalytic layers onto metallic substrates, specifically focusing on the coating of metallic honeycomb monoliths and open-cell foams. All the relevant steps, including substrate pre-treatments, means for catalytic activation and thermal treatments, are discussed.
[Show abstract][Hide abstract] ABSTRACT: Gas diffusion medium (GDM) is a crucial carbon-based component for water management in polymer electrolyte membrane fuel cells (PEMFCs). GDM consists of a macro-porous substrate, which is usually a carbon cloth or carbon paper, coated with a thin micro-porous layer (MPL). Traditionally, PTFE is used as hydrophobic agent and binder. In this work, three different GDMs were prepared using fluorinated polymers (polytetrafluoroethylene-co-hexafluoro-propylene (FEP), polytetrafluoroethylene-co-perfluoroalcoxy vinyl ether (PFA) and a fluorinated polyurethane based on perfluoropolyether blocks (PFPE)) in order to replace conventional PTFE as hydrophobic agent, which was used as reference. Inks composition and rheological behaviour were fixed in order to apply the blade coating technique for MPL deposition. These polymers allowed to decrease temperature during thermal treatments with respect to the one necessary for treating PTFE-based MPLs. Moreover, superhydrophobic layers were obtained for all the samples and the final electrical performances of the whole fuel cell system were improved with respect to the ones reached with PTFE-based samples. In particular, FEP allowed to reduce significantly mass transfer resistances in the operating conditions of the fuel cell.
No preview · Article · Jul 2014 · Progress in Organic Coatings
[Show abstract][Hide abstract] ABSTRACT: A 2D isothermal axisymmetric model of an anode-supported solid oxide fuel cell has been developed. The model, which is based on finite element approach, comprises electronic and ionic charge balance, Butler–Volmer charge transfer kinetic, flow distribution and gas phase mass balance in both channels and porous electrodes. The model has been validated using available experimental data coming from a single anode-supported cell comprising Ni–YSZ/YSZ/LSM–YSZ as anode, electrolyte and cathode, respectively. Hydrogen and steam were used as fuel inlet and air as an oxidant. The validation has been carried out at 1 atm, 1,500 ml min–1 air flow rate and three different operating conditions of temperature and fuel flow rate: 1,073 K and 400 ml min–1, 1,073 K and 500 ml min–1, and 1,003 K and 400 ml min–1. The polarization and power density versus current density curves show a good agreement with the experimental data. A parametric analysis has been carried out to highlight which parameters have main effect on the overall cell performance as measured by polarization curve, especially focusing on the influence of two geometrical characteristics, temperature and some effective material properties.
[Show abstract][Hide abstract] ABSTRACT: Microporous layers (MPLs) obtained from inks containing three fluorinated polymers (perfluoroalcoxy, fluorinated ethylene propylene and a fluorinated polyurethane based on perfluoropolyether blocks) replacing conventional PTFE were prepared. Inks composition and rheological behaviour were fixed in order to apply the blade coating technique for MPL deposition. Superhydrophobic layers were obtained since contact angles higher than 150 degrees were measured. The samples, tested in a single fuel cell at lab scale, at 60 degrees C and different relative humidity (RH 80/100 and 80/60, hydrogen/air) evidenced that new polymers are able to improve electrical performances reaching maximum power density values higher than those showed by conventional MPLs based fuel cells. Electrochemical impedance spectroscopy (EIS) was also carried out on the running cell using a Frequency Response Analyzer to assess the different dissipation phenomena and related losses. Copyright
No preview · Article · Mar 2014 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: This work presents the application of FT IR spectroscopy to study the thermal evolution of PEG-based nanocomposites prepared using montmorillonite STx intercalated with polyethylene-oxides PEG 1500 and PEG 4000 and polyethylene oxide Brij. The effect of different polymer molecular weight and polymer loadings has been evaluated by means of diagnostic mid-IR bands. PEG fragmentation through the cleavage of the C-O bond appears to be the main reaction step, leading to the formation of short chain carbonyl adsorbed species (such as acetaldehyde), alcohols (ethanol and methanol) and, to a lesser extent, esters species, characterized by the frequency of the carbonyl stretching band. The detection of carbonyl band evidenced the formation of partial oxidation products as first step of the thermal degradation.
Increasing polymer loadings, as well as increasing polymer molecular weight leads to lower temperature of formation of the first oxidation products. No clear indication of the effect of the chemical nature for the intercalated polymers can be obtained. BRIJ thermal decomposition seems to be mainly driven by the PEG-like moiety chemistry.
CH stretching bands detected at 450-500 °C for the samples intercalated with PEG samples indicated the formation of residual organic compounds resisting oxidation, possibly char species preserved from further oxidation by the interlayer galleries.
No preview · Article · Mar 2014 · Vibrational Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: Micro-porous layer (MPL) is a crucial component for an efficient water management in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). Nowadays, MPLs are obtained by depositing a dispersion, commonly known as ink, containing carbon black particles and PTFE onto a carbon cloth substrate. In this work PTFE was replaced by an innovative fluorinated polymer in order to improve hydrophobic properties of MPLs and consequently the water management of the whole system. Moreover, carbon nanotubes (CNTs) partially substituted carbon black in ink formulation. The new polymer allowed to decrease considerably the treatment temperature (260°C) with respect to the one necessary with conventional samples based on PTFE (350°C). Fuel cells assembled with the sample containing CNTs showed better performances than those obtained with traditional CNTs-free MPLs. Durability of the most performant sample was assessed. Ad-hoc Accelerated Stress Tests (ASTs) were developed; they showed that the main degradation for MPL is due to mechanical stresses, caused by reactants and water flow, which leads to detachment of materials and to a consequent dramatic mass transfer resistance increase.
No preview · Article · Jan 2014 · Chemical Engineering Transactions
[Show abstract][Hide abstract] ABSTRACT: The present work focuses on the use of an alternative polymer (Fluorolink® P56, a commercially available, anionic, segmented polyfluorourethane with high molecular weight) to be used as hydrophobic agent in GDMs production for PEMFCs. Prepared samples were physically evaluated by static contact angle, SEM analysis, porosimetry and finally tested in a single lab-scale fuel cell in order to assess electrochemical performances. In a typical experiment, carbon black (CB), Fluorolink P56 (two different concentrations) and isopropyl alcohol were mixed at 8000 rpm by using an Ultra Turrax homogeneizator. Inks produced were blade coated on hydrophobized commercial GDLs (SAATI Group). Then the samples were treated for 30 minutes at 150°C in order to remove the wetting medium and to make the polymer fibrous. The layers based on Fluorolink P56 showed good surface uniformity and a superhydrophobic behavior (i.e. mean contact angle higher than 150°). Electrochemical tests, performed at 60°C and 80°C and low (60%) and high (100%) relative humidities, demonstrated that innovative GDMs are able to guarantee higher power density values in certain operating conditions and very low overall ohmic resistances, even though some critical issues still remain in diffusion limitations at high current densities, when more water is generated.
No preview · Article · Jan 2014 · Chemical Engineering Transactions
[Show abstract][Hide abstract] ABSTRACT: A very simple, cost-effective, chloride- and alkali-free, carbonate co-precipitation synthesis in aqueous medium was applied in the preparation of perovskite-type lanthanum manganese oxide-based powders, i.e. La0.70Sr0.30MnO3−δ
(LSM) and La0.75Sr0.25Cr0.5Mn0.5O3−δ
(LSCrM). The precursors so obtained yielded nano-structured perovskite oxides when treated at 900°C and 800°C, respectively. The measured BET surface areas were in the low-end range for high temperature oxides (4 m2 g−1 and 10 m2 g−1) but the X-ray crystallite size was as low as 50 nm for LSCrM and 90 nm for LSM.
No preview · Article · May 2013 · Chemical Papers- Slovak Academy of Sciences