WO2024089403A1 - Metal oxide sol - Google Patents

Metal oxide sol Download PDF

Info

Publication number
WO2024089403A1
WO2024089403A1 PCT/GB2023/052765 GB2023052765W WO2024089403A1 WO 2024089403 A1 WO2024089403 A1 WO 2024089403A1 GB 2023052765 W GB2023052765 W GB 2023052765W WO 2024089403 A1 WO2024089403 A1 WO 2024089403A1
Authority
WO
WIPO (PCT)
Prior art keywords
composition
acid
membrane
catalyst layer
fluorinated
Prior art date
Application number
PCT/GB2023/052765
Other languages
French (fr)
Inventor
David Thompsett
Original Assignee
Johnson Matthey Hydrogen Technologies Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB2215718.4A external-priority patent/GB202215718D0/en
Priority claimed from GBGB2215716.8A external-priority patent/GB202215716D0/en
Application filed by Johnson Matthey Hydrogen Technologies Limited filed Critical Johnson Matthey Hydrogen Technologies Limited
Publication of WO2024089403A1 publication Critical patent/WO2024089403A1/en

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F17/00—Compounds of rare earth metals
    • C01F17/20—Compounds containing only rare earth metals as the metal element
    • C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
    • C01F17/224—Oxides or hydroxides of lanthanides
    • C01F17/235—Cerium oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8663—Selection of inactive substances as ingredients for catalytic active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/881—Electrolytic membranes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/8814—Temporary supports, e.g. decal
    • 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
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/1041—Polymer electrolyte composites, mixtures or blends
    • H01M8/1046—Mixtures of at least one polymer and at least one additive
    • H01M8/1051—Non-ion-conducting additives, e.g. stabilisers, SiO2 or ZrO2
    • 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
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • 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 a metal oxide sol, in particular a ceria sol, its method of preparation and applications thereof.
  • colloidal dispersions of metal oxides, including of a cerium (IV) compound are known; they are useful for a wide variety of applications.
  • LIS5132048 describes weakly acidic colloidal aqueous dispersions of particulates of a cerium (IV) compound, having a pH ranging from 1.5 to 5.
  • the dispersions are prepared by (a) acidulating a cerium (IV) hydroxide with an acid having a pKa ranging from 2.5 to 5.0, or with a salt or mixture thereof, (b) next separating the resulting cerium (IV) compound that precipitates from the medium of acidulation, and then (c) colloidally dispersing such cerium (IV) precipitate in an aqueous medium.
  • W02005123594 Johnson Matthey PLC describes a sol comprising metal oxide nanoparticles dispersed in an aqueous liquid, and further comprising stabilizer ions.
  • the metal oxide particles comprise one or more metals selected from a first group consisting of cerium, zirconium, iron, manganese and titanium, and one or more metals selected from a second group consisting of platinum, palladium, rhodium, ruthenium, iridium and osmium.
  • the sols can be used to deposit catalytic coatings onto catalyst substrates, including substrates with narrow channels (i.e. channels with a diameter of less than 500pm).
  • the present invention provides new cerium oxide sols and applications thereof.
  • a composition comprising nanoparticles suspended in a liquid, the nanoparticles comprising metal oxide and the composition additionally comprising stabilizer ions, wherein the stabilizer ions are the anions of a fluorinated acid.
  • the first aspect of the disclosure provides a composition comprising nanoparticles suspended in a liquid, the nanoparticles comprising cerium oxide and the composition additionally comprising stabilizer ions, wherein the stabilizer ions are the anions of a fluorinated acid.
  • the metal oxide may optionally be cerium oxide (ceria).
  • the composition may be described as a colloid, specifically as a sol, e.g., a metal oxide sol, e.g. a cerium oxide sol.
  • a colloid is a mixture having a dispersed phase (the suspended nanoparticles) and a continuous phase (the liquid, which is acting as a medium for suspension of the particles).
  • the inventors propose that the fluorinated acid stabilizes the colloidal system.
  • compositions of the present invention are stable and can be stored before they are used, e.g., to coat substrates. They can be contrasted with "sols" produced during sol-gel processes that are often used to prepare catalysts.
  • sol-gel process the aim is not to produce a stable sol that can be stored and subsequently used, instead the sol is produced and further transformed to provide a gel, which is further transformed to provide a solid.
  • Metal oxide sols such as colloidal zirconia, colloidal ceria, colloidal alumina, and colloidal titania are commercially available. They comprise metal oxide, such as CeC>2, nanoparticles suspended in a water. In some cases, a stabilizer is added, e.g., acetate or nitrate.
  • the inventors have recognised some drawbacks associated with conventional metal oxide sols, including ceria sols, such as instability in the presence of organic solvents.
  • the composition of the present invention is shown to be stable to aggregation in organic solvents.
  • the sol has many useful applications.
  • the ceria sol of the invention may be employed in the preparation of components (e.g., a membrane, a catalyst-coated membrane (CCM), or a membrane electrode assembly (MEA)) for use in a fuel cell or electrolyser.
  • components e.g., a membrane, a catalyst-coated membrane (CCM), or a membrane electrode assembly (MEA)
  • a process for preparing the composition of the first aspect comprising reacting metal hydroxide with an acid, wherein the acid comprises a fluorinated acid.
  • the second aspect of the invention also provides a process for preparing the composition of the first aspect, the process comprising reacting cerium hydroxide with an acid, wherein the acid comprises a fluorinated acid.
  • an ink comprising the composition of the first aspect.
  • the ink may comprise an ion-conducting polymer and/or an electrocatalyst.
  • the invention also resides in processes employing the metal oxide sol of the invention, and products made by those processes.
  • the resulting products will comprise metal oxide and fluorinated acids (or traces thereof).
  • the invention also resides in processes employing the ceria sol of the invention, and products made by those processes.
  • the resulting products will comprise ceria and fluorinated acids (or traces thereof).
  • a process for preparing a ion-conducting membrane comprising metal oxide comprises (directly) applying the sol of the invention to an ion-conducting membrane.
  • the composition of the fourth aspect may be combined with an ion-conducting polymer to form an ink and the ink may be cast as membrane layers.
  • a process for preparing a ion-conducting membrane comprising ceria comprises (directly) applying the sol of the invention to an ion-conducting membrane.
  • the composition of the fourth aspect may be combined with an ion-conducting polymer to form an ink and the ink may be cast as membrane layers.
  • a process for preparing a catalyst layer comprising metal oxide comprising metal oxide.
  • the composition of the first aspect may be combined with an electrocatalyst (and optionally an ion-conducting polymer) to form an ink; and the ink may be cast as a catalyst layer.
  • a process for preparing a catalyst layer comprising ceria comprising ceria.
  • the composition of the first aspect may be combined with an electrocatalyst (and optionally an ion-conducting polymer) to form an ink; and the ink may be cast as a catalyst layer.
  • the fluorinated acid comprises one or more fluorine (F) atoms.
  • the fluorinated acid may comprise two or more, three or more, or four or more fluorine atoms; and/or the acid may comprise 10 or fewer, 6 or fewer or 3 or fewer fluorine atoms.
  • the acid may comprise from 1 to 9, from 1 to 7, from 2 to 6, or from 3 to 5 fluorine atoms.
  • the anion of the fluorinated acid comprises one or more fluorine atoms and may be described as a fluorinated anion.
  • the fluorinated anion (which acts as a stabilizer anion) may comprise 2 or more, 3 or more, or 4 or more fluorine atoms and/or the anion may comprise 10 or fewer, 6 or fewer or 3 or fewer fluorine atoms.
  • the anion may comprise from 1 to 9, from 1 to 7, from 2 to 6, or from 3 to 5 fluorine atoms.
  • the fluorinated acid may be described as a Bronsted-Lowry acid; capable of donating a proton (H + ), i.e. , by dissociation of the acid HA into A" and H + .
  • the inventors submit that the anion (A-) provides electrostatic stabilization to the metal oxide nanoparticles, keeping the nanoparticles in suspension.
  • the acid may be a mineral (inorganic) acid, such as such as fluoro sulphuric acid (FSO3H).
  • FSO3H fluoro sulphuric acid
  • the stabilizer ion is FSO3".
  • the fluorinated acid may be a fluorinated organic acid, such as a fluorinated sulphonic acid or a fluorinated carboxylic acid.
  • the fluorinated organic acid may comprise 15 carbon atoms or fewer, 10 carbon atoms or fewer or 5 carbon atoms or fewer.
  • the fluorinated acid may be a fluorinated sulphonic acid.
  • the fluorinated acid may be described as RSO3H where R is an alkyl or aryl group having at least one fluorine substituent.
  • the stabilizer ion is RSO3- .
  • Alkyl refers to a straight-chain, branched or cyclic saturated hydrocarbon group.
  • the alkyl group may have from 1-10 carbon atoms, in certain embodiments from 1-5 carbon atoms, in certain embodiments, 1-3 carbon atoms.
  • the number of carbon atoms is appropriate to the group, e.g. a cycloalkyl group must have at least 3 carbon atoms to form a ring.
  • the alkyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom.
  • Typical alkyl groups include but are not limited to methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n- butyl, iso-butyl, sec-butyl, tert-butyl, cyclobutyl, n- pentyl, cyclopentyl, n-hexyl, cyclohexyl and the like.
  • Aryl refers to an aromatic carbocyclic group.
  • the aryl group may have a single ring or multiple condensed rings.
  • the aryl group can have from 6-20 carbon atoms, in certain embodiments from 6-15 carbon atoms, in certain embodiments, 6- 10 carbon atoms.
  • the aryl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom.
  • aryl groups include, but are not limited to, phenyl, naphthyl, anthracenyl and the like.
  • Trifluoromethanesulfonic acid corresponds to RSO3H where R is CF3, which can be viewed as methyl with all hydrogen atoms substituted with fluorine.
  • the stabilizer ion is CF3SO3 .
  • the examples demonstrate particularly stable sols that are made using TFMS.
  • Fig. 1 demonstrates that the TFMS stabilized sol is more stable in ethanol than in water.
  • the acid may be a fluorinated carboxylic acid.
  • the fluorinated carboxylic acid may be derived from the corresponding carboxylic acid by substitution of one or more hydrogen atoms by one or more fluorine atoms.
  • the acid may be described as RCO2H where R is an alkyl or aryl group having at least one fluorine substituent.
  • the stabilizer ion is RCC>2'.
  • Trifluoroacetic acid corresponds to RCO2H where R is CF3, which can be viewed as methyl with all hydrogen atoms substituted with fluorine.
  • the examples demonstrate particularly stable sols that are made using trifluoroacetic acid. Referring to example 2, a higher concentration of ceria can be obtained when the ceria nanoparticles are suspended in ethanol rather than in water (greater than 75gl -1 rather 50 gl’ 1 ).
  • the acid may be an alpha fluorinated carboxylic acid such as CH3CF2CO2H or CH2CH5CF3CO2H.
  • the acid may be a beta fluorinated carboxylic acid such as CF3CH2CO2H or CH3CF2CH2CO2H.
  • the acid may comprise CF3CO2H and/or CF3SO3H.
  • the acid does not comprise hydrofluoric acid (HF). HF could pose a safety risk.
  • the acid may be described with reference to its p/ ⁇ a , where K a is the acid dissociation constant for the dissociation of an acid HA into A' and H + .
  • K a is the acid dissociation constant for the dissociation of an acid HA into A' and H + .
  • the acid may have a p/ ⁇ a in water at standard ambient temperature and pressure (SATP) of 4 or less, 3 or less, 2 or less, 1 or less or 0 or less; and/or a p/ ⁇ a in water at SATP of -14 or more, -10 or more, -6 or more, or -3 or more.
  • SATP standard ambient temperature and pressure
  • the acid may have a p/ ⁇ a in water at SATP of from -14 to 1 , such as -14 to - 6.
  • the fluorinated acid may have a molar mass of 500g/mol or less, 400g/mol or less, 300g/mol or less, 200g/mol or less or 100g/mol or less; and/or the fluorinated acid may have a molar mass of 75g/mol or more, 95g/mol or more, 125g/mol or more or 145g/mol or more.
  • fluorinated acids examples include a polymer, such as a PFSA polymer, i.e. the fluorinated acid is non-polymeric.
  • the inventors submit that the corresponding polymeric anions would not constitute stabilizer ions in the context of the present invention. Without being bound by theory we submit that polymers are the wrong size to stabilize the metal oxide nanoparticles against agglomeration.
  • the nanoparticles comprise or consist of metal oxide and may be hydrated. It will be understood that the nanoparticles are solid, i.e., they are suspended in the liquid, rather than being dissolved therein.
  • the metal oxide sol of the present invention is stable over time, i.e. the nanoparticles remain in suspension, rather than agglomerating.
  • Properties of the nanoparticles in the composition can be monitored at intervals. For example, a property (e.g. particle size or zeta potential) may be measured at a specific time and again after 1 week, 4 weeks, 12 weeks, and/or 16 weeks.
  • the particle size can be characterized by obtaining a Z-average particle size of a sample.
  • the Z-average is the intensity weighted mean hydrodynamic size of the ensemble collection of particles measured by dynamic light scattering (DLS).
  • the Z-average is derived from a cumulants analysis of the measured correlation curve, wherein a single particle size is assumed and a single exponential fit is applied to the autocorrelation function.
  • the particle size measurements necessary to obtain Z-average particle size of the nanoparticles can be obtained by Dynamic Light Scattering Particle Size Analysis using a Malvern Zetasizer Nano.
  • the nanoparticles may have an average diameter (e.g. Z-average particle size) of 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less, 100 nm or less or 50 nm or less; and/or the nanoparticles may have an average diameter of 5 nm or more, 10 nm or more, 20 nm or more, 30nm or more, 40 nm or more or 50 nm or more.
  • an average diameter e.g. Z-average particle size
  • the nanoparticles may be described with reference to their particle charge (zeta potential).
  • Zeta potential of colloidal particles e.g. in D.l. water in the pH range from 0 to 7
  • Zeta potential is an indicator of the stability of colloidal dispersions.
  • the magnitude of the zeta potential indicates the degree of electrostatic repulsion between adjacent, similarly charged particles in a dispersion. For particles that are small enough, a high zeta potential will confer stability, i.e., the dispersion will resist aggregation.
  • the magnitude of the zeta potential (mV) of the nanoparticles in the composition may be 20 or more, 30 or more, 40 or more, 50 or more, or 60 or more. It will be appreciated that zeta potential will depend on the pH. For example, the composition may have a pH of 3 or less, and the magnitude of the zeta potential (mV) of the nanoparticles in the composition may be 20 or more.
  • the nanoparticles may have a positive zeta potential when the pH is less than 7.
  • the nanoparticles may consist of metal oxide, i.e. nothing else is present, or consist essentially of metal oxide, i.e. only trace amounts of other components are present.
  • Each nanoparticle comprises or consists of one or more metal oxides.
  • the one or more metal oxides may be selected from oxides of Al, Ce, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Ru, Pd, Sn Ta, V, W or Zr.
  • the metal oxide may comprise an oxide of Al, Nb, Ta, or Zr, or a mixture thereof.
  • each nanoparticle may comprise zirconia, alumina, titania, or a mixture thereof.
  • each nanoparticle comprises an oxide of V, Co, Fe, Cr, Mn, Cu, Ru, Pd, Ni, Mo, Sn, or W, or a mixture thereof.
  • Each nanoparticle may comprise a single metal oxide, e.g. a ceria (cerium oxide) nanoparticle or a zirconia (zirconium oxide) nanoparticle (see Fig. 5A).
  • a ceria (cerium oxide) nanoparticle or a zirconia (zirconium oxide) nanoparticle (see Fig. 5A).
  • the nanoparticles comprising ceria may consist of ceria, i.e. no other metal oxide is present with the ceria nanoparticle or consist essentially of ceria, i.e. only trace amounts of other metal oxides are present.
  • a single nanoparticle could comprise a mixture of metal oxides, e.g. a nanoparticle containing both ceria and zirconia within the same nanoparticle (see Fig 5B).
  • all of the nanoparticles in the composition are of the same type, i.e. comprise the same metal oxide(s) as in Fig. 5B.
  • the composition could comprise two or more types of nanoparticle, e.g. a mixture of ceria nanoparticles and zirconia nanoparticles. This is illustrated in Fig. 5A.
  • the composition may additionally comprise zirconium oxide nanoparticles; niobium dioxide nanoparticles; and/or aluminium oxide nanoparticles.
  • the ceria nanoparticles may constitute at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 90 wt%, at least 95%, or at least 97 wt% of the nanoparticles.
  • the liquid may comprise water and/or an organic solvent.
  • the liquid comprises water, hence an aqueous solution of the fluorinated acid.
  • suitable organic solvents include ketones, such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, t-butyl acetate, amyl acetate, methyl lactate, ethyl lactate, n-propyl lactate, isopropyl lactate, n-butyl lactate, and methoxypropyl acetate; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, t-butanol, n-pentanol, and n-hexanol; glycols such as ethylene glycol, propylene glycol, glycerin, and di
  • the liquid comprises water and an organic solvent.
  • the ratio of water: organic solvent may be from 0.9 or less ( ⁇ 90wt% water: >10wt organic solvent), 0.80 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less; and/or the ratio of water: organic solvent may be 0.1 or more (> 10wt% water : ⁇ 90w % organic solvent), 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more or 0.9 or more.
  • the liquid may comprise from 40 to 60wt% water and from 60 to 40wt% organic solvent
  • composition metal oxide sol
  • the composition comprises metal oxide nanoparticles, e.g. cerium oxide nanoparticles, (nanoparticles comprising or consisting of metal oxide, e.g. cerium oxide) that are suspended in a liquid together with the stabilizer ions (anions of a fluorinated acid, also described as fluorinated stabilizer ions).
  • metal oxide nanoparticles e.g. cerium oxide nanoparticles
  • nanoparticles comprising or consisting of metal oxide, e.g. cerium oxide
  • stabilizer ions anions of a fluorinated acid, also described as fluorinated stabilizer ions
  • the molar ratio of (fluorinated) stabilizer ions: metal oxide may be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more; or 0.9 or more; and/or the molar ratio of stabilizer ions: metal oxide may be 2 or less, 1.5 or less, 1.3 or less, 1.0 or less, 0.8 or less or 0.6 or less.
  • the molar ratio of (fluorinated) stabilizer ions: metal oxide is from 0.3 to 0.9, such as 0.4 to 0.6.
  • the examples demonstrate stable sols having a molar ratio of around 0.4 to 0.6.
  • the composition may have a total solids content (nanoparticles + any other solids) of 50 gl’ 1 or more, 100 gl’ 1 or more, 200 gl’ 1 or more, 300 gl’ 1 or more, 400 gl’ 1 or more, 500 gl’ 1 or more, 600 gl’ 1 or more or 700 gl’ 1 or more; and/or the composition may have a total solids content of 900 gl’ 1 or less, 800 gl’ 1 or less; 600 gl’ 1 or less.
  • the composition may have a metal oxide content of 100 gl’ 1 or more, 200 gl’ 1 or more, 300 gl’ 1 , 400 gl’ 1 or more, 500 gl’ 1 or more, 600 gl’ 1 or more or 700 gl’ 1 or more; and/or the composition may have a metal oxide content of 900 gl’ 1 or less, 800 gl’ 1 or less; 600 gl’ 1 or less.
  • the solids content can be determined by calcination in air (e.g., 900°C for 2 hours).
  • the TFMS examples (examples 1 and 3) achieve a ceria content of over 600gl’ 1 .
  • the composition may have a density of 1 .0 gem -3 or more; 1 .2 gem -3 or more; 1.4 gem -3 or more; 1 .6 gem -3 or more, or 1 .8 gem -3 or more; and/or the composition may have a density of 3.0 gem -3 or less, 2.5 gem -3 or less, 2.0 gem -3 or less or 1 .8 gem -3 or less.
  • the density may be determined at SATP.
  • the TFMS examples (examples 1 and 3) achieve a density of more than 1 .7 gem -3 .
  • the composition may have a pH of 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less or 1 or less; and/or the composition may have a pH of 0 or more, 0.5 or more, 1 or more, 3 or more, or 5 or more. pH may be determined at standard ambient temperature and pressure (SATP, 25°C and 100 kPa).
  • composition of the first aspect may be prepared by reacting metal hydroxide, e.g. cerium hydroxide, with an acid, wherein the acid comprises a fluorinated acid.
  • metal hydroxide e.g. cerium hydroxide
  • a CeC>2 wet cake is employed. This is generally made by adding an aqueous cerium salt to a stirred aqueous ammonia solution. The precipitation can also be done in reverse (e.g., base to salt). It is common when using Ce(lll) salts to also add hydrogen peroxide to assist the oxidation of Ce(lll) to Ce(IV) to form hydrate CeC>2 (known as ceria hydrate). The precipitate is then filtered and washed with demineralised H2O to remove residual salts (ammonium nitrate).
  • the process comprises: providing an aqueous solution of a metal salt; reacting the aqueous solution of the metal salt with a base to precipitate metal hydroxide; and peptising (reacting) the metal hydroxide with an acid to form a sol, wherein the acid is a fluorinated acid.
  • the metal salt may be a metal nitrate, such as a zirconium nitrate or cerium nitrate.
  • the metal salt may be a cerium salt, such as a Ce(lll) or Ce (IV) salt.
  • the cerium salt may be a cerium nitrate.
  • Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state.
  • the cerium salt may be ceric ammonium nitrate (CAN) (NH4)2[Ce(NOs)6].
  • CAN ceric ammonium nitrate
  • the examples demonstrate the preparation of nanoparticles with especially small particle size when CAN is employed.
  • the aqueous solution of metal (e.g. cerium) salt is suitably mixed and is added to a base such as ammonia, providing a precipitate (e.g. the hydroxide Ce(OH)4).
  • the precipitate is suitably filtered and washed thoroughly to remove any remaining salts.
  • the hydroxide precipitate is then peptised by an acid that provides a stabiliser ion (“peptise” means to disperse a substance into a colloidal state).
  • peptise means to disperse a substance into a colloidal state.
  • the sol is stabilised by the conjugate base of the acid and the acid acts as a peptising agent.
  • the wet cake can be used as is or can be dried to remove some of the residual H2O.
  • the inventors recommend that at least 50wt% H2O is retained in the wet cake to allow for best peptization with the chosen acid.
  • the resulting metal oxide (e.g. ceria) sol has a zeta potential more positive than + 25 mV or more negative than - 25 mV (i.e. the magnitude of the zeta potential is 25 mV or more).
  • the zeta potential may be measured using electrophoretic light scattering, for example using a Zetasizer Ultra (Malvern Panalytical).
  • the invention also resides in the use of the metal oxide sol in the preparation of components for an electrochemical device such as a fuel cell or an electrolyser.
  • Ceria and manganese oxide may be employed to promote the decomposition of hydrogen peroxide.
  • the ceria sol can be mixed with an ion-conducting polymer and/or an electrocatalyst to form an ink that is cast to form an ion-conducting membrane I catalyst layer.
  • the electrolysis of water to produce high purity hydrogen and oxygen can be carried out in both alkaline and acidic systems.
  • Those electrolysers that employ a solid protonconducting polymer electrolyte membrane, or proton exchange membrane (PEM) are known as proton exchange membrane water electrolysers (PEMWEs).
  • Those electrolysers that utilise a solid anion-conducting polymer electrolyte membrane, or anion exchange membrane (AEM), are known as anion exchange membrane water electrolysers (AEMWEs).
  • a fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte.
  • a fuel e.g., hydrogen, an alcohol such as methanol or ethanol, or formic acid
  • an oxidant e.g., oxygen or air
  • Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat.
  • Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.
  • Fuel cells are usually classified according to the nature of the electrolyte employed. Often the electrolyte is a solid polymeric membrane, in which the membrane is electronically insulating but ionically conducting. In the proton exchange membrane fuel cell (PEMFC) the membrane is proton conducting, and protons, produced at the anode, are transported across the membrane to the cathode, where they combine with oxygen to form water.
  • PEMFC proton exchange membrane fuel cell
  • MEA membrane electrode assembly
  • the central layer is the polymer ionconducting membrane.
  • electrocatalyst layer On either side of the ion-conducting membrane there is an electrocatalyst layer, containing an electrocatalyst material designed for the specific electrolytic reaction.
  • gas diffusion layer adjacent to each electrocatalyst layer there is a gas diffusion layer.
  • the gas diffusion layer must allow the reactants to reach the electrocatalyst layer and must conduct the electric current that is generated by the electrochemical reactions. Therefore, the gas diffusion layer must be porous and electrically conducting.
  • the electrocatalyst layers generally comprise an electrocatalyst material comprising a metal or metal alloy suitable for the fuel oxidation or oxygen reduction reaction, depending on whether the layer is to be used at the anode or cathode.
  • the electrocatalyst is typically based on platinum or platinum alloyed with one or more other metals.
  • the platinum or platinum alloy catalyst can be in the form of unsupported nanoparticles (such as metal blacks or other unsupported particulate metal powders) but more conventionally the platinum or platinum alloy is deposited as higher surface area nanoparticles onto a high surface area conductive carbon material, such as a carbon black or heat treated versions thereof.
  • the electrocatalyst layers also generally comprise a proton conducting material, such as a proton conducting polymer, to aid transfer of protons from the anode catalyst to the membrane and/or from the membrane to the cathode catalyst.
  • a proton conducting material such as a proton conducting polymer
  • the MEA can be constructed by a number of methods outlined hereinafter: (i) The electrocatalyst layer may be applied to the gas diffusion layer to form a gas diffusion electrode. A gas diffusion electrode is placed on each side of an ion-conducting membrane and laminated together to form the five-layer MEA;
  • the electrocatalyst layer may be applied to both faces of the ion-conducting membrane to form a catalyst coated ion-conducting membrane. Subsequently, a gas diffusion layer is applied to each face of the catalyst coated ion-conducting membrane.
  • An MEA can be formed from an ion-conducting membrane coated on one side with an electrocatalyst layer, a gas diffusion layer adjacent to that electrocatalyst layer, and a gas diffusion electrode on the other side of the ion-conducting membrane.
  • MEAs typically, tens or hundreds of MEAs are required to provide enough power for most applications, so multiple MEAs are assembled to make up a fuel cell stack.
  • Field flow plates are used to separate the MEAs. The plates perform several functions: supplying the reactants to the MEAs; removing products; providing electrical connections; and providing physical support.
  • the metal oxide sol may be employed in the preparation of an ion-conducting membrane; a catalyst coated membrane (CCM); a catalyst layer; a membrane electrode assembly (MEA); or a gas diffusion electrode.
  • CCM catalyst coated membrane
  • MEA membrane electrode assembly
  • the metal oxide sol may be combined with an ion-conducting polymer to form an ink and the ink may be cast to form an ion-conducting membrane.
  • the ion-conducting polymer can be a proton-conducting polymer or an anion-conducting polymer, such as a hydroxyl anion- conducting polymer.
  • suitable proton-conducting polymers include perfluorosulphonic acid ionomers (e.g. National® (E.l.
  • DuPont de Nemours and Co. DuPont de Nemours and Co.
  • Aciplex® Aciplex® (Asahi Kasei), AquivionTM (Solvay Speciality Polymers), Flemion® (Asahi Glass Co.)
  • ionomers based on a sulphonated hydrocarbon such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products (JSR Corporation, Toyobo Corporation, and others).
  • suitable anion-conducting polymers include A901 and A201 made by Tokuyama Corporation, Fumasep FAA from FuMA-Tech GmbH, and Aemion polymers from lonomr.
  • the metal oxide sol of the invention can be combined with an electrocatalyst to form an ink (a catalyst ink) and the ink can be case to form a catalyst layer.
  • the catalyst ink comprises an electrocatalyst, metal oxide, a dispersant, and a fluorinated acid (defined as above).
  • the catalyst ink may additionally comprise ion conducting polymer.
  • the dispersant may be the same as or different from the liquid employed to suspend the nanoparticles in the metal oxide sol.
  • the dispersant may comprise water and/or an organic solvent (e.g., an alcohol such as methanol, ethanol or propanol).
  • the dispersant preferably comprises an organic solvent.
  • the sols of the present invention are shown to have greater stability in organic solvents than conventional (e.g. nitrate stabilized) sols.
  • the electrocatalyst may comprise any metal or metal alloy known to have activity for an electrochemical reaction, such as a hydrogen oxidation reaction, oxygen reduction reaction, oxygen evolution reaction etc.
  • the metal or metal alloy comprises a primary metal suitably selected from
  • platinum group metals platinum, palladium, rhodium, ruthenium, iridium and osmium
  • a base metal e.g., tin, lead, zinc, copper.
  • the primary metal may be alloyed or mixed with one or more different metals selected from the above i.e. (i) the platinum group metals, (ii) gold or silver (iii) and a base metal or their oxides.
  • a base metal is tin or a transition metal which is not a precious metal.
  • a precious metal metal is a platinum group metal (platinum, palladium, rhodium, ruthenium, iridium or osmium) or gold or silver.
  • Suitable base metals are copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium and tin.
  • Preferred base metals in the electrocatalyst include nickel, copper, cobalt, and chromium. More preferred base metals are nickel, cobalt and copper.
  • the primary metal is preferably platinum, which may be alloyed with other precious metals, such as ruthenium, or one or more base metals.
  • the loading of the primary metal in the electrocatalyst material is suitably 10-70 wt%, more suitably 20-50 wt%, more suitably 20- 30 wt% based on the total weight of the electrocatalyst material (metal/metal alloy + support).
  • the resulting membrane or catalyst layer may comprise fluorinated acid as defined above (e.g. RSO3H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent or RCO2H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent) or traces thereof.
  • fluorinated acid as defined above (e.g. RSO3H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent) or traces thereof.
  • the catalyst layer may be prepared by a number of methods known to those skilled in the art, for example by preparation of an ink and applying the ink to a membrane, gas diffusion layer or transfer substrate by standard methods such as gravure coating, slot die (slot, extrusion) coating (whereby the coating is squeezed out under pressure via a slot onto the substrate), screen printing, rotary screen printing, inkjet printing, spraying, painting, bar coating, pad coating, gap coating techniques such as knife or doctor blade over roll (whereby the coating is applied to the substrate then passes through a split between the knife and a support roller), and metering rod application such as with a Meyer bar.
  • the thickness of the catalyst layer and loading of primary metal in the catalyst layer will depend on whether the catalyst layer is for use at the anode or cathode.
  • the catalyst layer is suitably > 1 pm; more suitably > 2 pm in thickness; preferably > 5 pm;
  • the catalyst layer is suitably ⁇ 15 pm; more suitably ⁇ 10 pm in thickness;
  • the loading of primary metal is suitably ⁇ 0.3 mg/cm 2 ; suitably ⁇ 0.2 mg/cm 2 ; more suitably ⁇ 0.15 mg/cm 2 ;
  • the loading of primary metal is suitably > 0.02 mg/cm 2 .
  • the catalyst layer is suitably > 2pm; more suitably > 5 pm in thickness;
  • the catalyst layer is suitably ⁇ 20 pm; more suitably ⁇ 15 pm in thickness;
  • the loading of primary metal in the catalyst layer is ⁇ 0.4 mg/cm 2 ;
  • the loading of primary metal in the catalyst layer is > 0.05 mg/cm 2 .
  • the catalyst layer may also comprise additional components.
  • additional components include, but are not limited to: a hydrophobic (a polymer such as PTFE or an inorganic solid with or without surface treatment) or a hydrophilic (a polymer or an inorganic solid, such as an oxide) additive to control water transport.
  • the catalyst layer may also comprise a further catalytic material, which may or may not have the same function as the electrocatalyst material of the invention.
  • the invention further provides a gas diffusion electrode comprising a gas diffusion layer (GDL) and a catalyst layer as described above.
  • GDLs are suitably based on conventional non-woven carbon fibre gas diffusion substrates such as rigid sheet carbon fibre papers (e.g. the TGP-H series of carbon fibre papers available from Toray Industries Inc., Japan) or roll-good carbon fibre papers (e.g. the H2315 based series available from Freudenberg FCCT KG, Germany; the Sigracet® series available from SGL Technologies GmbH, Germany; the AvCarb® series available from Ballard Material Products, United States of America; or the NOS series available from CeTech Co., Ltd. Taiwan), or on woven carbon fibre cloth substrates (e.g.
  • the non-woven carbon fibre paper, or woven carbon fibre cloth substrates are typically modified with a hydrophobic polymer treatment and/or application of a microporous layer comprising particulate material either embedded within the substrate or coated onto the planar faces, or a combination of both to form the gas diffusion layer.
  • the particulate material is typically a mixture of carbon black and a polymer such as polytetrafluoroethylene (PTFE).
  • PTFE polytetrafluoroethylene
  • the GDLs are between 100 and 400pm thick.
  • the invention further provides a catalyst coated ion-conducting membrane for a PEMFC/PEMWE comprising a membrane and a catalyst layer as defined above.
  • the membrane may be any membrane suitable for use in a PEMFC, for example the membrane may be based on a perfluorinated sulphonic acid material such as National® (DuPont), Aquivion® (Solvay Plastics), Flemion® (Asahi Glass) and Aciplex® (Asahi Kasei); these membranes may be used unmodified, or may be modified to improve the high temperature performance, for example by incorporating an additive.
  • the membrane may be based on a sulphonated hydrocarbon membrane such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others.
  • the membrane may be a composite membrane, containing the proton-conducting material and other materials that confer properties such as mechanical strength.
  • the membrane may comprise an expanded PTFE substrate.
  • the membrane may be based on polybenzimidazole doped with phosphoric acid and include membranes from developers such as BASF Fuel Cell GmbH, for example the Celtec®-P membrane which will operate in the range 120°C to 180°C.
  • Figure 5 is a schematic diagram showing a sol comprising a mixture two types of metal oxide nanoparticles (5A), a sol comprising nanoparticles where each nanoparticle comprises two different metal oxides (5B); and a sol comprising mixed metal oxide nanoparticles (5C);
  • Figure 6 is a schematic diagram of a COM made using the metal oxide sol of the invention.
  • the resulting sol was centrifuged for 5 mins (4000 rpm) which gave a clear sol supernatant and a very small amount of off-white residue, which was discarded.
  • Solids of the sol were determined (using 1.0 cm 3 sol) by calcination in air (900°C, 2 hrs). Oxide content of the sol was determined to be 641 gCeO2/l equivalent and the sol had a density of 1.76 g cm -3 .
  • the CeO2 particle size of the sol was determined using Dynamic Light Scattering (Malvern Zetasizer). The z-average was found to be 53 nm with a broad distribution from 11 to 490 nm (see Fig 1 (TFMS - CeO2 in H2O).
  • the fluoroacetic acid stabilised sol showed a z-average particle size of 22 nm with a range between 5 and 200 nm.
  • the fluoroacetic acid stabilised sol showed a z-average of 24 nm with a range between 3 and 170 nm.
  • the sol particle size in H2O and EtOH was measured using DLS.
  • the z-average particle size in H2O was found to be 6.4 nm with a range of 1 .8 to 40 nm.
  • the z-average particle size in EtOH was found to be 7.8 nm with a range of 3.4 to 24 nm.
  • the cake was redispersed in c 50 ml H2O, mixed and centrifuged (4000 rpm, 10 mins). A small amount of solid was separated and discarded to give a stable CeC>2 sol. Solid content was determined to be 181 g I’ 1 with a density of 1.18 g cm -3 .
  • Particle size was determined in H2O and EtOH using DLS (figure 4).
  • the acetate stabilized CeO2 sol was equally stable in H2O and EtOH with very similar particle size distributions. However, compared to the trifluoromethanesulphonic acid and trifluoroacetic acid stabilized sols the CeO2 particle sizes are significantly larger.
  • the inventors have recognised that conventional nitrate stabilized metal oxide sols are unstable in EtOH and they have developed a new sol that is stable in H2O and EtOH.
  • the new sol can be employed in a range of applications.
  • the composition may be employed in the preparation of a membrane electrode assembly (MEA) in order to incorporate metal oxide (e.g. ceria or manganese oxide) as a hydrogen peroxide decomposition catalyst.
  • MEA membrane electrode assembly
  • metal oxide e.g. ceria or manganese oxide
  • the sol may be employed in the manufacture of an ionconducting membrane; and/or a catalyst layer to form a catalyst-coated membrane (CCM).
  • CCM catalyst-coated membrane
  • FIG. 6 shows a schematic cross-section (not to scale) of a catalyst-coated membrane 500 produced using the sol of the present invention.
  • the catalyst-coated ion-conducting membrane 500 comprises a first catalyst layer 510, a second catalyst 520 layer and an ionconducting membrane 530 disposed between the first and second catalyst layers 510, 520.
  • the first catalyst layer 510 is on a first face of the ion-conducting membrane 530.
  • the second catalyst layer 520 is on a second face of the ion-conducting membrane 530.
  • the first catalyst layer 510 is a cathode catalyst layer
  • the second catalyst layer 520 is an anode catalyst layer.
  • the first and second catalyst layers 510, 520 are an anode catalyst layer and a cathode catalyst layer respectively.
  • metal oxide e.g. zirconia and/or ceria may be present in the first catalyst layer 510, the second catalyst layer 520 and/or the ion-conducting membrane 530.
  • the catalyst-coated ion-conducting membrane 500 can be used in electrochemical devices, such as fuel cells and water electrolysers.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Electrochemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Geology (AREA)
  • Composite Materials (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Catalysts (AREA)

Abstract

The present invention provides a composition comprising nanoparticles suspended in a liquid, the nanoparticles comprising metal oxide and the composition additionally comprising stabilizer ions, wherein the stabilizer ions comprise the anions of a fluorinated acid.

Description

Metal oxide sol
The present invention relates to a metal oxide sol, in particular a ceria sol, its method of preparation and applications thereof.
Background
Colloidal dispersions of metal oxides, including of a cerium (IV) compound, are known; they are useful for a wide variety of applications. LIS5132048 describes weakly acidic colloidal aqueous dispersions of particulates of a cerium (IV) compound, having a pH ranging from 1.5 to 5. The dispersions are prepared by (a) acidulating a cerium (IV) hydroxide with an acid having a pKa ranging from 2.5 to 5.0, or with a salt or mixture thereof, (b) next separating the resulting cerium (IV) compound that precipitates from the medium of acidulation, and then (c) colloidally dispersing such cerium (IV) precipitate in an aqueous medium.
W02005123594 (Johnson Matthey PLC) describes a sol comprising metal oxide nanoparticles dispersed in an aqueous liquid, and further comprising stabilizer ions. The metal oxide particles comprise one or more metals selected from a first group consisting of cerium, zirconium, iron, manganese and titanium, and one or more metals selected from a second group consisting of platinum, palladium, rhodium, ruthenium, iridium and osmium. The sols can be used to deposit catalytic coatings onto catalyst substrates, including substrates with narrow channels (i.e. channels with a diameter of less than 500pm).
The present invention provides new cerium oxide sols and applications thereof.
Summary of the disclosure
In a first aspect of the present disclosure there is provided a composition comprising nanoparticles suspended in a liquid, the nanoparticles comprising metal oxide and the composition additionally comprising stabilizer ions, wherein the stabilizer ions are the anions of a fluorinated acid.
Also, the first aspect of the disclosure provides a composition comprising nanoparticles suspended in a liquid, the nanoparticles comprising cerium oxide and the composition additionally comprising stabilizer ions, wherein the stabilizer ions are the anions of a fluorinated acid.
Accordingly, in this disclosure the metal oxide may optionally be cerium oxide (ceria).
The composition may be described as a colloid, specifically as a sol, e.g., a metal oxide sol, e.g. a cerium oxide sol. A colloid is a mixture having a dispersed phase (the suspended nanoparticles) and a continuous phase (the liquid, which is acting as a medium for suspension of the particles). Without being bound by theory, the inventors propose that the fluorinated acid stabilizes the colloidal system.
The compositions of the present invention are stable and can be stored before they are used, e.g., to coat substrates. They can be contrasted with "sols" produced during sol-gel processes that are often used to prepare catalysts. In a sol-gel process, the aim is not to produce a stable sol that can be stored and subsequently used, instead the sol is produced and further transformed to provide a gel, which is further transformed to provide a solid.
Metal oxide sols, such as colloidal zirconia, colloidal ceria, colloidal alumina, and colloidal titania are commercially available. They comprise metal oxide, such as CeC>2, nanoparticles suspended in a water. In some cases, a stabilizer is added, e.g., acetate or nitrate.
The inventors have recognised some drawbacks associated with conventional metal oxide sols, including ceria sols, such as instability in the presence of organic solvents. In contrast, the composition of the present invention is shown to be stable to aggregation in organic solvents. As such, the sol has many useful applications. In particular, the ceria sol of the invention may be employed in the preparation of components (e.g., a membrane, a catalyst-coated membrane (CCM), or a membrane electrode assembly (MEA)) for use in a fuel cell or electrolyser.
According to a second aspect of the invention, there is provided a process for preparing the composition of the first aspect, the process comprising reacting metal hydroxide with an acid, wherein the acid comprises a fluorinated acid. The second aspect of the invention also provides a process for preparing the composition of the first aspect, the process comprising reacting cerium hydroxide with an acid, wherein the acid comprises a fluorinated acid.
According to a third aspect of the invention there is provided an ink comprising the composition of the first aspect. The ink may comprise an ion-conducting polymer and/or an electrocatalyst.
The invention also resides in processes employing the metal oxide sol of the invention, and products made by those processes. The resulting products will comprise metal oxide and fluorinated acids (or traces thereof).
The invention also resides in processes employing the ceria sol of the invention, and products made by those processes. The resulting products will comprise ceria and fluorinated acids (or traces thereof).
According to a fourth aspect of the invention there is provided a process for preparing a ion-conducting membrane comprising metal oxide. In one embodiment the process comprises (directly) applying the sol of the invention to an ion-conducting membrane. Alternatively, the composition of the fourth aspect may be combined with an ion-conducting polymer to form an ink and the ink may be cast as membrane layers.
According to a fourth aspect of the invention there is provided a process for preparing a ion-conducting membrane comprising ceria. In one embodiment the process comprises (directly) applying the sol of the invention to an ion-conducting membrane. Alternatively, the composition of the fourth aspect may be combined with an ion-conducting polymer to form an ink and the ink may be cast as membrane layers.
According to a fifth aspect of the invention there is provided a process for preparing a catalyst layer comprising metal oxide. The composition of the first aspect may be combined with an electrocatalyst (and optionally an ion-conducting polymer) to form an ink; and the ink may be cast as a catalyst layer.
According to a fifth aspect of the invention there is provided a process for preparing a catalyst layer comprising ceria. The composition of the first aspect may be combined with an electrocatalyst (and optionally an ion-conducting polymer) to form an ink; and the ink may be cast as a catalyst layer.
Fluorinated acid and anion
The fluorinated acid comprises one or more fluorine (F) atoms. The fluorinated acid may comprise two or more, three or more, or four or more fluorine atoms; and/or the acid may comprise 10 or fewer, 6 or fewer or 3 or fewer fluorine atoms. For example, the acid may comprise from 1 to 9, from 1 to 7, from 2 to 6, or from 3 to 5 fluorine atoms.
Similarly, the anion of the fluorinated acid comprises one or more fluorine atoms and may be described as a fluorinated anion. For example, the fluorinated anion ( which acts as a stabilizer anion) may comprise 2 or more, 3 or more, or 4 or more fluorine atoms and/or the anion may comprise 10 or fewer, 6 or fewer or 3 or fewer fluorine atoms. For example, the anion may comprise from 1 to 9, from 1 to 7, from 2 to 6, or from 3 to 5 fluorine atoms.
The fluorinated acid may be described as a Bronsted-Lowry acid; capable of donating a proton (H+), i.e. , by dissociation of the acid HA into A" and H+. The inventors submit that the anion (A-) provides electrostatic stabilization to the metal oxide nanoparticles, keeping the nanoparticles in suspension.
The acid may be a mineral (inorganic) acid, such as such as fluoro sulphuric acid (FSO3H). The stabilizer ion is FSO3".
The fluorinated acid may be a fluorinated organic acid, such as a fluorinated sulphonic acid or a fluorinated carboxylic acid. The fluorinated organic acid may comprise 15 carbon atoms or fewer, 10 carbon atoms or fewer or 5 carbon atoms or fewer.
The fluorinated acid may be a fluorinated sulphonic acid. The fluorinated acid may be described as RSO3H where R is an alkyl or aryl group having at least one fluorine substituent. The stabilizer ion is RSO3- .
"Alkyl" refers to a straight-chain, branched or cyclic saturated hydrocarbon group. In certain embodiments, the alkyl group may have from 1-10 carbon atoms, in certain embodiments from 1-5 carbon atoms, in certain embodiments, 1-3 carbon atoms. The number of carbon atoms is appropriate to the group, e.g. a cycloalkyl group must have at least 3 carbon atoms to form a ring. Unless otherwise specified, the alkyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Typical alkyl groups include but are not limited to methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n- butyl, iso-butyl, sec-butyl, tert-butyl, cyclobutyl, n- pentyl, cyclopentyl, n-hexyl, cyclohexyl and the like.
"Aryl" refers to an aromatic carbocyclic group. The aryl group may have a single ring or multiple condensed rings. In certain embodiments, the aryl group can have from 6-20 carbon atoms, in certain embodiments from 6-15 carbon atoms, in certain embodiments, 6- 10 carbon atoms. Unless otherwise specified, the aryl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom.
Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anthracenyl and the like.
Trifluoromethanesulfonic acid (TFMS, CF3SO3H) corresponds to RSO3H where R is CF3, which can be viewed as methyl with all hydrogen atoms substituted with fluorine. The stabilizer ion is CF3SO3 . The examples demonstrate particularly stable sols that are made using TFMS. Fig. 1 demonstrates that the TFMS stabilized sol is more stable in ethanol than in water.
The acid may be a fluorinated carboxylic acid. The fluorinated carboxylic acid may be derived from the corresponding carboxylic acid by substitution of one or more hydrogen atoms by one or more fluorine atoms. The acid may be described as RCO2H where R is an alkyl or aryl group having at least one fluorine substituent. The stabilizer ion is RCC>2'.
Trifluoroacetic acid (CF3CO2H) corresponds to RCO2H where R is CF3, which can be viewed as methyl with all hydrogen atoms substituted with fluorine. The examples demonstrate particularly stable sols that are made using trifluoroacetic acid. Referring to example 2, a higher concentration of ceria can be obtained when the ceria nanoparticles are suspended in ethanol rather than in water (greater than 75gl-1 rather 50 gl’1).
The acid may be an alpha fluorinated carboxylic acid such as CH3CF2CO2H or CH2CH5CF3CO2H. The acid may be a beta fluorinated carboxylic acid such as CF3CH2CO2H or CH3CF2CH2CO2H. The acid may comprise CF3CO2H and/or CF3SO3H. In one embodiment, the acid does not comprise hydrofluoric acid (HF). HF could pose a safety risk.
The acid may be described with reference to its p/<a, where Ka is the acid dissociation constant for the dissociation of an acid HA into A' and H+. pKa is defined by the equation below where quantities in square brackets represent the concentrations of the species at equilibrium p a = - log Ka = log [HA]/[A ][H+]
The lower the p/<a the stronger the acid. The acid may have a p/<a in water at standard ambient temperature and pressure (SATP) of 4 or less, 3 or less, 2 or less, 1 or less or 0 or less; and/or a p/<a in water at SATP of -14 or more, -10 or more, -6 or more, or -3 or more.
The acid may have a p/<a in water at SATP of from -14 to 1 , such as -14 to - 6.
The fluorinated acid may have a molar mass of 500g/mol or less, 400g/mol or less, 300g/mol or less, 200g/mol or less or 100g/mol or less; and/or the fluorinated acid may have a molar mass of 75g/mol or more, 95g/mol or more, 125g/mol or more or 145g/mol or more.
Examples of fluorinated acids are provided below.
Figure imgf000007_0001
It will be appreciated that the fluorinated acid is not a polymer, such as a PFSA polymer, i.e. the fluorinated acid is non-polymeric. The inventors submit that the corresponding polymeric anions would not constitute stabilizer ions in the context of the present invention. Without being bound by theory we submit that polymers are the wrong size to stabilize the metal oxide nanoparticles against agglomeration.
Nanoparticles
The nanoparticles (metal oxide nanoparticles) comprise or consist of metal oxide and may be hydrated. It will be understood that the nanoparticles are solid, i.e., they are suspended in the liquid, rather than being dissolved therein.
The metal oxide sol of the present invention is stable over time, i.e. the nanoparticles remain in suspension, rather than agglomerating. Properties of the nanoparticles in the composition can be monitored at intervals. For example, a property (e.g. particle size or zeta potential) may be measured at a specific time and again after 1 week, 4 weeks, 12 weeks, and/or 16 weeks.
The particle size can be characterized by obtaining a Z-average particle size of a sample. The Z-average is the intensity weighted mean hydrodynamic size of the ensemble collection of particles measured by dynamic light scattering (DLS). The Z-average is derived from a cumulants analysis of the measured correlation curve, wherein a single particle size is assumed and a single exponential fit is applied to the autocorrelation function.
The particle size measurements necessary to obtain Z-average particle size of the nanoparticles can be obtained by Dynamic Light Scattering Particle Size Analysis using a Malvern Zetasizer Nano.
The nanoparticles may have an average diameter (e.g. Z-average particle size) of 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less, 100 nm or less or 50 nm or less; and/or the nanoparticles may have an average diameter of 5 nm or more, 10 nm or more, 20 nm or more, 30nm or more, 40 nm or more or 50 nm or more.
The nanoparticles may be described with reference to their particle charge (zeta potential). Zeta potential of colloidal particles (e.g. in D.l. water in the pH range from 0 to 7) can be measured using a zeta plus particle apparatus (Nano-ZS or Zetasizer Ultra (Malvern Panalytical). Zeta potential is an indicator of the stability of colloidal dispersions. The magnitude of the zeta potential indicates the degree of electrostatic repulsion between adjacent, similarly charged particles in a dispersion. For particles that are small enough, a high zeta potential will confer stability, i.e., the dispersion will resist aggregation.
The magnitude of the zeta potential (mV) of the nanoparticles in the composition may be 20 or more, 30 or more, 40 or more, 50 or more, or 60 or more. It will be appreciated that zeta potential will depend on the pH. For example, the composition may have a pH of 3 or less, and the magnitude of the zeta potential (mV) of the nanoparticles in the composition may be 20 or more.
The nanoparticles may have a positive zeta potential when the pH is less than 7.
The nanoparticles may consist of metal oxide, i.e. nothing else is present, or consist essentially of metal oxide, i.e. only trace amounts of other components are present.
Each nanoparticle comprises or consists of one or more metal oxides. The one or more metal oxides may be selected from oxides of Al, Ce, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Ru, Pd, Sn Ta, V, W or Zr.
In particular, the metal oxide may comprise an oxide of Al, Nb, Ta, or Zr, or a mixture thereof. For example, each nanoparticle may comprise zirconia, alumina, titania, or a mixture thereof.
In one embodiment, each nanoparticle comprises an oxide of V, Co, Fe, Cr, Mn, Cu, Ru, Pd, Ni, Mo, Sn, or W, or a mixture thereof.
Each nanoparticle may comprise a single metal oxide, e.g. a ceria (cerium oxide) nanoparticle or a zirconia (zirconium oxide) nanoparticle (see Fig. 5A).
The nanoparticles comprising ceria may consist of ceria, i.e. no other metal oxide is present with the ceria nanoparticle or consist essentially of ceria, i.e. only trace amounts of other metal oxides are present. A single nanoparticle could comprise a mixture of metal oxides, e.g. a nanoparticle containing both ceria and zirconia within the same nanoparticle (see Fig 5B).
It will be understood that this is different from a mixed metal oxide, e.g., CexZri-xO2 wherein a crystalline oxide phase comprises a single phase oxide structure comprising cerium and zirconium (see Fig.5C).
Typically, all of the nanoparticles in the composition are of the same type, i.e. comprise the same metal oxide(s) as in Fig. 5B.
However, the composition could comprise two or more types of nanoparticle, e.g. a mixture of ceria nanoparticles and zirconia nanoparticles. This is illustrated in Fig. 5A. The composition may additionally comprise zirconium oxide nanoparticles; niobium dioxide nanoparticles; and/or aluminium oxide nanoparticles. Where ceria nanoparticles are present together with another type of nanoparticles (e.g., zirconia nanoparticles), the ceria nanoparticles may constitute at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 90 wt%, at least 95%, or at least 97 wt% of the nanoparticles.
Liquid (suspension medium)
The liquid may comprise water and/or an organic solvent. Typically, the liquid comprises water, hence an aqueous solution of the fluorinated acid.
Examples of suitable organic solvents include ketones, such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, t-butyl acetate, amyl acetate, methyl lactate, ethyl lactate, n-propyl lactate, isopropyl lactate, n-butyl lactate, and methoxypropyl acetate; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, t-butanol, n-pentanol, and n-hexanol; glycols such as ethylene glycol, propylene glycol, glycerin, and diethylene glycol; glycol ethers such as methoxypropanol, ethylene glycol dimethyl ether, ethylene glycol diethylether, cellosolve, diethyleneglycol dimethylether, and diethylene glycol diethylether; and amides, as well as mixtures of two or more of the foregoing. Preferably, the organic solvent comprises an alcohol, such as methanol, ethanol, and/or propanol.
In one embodiment the liquid comprises water and an organic solvent. The ratio of water: organic solvent may be from 0.9 or less (<90wt% water: >10wt organic solvent), 0.80 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less; and/or the ratio of water: organic solvent may be 0.1 or more (> 10wt% water : < 90w % organic solvent), 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more or 0.9 or more. The liquid may comprise from 40 to 60wt% water and from 60 to 40wt% organic solvent
The composition (metal oxide sol)
The composition comprises metal oxide nanoparticles, e.g. cerium oxide nanoparticles, (nanoparticles comprising or consisting of metal oxide, e.g. cerium oxide) that are suspended in a liquid together with the stabilizer ions (anions of a fluorinated acid, also described as fluorinated stabilizer ions).
The molar ratio of (fluorinated) stabilizer ions: metal oxide may be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more; or 0.9 or more; and/or the molar ratio of stabilizer ions: metal oxide may be 2 or less, 1.5 or less, 1.3 or less, 1.0 or less, 0.8 or less or 0.6 or less. In one embodiment the molar ratio of (fluorinated) stabilizer ions: metal oxide is from 0.3 to 0.9, such as 0.4 to 0.6. The examples demonstrate stable sols having a molar ratio of around 0.4 to 0.6.
The composition may have a total solids content (nanoparticles + any other solids) of 50 gl’ 1 or more, 100 gl’1 or more, 200 gl’1 or more, 300 gl’1 or more, 400 gl’1 or more, 500 gl’1 or more, 600 gl’1 or more or 700 gl’1 or more; and/or the composition may have a total solids content of 900 gl’1 or less, 800 gl’1 or less; 600 gl’1 or less.
The composition may have a metal oxide content of 100 gl’1 or more, 200 gl’1 or more, 300 gl’1, 400 gl’1 or more, 500 gl’1 or more, 600 gl’1 or more or 700 gl’1 or more; and/or the composition may have a metal oxide content of 900 gl’1 or less, 800 gl’1 or less; 600 gl’1 or less. The solids content can be determined by calcination in air (e.g., 900°C for 2 hours). The TFMS examples (examples 1 and 3) achieve a ceria content of over 600gl’1.
The composition may have a density of 1 .0 gem-3 or more; 1 .2 gem-3 or more; 1.4 gem-3 or more; 1 .6 gem-3 or more, or 1 .8 gem-3 or more; and/or the composition may have a density of 3.0 gem-3 or less, 2.5 gem-3 or less, 2.0 gem-3 or less or 1 .8 gem-3 or less. The density may be determined at SATP. The TFMS examples (examples 1 and 3) achieve a density of more than 1 .7 gem-3. The composition may have a pH of 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less or 1 or less; and/or the composition may have a pH of 0 or more, 0.5 or more, 1 or more, 3 or more, or 5 or more. pH may be determined at standard ambient temperature and pressure (SATP, 25°C and 100 kPa).
Preparation of the metal oxide sol
The composition of the first aspect may be prepared by reacting metal hydroxide, e.g. cerium hydroxide, with an acid, wherein the acid comprises a fluorinated acid.
Typically, a CeC>2 wet cake is employed. This is generally made by adding an aqueous cerium salt to a stirred aqueous ammonia solution. The precipitation can also be done in reverse (e.g., base to salt). It is common when using Ce(lll) salts to also add hydrogen peroxide to assist the oxidation of Ce(lll) to Ce(IV) to form hydrate CeC>2 (known as ceria hydrate). The precipitate is then filtered and washed with demineralised H2O to remove residual salts (ammonium nitrate).
In one embodiment the process comprises: providing an aqueous solution of a metal salt; reacting the aqueous solution of the metal salt with a base to precipitate metal hydroxide; and peptising (reacting) the metal hydroxide with an acid to form a sol, wherein the acid is a fluorinated acid.
The metal salt may be a metal nitrate, such as a zirconium nitrate or cerium nitrate.
The metal salt may be a cerium salt, such as a Ce(lll) or Ce (IV) salt. The cerium salt may be a cerium nitrate. Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state.
The cerium salt may be ceric ammonium nitrate (CAN) (NH4)2[Ce(NOs)6]. The examples demonstrate the preparation of nanoparticles with especially small particle size when CAN is employed. The aqueous solution of metal (e.g. cerium) salt is suitably mixed and is added to a base such as ammonia, providing a precipitate (e.g. the hydroxide Ce(OH)4). The precipitate is suitably filtered and washed thoroughly to remove any remaining salts. The hydroxide precipitate is then peptised by an acid that provides a stabiliser ion (“peptise” means to disperse a substance into a colloidal state). We propose that the sol is stabilised by the conjugate base of the acid and the acid acts as a peptising agent.
The wet cake can be used as is or can be dried to remove some of the residual H2O. The inventors recommend that at least 50wt% H2O is retained in the wet cake to allow for best peptization with the chosen acid.
Suitably, the resulting metal oxide (e.g. ceria) sol has a zeta potential more positive than + 25 mV or more negative than - 25 mV (i.e. the magnitude of the zeta potential is 25 mV or more). The zeta potential may be measured using electrophoretic light scattering, for example using a Zetasizer Ultra (Malvern Panalytical).
Applications
The invention also resides in the use of the metal oxide sol in the preparation of components for an electrochemical device such as a fuel cell or an electrolyser. Ceria and manganese oxide may be employed to promote the decomposition of hydrogen peroxide. The ceria sol can be mixed with an ion-conducting polymer and/or an electrocatalyst to form an ink that is cast to form an ion-conducting membrane I catalyst layer.
The electrolysis of water to produce high purity hydrogen and oxygen can be carried out in both alkaline and acidic systems. Those electrolysers that employ a solid protonconducting polymer electrolyte membrane, or proton exchange membrane (PEM), are known as proton exchange membrane water electrolysers (PEMWEs). Those electrolysers that utilise a solid anion-conducting polymer electrolyte membrane, or anion exchange membrane (AEM), are known as anion exchange membrane water electrolysers (AEMWEs).
A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. A fuel, e.g., hydrogen, an alcohol such as methanol or ethanol, or formic acid, is supplied to the anode and an oxidant, e.g., oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.
Fuel cells are usually classified according to the nature of the electrolyte employed. Often the electrolyte is a solid polymeric membrane, in which the membrane is electronically insulating but ionically conducting. In the proton exchange membrane fuel cell (PEMFC) the membrane is proton conducting, and protons, produced at the anode, are transported across the membrane to the cathode, where they combine with oxygen to form water.
A principal component of the PEMFC or PEMWE is the membrane electrode assembly (MEA), which is essentially composed of five layers. The central layer is the polymer ionconducting membrane. On either side of the ion-conducting membrane there is an electrocatalyst layer, containing an electrocatalyst material designed for the specific electrolytic reaction. Finally, adjacent to each electrocatalyst layer there is a gas diffusion layer. The gas diffusion layer must allow the reactants to reach the electrocatalyst layer and must conduct the electric current that is generated by the electrochemical reactions. Therefore, the gas diffusion layer must be porous and electrically conducting.
The electrocatalyst layers generally comprise an electrocatalyst material comprising a metal or metal alloy suitable for the fuel oxidation or oxygen reduction reaction, depending on whether the layer is to be used at the anode or cathode. The electrocatalyst is typically based on platinum or platinum alloyed with one or more other metals. The platinum or platinum alloy catalyst can be in the form of unsupported nanoparticles (such as metal blacks or other unsupported particulate metal powders) but more conventionally the platinum or platinum alloy is deposited as higher surface area nanoparticles onto a high surface area conductive carbon material, such as a carbon black or heat treated versions thereof.
The electrocatalyst layers also generally comprise a proton conducting material, such as a proton conducting polymer, to aid transfer of protons from the anode catalyst to the membrane and/or from the membrane to the cathode catalyst.
Conventionally, the MEA can be constructed by a number of methods outlined hereinafter: (i) The electrocatalyst layer may be applied to the gas diffusion layer to form a gas diffusion electrode. A gas diffusion electrode is placed on each side of an ion-conducting membrane and laminated together to form the five-layer MEA;
(ii) The electrocatalyst layer may be applied to both faces of the ion-conducting membrane to form a catalyst coated ion-conducting membrane. Subsequently, a gas diffusion layer is applied to each face of the catalyst coated ion-conducting membrane.
(iii) An MEA can be formed from an ion-conducting membrane coated on one side with an electrocatalyst layer, a gas diffusion layer adjacent to that electrocatalyst layer, and a gas diffusion electrode on the other side of the ion-conducting membrane.
Typically, tens or hundreds of MEAs are required to provide enough power for most applications, so multiple MEAs are assembled to make up a fuel cell stack. Field flow plates are used to separate the MEAs. The plates perform several functions: supplying the reactants to the MEAs; removing products; providing electrical connections; and providing physical support.
The metal oxide sol may be employed in the preparation of an ion-conducting membrane; a catalyst coated membrane (CCM); a catalyst layer; a membrane electrode assembly (MEA); or a gas diffusion electrode.
The metal oxide sol may be combined with an ion-conducting polymer to form an ink and the ink may be cast to form an ion-conducting membrane. The ion-conducting polymer can be a proton-conducting polymer or an anion-conducting polymer, such as a hydroxyl anion- conducting polymer. Examples of suitable proton-conducting polymers include perfluorosulphonic acid ionomers (e.g. Nation® (E.l. DuPont de Nemours and Co.), Aciplex® (Asahi Kasei), Aquivion™ (Solvay Speciality Polymers), Flemion® (Asahi Glass Co.), or ionomers based on a sulphonated hydrocarbon such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products (JSR Corporation, Toyobo Corporation, and others). Examples of suitable anion-conducting polymers include A901 and A201 made by Tokuyama Corporation, Fumasep FAA from FuMA-Tech GmbH, and Aemion polymers from lonomr.
The metal oxide sol of the invention can be combined with an electrocatalyst to form an ink (a catalyst ink) and the ink can be case to form a catalyst layer. In one embodiment the catalyst ink comprises an electrocatalyst, metal oxide, a dispersant, and a fluorinated acid (defined as above). The catalyst ink may additionally comprise ion conducting polymer. The dispersant may be the same as or different from the liquid employed to suspend the nanoparticles in the metal oxide sol. The dispersant may comprise water and/or an organic solvent (e.g., an alcohol such as methanol, ethanol or propanol). The dispersant preferably comprises an organic solvent. The sols of the present invention are shown to have greater stability in organic solvents than conventional (e.g. nitrate stabilized) sols.
The electrocatalyst may comprise any metal or metal alloy known to have activity for an electrochemical reaction, such as a hydrogen oxidation reaction, oxygen reduction reaction, oxygen evolution reaction etc.
The metal or metal alloy comprises a primary metal suitably selected from
(i) the platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium),
(ii) gold or silver,
(iii) a base metal (e.g., tin, lead, zinc, copper).
The primary metal may be alloyed or mixed with one or more different metals selected from the above i.e. (i) the platinum group metals, (ii) gold or silver (iii) and a base metal or their oxides.
A base metal is tin or a transition metal which is not a precious metal. A precious metal metal is a platinum group metal (platinum, palladium, rhodium, ruthenium, iridium or osmium) or gold or silver. Suitable base metals are copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium and tin. Preferred base metals in the electrocatalyst include nickel, copper, cobalt, and chromium. More preferred base metals are nickel, cobalt and copper.
The primary metal is preferably platinum, which may be alloyed with other precious metals, such as ruthenium, or one or more base metals. The loading of the primary metal in the electrocatalyst material is suitably 10-70 wt%, more suitably 20-50 wt%, more suitably 20- 30 wt% based on the total weight of the electrocatalyst material (metal/metal alloy + support).
The resulting membrane or catalyst layer may comprise fluorinated acid as defined above (e.g. RSO3H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent or RCO2H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent) or traces thereof.
The catalyst layer may be prepared by a number of methods known to those skilled in the art, for example by preparation of an ink and applying the ink to a membrane, gas diffusion layer or transfer substrate by standard methods such as gravure coating, slot die (slot, extrusion) coating (whereby the coating is squeezed out under pressure via a slot onto the substrate), screen printing, rotary screen printing, inkjet printing, spraying, painting, bar coating, pad coating, gap coating techniques such as knife or doctor blade over roll (whereby the coating is applied to the substrate then passes through a split between the knife and a support roller), and metering rod application such as with a Meyer bar.
The thickness of the catalyst layer and loading of primary metal in the catalyst layer will depend on whether the catalyst layer is for use at the anode or cathode.
If for use at the anode:
- the catalyst layer is suitably > 1 pm; more suitably > 2 pm in thickness; preferably > 5 pm;
- the catalyst layer is suitably < 15 pm; more suitably < 10 pm in thickness;
- the loading of primary metal is suitably < 0.3 mg/cm2; suitably < 0.2 mg/cm2; more suitably < 0.15 mg/cm2;
- the loading of primary metal is suitably > 0.02 mg/cm2.
If for use at the cathode:
- the catalyst layer is suitably > 2pm; more suitably > 5 pm in thickness;
- the catalyst layer is suitably < 20 pm; more suitably < 15 pm in thickness;
- the loading of primary metal in the catalyst layer is < 0.4 mg/cm2;
- the loading of primary metal in the catalyst layer is > 0.05 mg/cm2.
The catalyst layer may also comprise additional components. Such components include, but are not limited to: a hydrophobic (a polymer such as PTFE or an inorganic solid with or without surface treatment) or a hydrophilic (a polymer or an inorganic solid, such as an oxide) additive to control water transport. In addition, the catalyst layer may also comprise a further catalytic material, which may or may not have the same function as the electrocatalyst material of the invention.
The invention further provides a gas diffusion electrode comprising a gas diffusion layer (GDL) and a catalyst layer as described above. Typical GDLs are suitably based on conventional non-woven carbon fibre gas diffusion substrates such as rigid sheet carbon fibre papers (e.g. the TGP-H series of carbon fibre papers available from Toray Industries Inc., Japan) or roll-good carbon fibre papers (e.g. the H2315 based series available from Freudenberg FCCT KG, Germany; the Sigracet® series available from SGL Technologies GmbH, Germany; the AvCarb® series available from Ballard Material Products, United States of America; or the NOS series available from CeTech Co., Ltd. Taiwan), or on woven carbon fibre cloth substrates (e.g. the SCCG series of carbon cloths available from the SAATI Group, S.p.A., Italy; or the WOS series available from CeTech Co., Ltd, Taiwan). For many PEMFC (including direct methanol fuel cell (DMFC)) applications the non-woven carbon fibre paper, or woven carbon fibre cloth substrates are typically modified with a hydrophobic polymer treatment and/or application of a microporous layer comprising particulate material either embedded within the substrate or coated onto the planar faces, or a combination of both to form the gas diffusion layer. The particulate material is typically a mixture of carbon black and a polymer such as polytetrafluoroethylene (PTFE). Suitably the GDLs are between 100 and 400pm thick. Preferably there is a layer of particulate material such as carbon black and PTFE on the face of the GDL that contacts the catalyst layer.
The invention further provides a catalyst coated ion-conducting membrane for a PEMFC/PEMWE comprising a membrane and a catalyst layer as defined above. The membrane may be any membrane suitable for use in a PEMFC, for example the membrane may be based on a perfluorinated sulphonic acid material such as Nation® (DuPont), Aquivion® (Solvay Plastics), Flemion® (Asahi Glass) and Aciplex® (Asahi Kasei); these membranes may be used unmodified, or may be modified to improve the high temperature performance, for example by incorporating an additive. Alternatively, the membrane may be based on a sulphonated hydrocarbon membrane such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others. The membrane may be a composite membrane, containing the proton-conducting material and other materials that confer properties such as mechanical strength. For example, the membrane may comprise an expanded PTFE substrate. Alternatively, the membrane may be based on polybenzimidazole doped with phosphoric acid and include membranes from developers such as BASF Fuel Cell GmbH, for example the Celtec®-P membrane which will operate in the range 120°C to 180°C. Brief description of the drawings
Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 DLS particle size distribution of CF3SO3 stabilized CeC>2 sol in H2O and EtOH; Figure 2 DLS particle size distribution of CF3SO3 stabilized CeC>2 sol in H2O and EtOH; Figure 3 DLS particle size distribution of nitrate stabilized Ce02 sol in H2O and EtOH (comparative example);
Figure 4 DLS particle size distribution of acetate stabilized Ce02 sol in H2O and EtOH (comparative example);
Figure 5 is a schematic diagram showing a sol comprising a mixture two types of metal oxide nanoparticles (5A), a sol comprising nanoparticles where each nanoparticle comprises two different metal oxides (5B); and a sol comprising mixed metal oxide nanoparticles (5C);
Figure 6 is a schematic diagram of a COM made using the metal oxide sol of the invention.
Preparation of cerium oxide wet cake A.
To 251.88 g of ceric nitrate solution (337 gCeO2/l equivalent) was added dropwise 32 cm3 of 0.88 NH3 solution with stirring. On addition, yellow precipitate (ppt) formed but quickly redissolved on stirring. On the final addition, the solution was stirred until it gave a clear orange solution.
The solution was added to 85 cm3 0.88 NH3 diluted to 360 cm3 with demineralised (demin.) H2O via peristaltic pump over 12 mins. This gave a pale brown precipitate. This was stirred for 30 mins and filtered. The wet cake was washed with demin. H2O until filtrate conductivity was 14 .S. Yield of wet cake = 174.56 g. The wet cake was allowed to air dry at ambient temperature for 4 days to give 117.36 g of wet cake. Oxide content = 44.3 wt%.
Example 1 CeO2 sol stabilized by CF3SO3H (TFMS)
To 22.57 g (9.99 g CeO2) of CeO2 wet cake A (44.3% CeO2 oxide content) was added c. 2.3 ml of CF3SO3H (measured via measuring cylinder rather than weight due to the fuming nature of the acid) [CF3SO3:Ce ~ 0.41*] and stirred manually. This formed a fluid paste, which was then heated and stirred to c. 90 °C for 30 mins to give a yellow near transparent dispersion with a pale yellow froth that subsided over time. *The ratio is a mole ratio. The CeC>2 (molar mass = 172 gmol-1) content is calculated from them wet cake solids content i.e. 9.99/172 = 0.058 mols. The TFMS (molar mass = 150 gmol-1) amount is calculated from the volume and density i.e. 2.3*1.7 divided by the mol wt (150) = 0.026 mols. Hence the ratio of 0.0261 0.058 = 0.45.
The resulting sol was centrifuged for 5 mins (4000 rpm) which gave a clear sol supernatant and a very small amount of off-white residue, which was discarded.
Solids of the sol were determined (using 1.0 cm3 sol) by calcination in air (900°C, 2 hrs). Oxide content of the sol was determined to be 641 gCeO2/l equivalent and the sol had a density of 1.76 g cm-3.
The CeO2 particle size of the sol was determined using Dynamic Light Scattering (Malvern Zetasizer). The z-average was found to be 53 nm with a broad distribution from 11 to 490 nm (see Fig 1 (TFMS - CeO2 in H2O).
A portion of the H2O based CeO2 sol was added to EtOH to give a transparent yellow sol which appeared stable over time. The particle size of this dispersion was also measured using DLS (see Fig 1 , TFMS - CeC>2 in EtOH). The CeO2 z-average particle size was found to be 22 nm with a much narrower distribution indicating the CeO2 nanoparticles was better stabilized in EtOH than H2O.
Example 2 CeO2 sol stabilized by CF3CO2H (fluoroacetic acid)
To 22.58g CeO2 wet cake A (10.00g CeO2) was added 2.74g CF3CO2H (CF3CO2H:Ce = 0.41) with a small amount of H2O (few cm3) to give a fluid paste. This was magnetically stirred and heated. The paste stiffened which didn't thin on heating. Further H2O was added (c. 2 ml) to make a more fluid paste. On heating to c. 90°C a yellow slurry formed with surface foam. After 60 mins, the slurry was cooled and centrifuged (4000 rpm, 15 mins) to give a yellow solid and clear supernatant. The supernatant was discarded and yellow assessed for dispersibility in H2O and EtOH.
The solid dispersed easily in EtOH to give a clear yellow sol, while the solid dispersed with more difficulty in H2O to give a translucent yellow sol. Maximum concentration in H2O was found to 50 gCeO2/l, while in EtOH it was above 75 gCeO2/l. The resulting sols were assessed using DLS (see Figure 2).
In H2O the fluoroacetic acid stabilised sol showed a z-average particle size of 22 nm with a range between 5 and 200 nm.
In EtOH the fluoroacetic acid stabilised sol showed a z-average of 24 nm with a range between 3 and 170 nm.
Preparation of cerium oxide wet cake B (smaller particle size)
159.32g of (NH4)2[Ce(NOs)6] (0.29M) was dissolved in 300 cm3 H2O (0.97 M solution). This was added via peristaltic pump over 15 mins to 80 ml 0.88 NH3 solution diluted to c. 400 cm3. This gave a pale yellow precipitate. On full addition the slurry was stirred for 2 hrs and then filtered and washed with demineralised H2O until filtrate conductivity was 28 pS. Yield of wet cake = 207.18 g. The wet cake was dried at ambient for 5 days after which the yield was 118.60 g with an oxide content of 42.8 wt%.
Example 3 CeO2 sol stabilized by CF3SO3H (TFMS)
To 23.31g of ceria hydrate wet cake B (9.98g CeO2) (prepared as described in Example 5) was added 2.6 cm3 CF3SO3H (CF3SO3:Ce = 0.51) and mixed to give a fluid yellow paste (total slurry volume c. 20 cm3). This was magnetically stirred and heated to 85°C. The slurry turned firstly into an opaque yellow and with further heating to a transparent yellow sol. This was kept at c. 85°C for 3hrs and then cooled. Oxide content was 690 gCeO2/l and density = 1.78 gem-3.
The sol particle size in H2O and EtOH was measured using DLS. The z-average particle size in H2O was found to be 6.4 nm with a range of 1 .8 to 40 nm. The z-average particle size in EtOH was found to be 7.8 nm with a range of 3.4 to 24 nm.
Preparation of cerium wet cake C
To 290 cm3 0.88 NH3 solution diluted to 1 .3 I with demineralised H2O was added 685.1 g of ceric nitrate solution (337 gCeO2/l equivalent) via peristaltic pump over 19 mins. The resulting precipitate was stirred for 30 mins and filtered. The wet cake was washed with demineralised H2O until filtrate conductivity was 50 pS. Yield of wet cake = 534.2 g. The ceria hydrate wet cake was allowed to air dry at ambient temperature for 4 days to give 467.3 g of solid. Oxide content = 29.3 wt%.
Comparative Example 1 - Nitrate stabilized Ce02 sol
To 467.3 of the ceria hydrate wet cake C was added 42.9 g of concentrated HNO3, together with 20 cm3 of H2O. This was mixed to give a thick paste and then heated at 90°C with stirring for 2 hrs. On cooling this gave a pale yellow solid and bright yellow supernatant. The slurry was filtered and the supernatant discarded. To the solid was added 200 cm3 of H2O and mixed to give a yellow CeO2 sol. Solid content was 514 gl’1 and density = 1.49 g cm-3. The particle size of the sol was measured using DLS. This gave a z-average particle size of 9.5 nm with a range of 1.8 to 60 nm.
On adding the sol to EtOH immediate flocculation was observed with aggregated CeO2 particles separating from the solvent over a few minutes. DLS was not able to observe any CeO2 particles below 1000 nm.
It is clear that the nitrate stabilized CeO2 sol of Comparative Example 1 is not stable in EtOH and unsuitable for application where good dispersibility is required in EtOH.
Comparative Example 2 - Small particle size nitrate stabilized CeO2 sol
To 23.35g of ceria hydrate wet cake C (9.99 g CeO2) (as prepared above) was added 2.10g cone HNO3 (NOs:Ce = 0.40) and manually stirred to form a fluid slurry. This slurry for heated to c. 90°C for 30 mins to form a bright yellow sol (total volume = 14 ml). Solid content was 674 gCeO2/l with a density = 1.63 gem-3. Particle size of the sol was measured using DLS. This gave a z-average = 6.8 nm with a range of 1.2 to 32 nm.
The stability of the sol in EtOH was assessed using DLS, shown in figure 3. On the initial addition of the sol to EtOH, a homogeneous dispersion was formed. However, over 10 mins flocculation was observed with separation of CeO2 particles from the solvent. This was tracked using successive DLS experiments. Compared to the particle size distribution observed in H2O, run 1 shows the growth of the CeO2 particle size to show a broad distribution between 15 and 5500 nm. Further particle growth is observed in runs 2 and 3 with particle size distributions being 1600 - 5500 and 2600 - 5500 nm respectively. Compared to Comparative Example 1 , the smaller particle size nitrate stabilized CeC>2 sol shows better transient stability in EtOH. However, over a period of minutes, flocculation is observed leading to CeC>2 particle separation.
Comparative Example 3 - Acetate stabilized CeC>2 sol
To 23.38 g of ceria hydrate wet cake A (10.03 g CeC>2) (prepared as described above) was added 5.5 ml of glacial acetic acid diluted to 11 ml with H2O (OAc:Ce = 1 .61). This was stirred manually to break up the cake and give a slurry capable of being magnetically stirred and heated. After 60 mins, the slurry was cooled and centrifuged (4000 rpm, 20 mins). This gave some separation but still with significant solids in the supernatant. Further glacial acetic acid (2 ml) was added and left overnight. No significant extra solid separation was observed, and the slurry was filtered. This gave a clear filtrate and a paste-like filter cake. The cake was redispersed in c 50 ml H2O, mixed and centrifuged (4000 rpm, 10 mins). A small amount of solid was separated and discarded to give a stable CeC>2 sol. Solid content was determined to be 181 g I’1 with a density of 1.18 g cm-3.
Particle size was determined in H2O and EtOH using DLS (figure 4). In H2O, z-average = 84 nm with a range of 13 to 310 nm, while in EtOH, z-average = 100 nm with a range of 38 to 360 nm.
The acetate stabilized CeO2 sol was equally stable in H2O and EtOH with very similar particle size distributions. However, compared to the trifluoromethanesulphonic acid and trifluoroacetic acid stabilized sols the CeO2 particle sizes are significantly larger.
Summary of results
Figure imgf000023_0001
Figure imgf000024_0001
The inventors have recognised that conventional nitrate stabilized metal oxide sols are unstable in EtOH and they have developed a new sol that is stable in H2O and EtOH. The new sol can be employed in a range of applications.
The composition may be employed in the preparation of a membrane electrode assembly (MEA) in order to incorporate metal oxide (e.g. ceria or manganese oxide) as a hydrogen peroxide decomposition catalyst. The sol may be employed in the manufacture of an ionconducting membrane; and/or a catalyst layer to form a catalyst-coated membrane (CCM).
Figure 6 shows a schematic cross-section (not to scale) of a catalyst-coated membrane 500 produced using the sol of the present invention. The catalyst-coated ion-conducting membrane 500 comprises a first catalyst layer 510, a second catalyst 520 layer and an ionconducting membrane 530 disposed between the first and second catalyst layers 510, 520. The first catalyst layer 510 is on a first face of the ion-conducting membrane 530. The second catalyst layer 520 is on a second face of the ion-conducting membrane 530. In one embodiment, the first catalyst layer 510 is a cathode catalyst layer, and the second catalyst layer 520 is an anode catalyst layer. In an alternative embodiment, the first and second catalyst layers 510, 520 are an anode catalyst layer and a cathode catalyst layer respectively.
Hence, metal oxide (e.g. zirconia and/or ceria may be present in the first catalyst layer 510, the second catalyst layer 520 and/or the ion-conducting membrane 530.
The catalyst-coated ion-conducting membrane 500 can be used in electrochemical devices, such as fuel cells and water electrolysers.

Claims

Claims
1. A composition comprising nanoparticles suspended in a liquid, the nanoparticles comprising metal oxide and the composition additionally comprising stabilizer ions, wherein the stabilizer ions comprise the anions of a fluorinated acid.
2. The composition of claim 1 , wherein the fluorinated acid comprises from one to five fluorine atoms.
3. The composition of claim 1 or claim 2, wherein the liquid comprises an organic solvent.
4. The composition of any one of the preceding claims, wherein the fluorinated acid is a fluorinated organic acid, and optionally has a molar mass of 300gmol-1 or less.
5. The composition of claim 4, wherein the fluorinated acid is a fluorinated sulphonic acid having the general formula RSO3H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent.
6. The composition of claim 5, wherein the fluorinated sulphonic acid is trifluoromethanesulfonic acid (TFMS, CF3SO3H) thereby providing CF3SO3" stabilizer ions.
7. The composition of any one of claims 1 to 4, wherein the fluorinated acid is a fluorinated carboxylic acid having the general formula RCO2H where R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent.
8. The composition of claim 7, wherein the fluorinated carboxylic acid is trifluoroacetic acid (CF3CO2H), thereby providing CF3CO2" stabilizer ions.
9. The composition of any one of the preceding claims, comprising at least 100g metal oxide per litre.
10. The composition of any one of the preceding claims, wherein the molar ratio of anions of the fluorinated acid : metal oxide is from 0.3 to 0.9.
11. The composition of any one of the preceding claims, wherein the anions of the fluorinated acid comprise RSO3" or RCO2", wherein R is an alkyl or aryl group having from one to ten carbon atoms and at least one fluorine substituent.
12. The composition of any one of the preceding claims, wherein the liquid comprises an organic solvent selected from an alcohol, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, t-butanol, n-pentanol, and n-hexanol; a ketone, such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, t-butyl acetate, amyl acetate, methyl lactate, ethyl lactate, n-propyl lactate, isopropyl lactate, n-butyl lactate, and methoxypropyl acetate; glycols such as ethylene glycol, propylene glycol, glycerin, and diethylene glycol; glycol ethers such as methoxypropanol, ethylene glycol dimethyl ether, ethylene glycol diethylether, diethyleneglycol dimethylether, and diethylene glycol diethylether; and amides, as well as mixtures of two or more of the foregoing.
13. The composition of any one of the preceding claims, wherein the metal oxide comprises an oxide of Al, Ce, Nb,Ta, or Zr, or a mixture thereof.
14. The composition of any one of the preceding claims, wherein the metal oxide comprises an oxide of V, Co, Fe, Cr, Mn, Cu, V, Ru, Pd, Ni, Mo, Sn, or and W or a mixture thereof.
15. The composition of any one of the preceding claims, wherein the metal oxide is cerium oxide.
16. The composition of any one of the preceding claims, wherein the nanoparticles comprise (i) cerium oxide and zirconium oxide; (ii) cerium oxide and niobium oxide; (iii) or (iii) cerium oxide and aluminium oxide.
17. The composition of any one of the preceding claims, additionally comprising (i) an ion-conducting polymer; and/or (ii) an electrocatalyst.
18. A process for preparing the composition of any one of claims 1 to 16, the process comprising reacting metal hydroxide with an acid, wherein the acid comprises a fluorinated acid.
19. The process of claim 18, comprising: reacting an aqueous solution of a metal salt with a base to form a precipitate; and peptising the precipitate with an acid to form a sol, wherein the acid is a fluorinated acid.
20. The process of claim 19, wherein the metal salt is a cerium salt, optionally wherein the cerium salt is a cerium nitrate, such as ceric ammonium nitrate (CAN) [(NH4)2[Ce(NO3)6].
21. A process for producing an ion-conducting membrane comprising a metal oxidecontaining membrane layer, the process comprising mixing the composition of any one of claims 1 to 16 with an ion-conducting polymer to form an ink; and fabricating the membrane layer from the ink, optionally wherein fabricating the membrane layer from the ink comprises depositing the ink onto a substate, such as a backing sheet, an ion-conducting polymer layer, or a catalyst layer on a backing sheet.
22 An ion-conducting membrane for an electrochemical device, such as a fuel cell or a water electrolyser, wherein the ion-conducting membrane is produced by the process of claim 21 or using the composition according to claim 17.
23. A process for producing a catalyst layer comprising a metal oxide-containing catalyst layer, the process comprising mixing the composition of any one of claims 1 to 16 with an electrocatalyst to form an ink; and fabricating the catalyst layer from the ink, optionally wherein fabricating the catalyst layer from the ink comprises depositing the ink onto a substate, such as a backing sheet, an ionconducting polymer layer, or a catalyst layer on a backing sheet.
24. A catalyst layer for an electrochemical device, such as a fuel cell or a water electrolyser, wherein the catalyst layer is produced by the process of claim 23 or using the composition according to claim 17.
25. An ion-conducting membrane for an electrochemical device, such as a fuel cell or a water electrolyser, the ion conducting membrane comprising metal oxide, optionally cerium oxide, and a fluorinated acid, wherein the fluorinated acid comprises from one to five fluorine atoms.
26. A catalyst layer for an electrochemical device, such as a fuel cell or a water electrolyser, the catalyst layer comprising an electrocatalyst, metal oxide, optionally cerium oxide, and a fluorinated acid, wherein the fluorinated acid comprises from one to five fluorine atoms.
27. A gas diffusion electrode comprising a gas diffusion layer and one or more of: the ion conducting membrane of claim 22, the catalyst layer of claim 24, the ion conducting membrane of claim 25, and the catalyst layer of claim 26.
28. A catalysed membrane comprising an ion-conducting membrane and a catalyst layer as claimed in claim 24 or 26.
29. A membrane electrode assembly comprising an ion-conducting membrane as claimed in claim 22 or 25, a catalyst layer as claimed in claim 24 or 26, a gas diffusion electrode as claimed in claim 27, or a catalysed membrane as claimed in claim 28.
30. A fuel cell or electrolyser comprising an ion-conducting membrane as claimed in claim 22 or 25, a catalyst layer as claimed in claim 24 or 26, a gas diffusion electrode as claimed in claim 27, a catalysed membrane as claimed in claim 28, or a membrane electrode assembly as claimed in claim 29.
PCT/GB2023/052765 2022-10-24 2023-10-23 Metal oxide sol WO2024089403A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GBGB2215718.4A GB202215718D0 (en) 2022-10-24 2022-10-24 Cerium oxide sol
GB2215718.4 2022-10-24
GB2215716.8 2022-10-24
GBGB2215716.8A GB202215716D0 (en) 2022-10-24 2022-10-24 Metal oxide sol

Publications (1)

Publication Number Publication Date
WO2024089403A1 true WO2024089403A1 (en) 2024-05-02

Family

ID=88695367

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2023/052765 WO2024089403A1 (en) 2022-10-24 2023-10-23 Metal oxide sol

Country Status (1)

Country Link
WO (1) WO2024089403A1 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5132048A (en) 1989-12-15 1992-07-21 Rhone-Poulenc Chimie Weakly acidic colloidal dispersions of cerium (iv) compounds
WO2005123594A2 (en) 2004-06-21 2005-12-29 Johnson Matthey Public Limited Company Sols comprising mixed transitional metal oxide nanoparticles
US20150230737A1 (en) * 2012-09-21 2015-08-20 Abbott Diabetes Care Inc. In Vivo Sensors Having Ceria Nanoparticle Electrodes
CN113230988A (en) * 2021-05-28 2021-08-10 扬州大学 Preparation method of coating sol

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5132048A (en) 1989-12-15 1992-07-21 Rhone-Poulenc Chimie Weakly acidic colloidal dispersions of cerium (iv) compounds
WO2005123594A2 (en) 2004-06-21 2005-12-29 Johnson Matthey Public Limited Company Sols comprising mixed transitional metal oxide nanoparticles
US20150230737A1 (en) * 2012-09-21 2015-08-20 Abbott Diabetes Care Inc. In Vivo Sensors Having Ceria Nanoparticle Electrodes
CN113230988A (en) * 2021-05-28 2021-08-10 扬州大学 Preparation method of coating sol

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CAYADO P ET AL: "Epitaxial YBaCuO nanocomposite thin films from colloidal solutions", SUPERCONDUCTOR SCIENCE AND TECHNOLOGY, IOP PUBLISHING, TECHNO HOUSE, BRISTOL, GB, vol. 28, no. 12, 16 November 2015 (2015-11-16), pages 124007, XP020292739, ISSN: 0953-2048, [retrieved on 20151116], DOI: 10.1088/0953-2048/28/12/124007 *

Similar Documents

Publication Publication Date Title
US20150236354A1 (en) COLLOIDAL DISPERSIONS COMPRISING PRECIOUS METAL PARTICLES AND ACIDIC lONOMER COMPONENTS AND METHODS OF THEIR MANUFACTURE AND USE
JP5332429B2 (en) Electrocatalyst
Bharti et al. Surfactant assisted synthesis of Pt-Pd/MWCNT and evaluation as cathode catalyst for proton exchange membrane fuel cell
WO2014002756A1 (en) Ion conductor, and electrochemical device using same
KR102225982B1 (en) Catalyst
CN108475791B (en) Catalyst and process for preparing same
KR102039332B1 (en) Fuel cell electrode catalyst layer, production method therefor, membrane electrode assembly, and solid polymer fuel cell
WO2017183475A1 (en) Electrocatalyst, membrane electrode assembly using said electrocatalyst, and fuel cell
JP2002246033A (en) Electrode, electrode composition, fuel cell using the same and electrode producing method
US11124885B2 (en) Anode catalyst suitable for use in an electrolyzer
US20220181643A1 (en) Catalyst for a fuel cell
Kim et al. Synthesis and electrochemical properties of nano-composite IrO2/TiO2 anode catalyst for SPE electrolysis cell
JP2013176717A (en) Metal oxide catalyst and method of manufacturing the same, and fuel cell using the same
JP5400924B2 (en) Method for producing gold-supported carbon catalyst
CN116600892A (en) Iridium-containing oxide, method for producing same, and catalyst containing iridium-containing oxide
US20230105398A1 (en) Electrode catalyst layer for electrochemical cells, membrane electrode assembly for electrochemical cells, and electrochemical cell
JP3824487B2 (en) Catalyst production method
US11069903B2 (en) Metal particle supported catalysts, methods for producing same, and fuel cells using same
WO2024089403A1 (en) Metal oxide sol
JP2007087827A (en) Electrode catalyst and its manufacturing method
CN117652042A (en) Oxygen evolution reaction catalyst
JP2010075857A (en) Metal-supported porous body, method of manufacturing the same, and catalyst for fuel cell electrode containing metal-supported porous body
WO2023095858A1 (en) Oxygen evolution reaction catalyst and method for producing same
US20230304175A1 (en) Catalyst for an electrochemical cell, and methods of making and using the catalyst
CN117581403A (en) Oxygen evolution reaction catalyst

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 23800937

Country of ref document: EP

Kind code of ref document: A1