Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2002-02-20
2003-09-23
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S101000, C502S183000, C502S184000, C502S185000, C502S418000, C423S417000, C423S418000, C423S447500, C429S209000, C429S218100, C429S220000, C429S221000, C429S223000, C429S225000, C429S226000, C429S228000, C429S229000, C429S231800
Reexamination Certificate
active
06624108
ABSTRACT:
The present invention relates to reticulated vitrified carbon compositions which contain a metal and/or a metal salt dispersed therein, in particular containing up to 1000 mg/cm
3
of Cu, Sn, Zn, Pb, Ni, Fe, or alloys or mixtures thereof and/or salts or mixtures of salts thereof, dispersed therein, and to processes for the preparation of such vitrified carbon compositions.
Electrodes which are used in energy storage and power generation systems may be surfaced with graphite. However, in some aggressive environments such as in the cell described in U.S. Pat. No. 4,485,154 which uses a sulfide-polysulfide catholyte system and an iodide-polyiodide, chloride-chlorine or bromide-bromine anolyte system, the anolyte may migrate into the graphite of the electrode and destroy or damage its integrity. It is therefore desirable for the electrode used in such a cell to be resistant to such aggressive environments.
It is also desirable for the electrode for use with the sulfide-polysulfide electrolyte described above to be metal-containing because some or all of the metal can be converted to a salt, preferably a sulfide which acts as an electrocatalyst for the sulfide-polysulfide catholyte system. Such an electrode must be chemically, electrochemically and physically stable in the electrolyte and have a high surface area.
It is known that carbon compositions may be coated with a metal plating. U.S. Pat. No. 4,851,285 discloses a cellular carbon foam with metallic plating on the interior of its cells and various methods for the production thereof. U.S. Pat. No. 4,136,428 discloses a method for producing an improved heat transfer surface on a metal tube by electroplating a thin metal coating onto a very porous reticulated organic foam layer which has been wound onto the metal tube, said foam having been precoated with graphite. The organic foam may optionally be pyrolysed. U.S. Pat. No. 4,579,632 discloses a method of electroforming by:
(i) creating the shape to be electro-formed of a polystyrene or other material,
(ii) coating with a carbonizable resin,
(iii) carbonising the resin and vaporising the internal form, and
(iv) metal plating the resulting structure.
It is also known that glassy carbons containing metal particles can be formed. WO93/04220 discloses glassy carbons including a dispersion of metal particles having a small particle size. The glassy carbons are formed by heating a metal complexed to a molecule for a sufficient period of time for the molecule to cross-link to provide glassy carbon. A similar method of forming carbon composites containing ultrafine metal particles by pyrolysis of organometallic polymers is disclosed in a paper by H. Yasuda, S. Miyanaga, A. Nakamura and H. Sakai (Journal of Inorganic and Organometallic Polymers, Vol 1, No 1, 1991).
Incorporating metal into the structure of the carbon surface of an electrode is difficult and plating of the carbon surface by the methods known in the art results in mechanical instability because the metal particles are not mechanically locked into the carbon surface. Poor adherence of the metal plate also causes problems when the metal is converted into a catalytically active salt such as a metal sulfide. Considerable volumetric expansion occurs on conversion putting strain on the bonding at the metal sulfide/carbon interface leading to a loss of catalyst. The use of organometallic polymers for forming vitrified carbon compositions with metal particles disperse therein necessitates synthesis of the precursor organometallics which is an expensive and time-consuming process.
Electrodes containing electrocatalytic species such as copper sulfide, and methods for their production are also known. GB-A-1330252 discloses an electrode structure comprising copper sulfide with a porosity of at least 50% and a resistivity of less than 0.5 ohm-cm together with a process for forming such an electrode from a homogeneous mixture of finely divided particulate sulfur and finely divided particulate copper metal. U.S. Pat. No. 3,847,674 discloses similar electrode structures and methods for their formation and also suggests that the cathodes may be prepared in intimate physical and electrical contact with a conductor, including carbon meshes. GB-A-1464998 discloses a lithium-molten salt cell with a transition metal chalcogenide positive electrode. The electrode may be formed by impregnating a lattice of porous graphite with a slurry of the chalcogenide in a liquid such as alcohol, then baking to evaporate the liquid and leave the chalcogenide distributed throughout the interstices of the porous graphite matrix. GB-A-1482850 discloses an electrode comprising a porous compressible felt matrix formed from resilient carbon fibres, said matrix being impregnated with particles of transition metal chalcogenide. The electrode may be formed by placing the porous felt matrix in a suitable container, substantially covering the matrix with finely divided particles of the selected chalcogenide and vibrating the container to cause the finely divided particles of chalcogenide to permeate through the interstices of the porous matrix. GB-A-2042250 discloses catalytically active electrodes for use in polychalcogenide redox systems which comprise, as active material, a sulfide, selenide or telluride, or a mixture thereof, of one or more transition metals, copper or lead. The electrodes may be formed by forming a layer of precursor on a support, such as porous carbon and converting the precursor to the active material. In one method the precursor is a layer of metal formed on the support by electrolysis and converted to the sulfide, selenide or telluride by reaction with a chalcogen-chalcogenide-hydroxide electrolyte composition.
The electrodes described above suffer however from mechanical instability in the aggressive environments of electrochemical cells, such as in the cell described in U.S. Pat. No. 4,485,154. There is therefore a need for improved electrodes for use with such systems.
We have now developed a reticulated vitreous carbon body containing Cu, Sn, Zn, Pb, Ni, Fe, or alloys or mixtures thereof and/or salts or mixtures of salts thereof, dispersed therein, which may be used as an electrode or electrode surfacing material and which is more resistant to the aggressive environments discussed above and exhibits excellent electrocatalytic activity.
Accordingly, in one aspect, the present invention provides a reticulated vitrified carbon composition which contains particles of Cu, Sn, Zn, Pb, Ni, Fe, or alloys or mixtures thereof dispersed therein.
By the term “reticulated” as used herein is meant a three dimensional netlike structure. Preferably, such a structure has a porosity of from 10 to 200 pores per linear inch. Preferably, such a structure also has a total void space of 50%, more preferably 80%, of the total volume of the structure.
By the term “vitrified carbon” as used herein is meant carbon which is in an amorphous glassy form which is produced by the pyrolysis of certain polymers.
The reticulated vitrified carbon composition preferably comprises up to approximately 1000 mg/cm
3
, more preferably from 30 to 130 mg/cm
3
, of the said metal or alloy particles dispersed therein.
Preferably the metal or alloy particles are substantially spherical in shape. This shape provides an advantage when the composition is cut into thin sheets, for example for use in electrochemical cells. This shape of particle does not result in damage to the surrounding vitrified carbon structure on cutting.
Whilst not wishing to be bound by theory, it is believed that spherical particles are more easily dislodged from their position in the vitreous carbon structure than non-spherical particles. Thus, when contacted by a cutting edge they do not grip the vitreous carbon so tightly, causing it to fracture, but rather dislodge from their position without causing damage.
The preferred metal for use in the present invention is Cu which has particularly good conductive properties and which can subsequently be converted to the electrocatalytic salt copper sulfide.
The metal or
Clark Duncan Guy
Cooley Graham Edward
Turpin Mark Christopher
Whyte Ian
Bell Mark L.
Hailey Patricia L.
Regenesys Technologies Limited
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