F. M.B. Marques

F. M.B. Marques
University of Aveiro | UA · Department of Materials and Ceramics Engineering

Professor

About

276
Publications
17,052
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8,661
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November 1979 - present
University of Aveiro
November 1979 - present
University of Aveiro
Position
  • Professor (Full)

Publications

Publications (276)
Article
MgO-doped partially stabilized zirconia (xMgPSZ, with x = 8 or 10 mol%) materials sintered at 1700°C, were characterized with respect to structure, microstructure, thermal expansion and electrical performance. The monoclinic (M) phase content is almost vestigial in 10MgPSZ, unlike in 8MgPSZ. Combined powder XRD and customized thermal expansion data...
Article
Composite membranes for CO2 separation based on CGO (Gd-doped ceria) and the eutectic mixture of Na and Li carbonates, with distinct salt content (around 20 and 40 vol%) and microstructures (starting oxide grain size in the 170–220 nm range), were prepared and tested up to 250 h, at 650 °C, under distinct atmospheres (CO2 gradient or fully immersed...
Article
Alkali metal nitrates were successfully used as starting chemicals in the production of composite CO2 separation membranes. The easy conversion of nitrates into carbonates after high temperature annealing in CO2 is confirmed using techniques like FTIR (Fourier transform infrared) or selective NO3⁻ electrodes. This conversion shows a step like incre...
Article
Partially Stabilized Zirconia samples with 7, 8 and 9 mol% MgO (Mg-PSZ) were sintered at 1700°C for 2 h and cooled to room temperature (2°C.min⁻¹), to obtain distinct phase compositions and microstructures. These materials were studied by dilatometry (DIL) up to about 1500°C (heating rate of 10°C.min⁻¹). A detailed analysis of DIL curves is used to...
Article
Gd‐doped ceria (GDC)‐based composites, including a eutectic mixture of lithium and sodium carbonate (NLC) as second phase, were prepared using several processing routes, namely chemical synthesis, co‐firing of both phases, or impregnation of a presintered porous matrix. LiAlO2‐based composites were also prepared and used as reference. The structura...
Article
Previously sintered (1500 °C, 4 h) dense pellets of Ce0.9Gd0.1O1.95 (GDC) were covered and heat treated with eutectic mixtures of Na2CO3 and Li2CO3 (NLC), and their electrical performance was assessed against pure GDC and chemically synthesized GDC + NLC. Microstructural analysis of NLC impregnated samples confirmed slight migration of the molten p...
Article
Pure NiO or lithiated NiO with distinct Li/Ni atomic proportions (50/50—LN55 and 30/70—LN37) were tested as protective barrier layers (PBLs) to enhance the stability of LaCoO3 (LC) electrodes in cells with composite electrolytes (CEs) consisting of Gd‐doped ceria (CGO) and a eutectic mixture of Na and Li carbonates (NLCs). PBLs and LC layers were s...
Article
Oxide + salt composites can be used in CO2 and NOx separation membranes, where high oxide-ion conductivity is crucial to improve performance. Pursuing this goal, the stability of three different bismuth oxide-based electrolytes (Cu + V, Y and Yb-doped) against molten alkali carbonates (Li, Na, K) or nitrates (Na, K) was tested firing them in the 45...
Article
Within this study, a layered cathode for use in a Molten Carbonate Fuel Cell (MCFC) has been developed. The substrate layer and reference MCFC cathode made of porous nickel was covered by a porous silver film with defined porosity and pore size. Both layers were fabricated using the tape casting method and further fired in a reductive atmosphere. T...
Article
Composite ceramic membranes were prepared according to two routes: i) vacuum impregnation of molten eutectic sodium-lithium carbonates (NLC) into porous ceria-20 mol% gadolinia (20GDC) solid electrolytes; ii) electric field-assisted sintering of a 25 wt.% NLC/75 wt.% 20GDC mixture. Porous 20GDC ceramics were obtained by controlled thermal removal o...
Article
Gd-doped ceria electrolytes (GDC, 10 at.% Gd) were prepared using a eutectic mixture of Li and Na carbonates as sintering aid (NLC - 0, 1, 3 and 5 mol%), using two processing routes (ceramic and chemical). Structural and microstructural characterization provided no evidence for significant solubility of alkali metal cations in GDC. Materials sinter...
Article
Samples of Gd-doped ceria (GDC, Ce0.9Gd0.1O1.95) with eutectic mixtures of Na2CO3 and Li2CO3 (NLC), or K2CO3, Na2CO3 and Li2CO3 (KNLC) as sintering aids (5 mol%) were studied against pure GDC and cobalt doped GDC. The former electrolytes reached densifications in excess of 95% when sintered at 1100 °C, values comparable to pure GDC sintered at 1500...
Article
The optimization of the performance of electrodes (oxide‐based) for composite electrolytes (Ce0.9Gd0.1O1.95 + (Li0.52Na0.48)2CO3) is addressed in this work acting mostly on the electrode chemical nature (eg, LaCoO3, Li0.43NiO2, or LiNiO2), thickness (single and multiple screen‐printed layers), and cell layer concept (with/without barrier layers bet...
Article
MgO-doped partially stabilized zirconia (MgPSZ) is a ceramic where three phases (cubic, tetragonal and monoclinic zirconia) might coexist due to non-equilibrium conditions and proper quantification of phase content is difficult. Here, a few selected compositions (in the 7-10 mol% MgO range) and firing profiles were studied in order to cover several...
Article
Full-text available
MgO-doped partially stabilized zirconia is a complex ceramic electrolyte in which all properties, phase composition, and microstructure are strongly influenced by thermal history besides chemical composition. The electrochemical performance of this ceramic used in oxygen sensors for molten steel is reviewed here. A wide collection of data on electr...
Article
A recent commentary suggesting mishandled literature data in the analysis of the performance of composites including salts (alkaline carbonates) and oxides (pure ceria) is shown here as invalid. Even inadequately invoked data for the salt conductivity is shown to remain below the required performance. This conclusion is inevitable when due attentio...
Article
The electrical performance and CO2 permeation of composite membranes based on Gd-doped ceria skeletons impregnated with molten alkaline carbonates are benchmarked against their predictable performance based on ambipolar conductivity governed kinetics (best scenario), using customized diagrams. Experiments performed in the 550–850 °C temperature ran...
Article
NiO-C ⁠ 0.9 Gd ⁠ 0.1 O ⁠ 1.95 (NiO-GDC) composites obtained using a chemical route (one-step synthesis) were characterized by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spec-troscopy (between 300 and 650 °C in air). Rietveld refinement of XRD data indicated that synthesized powders are ultrafine and...
Article
LaWxNb1−xO4+x/2 ceramics (x = 0.16) were prepared via a solid state route and studied with respect to phase stability and mixed ionic and electronic conductivity under conditions of technological relevance for fuel cell applications. The chemical compatibility against standard cathode materials revealed that Sr-doped LaMnO3 could be used without de...
Article
Composite electrolytes including an oxide (Gd-doped ceria, 70, 80, and 90 vol%) and a eutectic mixture of alkaline carbonates (Na2CO3 and Li2CO3) were produced by joint milling and firing of all constituents. The microstructure of these composites was studied by scanning electron microscopy/energy-dispersive X-ray spectroscopy, and they were furthe...
Article
The present study reports the synthesis of Ce0.8Sm0.2O1.9 solid electrolyte by a novel proteic sol-gel method which uses gelatin as polymerizing agent. The as-synthesized powder material was calcined at 700 °C for 2 h, with X-ray diffraction revealing a single cubic phase with lattice parameter a = 0.5435 nm and theoretical density of 7.144 gcm-3....
Article
A simple model on the performance of composite CO2 separation membranes (ceramic oxide-ion conductor and molten alkaline carbonates) is derived from an equivalent circuit comprising two interlinked cells, using the main electrical circuit component analogs of the electrochemical characteristics of each composite phase (thermodynamic voltages and io...
Article
Several composite materials were produced using ceria nanoparticles (<25 nm) and LiAlO2 (particle size >1 μm). The oxides were combined with a mixture of Na2CO3 and Li2CO3 (eutectic composition), and fired at temperatures in the 600-700 °C range (vacuum assisted in a few cases). The composites were characterized by scanning electron microscopy, X-r...
Article
The CO2 permeation of composite membranes obtained by impregnation of molten alkaline carbonates into a Gd-doped ceria ceramic skeleton was tested using several gas mixtures with up to 50 vol% CO2 as feed gas and Ar in the membrane permeate side. Experiments performed in the 550–850 °C temperature range showed high permeation rates reaching 0.6 cm−...
Article
Full-text available
Solid oxide-alkaline carbonate (Li2CO3:Na2CO3, 1:1 molar ratio) composite electrolytes were prepared using different solid oxide matrices (TiO2, HfO2, Yb2O3, Y2O3, Dy2O3, Gd2O3 and La2O3), to cover a wide range of ceramic chemical characteristics. The chemical and microstructural stability of these oxides with the mixed carbonates were studied by p...
Article
Full-text available
This work reports the synthesis of apatite-type lanthanum silicate powders with nominal composition La 10 Si 6 O 27 by an innovative chemical route which combines co-precipitation and sol-gel approaches. The herein proposed synthetic procedure is advantageous in reducing energy consumption and processing time, key elements to decrease the total man...
Article
In this study, composite powders synthesized by a novel one-step sol–gel method were used to obtain Ni–CGO anodes, while anodes of the same composition prepared from commercial powders were used as reference. The anodes performance was studied by impedance spectroscopy and dc polarization in the temperature range of 650–750 °C in flowing humidified...
Article
Composites based on Gd-doped ceria and alkaline carbonates were produced in different manners to identify key compositional and microstructural features determining their mixed oxide and carbonate-ion conductivity. Co-firing of fine powder precursors yielded composites with delicate ceramic skeletons. After impregnation with alkaline carbonates, pr...
Article
Gd-doped ceria (CGO) nanopowders were mixed with up to 1 mol% of Zn (as nitrate) to exploit the role of this dopant on sintering and electrical performance. All samples were prepared by two-step sintering schedules to try to combine the advantages of both effects on low-temperature densification. Structural and microstructural analyses were complem...
Article
Full-text available
The development of electrochemical devices towards clean energy generation has been intensified in the last years. In this context, fuel cells, and especially intermediate temperature solid oxide fuel cells (IT-SOFC) have received much attention. Perovskite type materials of composition Ba 1-x Sr x Co 1-y Fe y O 3-δ , doped or not with rare earth i...
Article
A bi-layered concept of glass-ceramic (GC) sealant is proposed to overcome the challenges being faced by solid oxide fuel cells’ (SOFCs). Two separated layers composed of glasses (Gd-0.3 and Sr-0.3) were prepared and deposited onto interconnect materials using a tape casting approach. After heat treating the bi-layered structure at 850 °C for 1–100...
Article
Composite electrolytes based on Gd-doped ceria (from 50 to 95 vol%) and one eutectic mixture of sodium and lithium carbonates were prepared by co-firing, in order to identify the compositional range where both oxide and carbonate-ion transport are balanced, as required for high performance CO2 separation membranes. Considering the adequacy of this...
Article
Ceria-based composites (50 vol% of the ceramic phase) including one mixture of Li and Na carbonates (1:1 molar ratio), were prepared using either pure ceria (modest conductor) or Gd-doped ceria (excellent oxide ion conductor) as ceramic matrix. These materials were aged for periods of up to 1000 h at 550 degrees C, under pure CO2, in air and in H-2...
Article
a b s t r a c t Europium-doped ceria (EDC, Ce 0.9 Eu 0.1 O 2Àd)/alkaline carbonate (LNC, (Li,Na) 2 CO 3) compos-ite ceramics prepared through a one-step citrate-based route were analyzed by powder X-ray diffraction, infrared and laser Raman spectroscopies as well as scanning and trans-mission electron microscopy. The electrochemical behavior of the...
Article
Full-text available
The correlation between the microstructure and electrical properties of NiO-Ce 0.9 Gd 0.1 O 1.95 (NiO-CGO) composites prepared by a one-step synthesis method is reported in the present work, and compared to conventional samples synthesized by mechanically mixing commercial powders. Samples sintered between 1350 and 1450 °C had their microstructures...
Data
Full-text available
a b s t r a c t Ceria-based composite electrolytes (50 and 70 vol%) including one mixture of Li and Na carbonates (1:1 molar ratio) were prepared using either pure CeO 2 (modest conductor) or Gd-doped ceria (excellent oxide-ion conductor) as ceramic matrix. The composite electrolytes and their phase constituents were tested under pure CO 2 , air, a...
Article
a b s t r a c t Multilayer ceramic and salt composite cells were prepared superimposing up to seven alternate layers of Ce 0.9 Gd 0.1 O 1.95 (CGO) and mixtures of Na 2 CO 3 (NC) and Li 2 CO 3 (LC), with final sintering around 500 C. Various other single component cells (CGO or NC þ LC) and homogeneous composites (consisting of intimate mixtures of...
Article
Ceria-based composites (ranging from 30 to 70 vol%) including a mixture of Li and Na carbonates (1:2 M ratio, respectively) were sequentially exposed to pure CO2, O2 and a mixture of 10 vol% H2 diluted in N2, at temperatures ranging from300 to 580 �C, to study the role of composite/gas interaction on electrical performance. Impedance spectroscopy m...
Article
Solid oxide fuel cells are extremely flexible energy conversion systems able to operate within a broad temperature range (500–1000°C), with a variety of fuels (from hydrogen to liquid fuels), including concepts able to be scaled to deliver power from the milliwatt to the megawatt range. The solid electrolyte, as an ionic charge carrier, is one cent...
Article
A comparative microstructural study between Ni–Ce0.9Gd0.1O1.95 (Ni–CGO) anodes obtained from NiO–CGO nanocomposite powders prepared by in situ one-step synthesis and by mechanical mixture (two-step synthesis) of NiO and CGO powders is reported. The open porosity and microstructure of sintered and reduced pellets were investigated as a function of t...
Article
Sixteen different thermal profiles were used to exploit the role of thermal treatment on the structure, microstructure and electrical conductivity of yttrium- and gadolinium-doped ceria electrolytes. Samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and impedance spectroscopy in air....
Article
Full-text available
Steady state polarisation measurements can be affected by electrode microstructure and geometrical arrangement. In particular, the relative position of the reference electrode with respect to the working and counter electrodes may influence the reference potential and therefore effect the overvoltage readings. The influence of the geometrical arran...
Article
Polycrystalline Bi 2-x La x V 0.90 Cu 0.10 O 5.5-δ (x = 0, 0.10 and 0.20) and Bi 1.90 Pr 0.10 V 0.90 Cu 0.10 O 5.5-δ were prepared by the standard ceramic-synthesis technique. The total electrical conductivity of Bi 1.90 La 0.10 V 0.90 Cu 0.10 O 5.5-δ at temperatures above 500 K is slightly lower than undoped BICUVOX.10, but transport properties in...
Article
Composite ionic conductors were produced by combination of alkaline carbonates with various ceramic oxides, including ceria, zirconia and alumina. The adopted mechano-thermal processing routes originated materials with the same nominal composition but with significantly different microstructures. The electrical performance of these composites, stud...
Article
Full-text available
Composite materials based on gadolinium doped ceria (CGO) with additions of silica, with both silica and lanthanum oxide, and with lanthanum silicate, were prepared by the conventional ceramic route, to assess the silica scavenging role of lanthanum oxide additions. Structural, microstructural and electrical characterization of these samples confir...
Article
Full-text available
C. Yttria doped with CaO exhibits reasonably high ionic conduction via the vacancy mechanism. Samples doped with ZrO 2 and HfO 2 possess oxygen interstitials as dominant defects, but show poor ionic conductivity when compared to Ca-doped materials. These tendencies, known for other fluorite-related phases such as pyrochlores, are opposite to those...
Article
The structure, microstructure and low-temperature electrical properties of core-shell-type mixed conductors based on lanthanum gallate with Fe-doped grain boundaries are analyzed in depth. Electron probe microanalysis revealed that the iron concentration in the grain-boundary regions (shell) is below 1 at.% and their thickness is no more than 1.5 m...
Article
Composite ionic conductors for fuel cells were produced by combination of one ceria-based ceramic electrolyte and various mixtures of Na and Li carbonates, using several processing routes. These materials were characterized by impedance spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction and Fourier tra...
Article
Yttrium and gadolinium-doped ceria-based electrolytes (20 at% dopant cation) with and without small Ga2O3-additions (0.5 mol%) were fired at peak temperatures of 1250 and 1300 °C, or following a two-step sintering profile including one peak temperature and subsequent dwell at 1150 °C, 10 h. All materials were characterized by scanning electron micr...
Article
Samaria-doped ceria-based composites with a 2:1 addition of Li and Na carbonates (or simple Na carbonate as admixture) were prepared mixing nanosized powders of the ceramic phase with the remaining constituents. Samples fired at relatively low temperatures (below 700 °C) were characterized by X-ray diffraction, scanning electron microscopy combined...
Article
AbstractA study of the influence of the substitution of Al for Ga in the ceramic processing and electrical properties of La0.95Sr0.05Ga0.90–x Al x Mg0.10O3–δ (0≤x≤0.3) solid electrolytes is presented. The materials retained orthorhombic symmetry over the entire substitution range, whereas a deviation from Vegard’s law for x>0.20 suggested a maximum...
Article
Gadolinium-doped ceria-based materials with and without Ga-additions were prepared following several firing schedules including one peak sintering temperature (up to 1300°C) with or without subsequent dwell at lower temperature (at 1150°C). Sintered disks with submicrometric grain size and densifications in the order of 92% or higher, were obtained...
Article
Mixed conductors based on grain boundary Fe-doped La0.95Sr0.05Ga0.90Mg0.10O3−δ (LSGM) ceramics were obtained by selectively doping the grain boundaries with Fe. This was achieved using LaFeO3−δ layers screen-printed onto LSGM, after annealing at high temperature in air for several hours to promote Fe diffusion into LSGM. The influence of the number...
Article
The electrical properties of La0.95Sr0.05Ga0.90Mg0.10O3−δ (LSGM) were modified by selective doping of the grain boundaries, using LaFeO3 screen-printed layers and annealing at high temperature to promote Fe diffusion into LSGM. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses showed that iron was mainly located a...
Article
Two examples were selected to emphasize the potential of grain boundary engineering in the performance design of heterogeneous ceramics. Gadolinium-doped ceria-based powders were co-fired with additions of silica, and silica and lanthanum oxide, to test the silica scavenging role of lanthanum. The formation of one ionic conducting secondary phase,...
Article
The stability and oxygen permeability of dense tubular membranes, made of (SrFeO3−δ)0.7(SrAl2O4)0.3 (SFSA) composite by cold isostatic pressing, were assessed under air/CO2 and air/(CH4 + CO2) gradients at 973–1173 K. Mixed-conducting SFSA, comprising SrFe(Al)O3−δ perovskite-like and SrAl2O4-based phases, was selected as a model membrane material f...
Article
Full-text available
Composite materials based on gadolinium doped ceria (CGO) with additions of silica, with both silica and lanthanum oxide, and with lanthanum silicate, were prepared by the conventional ceramic route, to assess the silica scavenging role of lanthanum oxide additions. Structural, microstructural and electrical characterization of these samples confir...
Article
Electrode polarization in potentiometric oxygen sensors may lead to significant errors in the oxygen activity measurements, due to minor electronic conduction in solid electrolytes. These errors increase with increasing electronic contribution to total conductivity and electrode polarization resistance, and with decreasing electrolyte thickness. Si...
Article
The solubility of Ti4+ in the lattice of apatite-type La9.83Si6-xTixO26.75 corresponds to approximately 28% of the Si-site density. The conductivity of La9.83Si6-xTixO26.75 (x = 1-2) is predominantly oxygen-ionic and independent of the oxygen partial pressure in the p(O2) range from 10-20 to 0.3 atm. The electron transference numbers determined by...
Article
In order to appraise a two-stage compaction procedure using pore-forming additives for the fabrication of asymmetric mixed-conducting membranes where the porous and dense layers are made of the same composition, the oxygen permeability of a series of (SrFeO3−δ)0.7(SrAl2O4)0.3 composite samples with varying architecture was studied at 1073–1223 K. T...
Article
At 298 K cation conducting mixed antimonate Na0.8Ni0.6Sb0.4O2 exhibits an O3-type structure, with sodium ions in a distorted octahedral coordination, space group R-3m, a=3.0496(1)Å, c=16.4060(4)Å. 23Na NMR at 197–288 K reveals two main types of sodium atoms in the structure, ascribed to 18g and 3b positions. The temperature increase results in the...
Article
Additions of SrAl2O4 phase to mixed-conducting SrCo0.8Fe0.2O3-delta promote oxygen-vacancy ordering and brownmillerite formation at temperatures below 1050 K due to Al3+ incorporation, but also decrease thermal expansion coefficients (TECs) and improve thermal shock stability. The (SrCo0.8Fe0.2O3-delta SrAl2O4)-Sr-_ composite membranes exhibit also...
Article
The steady-state CH4 conversion by oxygen permeating through mixed-conducting (SrFe)0.7(SrAl2)0.3Oz composite membranes, comprising strontium-deficient SrFe(Al)O3-delta perovskite and monoclinic SrAl2O4-based phases, occurs via different mechanisms in comparison to the dry methane interaction with the lattice oxygen. The catalytic behavior of powde...