Electrode for electrochlorination and associated processes

Abstract

Title: Electrode for Electrochlorination and Associated Processes The invention relates to an electrode (1) for electrochlorination, and the associated manufacturing process, comprising an electrically conductive substrate (10), at least one catalytic layer (11) comprising metallic and metalloid chemical elements, characterized in that the at least one catalytic layer (11) comprises ruthenium in a mass proportion of between 10% and 40%, titanium in a mass proportion of between 40% and 79%, and boron in a mass proportion of between 1% and 20%, the mass proportions being given relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer (11). Figure for the abstract: Fig. 1

Description

Title of the invention: Electrode for electrochlorination and associated methods Technical field

[0001] The present invention relates to the field of electrodes for electrochlorination. It finds particularly advantageous application in the electrochlorination of water, and in particular for the electrochlorination of low salinity water, for example for the purpose of its disinfection. STATE OF THE ART

[0002] Electrochlorination is a technology consisting in particular of oxidizing the chloride ions present, generally in salt water, by applying an electric current between two electrodes. The chemical reaction, commonly referred to as CER (from the English Chlorine Evolving Reaction, which can be translated as chlorine transformation reaction), produces gaseous chlorine Cl2, which in contact with water generates hypochlorous acid HOC1 or hypochlorite CIO depending on the pH. These reaction products are biocidal, which makes it possible to disinfect the water.

[0003] CER competes with the oxidation of water called OER (from the English Oxygen Evolving Reaction). Electrodes for electrochlorination include at least one specific catalyst to promote CER. Furthermore, the reaction conditions of CER are highly oxidizing and corrosive. These conditions therefore limit the choice of electrode materials and catalysts.

[0004] Today, the large-scale deployment of electrochlorination for water disinfection is hampered in particular by the price of electrodes. This technology is in demand as part of the energy transition but consumes noble metals and transition metals, mostly considered strategic resources.

[0005] There is therefore a need to obtain an electrode comprising catalysts based on abundant elements, promoting CER and resisting corrosion.

[0006] Historically, the most efficient catalyst for the CER reaction is ruthenium oxide RuO2. Although very efficient, ruthenium oxide is limited by its low stability against corrosion. During the catalytic cycle, ruthenium oxide can be oxidized to RuO42 which is soluble in aqueous media. The catalyst is therefore quickly destroyed.

[0007] Efforts have been made to stabilize ruthenium oxide catalysts. A widely marketed model comprises titanium plates with a coating composed of an alloy of ruthenium and titanium. This model, however, has

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[0015] fairly low faradic yields for the CER, especially when the water is weakly saline. Document WO2019175280A1 discloses an electrode with a ruthenium and titanium alloy including dopants for operating at low salinity. However, this solution remains improvable. An object of the present invention is therefore to provide an improved electrode for electrochlorination, and in particular the electrochlorination of low salinity water. More particularly, an objective of the invention is to provide an electrode reducing the use of strategic resources while maintaining good electrochlorination performance. Other objects, features, and advantages of the present invention will become apparent from the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY To achieve this objective, according to a first aspect, an electrode for electrochlorination is provided comprising: - an electrically conductive substrate, - at least one catalytic layer comprising metallic and metalloid chemical elements. Advantageously, the at least one catalytic layer comprises: - ruthenium with a mass proportion of between 10% and 40%, - titanium with a mass proportion of between 40% and 79%, and - boron with a mass proportion of between 1% and 20%, the mass proportions being given in relation to the total mass of the metallic and metalloid elements in the at least one catalytic layer. The catalytic layer is thus formed from a Ru-Ti-B mixture. Boron makes it possible to increase the number of defects in the layer comprising ruthenium and titanium and thus increase its active surface area. Titanium forms a matrix with ruthenium, which limits corrosion of the catalytic layer and more particularly of ruthenium. During the development of the invention, it was demonstrated that the combination of titanium and boron with ruthenium synergistically improved the efficiency and lifetime of the coating, with a limited proportion of ruthenium. A better compromise between electrocatalytic efficiency of the electrode, quantity of ruthenium and lifetime can thus be obtained. The electrode is thus particularly suitable for electrochlorination, and in particular of saline water, with a cost compatible with an industrial application. A second aspect relates to a method of manufacturing the electrode according to the first aspect, comprising: - a supply of an electrically conductive substrate, - a supply of a solution of precursors of metallic and metalloid elements comprising: • a ruthenium precursor, the ruthenium being in a mass proportion of between 10% and 40% relative to the total mass of the metallic and metalloid elements in said solution, • a titanium precursor, the titanium being at a mass proportion of between 40% and 79% relative to the total mass of the metallic and metalloid elements in said solution, and • a boron precursor, the boron being in a mass proportion of between 1% and 20% relative to the total mass of metallic and metalloid elements in said solution, - a deposition, from the precursor solution, of at least one layer on the substrate, - calcination of the substrate and of the at least one deposited layer to obtain the catalytic layer.

[0016] A third aspect relates to a use of the electrode according to the first aspect, and / or resulting from the method according to the second aspect, for the electrochlorination of water.

[0017] According to one example, the water comprises, prior to electrochlorination, a proportion of chloride ions less than or equal to 4g.L *.

[0018] Equivalently, one aspect of the invention relates to an electrochlorination method using the electrode according to the first aspect, and / or resulting from the method according to the second aspect. The electrochlorination method comprises immersing the electrode in a solution comprising water, and electrochlorinating the water. BRIEF DESCRIPTION OF THE FIGURES

[0019] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0020] [Fig.l] [Fig.l] represents an electrolyser comprising the electrode, for the electrochlorination of a solution, according to an exemplary embodiment.

[0021] [Fig.2A] Figures 2A to 2D show cross-sectional views of steps in manufacturing the electrode.

[0022] [Fig.2B]

[0023] [Fig.2C]

[0024] [Fig.2D]

[0025] [Fig.3] [Fig.3] represents a cross-sectional view of an electrode comprising an external protective layer, according to an exemplary embodiment.

[0026] [Fig.4] [Fig.4] represents a cross-sectional view of an electrode comprising intermediate protective layers, according to an exemplary embodiment.

[0027] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular the relative dimensions of the layers and the substrate are not representative of reality. DETAILED DESCRIPTION

[0028] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below.

[0029] According to one example, in the at least one catalytic layer: - the mass proportion of ruthenium is between 22% and 30%, - the mass proportion of titanium is between 40% and 76%, and - the mass proportion of boron is between 2% and 5%.

[0030] During the development of the invention, these proportions showed electrocatalytic efficiencies and particularly advantageous lifetimes for the electrochlorination of water, for a limited quantity of ruthenium.

[0031] According to one example, the mass of ruthenium in the at least one catalytic layer is less than or equal to 10 g / m2, preferably less than or equal to 5 g / m2, and more preferably still less than or equal to 4 g / m2. The quantity of ruthenium is thus limited, while offering electrocatalytic efficiency and a lifetime compatible with an industrial application.

[0032] According to one example, the at least one catalytic layer comprises a first dopant comprising a chemical element at a mass proportion of between 1% and 10%, preferably between 1% and 5%, relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer. The dopant makes it possible to further improve the electrocatalytic efficiency of the electrode, in synergy with the Ru-Ti-B catalytic layer with the indicated proportions. The use of at least one dopant makes it possible, without increasing the proportion of ruthenium, titanium and boron, to improve the performance of the electrode in terms of electrocatalytic efficiency and lifetime. When a dopant is added to an alloy, the properties of the resulting electrode are modified according to the contribution of the dopant.

[0033] According to one example, said chemical element is chosen from the group consisting of cobalt, scandium, cerium, yttrium, antimony, vanadium, lanthanum, tin, nickel, iron, manganese, calcium, bismuth, hafnium, osmium, rhodium, platinum, palladium, iridium.

[0034] According to one example, said element is present in the catalytic layer in a proportion distinct from the proportion of boron. According to one example, the dopant is not boron. Preferably, the first dopant comprises a chemical element selected from the group consisting of yttrium, antimony, vanadium, rhodium, platinum, palladium, iridium.

[0035] According to one example, the at least one catalytic layer further comprises a second dopant, different from the first dopant, comprising a chemical element at a mass proportion of between 1% and 5%, relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer. The second dopant may be chosen so as to improve at least one property of the electrode, this property being different from that(those) improved by the first dopant.

[0036] According to one example, said chemical element is chosen from the group consisting of cobalt, scandium, cerium, yttrium, antimony, vanadium, lanthanum, tin, nickel, iron, manganese, calcium, bismuth, hafnium, osmium, rhodium, platinum, palladium, iridium.

[0037] According to this example, the mass proportion of titanium is then between 40% and 78% relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer.

[0038] According to one example, in the at least one catalytic layer, the mass proportion of ruthenium is between 22% and 30%.

[0039] According to one example, in the at least one catalytic layer, the mass proportion of titanium is between 40% and 75.5%.

[0040] According to one example, in the at least one catalytic layer, the mass proportion of boron is between 2% and 5%.

[0041] According to one example, in the at least one catalytic layer, the mass proportion of the chemical element of the first dopant is between 1% and 5%.

[0042] According to one example, in the at least one catalytic layer, the mass proportion of the chemical element of the second dopant is between 0.5% and 2.5%.

[0043] During the development of the invention, it was demonstrated that the electrode according to each of these proportions offered an even better compromise between electrocatalytic efficiency, quantity of ruthenium and lifetime of the electrode. The proportion of ruthenium can thus be lowered compared to existing solutions, while offering satisfactory performance for electrochlorination.

[0044] According to one example, the electrode further comprises a so-called protective layer surrounding at least in part, and preferably entirely, the at least one catalytic layer, the protective layer comprising, and preferably being essentially composed of: - a catalytically inert metal or its oxide, for example titanium, silicon, niobium, tantalum, tin, and / or - a polymer.

[0045] The protective layer protects the catalytic layer from corrosion. The corrosion resistance of the electrode is thus further improved.

[0046] According to one example, the protective layer comprises, and preferably consists essentially of, titanium.

[0047] According to one example, the protective layer is free of a catalytically active metal. According to one example, the protective layer is free of a metal from the platinoid group, and more particularly is free of ruthenium.

[0048] According to one example, the protective layer comprising a catalytically inert metal or its oxide, the protective layer has a thickness substantially less than or equal to 5 μm, preferably substantially less than or equal to 50 nm, and more preferably still substantially less than or equal to 15 nm.

[0049] According to one example, the protective layer comprising a polymer, the protective layer has a thickness substantially less than or equal to 5 μm.

[0050] According to one example, the polymer is a polypyrrole or its derivatives.

[0051] The protective layer comprising polypyrrole makes it possible to obtain properties distinct from those conferred by a metallic protective layer. This protective layer can in particular allow a morphological modification of the surface of the electrode. This modification can in particular influence the way in which the electrolyte reaches the electrode and therefore the efficiency of the reaction.

[0052] According to one example, the electrode comprises several superimposed catalytic layers, and in which at least two successively superimposed catalytic layers are separated by a so-called intermediate protection layer comprising a catalytically inert metal or its oxide, for example titanium, silicon, niobium, tantalum, tin.

[0053] The intermediate protective layer(s) make it possible to delay the corrosion of the catalytic layers by creating a barrier effect. Corrosion propagates rather in the intermediate protective layer, and more particularly in its main plane of extension. This limits the progression of corrosion through the layers of the coating.

[0054] According to one example, the intermediate protective layer(s) are free of a catalytically active metal. According to one example, the protective layer is free of a metal from the platinoid group, and more particularly is free of ruthenium.

[0055] According to one example, at least one of ruthenium, titanium and boron is in metallic or oxide form. At the end of the manufacturing process, these elements may be in oxide form. In use, the oxidation states can be modified. In the context of a cathode, for example, these elements can be in metallic form.

[0056] According to one example, the boron precursor is boric acid. Boric acid improves the formation of the catalytic layer. In addition, this simplifies the incorporation of boron into the catalytic layer.

[0057] According to one example, the precursor solution is an acid solution comprising a mixture of water and an organic solvent, preferably an alcohol and for example isopropanol.

[0058] An element “based on” a material A is understood to mean an element comprising this material A only or this material A and possibly other materials.

[0059] A parameter “substantially equal / greater / less than” a given value means that this parameter is equal / greater / less than the given value, to within plus or minus 10%, or even plus or minus 5%, of this value.

[0060] It is specified that in the context of the present invention, the thickness of a layer or coating is measured in a direction perpendicular to the surface or plane along which this layer or coating has its maximum extension (for example the plane (x,y)). The thickness is thus taken in a direction perpendicular to the main faces of the substrate on which the different layers and / or the coating rest, and more particularly in the z direction with reference to the figures.

[0061] When an element is said to be "homogeneous" in another element or volume, the quantity of the element per unit of volume is substantially identical in any portion of the same determined size of the other element or volume.

[0062] Generally speaking, in the field of chemistry, a catalyst is understood to mean a compound that increases the speed of a chemical reaction by participating in the reaction without being part of the reactants and products. A catalyst makes it possible, in particular, to introduce new reaction pathways; for example, it does not participate directly in the reaction but its presence facilitates the breaking of bonds, or, for example, it participates in it and is regenerated during the reaction.

[0063] The term "monomer unit" means a molecular structure repeating in a polymer, formed from a monomer. Polymers formed from a single monomer unit are called homopolymers. A copolymer is used when at least two monomer units, with different molecular structures, constitute the polymer.

[0064] In the context of the present invention, the average molar masses of polymer are mass average molar masses (as distinguished from number average molar masses), and given in g / mol.

[0065] The expression "A and / or B" means (A), (B), or (A and B). The expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0066] The electrode 1 for electrochlorination, its manufacturing method and its use for electrochlorination are now described according to several exemplary embodiments.

[0067] The electrode 1 comprises an electrically conductive substrate 10 and at least one catalytic layer 11, as illustrated for example in [Fig.2D]. The catalytic layer 11 is configured to increase the rate of the electrochlorination chemical reaction (or CER). As illustrated for example in [Fig.1], the electrode 1 may be included in an electrolyzer device. The electrolyzer may comprise an electrode 1 and a counter-electrode 3, connected together by an electrical power source 14. The electrode 1 and the counter-electrode 3 are at least partially immersed in a solution 2, and more particularly a water solution comprising chloride ions. The electrode 1 and the counter-electrode 3 may each be an electrode according to the first aspect of the invention. According to an alternative example, the counter-electrode 3, for example the cathode, may be a different electrode.For example, and in particular in the case where there is no polarity inversion, the cathode may be different from an electrode according to the first aspect. The person skilled in the art is then able to choose the appropriate electrode. The application of an electric current between the electrode 1 and the counter-electrode 3 makes it possible to induce the CER. The electrochlorination process described can be implemented in a water disinfection process.

[0068] As will be described in more detail below, the electrode 1 is particularly suitable for the electrochlorination of water. According to one example, the water comprises, prior to electrochlorination, a proportion of chloride ions, and more particularly sodium chloride, less than or equal to 4 g.L *. The electrode 1 is in fact particularly suitable for the electrochlorination of slightly saline water, due to its performance in terms of electrocatalytic efficiency and lifetime. However, it should be noted that the electrode can be used at a higher degree of salinity, for example for an application for the production of alkali chlorine or for salt electrolyzers which operate in saturated solution.

[0069] In the figures, it has been chosen to represent stacks of layers on the substrate 10. Note that the catalytic layer(s) 11 as well as any other protective layers may be present on either side of the substrate 10. These layers may cover several and preferably all of the faces of the substrate 10, at least at the level of the zones intended to be immersed in the solution 2 to be electrochlorinated.

[0070] The catalytic layer 11 comprises metallic and metalloid chemical elements. These metallic and metalloid chemical elements comprise, and are preferably chosen from the group essentially consisting of, ruthenium, titanium, boron and possible dopants.

[0071] The catalytic layer 11 comprises, and preferably consists essentially of (with any dopants): - ruthenium with a mass proportion of between 10% and 40% relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer 11, - titanium with a mass proportion of between 40% and 79% relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer 11, and - boron with a mass proportion of between 1% and 20% relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer 11.

[0072] When it is stated that the catalytic layer comprises a chemical element, and in particular a metallic or metalloid chemical element, it is understood that this chemical element may be present alone or in combination with other chemical elements. For example, a metallic chemical element may be present in its metal form or in its oxidized form. Thus, it is understood that ruthenium may be in the form of ruthenium metal or ruthenium oxide, titanium may be in the form of titanium metal or titanium oxide, boron may be in the form of boron metalloid or boron oxide. The same applies to the other chemical elements described, and more particularly to the dopants. Whether these elements are in the form of oxide or in the form of metal, it is considered that the material of the catalytic layer 11 is an alloy of these elements. The material of the catalytic layer 11 is preferably non-composite.This material is preferably formed from a single phase in which the elements Ru, Ti and B, as well as any dopants, are distributed homogeneously.

[0073] When it is said that the layer may be essentially "made up of" the above chemical elements (with any dopants), it is understood that the layer is made up of ruthenium, titanium, boron and any dopants as described above, in their metallic or oxide form.

[0074] In the context of the present invention, the proportions of chemical elements in the catalytic layer 11 are given in mass relative to the total mass of the metallic and metalloid elements, and in particular per catalytic layer 11. In the total mass of the metallic and metalloid elements, only the chemical elements alone are considered, that is to say without any oxygen atoms and other atoms that may be bonded to the chemical element. It is understood that the proportions are chosen so that the sum of the percentages of the metallic and metalloid elements is equal to 100%.

[0075] Mass proportions in the catalytic layer 11 are given below.

[0076] According to one example, the mass proportion of ruthenium is substantially lower or equal to 30%. According to one example, the mass proportion of ruthenium is substantially less than or equal to 25%. According to one example, the mass proportion of ruthenium is substantially greater than or equal to 22%. During the development of the invention, it was indeed demonstrated that these ranges, in synergy with titanium and boron, allowed satisfactory, and preferably even increased, performance in terms of electrocatalytic efficiency and lifetime, while limiting the use of strategic resources.

[0077] It is therefore understood that the quantity of ruthenium in the catalytic layer 11 can be limited. For example, the mass of ruthenium in the at least one catalytic layer 11 is less than or equal to 10 g / m2, preferably less than or equal to 5 g / m2, and even more preferably substantially less than or equal to 4 g / m2. The mass of ruthenium is here counted for the total number of catalytic layers 11 present on the electrode 1. The number of catalytic layers 11 can be chosen so as to obtain a desired quantity of ruthenium, for example a quantity in these ranges.

[0078] According to one example, the mass proportion of titanium is substantially between 40% and 76%.

[0079] According to one example, the mass proportion of boron is substantially greater than or equal to 2%, and preferably substantially greater than or equal to 3%. The mass proportion of boron may be substantially less than or equal to 5%. Preferably, the mass proportion of boron may be substantially equal to 3%. During the development of the invention, it was in fact demonstrated that a proportion of boron in these ranges was sufficient to induce the appearance of defects in the Ru-Ti-B alloy and thus improve the performance of the electrode 1.

[0080] In order to improve the performance of the catalytic layer 11, it may comprise at least one dopant. The dopant may in particular comprise a chemical element chosen from cobalt, scandium, cerium, yttrium, antimony, vanadium, lanthanum, tin, nickel, iron, manganese, calcium, bismuth, hafnium, osmium, rhodium, platinum, palladium, iridium.

[0081] Preferably, the dopant comprises a chemical element chosen from yttrium, antimony, vanadium, rhodium, platinum, palladium, iridium. During the development of the invention, it was in fact shown that this selection of dopant was particularly suitable for electrochlorination, in synergy with the Ru-Ti-B alloy.

[0082] According to one example, the catalytic layer 11 comprises a first dopant. The mass proportion of the first dopant may be substantially greater than or equal to 0.5%, preferably greater than or equal to 1%. The mass proportion of the first dopant may be substantially less than or equal to 10%, and preferably substantially less than or equal to 5%, and even more preferably less than or equal to 2.5%.

[0083] The catalytic layer 11 may comprise a second dopant, different from the first dopant. The second dopant may be present in the same proportions as the first dopant or different proportions, and in particular in the proportions indicated above relative to the first dopant. Depending on the added dopant and its physicochemical contribution, it is thus possible to modify the properties of the electrode. For example, Pd is known to be a very good catalyst but not very stable with respect to polarity inversions. The second dopant may be chosen so as to improve different properties of the electrode compared to the first dopant, to improve this stability for example. The mass proportion of the second dopant may be less than or equal to that of the first dopant.

[0084] The relative proportions of the different chemical elements can be adapted according to the composition of the catalytic layer 11, within the indicated ranges.

[0085] According to a particular preferred example: - the mass proportion of ruthenium is between 22% and 30%, - the mass proportion of titanium is between 40% and 75.5%, - the mass proportion of boron is between 2% and 5%, - the mass proportion of the chemical element of the first dopant is included between 1% and 5%, and - the mass proportion of the chemical element of the second dopant is between 0.5% and 2.5%.

[0086] The substrate 10 may comprise, and preferably consists essentially of, carbon. The substrate 10 comprises, for example, carbon fibers, a carbon sheet and preferably graphite. Graphite electrodes are, however, fragile. According to a preferred example, the substrate 10 comprises, and preferably consists essentially of, titanium. The electrode 1 is thus made more mechanically robust. In addition, the adhesion of the catalytic layer 11 to the substrate 10 is promoted. The catalytic layer 11 comprising titanium allows a certain chemical continuity between the substrate 10 and the catalytic layer 11, to facilitate adhesion.

[0087] The method of manufacturing the electrode 1 is now described with reference to FIGS. 2A to 2D.

[0088] The method firstly comprises providing the substrate 10, as illustrated in [Fig.2A].

[0089] The method may then comprise depositing a solution of precursors of the metallic or metalloid chemical elements to form a layer 11a on the exposed surface of the substrate 10, as illustrated for example in [Fig.2B]. The method may comprise forming the precursor solution, prior to its deposition.

[0090] The concentration of ruthenium in solution is preferably between 0.5 g / L and 2 g / L. Depending on the quantity deposited, it is thus possible to deposit between 0.1 gRu / ni2 and 0.4 gRu / m2 of electrode per IL catalytic layer.

[0091] The proportions of the precursors may be substantially equal to those indicated relatively for the metal layer, and therefore given in relation to the total mass of the metallic and metalloid elements in said solution. The proportions of chemical elements in the precursor solution are given in mass in relation to the total mass of the metallic and metalloid elements. In the total mass of the metallic and metalloid elements, only the chemical elements alone are considered, that is to say without any oxygen, chlorine and other atoms that may be bonded to the chemical element. It is understood that the proportions are chosen so that the sum of the percentages of the metallic and metalloid elements is equal to 100%.

[0092] The precursors of ruthenium, titanium, boron, and possible dopants can in particular be in the form: - salts of these chemical elements, for example chloride salts, and / or - organometallic precursors, and / or - acid of these chemical elements.

[0093] Preferably, the boron precursor is boric acid B(OH)3. Boric acid improves the formation of the catalytic layer by promoting the bonding between boron and titanium and ruthenium. In addition, this simplifies the incorporation of boron into the catalytic layer. Indeed, the use of boron oxide is often limited by its solubility in the precursor solution. It is therefore easier to adapt the proportion of boron in the catalytic layer 11 thanks to the use of boric acid as a precursor.

[0094] For example, the precursor solution is prepared from RuC13, titanium isopropoxide Ti(C3H7O)4, and boric acid B(OH)3. The dopant(s) may be in the form of chloride salts, in the form XC1Z or YC1Z, X and Y being a dopant, for example the first or second dopant. Z is a non-zero coefficient which is not necessarily equal between different dopants.

[0095] According to one example, the precursor solution is a solution comprising a mixture of water and an organic solvent. The fact that this solution is partially aqueous simplifies the implementation of the process on an industrial scale. The use of an organic solvent also makes it possible to improve the solubility of the precursors in the precursor solution. Thus, it is easier to adapt, as required, the proportions of precursors to obtain the final proportions of Ru, Ti, B and possible dopants in the catalytic layer 11. According to one example, the organic solvent is an alcohol, and preferably isopropanol. When developing the invention, Isopropanol was identified as the most suitable for solubilizing the precursors.

[0096] The ratio between the aqueous part and the organic solvent can be adapted according to the needs. For example, the volume ratio between the aqueous part and the organic solvent is 2:1. The volume proportion of the aqueous part, for example hydrochloric acid solution, can be between 50% and 95%. The volume proportion of the organic part can be between 5% and 50%. The sum of these two proportions preferably gives 100%.

[0097] Preferably, the precursor solution is an acid solution. Equivalently, the pH of the precursor solution may be less than or equal to 7 and preferably strictly less than 7. Even more preferably, the pH of the precursor solution is substantially between 0 and 1. The acid solution may, for example, comprise hydrochloric acid.

[0098] The precursor solution is deposited on the substrate 10 to form the layer 11a, as illustrated in [Fig.2B]. The precursor solution is preferably deposited by drop-by-drop deposition or by spraying onto the substrate 10. These methods are compatible with the nature of the precursor solution and are more easily industrializable. Note that those skilled in the art may consider other deposition methods.

[0099] After the deposition of the layer 11a, this layer can be treated to obtain the catalytic layer 11, as illustrated for example in [Fig.2C]. The layer 11a can be calcined, preferably in an aerobic environment. The layer 11a can be calcined at a temperature between 350°C and 500°C, preferably substantially equal to 400°C. The layer 11a can be calcined for example in air at 400°C. Preferably, prior to this calcination step, the layer 11a is subjected to a thermal pretreatment configured to partially evaporate the solvent from the precursor solution. This makes it possible to limit, and preferably to avoid, damage to the catalytic layer by excessive removal of the solvent.

[0100] The deposition of the precursor solution, possibly followed by drying and / or the calcination described above, can be repeated several times to obtain a plurality of catalytic layers 11. It is thus possible to modulate the quantity of ruthenium present in the electrode as a function, for example, of the concentration of the precursor solution. These steps are in particular repeated until the desired quantity of ruthenium per square meter of electrode is reached.

[0101] Following the deposition of the catalytic layer(s) 11a, 11, the substrate 10 as well as these layers can be calcined, preferably in an aerobic environment, to obtain the final electrode, illustrated for example in [Fig.2D]. The calcination can be carried out for example at 400°C for 1 hour.

[0102] It is therefore understood that a calcination step can be carried out between successive depositions of layers 11a and / or after several depositions of catalytic layers 11. preferably, calcination is carried out between successive deposits of layers 11a and after the formation of several catalytic layers 11.

[0103] A particular method of manufacturing the electrode is now described. The performances obtained for electrodes according to this example are then described.

[0104] A hydroalcoholic solution of metals is prepared from metal precursors RuC13, titanium isopropoxide Ti(C3H7O)4, boric acid B(OH)3, and where appropriate the dopant XC1Z, so as to obtain the mass composition indicated below. In the table below, the mass proportions of the alloys are denoted so that the sum of the metal or metalloid chemical elements is equal to 100%. All of the precursors are solubilized in a mixture of HCl 1M / isopropanol with the ratio 2:1 (v / v). The deposited quantity of precursor solution is equal to 20 μL per square centimeter of substrate 10. The solution is then dried at 80°C and then the electrode is calcined in an oven under air at 400°C for 10 minutes. 10 layers of 0.2 gRu / m2 are deposited on each side of a titanium substrate 10.

[0105] In order to test the performance of the electrodes, the accelerated aging method described in document WO2019175280A1 is used. In this method, two electrodes 1 are arranged in parallel in a bath containing an aqueous solution of 4 g / L of NaCl and 70 g / L of Na2SO4. These electrodes are separated by a distance of 3 mm in the solution. The electrodes undergo polarity reversals every minute until they reach a cell potential of 8.5 V. The total duration of the experiment makes it possible to determine the value h / (gRu.m2) for a given electrode, corresponding to the accelerated lifetime. The higher the value obtained, the more efficient the electrode is considered.

[0106] Examples of electrodes according to the invention were produced and their lifespan accelerated compared to a comparative example of electrode, taken from document WO2019175280A1 and described in the table below.

[0107] [Tableauxl] Comparative example of WO2019175280A1 Alloy Mass composition (%) Mass Ru (g / m2) Accelerated life (h / (g Ru-m2)) Ru Ti Sc Rh RuTiScRh 30 67 2 1 20 13.4 Invention Alloy Mass composition (%) Mass Ru (g / m2) Accelerated life (h / (g Ru-m2)) Ru Ti BX RuTiB Ir 20 60 10 10 4 12.5 RuTiB 25 70 5 - 4 9.8 RuTiBCo 25 70 3 2 4 5.0 RuTiBSc 25 70 3 2 4 9.8 RuTiBCe 25 70 3 2 4 4.3 RuTiBRh 25 70 3 2 4 13.0 RuTiB Pt 25 70 3 2 4 17.1 RuTiBPd 25 70 3 2 4 15.5 RuTiB Ir 25 70 3 2 4 20.4 RuTiBY 25 70 3 2 4 10.0 RuTiBV 25 70 3 2 4 19.0 RuTiBSb 25 70 3 2 4 13.0

[0108] For the best electrode described in document WO2019175280A1, in which the alloy does not include boron, an accelerated lifetime of 13.4 h / (gRu.m2) is obtained.

[0109] . In the case of a RuTiB alloy, the replacement of critical metals (Rh and Sc) by boron, an abundant and inexpensive element, leads here to an accelerated lifetime of 9.8 h / (gRu.m2), or 73% of the performance of the comparative example.

[0110] The addition of dopant to the RuTiB alloy makes it possible to significantly improve the performance of the electrode. Several electrodes according to the invention have in fact exceeded the performance of the comparative example from WO2019175280A1. The best alloy tested was obtained for RuTiBIr in the proportions indicated above, with an accelerated lifetime of 20.4 h / (gRu.m2).

[0111] Electrodes with a carbon substrate (graphite, thickness 2 mm, dimensions 10x30 mm) were prepared with the same protocol. The characterization of the per The properties of this type of electrode are incompatible with the accelerated aging protocol described above for titanium substrate electrodes. Indeed, carbon materials such as graphite do not undergo chemical passivation. After prolonged use of a graphite electrode in a corrosive environment such as for electrochlorination, exfoliation or deplating phenomena are observed at the surface level and therefore a loss of the catalytic layer.

[0112] However, graphite is a conductive material and the anodic and cathodic potentials do not vary sufficiently to detect the loss of the catalytic layer. To study the performance of this type of electrode, we carried out a long-term electrolysis to simulate the conditions in a salt electrolyzer (30 mA.cm 2, tap water, 4 g.L1 of NaCl, polarity reversal every 4 hours) and we measured the production of the HOC1 / C1O couple by photometric assay. With a graphite electrode prepared with an alloy Ru0.25Ti0.70Ir0.02B0.03 we measured an overall production efficiency of 63.8% over an 8-day electrolysis.

[0113] In order to measure the composition of the catalytic layer 11, the following method can be used. The techniques that can be used are scanning electron microscopy equipped with an energy dispersive X-ray detector (commonly abbreviated SEM - EDX, from the English Scanning Electron Microscopy with Energy Dispersive X-Ray) and X-ray induced photoelectron spectrometry (commonly abbreviated XPS, from the English X-ray Photoelectron Spectroscopy). In both cases, samples of size 10x30 mm can be prepared.

[0114] SEM-EDX is a technique for analyzing the surface of the sample and allows both images to be obtained to check the homogeneity of the deposit as well as the presence of a protective polymer layer. The analysis also allows the composition of the surface layer of the sample to be determined. However, boron is not an element detected by the device.

[0115] XPS is a technique that allows the oxidation state of metals inside the material to be determined. It is also possible with a deconvolution of the signals to determine the ratio of the elements to each other. Thus, for example, on a sample prepared for a theoretical proportion Ru0.20Ti0.60Ir0.10B 0.10, we experimentally obtained Ruo.1oTio.7oIroo6Bo.14. Taking into account the uncertainty of the measurement, the theoretical proportion of the alloy in the solution is substantially respected after preparation of electrode 1.

[0116] In order to further improve the performance and lifetime of the electrode 1, the electrode 1 may comprise a protective layer 12 at least partially surrounding the catalytic layer(s) 11. As illustrated for example in [Fig.3], the protective layer 12 may be an external layer covering all of the deposited catalytic layers 11. The protective layer 12 may cover at least partially the catalytic layer(s) 11, preferably on at least several faces of the electrode 1. Preferably, the protective layer 12 can completely cover the catalytic layer(s) 11. The catalytic layers 11 are thus arranged between the substrate 10 and the protective layer 12, which isolates them from the solution to be electrochlorinated. The propagation of corrosion in the catalytic layers 11 is therefore slowed. The corrosion resistance of the electrode 1 is thus improved. The external protective layer 12 extends along a main extension plane parallel to the main extension plane of the catalytic layer(s) 11 which it covers. The external protective layer 12 preferably has a surface exposed to the surrounding environment.

[0117] The external protective layer 12 comprises, and preferably consists essentially of: - a catalytically inert metal for the CER or its oxide, for example titanium, silicon, niobium, tantalum, tin, and / or - a polymer, and more particularly polypyrrole or its derivatives.

[0118] The thickness of the protective layer 12 may be configured to sufficiently isolate the catalytic layer from the corrosive environment while allowing the catalysts to facilitate CER. According to one example, when the outer protective layer 12 comprises an inert metal or its oxide, the protective layer 12 has a thickness substantially between 5 nm and 5 μm, preferably substantially less than or equal to 50 nm, and even more preferably substantially equal to 15 nm. According to one example, when the outer protective layer 12 comprises a polymer, the protective layer 12 has a thickness substantially between 1 μm and 5 μm, preferably substantially equal to 4 μm.

[0119] It may be provided that the protective layer 12 comprises several sub-layers, for example one comprising a metal and the other comprising a polymer.

[0120] A metallic or oxide layer can be deposited, for example with a metallizer, and more particularly a plasma metallizer. This method has the advantage of being simple to implement, which reduces the cost of the electrode.

[0121] A polymer layer, for example polypyrrole, can be obtained by electrochemical polymerization. For example, the electrode can be immersed in a bath containing a solution of malic acid (0.1 M, pH 6.9) and pyrrole monomer (between 10 and 50 mM). A current density of 15 mA / cm2 is then applied for 4 minutes; a polymer film with a thickness of substantially 4 pm is obtained. Several monomer units have been tested. Depending on the side chain functionalizing the monomer unit, for example polypyrrole, the yield of the electrochlorination reaction can be improved.

[0122] The polymer of the outer protective layer 12 may have fillers positive and / or negative charges. When the polymer is charged, the efficiency of the electrochlorination reaction can be improved. As examples, the following monomer units were tested. It is understood that other derivatives of the pyrrole monomer units can be used.

[0123] Example 1

[0124] [Chem.l]

[0125] Example 2

[0126] [Chem.2]

[0127] Example 3

[0128] [Chem.3]

[0129] Electrodes with a catalytic layer of composition Ruo.2oTio.6oIro.ioBo.io (with 4gRu / m2) were prepared with an external protective layer 12 according to the examples described above. The results of the accelerated aging tests are presented in the table below

[0130] [Tables2] Invention Alloy Protective layer 12 Mass Ru (g / m2) Accelerated lifetime (h / (gRu •m2)) RuTiBIr - 4 12.5 RuTiBIr 10 nm Ti 4 28 RuTiBIr 4 pm Unsubstituted Ppy (example 1) 4 26.8 RuTiBIr 4 pm Anionic Ppy (example 2) 4 25.5 RuTiBIr 4 pm Cationic Ppy (example 3) 4 19.5

[0131] For each of the electrodes comprising an external protective layer, higher accelerated lifetimes were obtained compared to the electrode without a protective layer. The electrodes with an external protective layer have a lifetime up to 220% longer than those without a protective layer.

[0132] According to an alternative or complementary example, the electrode 1 may comprise intermediate protective layers 13 in order to further increase the lifetime of the electrode 1. The electrode 1 then comprises several catalytic layers 11 at least partly superimposed. As illustrated for example by [Fig.4], at least two successively superimposed catalytic layers are separated by an intermediate protective layer 13. The intermediate protective layer 13 extends along a main extension plane parallel to the main extension plane of the catalytic layers 11 that it separates. Preferably, each of the successively superimposed catalytic layers 11 are separated two by two by an intermediate protective layer 13. The electrode 1 may therefore comprise several intermediate protective layers 13.

[0133] The intermediate protective layer 13 thus forms a barrier to the propagation of corrosion in the electrode. Thanks to the intermediate protective layer 13, the corrosion is slowed down when it reaches the intermediate protective layer 13. The corrosion then propagates rather along the intermediate protective layer 13, and more particularly in its main extension plane. This therefore limits the progression of corrosion through the successive layers of the electrode 1.

[0134] The intermediate protective layer 13 may have the same characteristics as the external protective layer 12, and in particular in terms of thickness, and be deposited according to the same methods. Preferably, the intermediate protective layer 13 comprises, and preferably is essentially made of, a metal that is catalytically inert with respect to the CER or its oxide, for example titanium, silicon, niobium, tantalum, tin. The intermediate protective layer 13 extends between catalytic layers 11, it is preferable that the material of the protective layer 13 resists the calcination step implemented following the deposition of the precursor solution. For this, it is preferable not to use protective layers based on polypyrrole, which may be degraded during calcination. Heat-resistant polymers may be considered for producing this intermediate protective layer 13.

[0135] From the arrangement of the protective layer 13, it is understood that the deposition of this intermediate protective layer 13 is carried out between the production of successive catalytic layers 11 on the substrate 10.

[0136] According to one example, the electrode 1 comprises both an external protective layer 12 and at least one intermediate protective layer 13, in order to further optimize the corrosion resistance of electrode 1 and therefore increase its service life.

[0137] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention. The present invention is not limited to the examples previously described. Many other variant embodiments are possible, for example by combining features previously described, without departing from the scope of the invention. In addition, the features described in relation to one aspect of the invention may be combined with another aspect of the invention.

Claims

Claims

1. Electrode (1) for electrochlorination comprising: • an electrically conductive substrate (10), • at least one catalytic layer (11) comprising metallic and metalloid chemical elements, characterized in that the at least one catalytic layer (11) comprises: • ruthenium with a mass proportion of between 10% and 40%, • titanium with a mass proportion of between 40% and 79%, and • boron with a mass proportion of between 1% and 20%, the mass proportions being given relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer (11).

2. Electrode (1) according to the preceding claim, in which, in the at least one catalytic layer (11): • the mass proportion of ruthenium is between 22% and 30%, • the mass proportion of titanium is between 40% and 76%, and • the mass proportion of boron is between 2% and 5%.

3. Electrode (1) according to any one of the preceding claims, in which the mass of ruthenium in the at least one catalytic layer (11) is less than or equal to 10 g / m2, preferably less than or equal to 5 g / m2, and more preferably still less than or equal to 4 g / m2.

4. Electrode (1) according to any one of the preceding claims, in which the at least one catalytic layer (11) comprises a first dopant comprising a chemical element at a mass proportion of between 1% and 10%, relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer (11). talytic, said chemical element being chosen from the group consisting of cobalt, scandium, cerium, yttrium, antimony, vanadium, lanthanum, tin, nickel, iron, manganese, calcium, bismuth, hafnium, osmium, rhodium, platinum, palladium, iridium.

5. Electrode (1) according to the preceding claim, in which the at least one catalytic layer (11) further comprises a second dopant, different from the first dopant, comprising a chemical element at a mass proportion of between 1% and 5% relative to the total mass of the metallic and metalloid elements in the at least one catalytic layer, said chemical element being chosen from the group consisting of cobalt, scandium, cerium, yttrium, antimony, vanadium, lanthanum, tin, nickel, iron, manganese, calcium, bismuth, hafnium, osmium, rhodium, platinum, palladium, iridium.

6. Electrode (1) according to the preceding claim, in which, in the at least one catalytic layer (11): • the mass proportion of ruthenium is between 22% and 30%, • the mass proportion of titanium is between 40% and 75.5%, • the mass proportion of boron is between 2% and 5%, • the mass proportion of the chemical element of the first dopant is between 1% and 5%, and • the mass proportion of the chemical element of the second dopant is between 0.5% and 2.5%.

7. Electrode (1) according to any one of the preceding claims, further comprising a so-called protective layer (12) at least partly surrounding the at least one catalytic layer (11), the protective layer (12) comprising: • a catalytically inert metal or its oxide, for example titanium, silicon, niobium, tantalum, tin, and / or • a polymer.

8. Electrode (1) according to the preceding claim, in which the polymer is a polypyrrole or its derivatives.

9. Electrode (1) according to any one of the preceding claims,

10.

11.

12.

13.

14. comprising several superimposed catalytic layers (11), and in which at least two successively superimposed catalytic layers (11) are separated by a so-called intermediate protection layer (13) comprising a catalytically inert metal or its oxide, for example titanium, silicon, niobium, tantalum, tin. An electrode (1) according to any preceding claim, wherein at least one of ruthenium, titanium and boron is in metallic or oxide form. A method of manufacturing the electrode (1) according to any one of the preceding claims, comprising: • a supply of an electrically conductive substrate (10), • a supply of a solution of precursors of metallic and metalloid elements comprising: • a ruthenium precursor, the ruthenium being in a mass proportion of between 10% and 40% relative to the total mass of the metallic and metalloid elements in said solution • a titanium precursor, the titanium being at a mass proportion of between 40% and 79% relative to the total mass of the metallic and metalloid elements in said solution, and • a boron precursor, the boron being in a mass proportion of between 1% and 20% relative to the total mass of metallic and metalloid elements in said solution, • a deposition, from the precursor solution, of at least one layer (11a) on the substrate (10), • calcination of the substrate (10) and of the at least one deposited layer (11a) to obtain the catalytic layer (11). Method according to the preceding claim, in which the boron precursor is boric acid. A method according to either of the two preceding claims, wherein the precursor solution is an acidic solution comprising a mixture of water and an organic solvent, preferably an alcohol and for example isopropanol. Use of the electrode (1) according to any one of the claims 1 to 10, for the electrochlorination of water (2).

15. Use of the electrode (1) according to the preceding claim, in which the water (2) comprises, prior to electrochlorination, a proportion of chloride ions less than or equal to 4g.L *.

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