WO2011070312A1 - Phosphate de silicium et membrane le comprenant - Google Patents

Phosphate de silicium et membrane le comprenant Download PDF

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WO2011070312A1
WO2011070312A1 PCT/GB2010/002194 GB2010002194W WO2011070312A1 WO 2011070312 A1 WO2011070312 A1 WO 2011070312A1 GB 2010002194 W GB2010002194 W GB 2010002194W WO 2011070312 A1 WO2011070312 A1 WO 2011070312A1
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composition
phosphorus
fuel cell
membrane
silicon
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PCT/GB2010/002194
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John Thomas Sirr Irvine
Pierrot Sassou Attidekou
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University Court Of The University Of St Andrews
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Priority to JP2012542611A priority Critical patent/JP5887276B2/ja
Priority to CN201080062748.4A priority patent/CN102770198B/zh
Priority to US13/514,577 priority patent/US10322942B2/en
Priority to CA2783581A priority patent/CA2783581C/fr
Priority to EP10787527.0A priority patent/EP2509708B8/fr
Priority to DK10787527.0T priority patent/DK2509708T3/en
Publication of WO2011070312A1 publication Critical patent/WO2011070312A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0048—Inorganic membrane manufacture by sol-gel transition
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/024—Oxides
    • B01D71/027—Silicium oxide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/20—Manufacture of shaped structures of ion-exchange resins
    • C08J5/22—Films, membranes or diaphragms
    • C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
    • C08J5/2218—Synthetic macromolecular compounds
    • C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0289—Means for holding the electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/42—Ion-exchange membranes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/88—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by thermal analysis data, e.g. TGA, DTA, DSC
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2343/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and containing boron, silicon, phosphorus, selenium, tellurium or a metal; Derivatives of such polymers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to the use of phosphorus silicon oxide as an ionic conductor in a variety of electrochemical devices, in particular its use as a membrane in proton exchange membrane fuel cells, and to electrochemical devices comprising phosphorus silicon oxide as an ionic conductor.
  • PEMFCs proton exchange membrane fuel cells
  • PEMFCs polymer electrolyte membrane
  • PEM polymer electrolyte membrane
  • this membrane is referred to as a proton exchange membrane (also PEM) given the requirement of the membrane to facilitate the migration of protons (but not electrons) within the fuel cell.
  • PEM proton exchange membrane
  • the membrane must not permit the passage of gas in either direction and be able to withstand the reductive and oxidative chemistries taking place at the cathode and anode respectively.
  • Nafion ® which is a sulfonated tetrafluroroethylene- based fluoropolymer-copolymer discovered in the 1960's, is probably the PEM most commonly used.
  • the utility of Nafion ® in PEMFCs is believed to arise from its ability to transport protons as a consequence of its pendant sulfonic acid side groups, but that it is electrically insulating to anions or electrons. Over time, Nafion ® loses fluorine from its structure. Nafion relies on the presence of water to function as a conductor of protons.
  • PEMFCs employing Nafion ® as PEM are restricted to operating temperatures of less than 100 °C, implying low- temperature applications. At temperature approaching and in excess of 100 °C, so-called fuel cell dehydration takes place the PEM becomes too dry to conduct protons to the cathode effectively resulting in a drop in power output. This illustrates a particular difficulty inherent to PEMFCs: the presence and maintenance of appropriate amounts of water. Effective management of the water generated within PEMFCs is a key issue in relation to the success of PEMFCs. Whilst problems can exist in Nafion ® -based PEMFCs, with other PEMs too much water can also be detrimental.
  • PEMFCs high temperature PEMFCs - HTPEMFCs - in which alternative polymers such as polybenzimidazole (PBI) are used on account of their high thermal stability.
  • PBI polybenzimidazole
  • PBI-H3PO4 has been reported by O E Kondsteim ei al. (Energy 32 (2007) 418-422) to possess conductivity of approximately 6.8 x 10 "2 S/cm at 200 °C with approximately 560 mol %
  • pyrophosphoric acid (equating to about 5 molecules of H 3 P0 4 per repeat unit within the PBI).
  • a further disadvantage of PBI-based PEMs is the decrease in mechanical strength that takes place within increasing temperature and increased level of doping. Also, acid leaches out at temperatures of about 160 °C.
  • HPAs heteropolyacids
  • Polymer composites are mentioned in WO2007/082350 and are described as comprising at least one inorganic proton-conducting polymer functionalised with at least one ionisable group and/or at least one hybrid proton-conducting polymer functionalised with at least one ionisable group, and at least one organic polymer capable of forming hydrogen bonds.
  • compositions having the formula xX0 2 .y Y2O5, (wherein 0.5 ⁇ x ⁇ 0.7; 0.3 ⁇ y ⁇ 0.5; X comprises one or more of silicon, titanium, germanium and zirconium; and Y comprises one or more of phosphorus, vanadium, arsenic and antimony), have utility as ionic conducting materials, in particular as proton-conducting materials.
  • phosphorus silicon oxides e.g. silicon phosphates
  • Phosphorus silicon oxides and other compositions of the invention may therefore be used as a proton-exchange membrane in fuel cells enabling key transport applications.
  • the intrinsic conductive properties of these compositions may also be used in other technological applications, including electrolysis membranes, electrochemical sensors and electrode applications.
  • the invention provides a composition having the formula (I):
  • X comprises one or more of silicon, titanium, germanium and zirconium
  • Y comprises one or more of phosphorus, vanadium arsenic and antimony), or a hydrate thereof.
  • the composition comprises 50 wt % or more of crystalline material.
  • the invention provides a membrane, in particular a proton exchange membrane, comprising a composition according to the first aspect of the invention.
  • a membrane in particular a proton exchange membrane
  • an electrochemical device comprising an ionic conductor that comprises a composition according to the first aspect of the invention.
  • the invention provides a fuel cell stack comprising two or more fuel cells that comprise a composition according to the first aspect of the invention..
  • the invention provides an article powered by a fuel cell or a fuel cell that comprises a composition according to the first aspect of the invention.
  • the invention provides the use of a composition according to the first aspect of the invention as an ionic conductor in an
  • the invention provides a method of operating a fuel cell according to the third aspect of this invention comprising contacting the fuel cell with a reactant fuel and an oxidant whereby to generate electricity, wherein the fuel cell is operated at a temperature of up to about 200 °C and/or a humidity of less than about 50%.
  • Fig. 1 shows an X-ray diffraction pattern of a phosphorus silicon oxide produced in accordance with Synthetic Example 1.
  • Fig. 2(a) and 2(b) show Selected Area Electron Diffraction (SAED) images of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 , showing a hexagonal array to the spots.
  • SAED Selected Area Electron Diffraction
  • Fig. 3(a) and 3(b) show SAED images of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 , showing a perpendicular array of the spots.
  • Fig. 4(a) shows a scanning electron microscopy image of a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 (x 8000) showing the observation of agglomerated particles.
  • Fig. 4(b) shows a further scanning electrode microscope image of a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 dispersed in a matrix of PMMA (poly(methyl methacrylate)), (x14000) showing a defined hexagonal shape.
  • Fig. 5 shows an IR spectrum of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 , orthophosphoric acid and pyrophosphoric acid, with the region from 900 - 500 cm "1 .
  • Fig. 6 shows solid state 31 P NMR spectra of very dry phosphorus silicon oxide produced in accordance with Synthetic Example 1 (Fig. 6(a)), dry phosphorus silicon oxide ((Fig. 6(b)), wet phosphorus silicon oxide (Fig. 3(c)) and pyrophosphoric acid (Fig. 3(d)).
  • Fig. 7 shows a thermogravimetric trace obtained from heating a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 up to 200 °C showing no significant weight loss up to 200 °C.
  • Fig. 8 shows scanning electrode microscopy images of an electrode without platinum, expanded 500 times in (a) and 3000 times in (b); loaded with platinum expanded 500 times in (c) and 3000 times in (d).
  • Fig. 9 shows Arrhenius plots of a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 in air atmosphere (Fig. 9(a)) and wet-air atmosphere (Fig. 9(b)).
  • Fig. 10 shows a comparison of conductivity versus relative humidity and temperature of a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 , Nafion ® and acid-doped PBI.
  • Fig. 11 shows a fuel cell evaluation of a membrane electrode assembly made from a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 , recorded at 120 °C.
  • Fig. 12 shows a fuel cell evaluation of a membrane electrode assembly made from a sample of a phosphorus silicon oxide produced in accordance with Synthetic Example 1 , PVDF was used as polymer matrix and recorded at 130 °C.
  • Fig. 13 shows the AC-impedance of a fuel cell with a sample of phosphorus silicon oxide produced in accordance with Synthetic Example 1 as electrolyte with PVDF as a polymer matrix and recorded at 130 °C.
  • Fig. 14 depicts a graph of the volume of the unit cell of samples of phosphorus silicon oxide produced in accordance with Synthetic Example 2 with respect to their composition.
  • Fig. 15 depicts a scanning electron microscopic image showing the microstructure of a hot-pressed membrane of the invention produced in accordance with Membrane Fabrication Example 1.
  • Fig. 16 shows the fuel cell evaluation/electrochemical testing of a 400 pm membrane produced in accordance with Membrane Fabrication Example 1 with operating conditions H 2 /air at 130 °C.
  • Fig. 17 depicts a scanning electron microscopic image showing the microstructure of a hot-pressed membrane produced in accordance with Membrane Fabrication Example 2 (made from a phosphorus silicon oxide of the invention produced in accordance with Synthetic Example 2 and PTFE powder).
  • Fig. 18 shows X-ray diffractrograms of (a) a porous PTFE sample, (b) a phosphorus silicon oxide produced in accordance with Synthetic Example 2; and (c) a membrane produced in accordance with Membrane Fabrication Example 3.
  • Fig. 19 is a durability plot showing that the electrical conductivity of a MEA made according to Membrane Fabrication Example 3 is maintained at at least about 0.01 S/cm for up to 1000 hours.
  • Fig. 20 shows that an open cell voltage of approximately 0.7 V is maintained for about 1000 seconds (1 ks) of a membrane produced in accordance with
  • Membrane Fabrication Example 4 (made from a sample of phosphorus silicon oxide produced in accordance with Synthetic Example 2 and PTFE).
  • compositions of the formula (I) as defined herein may be used as an ionic conductor for a variety of electrochemical devices including fuel cells, electrolysis cells, electrochemical sensors and electrodes.
  • X in the compositions of formula (I) comprises one or more of silicon, titanium, germanium and zirconium.
  • X comprises one or more of silicon, titanium and germanium, e.g. silicon and titanium.
  • X is silicon.
  • Y may comprise one or more of phosphorus, vanadium, arsenic and antimony.
  • the compositions have formulae wherein X is silicon and Y is phosphorus whereby to provide phosphorus silicon oxides of formula (I). The remainder of the discussion focuses on such phosphorus silicon oxides although the invention is not to be understood to be so limited.
  • phosphorus silicon oxide embraces silicon phosphates and denotes a compounds or composition comprising, or that may be regarded as formally comprising, cationic silicon (Si + ) and anionic phosphate units although there is no intent through this definition to imply or insist that the a phosphorus silicon oxide is an ionic species.
  • a phosphorus silicon oxide of formula (I) may be regarded as a framework phosphate, i.e. comprising an extended molecular network.
  • a phosphorus silicon oxide may, and often does, comprise one or more silicon phosphorus oxides, e.g. silicon phosphates.
  • phosphorus silicon oxide also embraces within its ambit silicon hydrogen phosphates and hydrates thereof and of silicon phosphates. Silicon hydrogen phosphates and hydrates thereof and of silicon phosphates may be formed upon contact of silicon phosphates of formula (I) with water, for example within a fuel cell in situ, e.g. when the material is used in a membrane in a (HT)PEMFC.
  • the composition may comprise up to three molar equivalents of water with respect to the molar quantity of Y2O5 present.
  • hydrates may be represented by formula (I):
  • electrochemical devices are considerably less hydrated than this, e.g. having a value of 0 ⁇ w ⁇ 1 , e.g. 0 ⁇ w ⁇ 0.5.
  • compositions of formula (I) unless the context dictates to the contrary, embrace compositions as formula (I), or hydrates thereof, e.g. compositions of formula (la).
  • phosphorus silicon oxides are made by reacting a silicon-containing material and one or more phosphoric acids.
  • the phosphoric acid from which phosphorus silicon oxides of formula (I) may be made is not particularly limited. It may be, for example orthophosphoric acid (H 3 P0 4 ), pyrophosphoric acid (H 4 P 2 0 7 ) or a so-called polyphosphoric acid (such as tri- or tetraphosphoric acid (H 5 P 3 0 10 and H 6 P 4 0i 3 respectively).
  • Most phosphoric acids are oxyacids of phosphorus (V) and are of formula ⁇ ⁇ +2 ⁇ 0 3 ⁇ , + ⁇ .
  • a sample of phosphoric acid will comprise a mixture of lower phosphoric acids, i.e. wherein n is from 1 to 6, typically from 1 to 4, with such mixtures frequently being characterised by a so-called total phosphorus content, typically as a percentage with respect to pure phosphoric acid. Since the formula H n+2 P n 0 3n+1 dictates that phosphoric acids having n>1 have a phosphorus content (by weight) greater than orthophosphoric acid, mixtures of phosphoric acids generally have phosphorus contents with of more than 100%.
  • Phosphoric acid mixtures having phosphorus contents of between about
  • phosphorus silicon oxides of formula (I) 100% and about 120% may be used in the preparation of phosphorus silicon oxides of formula (I).
  • Pyrophosphoric acid may be conveniently used as the phosphoric acid component when making phosphorus silicon oxide of formula (I).
  • An appropriate phosphoric acid or mixture of phosphoric acids may be used as such or, optionally, generated in situ, e.g. by contact between phosphorus pentoxide and a phosphoric acid, e.g. orthophosphoric acid, as descried in US patent no. 3,611 ,801.
  • no phosphoric acid may be employed as the source of phosphorus, and the phosphorus silicon oxide made by heating a mixture of silica and phosphorus pentoxide (P 2 O 5 ).
  • the material with which the phosphoric acid is reacted may be any convenient silicon-containing material.
  • Examples of such materials are known to those in the art and include siliceous (i.e. Si0 2 -containing) materials known as diatomaceous earth or kieselguhr (diatomaceous earth and kieselguhr are often used interchangeably) and other natural or synthetic silica.
  • Non siliceous materials e.g. silicon chloride or tetraethyl orthosilicate may also be used. If used, a siliceous material will often comprise between 90 and 100 wt% silica.
  • Natural silicas that is to say silica-containing compositions, typically contain up to about 90 to 95 wt.% silica.
  • the silicon-containing material may comprise an aluminium silicate such as various clays, including kaolin.
  • the silicon-containing material from which phosphorus silicon oxide of formula (I) is made may be a silicon-containing glass such as Pyrex or other laboratory or other glassware. More typically, however, the silicon-containing material will be provided by way of specific provision of a suitable (typically siliceous) material, typically as a form of silica, usually powdered.
  • the silicon-containing material and thus compositions comprising compositions of formula (I), may comprise aluminium, for example in the form of aluminium oxide.
  • compositions of formula (I), be they phosphorus silicon oxides or otherwise, may alternatively or additionally comprise - i.e. be chemically doped with - one or more of any of the following elements: boron, sulfur, arsenic, aluminium, titanium, antimony, tin, germanium and indium. These may be introduced by contact of the precursors to the composition of formula (I), e.g. with an appropriate compound comprising of one of these elements, for example as described in US patent no. 3,112,350, or by introducing the element in elemental form. Alternatively the composition of formula (I), e.g. phosphorus silicon oxide, can be doped with an amount of one of these elements, either in elemental form or as part of a compound comprising it.
  • One example of a way of introducing an additional element into a phosphorus silicon oxide is by substituting a proportion of siliceous material for titanium dioxide since titanium dioxide is known to be able to form titanium phosphorus oxide in an analogous manner to the way in which phosphorus silicon oxide may be formed.
  • SnP 2 0 7 may be formed in accordance with the description in US patent application publication number US 2005/0221143. Alternatively, SnP 2 0 7 (or another phosphorus tin oxide) may be added as such.
  • the phosphorus silicon oxide may be formed by calcining a mixture comprising a phosphoric acid component and silica.
  • a phosphorus silicon oxide may be made that comprises silicon orthophosphosphate and/or silicon pyrophosphate. Typically these materials will be in the form of an intimate mixture.
  • Si 5 P 6 0 2 5 was the formula attributed to silicon orthophosphate by D. M.
  • Phase diagrams of the S1O2-P2O5 system have been presented (see Phase Equilibria diagrams, phase diagrams for ceramists, volume XI oxide, Robert S. Roth, compiled at the National Institute of Standards and Technology, edited and published by The American Ceramic Society, pp 173-174) claiming various crystal structures, e.g. cubic, hexagonal, tetragonal, monoclinic, tridymite and cristobalite across the compositional range.
  • Associated findings relating to one of the reported phase diagrams implied, through depiction of a line phase, that a solid solution series around the composition Si 5 P 6 0 2 5 did not exist, consistent with the later findings of Poojary ef a/, (infra).
  • the present invention is based, in part, on our finding that silicon
  • Si 5 P 6 025 is part of a solid solution system based around the composition Si 5 P 6 025, i.e. is based upon the Si 5 P 6 0 2 5 structure.
  • Si 5 P 6 0 2 5 may be alternatively represented as Si 5 0(P0 4 ) 6 and 5Si0 2 .3P 2 0 5 .
  • Vegard's rule states that there is a linear relation between lattice parameters and composition of solid solution alloys expressed as atomic percentage.
  • compositions based upon the Si5P 6 0 2 5 structure may be represented by formula (II):
  • typical hydrates may comprise w(3 + z/2) water molecules, wherein w is as hereinbefore defined.
  • compositions of formulae (I) and (III), e.g. of formula (II), of phosphorus silicon oxides are provided in accordance with the various aspects of the present invention that comprise regions of silicon orthophosphate having a composition of formulae (I) or (III), wherein X is silicon and Y is phosphorus. Additionally or alternatively the phosphorus silicon oxides according to the various aspects of the present invention comprise silicon pyrophosphate. Where both silicon
  • pyrophosphate and silicon orthophosphate are present these may be in intimate admixture, generally as a consequence of the manner in which the phosphorus silicon oxides have been made.
  • phosphorus silicon oxide may be prepared by calcining a mixture comprising the desired silicon and phosphorus sources.
  • a phosphoric acid i.e. one or more phosphoric acids
  • other phosphorus source such as P2O5 or a precursor therefor, such as the ammonium phosphates described above
  • a silicon-containing material i.e. one or more phosphoric acids
  • Suitable temperatures may be in the region of between about 200 to about 500 °C and for a period of between about 1 hour and 2 weeks.
  • heating under Dean-Stark conditions whereby to allow the removal of moisture may be convenient.
  • the silicon- containing material from which the phosphorus silicon oxide is made prior to contact with the phosphorus-containing component and subsequent heating of the mixture may be dried at a temperature of from about 500 to about 1000 °C, e.g. at about 800 °C, for an extended period, e.g. from about 30 minutes to 24 hours of more, typically between about 1 and 4 hours, to allow removal of any residual moisture and any absorbed gases.
  • a siliceous substrate e.g. silica
  • this may be dried at a temperature of from about 500 to about 1000 °C, e.g. at about 800 °C, for an extended period, e.g. from about 30 minutes to 24 hours of more, typically between about 1 and 4 hours, to allow removal of any residual moisture and any absorbed gases.
  • the silicon-containing material from which it is desired to form the phosphorus silicon oxide may be fine, free-flowing form.
  • a volatile organic solvent such as an alcohol (e.g. ethanol)
  • an appropriate amount of one or more ammonium phosphates may be mixed with a siliceous substrate (e.g. silica) and the mixture decomposed in a crucible, e.g. made of alumina, by heating to above 200 °C.
  • the resultant product may be removed, ground and heated slowly to a temperature of from above 500 to about 1000 °C, i.e. about 800 °C, to obtain the desired product - the pure Si 5 P 6 0 2 5 phase.
  • Such products are highly crystalline, i.e. contain large crystallites.
  • smaller crystallites e.g. nanocrystalline compositions as described hereinafter
  • small quantities of either acid or base may be added to the mixture comprising the silicon-containing material and phosphorus-containing component from which the phosphorus silicon oxide is formed. These may be added prior to initiation of the reaction between the phosphorus-containing component and the silicon-containing material and/or additional quantities may be added after initiation of the reaction.
  • suitable acids include mineral acids such as hydrochloric, nitric and sulfuric acid, for example sulfuric acid.
  • base is used as the catalyst, this may be, for example, ammonia, which may be added as an aqueous solution.
  • Other bases such as KOH, NaOH may be used.
  • the amount of catalyst is typically added in an amount of between 0.01 to 5% on a molar basis relative to the molar quantity of pyrophosphoric acid component used.
  • the mixture of components which is typically in the form of a gel-like slurry, is then heated, typically to a temperature of between 300 and 500 °C for a period of time between 1 and 6 hours.
  • the resultant product - the phosphorus silicon oxide - is cooled, which may be usefully effected in an inert atmosphere provided by a blanket of nitrogen or argon gas, for example.
  • a blanket of nitrogen or argon gas for example.
  • the product resultant from calcination is cooled to a temperature of between about 80 °C and about 180 °C and treated with a mixture of air and water vapour in accordance with EP-A-570070.
  • compositions of the invention including compositions of formulae (I) and (III) and compositions otherwise based upon the Si 5 P 6 025 structure are generally crystalline (in particular, comprise more than 50 wt % or more of crystalline material, e.g. up to about 100 wt % of crystalline material) but that, notwithstanding this, the compositions of the invention, including compositions of formulae (I) and (III) and compositions otherwise based upon the Si 5 P 6 025 structure are generally crystalline (in particular, comprise more than 50 wt % or more of crystalline material, e.g. up to about 100 wt % of crystalline material) but that, notwithstanding this, the compositions of the invention, including compositions of formulae (I) and (III) and compositions otherwise based upon the Si 5
  • compositions serve as efficient proton conductors, e.g. in (HT)PEMFCs.
  • compositions are nanocrystalline, by which is meant that the compositions comprise crystalline material (e.g. more than 50 wt% of nanocrystalline material, e.g. up to 00 wt% nanocrystalline material) having at least one dimension of a size between about 0.1 to 100 nm, e.g. about 1 to above 50 nm.
  • Typical nanocrystalline compositions have one dimension of from about 1 to about 5 or 10 nm, e.g. about 3 or 4 nm.
  • nanocrystalline form or otherwise may constitute or be part of nanoparticles, nanostructured materials, thin films, amorphous phases or ceramics.
  • references to crystalline material embrace nanocrystalline material and that where a composition comprises more than 50 wt% of crystalline material, this may be made up of material that is nanocrystalline and/or comprising larger crystallite-sized material and non-nanocrystalline material where nanocrystalline indicates at least one dimension of 10 nm or less).
  • the phosphorus silicon oxide may be pressed into pellets, or ground into fine powders, (e.g. by ball-milling, typically followed by drying (e.g. from 1 to 24 hours at a temperature from about 50 ° C to about 150 'C) allowing formation into a membrane for use as an ionic conductor, e.g. electrolyte membrane, for various applications.
  • the phosphorus-containing component results in more than 50% by weight of the phosphorus silicon oxide produced, often between about 60 and 80 % by weight.
  • the phosphorus silicon oxide is made from a siliceous material, in particular silica, and a phosphorus-containing component, in particular phosphorus pentoxide, or a precursor thereto.
  • a siliceous material in particular silica
  • a phosphorus-containing component in particular phosphorus pentoxide, or a precursor thereto.
  • it is possible to control the stoichiometric outcome of the subsequent reaction by controlling the stoichiometry of the silica and phosphorus-containing component submitted to the phosphorus silicon oxide-forming reaction, e.g. to control the stoichiometry of any silicon orthosphosphate.
  • silica and pyrophosphoric acid are used as the materials from which the phosphorus silicon oxide is made. Control over the stoichiometric ratios of these or other materials as described in the examples section below allows the constitution of the resultant phosphorus silicon oxide to be controllably varied, e.g. to control the stoichiometry of any silicon orthosphosphate.
  • a phosphorus silicon oxide is formed from a mixture comprising an inorganic, typically siliceous, support and a phosphoric acid component.
  • an inorganic, typically siliceous, support and a phosphoric acid component.
  • the silicon-containing, typically siliceous, material and the phosphorus-containing component characteristics of the phosphorus silicon oxide are provided by the silicon-containing, typically siliceous, material and the phosphorus-containing component. For this reason such phosphorus silicon oxides may be considered to be obtainable from mixtures consisting essentially of these components and in particular a silica and a phosphoric acid, such as pyrophosphoric acid (or a mixture of phosphoric acids and pyrophosphoric acid) or phosphorus pentoxide (or a precursor thereto, such as an ammonium phosphate) and optionally one or more of boron, sulfur, arsenic, aluminium, titanium, antimony, tin, germanium and indium as described infra.
  • a silica and a phosphoric acid such as pyrophosphoric acid (or a mixture of phosphoric acids and pyrophosphoric acid) or phosphorus pentoxide (or a precursor thereto, such as an ammonium phosphate
  • Phosphorus silicon oxides in particular those which comprise regions of S15P6O25 and variants thereof (as described herein, e.g. of formulae (I) or (III), wherein X is Si and Y is P) have been found to have ionic conductivities as high as 10 "2 to 10 "1 Scm '1 over a temperature range from ambient (about 20 °C) up to about 250 °C. Whilst the presence of water increases the ionic conductivity of phosphorus silicon oxide (e.g. Si 5 P 6 0 2 5-containing and related materials), good levels of conductivity are observed even at very low water concentrations (e.g. ⁇ 5% by volume in gas). Phosphorus silicon oxide has been found to be essentially insoluble in water.
  • Crystalline forms of S15P6O25 are known to be stable to temperatures in excess of 800°C. All of these properties make Si 5 P 6 0 2 5 and variants thereof, e.g. of formulae (I) or (III), wherein X is Si and Y is P, a highly useful ionic conductor for various electrochemical devices including fuel cells, electrolysis cells,
  • the phosphorus silicon oxide referred to in the various aspects of the invention comprises crystalline or amorphous, typically crystalline, regions of S15P6O25 and/or S1P2O7.
  • a synthesis of Si 5 P 6 025 (to > 95% purity) is taught by T R Krawietz et al. (infra) by reaction between silica and phosphorus pentoxide.
  • crystalline regions of Si 5 P 6 0 25 within the phosphorus silicon oxide are in intimate mixture with SiP 2 0 7 .
  • phosphorus silicon oxide is present in a membrane suitable for use as a proton exchange membrane in a fuel cell, e.g. a HTPEMFC.
  • a membrane suitable for use as a proton exchange membrane in a fuel cell e.g. a HTPEMFC.
  • a membrane for use in a fuel cell or otherwise, such a membrane is typically approximately about 1 to about 500 ⁇ thick, e.g. about 10 to about 250 ⁇ thick, typically about 10 to about 100 ⁇ thick.
  • Phosphorus silicon oxide-containing membranes useful in the present invention may be provided that comprise other polymers, typically organic polymers, not having proton- conducting properties, e.g. neutral polymers such as
  • poly(alkylenes) e.g. poly(ethylene) or poly(propylene)
  • PVC polyvinyl alcohol
  • PVA polyvinyl benzene
  • PVDF polyvinyl benzene
  • Such polymers are advantageously, like, phosphorus silicon oxide, stable at high temperatures.
  • neutral polymer is meant a polymer without cations or anions that are covalently bound to the polymer.
  • neutral polymers are non-polar (and so are not hydrophilic polymers such as PEG and PVA).
  • An example is PTFE.
  • phosphorus silicon oxide-containing membranes useful in the present invention may be provided that comprise other polymers, typically organic polymers, having proton-conducting properties.
  • polymers typically organic polymers, having proton-conducting properties.
  • Such polymers are known in the art and include, for example sulfonated polyether ether ketone (PEEK), PTFE or other polymers, e.g. poly(acrylic acid), optionally in the interstices of which zirconyl phosphate is deposited, as described, for example, in US patent no. 5,849,428.
  • Such polymers are advantageously, like, phosphorus silicon oxide, are stable at high temperatures.
  • mixtures of proton-conducting phosphorus silicon oxide and other polymers that have for example useful mechanical properties desirable combinations of mechanical and functional properties may be realised through techniques with which those of skill in the art are readily familiar, such as casting from dispersions whereby to provide membranes of appropriate thickness and other dimensions.
  • mixtures of composition of formula (I) according to the present invention and appropriate other polymers may be ball-milled together and subsequently hot-pressed.
  • phosphorus silicon oxide-containing membranes may be provided that have a porous, solid structure made of a polymer having a suitable, porous self-supporting structure, in the pores of which the silicon phosphorus oxide of the invention may be formed in situ.
  • a polymer having a suitable, porous self-supporting structure is porous PTFE commercially available from Porex Membrane (Alness, Scotland) such material, optionally after surface-modification (e.g. by boiling in an alcoholic solvent such as methanol and/or treatment with a mixture of hydrogen peroxide and sulfuric acid), may be treated with suitable precursor to the silicon phosphorus oxide (e.g.
  • silicon chloride or tetraethyl orthosilicate as the silicon source silicon chloride or tetraethyl orthosilicate as the silicon source
  • pyrophosphoric acid/phosphoric acid as the phosphorus source
  • the phosphorus silicon oxide of the invention is used as an ionic conductor, i.e. as a proton conductor in a fuel cell.
  • a fuel cell as described herein comprises an anode and a cathode in electrical communication through an external circuit, the anode being provided with a catalyst capable of catalysing the oxidation of the fuel and the cathode reduction of the oxidant.
  • fuel cells in accordance with the present invention are provided with an electrolyte, which comprises a phosphorus silicon oxide. This membrane, as with membranes in all fuel cells, serves to physically separate the oxidation and reduction reactions that take place at the anode and cathode.
  • the electrolyte membrane is a solid, it together with the electrodes and associated catalysts make up what is referred to in the art as the so-called membrane electrode assembly (MEA).
  • MEA membrane electrode assembly
  • the electrode material of the MEA comprises carbon (e.g. carbon cloth, felt or carbon paper) in or on which the catalyst is applied.
  • a characteristic feature of the relevant aspects of the present invention is the provision of a membrane comprising a phosphorus silicon oxide.
  • the fuel cells of, and used according to, the present invention are thus distinguished from the fuel cells in which a liquid phosphoric acid electrolyte is present.
  • the oxidant may be any oxygen-containing species that can provide hydroxide anions upon reduction.
  • the oxidant may be oxygen itself, and may be conveniently supplied as air. Alternatively, purified oxygen may but need not necessarily be used.
  • the oxidant may be gaseous or liquid.
  • a fuel cell stack is a plurality of fuel cells configured consecutively or in parallel, so as to yield either a higher voltage or allow a stronger current to be drawn.
  • the present invention contemplates the use of fuel cell stacks in practising the methods and according to the other embodiments of the present invention.
  • the present invention is thus of utility in allowing generation of electricity for supply to and/or powering a variety of articles, which may be stationary or non- stationary.
  • the device may or may not, but typically does, comprise the fuel cell, or fuel cell stack, operated according to the present invention.
  • Stationary devices may be non-portable devices such as fixed machinery or, more typically, portable devices such as mobile telephones, digital cameras, laptop computers or portable power packs where use of the present invention may allow the replacement or
  • the methods may be used to power non-stationary devices such as vehicles, e.g. cars.
  • non-stationary devices such as vehicles, e.g. cars.
  • the ability to operate at high temperatures (up to at least 200 °C, e.g. from about 80 or 120 °C to 160 °C) without a need for water management represents a particular advantage of the invention.
  • the invention permits the application of the compositions described herein, e.g. in (HT)PEMFCs at much lower humidities (e.g. from about 0% to about 50% humidity) than has hitherto been achievable with PEMs. Proton conductivity can be achieved with this invention at humidities of less than 50%.
  • compositions of this invention as a proton conducting material in PEMFCs can obviate the need for specific cooling on account of the membranes typically used in PEMFCs.
  • specific devices of the invention include rockets and other applications in aeronautics.
  • X-ray powder diffraction data were collected on a STOE StadiP diffractometer (Cu K a! radiation). XRD analyses were performed using STOE software.
  • SAED Selected Area Electron Diffraction
  • HRTEM transmission electron microscopy
  • the surface, the porosity and the morphology of particles of the electrolyte material were observed under microscopy by SEM using a JEOL 5600 where gold was sputtered at the surface of the sample under high vacuum before analysis.
  • IR spectroscopic analyses were performed on a Perkin Elmer system 2000 NIR FT- Raman spectrometer. Transmittance spectra were recorded on a thin film of the sample sandwiched between two IR plates. The spectra were measured with 4 cm "1 resolution.
  • Direct Polarisation Magic Angle Spinning NMR (DP-MAS-NMR) experiments were carried out using Brucker spectrometer operating at a Larmor frequency of 600.27 MHz for 1 H and 242.99 MHz for 31 P.
  • the samples were packed in a 4mm Zr0 2 rotor with a Vespel drive tip and teflon spacers and endcap.
  • One-dimensional (1 -D) direct polarisation magic angle spinning DP-MAS-NMR spectra were recorded at spinning speed of 10kHz using a 90° pulse length of 2 ⁇ and recycle delay of 80s for 31 P. All chemical shifts are expressed in ppm and referenced relative to BP0 4 for 31 P .
  • the TGA analysis was performed on the NETZSCH TG 209 instrument with TASC 414/3 controller from 25 to 200°C under flowing air at a rate of 35mL/min.
  • the electrodes were prepared from graphite (i.e. 100mg) and PVDF (i.e. 30mg). Both graphite and PVDF were mixed in a mortar and 2 thin films of ⁇ 1.3cm diameter and ⁇ ⁇ thickness were produced as electrodes.
  • a suspension of platinum was prepared by mixing in ultra-sonic bath platinum ink in isopropanol. Drops of the suspension were deposited at the surface of the electrodes and dried in an oven. This process was repeated several times (i.e. 3 times) in order to build a porous Gas Diffusion Layer (GDL).
  • GDL Gas Diffusion Layer
  • the active material was processed into a membrane of 2mm thick (i.e. electrolyte).
  • Two graphite pellets i.e. electrode
  • the membrane was sandwiched between the two painted electrodes. Measurements were performed in dry and wet air atmosphere for Ac-Impedance on a hp4192A a frequency response analyser.
  • the Fuel Cell testing was performed on the Membrane Electrolyte Assembly (MEA) prepared from the membrane sandwiched between the platinum loaded electrodes. Copper meshes were used as a current collector. The test was run under wet-5% hydrogen in argon at the anode side for the Hydrogen Oxidation
  • a phosphorus silicon oxide comprising Si 5 P 6 ⁇ 25 and variants thereof could be formed simply by heating pyrophosphoric acid to between 230 °C and 250 °C for around 48 hours in a glass (Pyrex) vessel in a Dean Stark apparatus. Hydrogen peroxide was present and a catalytic amounts of ammonia (or sulfuric acid). Si0 2 was leached directly from the glassware. Cooling and washing the resultant material (with methanol) to remove remaining catalyst affords silicon pyrophosphate materials of this family. This method is less preferred than synthetic Example 2 since it gives little control over the silicon content and clearly damages the reaction vessel. It does however serve to illustrate how easily phosphorus silicon oxide, and, in particular Si 5 P 6 0 2 5 can be made. A number of other variant methods also proved successful
  • Very fine S1O2 powder was dried for at least one hour at 800 °C to remove water and other absorbed gases prior to usage.
  • Si0 2 and H4P2O7 were weighed in the relevant stoichiometric amounts (as per Table 1 below). Ethanol was added to the Si0 2 powder to prevent the loss of the very fine solid particles during mixing. A few drops of hydrochloric acid were added to the silica/ethanol to achieve partial hydrolysis of the mixture. The resulting mixture becomes a slurry on mixing.
  • Si 5 P 6 0 25 and variant materials can be pressed into pellets, ground into fine powders for incorporation into polymer supported membranes and similar.
  • the crystalline materials can be sintered at temperatures up to 900°C without material change to the x-ray diffraction patterns (i.e. are very heat stable).
  • Table 1 describes some of the compositions formulated in accordance with Synthetic Example 2 above.
  • Lattice parameters and cell volume were extracted from X-ray diffraction patterns collected from these samples. These lattice parameters and cell volume were plotted against composition.
  • Fig. 14 shows the unit cell volume plotted against composition. The linear relationship between cell volume (and/or lattice parameter) indicates the existence of a solid solution series in accordance with Vegard's rule.
  • Table 1 Comprising evaluations of some compositions made by solid state reaction .
  • Tables 2 and 3 illustrate ionic conductivity data collected from two samples. These samples were of different composition and were made in different ways.
  • the refined volume of the cell is 872.13 ⁇ 0.20A 3 .
  • Sub-micron particles were observed from the images collected from the SEM (Fig. 4(a)). Agglomerated particles are observed in this image. When the particles are dispersed in a supported matrix such as PMMA (Fig. 4(b)), a very defined shape of the agglomerate particle can be observed exhibiting an hexagonal shape.
  • IR spectrum of H 3 P0 4 , H 4 P 2 0 7 and from the product resultant from Synthetic Example 1 are shown in Fig. 5(a). From Fig. 5, between 600 to 800 cm “1 , no peak is observed for H 3 P0 4 whereas one peak can be seen at 707 cm “1 for pyrophosphoric acid and three peaks are observed for the phosphorus silicon oxide at 790 and 707 and 630 cm "1 wavelength.
  • Fig. 6(d) The pyrophosphoric acid spectrum depicted in Fig. 6(d) has shown two different sites of phosphorus at about Oppm and at about -12ppm with broadened in the lineshape.
  • Fig. 6(c) shows in addition to the two peaks exhibited by pyrophosphoric acid 3 small features at -26, -29 and -42ppm.
  • Fig. 6(b) & (a) spin side band were observed and are related to the peak at -42ppm.
  • the peak at 0 ppm was assigned to Q° species, the peak -12 ppm to Q 1 species, the peak at -26, -30 ppm to Q 2 species in different crystallographic site.
  • the broadening of these peaks indicates that the phosphorus atoms occupy different crystallographic sites.
  • the thermal stability in air atmosphere is displayed in Fig. 7 and does not show any significant weight loss up to 200 °C. This indicates a thermal stability up to 200 °C.
  • the experimental density measure for the material is 2.8745g/cm 3 with a standard deviation of 0.0014g/cm 3 .
  • the SEM images show the porosity of the electrode some Fig. 8(a) & (b).
  • the pores are vital for the gas diffusion through the electrode to allow a triple phase boundary between the gas, the electrolyte and the catalyst. This will allow the Hydrogen oxidation reaction (HOR) at the cathode and the oxygen reduction reaction (ORR) at the anode.
  • HOR Hydrogen oxidation reaction
  • ORR oxygen reduction reaction
  • the variation of the conductivity with temperature of the material is tabulated in Table 2 above.
  • the conductivity versus relative humidity of the active material can be compared to National ® , and phosphoric acid doped polybenzimidazole (PBI) membrane as displayed in Fig. 10. From this it can be observed that phosphorus silicon oxide exhibits better conductivity with temperature and is water (humidity) independent as compared to National ® and phosphoric acid doped-PBI for conduction.
  • Another unoptimised Membrane was prepared from this active material by using PVDF as a polymer matrix.
  • An MEA was produced from this membrane which was 400 ⁇ in thickness and tested at 130 °C.
  • the l/V curve of this cell between 5% H 2 and air at 130 °C is shown in Fig. 12.
  • the resistance of the produced MEA operating at 130 °C (Fig. 13) was evaluated by AC-lmpedance and it shows ohmic resistance of about 0.5 ⁇ due to the ionic resistance of the electrolyte and an electrochemical resistance of about 0.75 ⁇ .
  • Phosphorus silicon oxide of the invention produced in accordance with Synthetic Example 2 was first ball-milled in methanol for 10 hours in order to obtain a very fine powder. The resultant slurry was dried in an oven at 80 ° C overnight. Nanometre (4-10 nm) sized scale particles were obtained by this process. These particles were then mixed with PVDF (Sigma-Aldrich) and pressed on a hot plate. The pressing temperature was varied but typically conducted between 140 and 160 ° C for a dwell time of 10 minutes. The applied pressure varies between 15 and 25 kN. Membranes with thicknesses of 150 to 400 pm were produced.
  • a MEA is produced by applying to each side of the membrane an electrode by hot-pressing together.
  • the applied pressure varies between 5 and 10 kN at a temperature of 120 ° C.
  • a single cell is ready to be mounted onto a jig and tested for AC-impedance and for fuel cell evaluation.
  • Fig. 15 depicts a scanning electron microscopic image (at a magnification of x 500) showing the microstructure of a hot-pressed membrane of the invention produced in this way.
  • Fig. 16 shows the fuel cell evaluation/electrochemical testing of a 400 pm membrane produced in accordance with this example with operating conditions H 2 /air at 130 °C. 2: PTFE/phosphorus silicon oxide membrane
  • Phosphorus silicon oxide of the invention produced in accordance with synthetic Example 2 was first ball-milled in methanol for 10 hours in order to obtain a very fine powder. The resultant slurry was dried in an oven at 80 ° C overnight. Nanometre (4-10 nm) sized scale particles were obtained by this process. These particles were then mixed with PTFE (Sigma-Aldrich) and pressed on a hot plate. The pressing temperature was varied but typically conducted between 140 and 160 ° C for a dwell time of 10 minutes. The applied pressure varies between 20 and 40 kN. Membranes with thicknesses of 120 to 400 ⁇ were produced.
  • MEAs were produced by applying to each side of the membrane an electrode by hot-pressing together.
  • the applied pressure varies between 5 and 10 kN at a temperature of 120 ° C.
  • a single cell is ready to be mounted onto a jig and tested for AC-impedance and for fuel cell evaluation.
  • Fig. 17 depicts a scanning electron microscopic image (at a magnification of x 200) showing the microstructure of a hot-pressed membrane produced in accordance with this example (made using PTFE powder.
  • 3 Porous PTFE/phosphorus silicon oxide membrane
  • Porous PTFE Porous PTFE (Porex® Product PM 21 M; port size: 14 pm; thickness: 0.13 mm; Porex membrane, Alness, Scotland) is surface-treated by boiling it in methanol and then in mixed hydrogen peroxide and sulfuric acid (H 2 O 2 /H 2 SO4). The membrane is then washed in deionised water and dried.
  • a porous PTFE membrane embedded with phosphorus silicon oxide in accordance with the present invention is thus produced.
  • a MEA is produced by applying to each side of the membrane an electrode by hot-pressing together.
  • the applied pressure varies between 5 and 10 kN at a temperature of 120 ° C.
  • a single cell is ready to be mounted onto a jig and tested for AC-impedance and for fuel cell evaluation.
  • Fig. 18 shows X-ray diffractrograms of (a) a porous PTFE sample, (b) a phosphorus silicon oxide produced in accordance with Synthetic Example 2; and (c) a membrane produced in accordance with this example with no impurity phase displaying crystallinity of the phosphorus silicon oxide and compatibility.
  • Fig. 19 is a durability plot showing that the electrical conductivity of a MEA made according to membrane fabrication Example 3 is maintained at at least about 0.01 S/cm for up to 1000 hours.
  • porous PTFE used in this example is illustrative and that the PTFE can be substituted for any convenient porous matrix.
  • Poly(acrylic acid) was heated at 140 ° C with a few drops (three or four) or ammonia solution for 1 hour. This serves to neutralise the poly(acrylic acid) to about pH 7 meaning that the subsequent conductivities cannot be attributable to initially protonated poly(acrylic acid). Then the poly(acrylic acid) was ball-milled with phosphorus silicon oxide prepared in accordance with Synthetic Example 2, the two components of the membrane being added in a ratio of 1:1 by weight. The temperature is then increased to 200 ° C after adding 5 ml or de-ionised water. The resultant mixture was stirred until a solid is formed after 3 hours.
  • the resultant solid is washed with ether, dried and mixed with either PTFE or PVDF in a ratio of 5:1 by weight and hot-pressed.
  • the resultant membrane was pressed at 80 ° C for a dwell time of about 10 minutes.
  • the applied pressure varies between 10 to 30 kN.
  • Membranes with thicknesses of between about 130 and 300 pm were produced.
  • a MEA is produced by applying to each side of the membrane an electrode by hot-pressing together.
  • the applied pressure varies between 5 and 10 kN at a temperature of 120 °C.
  • a single cell is ready to be mounted onto a jig and tested for AC-impedance and for fuel cell evaluation.
  • Fig. 20 shows that an open cell voltage of approximately 0.7 V is maintained for about 1000 seconds (1 ks) of a membrane produced in accordance with this example; membrane thickness: 300 pm; operating conditions: H 2 0/air at 140 ° C.

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Abstract

L'invention porte sur une composition représentée par la formule (I) : xXO2.yY2O5, (dans laquelle : 0,5 < x < 0,7; 0,3 < y < 0,5; X représente le silicium et/ou le titane et/ou le germanium et/ou le zirconium; et Y représente le phosphore et/ou le vanadium et/ou l'arsenic et/ou l'antimoine), ou un hydrate de celle-ci, la composition comprenant plus de 50 % en poids de matière cristalline.
PCT/GB2010/002194 2009-12-08 2010-11-29 Phosphate de silicium et membrane le comprenant WO2011070312A1 (fr)

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US13/514,577 US10322942B2 (en) 2009-12-08 2010-11-29 Silicon phosphate and membrane comprising the same
CA2783581A CA2783581C (fr) 2009-12-08 2010-11-29 Phosphate de silicium et membrane le comprenant
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