Yossi Gofer - Academia.edu (original) (raw)
Papers by Yossi Gofer
Electronically conducting polymers that can be switched between a semiconducting neutral state an... more Electronically conducting polymers that can be switched between a semiconducting neutral state and a conducting doped state are of interest for charge storage applications such as secondary batteries. We report on the electrochemical behavior of conducting polymer films of fluoro-substituted phenylene thienyls in which the fluorine atoms were systematically substituted onto the phenylene ring. An all-polymer secondary battery constructed using these materials exhibited an average discharge voltage of about 2.75 V and specific capacities of about 16 mAh g -1 . The lightweight and flexible construction provides a unique alternative for secondary battery technology.
Nanomaterials and Nanotechnology, 2011
The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocry... more The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of Ge-NC samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 8000C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of Ge-NC changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO2 surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface region.
The Journal of Physical Chemistry C, 2016
We show a simple technique to grow patterned carbon nanotube (CNT) forests by annealing the catal... more We show a simple technique to grow patterned carbon nanotube (CNT) forests by annealing the catalytic surface using copper patterns (as stencil or bridge) prior to, or during CNT growth. We demonstrate that copper diffused into the iron catalyst and deactivated it, thus preventing CNT growth on the areas where the copper was present. This technique is a promising and simple way to pattern CNT forests since it does not require the usual lithography and lift-off of the catalyst. This catalyst deactivating overlayer principle can be extended to pattern other 1D nanostructures such as carbon nanofibers or nanowires and 2D nanostructures such as graphene or transition metale dichalcogenides using chemical vapor deposition (CVD).
The Journal of Physical Chemistry C, 2017
We analyzed the effect of nickel overlayers positioned in close proximity (bridges) or in contact... more We analyzed the effect of nickel overlayers positioned in close proximity (bridges) or in contact (stencils) with the catalytic layer on the growth of vertically aligned carbon nanotubes (VACNTs) using thermal chemical vapor deposition (CVD). We studied the physical-chemical mechanisms, namely the interaction of the overlayer with the gases and with the catalyst. We demonstrate that nickel inhibits CNT growth by adsorbing carbon to form graphene and by interacting with the gas precursors, leading to their modification into species that do not nucleate and grow CNTs. We demonstrate that the effect of the nickel bridge extends to the length of its boundary layer. We tested overlayer patterns and showed that the patterns were replicated during CNT growth. This facile method is a valid alternative to pattern CNT forests without the need for complex lithography and lift-off of the catalyst in applications where lithographic precision is not required.
Journal of Applied Electrochemistry
This paper reports a study of the neutralization of Li-SOCl 2 batteries. Immersion of these batte... more This paper reports a study of the neutralization of Li-SOCl 2 batteries. Immersion of these batteries in acidic seawater solutions leads to their complete discharge by short circuit, followed by corrosion of the positive pin (made of an Fe/Ni alloy). This corrosion process is desirable because it allows penetration of water into the battery, and hence, neutralization of the active mass of the batteries through their reaction with water. The most efficient corrosion of Fe/Ni electrodes is obtained in seawater containing both HCl and H 2 SO 4 in a situation of no separation between the electrode compartments, due to the reaction of the H 2 liberated at the cathode with the surface films on the anode (Fe/Ni pin electrodes). This reaction prevents passivation of the positive pin. Indeed, used Li-SOCl 2 batteries whose insulating covers were removed, corroded much quicker than regular batteries because of the impact of H 2 evolved at the case (the negative pole of the battery) on the dissolution of the positive pin.
Nano Letters, 2015
Rechargeable magnesium batteries have lately received great attention for large-scale energy stor... more Rechargeable magnesium batteries have lately received great attention for large-scale energy storage systems due to their high volumetric capacities, low materials cost, and safe characteristic. However, the bivalency of Mg 2+ ions has made it challenging to find cathode materials operating at high voltages with decent (de)intercalation kinetics. In an effort to overcome this challenge, we adopt an unconventional approach of engaging crystal water in the layered structure of Birnessite MnO 2 because the crystal water can effectively screen electrostatic interactions between Mg 2+ ions and the host anions. The crucial role of the crystal water was revealed by directly visualizing its presence and dynamic rearrangement using scanning transmission electron microscopy (STEM). Moreover, the importance of lowering desolvation energy penalty at the cathode−electrolyte interface was elucidated by working with water containing nonaqueous electrolytes. In aqueous electrolytes, the decreased interfacial energy penalty by hydration of Mg 2+ allows Birnessite MnO 2 to achieve a large reversible capacity (231.1 mAh g −1) at high operating voltage (2.8 V vs Mg/Mg 2+) with excellent cycle life (62.5% retention after 10000 cycles), unveiling the importance of effective charge shielding in the host and facile Mg 2+ ions transfer through the cathode's interface.
ChemInform, 2005
[n thi s review, very recent studi es re lated to magnesium electroc hemi stry (in connecti on wi... more [n thi s review, very recent studi es re lated to magnesium electroc hemi stry (in connecti on with R&D of Mg batteri es) have been reported. These include the study of new electro lyte solutions, based on compl exes with th e fo rmal sto ichi ometry. Mg(AI CI 4 _ n R n)z in eth ers, th eir unique structures and analysis by elec troc hem ical and spectroscopi c meth ods. th e study of Mg depositi on processes by mi croelectrodes and mi croscopy, and th e study of Mg inserti on in to hosts based 0,1 th e so-called Chevrel ph ase structure (Mg O _ 2 M0 6 X S , X=S , Se). The ioni c Illobility of Mg2+ io ns and their ease of diffu sion within th ese structures are di sc ussed. It is demonstrated that th e use o f a nanostructured acti ve Illass may be hi ghl y important for reducing the diffusion length considerably. and hence, for increasing the kin eti cs of transport of the bi valent cati ons. We dea l herein with some key fac tors th at Illay affec t th e possibilit y of sillooth and reversibl e Mg insert ion in to ino rgani c host materi als, and th e possible advantages in the use of nanopart icles fo r th ese systems.
Russian Journal of Electrochemistry, 2004
Electrochemical impedance spectroscopy is used to characterize thin p-doped polypyrrole (PPy) fil... more Electrochemical impedance spectroscopy is used to characterize thin p-doped polypyrrole (PPy) films in propylene carbonate (PC) solutions and poly(trifluorophenyl)thiophene (PTFPT), in solutions based on sulfolane (SF). It appears that the latter film is much less swelled compared to the former one. One consequence of this difference is that the PTFPT film shows a much higher bulk resistance compared to that for the PPy film. Another important consequence is that the swelling of the PTFPT film is essentially physically non-homogeneous. Two parallel, uncoupled paths, with different chemical diffusion coefficients, model the experimental results adequately. In order to quantify the impedance spectra for both polymer films, we use a model proposed by Rubinstein et al. explaining the difference in the diffusion coefficients of within a thin Nafion film. The model can also predict the impedance spectra for composite powdery electrodes containing different particle sizes, such as composite cathodes and graphite anodes used in lithium batteries.
New Journal of Chemistry, 2005
Rhabdophane-type hexagonal lanthanide orthophosphate, LnPO 4 ·nH 2 O (Ln = La, Ce, Nd, Sm, Eu, Gd... more Rhabdophane-type hexagonal lanthanide orthophosphate, LnPO 4 ·nH 2 O (Ln = La, Ce, Nd, Sm, Eu, Gd and Tb, n = 0 to 0.6), and body-centered tetragonal ErPO 4 ·nH 2 O nanowires/nanorods have been successfully synthesized in high yield (>95%) by simple ...
MRS Bulletin, 2014
ABSTRACT
Langmuir, 2003
Metallic magnesium can be reversibly deposited from ethereal solutions of magnesium-aluminum comp... more Metallic magnesium can be reversibly deposited from ethereal solutions of magnesium-aluminum complex salts of the general structure Mg(AlCl4-nRn)2, where R) alkyl. In contrast to the case of lithium surfaces, already thoroughly investigated, the surface state of magnesium electrodes in contact with organic solutions is yet unclear. In this paper we report on a systematic surface analysis of magnesium electrodes in contact with various organic solutions, using XPS. We find in both clean tetrahydrofurane (THF) and THF solutions of dibutylmagnesium or butylmagnesium chloride that the metal surface consists of magnesium oxide and hydroxide (probably developed during manipulation and sample transfer); however, it does not develop thick passivation layers. In THF solutions containing Mg(AlEtBuCl 2)2, surface residuals of carbon, aluminum, and chlorine are detected yet are restricted to the outermost part of the surface, as physically adsorbed species. From their concentration one deduces that both the complex salt and the ether are not reduced at the magnesium surface but precipitate as an insoluble film. Metallic magnesium deposited from THF/ Mg(AlEtBuCl 2)2 solution on gold electrodes shows a very similar surface chemistry, providing an additional proof that, even in the most frail conditions available during electrochemical deposition, pure magnesium is deposited. The surface chemistry of magnesium in contact with propylene carbonate (PC) exhibits as well layered surface chemistry, most of it composed of magnesium oxide and hydroxide, but no evidence is found for reduction products of PC. It is concluded that the magnesium metal behaves like a surface film-free electrode in organo-haloaluminate/THF solutions. Our conclusions support several other studies on the properties of magnesium in such solutions.
Langmuir, 2003
A hydrolyzed silane ((C2H5O) 3Si-(CH2) 3-NH2) was anchored on the surface of silica nanoparticles... more A hydrolyzed silane ((C2H5O) 3Si-(CH2) 3-NH2) was anchored on the surface of silica nanoparticles, forming silica-immobilized silane. After calcination, the silane-modified silica (M-silica) can attract heteropoly acid (HPA) efficiently. It has been shown that the presence ...
Journal of the American Chemical Society, 2011
We report herein on a rigorous analysis of unique electrolyte solutions for novel rechargeable ma... more We report herein on a rigorous analysis of unique electrolyte solutions for novel rechargeable magnesium batteries and nonaqueous magnesium electrochemistry, which contain organometallic complex electrolyte species, by Raman spectroscopy. These solutions comprise ethereal solvents and products of reactions between R 2 Mg Lewis base species and AlCl 2 R Lewis acid species that exist in solution in dynamic multiple equilibria. The reactions involve the exchange of ligands between the magnesium and the aluminum to form ions such as MgCl + , Mg 2 Cl 3 + , and AlCl 4-n Rn (n e 4), stabilized by the ether molecules. The Raman peak assignments were based on a rigorous study of solutions containing reference compounds and some quantum-mechanical calculations. Raman spectroscopy enabled a quantitative analysis of the various species in solution.
Journal of Solid State Electrochemistry, 2005
A crystallographic approach was applied to elucidate the influence of the nature of the surface f... more A crystallographic approach was applied to elucidate the influence of the nature of the surface films on the electrochemical behavior of Li and Mg intercalation compounds. This paper presents two examples: (1) protection of graphite electrodes by Li 2 CO 3 surface films, and (2) the unique electrochemical behavior of Mg-containing Chevrel phases (MgCP) obtained by different synthetic routes. In the former case, the elucidation of the protection mechanism and the explanation of the high performance of such protected electrodes are based on the analysis of possible Li-ion motion in the carbonate crystal structure. In the latter case, a combination of synthesis, electrochemistry and XRD analysis was used to explain an unusual phenomenon: the difference between the excellent electrochemical behavior of the Chevrel phase (CP) based on Cu-leached Cu 2-Mo 6 S 8 (CuCP), and the poor electrochemical activity of the high-temperature synthesized MgCP, with the same phase composition. It is shown that this phenomenon is caused by MgO formation on the surface of the latter material. The different surface chemistry of the MgCPs obtained by the two different synthetic routes was substantiated by revealing the correlation between the electrochemical activity and the chemical stability of these materials under ambient atmosphere conditions. Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday.
Journal of Solid State Electrochemistry, 2005
In the present study, we explored how milling Mo 6 S 8 Chevrel phase in inert or air atmosphere a... more In the present study, we explored how milling Mo 6 S 8 Chevrel phase in inert or air atmosphere affects their electrochemical behavior as a Mg-ion insertion material for rechargeable Mg batteries. Electrochemical tools such as slow scan rate cyclic voltammograms and potentiostatic intermittent titration technique have been used in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. In contrast to the deterioration observed for milling Mo 6 S 8 in air, it's milling under Ar results in specific capacity increase due to improved Mg-ion diffusion kinetics. It was shown that in spite of the conservation of the bulk crystallographic structure, both for air and the Ar-milled materials, they differ significantly in the average particle sizes and the degree of surface oxidation state.
Journal of Materials Chemistry, 2004
Journal of Materials Chemistry, 2000
ABSTRACT
[sub 3]: A Salt for Rechargeable Lithium Ion Batteries](https://attachments.academia-assets.com/113575284/thumbnails/1.jpg)
](Journal of The Electrochemical Society, 2003
LiPF 3 (CF 2 CF 3) 3 from Merck KGaA ͑LiFAP͒ was tested as a new electrolyte for Li-ion batteries... more LiPF 3 (CF 2 CF 3) 3 from Merck KGaA ͑LiFAP͒ was tested as a new electrolyte for Li-ion batteries that can replace the commonly used LiPF 6. The latter salt is known to be unstable, to decompose thermally to LiF and PF 5 , and to readily undergo hydrolysis with protic species to form HF contamination in solutions. The latter contamination may have a detrimental impact on the performance of both anodes and cathodes for Li-ion batteries. Solutions comprising LiFAP, LiPF 6 , and LiN(SO 2 CF 2 CF 3) 2 ͑LiBETI͒ in mixtures of ethylene, dimethyl, and diethyl carbonates were tested with composite graphite and LiMn 2 O 4 electrodes. The tools for this study included voltammetry ͑fast and slow scan rates͒, chronopotentiometry, impedance spectroscopy, Fourier transform infrared, and X-ray and photoelectron spectroscopies. It was found that LiFAP is superior to LiPF 6 as an electrolyte for both graphite anodes and LiMn 2 O 4 cathodes. This should be attributed to the different surface chemistry developed on these electrodes when LiPF 6 is replaced by LiFAP. An important impact of such a replacement is probably the absence of possible pronounced HF contamination in LiFAP solutions.
Journal of The Electrochemical Society, 2010
Based on previous data and an understanding of possible reactions with electrodes, we selected fi... more Based on previous data and an understanding of possible reactions with electrodes, we selected five electrolyte solutions as promising components for Li-ion batteries that can operate down to , consisting of solutions of or LiTFSI electrolytes in optimized ternary carbonate solvent ...
Journal of The Electrochemical Society, 2001
Magnesium can be reversibly deposited from ethereal solutions of Grignard salts of the RMgX type ... more Magnesium can be reversibly deposited from ethereal solutions of Grignard salts of the RMgX type ( R = alkyl , aryl groups, and X = halides : Cl, Br), and complexes of the Mg ( AX 4 − n R n ′ R n ″ ′ ) 2 type ( A = Al , B; X = Cl , Br; R, R ′ = alkyl or aryl groups, and n ′ + n ″ = n ) . These complexes can be considered as interaction products between R 2 Mg bases and AX 3 − n R n Lewis acids. The use of such complexes in ether solvents enables us to obtain solutions of reasonable ionic conductivity and high anodic stability, which can be suitable for rechargeable Mg battery systems. In this paper we report on the study of variety of Mg ( AX 4 − n R n ) 2 complexes, where A = Al , B, Sb, P, As, Fe, and Ta; X = Cl , Br, and F; and R = butyl , ethyl, phenyl, and benzyl (Bu, Et, Ph, and Bz, respectively) in several solvents, including tetrahydrofuran (THF), 2Me-THF, 1-3 dioxolane, diethyl ether, and polyethers from the “glyme” family, including dimethoxyethane (glyme), ( CH 3 OCH 2 CH...
Electronically conducting polymers that can be switched between a semiconducting neutral state an... more Electronically conducting polymers that can be switched between a semiconducting neutral state and a conducting doped state are of interest for charge storage applications such as secondary batteries. We report on the electrochemical behavior of conducting polymer films of fluoro-substituted phenylene thienyls in which the fluorine atoms were systematically substituted onto the phenylene ring. An all-polymer secondary battery constructed using these materials exhibited an average discharge voltage of about 2.75 V and specific capacities of about 16 mAh g -1 . The lightweight and flexible construction provides a unique alternative for secondary battery technology.
Nanomaterials and Nanotechnology, 2011
The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocry... more The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of Ge-NC samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 8000C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of Ge-NC changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO2 surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface region.
The Journal of Physical Chemistry C, 2016
We show a simple technique to grow patterned carbon nanotube (CNT) forests by annealing the catal... more We show a simple technique to grow patterned carbon nanotube (CNT) forests by annealing the catalytic surface using copper patterns (as stencil or bridge) prior to, or during CNT growth. We demonstrate that copper diffused into the iron catalyst and deactivated it, thus preventing CNT growth on the areas where the copper was present. This technique is a promising and simple way to pattern CNT forests since it does not require the usual lithography and lift-off of the catalyst. This catalyst deactivating overlayer principle can be extended to pattern other 1D nanostructures such as carbon nanofibers or nanowires and 2D nanostructures such as graphene or transition metale dichalcogenides using chemical vapor deposition (CVD).
The Journal of Physical Chemistry C, 2017
We analyzed the effect of nickel overlayers positioned in close proximity (bridges) or in contact... more We analyzed the effect of nickel overlayers positioned in close proximity (bridges) or in contact (stencils) with the catalytic layer on the growth of vertically aligned carbon nanotubes (VACNTs) using thermal chemical vapor deposition (CVD). We studied the physical-chemical mechanisms, namely the interaction of the overlayer with the gases and with the catalyst. We demonstrate that nickel inhibits CNT growth by adsorbing carbon to form graphene and by interacting with the gas precursors, leading to their modification into species that do not nucleate and grow CNTs. We demonstrate that the effect of the nickel bridge extends to the length of its boundary layer. We tested overlayer patterns and showed that the patterns were replicated during CNT growth. This facile method is a valid alternative to pattern CNT forests without the need for complex lithography and lift-off of the catalyst in applications where lithographic precision is not required.
Journal of Applied Electrochemistry
This paper reports a study of the neutralization of Li-SOCl 2 batteries. Immersion of these batte... more This paper reports a study of the neutralization of Li-SOCl 2 batteries. Immersion of these batteries in acidic seawater solutions leads to their complete discharge by short circuit, followed by corrosion of the positive pin (made of an Fe/Ni alloy). This corrosion process is desirable because it allows penetration of water into the battery, and hence, neutralization of the active mass of the batteries through their reaction with water. The most efficient corrosion of Fe/Ni electrodes is obtained in seawater containing both HCl and H 2 SO 4 in a situation of no separation between the electrode compartments, due to the reaction of the H 2 liberated at the cathode with the surface films on the anode (Fe/Ni pin electrodes). This reaction prevents passivation of the positive pin. Indeed, used Li-SOCl 2 batteries whose insulating covers were removed, corroded much quicker than regular batteries because of the impact of H 2 evolved at the case (the negative pole of the battery) on the dissolution of the positive pin.
Nano Letters, 2015
Rechargeable magnesium batteries have lately received great attention for large-scale energy stor... more Rechargeable magnesium batteries have lately received great attention for large-scale energy storage systems due to their high volumetric capacities, low materials cost, and safe characteristic. However, the bivalency of Mg 2+ ions has made it challenging to find cathode materials operating at high voltages with decent (de)intercalation kinetics. In an effort to overcome this challenge, we adopt an unconventional approach of engaging crystal water in the layered structure of Birnessite MnO 2 because the crystal water can effectively screen electrostatic interactions between Mg 2+ ions and the host anions. The crucial role of the crystal water was revealed by directly visualizing its presence and dynamic rearrangement using scanning transmission electron microscopy (STEM). Moreover, the importance of lowering desolvation energy penalty at the cathode−electrolyte interface was elucidated by working with water containing nonaqueous electrolytes. In aqueous electrolytes, the decreased interfacial energy penalty by hydration of Mg 2+ allows Birnessite MnO 2 to achieve a large reversible capacity (231.1 mAh g −1) at high operating voltage (2.8 V vs Mg/Mg 2+) with excellent cycle life (62.5% retention after 10000 cycles), unveiling the importance of effective charge shielding in the host and facile Mg 2+ ions transfer through the cathode's interface.
ChemInform, 2005
[n thi s review, very recent studi es re lated to magnesium electroc hemi stry (in connecti on wi... more [n thi s review, very recent studi es re lated to magnesium electroc hemi stry (in connecti on with R&D of Mg batteri es) have been reported. These include the study of new electro lyte solutions, based on compl exes with th e fo rmal sto ichi ometry. Mg(AI CI 4 _ n R n)z in eth ers, th eir unique structures and analysis by elec troc hem ical and spectroscopi c meth ods. th e study of Mg depositi on processes by mi croelectrodes and mi croscopy, and th e study of Mg inserti on in to hosts based 0,1 th e so-called Chevrel ph ase structure (Mg O _ 2 M0 6 X S , X=S , Se). The ioni c Illobility of Mg2+ io ns and their ease of diffu sion within th ese structures are di sc ussed. It is demonstrated that th e use o f a nanostructured acti ve Illass may be hi ghl y important for reducing the diffusion length considerably. and hence, for increasing the kin eti cs of transport of the bi valent cati ons. We dea l herein with some key fac tors th at Illay affec t th e possibilit y of sillooth and reversibl e Mg insert ion in to ino rgani c host materi als, and th e possible advantages in the use of nanopart icles fo r th ese systems.
Russian Journal of Electrochemistry, 2004
Electrochemical impedance spectroscopy is used to characterize thin p-doped polypyrrole (PPy) fil... more Electrochemical impedance spectroscopy is used to characterize thin p-doped polypyrrole (PPy) films in propylene carbonate (PC) solutions and poly(trifluorophenyl)thiophene (PTFPT), in solutions based on sulfolane (SF). It appears that the latter film is much less swelled compared to the former one. One consequence of this difference is that the PTFPT film shows a much higher bulk resistance compared to that for the PPy film. Another important consequence is that the swelling of the PTFPT film is essentially physically non-homogeneous. Two parallel, uncoupled paths, with different chemical diffusion coefficients, model the experimental results adequately. In order to quantify the impedance spectra for both polymer films, we use a model proposed by Rubinstein et al. explaining the difference in the diffusion coefficients of within a thin Nafion film. The model can also predict the impedance spectra for composite powdery electrodes containing different particle sizes, such as composite cathodes and graphite anodes used in lithium batteries.
New Journal of Chemistry, 2005
Rhabdophane-type hexagonal lanthanide orthophosphate, LnPO 4 ·nH 2 O (Ln = La, Ce, Nd, Sm, Eu, Gd... more Rhabdophane-type hexagonal lanthanide orthophosphate, LnPO 4 ·nH 2 O (Ln = La, Ce, Nd, Sm, Eu, Gd and Tb, n = 0 to 0.6), and body-centered tetragonal ErPO 4 ·nH 2 O nanowires/nanorods have been successfully synthesized in high yield (>95%) by simple ...
MRS Bulletin, 2014
ABSTRACT
Langmuir, 2003
Metallic magnesium can be reversibly deposited from ethereal solutions of magnesium-aluminum comp... more Metallic magnesium can be reversibly deposited from ethereal solutions of magnesium-aluminum complex salts of the general structure Mg(AlCl4-nRn)2, where R) alkyl. In contrast to the case of lithium surfaces, already thoroughly investigated, the surface state of magnesium electrodes in contact with organic solutions is yet unclear. In this paper we report on a systematic surface analysis of magnesium electrodes in contact with various organic solutions, using XPS. We find in both clean tetrahydrofurane (THF) and THF solutions of dibutylmagnesium or butylmagnesium chloride that the metal surface consists of magnesium oxide and hydroxide (probably developed during manipulation and sample transfer); however, it does not develop thick passivation layers. In THF solutions containing Mg(AlEtBuCl 2)2, surface residuals of carbon, aluminum, and chlorine are detected yet are restricted to the outermost part of the surface, as physically adsorbed species. From their concentration one deduces that both the complex salt and the ether are not reduced at the magnesium surface but precipitate as an insoluble film. Metallic magnesium deposited from THF/ Mg(AlEtBuCl 2)2 solution on gold electrodes shows a very similar surface chemistry, providing an additional proof that, even in the most frail conditions available during electrochemical deposition, pure magnesium is deposited. The surface chemistry of magnesium in contact with propylene carbonate (PC) exhibits as well layered surface chemistry, most of it composed of magnesium oxide and hydroxide, but no evidence is found for reduction products of PC. It is concluded that the magnesium metal behaves like a surface film-free electrode in organo-haloaluminate/THF solutions. Our conclusions support several other studies on the properties of magnesium in such solutions.
Langmuir, 2003
A hydrolyzed silane ((C2H5O) 3Si-(CH2) 3-NH2) was anchored on the surface of silica nanoparticles... more A hydrolyzed silane ((C2H5O) 3Si-(CH2) 3-NH2) was anchored on the surface of silica nanoparticles, forming silica-immobilized silane. After calcination, the silane-modified silica (M-silica) can attract heteropoly acid (HPA) efficiently. It has been shown that the presence ...
Journal of the American Chemical Society, 2011
We report herein on a rigorous analysis of unique electrolyte solutions for novel rechargeable ma... more We report herein on a rigorous analysis of unique electrolyte solutions for novel rechargeable magnesium batteries and nonaqueous magnesium electrochemistry, which contain organometallic complex electrolyte species, by Raman spectroscopy. These solutions comprise ethereal solvents and products of reactions between R 2 Mg Lewis base species and AlCl 2 R Lewis acid species that exist in solution in dynamic multiple equilibria. The reactions involve the exchange of ligands between the magnesium and the aluminum to form ions such as MgCl + , Mg 2 Cl 3 + , and AlCl 4-n Rn (n e 4), stabilized by the ether molecules. The Raman peak assignments were based on a rigorous study of solutions containing reference compounds and some quantum-mechanical calculations. Raman spectroscopy enabled a quantitative analysis of the various species in solution.
Journal of Solid State Electrochemistry, 2005
A crystallographic approach was applied to elucidate the influence of the nature of the surface f... more A crystallographic approach was applied to elucidate the influence of the nature of the surface films on the electrochemical behavior of Li and Mg intercalation compounds. This paper presents two examples: (1) protection of graphite electrodes by Li 2 CO 3 surface films, and (2) the unique electrochemical behavior of Mg-containing Chevrel phases (MgCP) obtained by different synthetic routes. In the former case, the elucidation of the protection mechanism and the explanation of the high performance of such protected electrodes are based on the analysis of possible Li-ion motion in the carbonate crystal structure. In the latter case, a combination of synthesis, electrochemistry and XRD analysis was used to explain an unusual phenomenon: the difference between the excellent electrochemical behavior of the Chevrel phase (CP) based on Cu-leached Cu 2-Mo 6 S 8 (CuCP), and the poor electrochemical activity of the high-temperature synthesized MgCP, with the same phase composition. It is shown that this phenomenon is caused by MgO formation on the surface of the latter material. The different surface chemistry of the MgCPs obtained by the two different synthetic routes was substantiated by revealing the correlation between the electrochemical activity and the chemical stability of these materials under ambient atmosphere conditions. Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday.
Journal of Solid State Electrochemistry, 2005
In the present study, we explored how milling Mo 6 S 8 Chevrel phase in inert or air atmosphere a... more In the present study, we explored how milling Mo 6 S 8 Chevrel phase in inert or air atmosphere affects their electrochemical behavior as a Mg-ion insertion material for rechargeable Mg batteries. Electrochemical tools such as slow scan rate cyclic voltammograms and potentiostatic intermittent titration technique have been used in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. In contrast to the deterioration observed for milling Mo 6 S 8 in air, it's milling under Ar results in specific capacity increase due to improved Mg-ion diffusion kinetics. It was shown that in spite of the conservation of the bulk crystallographic structure, both for air and the Ar-milled materials, they differ significantly in the average particle sizes and the degree of surface oxidation state.
Journal of Materials Chemistry, 2004
Journal of Materials Chemistry, 2000
ABSTRACT
Journal of The Electrochemical Society, 2003
LiPF 3 (CF 2 CF 3) 3 from Merck KGaA ͑LiFAP͒ was tested as a new electrolyte for Li-ion batteries... more LiPF 3 (CF 2 CF 3) 3 from Merck KGaA ͑LiFAP͒ was tested as a new electrolyte for Li-ion batteries that can replace the commonly used LiPF 6. The latter salt is known to be unstable, to decompose thermally to LiF and PF 5 , and to readily undergo hydrolysis with protic species to form HF contamination in solutions. The latter contamination may have a detrimental impact on the performance of both anodes and cathodes for Li-ion batteries. Solutions comprising LiFAP, LiPF 6 , and LiN(SO 2 CF 2 CF 3) 2 ͑LiBETI͒ in mixtures of ethylene, dimethyl, and diethyl carbonates were tested with composite graphite and LiMn 2 O 4 electrodes. The tools for this study included voltammetry ͑fast and slow scan rates͒, chronopotentiometry, impedance spectroscopy, Fourier transform infrared, and X-ray and photoelectron spectroscopies. It was found that LiFAP is superior to LiPF 6 as an electrolyte for both graphite anodes and LiMn 2 O 4 cathodes. This should be attributed to the different surface chemistry developed on these electrodes when LiPF 6 is replaced by LiFAP. An important impact of such a replacement is probably the absence of possible pronounced HF contamination in LiFAP solutions.
Journal of The Electrochemical Society, 2010
Based on previous data and an understanding of possible reactions with electrodes, we selected fi... more Based on previous data and an understanding of possible reactions with electrodes, we selected five electrolyte solutions as promising components for Li-ion batteries that can operate down to , consisting of solutions of or LiTFSI electrolytes in optimized ternary carbonate solvent ...
Journal of The Electrochemical Society, 2001
Magnesium can be reversibly deposited from ethereal solutions of Grignard salts of the RMgX type ... more Magnesium can be reversibly deposited from ethereal solutions of Grignard salts of the RMgX type ( R = alkyl , aryl groups, and X = halides : Cl, Br), and complexes of the Mg ( AX 4 − n R n ′ R n ″ ′ ) 2 type ( A = Al , B; X = Cl , Br; R, R ′ = alkyl or aryl groups, and n ′ + n ″ = n ) . These complexes can be considered as interaction products between R 2 Mg bases and AX 3 − n R n Lewis acids. The use of such complexes in ether solvents enables us to obtain solutions of reasonable ionic conductivity and high anodic stability, which can be suitable for rechargeable Mg battery systems. In this paper we report on the study of variety of Mg ( AX 4 − n R n ) 2 complexes, where A = Al , B, Sb, P, As, Fe, and Ta; X = Cl , Br, and F; and R = butyl , ethyl, phenyl, and benzyl (Bu, Et, Ph, and Bz, respectively) in several solvents, including tetrahydrofuran (THF), 2Me-THF, 1-3 dioxolane, diethyl ether, and polyethers from the “glyme” family, including dimethoxyethane (glyme), ( CH 3 OCH 2 CH...