DE102010062659A1 - Electrode e.g. reference electrode, for electrochemical measuring system in e.g. medicine, has potential forming element arranged in chamber, and conductor contacting forming element, deriving potential from chamber and formed from fiber - Google Patents

Abstract

The electrode has a housing in which a chamber (8) is formed. An electrolyte (10) is arranged in the chamber. A potential forming element (3) is arranged in the chamber such that the electrolyte moistens the potential forming element. An electric conductor (1) contacts the potential forming element and derives the potential from the chamber. The electric conductor is formed from carbon fiber. A closure element (11) closes the chamber with the electrolytes and the potential forming element in a tight manner. The electric conductor is passed through the closure element. The potential forming element is made from metal salt e.g. Prussian blue and/or Prussian blue analog, and metal salt from silver and silver halide i.e. silver chloride. An independent claim is also included for a method for manufacturing an electrode.

Description

The present invention relates to an electrode for use in electrochemical measuring systems, for example for determining an electrochemical potential, and to a method for producing such an electrode. Electrochemical sensors are used, for example, in pH determination and are used in a variety of applications, for example in chemistry, medicine, industry, environmental or water analysis.

The problem underlying the invention will be explained with reference to potentiometric sensors. However, the invention is not limited to potentiometric sensors, but generally relates to electrodes for use in electrochemical measurement systems. Potentiometric sensors have a measuring electrode and a reference electrode between which a present potential difference is determined. In addition to systems of measuring electrode and reference electrode, which are introduced separately into the process medium, so-called single-rod measuring chains are also known in the field of pH measurement, which combine measuring electrode and reference electrode in a probe. The reference electrode has a mostly wire-shaped dissipation element, which usually consists of silver / silver chloride and is immersed in a reference solution, for example potassium chloride. The immersed portion of the diverter and the reference solution form a potential forming system. The reference solution is in electrochemical exchange with the measuring medium via a bushing. The dissipation element of the measuring electrode may also consist of silver / silver chloride and is immersed in a buffer solution. Discharge element and buffer solution are usually introduced into a glass tube, which is concluded messmedienseitig with a glass membrane. The potential between the reference electrode and the measuring electrode depends on the pH value of the measuring medium.

To delimit the area of the housing containing the buffer or reference solution from the environment, a sealing element, for example in the form of an adhesive layer, is usually provided in the housing, through which the discharge element is passed. The dissipation element usually consists of a potential-forming or potential-sensitive system and an electrical conductor in the form of a metal wire for the derivation and measurement of the potential. Since the metal wire itself is not intended to make any contribution to the electrochemical potential and has to be electrochemically stable, it generally also consists of silver or platinum.

A silver wire has the following disadvantage compared to a platinum wire: since a tight bonding of a silver wire or a dense melting of a silver wire in glass is hardly possible, it is not possible to achieve a completely sealed passage of the electrical conductor. It is known that an improved tightness can be achieved by extending a silver wire with a platinum wire, since platinum can be better fused or coated with a glass pillar and then glued better. However, the use of platinum entails high costs, in particular in the event that the tapping point of the electrochemical potential of the reference electrode is far away from the potential forming system and a corresponding amount of material for the electrical conductor is needed.

The object of the invention is to provide an electrode for electrochemical measurements, which is inexpensive to produce and yet electrochemically resistant. Another object is to specify a method for producing a corresponding electrode.

The object is achieved by an electrode according to the invention characterized in that the electrical conductor is constructed essentially of carbon fiber.

The electrical conductor consists of at least one carbon or carbon fiber. If a number of carbon fibers form the electrical conductor, they can for example be bundled, intertwined, twisted or otherwise connected to one another in a strand.

The inventive design of the electrode brings a number of advantages. Carbon fibers are more cost-effective than platinum wire, which has hitherto mostly been used to extend the potential-forming element and dissipate the potential. Furthermore, carbon fibers have a high stability even with a small fiber diameter, whereby a significantly lower material thickness compared to conventional noble metal wires is required. This saves on a raw material and costs. On the other hand, the small diameter of the derivation element made of carbon fiber allows a miniaturized structure of the contacted half-cell or the entire electrode.

In one embodiment, the electrode is a single measuring electrode or a measuring electrode of a combination electrode.

In a further embodiment, the electrode is a single reference electrode or a reference electrode of a combination electrode. Measuring electrode and reference electrode of a combination electrode can be designed according to the invention.

According to one embodiment of the invention, the electrode has a closure element, which tightly seals the chamber with the electrolyte and the potential-forming element. The electrical conductor is passed through the closure element. With the conductor made of carbon fiber, a tight passage of the electrical conductor through the closure element is possible. The closure element is for example a plug or a bond.

An embodiment of the electrode according to the invention provides that the potential-forming element of at least one metal or of at least one metal salt, preferably Berlin blue and / or a Berliner blue analog, or a combination of at least one metal and at least one metal salt is preferred Silver and a silver halide, in particular silver chloride exists.

According to one embodiment, the metal is in the form of a metallic wire, which is mechanically connected and / or glued to the electrical conductor in a transition region. The metallic wire may be coated at least in sections with a metal salt to form a potential-forming element. In another embodiment, the actual potential-forming element forms during introduction of the dissipation element into the electrolyte solution by addition of the metal salt contained therein on the metallic wire.

In one embodiment, the transition region is at least partially enclosed by a fastening means, preferably a staple. The fastening means can be attached as an alternative or in addition to a bond.

In one embodiment, at least the transition region is enclosed in a plastic tube. This provides protection against mechanical stress. Preferably, at least the region of the electrical conductor made of carbon fiber, which is located within the chamber, also surrounded by a plastic tube, or the same plastic tube surrounds both the transition region and the electrical conductor. A closure element occluding the chamber can tightly surround both the electrical conductor provided with a plastic tube and the non-enveloped electrical conductor, i. H. In any case, a tight passage of the electrical conductor is ensured by the closure element. Preferably, the plastic tube is attached in such a way that it is tightly closed by the adhesive or the fastening means. The carbon fiber or the carbon fiber strand is then completely sealed against the electrolyte, which prevents the formation of mixing, interference or foreign potentials by the contact of the electrical conductor with the electrolyte. The potential derived from the electrical conductor is thus determined only by the potential-forming element.

According to one embodiment of the electrode, the electrical conductor has a coating of at least one metal and / or at least one metal salt. As an alternative to this embodiment, in the case of an element which at least partially comprises a metal, the metal is present in the form of a wire, which is connected to the electrical conductor. A direct coating of the electrical conductor does not require gluing, pressing, or otherwise connecting two elements with a fastener.

Furthermore, the object is achieved with respect to the method in that a first end portion of a metallic wire is so connected to a first end portion of an electrical conductor made of carbon fiber, that forms a transition region in which the conductor contacts the metallic wire, and that the contacted metallic Wire and an electrolyte are introduced into a housing in such a way that at least one of the first end region different second end portion of the metallic wire is wetted by the electrolyte.

The electrical conductor made of carbon fiber is preferably designed as a carbon fiber strand. A carbon fiber strand is to be understood as an arrangement of a plurality of mutually contacting carbon fibers, which are connected to one another, for example, by bundling, twisting or braiding. The connection between the metallic wire and the carbon fiber electrical conductor is preferably made by bonding and / or mechanically bonding the first end portion of the metallic wire to the first end portion of the electrical conductor. Preferably, the metallic wire is deformed meandering in the first end region. This leads to a larger contact area and a more stable connection. The mechanical connection is made, for example, by pressing and / or clamping by means of a fastening means. In one embodiment, the metallic wire is both mechanically fastened and glued. Preferably, an electrically conductive adhesive is used for bonding to ensure the permanent electrical contact between the metallic wire and the electrical conductor.

To protect the connection point or the connection region against damage or as protection against the electrolyte, the transition region can additionally be coated with a protective layer, for example a lacquer, or be surrounded by a plastic tube. In the simplest case, the transition region is enclosed in a shrink tube. This is preferably so long that the entire region of the electrical conductor, which is arranged in the housing and could come into contact with the electrolyte, is surrounded by the plastic tube. The electrical conductor is led out of the housing by a closure element. Preferably, the second end portion is connected for contacting with a contact wire. The connection to the contact wire is preferably made identical to the connection arranged in the housing with the metallic wire.

In one embodiment of the method, the second end region of the metallic wire is coated with a salt of the metal of which the metallic wire substantially consists before being connected to the electrical conductor. The coating serves to form the potential-forming element. Alternatively, the potential-forming element is formed by the contact of the electrolyte containing the corresponding metal salt with the metallic wire by attaching the metal salt to the metallic wire.

An alternative embodiment of a method for producing an electrode for an electrochemical measuring system is that the surface of a first end region of a carbon fiber electrical conductor is activated with an oxidizing medium, that on the activated surface of the conductor at least one metal and / or metal salt is deposited and in that the electrical conductor and an electrolyte are introduced into a housing such that at least the first end region of the electrical conductor is wetted by the electrolyte. The coating with the metal and / or the metal salt takes place in a physical, chemical or electrochemical process.

This manufacturing method thus provides that a potential-forming element is formed directly on the carbon fiber electrical conductor, which serves to derive the potential. Advantageously, the carbon fiber or carbon fiber strand is at least in places coated and / or activated before coating with a metal or metal salt. For example, the electrical conductor is coated with an adhesion-promoting metal, which need not be a closed layer. In addition to the better adhesion of the metal or metal salt layer thereby a more uniform crystal growth is achieved. Preferably, an activation step is furthermore carried out in which functional groups are created on the surface of the electrical conductor and which likewise leads to improved adhesion of a coating of the electrical conductor. To activate the surface of the electrical conductor, it is etched in the partial region to be coated, for example with a strongly oxidizing acid, in particular nitrating acid. In an advantageous embodiment, bonding centers for the metal and / or the metal salt are created by addition of ions, for example tin and palladium ions.

Either the complete potential-forming element is deposited on the electrical conductor, or the potential-forming element is completely formed when the coated with a metal or metal salt electrical conductor is introduced into the electrolyte. The potential-forming element consists of at least one metal and / or of at least one metal salt. In one embodiment, Berlin blue and / or a Berliner blue analog is / are deposited on the carbon fiber electrical conductor. In another embodiment, silver and a silver halide, preferably silver chloride, are applied. For bonding a layer of palladium or tin can be applied under the silver layer, for example. It is also possible to apply only the silver layer to form a potential-forming element of silver and silver chloride. The silver chloride then attaches to the silver layer from the silver chloride-containing electrolyte.

According to one embodiment of the method, the uncoated region of the surface of the electrical conductor is at least partially deactivated by a chemical treatment of the surface. Deactivation prevents the formation of additional potentials between the electrical conductor and the electrolyte, which disturb the evaluation of the actual potential of the potential-forming element formed potential.

In one embodiment, functional groups on the surface of the conductor are blocked for deactivation, in particular esterified, etherified or decarboxylated.

The invention will be explained in more detail with reference to the following figures. The illustrations are schematic sketches and not shown to scale for clarity.

1 schematically shows the structure of a reference electrode;

2a shows a first embodiment of a connection between half-cell system electrical conductor,

2 B shows a second embodiment of a connection between half-cell system and electrical conductor;

3 shows an alternative embodiment of a half-cell system and conductor.

In 1 is a inventively designed reference electrode for introduction into a medium whose pH is to be determined, shown. However, the invention can equally be implemented in other electrodes, for example in a pH measuring electrode or the reference electrode and / or the measuring electrode of a combination electrode, as well as in redox electrodes.

The reference electrode comprises a housing, which is preferably made of glass and which partially with an electrolyte 10 is filled. For sealing the upper housing section with respect to the electrolyte 10 is a closure element 11 introduced into the housing. The part of the housing, which of the closure element 11 is limited, is hereinafter referred to as a chamber 8th designated. In the chamber 8th introduced is a potential-forming element 3 , which in the case shown from a metallic wire 21 and a supply 22 made of a salt of the metal. For example, it is a silver wire and a silver chloride supply. The electrolyte 10 wets the potential forming element 3 , In the wall of the chamber 8th there is a passage 9 which forms the power key to the medium.

For deriving the potential, which is at the potential forming element 3 is the latter with an electrical conductor 1 contacted. The electrical conductor 1 and the potential-forming element 3 are in a transition area 71 mechanically and / or firmly connected to one another via a splice. According to the invention, the electrical conductor 1 constructed of carbon fiber. The leader 1 This may consist of only one fiber or of several fibers, which are intertwined, twisted or bundled, for example. On the chamber 8th opposite side of the closure element 11 there is a second transition area 72 in which the electrical conductor 1 with a contacting element 12 , For example, a wire is connected. The contacting element 12 provides the connection to the - not shown here - transmitter, z. B. a voltmeter ago. The second transition area 72 is preferably analogous to the first transition region 71 designed. Alternatively, the electrical conductor 1 made of carbon fiber directly connected to the transmitter.

2a and 2 B schematically disclose two variants of a first embodiment of a contacted half-cell. The potential forming element 3 is made of a metallic wire 21 and a supply 22 a salt containing the corresponding metal is formed. Stock 22 is for example in the form of a coating on an end region of the metallic wire 21 applied or has contact with the electrolyte 10 on the metallic wire 21 deposited. The contacting of the potential-forming element 3 takes place by means of the electrical conductor 1 made of carbon fiber.

The connection between the potential-forming element 3 and the electrical conductor 1 is in a first, in 2a illustrated embodiment by means of an adhesive layer 4 and a clip element 5 produced. However, embodiments are also possible in which the connection only by an adhesive layer 4 or only by a clamp element 5 is realized. In the latter case, it is a purely mechanical connection. For example, it will not work with the supply 22 provided end portion of the metallic wire 21 with an end portion of the electrical conductor 1 compressed, so that a stable electrical contact is made, and the transition region 71 then with the clamp element 5 provided to ensure that the mechanical connection and the electrical contact remain.

In the in 2 B illustrated embodiment, the contact surface between the potential-forming element 3 and electrical conductor 1 increased because of the metallic wire 21 of the potential forming element 3 is meandered in the connecting first end region. This allows a stable connection to mechanical stress and at the same time ensures the electrical contact. In addition, the metallic wire 21 and the electrical conductor 1 bonded. In other embodiments, the connection is additional or alternative to the splice 4 by a clamp element 5 strengthened.

In both embodiments, the transition region 71 from a plastic tube 6 be surrounded. This protects the joint under mechanical stress, electrically isolated and provides protection against induced by the electrolyte corrosion of the potential-forming element 3 and the formation of mixed potentials. Advantageously, the plastic tube surrounds 6 the whole in the chamber 8th located portion of the electrical conductor 1 , For example, it is the plastic tube 6 around a shrink tube. This offers the advantage of being able to optimally adapt to the contours, so that in the transition area 71 There is almost no room for maneuver and a permanent, stable connection is guaranteed. In place of the plastic tube 6 it is also possible the transition area 71 to coat with a protective layer, for example in the form of a paint.

In one embodiment, the plastic tube 6 and the bonding is performed such that the plastic tube 6 from the splice 4 is sealed, ie in the direction of the potential-forming element 3 is tightly closed. Preferably, the plastic tube surrounds 6 the electrical conductor 1 furthermore at least up to the closure element 11 so that the electrical conductor 1 completely opposite to the electrolyte 10 is sealed and no interference potential due to the contact of the carbon fiber with the electrolyte 10 can train.

3 shows an alternative embodiment of the half-cell. As potential forming element 3 serves a corresponding coating on a portion of the electrical conductor 1 made of carbon fiber. The coating consists in one embodiment of at least one metal, for example silver. Preferred is a salt of the metal, for example silver chloride or another silver halide, to form a reservoir 22 applied as a further layer on the metal layer. Metal and metal salt together form the potential-forming element 3 ,

For better adhesion of the metal layer is the electrical conductor 1 preferably by activating, in particular etching the surface, z. B. by means of a strong oxidizing acid, and / or by applying catalytic centers, for example in the form of palladium pretreated. For this purpose, the electrical conductor 1 for example, introduced in a first step in a SnCl ₂ solution, so that attach Sn ²⁺ ions on the surface of the carbon fibers, and introduced in a second step in a PdCl ₂ solution, whereby Pd ²⁺ ions through the Sn ^{2 +} Ions are reduced to palladium and spread on the surface of the carbon fiber. Subsequently, for example, silver is deposited by electroless plating on the conductor, reducing silver ions from the plating bath on the palladium to silver. In addition to the better adhesion of the metal, such a pretreatment also allows a uniform crystal growth. Even without a closed adhesion-promoting layer, a closed metal layer is formed.

In another embodiment, the electrical conductor 1 coated directly with a metal salt. Preferably, the uncoated region of the electrical conductor 1 at least on the length, which is inside the chamber 8th is arranged disabled. The deactivation corresponds to a passivation of metals and is for example by esterification of functional groups on the surface of the conductor 1 or other chemical surface treatment techniques. The formation of interference or mixing potentials is thereby prevented or at least reduced.

The metallic coating is applied to the electrical conductor in a chemical, electrochemical or physical process 1 applied. The salt is preferably in a chemical or electrochemical process on the coated electrical conductor 1 deposited. An advantage of this in 3 illustrated embodiment of the half-cell is to be seen in that in an electrical conductor formed of a plurality of fibers 1 the surface of the formed on this potential forming element 3 opposite the structure of a coated wire 21 is increased. As a result, more stable potentials can be obtained. In addition, for a direct on the electrical conductor 1 deposited half-cell system requires a smaller amount of metal. Critical joints do not exist, so no fasteners or protective covers are required.

LIST OF REFERENCE NUMBERS

1

ladder

21

metal wire

22

stock

3

Potential forming element

4

adhesive layer

5

clip element

6

shrinkable tubing

71

Transition area

72

Transition area

8th

casing

9

execution

10

electrolyte

11

closure element

12

contacting

Claims (14)

Electrode for use in electrochemical measuring systems, comprising at least one housing in which at least one chamber ( 8th ) is formed, with at least one electrolyte ( 10 ), which in the chamber ( 8th ) is arranged with at least one potential-forming element ( 3 ), which is so in the chamber ( 8th ) is arranged such that the electrolyte ( 10 ) the potential-forming element ( 3 ) and at least one electrical conductor ( 1 ), which is the potential-forming element ( 3 ) and the potential from the chamber ( 8th ), characterized in that the electrical conductor ( 1 ) is constructed essentially of carbon fiber. Electrode according to Claim 1, characterized in that the electrode is a single measuring electrode or a measuring electrode of a combination electrode. Electrode according to Claim 1, characterized in that the electrode is a single reference electrode or a reference electrode of a combination electrode. Electrode according to one of the preceding claims, characterized in that the electrode has a closure element ( 11 ), which the chamber ( 8th ) with the electrolyte ( 10 ) and the potential-forming element ( 3 ) tightly closes, and that the electrical conductor ( 1 ) through the closure element ( 11 ) is passed. Electrode according to one of the preceding claims, characterized in that the potential-forming element ( 3 ) of at least one metal or of at least one metal salt, preferably Berlin blue and / or a Berliner blue analog, or a combination of at least one metal and at least one metal salt, preferably silver and a silver halide, in particular silver chloride. Electrode according to Claim 5, characterized in that the metal is in the form of a metallic wire ( 21 ), which is connected to the electrical conductor ( 1 ) in a transitional area ( 71 ) is mechanically connected and / or glued. Electrode according to Claim 6, characterized in that the transition region ( 71 ) at least partially by a fastener, preferably a bracket ( 5 ), is enclosed. Electrode according to Claim 6 or 7, characterized in that at least the transition region ( 71 ) in a plastic tube ( 6 ) is enclosed. Electrode according to Claim 5, characterized in that for the formation of the potential-forming element ( 3 ) at least one metal and / or at least one metal salt in the form of a coating on the electrical conductor ( 1 ) are / is applied. Process for producing an electrode for use in electrochemical measuring systems, characterized in that a first end region of a metallic wire ( 21 ) having a first end region of an electrical conductor ( 1 ) is made of carbon fiber, that a transition region ( 71 ) in which the leader ( 1 ) the metallic wire ( 21 ), and that the contacted metallic wire ( 21 ) and an electrolyte ( 10 ) are introduced into a housing in such a way that at least one second end region of the metallic wire, which is different from the first end region, ( 21 ) of the electrolyte ( 10 ) is wetted. A method according to claim 10, characterized in that the second end portion of the metallic wire ( 21 ) before connecting to the electrical conductor ( 1 ) with a salt ( 22 ) of the metal from which the metallic wire ( 21 ) is substantially coated. Method for producing an electrode for use in electrochemical measuring systems, characterized in that the surface of a first end region of an electrical conductor ( 1 ) of carbon fiber with an oxidizing medium is activated on the activated surface of the conductor ( 1 ) at least one metal and / or metal salt is deposited, and that the electrical conductor ( 1 ) and an electrolyte ( 10 ) are introduced into a housing such that at least the first end region of the electrical conductor ( 1 ) of the electrolyte ( 10 ) is wetted. Method according to claim 12, characterized in that the uncoated area of the surface of the electrical conductor ( 1 ) is at least partially deactivated by a chemical treatment of the surface. A method according to claim 13, characterized in that for deactivation functional groups on the surface of the conductor ( 1 ), in particular esterified, veretert or decarboxylated.

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