JPH02502320A - Electrochemical method for producing pore-free palladium-based membranes supported on porous metal elements - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Electrification of poreless membranes based on palladium supported on porous metal elements Field of scientific manufacturing method technology A pore-free membrane based on palladium supported by a porous metal element is Relating to a method of chemical production. To explain in more detail, precious metals such as brass Starting material is an alloy thin film consisting of a metal with little noble metal property, and fine Pd/Ag- The film is electrolytically deposited on one side of the alloy film, and the other side of the alloy film is electrically deposited for several hours. During periodic treatment, less precious metals are gradually and completely dissolved. , regarding a method for leaving copper in a porous metal element as a carrier for a Pa/Ag thin film. do.

technology background Separation or purification of gas mixtures often requires selective passage of the gas to preserve residual components. A semipermeable membrane is used to retain the fluid. Palladium/silver fines are still used for hydrogen purification. Pore-free membranes or synthetic resin membranes with capillary membranes are important for their ideal selectivity. be.

In this case, the proportion of palladium is usually between 75 and 80%; It has been carried out in a temperature range between 0 and 400°C. Palladium and many palladiums The alloy can be used with such membranes to have particularly good hydrogen dissolution ability. At low temperatures, hydrogen is applied to the surface of a suitable catalyst, especially a finely coated palladium or platinum. It was possible to substantially improve the adsorption or desorption of hydrogen. F, v , 5tur- German patent (DE Pat,) 1265257 (196g) describes the use of such Pd/Ag-membranes as thin film anodes in alkaline fuel cells. It has been proposed for use. The hydrogen and other things supplied at that time are in front. It may contain gas components such as carbon dioxide derived from the reforming process. P d/Ag-membrane, carbon dioxide gas is brought into contact with caustic potash used as an electrolyte; This prevents general neutralization and deactivation. Palladium-containing membranes also accumulate It can be used in hydrogen sensors with other components.

As the hydrogen permeability of such membranes increases with increasing thickness, Fick's law Considering the simple fact that palladium is reduced by Efforts have been made to produce membranes as thin as possible. High melting point of palladium and its hardness makes thin film production difficult. For example, in Sortiment Firsa Goodfellow has a palladium membrane as the membrane increases. The price of palladium has decreased, compared to the price of palladium, and in the case of thin (non-porous) membranes , can no longer be obtained, and thin films below 41 can only be provided on thin films of synthetic resin carriers. It's just that.

Various studies have been carried out to produce Pd/Ag-films grown at high temperatures and bonded to carriers. It's been coming. V., M., Grjaznov and others proposed a three-layer arrangement (Doi TS Patent Publication No. 2710277 (1978)). Is it nickel, copper or iron? and an organosilicon polymer with a thickness of 0.05-1 am. evaporated or plasma sprayed onto the film and 0.001-0.1 μm thick polymer , consisting of a palladium layer coated by chemical or electrolytic deposition. water The selectivity for semipermeable membranes is generally here palladium, which is not poreless. The objective is not only achieved by membranes, but also by organosilicon thin films.

This membrane, however, is particularly suitable for use in fuel cells when conducting current through thin Pd/Ag membranes. It conducts electricity insufficiently in one layer and is naturally unstable in the presence of a weak alkali (electrolyte). Therefore, it is not suitable. Johnson-Matthey perforated metal carrier Pd/Ag-membranes bonded to bodies or metal networks do not have this drawback (European Patent patent o+aso (t9g4)). However, here the Pd/Ag-thin film is under normal pressure. Palladium must be produced by rolling, so its thickness and palladium--all of which are in demand. There are limitations as discussed above.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention utilizes a single palladium-based membrane directly on a porous metal element. It shows how it can be manufactured. In this case, palladium, palladium alloys, especially palladium Electrochemical deposition of dium/silver alloys is gold-intensive, such as evaporation as a deposition method. Superior to less effective methods. Electrochemical deposition on copper is well known. On the other hand, electricity There are various methods to ensure that metal ions always exist as complexes in the solute. complex form As adults, for example, glycine) (LJ, 5cbuster and D, Heppner, German Patent Publication No. 2657925 (1987), Ann. Monia (B, Sturzenegger and J, CI.

Pu1pI)e, Plat, Met, Rev, H/3 (1984)), Fatty polyamines (J, A, Abys and E, S, Trop, Europe Patent Application 0.059452A2 (1982)), or halides (P, Bluibach et al., German Patent Publication No. 3041740Al (1981)) becomes a problem.

For example, sintered bodies, especially sintered thin films, may be considered as porous metal elements. . In contrast, it has the potential to deposit palladium alloys on smooth metal surfaces. Because of the problems when depositing pore-free membranes on porous metal elements, it In order to avoid A method using genus elements has been proposed.

For this purpose, a thin film alloy consisting of a precious metal and a metal with little precious metal properties is the starting point. Ru. For example, copper/zinc alloy (brass), copper/tin alloy (bronze),! / aluminum Mu alloys, nickel/aluminum alloys, etc. are problematic. In particular, comparison Commercially available thin brass films with a high zinc content are suitable.

Porosity selectively, in fact quantitatively, removes less noble metals, in this case zinc. It is manufactured by melting a thin film alloy without changing the dimensions of the parts.

The method is known, for example, Raney nickel (Raney-!1fcke). l). There, aluminum/di-kel powder was converted into a concentrated alkaline solution. Highly porous catalyst that selectively dissolves out less precious aluminum Active nickel remains.

The corresponding thin film itself is resistant to 200°C in a highly concentrated alkaline solution. It shows. The same is valid for thin films of brass or bronze. It's a precious metal The active components are selectively dissolved out by the acid, and the potential of the alloy is unified by the counter electrode. It is true that components that are not precious metals can be eluted theoretically, but precious metals Ingredients are not dissolved. Periodically changing the potential of a thin film alloy used as a working electrode Due to this change, the elution of less noble metal components is successful. reference electrode The potential measured for the positively charged and slightly positively charged (or slightly positively charged) (negative charge) is changed periodically for a long period of time between regions of negative charge (and negative charge), while positive charge (or slightly negative charge), metals with little noble metal properties and noble metals dissolve. selected so as to allow the precious metal to precipitate again. Selected for positively charged (or negatively charged) regions. This method electrifies precious metals, so to speak. results in chemically induced recrystallization. This method uses alkaline electrolytes as well as acidic electrolytes. in an electrolyte; in the latter case, the removal of non-noble metals (in excess) The ions must be dissolved, in which case concentrated caustic potash or caustic soda is used. be done.

In this method of electrochemically induced recrystallization, noble metal alloy components are carried out in solution. It is desirable that the change in the ions be as small as possible. Therefore, the outer shape of the thin film is the pore Undamaged by formation. This can be achieved by adding anions to the electrolyte. Implemented. When the potential is made positive, noble metals are oxidized and selectively precipitated, It migrates to an insoluble or very sparingly soluble form and forms a precipitate or no solution at all. Compounds that do not proceed must be reduced again in the negative potential region.

This effect is induced by 1 mole of sulfuric acid or 1 mole of zulfamine II (NnfSO,E). When using acidic electrolytes like brass and halides when using copper alloys like brass ions, especially chloride ions, hydrogen chloride, ammonium chloride or The alkali chloride is optimally added. Poorly soluble copper (1) halide is thereby made possible, with the latter being present in excess in the concentrated halide solution. The halide concentration must be very low. Especially KCl- When using a saturated sweet potato reference electrode, chloride ions are removed from the corresponding electrolyte container. The thin film prevents the working electrode from reaching the chloride concentration and prevents it from reaching the chloride concentration in an uncontrolled manner. It should be noted that This means that intermediates containing chloride-free potassium sulfate Blocked by electrolyte intervention.

Halide-ions can attack the counter electrode and are preferably complexed with platinum, for example. , which partially dissolves upon prolonged cyclic treatment. However, platinum melts Once the liquid is reached, undesirable deposits occur on the working electrode and also on the film-like alloy. commercially available half By installing a permeable membrane, halide ions can be removed and the electrolytic space of the counter electrode can be removed. Keep away from chloride-ions.

Similar considerations are effective when adding alkaline electrolytes. Especially with nickel In alloys with non-precious metals aluminum or zinc, nickel hydroxide is It is sparingly soluble in aluminum or zinc hydroxide in aqueous solutions; A more desirable method is to immobilize and remain.

In the case of a brass thin film, it is rather preferable to use sulfuric acid or a simple chloride-containing electrolyte. p When n is zero, the electrochemical cyclic treatment produces MCl− in the range between OiV and -200@v. This occurs advantageously for saturated agaric electrodes, when the periodic treatment period is in the range of minutes. The temperature of the electrolyte is approximately 50°C. Brass thin film is used to obtain reproducible results. Prior to use, it is chemically polished by conventional methods. The duration of the whole process depends on the thin film used. It is measured by the thickness of , and is in the range of several hours. Zinc consumption depends on the weight of the thin film and/or is EDAX (EnergY Dispersive Analyse or -ray) or by conventional analytical methods such as atomic absorption spectrometry (^AS) determination. be measured.

alloys of precious metals and less precious metals, A thin film of preferably brass is electroplated on one side with palladium in a first step. or coated with a palladium alloy, preferably a palladium/silver alloy, and coated with a second The other side is then transferred into a porous form by the electrochemical cyclic treatment described above, and its When the electrolyte added in the first step is removed, a tight fit around the thin film may be required. must be separated from the electrolyte added in the second stage.

In order to improve the adhesion of the palladium/silver layer, thin film alloys are generally made of palladium. /Silver-alloys may be treated chemically or especially electrochemically before electrolytic deposition. stomach. Therefore, components that are not precious metals are superficially treated in this case simply by the method described briefly. However, outside J is melted out. Additionally, catalysts like palladium black or platinum black is deposited electroplating with the addition of

Membranes produced in this way are not mechanically resistant, so electrochemical fabrication is required for stabilization. For construction, a thermal sintering process is carried out in a conventional manner. In this case, linear expansion coefficient is 16.6X 10°6°C゛1 for copper, and this value is the linear expansion of palladium. The coefficient of 11.7XIO-"℃-1 and the linear expansion coefficient of silver 19.7XIO-・℃ bow between the values, and by heating the porous copper support on the one hand and the palladium/silver single layer on the other hand. Very little stress is expected for the different elongations that occur.

It is clear that the proposed method can also be applied to other flat objects, such as thin tubes. be.

Palladium-based pores produced on porous metal supports in this way Membranes without hydrogen separation can be used in place of rolled palladium/silver membranes in the originally described manner. and can be installed as electrodes in fuel cells such as in electrolytes Ru. The use of such porous metal elements can also be considered without the palladium/silver layer. available. For example, as a hydrogenation catalyst for viscous liquids or solutions that are particularly difficult to filter. may be suitable as a porous electrode material in electrolytes or fuel cells. The metal can additionally be provided with a catalyst.

Next, the method of the present invention will be specifically explained in detail.

Example A circular large mirror disk with a diameter of 8@II and a thickness of 100 μm (zinc content 37% by weight, β-phase ) into the electrode holder with the help of the Viton packing ring. Contact with reagents placed in a tight fit.

The thin film was immediately polished for 2 minutes at 60°C in 25 ml of an etchant with the following composition: .

40 Vo1% acetic anhydride 50 Vo1% ortho-phosphoric acid (d=1.60) 10 Vo1% nitric acid (d= 1.40) Ag/Ag as intermediate electrolyte at 50°C on polished and water-washed thin film C1/saturated KCI/saturated KNO, at a constant potential of -goomV for 4 minutes, then A Pd/Ag-alloy is deposited in an electrolyte with a composition of .

5.00 g/I Pd tetramine-1.66 as palladium(II) nitrate g/I Ag as silver nitrate 100.0 g/l glycine 37.4 g/l KOH (pl! = 9.8. Pt pair electrode) A small brass plate coated with Pd/Ag on one side. The sample is placed upside down in the electrode holder, with the other side snug. It is brought into contact with the chemical and polished again with an etchant as described above for 2 minutes at 60°C.

Finally, the thin film was washed with water at 50°C in IM sulfuric acid 10.004M BCI. , 12 hours, potentiometer 1 stat and fa electrochemically using a pulsation generator.

1M sulfuric acid must be chloride-free in the electrolyte region of the Pt pair electrode. No. As a reference electrode, a standard calomel electrode (SCE) was used as an intermediate electrolyte. Used with Japanese potassium sulfate solution.

The potential of the working electrode is changed periodically in the following manner.

1) When the potential is OiV 50hs2) -200mV from O@V Up to 20hV/s slope 3) - 20hV potential 300m54) 200mV to OmV 400mV/s + 7) At the beginning of the slope 93% Zinc was removed.

The porous copper thin film is approximately 85 μm thick due to chemical attack, and the Pd/Ag-film is It contained 73% by weight of palladium and had a thickness of about 1 μm. That is in some cases It can also be coated with electrochemically and catalytically effective palladium black, or the like.

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Claims (15)

[Claims] 1. Pore-free thin membrane based on palladium supported on porous metal elements In the production of palladium, palladium alloys or palladium/silver - consists of an alloy and is electroplated by electrochemical deposition onto a porous metal element. The porous metal element is initially made of solid, non-porous gold. A method for producing a membrane, characterized in that it is produced from a genus element by electrochemical treatment. . 2. The thin film metal element is a thin film made of a noble metal and a metal with a small amount of precious metal. It is an alloy, and the less precious metals are selectively electrochemically melted and released. A patent characterized in that a noble metal component is left in the thin film metal element. A method for manufacturing a membrane according to claim 1. 3. A copper/zinc-alloy (brass) is used as the thin film alloy, and then zinc is melted. Claim No. 1 characterized in that the copper sludge drains and leaves behind a porous copper element. Membrane manufacturing method according to item 2. 4. Less precious metals are electrochemically dissolved and flowed out, and electrolyzed against a reference electrode. The potential of the thin film alloy (working electrode) measured in the specimen is determined by the counter electrode, positive and negative. between much less positive regions (or between slightly less negative and negative regions) It is changed periodically for a long period of time, and at that time, a positive (or slightly less) Select the potential region (negative) to melt less precious metals and precious metals, and Only precious metals are deposited in a slightly less positive (or negative) potential region. According to any one of claims 2 and 3 characterized in that Membrane manufacturing method. 5. The electrolyte contains anions, and oxidized noble metals are selectively precipitated when the electrolyte is at a positive potential. precipitates and transitions to an insoluble or very slightly soluble form, with the precipitated compound in the negative potential region. According to claim 4, which is characterized in that the invention must be reduced again in the Membrane manufacturing method. 6. When using brass thin film as a thin film alloy, 1 mol of sulfuric acid or 1 mol of sulfuric acid An acidic electrolyte of amic acid is used, and halide ions are added to this electrolyte, Chloride ions are added in the form of hydrogen chloride, ammonium chloride or alkali chloride. According to any one of claims 2 to 5, characterized in that Membrane manufacturing method. 7. The electrolytic space of the platinum counter electrode should be kept clear of halide ions. , separated from the electrolytic space of the working electrode by a semipermeable membrane. A membrane manufacturing method according to scope item 6. 8. The positive potential of the working electrode is 0 mV relative to the KCl-saturated sugar electrode. Claims characterized in that the negative potential is located at -200 mV. A method for producing a membrane according to any one of items 6 and 7. 9. Claims 6 to 7, characterized in that the period of the cycle is in the range of minutes. A method for producing a membrane according to item 9. 10. It is characterized by being processed at a temperature slightly higher than room temperature, approximately 50°C. A membrane manufacturing method according to claims 6 to 9. 11. The thin film alloy is composed of a noble metal, a metal with less noble metal properties, and a brass thin film, and In one step, one side of the thin film is electroplated with palladium or a palladium alloy, coated with palladium/silver-alloy and electrified the other side of the film in a second step The material added in the first step is transferred to a porous form by a periodic chemical treatment. The applied electrolyte is removed in the second stage by tight fittings around the membrane. Claims 1 to 10, characterized in that the method is separated from solutes. based on palladium supported by a porous metal element made of one of the following: A method for producing a pore-free membrane. 12. The brass thin film of the thin film alloy is made of palladium or palladium alloy. Chemically or electrochemically treated before the deposition by plating, Selective surface removal of non-noble metal alloy components by the methods described in paragraphs 1 to 10. Melting out and/or electroplating a catalyst such as palladium black or platinum black A method for producing a film according to claim 11, characterized in that the film is precipitated by . 13. The patent application is characterized in that electrochemical production is followed by thermal sintering. A mechanical curing method according to any one of items 1 to 12. 14. The membranes described in claims 1 to 13 are prepared using hydrogen gas. It can be used for hydrogen permeable electrodes in hydrogen separation or purification or in fuel cells or electrolyte cells. During this process, a suitable catalyst such as palladium black or platinum black is placed on the palladium/silver side. Use of a membrane characterized in that it is provided with an alkaline electrolyte. 15. Especially useful as a hydrogenation catalyst for the production of porous polycrystalline metal elements. Can be used for difficult to filter, viscous liquids or as a porous electrode material In this case, the metal may be added in some cases to provide a suitable catalyst. Any one of claims 2 to 10 and 13, characterized in that Application of membrane manufacturing method according to one.