Electrochemistry of metal chalcogenides
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Because of the highly reducing nature of O3-NaVS 2 , the as-prepared NaVS 2 samples may easily decompose to Na-deficient Na x VS 2 form during the high-temperature synthesis and subsequent sample handling process. The cell was discharged first and the subsequent charge-discharge cycle was designated as the 2nd cycle. The succeeding voltage profiles of selected cycle numbers inset of FIG.
The high electrochemical utilization of Na ions in Na x VS 2 is associated with high covalency in the VS 2 n host lattice, which reduces the electrostatic repulsion between two adjacent VS 2 n slabs. Therefore, as a result of reversible layer gliding, Na x VS 2 can maintain a layered structure even at a very low Na content i. After the plateau at about 1.
In FIG. Once a featureless XRD pattern forms during the discharge process below about 0. Therefore, the voltage plateau at 0.
The voltage profiles of the subsequent charge and discharge steps, as shown in the inset of FIG. However, the distance between an octahedral site and the adjacent tetrahedral site, which are face-sharing with each other, are too close to be occupied simultaneously, and consequently the introduction of additional alkali metals to tetrahedral sites forces the existing alkali metals at octahedral sites into empty tetrahedral sites, forming an A 2 VS 2 phase. This takes place as a two phase process resulting in a flat voltage response as seen in the case of Li intercalation into LiVS 2.
Therefore, the absence of a flat voltage curve between about 1. This can be attributed to Na ions being too large to be accommodated significantly into the relatively small tetrahedral sites. The ex-situ XRD pattern obtained at 0. The cooled material was then quenched in air. The resulting product was removed from the tube under Ar in a glove box, where it was thoroughly ground and pelletized.
Then pelletized material was then treated again at the same temperatures, heating times, cooling times, and processing. Since this compound is moisture-sensitive, the material was always handled in an Ar atmosphere. The 1st discharge and subsequent voltage profile number 2 FIG. The Na x TiS 2 electrode was used as an anode in this example. The cell was discharged first and the subsequent charge-discharge cycles are shown. The 1st discharge and subsequent voltage profiles nos.
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The electrode was used as an anode in this example. Na x MS 2 , in which M is a 1st row transition metal, has a structure consisting of hexagonal-close-packed sulfur with M and Na ions in alternate octahedral-site planes. On removal of Na, the MS 2 layers are held together by van der Waals bonding. Various phases of layered Na x MS 2 have been reported according to the types of the sulfur packing and the sodium ion coordination being octahedral O or trigonal prismatic P.
The letters O and P and the following number indicates, respectively, the Na ion coordination geometry and number of MS 2 n sheets in the unit cell. The structure of Na x VS 2 was first reported by Wiegers et al.
In their experiment, the quenched Na x VS 2 sample had an x value of 0. A slow phase transition from the P3-type to O1-type structure was observed when the sample was stored at room temperature for an extended period of time.
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Accordingly, the authors assigned the P3- and O1-type structures as the high and low temperature phases of Na x VS 2 0. High temperature synthesis commonly provides sodium deficient layered chalcogenide compounds, and NaVS 2 is so reducing, even at room temperature, that it could readily react with CO 2 in the environment to form Na 2 CO 3 on the surface of NaVS 2 particles. The Na x MS 2 materials described herein also are Na-deficient, based on electrochemical analysis, and present both O3- and P3-type phases as evidenced by X-ray diffraction of Na x VS 2 described herein XRD pattern fitted and indexed with both O3-type and P3-type phases by Le Bail whole-powder pattern decomposition method Mater.
An electrochemical cell as described herein is shown schematically in FIG. Cell 10 comprises negative electrode 12 separated from positive electrode 16 by an electrolyte 14 , all contained in insulating housing 18 with suitable terminals not shown being provided in electronic contact with negative electrode 12 and positive electrode 16 of the invention. Positive electrode 16 comprises metal current collector foil 15 and active layer 17 comprising the transition metal chalcogenide compound along with the carbon and binder, if utilized material as described herein.
Binders and other materials, such as carbon, normally associated with both the electrolyte and the negative and positive electrodes are well known in the art and are not described herein. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language e. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention.
Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law.
Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Electrodeposition of metals, chalcogenides, and metal chalcogenides from ionic liquids
Specific embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 1. The electrochemical cell of claim 1 wherein each M independently is a transition metal selected from the group consisting of V, Ti, Ta, Zr, and Nb. The electrochemical cell of claim 1 wherein each M independently is V or Ti. The electrochemical cell of claim 1 wherein X is S.
Electrochemistry of Metal Chalcogenides (Monographs in Electrochemistry)
The electrochemical cell of claim 1 wherein the organic carrier comprises at least one solvent selected from the group consisting of an organic carbonate, an organic ether, an organic ester, and an organic nitrile. The electrochemical cell of claim 1 wherein the at least one transition metal chalcogenide compound is a particulate material and the cathode is a composite comprising a layer of the particulate transition metal chalcogenide compound and, optionally, carbon particles, disposed on a metal current collector. The electrochemical cell of claim 8 wherein the layer of the particulate transition metal chalcogenide compound and the carbon particles further comprises a binder.
The electrochemical cell of claim 9 wherein binder comprises poly vinylidene difluoride. The electrochemical cell of claim 8 wherein the carbon particles are selected from the group consisting of carbon nanotubes, carbon nanoparticles, and carbon microparticles. The electrochemical cell of claim 7 wherein particles of the particulate transition metal chalcogenide compound are nanoparticles, microparticles, or a combination thereof.
Volume 11 , Issue 11 June 6, Pages Related Information. Close Figure Viewer. Browse All Figures Return to Figure.
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Previous Figure Next Figure. Email or Customer ID. Forgot password? Old Password. New Password. Password Changed Successfully Your password has been changed. Returning user. Request Username Can't sign in? Forgot your username? These films showed exceptional activity for the hydrogen evolution reaction.
The MoS [subscript x] catalyst was coupled with an organic layer protected p-Si substrate and was shown to exhibt high activity for the photoelectrocatalytic hydrogen evolution reaction. The deposition had to be altered due to the limitations of p-type silicon, this involved the addition of a proton source to induce cathodic deposition of the MoS [subscript x] catalyst.
RHE in the same system. Department Chemistry. Search Repository.