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Papers by Oleg Velikokhatnyi

Research paper thumbnail of Electronic structure and instability of Ni 2 MnGa

Phys Solid State, 1999

The nature of the magnetic and structural phase transitions in the Heusler alloy Ni2MnGa is studi... more The nature of the magnetic and structural phase transitions in the Heusler alloy Ni2MnGa is studied by numerical calculations of the electronic structure, generalized susceptibility, and various Fermi-surface cross sections.

Research paper thumbnail of Spinodal decomposition of metallic systems as an effect of proximity of the Fermi surface to the Brillouin zone faces

Physics of Metals and Metallography, 1992

Research paper thumbnail of Heterostructures for Improved Stability of Lithium Sulfur Batteries

Journal of the Electrochemical Society, 2014

ABSTRACT There is a need for exploring new battery chemistries demonstrating higher energy densit... more ABSTRACT There is a need for exploring new battery chemistries demonstrating higher energy density than currently used Li-ion systems. The recent development of sulfur cathodes, with theoretical capacities of similar to 1675 mAh/g in lithium based batteries therefore bears great relevance in designing the next generation mobile lithium based battery systems. Although promising, sulfur cathodes are hamstrung by a number of problems including but not limited to inherent electronic conductivity limitations, volumetric expansion and soluble polysulfide formation resulting in poor rate capabilities, poor areal capacity and poor cyclability. In this work, we implement a three-pronged strategy to overcome the issues stated above. Using a simple chemical procedure, we have successfully synthesized sulfur nanoparticles that display capacities up to similar to 1100 mAh/g. We have also demonstrated high areal capacities in thick electrodes prepared by solid-state processing exhibiting good capacity retention as a result of the same. Finally, we have successfully demonstrated the use of thin lithium ion conductive coatings (LIC) on sulfur to demonstrate significant improvement in capacity fade. The thick electrodes coated with a thin lithium ion conducting coating that we use in this study allow us to obtain very high areal capacities (of similar to 5 mAh/cm(2)) in contrast to hitherto published reports.

Research paper thumbnail of A CALPHAD study on the thermodynamic stability of calcium-, zinc-, and yttrium-doped magnesium in aqueous environments

Materials Science and Engineering: B, 2011

Magnesium has attracted the attention of the biomaterials community as a potential biodegradable ... more Magnesium has attracted the attention of the biomaterials community as a potential biodegradable metallic candidate for use in stents and orthopedic applications. Alloying of Mg with metals such as Ca, Y and Zn, etc., to form alloy precursors is important to optimize its corrosion rate in electrolytic and aqueous environments to understand the alloy response in body fluid environments. In

Research paper thumbnail of Nanostructured (Ir,Sn)O2:F - Oxygen Evolution Reaction Anode Electro-Catalyst Powders for PEM Based Water Electrolysis

Journal of the Electrochemical Society, 2014

ABSTRACT Nanostructured powder catalysts comprising solid solutions of F doped SnO2 and IrO2 of d... more ABSTRACT Nanostructured powder catalysts comprising solid solutions of F doped SnO2 and IrO2 of different compositions were synthesized by a simple two step approach. High surface area SnO2:F was prepared initially using CTAB as a surfactant. (Ir,Sn)O-2:F was then synthesized by forming a solid state solution with IrCl4 and SnO2:F followed by heat-treatment in air at 400 degrees C. The catalyst was then coated onto a porous Ti foil and has been studied as a promising anode electro-catalyst for oxygen evolution reaction (OER) in PEM based water electrolysis. The optimal composition of (Ir0.3Sn0.7)O-2:10 wt% F displayed electrochemical activity comparable to the commercially available pure IrO2 demonstrating similar to 70 mol% reduction in noble metal content. The electrochemical stability tests also showed that (Ir,Sn)O-2:F solid solution exhibits much better durability compared to commercial IrO2, the standard (OER) catalyst.

Research paper thumbnail of Noble metal-free bifunctional oxygen evolution and oxygen reduction acidic media electro-catalysts

Scientific Reports, 2016

Identification of low cost, highly active, durable completely noble metal-free electro-catalyst f... more Identification of low cost, highly active, durable completely noble metal-free electro-catalyst for oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells, oxygen evolution reaction (OER) in PEM based water electrolysis and metal air batteries remains one of the major unfulfilled scientific and technological challenges of PEM based acid mediated electro-catalysts. In contrast, several non-noble metals based electro-catalysts have been identified for alkaline and neutral medium water electrolysis and fuel cells. Herein we report for the very first time, F doped Cu1.5Mn1.5O4, identified by exploiting theoretical first principles calculations for ORR and OER in PEM based systems. The identified novel noble metal-free electro-catalyst showed similar onset potential (1.43 V for OER and 1 V for ORR vs RHE) to that of IrO2 and Pt/C, respectively. The system also displayed excellent electrochemical activity comparable to IrO2 for OER and Pt/C for ORR, respectively, along with remarkable long term stability for 6000 cycles in acidic media validating theory, while also displaying superior methanol tolerance and yielding recommended power densities in full cell configurations.

Research paper thumbnail of Non-Noble Metal Based Electro-Catalyst Compositions for Proton Exchange Membrane Based Water Electrolysis and Methods of Making

Research paper thumbnail of Effect of Magnesium Substitution in Lithium Nickel Oxide An Ab Initio Study

Journal of the Electrochemical Society, 2004

ABSTRACT

Research paper thumbnail of Phase stability and electronic structure of NaMnO2

Journal of the Electrochemical Society, 2003

ABSTRACT

Research paper thumbnail of Fermi surface nesting and pre-martensitic softening in V and Nb at high pressures

Journal of Physics Condensed Matter, May 18, 2006

First-principles total-energy calculations were performed for the trigonal shear elastic constant... more First-principles total-energy calculations were performed for the trigonal shear elastic constant (C44) of body-centred cubic (bcc) V and Nb. A mechanical instability in C44 is found for V at pressures of ~2 Mbar which also shows a softening in Nb at pressures of ~0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.

Research paper thumbnail of Biodegradable Iron-Containing Compositions, Methods of Preparing and Applications Therefor

Research paper thumbnail of Doped Transition Metal Nitride Supercapacitors (DTMSCs): Mechanisms of Charge Storage

Meeting Abstracts, Aug 5, 2014

ABSTRACT

Research paper thumbnail of Fermi surface nesting and pre-martensitic softening in V-Nb system under high pressure

First-principles total-energy calculations were performed for the trigonal shear elastic constant... more First-principles total-energy calculations were performed for the trigonal shear elastic constant (C 44 ) of body-centred cubic (bcc) V and Nb. A mechanical instability in C 44 is found for V at pressures of ∼2 Mbar which also shows a softening in Nb at pressures of ∼0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.

Research paper thumbnail of Nitrogen and cobalt co-doped zinc oxide nanowires – Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

Journal of Power Sources, 2015

Research paper thumbnail of Fluorine Doped (Sn,Ru)O2 electro-Catalysts for Oxygen Evolution Reaction (OER) in PEM Based Water Electrolysis

Research paper thumbnail of 341202 High Performance Fluorine Doped Oxygen Evolution Reaction (OER) Electro-Catalysts for PEM Based Water Electrolysis

Identification of electro-catalysts containing non noble metal or significantly reduced amounts o... more Identification of electro-catalysts containing non noble metal or significantly reduced amounts of expensive noble metals (e. g. RuO2) is highly desirable. Development of such a catalyst with comparable electrochemical performance to the standard noble metal oxide counterpart for the proton exchange membrane (PEM) based water electrolysis would constitute a major advancement in generation of hydrogen by water electrolysis. We have accordingly developed a two-pronged theoretical first principles and experimental approach to generate a nano-structured solid solution of SnO2:10wt.% F containing only 20at.% RuO2 [e.g. (Sn0.80Ru0.20)O2:10F] that displays a remarkably similar electrochemical activity and moreover, comparable or even much improved electrochemical stability and durability compared to pure the noble metal counterpart, RuO2. Results of these studies will be presented and discussed.

Research paper thumbnail of WO 3 based solid solution oxide – promising proton exchange membrane fuel cell anode electro-catalyst

J. Mater. Chem. A, 2015

ABSTRACT

Research paper thumbnail of Ceramic Materials for Lithium-Ion Battery Applications

Materials Engineering, 2005

Research paper thumbnail of A Complexed Sol-Gel (CSG) Approach to High Surface Area (HSA) Durable Ultra Active Platinum-Ruthenium Electro-Catalysts for Direct Methanol Fuel Cells

Journal of the Electrochemical Society, 2014

ABSTRACT Direct Methanol Fuel Cell (DMFC) is a promising power source for continuous generation o... more ABSTRACT Direct Methanol Fuel Cell (DMFC) is a promising power source for continuous generation of energy without evolution of any toxic by-products and greenhouse gases. Pt-Ru has been the accepted gold standard anode electro-catalyst for DMFC, but significant advances are required to enhance its performance and stability. A complexed sol-gel (CSG) approach has been used to develop nanostructured powder materials. Herein we report a novel CSG process to synthesize nanoparticulate high specific surface area (HSA), completely unsupported Pt(Ru) based electro-catalyst exhibiting three fold higher electrochemically active surface area (ECSA) and ultra high electrochemical performance compared to commercially available Johnson Matthey Pt-Ru black catalyst, the currently accepted gold standard. Furthermore, in identical single full cell DMFC configuration tests for methanol oxidation, current and power densities similar to 40% higher than that displayed by Johnson Matthey catalyst is achieved. (c) 2014 The Electrochemical Society. All rights reserved.

Research paper thumbnail of Nanostructured robust cobalt metal alloy based anode electro-catalysts exhibiting remarkably high performance and durability for proton exchange membrane fuel cells

J. Mater. Chem. A, 2015

ABSTRACT

Research paper thumbnail of Electronic structure and instability of Ni 2 MnGa

Phys Solid State, 1999

The nature of the magnetic and structural phase transitions in the Heusler alloy Ni2MnGa is studi... more The nature of the magnetic and structural phase transitions in the Heusler alloy Ni2MnGa is studied by numerical calculations of the electronic structure, generalized susceptibility, and various Fermi-surface cross sections.

Research paper thumbnail of Spinodal decomposition of metallic systems as an effect of proximity of the Fermi surface to the Brillouin zone faces

Physics of Metals and Metallography, 1992

Research paper thumbnail of Heterostructures for Improved Stability of Lithium Sulfur Batteries

Journal of the Electrochemical Society, 2014

ABSTRACT There is a need for exploring new battery chemistries demonstrating higher energy densit... more ABSTRACT There is a need for exploring new battery chemistries demonstrating higher energy density than currently used Li-ion systems. The recent development of sulfur cathodes, with theoretical capacities of similar to 1675 mAh/g in lithium based batteries therefore bears great relevance in designing the next generation mobile lithium based battery systems. Although promising, sulfur cathodes are hamstrung by a number of problems including but not limited to inherent electronic conductivity limitations, volumetric expansion and soluble polysulfide formation resulting in poor rate capabilities, poor areal capacity and poor cyclability. In this work, we implement a three-pronged strategy to overcome the issues stated above. Using a simple chemical procedure, we have successfully synthesized sulfur nanoparticles that display capacities up to similar to 1100 mAh/g. We have also demonstrated high areal capacities in thick electrodes prepared by solid-state processing exhibiting good capacity retention as a result of the same. Finally, we have successfully demonstrated the use of thin lithium ion conductive coatings (LIC) on sulfur to demonstrate significant improvement in capacity fade. The thick electrodes coated with a thin lithium ion conducting coating that we use in this study allow us to obtain very high areal capacities (of similar to 5 mAh/cm(2)) in contrast to hitherto published reports.

Research paper thumbnail of A CALPHAD study on the thermodynamic stability of calcium-, zinc-, and yttrium-doped magnesium in aqueous environments

Materials Science and Engineering: B, 2011

Magnesium has attracted the attention of the biomaterials community as a potential biodegradable ... more Magnesium has attracted the attention of the biomaterials community as a potential biodegradable metallic candidate for use in stents and orthopedic applications. Alloying of Mg with metals such as Ca, Y and Zn, etc., to form alloy precursors is important to optimize its corrosion rate in electrolytic and aqueous environments to understand the alloy response in body fluid environments. In

Research paper thumbnail of Nanostructured (Ir,Sn)O2:F - Oxygen Evolution Reaction Anode Electro-Catalyst Powders for PEM Based Water Electrolysis

Journal of the Electrochemical Society, 2014

ABSTRACT Nanostructured powder catalysts comprising solid solutions of F doped SnO2 and IrO2 of d... more ABSTRACT Nanostructured powder catalysts comprising solid solutions of F doped SnO2 and IrO2 of different compositions were synthesized by a simple two step approach. High surface area SnO2:F was prepared initially using CTAB as a surfactant. (Ir,Sn)O-2:F was then synthesized by forming a solid state solution with IrCl4 and SnO2:F followed by heat-treatment in air at 400 degrees C. The catalyst was then coated onto a porous Ti foil and has been studied as a promising anode electro-catalyst for oxygen evolution reaction (OER) in PEM based water electrolysis. The optimal composition of (Ir0.3Sn0.7)O-2:10 wt% F displayed electrochemical activity comparable to the commercially available pure IrO2 demonstrating similar to 70 mol% reduction in noble metal content. The electrochemical stability tests also showed that (Ir,Sn)O-2:F solid solution exhibits much better durability compared to commercial IrO2, the standard (OER) catalyst.

Research paper thumbnail of Noble metal-free bifunctional oxygen evolution and oxygen reduction acidic media electro-catalysts

Scientific Reports, 2016

Identification of low cost, highly active, durable completely noble metal-free electro-catalyst f... more Identification of low cost, highly active, durable completely noble metal-free electro-catalyst for oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells, oxygen evolution reaction (OER) in PEM based water electrolysis and metal air batteries remains one of the major unfulfilled scientific and technological challenges of PEM based acid mediated electro-catalysts. In contrast, several non-noble metals based electro-catalysts have been identified for alkaline and neutral medium water electrolysis and fuel cells. Herein we report for the very first time, F doped Cu1.5Mn1.5O4, identified by exploiting theoretical first principles calculations for ORR and OER in PEM based systems. The identified novel noble metal-free electro-catalyst showed similar onset potential (1.43 V for OER and 1 V for ORR vs RHE) to that of IrO2 and Pt/C, respectively. The system also displayed excellent electrochemical activity comparable to IrO2 for OER and Pt/C for ORR, respectively, along with remarkable long term stability for 6000 cycles in acidic media validating theory, while also displaying superior methanol tolerance and yielding recommended power densities in full cell configurations.

Research paper thumbnail of Non-Noble Metal Based Electro-Catalyst Compositions for Proton Exchange Membrane Based Water Electrolysis and Methods of Making

Research paper thumbnail of Effect of Magnesium Substitution in Lithium Nickel Oxide An Ab Initio Study

Journal of the Electrochemical Society, 2004

ABSTRACT

Research paper thumbnail of Phase stability and electronic structure of NaMnO2

Journal of the Electrochemical Society, 2003

ABSTRACT

Research paper thumbnail of Fermi surface nesting and pre-martensitic softening in V and Nb at high pressures

Journal of Physics Condensed Matter, May 18, 2006

First-principles total-energy calculations were performed for the trigonal shear elastic constant... more First-principles total-energy calculations were performed for the trigonal shear elastic constant (C44) of body-centred cubic (bcc) V and Nb. A mechanical instability in C44 is found for V at pressures of ~2 Mbar which also shows a softening in Nb at pressures of ~0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.

Research paper thumbnail of Biodegradable Iron-Containing Compositions, Methods of Preparing and Applications Therefor

Research paper thumbnail of Doped Transition Metal Nitride Supercapacitors (DTMSCs): Mechanisms of Charge Storage

Meeting Abstracts, Aug 5, 2014

ABSTRACT

Research paper thumbnail of Fermi surface nesting and pre-martensitic softening in V-Nb system under high pressure

First-principles total-energy calculations were performed for the trigonal shear elastic constant... more First-principles total-energy calculations were performed for the trigonal shear elastic constant (C 44 ) of body-centred cubic (bcc) V and Nb. A mechanical instability in C 44 is found for V at pressures of ∼2 Mbar which also shows a softening in Nb at pressures of ∼0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.

Research paper thumbnail of Nitrogen and cobalt co-doped zinc oxide nanowires – Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

Journal of Power Sources, 2015

Research paper thumbnail of Fluorine Doped (Sn,Ru)O2 electro-Catalysts for Oxygen Evolution Reaction (OER) in PEM Based Water Electrolysis

Research paper thumbnail of 341202 High Performance Fluorine Doped Oxygen Evolution Reaction (OER) Electro-Catalysts for PEM Based Water Electrolysis

Identification of electro-catalysts containing non noble metal or significantly reduced amounts o... more Identification of electro-catalysts containing non noble metal or significantly reduced amounts of expensive noble metals (e. g. RuO2) is highly desirable. Development of such a catalyst with comparable electrochemical performance to the standard noble metal oxide counterpart for the proton exchange membrane (PEM) based water electrolysis would constitute a major advancement in generation of hydrogen by water electrolysis. We have accordingly developed a two-pronged theoretical first principles and experimental approach to generate a nano-structured solid solution of SnO2:10wt.% F containing only 20at.% RuO2 [e.g. (Sn0.80Ru0.20)O2:10F] that displays a remarkably similar electrochemical activity and moreover, comparable or even much improved electrochemical stability and durability compared to pure the noble metal counterpart, RuO2. Results of these studies will be presented and discussed.

Research paper thumbnail of WO 3 based solid solution oxide – promising proton exchange membrane fuel cell anode electro-catalyst

J. Mater. Chem. A, 2015

ABSTRACT

Research paper thumbnail of Ceramic Materials for Lithium-Ion Battery Applications

Materials Engineering, 2005

Research paper thumbnail of A Complexed Sol-Gel (CSG) Approach to High Surface Area (HSA) Durable Ultra Active Platinum-Ruthenium Electro-Catalysts for Direct Methanol Fuel Cells

Journal of the Electrochemical Society, 2014

ABSTRACT Direct Methanol Fuel Cell (DMFC) is a promising power source for continuous generation o... more ABSTRACT Direct Methanol Fuel Cell (DMFC) is a promising power source for continuous generation of energy without evolution of any toxic by-products and greenhouse gases. Pt-Ru has been the accepted gold standard anode electro-catalyst for DMFC, but significant advances are required to enhance its performance and stability. A complexed sol-gel (CSG) approach has been used to develop nanostructured powder materials. Herein we report a novel CSG process to synthesize nanoparticulate high specific surface area (HSA), completely unsupported Pt(Ru) based electro-catalyst exhibiting three fold higher electrochemically active surface area (ECSA) and ultra high electrochemical performance compared to commercially available Johnson Matthey Pt-Ru black catalyst, the currently accepted gold standard. Furthermore, in identical single full cell DMFC configuration tests for methanol oxidation, current and power densities similar to 40% higher than that displayed by Johnson Matthey catalyst is achieved. (c) 2014 The Electrochemical Society. All rights reserved.

Research paper thumbnail of Nanostructured robust cobalt metal alloy based anode electro-catalysts exhibiting remarkably high performance and durability for proton exchange membrane fuel cells

J. Mater. Chem. A, 2015

ABSTRACT