Method for manufacturing an electrode and device comprising such an electrode

Abstract

The invention relates to a method for manufacturing an electrode (1) for electrochemical measurements, comprising: - a step of providing a dielectric substrate (110), - a step of providing an electrically conductive wire (120), - an embedding step during which at least a portion of the wire (120) is embedded in the thickness of the substrate (110), - a cutting step during which the substrate (110) is cut into a plurality of units, each unit supporting at least one electrode (1) formed from the electrically conductive wire (120) at least partially embedded in the substrate (110). Also disclosed is a device comprising an electrode obtained by this method.

Description

Description Title of the invention: Method for manufacturing an electrode and a device comprising such an electrode. Technical field

[0001] The invention relates to devices for performing electrochemical measurements using at least one electrochemical electrode, as well as methods for manufacturing such devices. Devices of this type are intended, for example, for measurements in chemistry, life sciences, the food industry, for monitoring water quality in swimming pools, environmental monitoring, decentralized healthcare, etc. State of the art

[0002] For example, the electrochemical detection of active molecules may require the use of an electrochemical electrode. Similarly, a reliable reference electrode may be necessary.

[0003] Among the most effective reference electrodes are laboratory electrodes with glass tubes containing a silver wire coated with a layer of silver chloride. For example, the silver is chlorinated using a saturated potassium chloride solution.

[0004] There are also Ag / AgCl reference electrodes formed on a flexible circuit, on which an Ag / AgCl ink or paste is deposited, or a layer of silver which is then chlorinated.

[0005] For example, patent application KR20200132389 A describes a device comprising two electrodes made on a flexible dielectric substrate. A material, in the form of ink or paste, is deposited onto one of these electrodes using screen printing, inkjet printing, and photolithography techniques, for example, to form an Ag / AgCl electrode. In this case, the Ag / AgCl particles are dispersed in a synthetic matrix that may not be compatible with certain applications (in the medical field, for example). Patent application WO2022219074A1 also describes a device in which a layer of silver chloride is deposited by inkjet printing, screen printing, or is formed from an electrolytic silver deposit followed by chlorination.

[0006] However, during chlorination, chlorine can attack metallic layers (for example copper and / or nickel) that constitute conductive tracks underlying the silver layer.

[0007] The production of a reference electrode was taken as an example above, but in general there is a need to develop a manufacturing process for electrodes which has at least one of the following advantages: economical and / or simple to implement in large series, allowing for robust products, suitable for making various types of electrodes with essentially the same technology, relatively easy to weld (in particular for example, to connect the electrode to a measuring device), purity (no organic binders as in screen-printed electrodes), chemical stability, no dissolution in acidic or alkaline media, no absorption of water or contaminants, etc.

[0008] The invention aims in particular to propose a method for manufacturing an electrode (not necessarily only of the Ag / AgCl type), different from those of the prior art, more particularly different from the methods using screen printing techniques, and which also offers at least certain advantages compared to the methods of the prior art. Summary of the invention

[0009] To this end, a method for manufacturing an electrode for electrochemical measurements is proposed, comprising - a step of supplying a substrate comprising a dielectric material, this substrate having a thickness delimited by a first and a second principal face, - a step involving the supply of an electrically conductive wire, - an embedding step during which at least a portion of the electrically conductive wire is embedded, by deformation of the substrate, into the thickness of the substrate, on at least the first face, the substrate thus at least partially supporting the electrically conductive wire, and this embedding step leaving a free surface of the electrically conductive wire, while another portion of the wire surface is in contact with the dielectric material of the substrate, - a cutting step during which the substrate is cut into a plurality of units, each unit supporting at least one electrode formed from the electrically conductive wire at least partially embedded in the substrate.

[0010] The processes for embedding an electrically conductive wire into a substrate or dielectric support (known as "wire embedding") are well-known and well-established. For example, see patent document US6698089B2. These processes are fast, reliable, and produce robust products with high yields. They are also more economical than processes in which conductive tracks are etched into a layer of electrically conductive material, since these processes do not involve the waste of material removed by etching. Thus, embedding an electrically conductive wire into a substrate offers advantages over creating conductive tracks by screen printing, etching, etc. The electrically conductive wire can be a precious metal suitable for forming an electrode, such as gold or platinum.

[0011] A "unit" as mentioned above may include one or more electrodes, but also possibly means of connecting the electrode(s) (connection pads added by screen printing or etching into a conductive layer) and / or one or more electronic circuits (with one or more electronic components), etc.

[0012] The process according to the invention is versatile in that simply changing the nature of the electrically conductive wire embedded in the substrate is sufficient to change the type of electrode. For example, changing the nature of the electrically conductive wire embedded in the substrate allows it to be adapted (possibly to obtain a specific redox couple) to the intended application of the electrode thus manufactured. Thus, for example, it is possible to manufacture, using the process according to the invention, simple electrodes in which the electrically conductive wire is made of a metal or a metal alloy comprising, for example (but not limited to), an inert metal such as gold or platinum, or another type of solid metal or solid alloy (for example, comprising copper).

[0013] The method according to the invention may also include one or more of the following features, each considered independently of the other or in combination with one or more others:

[0014] - it includes a step of forming a redox couple on at least a portion of said free surface of the electrically conductive wire; alternatively, the step of forming a redox couple is implemented before the encrustation step;

[0015] - the redox couple is formed by the silver / silver chloride couple; silver may be present in the electrically conductive wire before the encrustation step (for example, the electrically conductive wire is a silver or silver alloy wire); alternatively, a layer including silver is deposited on the electrically conductive wire before or after the encrustation step; the process then includes a step of forming a layer of silver chloride on the silver present in or on the electrically conductive wire; it is thus possible to form an Ag / AgCl type reference electrode;an Ag / AgCl reference electrode is particularly stable in aqueous and non-aqueous environments, it has a constant and reproducible potential (resistant to potential drift and compatible with a wide range of solvents and electrolytes), it is easy to use (interactions between the reference electrode and the solution to be analyzed can be minimized using a KC1 solution and a membrane or porous wall limiting exchanges between the electrode and its environment);

[0016] - the step of forming a silver chloride layer is carried out by electrolytic means from the silver present in the electrically conductive wire or on the layer containing silver; for example, the step of forming a silver chloride layer includes a chlorination step carried out by positively polarizing the electrically conductive wire and immersing at least a portion of this electrically conductive wire containing silver in a solution containing chloride ions; thanks to the positive polarization of the electrically conductive wire, its surface is positively charged and the following interface is thus obtained: silver, chloride ions (in solution initially) and the cations associated with the chloride ions (for example, potassium ions if a potassium chloride solution is used, hydrogen ions if a hydrogen chloride solution is used, etc.);This results in oxidation of the silver on the surface (Ag+ cations are formed) and chlorination by chelation of the Ag+ ions in the presence of chloride ions (Cl-); the silver oxide layer at the interface thus traps the chloride ions; the resulting layer, which includes silver oxides and silver chloride, protects the underlying layers; in other words, "chlorination" (controlled electrolysis in the presence of chlorides in which the electrically conductive silver wire acts as an anode) allows the addition of a portion of silver chloride (AgCl) on the surface to the passivation of the silver;Alternatively, the step of forming a silver chloride layer is carried out by screen printing or dispensing onto the silver present in the electrically conductive wire or onto the layer containing silver (in this case, the process has the advantage of being quick to implement, as well as the advantage of not having to make the conductive tracks which are necessary for the control of chlorination);

[0017] - the electrically conductive wire is made of copper or a copper alloy; the process then comprises, between the inlay step and the redox couple formation step, a step of forming a nickel layer by electrolytic deposition on at least a portion of said free surface of the electrically conductive wire, followed by a step of forming a gold layer on at least a portion of the nickel layer by electrolytic means, the redox couple formation step comprising an electrolytic silver deposition step on at least a portion of the gold layer; this stacking of layers has the advantage of preventing the diffusion of silver into the copper; the use of an electrically conductive wire made of copper or a copper alloy coated with a layer of silver has the advantage of being more economical; alternatively, if the conductive wire is a silver wire or a silver alloy;The process is simplified since a step of forming the silver layer can be avoided; moreover, the wires are thinner (which may allow for electrodes with a smaller footprint); very little equipment is required; in the case of amperometric measurements, the conductivity of the electrodes obtained using the process according to the invention is high compared to those of screen-printed electrodes;

[0018] - a step of forming a layer of potassium chloride gel on at least one area of ​​the silver chloride layer; the use of a saturated potassium chloride gel layer in particular has the advantage of stabilizing the Ag / AgCl redox couple (very useful for electrochemical analyses); alternatively, the process includes a step of forming a porous barrier covering at least one area of ​​the silver chloride layer and enclosing a potassium chloride layer solution; this option is more complex to implement than the one involving the deposition of a gel, but the electrode thus produced is more robust, stable and reliable for electrochemical analyses; it can be used more times (because the salt layer stabilizes the system and allows performance to be maintained over time);An electrode with a gel can be used, for example, for single-use applications, whereas an electrode with a solution contained in a porous barrier can be reused more often; - the deformation of the substrate during the inlay stage includes the implementation of at least one of the following techniques: heating of the wire and / or substrate, application of ultrasound to the wire and / or substrate, application of pressure to the wire and / or substrate.

[0019] According to another aspect, the invention relates to a device for electrochemical measurements comprising at least one electrode, this device comprising - a substrate comprising a dielectric material, this substrate having a thickness delimited by a first and a second principal face, - an electrically conductive wire, at least part of which is embedded in the thickness of the substrate, deforming the substrate, on at least the first face, the substrate thus at least partially supporting the electrically conductive wire, and one surface of the electrically conductive wire being left free, while another part of the surface of the wire is in contact with the dielectric material of the substrate.

[0020] Furthermore, the substrate is in the form of a unit supporting at least one electrode formed from electrically conductive wire, at least partially embedded in the substrate. This unit may include, for example, means for connecting each electrode, configured to measure the potential of each electrode and / or the current flowing through each electrode. This unit may also include, for example, one or more electronic components.

[0021] This device further includes a layer formed by a redox couple on the free surface of the electrically conductive wire; for example, the redox couple is silver / silver chloride. Brief description of the drawings

[0022] Other features and advantages of the invention will become apparent from the detailed description that follows, as well as from the accompanying drawings. These drawings include:

[0023] [Fig. 1] schematically represents an example of a measuring sensor equipped with a device according to the invention;

[0024] [Fig. 2] schematically represents successive steps of an example of implementation of a process according to the present invention;

[0025] [Fig. 3] schematically represents in cross-section an example of an embodiment of an electrode according to the invention (for example obtained using the process illustrated in Figure 2);

[0026] [Fig. 4] schematically represents successive steps of another example of the implementation of a process according to the present invention;

[0027] [Fig. 5] schematically represents in cross-section another example of an embodiment of an electrode according to the invention (for example, obtained using the process illustrated in Figure 4); and

[0028] [Fig. 6] schematically represents, in cross-section, yet another example of an embodiment of an electrode according to the invention. Detailed description

[0029] By way of example, the invention is described in relation to the fabrication of flexible devices 100, equipped with at least one electrode 1. This device 100 is, for example, configured to be mounted in a more complex measuring sensor 200 (incorporating, for example, one or more electronic components and / or wired or wireless connectors, and / or a display device, etc.). However, the invention can also be applied to the fabrication of a single reference electrode 1.

[0030] Figure 1 shows a measuring sensor 200 intended to be immersed in a solution 300. This measuring sensor 200 incorporates an example of a device 300 according to the invention.

[0031] Such a device 100 is, for example, made from a flexible dielectric substrate 110 in which a wire 120 of electrically conductive material is embedded, at least on one or more portions thereof (see Figures 2 to 6). For example, the substrate 110 is made of polyethylene terephthalate (PET), polyimide (PI), or glass epoxy. The substrate 110 has, for example, a thickness of between 25 and 500 micrometers, and more preferably equal to or close to 250 micrometers. The substrate 110 is suitable for plate or continuous roll-to-roll ("reel-to-reel") processing of the method according to the invention.

[0032] Wire 120, for example, is made of one of the following metals, or one of their alloys: copper, aluminum, steel.

[0033] According to one example of an embodiment of the method according to the invention (for example, illustrated by Figure 2), a substrate 110 is provided (Step A). ​​A wire 120 is embedded in the substrate 110, on one of its principal faces 112, 114, by means of a known technique (Step B). The wire 120 is made of copper or a copper alloy having a diameter equal, for example, to 100, 120 or 150 µm.For example, wire 120 is embedded in substrate 110 over approximately 30 percent to 60 percent of its diameter; for example, 50% of the surface of the conductive wire is active; wire 120 is configured so that the active surface is sufficient to obtain a functional electrode; the active surface can be increased by making at least one cut in the substrate (for example, over the entire thickness of the substrate) so that the electrically conductive wire passes over this cut and is embedded in the substrate on both sides of it; the portion or portions of the electrically conductive wire more or less taut above the cut then offer 100% of their surface for possible measurement.

[0034] For example, the 120 wire is embedded in the substrate over a length ranging from a few micrometers to a few centimeters or tens of centimeters (for example, from 1 µm to 1 m). More specifically, for example, the 120 wire is embedded in the substrate over a length of 1 to 2 centimeters. Optionally, the 120 wire is embedded in patterns such as loops, meanders, zigzags, etc., in order to potentially increase the usable surface area for measurements performed with electrodes manufactured using the method according to the invention.

[0035] Wire 120 is configured to be connected or linked at one or more points to a measuring device (not shown) (See step C).

[0036] The 120 wire undergoes electrolytic surface treatments (See step D) in order to successively deposit a layer of nickel (with a minimum thickness of 4 pm for example), a layer of gold (with a maximum thickness of 0.3 pm for example) and a layer of silver whose thickness is for example between 10 nanometers and 10 micrometers, for example between 100 and 600 nanometers.

[0037] To simplify, in this document, a "nickel layer," a "gold layer," a "silver layer," and a "silver chloride layer" are layers composed primarily of nickel, gold, silver, or silver chloride, respectively. However, these metals or compounds are not necessarily pure. They may, to some extent, be alloys.

[0038] Alternatively, the gold layer is replaced by a palladium layer. The nickel layer forms a barrier layer that helps prevent, or at least limit, the diffusion of metals deposited on the nickel layer into the copper wire 120. For example, the thickness of the silver layer is equal to or close to 200 nanometers. This relatively thin silver layer allows for a reference Ag / AgCl electrode of significantly higher quality compared to the same type of electrode produced by screen printing. All of these layers (Ni / Au / Ag) are referenced as 130 in Figure 3.

[0039] A layer of silver chloride 140 is then formed on the wire 120 (Step E). This layer of silver chloride 140 can be formed in several ways.

[0040] For example, it is formed by chlorination in a solution containing chloride ions. For example, this chosen solution is a hydrogen chloride solution or a potassium chloride solution. For example, the AgCl layer is formed from the silver layer previously deposited on wire 120 (with nickel and gold in underlying layers). For example, the chlorination of the silver layer previously deposited on wire 120 is carried out by chronopotentiometry or chronoamperometry. For example, the silver chloride layer 140 is produced by chlorination by immersing at least a portion of the silver-coated wire 120 in a potassium chloride solution.

[0041] For example, this solution is obtained by dissolving solid potassium chloride in a sulfuric acid solution to obtain a 0.2M concentration of chloride ions.

[0042] Alternatively, a potassium chloride solution prepared from a hydrogen chloride solution to which solid potassium chloride is added can be used.

[0043] Advantageously, chlorination is carried out at a constant current, in the presence of a counter electrode and another electrode (which then serves as the reference electrode during chlorination). Wire 120 then acts as a working electrode (in other words, it forms a working electrode during the chlorination step, but once the AgCl layer is formed, wire 120 is intended to be used as a reference electrode). For example, chlorination is carried out with a current intensity between the working electrode, the counter electrode, and an external reference electrode of between 0.9 and 100 pA, for a duration of between 1 and 2 minutes. With a silver layer 200 nanometers thick, a current of 0.9 microamperes is passed for 1 minute between the working electrode (which will become reference electrode 1) and the counter electrode, while simultaneously polarizing the working electrode.A layer of silver chloride then forms on the area where silver has been deposited. For example, the silver chloride layer thus obtained has a thickness of less than 1 micrometer. Advantageously, it has a thickness between 100 and 600 nanometers.

[0044] Alternatively, the silver chloride 140 layer is deposited on the wire 120. For example, the silver chloride 140 layer is produced by screen printing on the silver layer.

[0045] A layer of saturated potassium chloride gel 150 is then deposited onto the silver- and silver chloride-coated portion of wire 120 (Step F). This layer has a thickness between 10 and 10 micrometers. It consists of a polymer matrix mixed with a potassium chloride solution and a resin. It can be deposited by screen printing or dispensing.

[0046] The structure of the reference electrode 1 thus obtained is schematically represented in Figure 3.

[0047] According to another example of an implementation of the process according to the invention (for example, illustrated by Figure 4). According to this other example, step A' of supplying the substrate 110 is essentially the same as step A described above.

[0048] The inlay operation (Step B') differs essentially from Step B described previously in that the 120 wire is a silver (or silver alloy) wire. The 120 silver wire may be pure silver or it may consist of a copper wire coated with a layer of silver. The diameter of this 120 wire is, for example, between 10 and 30 micrometers.

[0049] Wire 120 is configured to be connected or linked at one or more points to a measuring device (not shown) (See step C').

[0050] In this implementation mode, there is no step equivalent to step D described previously and steps E' and F' are similar or identical respectively to steps E and F described previously.

[0051] The structure of the reference electrode 1 thus obtained is schematically represented in Figure 5.

[0052] According to yet another example of an implementation of the process according to the invention, the step F or F' of forming the saturated potassium chloride gel layer 150, is replaced by the making of an encapsulation envelope 160, comprising a microporous window 170 and filling the encapsulation envelope 160 with a saturated potassium chloride solution 180.

[0053] Encapsulation is achieved for example by applying a photocurable epoxy resin (for example, curable under infrared radiation).

[0054] The encapsulation envelope 160 and the microporous window 170 are for example made by lamination and ultrasonic welding, on the substrate 110.

[0055] An example of the reference electrode structure thus obtained is shown schematically in Figure 6.

[0056] Numerous variations on the examples of processes described above can be considered.

[0057] For example, the wire 120 can be embedded on the two main faces 112, 114 of the substrate 110, the connection between these two faces 112, 114 then being made for example by means of a conductor via.

[0058] For example, other redox couples can be used instead of Ag / AgCl.

[0059] For example, at least one other electrode (working and / or counter electrode) can be formed on one and / or the other of the main faces 112, 114 of the substrate 110.

Claims

Demands

1. A method for manufacturing an electrode (1) for electrochemical measurements comprising - a step (A, A') of supplying a substrate (110) comprising a dielectric material, this substrate (110) having a thickness delimited by a first (112) and a second (114) principal face, - a step of supplying an electrically conductive wire (120), - an embedding step (B, B') during which at least a part of the electrically conductive wire (120) is embedded, by deformation of the substrate (110), in the thickness of the substrate (110), on at least the first face (112), the substrate (110) thus at least partially supporting the electrically conductive wire (120), and this embedding step (B, B') leaving a free surface of the electrically conductive wire (120), while another part of the surface of the wire (120) is in contact with the dielectric material of the substrate (HO), - a cutting step during which the substrate is cut into a plurality of units, each unit supporting at least one electrode formed from the electrically conductive wire at least partially embedded in the substrate.

2. Method according to claim 1, comprising a step of forming (D, E / D', E') a redox couple on at least a portion of said free surface of the electrically conductive wire (120).

3. A method according to claim 2, wherein the redox couple is formed from the silver / silver chloride couple, silver being present in the electrically conductive wire (120) before the incrustation step (B, B') or a layer comprising silver having been deposited on the electrically conductive wire (120) after the incrustation step (B, B'), and the method comprising a step of forming (E, E') a layer of silver chloride (140) on the silver present in the electrically conductive wire (120) before the incrustation step (B, B') or on the layer comprising silver deposited on the electrically conductive wire (120) after the incrustation step (B, B').

4. A method according to claim 3, wherein the formation step (E, E') of a layer of silver chloride (140) is produced by electrolytic means from the silver present in the electrically conductive wire (120) or on the layer comprising silver.

5. A method according to claim 4, wherein the formation step (E, E') of a layer of silver chloride (140) includes a chlorination step carried out by positively polarizing the electrically conductive wire (120) and immersing at least a portion of this electrically conductive wire (120) comprising silver in a solution comprising chloride ions.

6. A method according to claim 3 or 4, wherein the step of forming (E, E') a layer of silver chloride (140) is carried out by screen printing on the silver present in the electrically conductive wire (120) or on the layer comprising silver.

7. A method according to any one of claims 4 to 6, wherein the electrically conductive wire (120) is formed of copper or a copper alloy, said method comprising, between the inlay step (B, B') and the redox couple formation step (D, E / D', E'), a nickel layer formation step by electrolytic deposition on said free surface of the electrically conductive wire, followed by a gold layer formation step on the nickel layer by electrolytic means, the redox couple formation step (D, E / D', E') comprising an electrolytic silver deposition step on the gold layer.

8. A method according to any one of claims 4 to 6, wherein the conducting wire (120) is a silver wire or a silver alloy wire.

9. A method according to any one of claims 3 to 8, comprising a step of forming (F, F') a layer of potassium chloride gel (150) on at least one area of ​​the silver chloride layer (140).

10. A method according to any one of claims 3 to 8, comprising a step of forming a porous barrier (170) covering at least an area of ​​the silver chloride layer (140) and enclosing a potassium chloride layer solution (180).

11. A method according to any one of the preceding claims, wherein the deformation of the substrate (110) during the inlay step (B, B') comprises the implementation of at least one of the following techniques: heating the wire (120) and / or the substrate (110), applying ultrasound to the wire (120) and / or the substrate (110), applying pressure to the wire (120) and / or the substrate (110).

12. Electrode for electrochemical measurements comprising - a substrate (110) comprising a dielectric material, this substrate (110) having a thickness delimited by a first (112) and a second (114) face, - an electrically conductive wire (120) at least a part of which is embedded in the thickness of the substrate (110), by deforming the substrate (110), on at least the first face (112), the substrate (110) thus at least partially supporting the electrically conductive wire (120), and a surface of the electrically conductive wire (120) being left free, while another part of the surface of the wire is in contact with the dielectric material of the substrate (110), in which the substrate (110) is in the form of a unit supporting at least one electrode (1) formed from the electrically conductive wire (120) at least partly embedded in the substrate (110).

13. Electrode according to claim 11, wherein a layer formed of a redox couple is formed on said free surface of the electrically conductive wire (120).

14. Electrode according to claim 12, wherein the redox couple is the silver / silver chloride couple.

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