Radostina Stoyanova - Academia.edu (original) (raw)
Papers by Radostina Stoyanova
Inorganic Chemistry, 1998
ABSTRACT
ECS transactions, Dec 6, 2016
This study provides new data on the fabrication of hybrid battery-supercapacitor with an excellen... more This study provides new data on the fabrication of hybrid battery-supercapacitor with an excellent cycling stability based on composites of α-Ni(OH)2 and activated carbon (AC). The α-phase, Ni(OH)2.0.3H2O, consists of charged Ni(OH)2-x layers, SO2- 4 anions being intercalated in the interlayer spaces. The hydroxide has a mesoporous structure and contains nanometric primary particles bounded into micrometric aggregates. The supercapacitor performance of α-Ni(OH)2 mixed with AC is tested by galvanostatic experiments in KOH-LiOH electrolyte. The ratio between α-Ni(OH)2 and AC is varied in a whole concentration range: 0≤x≤100 wt.%. In comparison with the symmetrical supercapacitor, the composite electrodes containing α-Ni(OH)2 between 6 and 35 wt. % demonstrate higher and more stable discharge capacitance, as well as a higher effectiveness of charge-discharge process. α-Ni(OH)2 has a better cycling stability in comparison with the β-phase. The supercapacitor performance is discussed in terms of structure and morphology stability of α-Ni(OH)2 in alkaline electrolyte.
Batteries
Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical applicati... more Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 °C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 °C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity a...
Materials
To make supercapattery devices feasible, there is an urgent need to find electrode materials that... more To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20–60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperatur...
Batteries
Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries tha... more Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migrat...
Molecules
The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and... more The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and salinomycinic acids (HL) with metal ions of type M4+ and the known antiproliferative potential of antibiotics has provoked our interest in exploring the coordination processes between MonH/SalH and ions of Ce4+. (1) Methods: Novel monensinate and salinomycinate cerium(IV)-based complexes were synthesized and structurally characterized by elemental analysis, a plethora of physicochemical methods, density functional theory, molecular dynamics, and biological assays. (2) Results: The formation of coordination species of a general composition [CeL2(OH)2] and [CeL(NO3)2(OH)], depending on reaction conditions, was proven both experimentally and theoretically. The metal(IV) complexes [CeL(NO3)2(OH)] possess promising cytotoxic activity against the human tumor uterine cervix (HeLa) cell line, being highly selective (non-tumor embryo Lep-3 vs. HeLa) compared to cisplatin, oxaliplatin, and epirub...
Materials
After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerg... more After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in the...
Batteries
The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode ... more The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabr...
ChemPhysChem, 2021
The construction of hybrid metal-ion batteries faces a plethora of challenges. A critical one is ... more The construction of hybrid metal-ion batteries faces a plethora of challenges. A critical one is to unveil the solvation/desolvation processes at the molecular level in electrolytes that ensure efficient transfer of several types of charge carriers. This study reports first results on simulations of mixed ionic electrolytes. All combinations of homo- and hetero-binuclear complexes of Li+, Na+ and Mg2+, solvated with varying number of ethylene carbonate (EC) molecules are modeled in non-polar and polar environment by means of first principles calculations and compared to the mononuclear analogues in terms of stability, spatial organization, charge distribution and solvation/desolvation behavior. The used PF6¯ counterion is shown to have minor impact on the geometry of the complexes. The desolvation energy penalty of binuclear complexes can be lowered by the fluoride ions, emerging upon the PF6¯ decay. These model investigations could be extended to rationalize the solvation structure and ionic mobility in dual-ion electrolytes.
Journal of Molecular Structure, 2017
Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characteri... more Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characterized. The photophysical properties of the new compounds have been investigated in organic solvents of different polarity. It has been shown that both compounds are solvent depended. Cu(II) and Zn(II) complexes of NI2 were obtained and characterized by IR-NMR, fluorescence and EPR spectroscopy. The influence of different metal cations on the fluorescence intensity has been investigated in acetonitrile solution. Antimicrobial composite PLA-metal complexes materials have been obtained for the first time. Microbiological activity of both metal complexes has been investigated in vitro against different Gram-positive and Gram-negative bacteria and two yeasts. The various antimicrobial activities and the minimum inhibitory concentrations (MICs) of both complexes have been determined. The microbiological activity of composite materials PLA-metal complexes in thin polymeric film has also been investigated. The results suggest that the new metal complexes could find application in designing new antimicrobial preparations to control the spread of infections.
Journal of Materials Science, 2007
The SizeMat workshop was devoted to the size-dependent phenomena as a promising way to control th... more The SizeMat workshop was devoted to the size-dependent phenomena as a promising way to control the properties of materials forming the basis of modern technologies, particularly with regard to clean energy production and environmental protection. The workshop program included the following specific topics: ■ize effects in supported metal catalysts; ■Catalysts activation & deactivation caused by re-dispersion or sintering; ■Novel high surface area sorbents; ■Nanostructural design of composite electrode materials for lithium-ion batteries; ■Material for hydrogen storage at a nano-scale level; ■Microstructural effects in SOFCs
Journal of Materials Science
Solid State Ionics, 2003
Novel compositions Li[LixNi1−x]O2, 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;x... more Novel compositions Li[LixNi1−x]O2, 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;x&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.2, with a layered structure, have been prepared under high-pressure in an oxygen-rich atmosphere using a piston-cylinder type apparatus. A new structural feature of these compositions as compared to well-known Li[Ni]O2 is the development of mixed [LixNi1−x]O2-layers in addition to nearly pure Li-layers. The replacement of Ni3+ by Li+ in nickel-rich layers is compensated for by the
Solid State Ionics, 2000
6 2 7 3 1 solid solutions. The stabilisation of Al in non-octahedral positions in the trigonal cr... more 6 2 7 3 1 solid solutions. The stabilisation of Al in non-octahedral positions in the trigonal crystal structure of LiCo / Ni Al O is 12y y 2 discussed.
Journal of Pharmacy And Bioallied Sciences, 2011
... Veselin Ivanov, 1 Rajesh Arora, 1, 2 Vasil Hadjiiliev, 1 Radostina Stoyanova, 3 Rosica Ruseva... more ... Veselin Ivanov, 1 Rajesh Arora, 1, 2 Vasil Hadjiiliev, 1 Radostina Stoyanova, 3 Rosica Ruseva, 1 Radostin Nikolov, 3 Raj Kumar, 2 and Rakesh Kumar Sharma 2. ... 3 Institute of General and Inorganic Chemistry, Sofia, Bulgaria. ...
Molecules, 2021
The transition to a hydrogen economy requires the development of cost-effective methods for purif... more The transition to a hydrogen economy requires the development of cost-effective methods for purifying hydrogen from CO. In this study, we explore the possibilities of Cu/ZSM-5 as an adsorbent for this purpose. Samples obtained by cation exchange from aqueous solution (AE) and solid-state exchange with CuCl (SE) were characterized by in situ EPR and FTIR, H2-TPR, CO-TPD, etc. The AE samples possess mainly isolated Cu2+ cations not adsorbing CO. Reduction generates Cu+ sites demonstrating different affinity to CO, with the strongest centres desorbing CO at about 350 °C. The SE samples have about twice higher Cu/Al ratios, as one H+ is exchanged with one Cu+ cation. Although some of the introduced Cu+ sites are oxidized to Cu2+ upon contact with air, they easily recover their original oxidation state after thermal treatment in vacuum or under inert gas stream. In addition, these Cu+ centres regenerate at relatively low temperatures. It is important that water does not block the CO adso...
Dalton Transactions, 2021
Nanosized maricite-type NaFePO4 is oxidized to NASICON-type Na3Fe2(PO4)3 at mild conditions. The ... more Nanosized maricite-type NaFePO4 is oxidized to NASICON-type Na3Fe2(PO4)3 at mild conditions. The oxidized maricite displays a dramatic improvement of the specific capacity and cycling stability when used as an electrode in Na- and Li half-cells.
Materials Science and Engineering: C, 2020
Novel fibrous materials from polylactide (PLA) and Schiff base from Jeffamine ED® and 8-hydroxyqu... more Novel fibrous materials from polylactide (PLA) and Schiff base from Jeffamine ED® and 8-hydroxyquinoline-2carboxaldehyde (Jeff-8Q) or its complex with Cu 2+ (Jeff-8Q.Cu 2+) were successfully prepared by using one-pot electrospinning or electrospinning combined with dip-coating. These approaches enabled the fabrication of materials of diverse design: non-woven textile in which Jeff-8Q or Jeff-8Q.Cu 2+ was predominantly in the fibers' bulk (type "in") or was deposited as a thin film on the surface of the fibers (type "on"). The morphology of the mats and chemical composition of their surface were analyzed by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The coordination of Cu 2+ ions in Jeff-8Q.Cu 2+ /inPLA and Jeff-8Q.Cu 2+ /onPLA mats was examined by electron paramagnetic resonance (EPR) spectroscopy. It was found that the in vitro release of Jeff-8Q (Jeff-8Q.Cu 2+) from the type "on" mats was more rapid than that of the type "in" mats. Enhancement of the antioxidant activity of the Jeff-8Q.Cu 2+-containing fibrous mats as compared to mats containing Jeff-8Q was observed. In contrast to the neat PLA mat, the Jeff-8Q-and Jeff-8Q.Cu 2+-containing mats (both type "in" and "on") displayed high in vitro antitumor activity against human cervical HeLa cells. The obtained materials are promising for use in local tumor treatment.
Frontiers in Chemistry, 2020
Hybrid metal ion batteries are perceived as competitive alternatives to lithium ion batteries bec... more Hybrid metal ion batteries are perceived as competitive alternatives to lithium ion batteries because they provide better balance between energy/power density, battery cost, and environmental requirements. However, their cycling stability and high-temperature storage performance are still far from the desired. Herein, we first examine the temperature-induced reactivity of three-layered oxide, P3-Na2/3Ni1/3Mg1/6Mn1/2O2, toward lithium ionic liquid electrolyte upon cycling in hybrid Li/Na ion cells. Through ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, the structural and surface changes in P3-Na2/3Ni1/3Mg1/6Mn1/2O2 are monitored and discussed. Understanding the relevant changes occurring during dual Li+ and Na+ intercalation into P3-Na2/3Ni1/3Mg1/6Mn1/2O2 is of crucial importance to enhance the overall performance of hybrid Li/Na ion batteries at elevated temperatures.
Inorganic Chemistry, 1998
ABSTRACT
ECS transactions, Dec 6, 2016
This study provides new data on the fabrication of hybrid battery-supercapacitor with an excellen... more This study provides new data on the fabrication of hybrid battery-supercapacitor with an excellent cycling stability based on composites of α-Ni(OH)2 and activated carbon (AC). The α-phase, Ni(OH)2.0.3H2O, consists of charged Ni(OH)2-x layers, SO2- 4 anions being intercalated in the interlayer spaces. The hydroxide has a mesoporous structure and contains nanometric primary particles bounded into micrometric aggregates. The supercapacitor performance of α-Ni(OH)2 mixed with AC is tested by galvanostatic experiments in KOH-LiOH electrolyte. The ratio between α-Ni(OH)2 and AC is varied in a whole concentration range: 0≤x≤100 wt.%. In comparison with the symmetrical supercapacitor, the composite electrodes containing α-Ni(OH)2 between 6 and 35 wt. % demonstrate higher and more stable discharge capacitance, as well as a higher effectiveness of charge-discharge process. α-Ni(OH)2 has a better cycling stability in comparison with the β-phase. The supercapacitor performance is discussed in terms of structure and morphology stability of α-Ni(OH)2 in alkaline electrolyte.
Batteries
Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical applicati... more Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 °C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 °C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity a...
Materials
To make supercapattery devices feasible, there is an urgent need to find electrode materials that... more To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20–60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperatur...
Batteries
Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries tha... more Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migrat...
Molecules
The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and... more The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and salinomycinic acids (HL) with metal ions of type M4+ and the known antiproliferative potential of antibiotics has provoked our interest in exploring the coordination processes between MonH/SalH and ions of Ce4+. (1) Methods: Novel monensinate and salinomycinate cerium(IV)-based complexes were synthesized and structurally characterized by elemental analysis, a plethora of physicochemical methods, density functional theory, molecular dynamics, and biological assays. (2) Results: The formation of coordination species of a general composition [CeL2(OH)2] and [CeL(NO3)2(OH)], depending on reaction conditions, was proven both experimentally and theoretically. The metal(IV) complexes [CeL(NO3)2(OH)] possess promising cytotoxic activity against the human tumor uterine cervix (HeLa) cell line, being highly selective (non-tumor embryo Lep-3 vs. HeLa) compared to cisplatin, oxaliplatin, and epirub...
Materials
After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerg... more After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in the...
Batteries
The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode ... more The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabr...
ChemPhysChem, 2021
The construction of hybrid metal-ion batteries faces a plethora of challenges. A critical one is ... more The construction of hybrid metal-ion batteries faces a plethora of challenges. A critical one is to unveil the solvation/desolvation processes at the molecular level in electrolytes that ensure efficient transfer of several types of charge carriers. This study reports first results on simulations of mixed ionic electrolytes. All combinations of homo- and hetero-binuclear complexes of Li+, Na+ and Mg2+, solvated with varying number of ethylene carbonate (EC) molecules are modeled in non-polar and polar environment by means of first principles calculations and compared to the mononuclear analogues in terms of stability, spatial organization, charge distribution and solvation/desolvation behavior. The used PF6¯ counterion is shown to have minor impact on the geometry of the complexes. The desolvation energy penalty of binuclear complexes can be lowered by the fluoride ions, emerging upon the PF6¯ decay. These model investigations could be extended to rationalize the solvation structure and ionic mobility in dual-ion electrolytes.
Journal of Molecular Structure, 2017
Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characteri... more Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characterized. The photophysical properties of the new compounds have been investigated in organic solvents of different polarity. It has been shown that both compounds are solvent depended. Cu(II) and Zn(II) complexes of NI2 were obtained and characterized by IR-NMR, fluorescence and EPR spectroscopy. The influence of different metal cations on the fluorescence intensity has been investigated in acetonitrile solution. Antimicrobial composite PLA-metal complexes materials have been obtained for the first time. Microbiological activity of both metal complexes has been investigated in vitro against different Gram-positive and Gram-negative bacteria and two yeasts. The various antimicrobial activities and the minimum inhibitory concentrations (MICs) of both complexes have been determined. The microbiological activity of composite materials PLA-metal complexes in thin polymeric film has also been investigated. The results suggest that the new metal complexes could find application in designing new antimicrobial preparations to control the spread of infections.
Journal of Materials Science, 2007
The SizeMat workshop was devoted to the size-dependent phenomena as a promising way to control th... more The SizeMat workshop was devoted to the size-dependent phenomena as a promising way to control the properties of materials forming the basis of modern technologies, particularly with regard to clean energy production and environmental protection. The workshop program included the following specific topics: ■ize effects in supported metal catalysts; ■Catalysts activation & deactivation caused by re-dispersion or sintering; ■Novel high surface area sorbents; ■Nanostructural design of composite electrode materials for lithium-ion batteries; ■Material for hydrogen storage at a nano-scale level; ■Microstructural effects in SOFCs
Journal of Materials Science
Solid State Ionics, 2003
Novel compositions Li[LixNi1−x]O2, 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;x... more Novel compositions Li[LixNi1−x]O2, 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;x&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.2, with a layered structure, have been prepared under high-pressure in an oxygen-rich atmosphere using a piston-cylinder type apparatus. A new structural feature of these compositions as compared to well-known Li[Ni]O2 is the development of mixed [LixNi1−x]O2-layers in addition to nearly pure Li-layers. The replacement of Ni3+ by Li+ in nickel-rich layers is compensated for by the
Solid State Ionics, 2000
6 2 7 3 1 solid solutions. The stabilisation of Al in non-octahedral positions in the trigonal cr... more 6 2 7 3 1 solid solutions. The stabilisation of Al in non-octahedral positions in the trigonal crystal structure of LiCo / Ni Al O is 12y y 2 discussed.
Journal of Pharmacy And Bioallied Sciences, 2011
... Veselin Ivanov, 1 Rajesh Arora, 1, 2 Vasil Hadjiiliev, 1 Radostina Stoyanova, 3 Rosica Ruseva... more ... Veselin Ivanov, 1 Rajesh Arora, 1, 2 Vasil Hadjiiliev, 1 Radostina Stoyanova, 3 Rosica Ruseva, 1 Radostin Nikolov, 3 Raj Kumar, 2 and Rakesh Kumar Sharma 2. ... 3 Institute of General and Inorganic Chemistry, Sofia, Bulgaria. ...
Molecules, 2021
The transition to a hydrogen economy requires the development of cost-effective methods for purif... more The transition to a hydrogen economy requires the development of cost-effective methods for purifying hydrogen from CO. In this study, we explore the possibilities of Cu/ZSM-5 as an adsorbent for this purpose. Samples obtained by cation exchange from aqueous solution (AE) and solid-state exchange with CuCl (SE) were characterized by in situ EPR and FTIR, H2-TPR, CO-TPD, etc. The AE samples possess mainly isolated Cu2+ cations not adsorbing CO. Reduction generates Cu+ sites demonstrating different affinity to CO, with the strongest centres desorbing CO at about 350 °C. The SE samples have about twice higher Cu/Al ratios, as one H+ is exchanged with one Cu+ cation. Although some of the introduced Cu+ sites are oxidized to Cu2+ upon contact with air, they easily recover their original oxidation state after thermal treatment in vacuum or under inert gas stream. In addition, these Cu+ centres regenerate at relatively low temperatures. It is important that water does not block the CO adso...
Dalton Transactions, 2021
Nanosized maricite-type NaFePO4 is oxidized to NASICON-type Na3Fe2(PO4)3 at mild conditions. The ... more Nanosized maricite-type NaFePO4 is oxidized to NASICON-type Na3Fe2(PO4)3 at mild conditions. The oxidized maricite displays a dramatic improvement of the specific capacity and cycling stability when used as an electrode in Na- and Li half-cells.
Materials Science and Engineering: C, 2020
Novel fibrous materials from polylactide (PLA) and Schiff base from Jeffamine ED® and 8-hydroxyqu... more Novel fibrous materials from polylactide (PLA) and Schiff base from Jeffamine ED® and 8-hydroxyquinoline-2carboxaldehyde (Jeff-8Q) or its complex with Cu 2+ (Jeff-8Q.Cu 2+) were successfully prepared by using one-pot electrospinning or electrospinning combined with dip-coating. These approaches enabled the fabrication of materials of diverse design: non-woven textile in which Jeff-8Q or Jeff-8Q.Cu 2+ was predominantly in the fibers' bulk (type "in") or was deposited as a thin film on the surface of the fibers (type "on"). The morphology of the mats and chemical composition of their surface were analyzed by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The coordination of Cu 2+ ions in Jeff-8Q.Cu 2+ /inPLA and Jeff-8Q.Cu 2+ /onPLA mats was examined by electron paramagnetic resonance (EPR) spectroscopy. It was found that the in vitro release of Jeff-8Q (Jeff-8Q.Cu 2+) from the type "on" mats was more rapid than that of the type "in" mats. Enhancement of the antioxidant activity of the Jeff-8Q.Cu 2+-containing fibrous mats as compared to mats containing Jeff-8Q was observed. In contrast to the neat PLA mat, the Jeff-8Q-and Jeff-8Q.Cu 2+-containing mats (both type "in" and "on") displayed high in vitro antitumor activity against human cervical HeLa cells. The obtained materials are promising for use in local tumor treatment.
Frontiers in Chemistry, 2020
Hybrid metal ion batteries are perceived as competitive alternatives to lithium ion batteries bec... more Hybrid metal ion batteries are perceived as competitive alternatives to lithium ion batteries because they provide better balance between energy/power density, battery cost, and environmental requirements. However, their cycling stability and high-temperature storage performance are still far from the desired. Herein, we first examine the temperature-induced reactivity of three-layered oxide, P3-Na2/3Ni1/3Mg1/6Mn1/2O2, toward lithium ionic liquid electrolyte upon cycling in hybrid Li/Na ion cells. Through ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, the structural and surface changes in P3-Na2/3Ni1/3Mg1/6Mn1/2O2 are monitored and discussed. Understanding the relevant changes occurring during dual Li+ and Na+ intercalation into P3-Na2/3Ni1/3Mg1/6Mn1/2O2 is of crucial importance to enhance the overall performance of hybrid Li/Na ion batteries at elevated temperatures.