DE3004262A1 - EFFECTIVE ELECTRODE FOR ELECTROCHEMICAL CELLS WITH REDOX SYSTEMS AND METHOD FOR PRODUCING THE ELECTRODE - Google Patents

Description

DR. ING. HANS LICHTI · DIPL. "ING. HEINER LICHTI

DIPL.-PHYS. DR.KLAUS LEUTWEIN 3004262

PATENT LAWYERS

D-7500 KARLSRUHE4IIGRÖTZINGEN) DURLACHER STR. 3! (SKYSCRAPER) TELEPHONE (0721) 48511. TELEX 7825986 LIPA D

February 05, 1980 5498/80-Ls

Yeda Research and Development Company Ltd. The Weizmann Institute of Science
PO Box 95, Rehovot, Israel

Effective electrode for electrochemical cells with redox systems and processes for the production of the electrode

The invention relates to a new effective electrode for a redox system such as S / S, Se / Se ⁼ and Te / Te ⁼ , or mixtures thereof, and to a method for producing the electrodes, as well as to electrochemical cells which contain such electrodes contain.

The use of electric catalysts in polychalcogenide redox systems has received little attention to date. Allen et al. (Trans. Far. Soc. 53 (1957) 1626) examined the anodic

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Oxidation of aqueous polysulphide solutions on various electrode materials. Recently, however, photo-electrochemical cells based on polychaikogeninds have been used to convert light into Electricity gained significant interest (USP 4,064,326 and Nozik: Ann. Rev. Phys. Chem. 1978).

It has been shown that there is a minimum for such systems Should have polarization, since the polarization reduces the work performance of such cells and thus their effectiveness, at suitable Counter electrodes are missing.

U.S. Patent 4,064,326 discloses various metal sulfides that can be used for the polychalcogenide system are good electrocatalysts. In the meantime The manufacture of such electrodes requires a plurality of operations, some of which are tedious and labor intensive.

According to the invention, improved, catalytically active electrodes are to be provided for use in polychalcogenide redox systems, which preferably ^{belong to the types S / S =} , Se / Se ~ and / or Te / Te ~. The redox pairs can be oxidized or reduced with only very low polarization on the new electrodes according to the invention. Such redox reactions can be effected at ambient temperatures.

The invention further relates to electrochemical cells and other devices in which such electrodes are required.

Finally, the invention also relates to a method of production such electrocatalytically active electrodes.

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The new electrodes according to the invention can be produced by Application of the proposed electro-catalysts or precursors of this on a suitable electrically conductive carrier.

According to another embodiment of the invention, an element is which serves as a catalyst, or which is a precursor of such a catalyst is, and a second element, which is used as the matrix of the catalyst or whose preliminary product is used, containing alloy is used.

Some of the electrodes of the invention can be in situ, i.e. H. in the Solution of the system in which they are used, or they can be produced in a separate system and in a redox system in which they are used should be transferred.

The new electrodes according to the invention can specifically in such Photo-electro-chemical cells in which difficulties have to be overcome based on polarization can be used. They are advantageously used as counter electrodes (e.g. as additional Electrodes next to the anode and cathode) in electrochemical cells, in which polychalcogenides increase performance and stability.

The new electrodes are superior to all previously described electrodes and in many cases cheaper and relatively easy to manufacture.

The active substances of the new electro-catalytically active electrodes according to the invention sulfides, selenides or tellurides are of suitable ones Transition metals, as well as copper and lead combinations of such sulfides, selenides and / or tellurides can be used.

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The terms sulfide, selenide and tel luride also include from the stoichiometric ratios deviating compounds. T he active substance can accordingly be a sulfide, selenide, Tel lurid or a mixture thereof of cobalt, nickel, copper, lead, molybdenum or ruthenium. Mixtures of various sulfides, selenides and tellurides can also be used. The proposed Connections have good electrical conductivity and good mechanical stability in the system in which they are to be used. The connections should eventually be chemically stable so that to the extent of chemical exchange some of them might make with the electrolyte, no significant harmful effects occur. Suitable active substances are: CoS, Cu S, PbSe, RuS, MoS NiTe, Cu Se and the like. Substances whose composition deviates from the stoichiometric ratios in a wider range can also be used. This relates especially on copper chalcogenides. Substances such as Cu S

1, / θ

are very effective electro-catalysts. Preferably sol! ¹ ^ n is the effective substance in such a way hergestel It can be that they have a highly developed surface. For this purpose, according to the invention, use can be made of various methods of producing electrodes.

The base or support that is inert in its mass in the system, can be from the following group:

Steel, stainless steel, porous coal, graphite, cobalt, Titanium, tantalum, tungsten, vandaium, chrome

be selected.

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In some cases, such as the sulphidation of brass, this can Starting material of the electrode (in this case brass) his own Carrier- The reason for using alloys with this type of electrode - CuZn instead of the initially more active pure copper is that copper is less dimensionally stable in chalcogenide solutions and gradually dissolves or disintegrates. By adding increasing Quantities of a matrix metal, e.g. B. zinc, the dimensional stability is increased. It should be noted that in addition to commercially available alloys (such as brass) also other copper-containing alloys can be used as long as and as long as the other alloy constituents do not have a disruptive effect exercise on the electrodic conversion. Such alloys can be made by conventional methods, e.g. B. by plating an alloy on a stainless steel carrier, which considerably reduces the amount of alloy required.

It should be emphasized that the activity of the electrocatalytic electrode according to the invention is strongly dependent on the composition and the temperature of the electrolyte. As in any normal electrochemical system, the activity increases with the rise in temperature and with increasing concentration of the electroactive constituents (i.e. the reduced form of the chaikogenide, e.g. S ⁼ for the anodic process and the oxidized form for the cathodic process). If, however, the ratio of the oxidized to the reduced form becomes greater than 1, e.g. B. X / X ~ ■> 1 the activity for both processes, the cathodic and the anodic process, decreases, the decrease increasing as the ratio increases. In short, the best concentration is the maximum concentration of the electroactive constituents, but with the ratio X / X <1. According to a preferred embodiment, a

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Electrolyte composition used with: [OHj = 1; | _X J ⁼ ^> £ xj = 1 · This composition is close to the optimal composition for the counter electrode. A composition of LOHj = 2; £ x ~ j = 2; [_xj = 2 is actually a little better, although the difference is not very significant.

The invention is illustrated below by means of the following examples the content of which the invention is not limited, explained.

Example 1 : Cobalt Sulphide on Stainless Steel.

A diluted solution of Co-Salt, buffered to a pH value between three and seven, is used as the electroplating solution to create an even galvanic coating on both sides of the substrate. The electrolysis conditions can vary. The electrolyte contained 20 g CoS0 ₄ / liter, which was buffered to a pH of 4.5 by means of potassium diphthalate and NaOH.

The electrolysis was carried out at room temperature without stirring with a

2
Current density of 40 mA / cm of the surface of the pad during 5 minutes carried out. The lower the pH value, the greater the necessary current density. Too low a current density, below about 20 mA / cm, or too low a pH value below about 3, leads to a deposit rich in cobalt metal, which is less active than the deposit of Co (OH) deposited under optimal conditions.

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The deposited plaque is placed in a chalcogenide ion electrolyte immersed and converted to CoX; z. B. is contained in a S ~ ions Solution CoS formed. An electrolytic reduction to about -1.2V with respect to the standard calomel electrode improves conversion. Such an electrode gives under standard conditions (30 C,

1M KOH, 1M Na S · 9 HO ₁ 1M S) 8 mA / cm ² with a polarization of

2 10 mV and follows a straight line behavior up to at least 60 mA / cm

2 both in cathodic and anodic direction, i.e. H. i.e. 16 mA / cm at 20 mV polarization, etc. If a thicker layer is deposited, the electrode is more active, but less mechanically stable.

Example 2 : PbS _{Q g} Se _{0 1} on stainless steel.

A base made of stainless steel is applied to an aqueous base Solution of 0.3 IvI lead acetate or lead nitrate using a platinum cathode A coating of PbOp is galvanically deposited by anodic oxidation.

2 T he galvanic electrolysis was carried out with a current of 40 mA / cm uei Room temperature carried out for 5 minutes, with a dark red-brown Overlay approximately 5 microns thick was obtained. T he electrode was then in a polychalcogenide solution under greedy conditions as for CoS in example 1 reduced. In this case the reduction is one

Need. In an electrolyte with 1M S, consisting of 0.9 M S and 0.1 M Se, a mixed bisulfide / selenide is formed which

2
in the same electrolyte resulted in 7.5 mA / cm with a Pdarization of 10 mV

:

and a linear I-V behavior in both directions up to at least 60 mA / cm showed.

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Example 3 : Cu S on an alloy matrix.

2 brass wire gauze (66% Cu, 34% Zn, 70 mesh / cm) was made into a

Polysulphide solution with 1 MS, 1 MS ⁼ and 1 M OH "" which at the same time can be the polysulphide or polychalcogenide electrolyte in which the electrode is to be used, immersed. The brass blackens in the course of a few days, which indicates the sulphidation of the copper contained in the brass. The process can be accelerated by anodic oxidation of the brass in the polysulfide electrolyte at a potential of 0.5 to 1.0 V versus the standard calomel electrode, in which case the process only takes about 5 minutes. One prepared in this way

2 electrode gives 25.5 mA at 10 mV polarization on 3 cm electrode area,

2
ie 8.5 mA / cm when immersed in an electrolyte with 1 M KOH, Na S · 9HO and S. at 30 C. It shows a linear IV behavior up to

at least 70 mA / cm upwards in both directions. The brass gauze may contain 60 to 90 mole percent copper, 30 to 150 mole percent for gauzes

Meshes / cm can be obtained without the conversion being significant being affected.

Example 4 : Alloy coating of copper-containing alloy and sulfidation.

A solution of 4 g of CuCN, 1.2 g of Zn (CN) and 6.5 g of NaCN was obtained made in 100 ml of water. A piece of stainless steel was carefully cleaned and degreased by washing in trichlorethylene. As with example 1 was made of stainless steel as a cathode with a composite Anode of copper and zinc with an area ratio of 9 Cu / 1 Zn

2 connected. The electrode was rust-free at a rate of 6 mA / cm Stahls loaded at 40 C for 30 minutes. The Electorde thus obtained was used as an electrolyte in a chalcogenide solution without further treatment.

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Under the standard conditions of Example 1, this gave an electrode

2

10 mA / cm at a polarization of 10 mV and showed up to i> 80 mA / cm upwards a linear behavior.

Example 5 : CoS on steel.

Equivalent solutions of cobalt acetate and kai imhydroxyd were made mixed rapidly to give a green precipitate.

2 A stainless steel sheet 0.7 mm thick and 4 cm in size

was thoroughly cleaned by sandblasting. The green precipitate was applied to the sheet metal base using a paintbrush and leave to dry in the air under ambient conditions. After drying, a second coat was painted on top of the first. To renewed drying, the electrode was in a solution with 1 M KOH, Na S 9 HO and S / liter immersed. The electrode was in this solution for 5 minutes at a potential of 1.2 V with respect to the standard calomel electrode reduced. After reduction, this electrode shows a

Polarization of up to 20 mV at a current density of 10 mA / cm (total 40 mA). It is relatively stable in the air, but should be longer Lingering in an atmosphere containing oxygen can be avoided.

Ex a mp le 6: ruthenium sulfide electrodes.

An aqueous solution of 5 mg RuCl in 10 ml water was

2 ³ rides. In this sheet metal sheet 1 cm in size was used as the anode

2 and on both sides of the same a steel sheet 1 cm in size was used as Arranged cathode. The electroplating was carried out for 10 minutes

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performed at currents up to 60 mA (30 mA / cm). Then the Electrode for sulfidation in a solution with 1 M S, Na S · 9 HO each and brought KOH. A polarization of up to 90 mV for current

2
densities of 10 mA / cm measured - After the electrode had then been reduced with approximately 1 V negative relative to the standard calomel electrode, the polarization was measured at the same current density as 48 mV.

Example 7 : Nickel Sulphide on Stainless Steel.

A solution of 4 g of nickel ammonium sulfate per liter of water was prepared (alternatively, a solution similar to the described in Example 1, but with nickel sulfate instead of cobalt sulfate The electrolysis conditions were the same, as described in Example 1. The applied coating was immersed in a solution of 1 M each of KOH, Na S 9 HO and S. It became

2 a polarization of 10 mV measured at a current density of 5.8 mA / cm. The behavior of the electrode follows a linear I-V curve

2
up to about 50 mA / cm.

Example 8: Nickel Selenide Electrode

An electrode was prepared analogously to Example 7, but was

the prepared electrode in a solution of 3 M KOH, 0.3 M Se and

0.3 M Be submerged. After reduction at 30 mA / cm during 5 minutes this electrode shows a polarization of 10 mV for a

Current passage of 2.4 mA / cm, -under standard conditions (example 1) such an electrode shows a polarization of 10 mA for a

Current passage of 4.8 mA / cm.

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Example 9 : NiSe Te electrode.

An electrode as in Example 7 was prepared. The galvanic Precipitated plaque was dissolved in a solution of 2 M KOH; 0.25 M Se; 0.05 M Te and 0.25 M selenide dipped and then with a

ari-

2
Current load of 20 mA / cm reduced for 5 minutes. The polarization of the electrode was 10 mV with a current passage of 4.5 mA / cm

2 under standard conditions (example 1) gave a current of 5.5 mA / cm a polarization up to 10 mV.

Example 10 : Cobalt Telluride Electrode.

An electrode similar to that in Example 1 was prepared and reduced

in a telluride solution (0.1 Μ Te ⁼ ; 4 M KOH; 0.1 M Te). After

Reduction in a Tel lurid solution with 15 mA / cm for 5 minutes

2
the electrode was polarized at 7 mA / cm current passage for 5 minutes, the polarization being up to 20 mV. Under standard conditions in a polysulfide solution of the type as in Example 1 were

a current passage of 6 mA / cm an increase in polarization up to

Example 11: CoSe Te_ electrode.

An electrode similar to that in Example 1 was prepared and used in

a telluride-selenide solution similar to that in Example 9 for 5 minutes

2
reduced under a current load of 20 mA / cm. In this solution results

a current of 5 mA / cm a polarization of 10 mV, while in the standard solution of Example 1 the polarization is 6 mV.

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Example 12: Lead-Tel lurid-Electrode.

An electrode was prepared as in Example 2 and in a

Telluride solution as in Example 10 for 5 minutes with a current

2
load of 15 mA / cm reduced - The electrode results in a polar

2 station voltage of 24 mV with a current load of 7 mA / cm.

Under the standard conditions of Example 1, the polarization

2 voltage 10 mV with a current load of 5.8 mA / cm.

Example 13: Lead Selenide Tel luride Electrode.

An electrode like the one in Bei spie! 2 prepared and in one

Seienid telluride solution as in Example 9 for 5 minutes with a

2
Current load reduced by 20 mA / cm. The electrode makes a

2 polarization voltage of 10 mV with a current load of 4.0 mA / cm

Under the standard conditions of Example 1, the current load is

2
5.7 mA / cm with the same polarization voltage.

Example 14 : Molybdenum-SuIfid-Electrode.

A MoS electrode on molybdenum metal was painted on

from Molycote (Cl imax molybdenum in ethylene glycol to molybdenum metal I,

ο Drying in the air and heating for 10 minutes at 450 C on the

Air made. Under the standard conditions of Example 1 was

2 the polarization voltage 10 mV with a current passage of 1 mA / cm

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In the table are electrodes according to the invention, their manufacture and The way of treatment, its catalytic activity and the electrolytes, in which their catalytic activity was measured, recorded. The polarization voltage was used as a measure of the catalytic activity

2 in mV with a current load of 10 mA on an electrode of 1 cm geometrical area viewed with double-sided coverage with the electro-catalyst. The lower the polarization voltage, the more the electric catalytic converter is more active. Because the I-V behavior is about the redox potential runs linearly, these values apply to both, namely the anodic and the cathodic direction.

Although the invention has been described above with reference to certain active substances, supports, electrochemical cells and procedures for their application have been described, it is in no way restricted to the special cases explained, but rather extended refer to all corresponding and similar Falb insofar as these fall under the scope of the claims.

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T a b e I Ie 300426 2 ^ <: Electrodes
material Way of
Manufacture (preparation) activity Solution (300) (mV) OH / X ² "/ X
(X = S if nothing
in other words) CoS Spread of
Co (OH) ₂ gel 15.0 1/1/1 NiSe Galvanic down
blow Ni (OH) 43.0 3 / 3Se ² "/.3 Se. Cu ₀ S Sulphidation in situ of 15.0 1/1/1 2 Normal measurement M S 65 CoS Galvanic down
blow from Co (OH) 14.0 1/1/1 Cu ₂ S Suppression of
Cu S in coal 11.0 1/1/1 PbTe Galvanic low 40.0 1/1/1

beat of PbO and reduction in
Te X solution

^PbS 0.9 ^Se 0.1

13.0

Galvanic precipitation of PbO2 and Reduction in S Se 0.11 solution

MoS,

Galvanic precipitation

Brushing MoS on molybdenum metal

Platinized

Platinum for electroplating comparison

75.0

75.0

110

r / 1/1

1/1/1 1/1/1

1/1/1

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Claims (28)

DR. ING. HANS LICHTI · DIPL. "ING. HEINER LICHTI DIPL.-PHYS. DR. KLAUS LEUTWElN 30 0 4 26 PATE NTA N WALTE D-7500 KARLSRU HE 4! (GRÖTZINCEN) · DURLACHER STR. 31 (HOCH HOUSE) TELEPHONE <072I) 48511. TELEX 7825986 LIPA D February 05, 1980 5498/80-Ls Yeda Research and Development Company Ltd. The Weizmann Institute of Science PO Box 95, Rehovot, Israel claims 1. Electrode for use in electrochemical cells with a redox system en, characterized, that as active substance they are a sulphide, a selenide, a telluride or mixtures thereof from a transition metal, from copper, Possess lead or mixtures thereof. 2. Electrode according to claim 1, characterized in that the active Substance is applied to a base or a carrier, which is inert in its mass to the electrochemical system. 3. Electrode according to claim 2, characterized in that the carrier from one of the following group: Steel, stainless steel, porous carbon, graphite, cobalt, titanium, tantalum, tungsten, molybdenum, vanadium and chromium selected material. 030036/0591 " ² " BATH ORIGINAL y 5498/80-Ls 4. Electrode according to one of claims 1 to 3, characterized in that that the carrier is stored in a matrix, the material of which is inert in its mass with respect to the electrochemical system, and that the electrode consists of a metal or metal alloy whose Surface layer in the sulfide, selenium id or Tel lurid respectively a Mixture of the same is converted as an active pavement layer. 5. Electrode according to claim 4, characterized in that it is made of brass consists. 6. Electrode according to claim 1, characterized in that the active Substance has a sophisticated surface. 7. Electrode according to claim 1, characterized in that the active Substance a sulfide, selenide or tel luride, or a mixture of the same of cobalt, nickel, copper, lead, molybdenum or ruthenium is. 8. Electrode according to claim 7, characterized in that the active Substance from the group: CoS, Cu S, RuS, MoS, PbSr Cu Se, NiTe is selected. 9. Electrochemical cell with an electrode according to claim 1, the as active substance a sulfide, a selenide, a telluride or a mixture thereof from a transition metal, from copper, lead or Mixtures of the same contains. 030038/0 591
BATH ORIGINAL -. 5498/80-Ls 10. Electrochemical cell according to claim 9, characterized in that that the cell is a photosensitive, electrochemical cell (Photo-electrochemical cell, PEC) is. 11. Electrochemical cell according to claim 9, characterized in that that the active substance is applied to a carrier which is inert in its mass to the electrochemical system. 12. Electrochemical cell according to claim 11, characterized in that that the inert carrier is selected from one of the group: Steel, stainless steel, porous coal, graphite, cobalt, Titanium, tantalum, tungsten, vanadium and chromium selected material. 13. Electrochemical cell according to claim 11, characterized in that that in a matrix whose material is compared in its mass learn electrochemical system is inert, embedded electrode from a metal or a metal I alloy, whose or Surface layer in the sulfide, selenide or telluride or a mixture the same is converted as an active pavement layer. 14. Electrochemical cell according to claim 13, characterized in that that the electrode is made of brass. 15. Electrochemical cell according to claim 9, characterized in that that it contains at least one polychalcogenide redox couple, and that the active electrode substance is a sulfide, selenide, telluride or a Mixture thereof of cobalt, nickel, copper, lead, molybdenum or ruthenium. 030036/0591 -4- BAD ORiOIMAL 5498/80-Ls 16. Electrochemical cell according to claim 15, characterized in that that the active electrode substance from the group: CoS ₁ Cu S ₁ PbSe, RuS MoS, NiTe, Cu Se is selected. 17. Electrochemical cell according to claim 15, characterized in that that the electrode substance has a sophisticated surface. 18. Electrochemical cell according to claims 9 and 10, characterized characterized in that the electrode is a counter electrode. 19. A method of making an electrode for use in one electrochemical containing at least one polychalcogenide redox couple System, characterized, that an active electrode sub-punch layer is applied to a carrier which consists of a sulfide, a selenide, a Tel lurid or a mixture of these. 20. The method according to claim 19, characterized in that the active Substance or a preliminary product thereof is applied to the carrier by electrolysis. 21. The method according to claim 19, characterized in that the active Electrode dance by immersing in an appropriate solution the carrier is applied. 030036/0591 g 5498/80-Ls 22. The method according to claim 19, characterized in that the active Electrode substance is applied to the carrier by vapor deposition. 23. The method according to claim 19, characterized in that the active Electrode substance through deposition of chemical vapors the carrier is applied. 24. The method according to claim 19, characterized in that the active Electrode substance is applied to the carrier by spraying. 25. The method according to claim 19, characterized in that the total or partially representing a preliminary product of the active electrode substance Carrier material in its surface to the active electrode substance is converted. 26. The method according to claim 19, characterized in that on the Carrier applied a hydroxide coating and this is converted into a sulfide, selenide, Tellund or a mixture thereof. 27. The method according to claim 19, characterized in that on the Carrier applied a metal oxide or a hydrated metal oxide and this is converted to a sulfide, selenide, telluride or a mixture thereof. 28. The method according to claim 19, characterized in that on the Carrier applied a metal covering with a sophisticated surface and the metal coating is converted into a sulfide, selenide, telluride or a mixture thereof. _p 030036/0591 BATH ORIGINAL