Andrei Kovalevsky

University of Aveiro | UA · Department of Materials and Ceramics Engineering

Driven by a need to develop low-cost and thermally stable materials for thermoelectric applications, donor-substituted strontium titanate is considered as a promising alternative to traditional thermoelectrics. The complex defect chemistry of SrTiO3-based materials imposes various limitations on identifying the relevant effects exerted on the elect...

Inspired by recent research results that have demonstrated appealing thermoelectric performance of A-site cation-deficient titanates, this work focuses on detailed analysis of the changes in performance promoted by altering the defect chemistry mechanisms. The series of cation-stoichiometric SrTi1-xTaxO3±δ and A-site deficient Sr1-x/2Ti1-xTaxO3-δ c...

Donor-substituted strontium titanate is known as one of the best highly performing n-type oxide thermoelectrics. In the present work, structural, microstructural, and thermoelectric properties of Sr1–xPrxTiO3±δ, Sr1–1.5xPrxTiO3±δ, and Sr1–yTi0.8Nb0.2O3±δ (x = 0.05–0.30, y = 0–0.10) perovskite-type titanates were assessed to identify the impact of n...

The oxygen transport studies of dense Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3-δ (BSCF) ceramic membranes, prepared via glycine-nitrate route, demonstrated that the permeation rate is predominantly controlled by surface exchange kinetics when the membrane thickness is smaller than 1.00mm. In order to improve oxygen exchange, an asymmetric membrane concept inclu...

This work focuses on designing highly-porous cellular NiAl2O4-based spinel ceramics through combined suspension emulsification/reactive sintering and further decoration of the pore surfaces by Ni nanoparticles for potential applications in heterogeneous catalysis. Due to kinetic limitations and specific porous structure, the reduction occurs withou...

Carbon-based nanomaterials were prepared using a simple microwave-assisted hydrothermal carbonization method, with Chondrus crispus and Palmaria palmata algae as a sustainable feedstock. These materials were thoroughly characterized by FTIR spectroscopy, elemental microanalysis, and XPS analysis. The resulting hydrochars effectively removed ciprofl...

This work presents a comparative analysis of pure and Ag-intercalated Ca3Co4O9 multilayer thermoelectric materials prepared through the hot-uniaxial pressing technique. Samples were prepared by attrition milling and hotpressed at 900 °C and 55 MPa for 1 h. They were mirror polished, and some of them were stacked with and without intermediate Ag foi...

Material thermal conductivity is a key factor in various applications, from thermal management to energy harvesting. With microstructure engineering being a widely used method for customizing material properties, including thermal properties, understanding and controlling the role of extended phonon-scattering defects, like grain boundaries, is cru...

Bi1.6Pb0.4Sr2Co2O8 samples have been textured by the Laser Floating Zone (LFZ) process using Nd:YAG, and CO2 laser radiation. Using different wavelengths resulted in significant structural and microstructural modifications. Powder XRD patterns showed that the thermoelectric phase is the major one in both cases. Microstructural studies revealed that...

MXenes, a family of two-dimensional (2D) transition metal carbides, have been discovered as exciting candidates for various energy storage and conversion applications, including green hydrogen production by water splitting. Today, these materials mostly remain interesting objects for in-depth fundamental studies and scientific curiosity due to issu...

Herein, thermodynamic assessment is proposed to screen suitable precursors for the solid-state synthesis of manganese ferrite, by mechanosynthesis at room temperature or by subsequent calcination at relatively low temperatures, and the main findings are validated by experimental results for the representative precursor mixtures MnO + FeO3, MnO2 + F...

Iron electrowinning offers a greener path for steel production. While alkaline media has received the most significant attention, the acidic media declined due to low Faradaic efficiency and difficulties imposed by fragile deposits. This study proposes, for the first time, prospects for acidic Fe electrowinning using a mixed-acid electrolyte (H2SO4...

A set of graphitic carbon nitride samples was prepared using a straightforward experimental procedure without templates and any subsequent treatments. The materials were studied in‐depth using a range of physical and chemical methods such as X‐ray diffraction, FTIR spectroscopy, elemental analysis (CHN), nitrogen physisorption, SEM, XPS, TPD CO2. T...

A-, and B-site multiple-doped Ca0.97Y0.01La0.01Yb0.01Mn1–2xNbxMoxO3 was studied for improving its thermoelectric thermoelectric performance. Samples were prepared from planetary milled precursors and sintered at 1310ºC for 12 h. XRD showed that sintered samples are nearly single phase, with small amounts of CaMn2O4. SEM analysis revealed that grain...

Iron ore represents a potential feedstock for the alkaline electrowinning of iron from suspensions. However, several difficulties can be imposed during the electrowinning due to the presence of several iron oxide types with different iron valences (e.g. hematite with magnetite), requiring further studies for establishing electrowinning as an altern...

Ruddlesden-Popper La2−xBaxNiO4±δ (x = 0–1.1) nickelates were prepared by a glycine-nitrate combustion route combined with high-temperature processing and evaluated for potential application as electrocatalysts for solid oxide cells and electrochemical NOx elimination. The characterization included structural, microstructural and dilatometric studie...

Thermoelectric conversion may take a significant share in future energy technologies. Oxide‐based thermoelectric composite ceramics attract attention for promising routes for control of electrical and thermal conductivity for enhanced thermoelectric performance. However, the variability of the composite properties responsible for the thermoelectric...

Correction for ‘Photocatalytic removal of benzene over Ti 3 C 2 T x MXene and TiO 2 –MXene composite materials under solar and NIR irradiation’ by Sergii A. Sergiienko et al. , J. Mater. Chem. C , 2022, 10 , 626–639, https://doi.org/10.1039/D1TC03826E.

Attrition-milling process has been applied to Ce-doped CaMnO3 precursors to obtain small grain-size powders. The use of Ce4+ as dopant instead a Rare Earth3+ has allowed decreasing by 50% the atomic proportion of dopant, to obtain equivalent charge carrier concentration, which is required for attaining promising properties for thermoelectric applic...

Efficient energy storage from intermittent renewables can rely on the conversion of temporary energy excess by alkaline electrolysis, yielding oxygen and green hydrogen, which can be stored and used on demand. Electrodes made of laser-induced graphene (LIG) materials offer many advantages over the traditional graphene processing routes, due to inhe...

This work explores the possibility of involving aluminothermy in processing donor-doped zinc oxide-based thermoelectrics by relying on local, strong exothermic effects developed during sintering, with a potential positive impact on the electrical and thermal transport properties. The strategy was exemplified by using aluminium as a dopant, due to i...

The perovskite-type calcium manganite exhibits interesting magnetic properties that can be tuned and enhanced by the laser floating zone (LFZ) method. This work explores, for the first time, the application of an external magnetic field during the LFZ growth of CaMn0.9Gd0.1O3. The effects of the field direction on structural, microstructural, elect...

Steelmaking industries have been facing strict decarbonization guidelines. With a net zero carbon emissions target, European policies are expected to be accomplished before 2050. Traditional steelmaking industry still operates by the carbothermic reduction of iron ores for steel production. Consequently, the steel sector is responsible for a large...

In continuation with the results explored in our recent previous study (https://doi.org/10.1016/j.apsusc.2021.150062), the current work sheds more light regarding the active in situ catalytic species in ceria additive loaded hydrogen storage system, MgH2. For this study, two samples, MgH2+0.167CeO2 and MgH2+0.5CeO2 were processed through mechanical...

(Free download link until 10 July 2022: https://authors.elsevier.com/c/1f6W03PCJlLxkF ) *** Efficient use of barium-containing electrocatalysts for NOx decomposition in electrochemical solid oxide cells requires good chemical compatibility of these materials with the electrolyte in a temperature range 300–600 °C and imply the use of porous electrol...

This work assesses the feasibility of processing CuFe1-xNixO2 (x=0, 0.02) using the Laser Floating Zone (LFZ) technique to grow fibres with different pulling rates, to tune their thermoelectric performance. Structural analysis showed CuFeO2 as the major phase. Formation of secondary phases is promoted by Ni addition, diminishing with decreasing pul...

The alkaline electrolytic production of iron is gaining interest due to the absence of CO2 emissions and significantly lower electrical energy consumption when compared with traditional steelmaking. The possibility of using an iron-bearing pseudobrookite mineral, Fe2TiO5, is explored for the first time as an alternative feedstock for the electroche...

MXenes, a family of two-dimensional (2D) transition metal carbides, nitrides and carbonitrides based on earth-abundant constituents, are prospective candidates for energy conversion applications, including photocatalysis. While the activity of individual MXenes towards various photocatalytic processes is still debatable, these materials were proved...

Increasing Sr2+ concentration and the creation of A-site deficiency in La1-x-ySrxCoO3-δ (x = 0.3–0.7, y = 0–0.05) increase oxygen ionic conductivity, oxygen permeability of the dense ceramic membranes, and surface exchange limitations, in correlation with the oxygen nonstoichiometry variations. Regression analysis of the experimental data on oxygen...

Liquid metals have emerged as potential materials for fuel cell and battery applications due to their suitable redox potentials, fast redox kinetics, and/or active participation in electrode reactions. In this work, we study the electrochemical oxidation behavior of antimony-lead melts by the use of a robust, yttrium-stabilized zirconia based, test...

The electrochemical reduction of iron oxides in alkaline media arises as a novel approach for ironmaking and iron-rich waste valorisation. Strong advantages and attractive aspects of alkaline electroreduction include lower electric energy consumption, absence of CO2 emissions, and non-polluting valuable by-products such as H2 and O2. Another potent...

Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical properties and the solubility, and impact of the substituting cation also depends largely on the preparation and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole tra...

In this work, brownmillerite-type calcium ferrite (Ca2Fe2O5) ceramics were prepared by two distinct routes, namely by a proteic sol-gel synthesis using commercial flavorless gelatin, and by a solid-state reaction method using mollusk shells. XRD analyses revealed single phase brownmillerite-type calcium ferrites in both cases. SEM-EDS analysis of s...

This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components,...

This work explores the possibilities for the processing of Ni- and Ti3C2Tx (T = OH, O) MXene-containing composite electrodes, by co-pressing and plastic deformation or by etching of the electrodes prepared directly by self-propagation high-temperature synthesis (SHS). Various material design approaches were also explored. In order to tune the Ti3C2...

We present a study of magnetic and structural properties of La1−xGdxCoO3 compounds with x=0, 0.2, 0.5 and 1. The Gd term in magnetic susceptibility obeys the Curie–Weiss law with antiferromagnetic interaction between the magnetic moments of Gd3+ ions. The value of the paramagnetic Curie temperature Θ is proportional to Gd content and for GdCoO3 it...

The stability and reproducibility of the electric properties in n-type doped ZnO represent known bottlenecks towards potential thermoelectric applications. The degradation is promoted by the vanishing of the electronic defects on oxidation and irreversible exsolution of the phase impurities. This work proposes a microstructural mechanism showing th...

Porous 3 YTZ-Al2O3 membranes were processed aiming controlled cellular microstructures for potential separation and electrochemical applications. The processing method relies on emulsification of mixed suspensions of Al2O3 and 3 YTZ powders in sunflower oil. Taguchi experimental planning was used to seek guidelines for optimization of microstructur...

The present work aims to evaluate relevant effects of the size of substituting rare-earth cation on electrical conductivity and thermal expansion of donor-doped SrTiO3 as ceramic components of electrochemical solid electrolyte cells. A series of strontium titanate-based ceramics with a moderate doping level and different cation stoichiometry, Sr0.9...

For La1−x Prx CoO3 cobaltites with x = 0, 0.1, 0.2 and 0.3, the temperature dependence of magnetic susceptibility χ (T ) was studied in the temperature range from 5 to 400 K. Also the crystal structure of these cobaltites was investigated, and the effect of hydrostatic pressure up to 2 kbar on their susceptibility was measured at fixed temperatures...

Electrochemical reduction of iron oxides into zero-valent iron (ZVI, Fe0) is a promising alternative to the traditional methods used for iron production. The electrochemical deposition of Fe0 from hematite and hematite-based Fe2−xAlxO3 ceramic in alkaline suspensions (10 M of NaOH) was assessed at relatively low temperature (90 °C). Ceramic composi...

The present work reports the first attempt of thermoelectric module design, based on oxide materials grown through the laser floating zone technique. Two modules with 4-legs thermoelectric were assembled using Bi2Ba2Co2Oy fibres as p-type legs, while Ca0.9La0.1MnO3 and CaMn0.95Nb0.05O3 fibres were used as n-type legs. Structural and electrical char...

The crystal structure, magnetic susceptibility as a function of temperature χ(T) in the range 5–400 K, and the hydrostatic pressure effect on χ at fixed temperatures T = 78, 150, and 300 K, were studied in perovskite-like compounds La1−xPrxCoO3 (x = 0, 0.1, 0.2, and 0.3). The obtained experimental data were analyzed using a two-level model with an...

Eco-benign and high-temperature-stable oxides are considered a promising alternative to traditional Bi2Te3, Bi2Se3 and PbTe-based thermoelectric materials. The quest for high performing thermoelectric oxides is still open and, among other challenges, includes the screening of various materials systems for potentially promising electrical and therma...

Highly porous zirconia ceramics for prospective use as separators in alkaline electrolysis cells have been processed by emulsification of paraffin in concentrated zirconia suspensions. Effects of processing parameters on porosity, cell size distribution, and pore interconnectivity are studied through Taguchi statistical design. The porosity of zirc...

The development of thermoelectrics for high-temperature applications imposes several essential requirements on the material properties. In some energy-conversion scenarios, the cost and thermal stability requirements may dominate over efficiency issues, making abundant, high-temperature-stable and low-toxic oxides attractive alternative thermoelect...

The feasibility of recycling red mud waste by its direct transformation into highly-porous cellular ceramics was successfully demonstrated. Ceramic materials with designed cellular porosity were processed by emulsification of red mud suspensions with liquid paraffin. Taguchi method was used to study the effects provided by varying the red mud load...

This paper reports a novel composite-based processing route for improving the electrical performance of Ca3Co4O9 thermoelectric (TE) ceramics. The approach involves the addition of metallic Co, acting as a pore filler on oxidation, and considers two simple sintering schemes. The (1-x)Ca3Co4O9/xCo composites (x = 0%, 3%, 6% and 9% vol.) have been pr...

This work aims at the preparation of multifunctional titania-based photocatalysts with inherent capabilities for thermal co-activation and stabilisation of anatase polymorph, by designing the phase composition and microstructure of rutile-silicon carbide mixture. The processing involved a conventional solid state route, including partial pre-reduct...

In this work, the laser floating zone technique (LFZ) of donor-substituted calcium manganite-based thermoelectrics were assessed using Ca1-xPrxMnO3 (x = 0.03, 0.06, 0.1) as a model system. Fibres were grown by LFZ with pulling rates of 25, 100 and 200 mm h⁻¹ in various atmospheres (air, vacuum and argon). Strongly non-equilibrium conditions imposed...

CaMnO3–based materials represent a promising family of n-type oxide thermoelectrics. The objective of the present work is assessing the impacts on relevant structural, microstructural and thermoelectric properties of manganites when they are processed by the laser floating zone technique. For this purpose, donor-doped Ca0.9La0.1MnO3, CaMn0.95Nb0.05...

Electrochemical reduction of low-conductive hematite-based ceramics represents a novel approach for iron recovery and waste valorisation. The process itself allows a flexible switching between hydrogen generation and iron reduction, important for the intermittent renewable-energy-powered electrolytic process. The present study focuses on the direct...

Oxide-based thermoelectric materials are receiving a particular interest due to enhanced thermal and redox stability at high temperature, together with the absence of toxicity, and natural abundance of the constituent compounds. The objective of this work is to improve the thermoelectric performance of manganite-based oxide thermoelectrics processe...

This work reports the microstructural and thermoelectric characterization of the misfit [Ca2CoO3-δ]0.62[CoO2] compound obtained by a solid-state synthesis using mollusk shells and a proteic sol-gel method, which uses gelatin as a polymerizing agent. The results clearly demonstrate the capability of these routes to produce pure Ca3Co4O9 with plate-l...

Zinc oxide (ZnO) has being recognised as a potentially interesting thermoelectric material, allowing flexible tuning of the electrical properties by donor doping. This work focuses on the assessment of tantalum doping effects on the relevant structural, microstructural, optical and thermoelectric properties of ZnO. Processing of the samples with a...

Laser processing is known as one of the most versatile techniques to develop technological devices. The use of lasers constitutes nowadays an alternative methodology to the chemical routes for materials synthesis/growth. Bulk crystals, thin films and nanoparticles/nanostructures are currently achieved by laser processing techniques. The application...

Oxide materials based on calcium manganite show clear prospects as thermoelectrics, provided by their stability at high temperatures and inherent flexibility in tuning the relevant electrical and thermal transport properties. Donor-doped CaMnO3 is an n-type semiconductor with a perovskite structure and relatively high thermoelectric performance. In...

Polycrystalline Eu 1–x Ca x TiO 3–δ (0 ≤ x ≤ 1) samples were synthesised to investigate the interrelations among the crystal structure, local structural disorder, and thermoelectric properties. The Ca ²⁺ substitution is locally modifying (squeezing) the crystal structure, resulting in distinct differences between the long-range and local scales, e....

This work explores the possibilities for a further enhancement of the thermoelectric properties of Ca3Co4O9 by Sr-doping combined with hot-pressing. Modified hot-pressing process resulted in highly-textured and dense ceramics. Sr-doping significantly improves electrical properties, resulting in extremely large power factor (1.2 mW/K²m at 800 °C) du...

This work focuses on demonstration of reliable and versatile method for processing cellular mayenite (Ca12Al14O33) -based ceramics with designed porosity, with emphasis on potential catalytic applications. Highly porous (up to 82% of open porosity) monoliths were obtained by emulsification of liquid paraffin in aqueous suspensions of mixed CaCO3 an...

This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous co-doping with aluminum. At 1100–1223 K mixed-doped samples demonstrated around ∼2.3 times increase in ZT as compared to single-doped materials, reaching ∼0.12. The sim...