CeO2 as a radical scavenger supported on SiO2

Abstract

Cerium oxide (CeO2) coated silica (SiO2) particles optionally containing the inorganic group -SO2X and a method for the production of such particles. The addition of said cerium oxide (CeO2) coated silica (SiO2) particles to fluorinated polymers containing sulfonic acid functional groups increases their stability against radical decomposition when used in fuel cell or electrolysis applications.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. 22306930.3, filed December 19, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to cerium oxide (CeO2)-coated silica (SiO2) particles that can improve the resistance to radical decomposition of ion-exchange fluorinated polymer membranes used in fuel cell applications. The present invention further relates to compositions comprising cerium oxide-coated silica particles and ion-exchange fluorinated polymers, and ion-exchange membranes obtained therefrom. The present invention finally relates to a method for the preparation of CeO2 supported on SiO2. [Background technology]

[0003] Due to their ion-conducting properties, fluorinated polymers containing sulfonic acid ion-exchange groups are widely used to fabricate electrolyte membranes for electrochemical devices such as electrolysis cells and fuel cells, notable examples being proton exchange membrane (PEM) fuel cells, which use hydrogen as fuel and oxygen or air as the oxidant.

[0004] In a typical PEM fuel cell, hydrogen is introduced into the anode compartment, where it reacts and separates into protons and electrons. A membrane transports the protons to the cathode compartment, while allowing the electrons to flow through an external circuit to the cathode compartment to provide electrical power. Oxygen is introduced into the cathode compartment and reacts with the protons and electrons to produce water and heat.

[0005] The membrane must have excellent ionic conductivity, gas barrier properties (to prevent direct mixing of hydrogen and oxygen), mechanical strength, and chemical, electrochemical, and thermal stability under the operating conditions of the fuel cell. Long-term membrane stability is a key requirement. The lifetime target for stationary fuel cell applications is up to 40,000 hours of operation, while 20,000 hours of operation is required for automotive fuel cell applications.

[0006] Similar properties are required for proton exchange membranes for use in water electrolysis. In fact, in an electrolysis cell, water is introduced and the anode is charged with O2 and H + and is oxidized to H at the cathode. + is further reduced to H2, which is then recovered.

[0007] Hydrogen peroxide radicals (H2O2) generated during the operation of fuel cells or electrolysis cells · OH, · Attack of proton exchange membranes by hydrogen peroxide (OOH) is often cited as one of the causes of membrane degradation. Radical degradation of membranes is responsible for the reduced service life of fuel cells or electrolysis cells. It is generally believed that, among other mechanisms, hydrogen peroxide is generated as a result of the reaction between hydrogen and oxygen passing through the membrane. Hydrogen peroxide then decomposes to generate peroxy and hydroperoxy radicals. See, for example, Schlick, S., et al., "Degradation of fuel cell membranes using ESR methods: ex situ and in situ experiments." Polymer Preprints. 2009, vol. 50, no. 2, pp. 745-746. Direct generation of radicals is also considered possible.

[0008] For example, some attempts have been made to reduce the radical decomposition of fluorinated proton exchange membranes by incorporating salts or oxides of appropriate metals into the membrane. The use of salts of various metals, including rare earth metals, Al and Mn, to enhance the stability of ion exchange membranes for use in fuel cells is disclosed, inter alia, in EP 1702378A (BDF IP HOLDINGS LTD) (September 20, 2006) and EP 1662595A (Toyota Central R&D Labs) (May 31, 2006).

[0009] U.S. Patent Application Publication No. 20070213209 (EIDU PONT DE NEMOURS) / (September 13, 2007) discloses a compound for decomposing hydrogen peroxide in a fuel cell membrane electrode assembly, comprising a metal oxide selected from the group consisting of alumina, silica, titanium oxide, zirconium oxide, manganese dioxide, Y2O3, Fe2O3, FeO, tin oxide, copper oxide, nickel oxide, tungsten oxide, germanium oxide, and cerium oxide; a stabilizer selected from the group consisting of metal ions and metalloid ions (e.g., boron); and at least one catalyst, different from the stabilizer, selected from the group consisting of cerium and ruthenium. The compound disclosed in U.S. Patent Application Publication No. 20070213209 is prepared by adsorbing the catalyst onto a metal oxide previously modified with a stabilizer. The catalyst particles are therefore not incorporated into the crystal lattice of the metal oxide and can therefore leach into and then out of the membrane during fuel cell operation.

[0010] ZHAO, D., et al., "MnO2 / SiO2-SO3H nanocomposite as a hydrogen peroxide scavenger for durability improvement in proton exchange membranes." J. Membrane Science. 2010, vol. 346, pp. 143-151, discloses nanosized mixed MnO2 / SiO2 oxides with organic sulfonic acid groups grafted onto their surfaces. These compounds are prepared by depositing SiO2 on the surface of nanosized MnO2SiO and subsequently reacting the surface hydroxyl groups of SiO2 with an appropriate organic sulfonating agent, such as a cyclic sultonic acid ester. In the mixed MnO2 / SiO2 oxides disclosed by Zhao et al., MnO2 is only physically bound to SiO2, which may lead to the reduction of Mn(IV) to Mn(II) during fuel cell operation and, given the higher solubility of the Mn(II) species, their subsequent removal.

[0011] GILL, CS, et al., Sulfonic acid-functionalized silica-coated magnetic nanoparticle catalysts. J. Catalysis. 2007, vol. 251, pp. 145-152, discloses a hybrid organic / inorganic catalyst comprising an organic sulfonic acid grafted onto a silica-coated magnetic nanoparticle support.

[0012] In both of the above systems, the organic hydrogenated moieties anchor the -SO3H groups to the SiO2 surface. The presence of these hydrogenated organic sites in the inorganic oxide is believed to make the system less suitable for use in fuel cells, as it may provide an additional source of radical generation or decomposition at the membrane under the highly oxidizing operating conditions of the fuel cell.

[0013] WO 2014 / 009334 (Solvay Specialty Polymers Italy SpA) discloses that the addition of a specific mixed oxide of Si and at least one metal M to a fluorinated polymer containing sulfonic acid functional groups improves the stability of the proton exchange membrane produced therefrom against radical decomposition. However, because this mixed oxide generally has a Si / M weight ratio in the range of 1 to 40, i.e., because it contains a high to very high amount of SiO2, it contains almost no Ce species that are involved in preventing radical decomposition. Furthermore, the process disclosed therein involves a high-temperature pickling step that raises safety concerns and increases costs.

[0014] U.S. Patent No. 4,360,388 (Degussa Aktiengesellschaft) discloses compositions based on cerium-containing precipitated silica and diorganopolysiloxanes containing cerium-containing precipitated silica that are curable with elastomers. The cerium-containing precipitated silica is also disclosed as a flame retardant. The cerium-containing precipitated silica has a maximum viscosity of 140±40 m as measured by BET according to DIN 66 131. 2 / g. No mention is made of the size of the ceria crystallites. The method disclosed in U.S. Pat. No. 4,360,388 requires an aqueous solution of cerium (IV), such as Ce(SO4)2, 4H2O.

[0015] JP 10-230162 A (Daikin Industries, Ltd.) describes a ceria nanocrystal with a size of 4 nm or less as measured by half-width XRD and an overall specific surface area of ​​200 m2 as measured by BET using nitrogen adsorption. 2The publication discloses a ceria catalyst supported on silica with a pH exceeding 1.5 / g. No mention is made of the use of such materials to enhance the stability of proton exchange membranes against radical decomposition. The method disclosed in JP 10-230162 is carried out at a pH not exceeding 6.5 and requires the use of sodium hydroxide, sodium carbonate, or potassium hydroxide. The use of such bases may result in the presence of sodium or potassium salts in the final product. Summary of the Invention

[0016] In this study, the Ce content was 10% to 70% by weight based on the total weight of the particles, and the BET measurement value was 80m. 2 / g~220m 2 It has been found that the addition of cerium oxide (CeO2)-coated silica (SiO2) particles, which exhibit a specific surface area in the range of 1 / g and contain CeO2 crystallites with sizes in the range of 5.0 nm to 10.0 nm as measured by XRD, to a fluorinated polymer containing sulfonic acid functional groups increases the stability against radical decomposition of proton exchange membranes produced therefrom without the constraints of the prior art. The increased stability is reflected in longer membrane lifetimes when used in fuel cells.

[0017] With respect to the prior art, it has been found that a higher Ce content in the cerium oxide (CeO2)-coated silica (SiO2) particles according to the present invention, combined with a higher specific surface area and a well-defined cerium oxide crystallite size, improves the stability against radical decomposition of proton exchange membranes made from fluorinated polymers containing sulfonic acid functional groups.

[0018] Therefore, the first object of the present invention is to provide a ceramic material containing 10% by weight to 70% by weight of Ce element based on the total weight of the particles, and having a purity of 80m measured by the BET method. 2 / g~220m 2The cerium oxide (CeO2)-coated silica (SiO2) particles exhibit a specific surface area in the range of 1 / g and contain CeO2 crystallites having a size in the range of 5.0 nm to 10.0 nm as measured by XRD. The (CeO2)-coated silica (SiO2) particles may optionally contain inorganic -SO2OZ functional groups (where Z is selected from the group consisting of H, alkali metals, and NH4).

[0019] A second object of the present invention is a liquid composition (LC1) containing the cerium oxide coated silica particles of the first object dispersed in a liquid medium (L1).

[0020] A third object of the present invention is to provide a method A for producing cerium oxide-coated silica particles according to the first object, comprising: a) preparing an aqueous suspension (S1) containing SiO2 and setting the pH value of the suspension to 7-11 by adding an aqueous ammonia (NH3) solution; b) adding an aqueous solution of Ce(NO3)3 to the suspension (S1) under stirring while maintaining the pH value at 7 to 11 by adding an aqueous ammonia solution to obtain a slurry containing cerium hydroxide precipitated on SiO2; c) filtering the slurry obtained in step b) to recover the cerium hydroxide precipitated on the SiO2 in solid form; d) calcining the solid obtained in step c) in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain cerium oxide (CeO2)-coated silica (SiO2) in particulate form; e) optionally milling the recovered particles of step d) to obtain a desired particle size. Method A includes:

[0021] A fourth object of the present invention is to provide a method A' for producing cerium oxide coated silica particles according to the first object, comprising: a') preparing an aqueous ammonia solution (E) having a pH value set at 7 to 11; b') adding an aqueous suspension (S2) containing SiO2 suspended in a Ce(NO3)3 aqueous solution to the aqueous solution (E) under stirring while maintaining the pH value at 7 to 11 by adding an aqueous ammonia solution (E') to obtain a slurry containing cerium hydroxide precipitated on SiO2; c') filtering the slurry obtained in step b') to recover the cerium hydroxide precipitated on the SiO2 in solid form; d') calcining the solid obtained in step c') in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain cerium oxide (CeO2)-coated silica (SiO2) in particulate form; e') optionally milling the recovered particles of step d') to obtain a desired particle size. and Method A', which comprises:

[0022] A fifth object of the present invention is to provide a method B for producing cerium oxide (CeO2)-coated silica (SiO2) particles according to the first object, comprising: a″) providing an aqueous suspension (S3) containing SiO2, ammonia (NH3) and optionally at least one source of inorganic groups —SO2OZ; b'') adding an aqueous Ce(NO3)3 solution to the suspension (S3) under stirring in an amount such that the molar ratio of NH3 prepared in step a'') to elemental Ce is in the range of 2 to 4, to obtain a slurry containing cerium hydroxide precipitated on SiO2; c'') filtering the slurry to recover the cerium hydroxide Ce(OH)3 precipitated on SiO2 in solid form; d'') calcining the obtained solid in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain cerium oxide (CeO2)-coated silica (SiO2) in particulate form; e'') optionally milling the recovered particles of step d'') to obtain the desired particle size. and Method B, which includes:

[0023] The advantage of setting or adjusting the pH value with ammonia as described in Methods A, A' and B of the present invention, rather than with NaOH or KOH, is that there are no residual salts in the final product. Indeed, the presence of sodium or potassium salts can impair the efficiency and stability of polymer membranes when the cerium oxide-coated silica particles according to the present invention are used in fuel cell applications.

[0024] In fact, without being bound by any theory, if some ammonia remains in the product after step c), c'), or c''), respectively, before calcination, the ammonia is easily removed from the target product during the calcination carried out in step d), d'), or d''), respectively.

[0025] Therefore, the advantage of adjusting the pH value with ammonia is that it simplifies the process, as the salt does not need to be washed off before the final product is recovered.

[0026] Similarly, the advantage of using Ce(NO3)3 as a raw material is that if any nitrogen oxide (NO)3 remains in the product before calcination after each of steps c), c'), or c''), it can be easily removed from the target product during the calcination performed in steps d), d'), or d''), respectively. x ) and CeO2.

[0027] A sixth object of the present invention is a composition (C) containing at least one fluorinated polymer containing -SO2X functional groups, where X is selected from X' or OZ, X' is selected from the group consisting of F, Cl, Br, I, and Z is selected from the group consisting of H, alkali metals, NH4, and particles of the first object.

[0028] Another object of the invention is a liquid composition (LC) comprising composition (C).

[0029] Yet another object is a process for preparing the composition (C) or (LC).

[0030] A further object of the present invention is an article, in particular a membrane or an electrocatalytic layer, comprising at least one fluorinated polymer containing -SO2X functional groups and cerium oxide (CeO2)-coated silica (SiO2) particles as defined above.

[0031] Finally, another object is a fuel cell or electrolysis cell comprising an article according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The first object of the present invention is to provide a ceramic material containing 10% by weight to 70% by weight of Ce element based on the total weight of the particles, and having a purity of 80m as measured by BET. 2 / g~220m 2 / g and containing CeO2 crystallites with sizes ranging from 5.0 nm to 10.0 nm as measured by XRD.

[0033] The cerium oxide (CeO2)-coated silica (SiO2) particles optionally contain inorganic -S02OZ functional groups (Z is selected from the group consisting of H, alkali metals, and NH4). The term "inorganic group -S02H" is used herein with respect to the cerium oxide (CeO2)-coated silica (SiO2) particles to indicate that the -S02OZ groups present in the cerium oxide-coated silica particles are not bonded to organic moieties, and the expression "organic moiety" refers to any moiety containing at least one carbon atom. All -S02OZ groups in the cerium oxide-coated silica particles are inorganic groups -S02OZ.

[0034] Without being bound by theory, it is believed that the -SO2OZ group is bonded to the surface of the cerium oxide-coated silica particle via a sulfur atom. The -SO2OZ group is bonded to at least one Si, Ce, or oxygen atom via a sulfur atom. Typically, the -SO2OZ group is bonded to at least a portion of metallic Ce via a sulfur atom.

[0035] The cerium oxide (CeO2)-coated silica (SiO2) particles according to the present invention comprise 10 wt% to 70 wt% elemental Ce, based on the total weight of the particles. In some embodiments, the cerium oxide-coated silica particles comprise 40 wt% to 70 wt%, or even 40 wt% to 65 wt%, elemental Ce. In some other embodiments, the cerium oxide-coated silica particles comprise 50 wt% elemental Ce. In yet some other embodiments, the cerium oxide-coated silica particles comprise 10 wt% to 45 wt%, or even 10 wt% to 40 wt% elemental Ce.

[0036] The theoretical Ce content is set prior to particle production by using appropriate amounts of raw materials. This content can be confirmed after synthesis by using ICP-OES analysis performed on cerium oxide coated silica particles according to the present invention. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was performed on mineralized samples prepared by methods well known to those skilled in the art.

[0037] When present, the amount of inorganic groups -SO2OZ in the cerium oxide-coated silica particles is usually at least 0.2%, typically at least 0.5%, of the total amount of Ce atoms. The amount of inorganic groups -SO2OZ in the cerium oxide-coated silica particles can be up to 50% of the total amount of Ce atoms. The inorganic groups -SO2OZ may be bonded to Ce, Si, or oxygen atoms in the cerium oxide (CeO2)-coated silica (SiO2) particles.

[0038] The amount of inorganic group -SO2OZ in the cerium oxide coated silica particles can be determined by ICP-OES measurement of S content, which is commonly known to those skilled in the art.

[0039] Preferably, the cerium oxide coated silica particles do not contain any organic moieties, ie, any moieties containing at least one carbon atom as defined above.

[0040] The cerium oxide coated silica particles of the present invention have a viscosity of 80 m as measured by BET. 2 / g~220m 2 / g range; typically 100m 2 / g~220m 2 / g range; in some cases 130m 2 / g~220m 2 / g. In some cases, the specific surface area measured by BET is in the range of 215 m 2 / g or less, and even 210m 2 / g or less, or even 200m 2 / g or less.

[0041] The cerium oxide coated silica particles according to the present invention are 50 <0.20 μm, preferably D 50 The particle size distribution is <0.18 μm, which distribution is obtained by laser diffraction from a dispersion of the particles in 1-propanol.

[0042] D 50 has its usual meaning as used in the field of particle size distribution. For clarity, D n is the volumetric basis of the particles that are D n corresponds to the diameter of particles with a diameter less than . 50 The (median) is defined as the size value corresponding to 50% of the cumulative distribution, this distribution being a volume distribution.

[0043] Furthermore, the particles according to the invention generally have a D 90 <0.50 μm, preferably D 90 <0.45 μm, more preferably D 90 <0.42 μm, this distribution being obtained by laser diffraction from a dispersion of the particles in 1-propanol.

[0044] In some embodiments, the cerium oxide coated silica particles according to the present invention are D 50 <0.20μm and D 90 <0.50 μm.

[0045] The cerium oxide coated silica particles according to the present invention comprise CeO2 crystallites having sizes as measured by XRD in the ranges of 5.0 nm to 10.0 nm; 5.0 nm to 9.0 nm; 5.0 nm to 8.0 nm; and in some cases 5.0 nm to 7.8 nm.

[0046] Typically, the cerium oxide crystallites are formed on the silica particles and are thereby bonded to said silica particles.

[0047] It is believed that smaller sized CeO2 crystallites may cause problems of leaching of Ce ions from the particles when used in proton exchange membranes in electrochemical devices.

[0048] A second object of the invention is a liquid composition (LC1) containing cerium oxide coated silica particles according to the invention dispersed in a liquid medium (L1).

[0049] The cerium oxide coated silica particles contained in (LC1) are usually 50 <0.20 μm, preferably D 50 Characterized by <0.18 μm.

[0050] Furthermore, particles contained in (LC1) are usually D 90 <0.50 μm, preferably D 90 <0.45 μm, more preferably 90 Characterized by <0.42 μm.

[0051] In some embodiments, the cerium oxide coated silica particles included in (LC1) are D 50 <0.20μm and D 90 It is characterized by a particle size distribution such that the particle size is <0.50 μm.

[0052] In some embodiments, the liquid medium comprises water, alcohol, or a water / alcohol mixture (L1).

[0053] Suitable alcohols, which can be used in particular as water / alcohol mixtures, are in particular methanol, ethanol, propyl alcohol (ie 1-propanol, 2-propanol), ethylene glycol, diethylene glycol.

[0054] In some other embodiments, the liquid medium (L1) further comprises a polar aprotic organic solvent, such as ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate, dimethyl carbonate, diethyl carbonate, and ethyl acetate, nitriles such as acetonitrile, sulfoxides such as dimethyl sulfoxide (DMSO), sulfones such as dimethyl sulfone (DMSO), amides such as N,N-dimethylformamide and N,N-dimethylacetamide, and pyrrolidones such as N-methylpyrrolidone and N-ethylpyrrolidone.

[0055] In some embodiments, the liquid medium (L1) is water, alcohol, or a mixture of water and alcohol, preferably a mixture of water and propyl alcohol.

[0056] Good results were obtained with a liquid composition (LC1) comprising particles according to the invention dispersed in 1-propanol, 2-propanol and mixtures thereof.

[0057] Typically, the liquid composition (LC1) according to the invention is prepared by suspending the particles according to the invention in the liquid medium (L1) by stirring at room temperature.

[0058] In some embodiments, the liquid composition (LC1) is prepared by sonicating particles according to the present invention in a liquid medium (L1) for 0.5 to 6 hours to completely disperse the particles.

[0059] In some other embodiments, the liquid composition (LC1) is prepared by suspending particles according to the present invention in a liquid medium (L1) by stirring at room temperature, followed by further sonication to completely disperse the solids.

[0060] Furthermore, in some other embodiments, the liquid composition (LC1) is produced by wet-milling the cerium oxide-coated silica particles of the present invention in a liquid medium (L1) to achieve a desired particle size distribution, and then suspending the particles in an additional amount of (L1) as described above to achieve a target content (wt %) of the cerium oxide-coated silica particles based on the total weight of the liquid composition (LC1).

[0061] The liquid composition (LC1) according to the present invention typically comprises at least 0.1 wt. %, preferably at least 0.5 wt. %, more preferably at least 1.0 wt. % of cerium oxide-coated silica particles, based on the total weight of said liquid composition (LC1).

[0062] The liquid composition (LC1) according to the present invention typically comprises at most 25.0 wt. %, preferably at most 20.0 wt. %, more preferably at most 15.0 wt. % of cerium oxide-coated silica particles, based on the total weight of said liquid composition (LC1).

[0063] Typically, the liquid composition (LC1) according to the present invention contains 0.1 to 25.0 wt %, preferably 1.0 to 15.0 wt %, of the cerium oxide-coated silica particles based on the total weight of the liquid composition (LC1).

[0064] In some embodiments, the liquid composition (LC1) according to the present invention comprises additional components and / or additives, such as an amine or a carboxylic acid.

[0065] The cerium oxide (CeO2)-coated silica (SiO2) particles of the present invention are a) preparing an aqueous suspension (S1) containing SiO2 and setting the pH value of the suspension to 7-11 by adding an aqueous ammonia (NH3) solution; b) adding an aqueous solution of Ce(NO3)3 to the suspension (S1) under stirring while maintaining the pH value at 7 to 11 by adding an aqueous ammonia solution to obtain a slurry containing cerium hydroxide precipitated on SiO2; c) filtering the slurry obtained in step b) to recover the cerium hydroxide precipitated on the SiO2 in solid form; d) calcining the solid obtained in step c) in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain cerium oxide (CeO2)-coated silica (SiO2) in particulate form; e) optionally milling the recovered particles of step d) to obtain a desired particle size. It can be produced by method A, which includes:

[0066] Method A is usually carried out when the desired cerium oxide-coated silica particles contain 10% to 70% by weight of Ce element.

[0067] In some preferred embodiments, step A is carried out when the desired cerium oxide coated silica particles contain more than 40 wt % to 70 wt % Ce element.

[0068] In step a) of this method, the aqueous suspension (S1) typically contains 5 to 10% by weight of SiO2 relative to the total weight of said aqueous suspension (S1). The aqueous suspension (S1) preferably contains 5 to 8% by weight, more preferably 6 to 7% by weight of SiO2 relative to the total weight of the aqueous suspension (S1). Good results have been obtained with a suspension (S1) containing 6.5% by weight of SiO2.

[0069] The aqueous ammonia (NH3) solution used in steps a) and b) of this process typically contains 5% to 11% by weight of ammonia. Preferably, it contains 6% to 10% by weight, more preferably 7% to 9% by weight of ammonia. Good results have been obtained with an 8% by weight aqueous ammonia solution.

[0070] Typically, in steps a) and b), the pH value is set and maintained at 7 to 11 by adding aqueous ammonia. Good results have been obtained when the pH is set and maintained at 8.5.

[0071] In some embodiments, the pH in step a) is set to a value between 7 and 11 that is different from the pH value of 7 to 11 maintained in step b).

[0072] In step b), the concentration of the aqueous Ce(NO3)3 solution added to the suspension (S1) is usually in the range of 1.00 to 5.00 mol / L, preferably 1.50 to 4.00 mol / L. Good results were obtained at a concentration of 2.87 mol / L.

[0073] The Ce(NO3)3 solution is added to the suspension (S1) with stirring for a period of time usually ranging from 10 minutes to 3 hours, preferably from 30 minutes to 2 hours. Good results were obtained with a period of 1 hour.

[0074] In step c), filtration can be carried out, for example, using a Buchner funnel on a laboratory scale. On a larger scale, any filtration system known in the art for dewatering, such as a filter press, can be used.

[0075] In step d), the calcination can be carried out in any oven with an oxidizing atmosphere. For example, the calcination can be carried out in a rotary drum kiln. In some embodiments, air is the oxidizing atmosphere.

[0076] Usually, the firing is carried out at a temperature in the range of 250° C. to 800° C., preferably at a temperature in the range of 400° C. to 800° C. Good results were obtained when firing was carried out at 500° C.

[0077] In some embodiments, the firing is carried out at 800°C.

[0078] Typically, calcination is carried out for a time period ranging from 1 to 10 hours, preferably from 2 to 8 hours. Good results have been obtained when calcination is carried out at a temperature of 500°C for 3 hours. In some embodiments, calcination is carried out at 800°C for 3 hours.

[0079] In step e), the particles obtained in step d) can be milled by treating them with any device known to those skilled in the art, such as a hammer mill, a planetary ball mill, a blade mill, or a jet mill.

[0080] In some embodiments, the grinding can be carried out in the presence of at least one solvent, i.e., by so-called wet grinding using suitable known equipment. Suitable solvents for wet grinding are 1-propanol, 2-propanol, ethanol, water, and mixtures thereof. Good results have been obtained using 1-propanol or 2-propanol.

[0081] In some other embodiments, a preliminary dry milling is performed followed by a wet milling, typically using 1-propanol.

[0082] Typically, in step e), the cerium oxide (CeO2) coated silica (SiO2) particles are deagglomerated by dry milling.

[0083] D 50 <0.20μm and D 90 To obtain cerium oxide coated silica particles <0.50 μm, wet milling is usually used in step e).

[0084] In some embodiments, in step e), D 50 <0.20μm and D 90 Dry milling is performed before wet milling to obtain cerium oxide coated silica particles <0.50 μm.

[0085] In another embodiment, the inventive cerium oxide (CeO) coated silica (SiO) particles according to the present invention are a') preparing an aqueous ammonia solution (E) having a pH value set at 7 to 11; b') adding an aqueous suspension (S2) containing SiO2 suspended in a Ce(NO3)3 aqueous solution to the aqueous solution (E) under stirring while maintaining the pH value at 7 to 11 by adding an aqueous ammonia solution (E') to obtain a slurry containing cerium hydroxide precipitated on SiO2; c') filtering the slurry obtained in step b') to recover the cerium hydroxide precipitated on the SiO2 in solid form; d') calcining the solid obtained in step c') in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain cerium oxide (CeO2)-coated silica (SiO2) in particulate form; e') optionally milling the recovered particles of step d') to obtain a desired particle size. It can be produced by Method A', which includes:

[0086] Method A' is usually carried out when the target cerium oxide-coated silica particles contain 10% by weight to 70% by weight of Ce element.

[0087] In some preferred embodiments, step A' is carried out when the desired cerium oxide coated silica particles contain more than 40 wt % to 70 wt % Ce element.

[0088] The aqueous ammonia (NH3) solution (E) used in step a') of method A' typically contains 5 to 11% by weight of ammonia, sometimes 6 to 10% by weight, and often 7 to 9% by weight.

[0089] The aqueous ammonia (NH3) solution (E') used in step b') of method A' typically contains 5 to 11% by weight of ammonia, sometimes 6 to 10% by weight, and often 7 to 9% by weight.

[0090] In some embodiments, the aqueous ammonia (NH3) solution (E) is different from (E').

[0091] In some embodiments, the aqueous ammonia (NH3) solution (E) is the same as (E').

[0092] Usually, in steps a') and b'), the pH value is set and maintained at 7 to 11 by adding an ammonia solution. In some cases, the pH value is set and maintained at 8.5.

[0093] In some embodiments, in step a') the pH is set to a value between 7 and 11 that is different from the pH value of 7 to 11 maintained in step b').

[0094] In step b'), the concentration of the aqueous Ce(NO3)3 solution is usually in the range of 1 to 5 mol / L, and in some cases in the range of 1.5 to 4 mol / L.

[0095] In step b') of the method, the aqueous suspension (S2) typically comprises 2.5% to 15.0% by weight of SiO2 relative to the total weight of the aqueous suspension (S2).

[0096] In step b'), the aqueous suspension (S2) typically contains 2.5 wt % to 15.0 wt % of SiO2 relative to the total weight of the aqueous suspension (S2) dispersed in a 1 to 5 mol / L aqueous solution of Ce(NO3)3.

[0097] The suspension (S2) is usually added to the solution (E) with stirring for a time ranging from 10 minutes to 3 hours, sometimes from 30 minutes to 2 hours, and often for 1 hour.

[0098] Steps c'), d'), and e') are generally carried out as described above for steps c), d), and e), respectively.

[0099] In yet another embodiment, the inventive cerium oxide (CeO) coated silica (SiO) particles according to the present invention are a″) providing an aqueous suspension (S3) containing SiO2, ammonia (NH3) and, optionally, at least one source of inorganic groups —SO2OZ; b'') adding, under stirring, a Ce(NO3)3 solution to the suspension (S3) in an amount such that the molar ratio of NH3 prepared in step a'') to elemental Ce is in the range of 2 to 4, to obtain a slurry containing cerium hydroxide precipitated on SiO2; c'') filtering the slurry to recover the cerium hydroxide Ce(OH)3 precipitated on SiO2 in solid form; d'') calcining the obtained solid in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain cerium oxide-coated silica in particulate form; e'') optionally milling the recovered particles of step d'') to obtain the desired particle size. It is produced by method B, which includes:

[0100] Method B is usually carried out when the target cerium oxide (CeO2) coated silica (SiO2) particles contain 10% to 40% by weight of Ce element.

[0101] In step a'') of this process, the aqueous suspension (S3) typically contains 4 to 10% by weight of SiO2 relative to the total weight of said aqueous suspension (S3). The aqueous suspension (S3) preferably contains 4.5 to 8% by weight, more preferably 5 to 7% by weight of SiO2 relative to the total weight of the aqueous suspension (S3). Good results have been obtained with a suspension containing 6.5% by weight of SiO2.

[0102] In step b''), the concentration of the Ce(NO3)3 solution added to the suspension (S3) is usually in the range of 1 to 5 mol / L, preferably in the range of 1.5 to 4 mol / L. Good results were obtained with a concentration of 2.87 mol / L.

[0103] In step b''), the Ce(NO3)3 solution is usually added in an amount such that the molar ratio of NH3 supplied in step a'') to elemental Ce is 2.0 to 4.0, typically 2.5 to 3.5. Good results have been obtained when the Ce(NO3)3 solution is added in an amount such that the molar ratio of NH3 supplied in step a'') to elemental Ce is 3.0.

[0104] The Ce(NO3)3 solution is typically added to the suspension (S3) with stirring for a period ranging from 15 minutes to 3 hours, preferably from 30 minutes to 2 hours. Good results have been obtained when the Ce(NO3)3 solution is added to the suspension (S3) over a period of 1 hour.

[0105] Steps c''), d''), and e'') are generally carried out as described above for steps c), d), and e), respectively.

[0106] In some embodiments, step a″) of method B consists in providing an aqueous suspension comprising SiO 2 , ammonia (NH 3 ), and at least one source of inorganic groups —SO 2 OZ.

[0107] Suitable sources of the inorganic group -SO2OZ are, for example, NH4)2SO3 · Preferably, the source of the inorganic group -SO2X is selected from the group consisting of H2O, NH4SO3NH2, HSO3Cl, Na2S2O5 / NaHSO3, (NH4)HSO3, and H2SO4. · It's H2O.

[0108] The source of the inorganic group -SO2OZ, when present, typically represents 2-10 wt. % of the total amount of SiO2 and Ce(NO3)3 added throughout Process B, preferably 5-7 wt. %.

[0109] In some embodiments, the aqueous suspension (S1), (S2), or (S3) of Method A, A', or B, respectively, may include a polar solvent, such as an alcohol.

[0110] Typically, during methods A, A' and B according to the invention, cerium oxide crystallites are formed on the silica particles and are therefore bonded to said silica particles.

[0111] In some embodiments, the cerium oxide coated silica particles according to the present invention are substantially free of free cerium oxide crystallites that are not bound to silica particles.

[0112] In some other embodiments, the cerium oxide coated silica particles according to the present invention are completely free of free cerium oxide crystallites that are not attached to the silica particles.

[0113] For the production of cerium oxide (CeO)-coated silica (SiO) particles according to the present invention, any type of silica SiO can be used, such as colloidal silica, fumed silica, precipitated silica, etc. Preferably, SiO has a particle size of 1.0 nm to 100.0 nm, preferably 5.0 to 50.0 nm.

[0114] Notable non-limiting examples of suitable commercially available precipitated silicas are, for example, Tixosil® 73, Tixosil® 63, Tixosil® SoftClean, Tixosil® 43, Tixosil® 331, all available from Solvay SA.

[0115] Ludox® colloidal silica, available from WRGrace & Co., can also be used.

[0116] Ce(NO3)3 . 6H2O is usually used to prepare aqueous solutions of Ce(No3)3.

[0117] A further object of the present invention is a composition (C) containing at least one polymer containing -SO2X functional groups, where X is selected from X' or OZ, X' is selected from the group consisting of F, Cl, Br, I, and Z is selected from the group consisting of H, alkali metals, and NH4, and cerium oxide (CeO2) coated silica (SiO2) particles as described above.

[0118] Composition (C) can comprise at least one fluorinated polymer comprising -SO2X functional groups (wherein X is selected from X' or OZ, X' is selected from the group consisting of F, Cl, Br, I, and Z is selected from the group consisting of H, an alkali metal, and NH4), and cerium oxide (CeO2) coated silica (SiO2) particles as detailed above.

[0119] The expression "fluorinated" is used herein to mean a compound (e.g., a compound, polymer, monomer, etc.) that is either fully or partially fluorinated, i.e., all or only a portion of the hydrogen atoms have been replaced by fluorine atoms. Preferably, the term "fluorinated" refers to a compound that contains a higher proportion of fluorine atoms than hydrogen atoms, and more preferably, the term refers to a compound that does not contain any hydrogen atoms, i.e., all hydrogen atoms have been replaced by fluorine atoms.

[0120] In the context of the present invention, the expression "at least one" when referring to a "fluorinated polymer" is intended to denote one or more polymers. For the purposes of the present invention, mixtures of polymers can be used to advantage.

[0121] Composition (C) may comprise at least one fluorinated polymer in neutral form, where the term "neutral form" indicates that in the -SO2X functional group, X is X' and X' is selected from the group consisting of F, Cl, Br, and I. Preferably, X' is selected from F or Cl. More preferably, X' is F.

[0122] Alternatively, composition (C) may comprise at least one fluorinated polymer in ionic (acid or salt) form, where the term "ionic form" indicates that in the -SO2X functional group, X is OZ and Z is selected from the group consisting of H, alkali metals, NH4.

[0123] For the avoidance of doubt, the term "alkali metal" is intended herein to mean the following metals: Li, Na, K, Rb, Cs. Preferably, the alkali metal is selected from Li, Na, K.

[0124] Fluorinated polymers containing -SO3Z functional groups (X = OZ) are typically prepared from fluorinated polymers containing -SO2X' functional groups, preferably -SO2F functional groups, by methods known in the art.

[0125] Fluorinated polymers can be obtained in their salt form (i.e., where Z is a cation selected from the group consisting of NH and alkali metals) by treatment of the corresponding polymer containing -SO2X' functional groups, typically -SO2F functional groups, with a strong base (e.g., NaOH, KOH).

[0126] The fluorinated polymer can be obtained in its acid form (ie, where Z is H) by treatment of the corresponding salt form of the polymer with concentrated acidic solution.

[0127] Suitable fluorinated polymers comprising -SO2X' functional groups are those polymers comprising repeat units derived from at least one ethylenically unsaturated fluorinated monomer (monomer (A) as defined herein below) containing at least one -SO2X' functional group and repeat units derived from at least one ethylenically unsaturated fluorinated monomer (monomer (B) as defined herein below).

[0128] The phrase "at least one monomer" is used herein with respect to both types (A) and (B) of monomers to indicate that one or more monomers of each type may be present in the polymer. Hereinafter, the term monomer will be used to refer to both one and more than one monomer of a given type.

[0129] Non-limiting examples of suitable monomers (A) are: - Formula: CF2 = CF(CF2)p sulfonyl halide fluoroolefins of the formula SO2X', where p is an integer from 0 to 10, preferably from 1 to 6, more preferably p is equal to 2 or 3, and preferably X' = F; - Formula: CF2 = CF-O-(CF2) m sulfonyl halide fluorovinyl ethers of the formula SO2X', where m is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, even more preferably m is equal to 2, and preferably X' = F; - Formula: CF2 = CFCF2-O-(CF2) q sulfonyl halide fluoroallyl ethers of the formula SO2X', where q is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and even more preferably q is equal to 2, and preferably X' = F; - Formula: CF2 = CF-(OCF2CF(R F1 )) w -O-CF2(CF(R F2 )) y SO2X' (wherein w is an integer of 0 to 2, and may be equal to or different from each other; R F1 and R F2 are independently C1-C optionally substituted with F, Cl, or one or more ether oxygens. 10 is a fluoroalkyl group, y is an integer of 0 to 6; preferably w is 1, and R F1 is -CF3, y is 1, and R F2 is F, preferably X′═F); - Formula CF2=CF-Ar-SO2X' (wherein Ar is C5 to C 15 Sulfonyl halide aromatic fluoroolefins, where X' is an aromatic or heteroaromatic substituent, preferably where X' = F is.

[0130] Preferably, the monomer (A) is selected from the group of the sulfonyl fluorides (ie, where X'=F).

[0131] More preferably, the monomer (A) has the formula CF2=CF-O-(CF2) m The fluorovinyl ether is selected from the group consisting of -SO2F (wherein m is an integer of 1 to 6, preferably 2 to 4).

[0132] Even more preferably, monomer (A) is CF2=CFOCF2CF2-SO2F (perfluoro-5-sulfonylfluoride-3-oxa-1-pentene).

[0133] Non-limiting examples of suitable ethylenically unsaturated fluorinated monomers of type (B) are: - C2-C8 fluoroolefins such as tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, and hexafluoroisobutylene; - vinylidene fluoride; - C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefins, such as chlorotrifluoroethylene and bromotrifluoroethylene; - Formula CF2=CFOR f1 (In the formula, R f1 is C1-C6 fluoroalkyl, for example, -CF3, -C2F5, -C3F7) fluoroalkyl vinyl ether; - Formula CF2=CFOR O1 (In the formula, R O1 is a C1-C olefin having one or more ether groups 12 fluoro-oxyalkyl vinyl ethers, such as perfluoro-2-propoxy-propyl; - Formula CF2=CFOCF2OR f2 (In the formula, R f2 is a fluoroalkyl-methoxy-vinyl ether of C1-C6 fluoroalkyl, for example, C1-C6 fluorooxyalkyl having one or more ether groups such as -CF3, -C2F5, -C3F7 or -C2F5-O-CF3; - Formula: [ka] (wherein R f3 , R f4 , R f5 , R f6 each independently represents a C1-C6 fluoro(halo)fluoroalkyl group containing a fluorine atom and optionally one or more oxygen atoms, e.g., -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3. Fluorodioxole is.

[0134] Preferably, the monomer (B) is - C3-C8 fluoroolefins, preferably tetrafluoroethylene and / or hexafluoropropylene; - chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins, such as chlorotrifluoroethylene and / or bromotrifluoroethylene; - Formula CF2=CFOR f1 (In the formula, R f1 is C1-C6 fluoroalkyl, for example, -CF3, -C2F5, -C3F7) fluoroalkyl vinyl ether; - Formula CF2=CFOR O1 (In the formula, R O1 is a C1-C olefin having one or more ether groups 12 Fluoro-oxyalkyl vinyl ethers of fluorooxyalkyl, such as perfluoro-2-propoxy-propyl is selected from among:

[0135] More preferably, monomer (B) is tetrafluoroethylene.

[0136] Fluorinated polymers containing -SO2X' functional groups can be prepared by any polymerization method known in the art. Suitable methods for preparing such polymers are, for example, those described in EP 1 323 751 A (SOLVAY SOLEXIS SPA) (July 2, 2003) and EP 1 172 382 A (SOLVAY SOLEXIS SPA) (November 16, 2002).

[0137] Alternatively, the polymer comprising -SO2X functional groups may be a non-fluorinated polymer. The polymer may be an aromatic polymer.

[0138] Typical examples of aromatic polymers containing -SO2X functional groups suitable for composition (C) include polymers having aromatic rings in the main chain into which sulfonic acid groups have been introduced.

[0139] The polymer having an aromatic ring in the main chain may have a heteroatom such as an oxygen atom sandwiched between the main chain. Examples of such aromatic polymers include polyetherketone, polyetheretherketone, polysulfone, polyethersulfone, polyetherethersulfone, poly(arylene ether), polyimide, polyphenylene, poly((4-phenoxybenzoyl)-1,4-phenylene), polyphenylene sulfide, sulfoarylated polybenzimidazole, sulfoalkylated polybenzimidazole, phosphoalkylated polybenzimidazole, and phosphonate poly(phenylene ether).

[0140] The cerium oxide (CeO2) coated silica (SiO2) particles according to the present invention are present in composition (C) in an amount sufficient to reduce the extent of radical decomposition of the polymer containing -SO2X functional groups.

[0141] The amount of Ce element relative to the total weight of the polymer in the composition (C) containing cerium oxide (CeO2)-coated silica (SiO2) particles according to the present invention is usually at least 0.1 wt%, preferably at least 0.2 wt%, more preferably at least 0.5 wt%.

[0142] The amount of Ce element relative to the total weight of the polymer in the composition (C) containing the cerium oxide (CeO2)-coated silica (SiO2) particles according to the present invention usually does not exceed 20.0 wt%, preferably does not exceed 15.0 wt%, and more preferably does not exceed 10.0 wt%.

[0143] The polymer containing -SO2X functional groups in composition (C) is preferably a fluorinated polymer.

[0144] Composition (C) can be prepared using conventional methods.

[0145] When both the fluorinated polymer and the cerium oxide (CeO2) coated silica (SiO2) particles are supplied in solid form, such as powder, pellets, or granules, composition (C) can be manufactured using techniques such as dry blending, melt blending, or extrusion.

[0146] An object of the present invention is therefore a process for the preparation of composition (C), which comprises mixing in solid form the cerium oxide (CeO2)-coated silica (SiO2) of the present invention with at least one fluorinated polymer containing -SO2X functional groups.

[0147] Alternatively, another object of the present invention is a process for the preparation of a composition (C), comprising mixing the cerium oxide (CeO2) coated silica (SiO2) of the present invention and at least one fluorinated polymer containing -SO2X functional groups in a liquid medium (L) to obtain a liquid composition (LC).

[0148] These methods are advantageous for the preparation of compositions (C) in which the fluorinated polymer contains -SO3Z functional groups (Z is as defined above), in particular -SO3H functional groups.

[0149] The liquid composition (LC2) can be prepared by a dissolution process in which the fluorinated polymer is contacted with the liquid composition (LC2) at appropriate temperature conditions.

[0150] Typically, the liquid medium (L2) comprises water, alcohol, or a water / alcohol mixture, and optionally further components and / or additives.

[0151] Suitable alcohols, which can be used in particular as a water / alcohol mixture, are, inter alia, methanol, ethanol, propyl alcohol (ie isopropanol, n-propanol), ethylene glycol, diethylene glycol.

[0152] The liquid medium (L2) may further comprise a solvent selected from polar aprotic organic solvents such as ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate, dimethyl carbonate, diethyl carbonate, and ethyl acetate, nitriles such as acetonitrile, sulfoxides such as dimethyl sulfoxide (DMSO), sulfones such as dimethyl sulfone (DMSO2), amides such as N,N-dimethylformamide and N,N-dimethylacetamide, pyrrolidones such as N-methylpyrrolidone and N-ethylpyrrolidone, and mixtures thereof.

[0153] In some embodiments, the liquid medium (L2) comprises water or a mixture of water and alcohol, preferably a mixture of water and propyl alcohol.

[0154] Good results have been obtained when the liquid medium (L2) is water or a mixture of water and alcohol, preferably a mixture of water and propyl alcohol.

[0155] Good results were also obtained when the liquid medium (L2) was a mixture of water, propyl alcohol and DMSO2.

[0156] The liquid composition (LC2) can be advantageously prepared by contacting the fluorinated polymer with water or a mixture of water and alcohol at room temperature or in an autoclave at a temperature between 40°C and 300°C.

[0157] In some other embodiments, the liquid composition (LC2) can be advantageously prepared by contacting the fluorinated polymer with water, propyl alcohol, and DMSO2 at room temperature or in an autoclave at a temperature between 40°C and 300°C.

[0158] By adding cerium oxide (CeO2) coated silica (SiO2) particles to a liquid composition (LC2) comprising a fluorinated polymer alone or as the aforementioned liquid composition (LC1) according to the present invention, a liquid composition (LC) can be obtained comprising at least one fluorinated polymer containing -SO2X functional groups and cerium oxide (CeO2) coated silica (SiO2) particles dispersed or dissolved in a liquid medium (L).

[0159] Therefore, the liquid medium (L) is the liquid medium (L2) when the cerium oxide (CeO2)-coated silica (SiO2) particles are added alone, and when the cerium oxide (CeO2)-coated silica (SiO2) particles are added as liquid composition (LC1), the liquid medium (L) is a combination of the liquid medium (L2) and the liquid medium (L1).

[0160] A further object of the present invention is a liquid composition (LC) comprising at least one fluorinated polymer containing -SO2X functional groups as defined above and cerium oxide (CeO2) coated silica (SiO2) particles dispersed or dissolved in a liquid medium (L) as defined above. Typically, the liquid medium (L) is water or a mixture of water and alcohol.

[0161] In some embodiments, the liquid medium (L) is water or a mixture of water and propanol, preferably 1-propanol.

[0162] In some alternative embodiments, the liquid medium (L) is a mixture of water, propanol, preferably 1-propanol, and DMSO 2 .

[0163] Preferably, the fluorinated polymer in the liquid composition (LC) is in its ionic form, i.e. it contains -SO3Z functional groups (where Z is as defined above), in particular -SO3H functional groups.

[0164] The liquid composition (LC) comprising at least one fluorinated polymer and cerium oxide (CeO2) coated silica (SiO2) particles may optionally comprise additional components.

[0165] An object of the present invention is therefore a method for preparing a liquid composition (LC) comprising mixing, in a liquid medium (L), cerium oxide (CeO2) coated silica (SiO2) particles and at least one fluorinated polymer containing -SO2X functional groups.

[0166] The composition (C) of the present invention is particularly suitable for the manufacture of proton exchange membranes and electrocatalyst layers for fuel cell applications, and also for the manufacture of proton exchange membranes and electrocatalyst layers for use in water electrolysis applications. Indeed, the presence of the cerium oxide (CeO)-coated silica (SiO) particles of the present invention has been shown to improve the resistance to radical decomposition of fluorinated polymers containing -SO2X functional groups, as evidenced by the long lifetime of the resulting proton exchange membranes under use conditions.

[0167] As described above, during methods A, A', and B according to the present invention, cerium oxide crystallites are formed on the silica particles and are thus bonded to said silica particles. Therefore, the cerium oxide scavenger can be immobilized within the membrane, avoiding dissolution during the operation of the fuel cell or electrolysis cell. In other words, cerium oxide is more stable against leaching during the operation of the fuel cell or hydrolysis cell. Therefore, due to the high amount of cerium oxide present, the fluorinated membrane is protected for a longer period from radical-induced decomposition. Additionally, electrocatalyst poisoning by dissolved cerium oxide and shortening of the expected membrane life are avoided.

[0168] Cerium oxide leaching can be evaluated, for example, by treating a membrane containing the cerium oxide (CeO2)-coated silica (SiO2) particles of the present invention in a sulfuric acid solution. The amount of cerium oxide dissolved in sulfuric acid during membrane treatment can then be evaluated by ICP-OES. Typically, cerium oxide leaching from membranes containing the cerium oxide (CeO2)-coated silica (SiO2) particles of the present invention is reduced compared to cerium oxide leaching from membranes containing other cerium element sources.

[0169] A further object of the present invention is an article comprising at least one fluorinated polymer containing -SO2X functional groups and cerium oxide (CeO2) coated silica (SiO2) particles as defined above.

[0170] In a first embodiment, the article is a proton exchange membrane, also referred to herein as a "membrane," for fuel cell applications.

[0171] Typically, the composition (C), comprising at least one fluorinated polymer containing -SO2X' functional groups, preferably -SO2F functional groups, and cerium oxide (CeO2) coated silica (SiO2) particles in solid form, can be advantageously converted into a membrane by conventional extrusion techniques.

[0172] The extruded film can then be converted into an ion-conducting membrane by hydrolysis, ie, conversion of the -SO2X' functional groups to the corresponding -SO3H functional groups, as described above.

[0173] Membranes can be obtained from the liquid composition (LC) according to the present invention comprising at least one fluorinated polymer typically containing -SO3Z functional groups, preferably -SO3H functional groups, and cerium oxide (CeO2) coated silica (SiO2) particles using techniques known in the art, such as impregnation, casting, coating, e.g. roller coating, gravure coating, reverse roll coating, dip coating, spray coating, etc.

[0174] The membrane may optionally be reinforced, for example, by laminating the extruded membrane to a suitable reinforcing support or by impregnating the porous support with the liquid composition (LC). Suitable supports can be made from a wide variety of components. The porous support can be made from a woven or nonwoven polyolefin membrane, e.g., a hydrocarbon polymer such as polyethylene or polypropylene, or a polyester, e.g., poly(ethylene terephthalate). Fluorinated polymer porous supports are generally preferred for use in fuel cell applications due to their high chemical inertness. Biaxially expanded PTFE porous supports (otherwise known as ePTFE membranes) are particularly preferred supports. These supports are commercially available under the trade names GORE-TEX® and TETRATEX®, among others.

[0175] In a second embodiment, the article is an electrocatalytic layer.

[0176] The electrocatalytic layer can be advantageously produced starting from a liquid composition (LC) according to the present invention, which typically comprises at least one fluorinated polymer containing -SO3Z functional groups, preferably -SO3H functional groups, and cerium oxide (CeO2)-coated silica (SiO2) particles, as well as catalyst particles. The liquid composition is generally referred to as a "catalytic ink." Typical catalyst particles comprise an active compound selected from metals such as iron, manganese, cobalt, nickel, platinum, ruthenium, gold, palladium, rhodium, and iridium; their conductive oxides and alloys. The active compound is generally supported on a suitable, preferably electrically conductive, material, referred to herein as a "support." The support is advantageously selected from carbon powders, such as carbon black.

[0177] The amount of catalyst particles (including the support, if any) in the catalyst ink is generally at least 1 wt. % relative to the total weight of the catalyst ink. Preferably, the amount is at least 3 wt. %, more preferably at least 5 wt. Advantageously, the amount of catalyst particles (including the support, if any) in the catalyst ink is at most 50 wt. %, preferably at most 40 wt. %, more preferably at most 30 wt. %, based on the total weight of the catalyst ink.

[0178] The electrocatalyst layer can be fabricated, for example, by screen printing or solution coating a catalyst ink onto the surface of the proton exchange membrane. The proton exchange membrane may contain cerium oxide (CeO2)-coated silica (SiO2) particles having the same or different composition as the cerium oxide (CeO2)-coated silica (SiO2) particles present in the catalyst ink, or may be free of cerium oxide (CeO2)-coated silica (SiO2) particles.

[0179] In a third embodiment, the article is a membrane electrode assembly. The membrane electrode assembly includes a membrane having first and second surfaces, a first electrocatalytic layer adhered to the first surface, and a second electrocatalytic layer adhered to the second surface, wherein the membrane and at least one of the first or second electrocatalytic layers include at least one fluorinated polymer containing —SO₂X functional groups and cerium oxide (CeO₂)-coated silica (SiO₂) particles as defined above. When the cerium oxide (CeO₂)-coated silica (SiO₂) particles are present in two or more components of the membrane electrode assembly, they may be the same or different.

[0180] Finally, an object of the invention is a fuel cell or electrolysis cell comprising an article as defined above.

[0181] All definitions and preferences defined above in relation to the cerium oxide (CeO2) coated silica (SiO2) particles or the process for their production apply to the compositions comprising the cerium oxide (CeO2) coated silica (SiO2) particles and the fluoropolymer compositions, as well as to any articles comprising said compositions.

[0182] The present invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and is not intended to limit the scope of the invention. [Example]

[0183] Characterization Ce content by ICP-OES Inductively coupled plasma optical emission spectroscopy (ICP-OES) was performed on mineralized samples prepared by dissolving cerium oxide using a mixture of nitric acid and hydrochloric acid.

[0184] Emission spectroscopy was used to detect and quantify the ionized elements using wavelengths of 418.660 nm and 446.021 nm for Ce, and 180.672 nm and 181.975 nm for S.

[0185] Specific surface area of ​​particles by BET method The specific surface area of ​​the particles was measured according to the Brunauer-Emet-Teller (BET) method described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938.

[0186] Crystallite size by XRD XRD diffractograms of the powders were acquired on an XRD goniometer (Malvern Panalytical) in Bragg Brentano geometry using a Cu X-ray tube (Cu K-alpha wavelength of 1.5406 Å). Phase identification was performed using Highscore Plus analysis software provided by the manufacturer. The size of the ceria crystallites was measured using the half-width at half maximum of the main peak in the XRD pattern using Highscore Plus analysis software.

[0187] Particle size distribution by laser diffraction The particle size distribution was obtained by laser diffraction from a dispersion of the composition in 1-propanol.

[0188] D 50 has its usual meaning as used in the field of particle size distribution. n is the volumetric basis of the particles that are D n corresponds to the diameter of particles with a diameter less than D 50 The median is defined as the size value corresponding to the cumulative distribution at 50%. These parameters were determined from the volume diameter distribution of a dispersion of particles of solid material in solution, obtained using a Malvern Mastersizer 3000 laser diffractometer. The data were processed with the Fraunhofer optical model.

[0189] Laser diffractometers use the technique of laser diffraction to measure particle size by measuring the intensity of light scattered as a laser beam passes through a sample of dispersed particulates.

[0190] Particle crushing The product was ground to powder using an IKA blade mill for 15 seconds and then deagglomerated in a 1-propanol suspension using an ultraturrax stirrer.

[0191] The resulting product was further wet-milled in 1-propanol using a basket mill operating with yttrium-stabilized ZrO2 balls having a diameter of 0.1-0.2 mm.

[0192] Example 1: Preparation of cerium oxide (CeO)-coated silica (SiO) particles ([Ce-40]) containing 40 wt% Ce element relative to the total weight of the particles In a reactor, 230 g of SiO2 (Tixosil® 43 supplied by Solvay) was dispersed in 3318 g of water to obtain a suspension containing 6.5 wt% silica. 1092.1 ml of an 8 wt% aqueous NH3 solution was added while stirring.

[0193] Then, 683.20 g of a 2.87 mol / L aqueous solution of Ce(NO3)3 was added to the reactor at 400 rpm within 1 hour, and the resulting slurry was further stirred for at least 30 minutes.

[0194] The resulting slurry was filtered and dewatered using a Buchner funnel to obtain a solid cake, the pH of which was 9.2.

[0195] The resulting cake was then baked in a furnace at a temperature of 500°C for 3 hours.

[0196] The specific surface area of ​​the resulting powder measured using the BET method was 211 m 2 / g.

[0197] The size of the CeO2 crystallites measured by XRD was 7.7 nm.

[0198] The Ce content measured by ICP-OES was 37 wt%.

[0199] A suspension of cerium oxide (CeO2)-coated silica (SiO2) particles was prepared by wet grinding and further dilution in 1-propanol.

[0200] Example 2: Preparation of cerium oxide (CeO)-coated silica (SiO) particles ([Ce-50]) containing 50 wt% Ce element based on the total weight of the particles In a reactor, 175 g of SiO2 (Tixosil® 43 supplied by Solvay) was dispersed in 2517 g of water to obtain a suspension containing 6.5 wt.% silica. An 8 wt.% aqueous NH3 solution was added to set the pH to 8.5.

[0201] Then, 853.90 g of a 2.87 mol / L aqueous Ce(NO) solution was added to the reactor within 1 hour under stirring at 400 rpm while maintaining the pH at 8.5 by adding an 8 wt % aqueous NH solution. The resulting slurry was further stirred for at least 30 minutes.

[0202] The resulting slurry was filtered and dewatered using a Buchner funnel to obtain a solid cake.

[0203] The resulting cake was then baked in a furnace at a temperature of 500°C for 3 hours.

[0204] The specific surface area of ​​the resulting powder measured using the BET method was 166 m 2 / g.

[0205] The size of the CeO2 crystallites measured by XRD was 5.4 nm.

[0206] The Ce content measured by ICP-OES was 49 wt%.

[0207] A suspension of cerium oxide (CeO2) coated silica (SiO2) particles was prepared by wet grinding in 1-propanol and further dilution with 1-propanol.

[0208] Laser diffraction from a dispersion of the composition in 1-propanol revealed D 50 =0.18μm, D 90 A particle size distribution of 0.41 μm was obtained.

[0209] Example 3: Preparation of cerium oxide (CeO)-coated silica (SiO) particles ([Ce-60]) containing 60 wt% Ce element relative to the total weight of the particles In a reactor, 130.6 g of SiO2 (Tixosil® 43 supplied by Solvay) was dispersed in 1879 g of water to obtain a suspension containing 6.5 wt.% silica. The pH was set to 8.5 by adding an 8 wt.% aqueous NH3 solution.

[0210] Then, 1152.2 g of a 2.87 mol / L aqueous Ce(NO) solution was added to the reactor within 1 hour under stirring at 400 rpm while maintaining the pH at 8.5 by adding an 8 wt% aqueous NH solution, and the resulting slurry was further stirred for at least 30 minutes.

[0211] The resulting slurry was filtered and dewatered using a Buchner funnel to obtain a solid cake.

[0212] The resulting cake was then baked in a furnace at a temperature of 500°C for 3 hours.

[0213] The specific surface area of ​​the resulting powder measured using the BET method was 144 m 2 / g.

[0214] The size of the CeO2 crystallites measured by XRD was 6.6 nm.

[0215] The Ce content measured by ICP-OES was 57 wt%.

[0216] A suspension of cerium oxide (CeO2) coated silica (SiO2) particles was prepared by wet grinding in 1-propanol and further dilution with 1-propanol.

[0217] Comparative Example 1: Procedure for the production of mixed oxide [MO-CE-40] scavenger particles containing 40 wt. % Ce element relative to the total weight of the particles by the process described in WO 2014 / 009334 In a sealed container, SiO2, water-soluble Ce(NO3)3 . 6H2O, and ((NH4)2SO3 . H2O was suspended in water.

[0218] Weight ratio SiO2:Ce(NO3)3 . 6H2O:(NH4)2SO3 . The ratio of HO was 200:593:62.1. The slurry was stirred at 80°C for 10 hours to obtain a gel. The gel thus obtained was heat treated according to the following conditions: - from room temperature to 150°C (1 hour ramp, 2.5°C / min); - 2 hours at 150°C; - 150°C to 300°C (1 hour ramp, 2.5°C / min); - 300°C for 2 hours.

[0219] At the end of the heat treatment, the powder obtained was cooled to room temperature and then washed with 0.5 M H2SO4 solution at 70 °C until no change in the amount of metal M and sulfur was measured by ICP-OES analysis of the sample. The powder was dried under vacuum at 80 °C for 2 hours and then ground in a planetary ball mill at 200 rpm for 2 hours.

[0220] The characteristics of the cerium oxide (CeO2) coated silica (SiO2) particles [Ce-40], [Ce-50], [Ce-60] prepared in Examples 1 to 3, and the mixed oxide [Mo-Ce-40] scavenger particles prepared in Comparative Example 1 are reported in Table 1 below.

[0221] [Table 1]

[0222] Example 4: Preparation of fluorinated polymer (P1) containing SO3H functional groups In a 22 L autoclave, the following reagents were placed: 11.5L demineralized water; 980g of monomer of formula: CF2 = CF-O-CF2CF2-SO2F 3100g of CF2ClO(CF2CF(CF3)O) n (CF2O) m 5% wt% solution of CF2COOK (average molecular weight = 521, ratio n / m = 10) in water.

[0223] The autoclave, stirred at 470 rpm, was heated to 60° C. A 6 g / L aqueous solution of potassium persulfate was added in an amount of 150 mL. The pressure was maintained at a value of 12 bar (abs) by feeding tetrafluoroethylene.

[0224] After 1200 g of tetrafluoroethylene was added to the reactor, 220 g of the monomer CF2=CF-O-CF2CF2-SO2F was added for every 200 g of trifluoroethylene fed to the autoclave.

[0225] The reaction was stopped after 280 minutes by stopping the stirring, cooling the autoclave, and venting the tetrafluoroethylene to reduce the internal pressure. A total of 4000 g of tetrafluoroethylene had been fed.

[0226] The latex was then coagulated by freezing and thawing, and the recovered polymer was washed with water and dried for 24 hours at 150° C. The polymer was then treated with fluorine gas in a metal vessel at 80° C. for 8 hours, and then purged with nitrogen for several hours to remove any remaining unstable end groups.

[0227] The polymer thus obtained was immersed in a KOH solution (10 wt%) at 80 °C for 8 h, followed by washing with demineralized water at room temperature, and then immersed in a HNO solution (20 wt%) at room temperature for 2 h, followed by washing with demineralized water at room temperature to convert all functional groups to -SOH functional groups.

[0228] The resulting fluorinated polymer (P1) in -SO3H form was then dried in a vacuum oven at 80° C. The equivalent weight (EW) of the polymer was determined (by IR analysis of the precursor polymer) to be 790 g / eq.

[0229] Example 5: Suspension containing cerium oxide (CeO2) coated silica (SiO2) particles prepared in Example 2 and mixed oxide scavenger particles prepared in Comparative Example 1 dispersed in 1-propanol A suspension containing 15 wt% of the cerium oxide (CeO2)-coated silica (SiO2) particles [Ce-50] prepared in Example 2 in 1-propanol was sonicated for 2 hours to completely disperse the solids. The solid content of the dispersion was measured using a thermobalance (160 °C, 45 min).

[0230] Similarly, a suspension was prepared containing 15 wt % of the [Mo-Ce-40] mixed oxide scavenger of Comparative Example 1 in 1-propanol, based on the total weight of the suspension.

[0231] Example 6: Liquid compositions containing P1 and the (CeO2)-coated silica (SiO2) suspension prepared in Example 5 or the mixed oxide scavenger particle suspension prepared in Comparative Example 1 The suspension containing cerium oxide (CeO2)-coated silica (SiO2) particles [Ce-50] obtained in Example 5 was added to an aqueous dispersion of P1 (20 g) further containing 1-propanol (7.5 g), DMSO2 (1.6 g), and HO (3 g). The mixture was stirred at room temperature to make the dispersion uniform.

[0232] The amounts of cerium oxide (CeO2) coated silica (SiO2) particles [Ce-50] and P1 added in the preparation of the liquid composition were calculated so that the final cerium content in the composition was 0.7% ± 0.1% w / w, based on the fluorinated polymer P1.

[0233] A liquid composition was prepared from the suspension of mixed oxide scavenger particles prepared in Comparative Example 1 in the same manner.

[0234] Example 7: Membrane Fabrication - General Procedure The mixture of Example 6 was cast onto a glass substrate using a doctor blade technique at a wet thickness of 500 μm, then dried in a ventilated oven at 60° C. for 1 hour, ramped from 60° C. to 90° C. in 1 hour, and then ramped from 90° C. to 190° C. for 1 hour. The resulting film had a thickness of 50±5 μm.

[0235] The amount of Ce element in the film containing [Ce-50] measured by ICP-OES was 0.7%±0.1% w / w% with respect to the total weight of the film (M2).

[0236] The amount of Ce element in the film containing [MO-Ce-40] measured by ICP-OES was 0.8%±0.1% w / w% with respect to the total weight of the film (M3).

[0237] Example 8: Fuel cell characterization of the membranes prepared in Example 7 The membrane obtained as described in Example 7 was placed on a plate with an effective area of ​​50 cm 2The membranes were assembled in a custom stack fixture from Greenlight Innovations and tested on a Greenlight Innovation G100 test stand. The membranes were fabricated with a homemade catalyst-coated gas diffusion layer (Pt approx. 0.35 mg / cm). 2 ) was assembled using

[0238] The membranes were tested under the following operating conditions: - Anode flow: 250 nccm pure H2, dew point 61°C, 1 bar (abs) - Cathode flow: 250 nccm pure O2, dew point 61°C, 1 bar (abs) - Cell temperature: 90℃

[0239] The voltage was monitored during the test, and the end of the test was set at a voltage below 0.7 V, which is typically indicative of pinhole formation in the membrane. The results are reported in Table 2.

[0240] [Table 2]

[0241] Compared to the membrane containing only the fluorinated polymer (P1) (reference membrane (M1)), the membrane containing the cerium oxide-coated silica particles of the present invention (M2) shows a significant increase in stability under fuel cell operating conditions. In fact, for membrane (M2), the time to reach a voltage below 0.7 V is 660 hours.

[0242] Furthermore, membrane (M2) comprising the cerium oxide-coated silica particles of the present invention exhibits a significantly increased stability under fuel cell operating conditions compared to membrane (M3) comprising a mixed oxide scavenger prepared according to the method described in Comparative Example 1 of WO 2014 / 009334. In fact, the time to reach a voltage below 0.7 V is 660 hours for membrane (M2) compared to only 275 hours for membrane (M3).

[0243] Therefore, the use of cerium oxide (CeO2) coated silica (SiO2) particles according to the present invention is advantageous over the use of conventional radical scavenger particles obtained by different methods and is believed to be more stable against leaching over time during operation of a fuel cell or electrolysis cell.

[0244] Example 9: Determination of the stability of cerium oxide (CeO2)-coated silica (SiO2) particles containing 50 wt% Ce element relative to the total weight of the particles ([Ce-50]) against Ce leaching in acidic media The manufacturing protocol of Example 2 was followed, except that the baking of the cake was carried out at a temperature of 700°C.

[0245] The specific surface area of ​​the resulting powder measured using the BET method was 122 m 2 / g. The size of the CeO2 crystallites measured by XRD was 7.3 nm.

[0246] 2 g of the calcined product was dispersed in 100 mL of 1 M H2SO4. The suspension was heated at 80 °C for 24 hours (step 1). After 24 hours, the suspension was centrifuged (9600 rpm, 15 minutes, Sigma6 16KS, refrigerated benchtop centrifuge, rotor: Sigma 12269). The resulting solid was dispersed again in 100 mL of 1 M H2SO4 and heated at 80 °C for 24 hours (step 1).

[0247] Both supernatants were analyzed by ICP-OES to determine the amount of Ce leached. The results in Table 3 show that leaching was at very low levels under acidic conditions.

[0248] [Table 3]

Claims

1. Optionally inorganic -SO ２ OZ functional groups, where Z is H, alkali metals, and NH ４ Cerium oxide (CeO) ２ ) coated silica (SiO ２ ) particles containing 10 wt % to 70 wt % of Ce element based on the total weight of the particles, and having a surface roughness of 80 m as measured by the BET method ２ / g~220m ２ / g and having a size in the range of 5.0 nm to 10.0 nm as measured by XRD. ２ particles, including microcrystals.

2. Volumetric D ５０ is less than 0.20 μm, preferably D ５０ 10. The particles of claim 1, characterized by a particle size distribution such that .gtoreq.0.18 .mu.m, said distribution being obtained by laser diffraction from a dispersion of said particles in 1-propanol.

3. Volumetric D ９０ is less than 0.50 μm, preferably D ９０ is less than 0.45 μm, more preferably D ９０ 3. Particles according to claim 1 or 2, wherein the distribution is less than 0.42 μm, and said distribution is obtained by laser diffraction from a dispersion of said particles in 1-propanol.

4. A liquid composition (LC1) comprising particles according to any one of claims 1 to 3 dispersed in a liquid medium (L1).

5. The cerium oxide (CeO) according to any one of claims 1 to 3 ２ ) coated silica (SiO ２ ) a method for the production of particles (Method A), comprising: a) SiO ２ An aqueous suspension containing ammonia (NH ３ ) setting the pH value of the suspension to 8-9 by adding an aqueous solution; b) Adding Ce(N) to the suspension under stirring while maintaining the pH value at 8-9 by adding ammonia solution ３ ) ３ An aqueous solution was added to form SiO ２ obtaining a slurry containing cerium hydroxide precipitated thereon; c) filtering the slurry obtained in step b) to obtain SiO ２ recovering the cerium hydroxide deposited thereon in solid form; d) calcining the solid obtained in step c) in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain the cerium oxide (CeO ２ ) coated silica (SiO ２ ) obtaining a compound; e) optionally milling the recovered particles of step d) to obtain a desired particle size. A method comprising:

6. The cerium oxide (CeO) according to any one of claims 1 to 3 ２ ) coated silica (SiO ２ ) a method (Method A′) for the preparation of particles, comprising: a') preparing an aqueous ammonia solution (E) having a pH value set between 7 and 11; b') Adding aqueous ammonia (E') to maintain the pH value at 7-11, ３ ) ３ SiO suspended in aqueous solution ２ An aqueous suspension (S2) containing SiO ２ obtaining a slurry containing cerium hydroxide precipitated thereon; c') filtering the slurry obtained in step b') to remove SiO ２ recovering the cerium hydroxide deposited thereon in solid form; d') calcining the solid obtained in step c') in an oxidizing atmosphere at a temperature ranging from 250 to 800°C for a time ranging from 1 to 10 hours to obtain the cerium oxide (CeO ２ ) coated silica (SiO ２ ) obtaining a compound; e') optionally milling the recovered particles of step d') to obtain a desired particle size. A method comprising:

7. The cerium oxide (CeO) according to any one of claims 1 to 3 ２ ) coated silica (SiO ２ ) a method for the production of particles (Method B), comprising: a″) SiO ２ and ammonia (NH ３ ) and optionally at least one inorganic group —SO ２ providing an aqueous suspension containing a source of X; b″) Add Ce(NO ３ ) ３ The aqueous solution was treated with the NH ３ and Ce element in a molar ratio of 2 to 4, and SiO ２ obtaining a slurry containing cerium hydroxide precipitated thereon; c'') filtering the slurry obtained in step b'') to remove SiO ２ The cerium hydroxide Ce(OH) deposited on ３ recovering in solid form; d″) calcining the solid obtained in step c″) in an oxidizing atmosphere at a temperature ranging from 250 to 800° C. for a time ranging from 1 to 10 hours to obtain the cerium oxide (CeO ２ ) coated silica (SiO ２ ) obtaining a compound; e″) optionally milling the recovered particles of step d″) to obtain a desired particle size. A method comprising:

8. -SO ２ X functional group (wherein X is selected from X' or OZ, X' is selected from the group consisting of F, Cl, Br, I, and Z is H, an alkali metal, NH ４ and at least one polymer containing cerium oxide (CeO) according to any one of claims 1 to 3. ２ ) coated silica (SiO ２ ) particles.

9. The cerium oxide (CeO ２ ) coated silica (SiO ２ 9. The composition (C) of claim 8, wherein the .alpha.-.beta ...

10. -SO ２ 10. Composition (C) according to claim 8 or 9, wherein the polymer comprising X functional groups is a fluorinated polymer.

11. A liquid composition (LC) comprising a composition (C) according to any one of claims 8 to 10 dispersed in a liquid medium (L).

12. The liquid composition LC) of claim 11, wherein in said polymer X=OZ and Z=H.

13. The cerium oxide (CeO) according to any one of claims 1 to 3 ２ ) coated silica (SiO ２ ) particles and -SO ２ 13. A process for the preparation of a composition according to any one of claims 8 to 12, comprising mixing, in solid form or in a liquid medium (L), at least one polymer comprising an X functional group.

14. An article comprising the composition of any one of claims 8 to 10.

15. 15. The article of claim 14, which is a proton exchange membrane, an electrocatalyst layer, or a membrane electrode assembly.

16. 16. A method for the manufacture of an article according to claim 14 or 15, comprising impregnating, casting or coating with a liquid composition (LC) according to claim 11 or 12.

17. 16. A fuel cell or electrolysis cell comprising the article of claim 14 or 15.