EP2946430A1 - Proton conductive membrane deposited by hot wire cvd technique - Google Patents

Proton conductive membrane deposited by hot wire cvd technique

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Publication number
EP2946430A1
EP2946430A1 EP13718378.6A EP13718378A EP2946430A1 EP 2946430 A1 EP2946430 A1 EP 2946430A1 EP 13718378 A EP13718378 A EP 13718378A EP 2946430 A1 EP2946430 A1 EP 2946430A1
Authority
EP
European Patent Office
Prior art keywords
substrate
layer
anyone
immersing
polymer
Prior art date
Legal status (The legal status 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 status listed.)
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Application number
EP13718378.6A
Other languages
German (de)
French (fr)
Inventor
Jessica Thery
Delphine Boutry
Philippe Capron
Fabio Palumbo
Riccardo D'agostino
Anna Maria Coclite
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Universita degli Studi di Bari Aldo Moro
Original Assignee
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Universita degli Studi di Bari Aldo Moro
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Application filed by Commissariat a lEnergie Atomique et aux Energies Alternatives CEA, Universita degli Studi di Bari Aldo Moro filed Critical Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Publication of EP2946430A1 publication Critical patent/EP2946430A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/20—Manufacture of shaped structures of ion-exchange resins
    • C08J5/22—Films, membranes or diaphragms
    • 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
    • H01M8/1039—Polymeric electrolyte materials halogenated, e.g. sulfonated polyvinylidene fluorides
    • 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
    • H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the invention relates to a method for manufacturing a proton conductive membrane.
  • proton conductive membranes are made by wet polymerization. They are integrated in proton exchange membranes via a hot pressing step or via spraying / jet techniques.
  • the membranes were synthesized by plasma polymerization of triflic acid and styrene or 1 -3 butadiene.
  • the membranes obtained present strong mechanical limitations for being integrated in proton exchange membranes for fuel cells. Indeed, the precursors used in this prior art documents have short and strongly cross-linked fluoro-carbonated chains, so poor mechanical properties of the obtained membranes being associated. Indeed, the membranes used for proton conductive materials must present very good mechanical properties.
  • FR2909013 proposes to manufacture proton conductive layers by plasma assisted chemical vapour deposition of water with a fluorocarbon precursor.
  • the layers which are thus deposited are functionalised by carboxylic acid functions.
  • Carboxylic acids have pKa much higher than sulfonic acids. Consequently, to obtain high proton conductivities with carboxylic functions, a high concentration of carboxylic functions is required. This is responsible for the low mechanical properties of the obtained layers.
  • FR2928227 proposes to manufacture a proton conductive membrane using a chemical deposition by plasma vaporization.
  • Two precursors are polymerized, each containing at least one polymerizable group or one ionic group.
  • the precursors are chosen among phosphonyl ester, acyl ester, sulfonyl ester, carbonyl ester and thionyl halide. Because the precursors are plasma vaporized, there is a huge risk to damage the chemical structure of the precursors during this vaporization step. Taking into account the very low stability of the persilylated compounds, these latters can hardly be considered as viable precursors for a commercial application.
  • the invention aims to palliate these drawbacks of the prior art proton conductive membranes.
  • the invention proposes a method for depositing a proton conductive membrane on the surface of a substrate comprising the following steps:
  • - A is P or S
  • - R is a Ci-C 25 , saturated or unsaturated, linear or branched, alkyl chain optionally comprising a cyclic or aromatic group, and
  • the substrate temperature is comprised between 5 and 40°C, preferably is 20°C.
  • the polymerisation initiator is a radical initiator, preferably ter-butyl peroxide, or ter-amyl peroxide.
  • the polymerisation initiator in step a) is a photo-polymerisation initiator, preferably benzophenone or 2,20-azobiz (2- methylpropane).
  • step b) preferably comprises the following steps: bl) immersing the substrate covered with layer of polymer obtained in step a) in a basic solution having a pH > 7, preferably > 10, and
  • step bl immersing the substrate covered with layer obtained in step bl) in an acid solution having a pH ⁇ 7, preferably ⁇ 5.
  • step b) can also comprise the following steps:
  • step b'O peeling off the layer obtained in step a) from the substrate, b'l) immersing the layer in a basic solution having a pH > 7, preferably > 10, and
  • step b'2 immersing the substrate covered with layer obtained in step bl) in an acid solution having a pH ⁇ 7, preferably ⁇ 5.
  • the basic solution in step bl) or b'l) comprises a polar aprotic solvent, preferably chosen among dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or hexamethylphosphoramide (HMPA) and mixtures thereof.
  • a polar aprotic solvent preferably chosen among dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or hexamethylphosphoramide (HMPA) and mixtures thereof.
  • the gaseous mixture in step a) further comprises at least one monomer having a formula different from formula I, preferably ethylene glycol dimethacrylate (EGDMA).
  • EGDMA ethylene glycol dimethacrylate
  • the temperature of the wire (filament) is between 260 and 360°C, preferably 280°C.
  • the surface of the substrate on which the proton conductive membrane is preferably made of ceramic, glass, silica or silicon.
  • the surface of the substrate on which the layer of polymer is deposited has a root mean square (RMS) higher than 5 nm, preferably higher than 500 nm, and preferably lower than 1 nm.
  • RMS root mean square
  • the RMS is the mean value of the average geometric difference, as compared to the average line of the roughness.
  • a particularly preferred monomer of formula I used in the process of the invention is perfluoro(4-methyl-3,6-dioxaoct-7ene) sulfonylfluoride and the polymerisation initiator preferably is a radical initiator, preferably tert-butyl peroxide (TBO).
  • TBO tert-butyl peroxide
  • the invention proposes to manufacture a proton conductive membrane by depositing sulfonyl and/or phosphonyl halide precursors via a hot wire CVD mechanism on the surface of a substrate.
  • the temperature of the substrate is preferably comprised between 5 and 40°C. More preferably, the temperature of the substrate is 20°C.
  • the method of the invention then comprises the chemical transformation of the sulfonyl/phosphonyl halides of the obtained layer into the corresponding sulfonic/phosphonic acid forms.
  • the deposition of the polymer layer is made by a hot wire (filament)
  • initiated CVD will be used.
  • the layer is deposited using at least two monomers having the following formula I:
  • - A is P or S
  • - R is a CrC 25 , saturated or unsaturated, linear or branched, alkyl chain optionally comprising a cyclic or aromatic group.
  • each monomer at least one vinyl or fluorovinyl group is present.
  • These precursor monomers are into a gaseous flow together with a polymerisation initiator.
  • the initiator can be a radical initiator, such as tert-butyl peroxide (TBPO), or ter-amyl peroxide or similar peroxide compounds.
  • TBPO tert-butyl peroxide
  • ter-amyl peroxide or similar peroxide compounds.
  • the radical initiator is chosen among those able to dissociate in radicals at temperature lower than 300 °C.
  • the radical initiator is TBPO.
  • the initiator may be a photo-initiator such as benzophenone and 2,20-azobiz (2-methylpropane).
  • the substrate on which the polymer layer is deposited will be illuminated by the suitable radiation.
  • a UV radiation will be used.
  • the sulfonyl and/or phosphonyl halides of the obtained membrane are transformed into the corresponding sulfonic/phosphonic acid forms according to the following equations:
  • the temperature of the wire is between 260 and 360°C, preferably 280°C.
  • the layer is deposited on the surface of the substrate having a roughness higher than 500 nm, preferably higher than 500 nm RMS and preferably lower than 1 nm in order to improve the adhesion of the layer on the substrate.
  • the surface of the substrate on which the layer of polymer is deposited may be patterned. It may be made of ceramic such as alumina (A1 2 0 3 ), zirconium (Zr0 2 ) and titanium oxide (Ti0 2 ), glass, silica or silicon.
  • ceramic such as alumina (A1 2 0 3 ), zirconium (Zr0 2 ) and titanium oxide (Ti0 2 ), glass, silica or silicon.
  • the gaseous flow containing the monomer precursors and the polymerisation initiator may also contain monomers different from the monomers precursors of formula I to modulate the properties of the layer of polymer which is deposited.
  • molecules with specific groups such as aromatic groups, may be added to improve the mechanical resistance of the deposited layer.
  • Monomers with long linear chain may be also added to obtain a better elasticity of the larger of polymer which is deposited.
  • a radical polymerisation cross-linker such as ethylene glycol dimethacrylate (EGDMA) may be added to the flow to modulate the coating cross-linking, more particularly for improving the coating cross-linking.
  • EGDMA ethylene glycol dimethacrylate
  • EGDMA contains two groups which can participate to the polymerisation thus creating a highly reticulated network.
  • the chemical transformation of the sulfonyl/phosphonyl halides of the polymer which is deposited is a step of hydrolysis of the layer which has been deposited.
  • the layer after having been peeled off the substrate, or more preferably, the substrate covered of the layer, is immersed in a basic solution such as a NaOH or a KOH solution.
  • a basic solution such as a NaOH or a KOH solution.
  • This solution has a pH > 7, preferably > 10.
  • a solvent is added to the basic (or salt) solution.
  • a preferred solution is made of 15% of KOH, 50 wt% of solvent and 50 wt% of water.
  • the solvent is a polar aprotic solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and HMP A.
  • this solvent enables to expand the polymer layer so that the Na + or K + species may migrate into the layer.
  • the layer of polymer, or more preferably the substrate covered of the layer is immerged in an acid solution having a pH ⁇ 7, preferably ⁇ 5 such as a solution of HN0 3 or H 2 S0 4 , for acidifying the layer which is necessary for membranes for fuel cells.
  • an acid solution having a pH ⁇ 7, preferably ⁇ 5 such as a solution of HN0 3 or H 2 S0 4 , for acidifying the layer which is necessary for membranes for fuel cells.
  • the proton conductive membranes obtained by the method of the invention may be used in particular in micro fuel cells.
  • Perfluoro(4-methyl-3,6-dioxaoct-7ene) sulfonylfluoride is liquid. It is vaporized in the vacuum chamber with an initiator, TBPO, and nitrogen.
  • the filament (wire) of the CVD apparatus is heated at 280°C and the substrate is maintained at 20°C.
  • the NiCr filament of the CVD apparatus is heated by DC power supply of 36W (current 2 A at 18V) and the substrate holder is at 20 mm from the filament.
  • the substrate holder is cooled down at 20°C.
  • the monomer flow rate is 2 seem, TBPO and nitrogen are introduced at 2 and 1 seem respectively, and the total pressure is 2 torr during 1 h to obtain a thickness of membrane of 240 nm.
  • a fluorocarbon polymer coating of about 200 nm is obtained with a deposition rate of 4 nm/min.
  • This coating is then hydrolysed by immersing the polystyrene substrate with its fluorocarbon coating in a 7.68 M KOH basic solution consisting of KOH in a mixture of DMSO (dimethyl sulfoxide) and H 2 0 and then in an 0.25 M HN0 3 acidic solution consisting of HN0 3 and H 2 0.
  • the FTIR spectrum of the layer of sulfonylfluoride is shown in figure 1. As one can see on figure 1, a clear band can be distinguished at 1460 cm "1 , that confirms the presence of S0 2 -F groups.
  • Nanoindentation measures were made and a hardness value of 0.04 +/-0.01 GPa was found (for comparison, with the same method, hardness of 0.06 +/- 0.01 GPa was measured on a Nafion membrane 50 ⁇ thick and deposited via roller blade method).

Abstract

The invention relates to a method for manufacturing a proton conductive membrane. The method of the invention comprises the following steps: a) depositing on said surface of said substrate a layer of polymer material by hot wire chemical vapour deposition starting from a gaseous mixture comprising: at least two monomers having the following formula (I): RFyOzA02X wherein: A is P or S; X is F or C1; 1 ≤ y ≤ 25; 0 ≤ z ≤ 6; R is a C1-C25, saturated or unsaturated, linear or branched, alkyl chain optionally comprising a cyclic or aromatic group, and a polymerisation initiator, and b) hydrolysis of the layer of polymer obtained in step a). The invention is usable in the field of storage and restitution of energy, in particular.

Description

PROTON CONDUCTIVE MEMBRANE DEPOSITED BY HOT WIRE CVD TECHNIQUE
The invention relates to a method for manufacturing a proton conductive membrane.
Generally, proton conductive membranes are made by wet polymerization. They are integrated in proton exchange membranes via a hot pressing step or via spraying / jet techniques.
However, cohesive thin films having a thickness lower than ΙΟμηι cannot be deposited, and a deposition on 3D patterns is not possible, by this method.
Thus, alternative deposition methods have been proposed, such as vacuum deposition.
Various authors have studied the deposition of proton conductive membranes by vacuum techniques.
Zhongqing Jiang et al. in Plasma Process. Polym. 2010, 7, 382-389, have demonstrated a possibility of depositing sulfonic membranes by plasma enhanced chemical vapour deposition (PECVD). The membranes were synthesized by plasma polymerization of a mixture of styrene and trifluoromethane sulfonic acid monomers in a low-frequency after-glow Capacitively Coupled Plasma (CCP) discharge process.
In FR2894077, the membranes were synthesized by plasma polymerization of triflic acid and styrene or 1 -3 butadiene.
Brault et al, in Eur. Phys. J. Appl. Phys. 42, 9-15 (2008), describe the polymerization by PECVD of a carbonated monomer with an acid.
However, the membranes obtained present strong mechanical limitations for being integrated in proton exchange membranes for fuel cells. Indeed, the precursors used in this prior art documents have short and strongly cross-linked fluoro-carbonated chains, so poor mechanical properties of the obtained membranes being associated. Indeed, the membranes used for proton conductive materials must present very good mechanical properties.
FR2909013 proposes to manufacture proton conductive layers by plasma assisted chemical vapour deposition of water with a fluorocarbon precursor. The layers which are thus deposited are functionalised by carboxylic acid functions. Carboxylic acids have pKa much higher than sulfonic acids. Consequently, to obtain high proton conductivities with carboxylic functions, a high concentration of carboxylic functions is required. This is responsible for the low mechanical properties of the obtained layers.
Even though the materials are strongly cross-linked, they are also brittle and cannot sustain the strong deformation required for the working of the membrane.
FR2928227 proposes to manufacture a proton conductive membrane using a chemical deposition by plasma vaporization. Two precursors are polymerized, each containing at least one polymerizable group or one ionic group. The precursors are chosen among phosphonyl ester, acyl ester, sulfonyl ester, carbonyl ester and thionyl halide. Because the precursors are plasma vaporized, there is a huge risk to damage the chemical structure of the precursors during this vaporization step. Taking into account the very low stability of the persilylated compounds, these latters can hardly be considered as viable precursors for a commercial application. In addition, size effects during the hydrolysis may lead to the degradation of the membrane or to the formation of defects, since the size of the persylilated groups is far more elevated than the size of the hydrogen atoms. Furthermore, for all these precursors, the hydrolysis of the membranes from phosphonyl ester, sulfonyl ester and acyl ester precursors is quite difficult and the membrane may be damaged by the strong hydrolysis conditions. In addition, because the size of the ester group is much higher than the size of the hydrogen, defects can be created during the hydrolysis of the membrane. As to the thionyl halides precursors, they might be degraded into S02 during the hydrolysis reaction and will not lead to the formation of proton conductive groups.
Uchimoto et al., in Ber. Bunsenges. Phys. Chem. 97 (1993) No. 4, propose to deposit membranes with sulfonic acid groups using plasma enhanced chemical vapour deposition. However, the content of sulfonic groups drops drastically due to the elevated plasma power required for obtaining acceptable growth rates. In addition, working with PECVD at a low input energy per unit mass of monomer leads to a too low reticulation of the film formed and the film is permeable to hydrogen, which renders not possible its use in fuel cells. To summarize, some of the proton conductive membranes of the prior art do not present the adequate mechanical properties and some other suffers from degradation during the post treatment step or the vaporization step. Some other present a low density of cross-linked function.
The invention aims to palliate these drawbacks of the prior art proton conductive membranes.
For this aim, the invention proposes a method for depositing a proton conductive membrane on the surface of a substrate comprising the following steps:
a) depositing on said surface of said substrate a layer of polymer material by hot wire chemical vapour deposition starting from a gaseous mixture comprising:
. at least two monomers having the following formula I:
RFyOzA02X
wherein:
- A is P or S,
- X is F or CI,
- i < y < 25,
- 0 < z < 6,
- R is a Ci-C25, saturated or unsaturated, linear or branched, alkyl chain optionally comprising a cyclic or aromatic group, and
. a polymerisation initiator,
b) hydrolysis of the layer of polymer obtained in step a)
In one embodiment, the substrate temperature is comprised between 5 and 40°C, preferably is 20°C.
In one embodiment, in step a), the polymerisation initiator is a radical initiator, preferably ter-butyl peroxide, or ter-amyl peroxide.
In another embodiment, the polymerisation initiator in step a) is a photo-polymerisation initiator, preferably benzophenone or 2,20-azobiz (2- methylpropane).
In all the embodiments, step b) preferably comprises the following steps: bl) immersing the substrate covered with layer of polymer obtained in step a) in a basic solution having a pH > 7, preferably > 10, and
bl) immersing the substrate covered with layer obtained in step bl) in an acid solution having a pH < 7, preferably < 5.
But step b) can also comprise the following steps:
b'O) peeling off the layer obtained in step a) from the substrate, b'l) immersing the layer in a basic solution having a pH > 7, preferably > 10, and
b'2) immersing the substrate covered with layer obtained in step bl) in an acid solution having a pH < 7, preferably < 5.
In any case, preferably the basic solution in step bl) or b'l) comprises a polar aprotic solvent, preferably chosen among dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or hexamethylphosphoramide (HMPA) and mixtures thereof.
In all the embodiments, preferably, the gaseous mixture in step a) further comprises at least one monomer having a formula different from formula I, preferably ethylene glycol dimethacrylate (EGDMA).
Preferably, the temperature of the wire (filament) is between 260 and 360°C, preferably 280°C.
The surface of the substrate on which the proton conductive membrane is preferably made of ceramic, glass, silica or silicon.
Still preferably, the surface of the substrate on which the layer of polymer is deposited has a root mean square (RMS) higher than 5 nm, preferably higher than 500 nm, and preferably lower than 1 nm.
The RMS is the mean value of the average geometric difference, as compared to the average line of the roughness.
A particularly preferred monomer of formula I used in the process of the invention is perfluoro(4-methyl-3,6-dioxaoct-7ene) sulfonylfluoride and the polymerisation initiator preferably is a radical initiator, preferably tert-butyl peroxide (TBO).
The invention will be better understood and other features and advantages of the process of the invention will become more clearly apparent when reading the description which follows which is made in reference to annexed figure which shows the FTIR spectrum of a proton conductive membrane obtained with the process of the invention.
Briefly stated, the invention proposes to manufacture a proton conductive membrane by depositing sulfonyl and/or phosphonyl halide precursors via a hot wire CVD mechanism on the surface of a substrate.
The temperature of the substrate is preferably comprised between 5 and 40°C. More preferably, the temperature of the substrate is 20°C.
By using a hot wire CVD process, it is possible to choose the groups which will be "opened" to obtain the polymerisation.
The method of the invention then comprises the chemical transformation of the sulfonyl/phosphonyl halides of the obtained layer into the corresponding sulfonic/phosphonic acid forms.
The deposition of the polymer layer is made by a hot wire (filament)
CVD technique.
Preferably, initiated CVD will be used.
The layer is deposited using at least two monomers having the following formula I:
RFyOzA02X Formula I
in which:
- A is P or S,
- X is F or CI,
- l < y < 25,
- 0 < z < 6,
- R is a CrC25, saturated or unsaturated, linear or branched, alkyl chain optionally comprising a cyclic or aromatic group.
In each monomer, at least one vinyl or fluorovinyl group is present. These precursor monomers are into a gaseous flow together with a polymerisation initiator.
The initiator can be a radical initiator, such as tert-butyl peroxide (TBPO), or ter-amyl peroxide or similar peroxide compounds.
Generally speaking, the radical initiator is chosen among those able to dissociate in radicals at temperature lower than 300 °C.
Preferably, the radical initiator is TBPO. As an alternative, the initiator may be a photo-initiator such as benzophenone and 2,20-azobiz (2-methylpropane). When using such photo-initiators, the substrate on which the polymer layer is deposited will be illuminated by the suitable radiation. In the case of benzophenone or 2,20-azobiz (2-methylpropane), a UV radiation will be used.
Once the layer of polymer is deposited, the sulfonyl and/or phosphonyl halides of the obtained membrane are transformed into the corresponding sulfonic/phosphonic acid forms according to the following equations:
RS02X + NaOH (or KOH)- RS03Na (or K) + HX RS03Na (or K) + HN03 -» RSO3H + Na+ (or +) + N03 ".
Preferably, the temperature of the wire is between 260 and 360°C, preferably 280°C.
Also preferably, the layer is deposited on the surface of the substrate having a roughness higher than 500 nm, preferably higher than 500 nm RMS and preferably lower than 1 nm in order to improve the adhesion of the layer on the substrate.
The surface of the substrate on which the layer of polymer is deposited may be patterned. It may be made of ceramic such as alumina (A1203), zirconium (Zr02) and titanium oxide (Ti02), glass, silica or silicon.
The gaseous flow containing the monomer precursors and the polymerisation initiator may also contain monomers different from the monomers precursors of formula I to modulate the properties of the layer of polymer which is deposited.
For example, molecules with specific groups, such as aromatic groups, may be added to improve the mechanical resistance of the deposited layer.
Monomers with long linear chain may be also added to obtain a better elasticity of the larger of polymer which is deposited.
Furthermore, a radical polymerisation cross-linker, such as ethylene glycol dimethacrylate (EGDMA) may be added to the flow to modulate the coating cross-linking, more particularly for improving the coating cross-linking.
Indeed, EGDMA contains two groups which can participate to the polymerisation thus creating a highly reticulated network. The chemical transformation of the sulfonyl/phosphonyl halides of the polymer which is deposited is a step of hydrolysis of the layer which has been deposited.
For this aim, the layer after having been peeled off the substrate, or more preferably, the substrate covered of the layer, is immersed in a basic solution such as a NaOH or a KOH solution. This solution has a pH > 7, preferably > 10. Preferably, a solvent is added to the basic (or salt) solution. A preferred solution is made of 15% of KOH, 50 wt% of solvent and 50 wt% of water. Still preferably, the solvent is a polar aprotic solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and HMP A.
Indeed, this solvent enables to expand the polymer layer so that the Na+ or K+ species may migrate into the layer.
Then, the layer of polymer, or more preferably the substrate covered of the layer, is immerged in an acid solution having a pH < 7, preferably < 5 such as a solution of HN03 or H2S04, for acidifying the layer which is necessary for membranes for fuel cells.
The proton conductive membranes obtained by the method of the invention may be used in particular in micro fuel cells.
In order to better illustrate the invention, an example of carrying out the method of the invention is now given only for illustrative and in no case for limitative purposes.
Example 1:
In this example, perfluoro(4-methyl-3,6-dioxaoct-7ene) sulfonylfluoride is deposited by initiated CVD on a substrate made of polystyrene of 20 x 20 mm, thickness = 1 mm.
Perfluoro(4-methyl-3,6-dioxaoct-7ene) sulfonylfluoride is liquid. It is vaporized in the vacuum chamber with an initiator, TBPO, and nitrogen.
In this example, the filament (wire) of the CVD apparatus is heated at 280°C and the substrate is maintained at 20°C.
The NiCr filament of the CVD apparatus is heated by DC power supply of 36W (current 2 A at 18V) and the substrate holder is at 20 mm from the filament. The substrate holder is cooled down at 20°C.
The monomer flow rate is 2 seem, TBPO and nitrogen are introduced at 2 and 1 seem respectively, and the total pressure is 2 torr during 1 h to obtain a thickness of membrane of 240 nm.
A fluorocarbon polymer coating of about 200 nm is obtained with a deposition rate of 4 nm/min.
This coating is then hydrolysed by immersing the polystyrene substrate with its fluorocarbon coating in a 7.68 M KOH basic solution consisting of KOH in a mixture of DMSO (dimethyl sulfoxide) and H20 and then in an 0.25 M HN03 acidic solution consisting of HN03 and H20.
The FTIR spectrum of the layer of sulfonylfluoride is shown in figure 1. As one can see on figure 1, a clear band can be distinguished at 1460 cm"1, that confirms the presence of S02-F groups.
Nanoindentation measures were made and a hardness value of 0.04 +/-0.01 GPa was found (for comparison, with the same method, hardness of 0.06 +/- 0.01 GPa was measured on a Nafion membrane 50μπι thick and deposited via roller blade method).

Claims

1. A method for depositing a proton conductive membrane on the surface of a substrate comprising the following steps:
a) depositing on said surface of said substrate a layer of polymer material by hot wire chemical vapour deposition starting from a gaseous mixture comprising:
. at least two monomers having the following formula I:
RFyOzA02X
wherein:
- A is P or S,
- X is F or CI,
- i≤y < 25,
- 0 < z < 6,
- R is a Cj-C25, saturated or unsaturated, linear or branched, alkyl chain optionally comprising a cyclic or aromatic group, and
. a polymerisation initiator,
b) hydrolysis of the layer of polymer obtained in step a).
2. The method according to claim 1 , wherein the temperature of the substrate is comprised between 5 and 40°C, preferably is 20°C.
3. The method according to claim 1 or 2, wherein the polymerisation initiator in step a) is a radical initiator, preferably tert-butyl peroxide, or ter-amyl peroxide.
4. The method according to claim 1 or 2, wherein the polymerisation initiator in step a) is a photo-polymerisation initiator, preferably benzophenone or 2,20-azobiz (2-methylpropane).
5. The method according to anyone of the preceding claims, wherein step b) comprises the following steps:
bl) immersing the substrate covered with layer of polymer obtained in step a) in a basic solution having a pH > 7, preferably > 10, and
b2) immersing the substrate covered with layer obtained in step bl) in an acid solution having a pH < 7, preferably < 5.
6. The method according to anyone of claims 1-5, wherein step b) comprises the following steps:
b'O) peeling off the layer obtained in step a) from the substrate, b'l) immersing the layer in a basic solution having a pH > 7, preferably > 10, and
b'2) immersing the substrate covered with layer obtained in step bl) in an acid solution having a pH < 7, preferably < 5.
7. The method according to claim 5 or 6, wherein the basic solution in step bl) or b'l) comprises a polar aprotic solvent, preferably chosen among dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or hexamethylphosphoramide (HMPA), and mixtures thereof.
8. The method according to anyone of the preceding claims, wherein the gaseous mixture in step a) further comprises at least one monomer having a formula different from formula I, preferably ethylene glycol dimethacrylate (EGDMA).
9. The method according to anyone of the preceding claims, in which the temperature of the wire (filament), in step a) is between 260 and 300°C, preferably is 280°C.
10. The method according to anyone of the preceding claims, wherein the surface of the substrate is made of ceramic, glass, silica or silicium.
11. The method according to anyone of the preceding claims, wherein the surface of the substrate on which the layer of polymer is deposited as a root mean square (RMS) higher than 5 nm, preferably higher than 500 nm, and preferably lower than 1 mm.
12. The method according to anyone of the preceding claims, in which the monomer of formula I is perfluoro(4-methyl-3,6-dioxaoct-7ene) sulfonylfluoride and the polymerisation initiator is a radical initiator, preferably tert- butyl peroxide (TBO).
EP13718378.6A 2013-01-18 2013-01-18 Proton conductive membrane deposited by hot wire cvd technique Withdrawn EP2946430A1 (en)

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FR2909013B1 (en) 2006-11-28 2011-02-25 Commissariat Energie Atomique THIN FILM COATING PROCESS
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