Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8825—Methods for deposition of the catalytic active composition
  • H01M4/8853—Electrodeposition
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/50—Electroplating: Baths therefor from solutions of platinum group metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/50—Electroplating: Baths therefor from solutions of platinum group metals
  • C25D3/52—Electroplating: Baths therefor from solutions of platinum group metals characterised by the organic bath constituents used
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8803—Supports for the deposition of the catalytic active composition
  • H01M4/8807—Gas diffusion layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
  • H01M4/92—Metals of platinum group
  • H01M4/921—Alloys or mixtures with metallic elements
• • 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
• • 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
  • H01M2008/1095—Fuel cells with polymeric electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the field of the invention is that of electrochemically deposition processes for metal particles, in particular used for the formation of electrodes for fuel cells or for any type of electrode used in most electrochemical reactions (electrosynthesis, electrolysis of water, electrochemical sensors, supercapacities ...), whose active electrode surface must be important.
• the cost of the only noble metal used in fuel cells is currently estimated at 50% of the cost of the stack and between 20 to 25% of the total cost of the fuel cell system.
• One of the major objectives in the optimization of the electroplating technique is thus to reduce the size of the particles to diameters comparable to those obtained by chemical or physical synthesis, that is to say less than 10 nm. .
• Another method to reduce the particle size is to add a viscous agent in the electrolytic bath to slow down the diffusion of metal ions, which significantly reduces the particle size (from 5 to 30 nm) as described in the articles.
• a viscous agent in the electrolytic bath to slow down the diffusion of metal ions, which significantly reduces the particle size (from 5 to 30 nm) as described in the articles.
• the present invention relates to an original solution for limiting the size of the metal particles. It consists in using a chemical species having the property of easily and strongly adsorbing to the metal in order to limit the growth of the particles and to favor the germination phases during electroplating. In addition, this chemical species adsorbed on the surface of the metal must be easily desorbed (by electrochemical oxidation, for example).
• the subject of the present invention is a method for manufacturing an electronic and catalytic conductive electrode based on metal particles, comprising a step of electroplating a metal salt to form said metal particles on the surface of an electrode. characterized in that
• the step of electroplating the metal salt is carried out in the presence of a blocking chemical species having a high absorption capacity on the surface of said metal particles and having a higher oxidation potential than the reduction potential of said metal salt: In such a way that the blocking chemical species retains its blocking power during the reduction reaction of said metal salt and
• the high absorption capacity can be characterized by the absence of peaks on the voltammogram i versus the applied voltage E of the Pt, the absence of these peaks on the voltammogram reflecting the blocking of platinum adsorption sites by another species.
• the term voltammogram commonly used corresponding to the term voltammogram.
• voltammetry is a method of electroanalysis based on the measurement of the flow of current resulting from the reduction or oxidation of the compounds present in solution under the effect of a controlled variation of the potential difference between two specific electrodes. It makes it possible to identify and quantitatively measure a large number of compounds and also to study the chemical reactions including these compounds.
• the metal is platinum.
• the electrolytic deposition is carried out in the presence of a chemical blocking species of SO 2 .
• the electrolytic deposition is carried out in the presence of:
• the electrolytic deposition is carried out in the presence of nitrating blocking chemical species such as NO 2 - , NO 2 , NO 3 - .
• the electrolytic deposition is carried out in the presence of blocking chemical species of the sulfur compound type such as H 2 S.
• the desorption operation of the chemical species boquerante is carried out by oxidation of said species.
• the oxidation step is carried out by applying a sufficiently high potential relative to the equilibrium potential of the metal to be deposited, typically greater than about 0.76 V E RH. this case where the Pt is deposited from the platinic acid salt whose equilibrium potential is:
• Eeq ptci62- / pt 0.76 V ERH; the condition on the choice of the blocking species is that its oxidation potential is greater than 0.76 V E RH.
• the oxidation step is carried out by voltammetric scanning in an acid solution.
• the oxidation step is carried out by heat treatment.
• the electrolytic deposition step is performed on a porous electrode.
• the method further comprises depositing a microporous layer on the surface of the porous electrode.
• the method comprises the production of a hydrophilic surface at the level of the electrode, prior to the electrolytic deposition.
• the surface is rendered hydrophilic by deposition of an ink based on carbon black, glycerol and a suspension of Nafion in isopropanol.
• the process of the invention it is possible to reduce the particle size during the preparation of an electrode and in particular a fuel cell electrode.
• the process uses a chemical species known for its good adsorption properties on the metal after forming first seeds by electrodeposition. These germs become less favorable sites for growth and promote the formation of new metal particles.
• FIG. 1 illustrates the voltammetric curves of a solution of H 2 PtCl 6 without blocking agent and the voltammogram of Pt in a solution of 0.5M H 2 SO 4 with blocking agent (SO 2 );
• FIGS. 2a, 2b, 2c and 2d illustrate the various steps of an exemplary method of the invention
• FIG. 3 illustrates the voltage curve measured as a function of time, with regard to a pulsed signal applied
• FIG. 4 illustrates the effect of the oxidation of SO 2 on the electrochemical response of platinum
• FIG. 5 illustrates the size of the Pt particles obtained without and with SO 2 blocking chemical species in the electrolytic bath
• FIG. 6 illustrates the comparison of the voltammetry curves of electrodes obtained by electrodeposition with and without SO 2 chemical blocking species.
• the method of the invention requires the choice of potentials between the species to be deposited and the chemical blocking species.
• the metal to be deposited must have a lower reduction potential than the oxidation potential of the blocking chemical species. Compared with SO 2, other gases may be able to play this role in the case of Platinum.
• nitrated species such as: that oxidize at potentials greater than 0.9 V E RH,
• sulfur compounds such as hydrogen sulphide (H 2 S) whose oxidation potential is greater than 0.8V E RH as presented in article: R. Mohtadi, W.-k. Lee, S. Cowan, JW Van Zee, Mahesh Murthy, Electrochemical and Solid-State Letters, 2003, 6, 12, A272-A274, may also be an alternative for dispersion of platinum particles during electroplating.
• H 2 S hydrogen sulphide
• H 2 S hydrogen sulfide
• kP H2 s platinum kinetic adsorption constants of H 2 S for platinum measured at 50 ° C. are of the order of 0.0025 min -1 with an activation energy of the order of 28 kJ. mol "1 as described in the article by R. Mohtadi et al. / Applied Catalysis B: Environmental 56 (2005) 37-42].
• the adsorbed H 2 S is oxidized above 0.98 V at 50 ° C.
• the blocked sites and the growth sites may be different, which may lead to particles of different shapes. It thus becomes possible to improve the distribution and control the size of the metal particles for a desired catalytic application depending on the blocking chemical species. It should also be noted that if CO is not suitable for platinum, it may be interesting for other metals such as copper, nickel or tin among others, which have reduction potentials. less than 0.7 V E RH-
• the electrochemical deposition is carried out in an electrodeposition cell on a porous carbon support, such as the commercial diffusion layers (GDL "Gas Diffusion Layer” SGL Sigracet TM).
• the electrodeposition cell comprises a tantalum foam counter electrode spaced 1 cm from the working electrode on which the deposition takes place.
• the electrolytic bath is composed of a solution of platinum acid H 2 PtCl 6 at 20 mM diluted in 0.5 M sulfuric acid. 3.75 g of Na 2 SO 3 are added in the electrolytic bath so as to obtain a solution saturated with SO 2 according to the following reaction:
• Figure 1 illustrates the relevance of the choice of sulfur dioxide in this process. Indeed, it is clear that the oxidation potential of SO 2 is at 1 VERH (the ERH acronym denoting an electrode of
• Curve Ci a shows the evolution of the measurement by voltammetry in a 20mM solution of H 2 PtCl 6 , in the absence of SO 2 species.
• FIGS. 2a, 2b, 2c and 2d the various steps of an exemplary method of the invention are shown diagrammatically in FIGS. 2a, 2b, 2c and 2d.
• a microporous layer C 2 of porosity is deposited which is suitable for the application envisaged, in this example that of the fuel cell.
• This microporous layer may typically comprise a binder and carbon powder but has the disadvantage of being hydrophobic.
• a surface treatment is then carried out to render the latter hydrophilic with an ink layer C 3 deposition as illustrated in FIG. 2a.
• a first diffusion layer Ci which can be a 25 cm 2 commercial diffusion layer SGL is treated to render the surface hydrophilic.
• This treatment consists in spraying, as illustrated in FIG. 2b, an ink C 3 whose mass ratio of the various constituents is as follows: 1 / 0.5 / 45/1 for carbon black (CB), Nafion, isopropanol, and Glycerol, respectively.
• This deposit is then placed in an oven for complete evaporation of the solvents at 80 ° C for 30 min.
• the electrochemical deposition of Pt is then carried out as illustrated in FIG. 2c, forming a layer C ' 3 of particles of Pt.
• the deposition is carried out in the electrolytic bath described above by controlling the current with a pulsed signal such as that illustrated in FIG.
• the signal consists of the application of a so-called pulsed current whose parameters are as follows:
• jp C is the current applied during the draw: 100 imA / cm 2 ⁇ ⁇ is the duration of the draw and is worth: 10ms
• n peaks the number ofoperaes in this example is 24 Once the number of peaks reached, the signal is stopped to allow the system to return to a state of equilibrium. During this relaxation period, the concentration of PtCl 6 2 " returns to a non-zero value in the vicinity of the electrode, this relaxation time noted ⁇ 0 ⁇ is 45s.
• n b0U cies pulse signal + relaxation time
• FIG. 3a is a representation of the pulsed signal followed by the relaxation time.
• the voltage response to this galvanic signal is shown in FIG. 3b where each voltage drop corresponds to the signal (pulsed current) and each voltage jump corresponds to the moment at which the pulsed signal is stopped (relaxation time).
• the deposition signal can be applied twice, spraying 1 ml of hydrophilic ink between two deposits.
• the oxidation of SO2 is carried out by simple voltammetric scanning at 20 mV / s between -50 ITIVERH and 1400 ITIVERH in a solution of sulfuric acid at 0.5 M saturated with inert gas such as nitrogen. After a few cycles, the signal i versus E, becomes stable and the electrochemical signature of Pt is clearly observable. It can then be considered that the sulfur dioxide is completely oxidized to sulphate in the solution of 0.5M H 2 SO 4 as shown in FIG. 4. The presence of Pt particles at the diffusion layer surface makes it possible to obtain an electrode which will then have to undergo a heat treatment in order to eliminate the traces of glycerol present in the active layer. 4a is the curve C on a first cycle, in Figure 4 C.
• the active surface (gray zone) is larger, as can be seen in FIG. 6a relates to a deposit made with blocking case, the curve C 6 b relates to a deposit made without blocking case.
• the areas A C 6a and A C 6b are representative of the sizes of the metal particles thus formed for a given abscissa, the higher the area and the smaller the particle size.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Engineering & Computer Science (AREA)
• General Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Manufacturing & Machinery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Inert Electrodes (AREA)
• Catalysts (AREA)
• Electroplating Methods And Accessories (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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• 2011
  • 2011-04-27 FR FR1153606A patent/FR2974582A1/fr not_active Withdrawn
• 2012
  • 2012-04-18 JP JP2014506822A patent/JP6238889B2/ja active Active
  • 2012-04-18 KR KR1020137028339A patent/KR102040338B1/ko active Active
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