Nickel coated porous structure and method for manufacturing a nickel coated porous structure

Abstract

The invention relates to a method for manufacturing a nickel coated porous structure, the method comprising the following steps: a) obtaining one or more polymer fibers comprising nickel salt; b) reducing at least a part of the nickel salt to form metallic nickel; and c) electroless plating of the one or more polymer fibers obtained in step b), using a plating solution, the one or more polymer fibers to form one or more nickel coated polymer fibers, wherein step c) is performed after step b); and wherein the porous structure is a microporous and / or nanoporous structure.

Description

[0001] aera ref. P6549WOOO

[0002] NICKEL COATED POROUS STRUCTURE AND METHOD FOR MANUFACTURING A NICKEL COATED POROUS STRUCTURE

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a method for manufacturing a nickel coated porous structure, a nickel coated porous structure obtainable by the inventive method and a nickel coated porous structure. Furthermore, the present invention relates to a porous structure, an article made from a nickel porous structure, uses of a nickel coated structure and an electrochemical cell comprising the nickel coated structure.

[0005] BACKGROUND OF THE INVENTION

[0006] The energy transition toward green technologies, marked by the gradual departure from exhaustible sources, holds significant importance. Hydrogen, as an energy carrier, stands out notably in discussions and is considered one of the most promising alternatives, aiming for carbon neutrality. This element exhibits the ability to efficiently store and deliver substantial amounts of energy. Various methods exist for hydrogen production, with water electrolysis being one of them. By utilizing electrical energy, H2O molecules undergo a process of splitting into hydrogen and oxygen. When renewable sources like solar and wind power produce this energy, the resulting hydrogen is termed "green hydrogen". Three electrolysis techniques currently in use are Alkaline Electrolysis (AEL), Polymer Electrolyte Membrane Electrolysis (PEMEL), and Solid Oxide Electrolysis (SOEL). AEL, recognized for its safety and extended service life, takes center stage in this study.

[0007] Approximately 50% of the total cost involved in producing hydrogen through electrolysis is attributed to electricity consumption. It is imperative to explore methods to reduce the remaining 50% by optimizing electrolyzer production, with a primary focus on electrode manufacturing. The cost is notably influenced by the composition of the electrode, and nickel foam (NF) is commonly employed. While NF is chemically stable, its low specific surface area results in thick electrodes, presenting a challenge for mass transport processes.

[0008] Various baths, both acidic and alkaline, were explored with different ratios between nickel ion sources, reducing agents, complexing agents, stabilizers, buffers, pH regulators, and aera ref. P6549WOOO wetting agents. These experiments aimed to determine the most effective combination for achieving optimal results (Fabianne Delaunois, Veronique (2020), Electroless Nickel Plating: Fundamentals to Applications, Vitry, Luiza Bonin).

[0009] Additionally, catalysts are applied to enhance the performance of the electrodes. For the anode side, iron is introduced to improve the oxygen evolution reaction (OER), while molybdenum is added to the cathode side electrode for the hydrogen evolution reaction (HER).

[0010] To improve electrodes, high surface area nickel foams, as opposed to more conventional mesh or perforated plate-based electrode materials, are applied. While nickel foams have more surface area compared with their mesh counterparts, the specific surface areas are still relatively low unless further surface enhancements are carried out in the form of rough coatings. Additionally, the total electrode thickness remains substantial, potentially resulting in mass transport issues, gas entrapment, and additional ionic ohmic losses within the porous structure.

[0011] There is a need for electrode materials which have improved surface area and show good electrochemical performance. Besides, there is a need for electrodes with reduced thickness. It would also be beneficial to lower production costs.

[0012] It is therefore the object of the present invention to provide nickel coated porous structures having a high specific surface area and showing a good electrochemical performance. A further object is to provide nickel coated porous structures which have a low thickness being suitable for electrode applications.

[0013] The problem of the invention has been solved by the subject-matter as defined in the independent claims.

[0014] DESCRIPTION OF THE INVENTION

[0015] In a first aspect the present invention relates to a method for manufacturing a nickel coated porous structure, the method comprising of, or consisting of, the following steps: a) obtaining one or more polymer fibers comprising nickel salt, preferably nickel salt clusters and / or nickel salt particles; aera ref. P6549WOOO b) stabilizing the one or more polymer fibers obtained in step a); c) reducing at least a part of the nickel salt to form metallic nickel, preferably metallic nickel clusters and / or nickel particles; and d) electroless plating of the one or more polymer fibers obtained in step c), using a plating solution, the one or more polymer fibers to form one or more nickel coated polymer fibers, wherein step c) is performed after step b); and wherein the porous structure is a microporous and / or nanoporous structure.

[0016] In a further aspect, the present invention relates to a method for manufacturing a nickel coated porous structure, the method comprising, or consisting of, the following steps: i. obtaining one or more polymer fibers comprising nickel salt, preferably nickel salt clusters and / or nickel salt particles;

[0017] II. reducing at least a part of the nickel salt to form metallic nickel, preferably metallic nickel clusters and / or nickel particles; and ill. electroless plating of the one or more polymer fibers obtained in step (ii), using a plating solution, the one or more polymer fibers to form one or more nickel coated polymer fibers, wherein step (iii) is performed after step (ii); and wherein the porous structure is a microporous and / or nanoporous structure.

[0018] It is to be understood that step (i) corresponds to step (a). Similarly, steps (ii) and (iii) correspond to steps (c) and (d), respectively.

[0019] By the method according to the invention thin nickel coated porous structures can be obtained. These coated structures have a uniform nickel coating. In addition to that, the porous structures have a high porosity leading to a high surface area. The structure can be used as finely porous electrodes based on a polymer skeleton, coated with a homogenous layer of nickel. This method also reduces the environmental impact as the amount of nickel used is significantly lower than used in known nickel containing porous structures. Further, the porous structures result in an order of magnitude larger surface area, at approximately one-tenth of the electrode thickness. Hence, i.e., electrochemical performance by providing a higher surface area is enhanced. aera ref. P6549WOOO

[0020] An additional advantage of the nickel coated porous structures according to the invention is, when used as electrode, the diffusion path length for the evolved gasses is reduced, promoting mass transport properties, and helping to avoid commonly labeled bubble resistances, as well as potentially suppressing supersaturation effects.

[0021] A "porous structure" according to the invention refers to a material that contains pores - small, often interconnected cavities or voids - within its solid matrix. These pores can vary in size, shape, and distribution, and they play a significant role in determining the material's physical properties.

[0022] Microporous according to the invention refers to pores with a diameter predominantly in the micrometer range, typically less than 2 micrometers, such as in the range of about 0.1 micrometer to 2 micrometer.

[0023] Nanoporous refers to pores with a diameter predominantly in the nanometer range, typically ranging from 0.1 nm to 100 nm.

[0024] The porosity of the materials and the diameter of the pores can be determined by measurement methods known in the art. For example, the porosity of the pores can be determined using BET analysis and the diameter of the pores can be measured using microscopy.

[0025] The term “BET surface area” according to the present invention refers to the specific surface area of a material determined in accordance with the Brunauer-Emmett-Teller (BET) theory, which quantifies the total surface area available for physical adsorption of gas molecules. BET surface area is typically measured by nitrogen adsorption at cryogenic temperatures and is expressed in m2 / g. The “BET surface area” parameter is generally used to characterize porous and high surface area materials.

[0026] The term “stabilizing” according to the present invention refers to the process of keeping the polymer fibers and / or a mat thereof at a temperature between 100 and 350°C. Stabilization favors the formation of junction points between the different single polymer fibers of different layers. Stabilization forms a stable structure which is suitable for the electroless plating procedure and prevents delamination. Therefore, stabilization helps aera ref. P6549WOOO confer desirable properties to the polymer fibers and / or a mat thereof, such as stability to degradation at higher temperatures and mechanical strength.

[0027] It is known in the art that polymers have a glass transition temperature, also abbreviated as Tg, which refers to the range over which an amorphous or semi-crystalline polymer transitions form a hard, glassy state to a soft, rubbery state. Below the Tg, polymer chains have restricted mobility, resulting in a rigid and brittle material. Above the Tg, increased molecular motion imparts greater flexibility and elasticity to the polymer. Therefore, the person skilled in the art will know that the stabilization procedure can also be performed at temperatures close to the Tgof the polymer fibers according to the present invention. The stabilization procedure may be performed, for example, at a temperature T wherein T, in degrees Celsius, is within the range of Tg± 100 °C.

[0028] The term “Tg± X degrees Celsius” according to the present invention refers to the temperature range of the glass transition temperature (Tg) ± X °C, wherein X is a number from 0 to 100.

[0029] The term “delamination of polymer fibers” according to the present invention refers to the separation of polymer fiber layers, resulting due to a loss of adhesion or bonding. This separation can result in a weakened structure and reduced mechanical properties.

[0030] A cluster, or also referred to as a cluster of particles, according to the present invention refers to a group of particles that are closely located in space. These particles can be atoms, molecules, colloidal particles, or other small entities, and they exhibit collective behavior due to their proximity and interactions. A cluster according to the invention is to be understood as a small aggregate of atoms or molecules, such as nanoclusters, held together by interatomic forces.

[0031] The term “coated” is to be understood that at least 80 % of the surface of the porous structure are covered. The term “nickel coated” is to be understood that at least 80 % of the surface of the porous structure are covered by nickel.

[0032] The terms “polymer fibers” and “polymer nanofibers” are used interchangeably below herein. aera ref. P6549WOOO

[0033] In one embodiment step a) comprises, or consists of, the following steps: drying, preferably heating, the nickel salt; and adding the dried nickel salt to a polymeric solution; and preparing one or more polymer fibers from the polymeric solution.

[0034] Drying, preferably heating, the nickel salt is done at a temperature between 30 and 150°C, preferably between 50 and 120°C and more preferably between 75 and 110°C. It is preferred that the drying is performed for at least 15 min, preferably at least 30 min, and more preferably at least 45 min. Drying is not performed longer than 5 h.

[0035] The drying step is important when the nickel salt is used as a hydrate such as nickel chloride hexahydrate (NiCh-6 H2O). The drying facilitates the homogenization of the salt in the polymeric solution.

[0036] The solvent and the polymer are mixed so that a polymeric solution is obtained. The polymeric solution is used in step a).

[0037] In an embodiment the polymer fibers obtained in step a) comprise, or consist of, a polymer selected from the group consisting of polyolefines such as polypropylene, polyethylene or polybutene, polyacrylates such as poly(methyl methacrylate), polyesters such as polyethylene therephtahalate, polyvinylidene fluoride, polyamide, polylactic acid, polyglycolic acid, poly(lactic-co-glycolic) acid, polycyprolactone, polyurethane, polyvinylalcohol, polyhydroxyalkanoates, poly(butylene succinate), polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof, preferably are selected from the group consisting of polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof.

[0038] The aforementioned list comprises homopolymers and copolymers. The list also covers copolymers having the respective homopolymers as component, preferably as main component.

[0039] In a preferred embodiment, the polymer fibers obtained in step (a) comprise polysulfone and / or a copolymer of polysulfone. In one or more embodiments, the polymer fibers in step (a) comprise polysulfone. In one or more embodiments, the polymer fibers in step (a) comprise a copolymer of polysulfone. aera ref. P6549WOOO

[0040] According to another embodiment, the nickel salt in step a) is selected from the group consisting of nickel (II) chloride, nickel (II) sulfate, nickel (II) carbonate, nickel (II) nitrate, nickel (II) bromide, nickel (II) iodide, nickel (II) phosphate, or mixtures thereof.

[0041] In step a) various known methods can be applied to obtain one or more polymer fibers.

[0042] The polymer fibers obtained in step a) may be woven, non-woven and / or a collection of polymer fibers. The fibers may form a so-called mat, also called just a mat.

[0043] In one embodiment the average diameter of the one or more polymer fibers obtained in step a) is in the range from 20nm to 10pm, preferably 50nm to 5pm, and more preferably 75nm to 1 pm.

[0044] Methods which can be applied in step a) are electrospinning, melt spinning, melt-blowing, solution spinning, phase separation, self-assembly, drawing, co-electrospinning, force spinning, rotary jet spinning (RJS), or magneto spinning.

[0045] It is preferred that the polymer fibers are prepared by electrospinning. The electrospinning process, governed by electrostatic force, enables the production of polymer fibers with a smaller and more uniform fiber diameter compared to other known methods as listed above. The resulting smaller fiber diameter increases the surface area available for subsequent coating processes, thereby enhancing the electrochemical active surface area necessary for catalyzing reactions. The uniform diameter distribution of electrospun fibers contributes to a more defined pore size within the electrode layers, which can be precisely tailored to optimize mass transport.

[0046] In case the one or more polymer fibers are prepared via electrospinning a polymer mat is obtained.

[0047] The electrospinning method has the advantage that three-dimensional polymer mats, suitable for electrode applications, can be prepared. The method can also be used to prepare three-dimensional polymer mats using different polymers. These polymer mats are flexible substrates with enhanced surface area which is a critical property for electrochemical reactions. aera ref. P6549WOOO

[0048] A suitable electrospinning solution comprises 1 to 50 wt.% of a solvent, 1 to 40 wt.% of a polymer, preferably 6 to 30 wt.% of a polymer, and 0.05 to 5.0 wt.% of a nickel salt, preferably 0.1 to 3.0 wt.% of a nickel salt.

[0049] The solvent may be selected from organic solvents such as Dimethylformamide (DMF) or Dimethylacetamide (DMAC). Preferably the solvent is DMAC.

[0050] According to an embodiment, the polymeric solution applied in step a) comprises, or consists of, 1 to 20 wt.% polyacrylonitrile, preferably 6 to 14 wt.% polyacrylontrile, and / or 5 to 35 wt.% polysulfone, preferably 10 to 30 wt.% polysulfone, preferably Udel® polysulfone. In a further embodiment the polymeric solution in step a) comprises 0.05 to 5 wt.% and preferably 0.1 to 2 wt.% nickel chloride hexahydrate (NiCl2’6H2O).

[0051] According to a preferred embodiment, the polymeric solution in step a) comprises, or consists of, polyacrylonitrile / dimethylacetamide (PAN / DMAC) 4 to 15 wt.% and preferably 0.5 to 2 wt.% nickel chloride hexahydrate (NiCl2’6H2O).

[0052] According to another preferred embodiment, the polymeric solution in step a) comprises, or consists of, polysulfone (PSU) 20 wt.%, preferably Udel® PSU, and 1 wt.% nickel chloride hexahydrate (NiCl2’6H2O).

[0053] According to another preferred embodiment, the polymeric solution in step a) comprises, or consists of, of 5 wt.% polyacrylonitrile (PAN) with 1 wt.% polysulfone, preferably Udel® PSU, and 0.5 wt.% nickel chloride hexahydrate (NiCl2’6H2O).

[0054] In one embodiment the polymer fibers obtained in step a) are subjected to a carbonization step. Preferably the carbonization is performed at a temperature between 500 and 1000°C. It is further preferred that the carbonization is performed in an inert atmosphere, preferably in a nitrogen and / or argon atmosphere.

[0055] In one or more embodiments, step b) comprises keeping the one or more polymer fibers obtained in step a) at a temperature between 100 and 350°C, preferably at a temperature between 150 and 300°C. aera ref. P6549WOOO

[0056] In one or more embodiments, step b) comprises keeping the one or more polymer fibers obtained in step a) at a temperature T within the range of transition temperature (Tg) of said polymer fibers ± 100°C, preferably at a temperature T within the range of transition temperature (Tg) of said polymer fibers ± 50°C, more preferably, at a temperature T within the range of transition temperature (Tg) of said polymer fibers ± 30°C.

[0057] In one or more embodiments, step b) is performed for 0.5 to 2 hours, more preferably for 1 to 2 hours.

[0058] In one or more embodiments, the stabilization step is performed after the polymer fiber preparation in step a) and / or before the carbonization step. In one or more embodiments, the stabilization procedure is performed before the carbonization step. In one or more embodiments, the stabilization procedure is performed in an air atmosphere.

[0059] Performing a stabilization procedure of the one or more polymer fibers comprising nickel salt obtained in step a) results in a more relaxed structure of the polymer fibers. This process creates interlayer connection points between the polymer fibers, resulting in a strong and a stable structure.

[0060] During water-based electroless plating of hydrophobic polymer fibers, such as polysulfone, the electroless plating solution tends to infiltrate the fiber structure. Gas evolution causing a side effect referred to as “ballooning” also known as the “bubbling phenomenon” can be observed which leads to the delamination of the fiber layers and unusable samples. Therefore, the stabilization procedure also helps to achieve good electroless coating and prevents delamination of the fibers.

[0061] The stabilization procedure comprises keeping the one or more polymer fibers obtained in step a) at a temperature between 100 and 350°C for 0.5 to 2 hours. This can be performed by keeping the one or more polymer fibers or a mat thereof between two glass discs in a furnace, optionally in an air atmosphere, set at a temperature between 100 and 350°C, for 0.5 to 2 hours. Alternatively, the stabilization procedure may be performed by keeping the one or more polymer fibers or a mat thereof between two glass discs in a furnace, optionally in an air atmosphere set at a temperature T within the range of transition temperature (Tg) of the said polymer fibers ± 100 degrees Celsius for 0.5 to 2 hours. aera ref. P6549WOOO

[0062] In a further embodiment step c) comprises, or consists of, applying a reducing agent to the one or more polymer fibers, preferably spraying a reducing agent onto the one or more polymer fibers.

[0063] According to another embodiment, the reducing agent in step c) is a solution comprising, or consisting of, an organic or inorganic reducing agent, preferably an inorganic reducing agent.

[0064] It is preferred that the reducing agent is selected from the group consisting of sodium borohydride, potassium borohydride, lithium borohydride, sodium bis(2-methoxyethoxy) aluminum hydride, hydrogen or combinations thereof, preferably the reducing agent is sodium borohydride.

[0065] In one embodiment, the method comprises the following steps: a) obtaining one or more polysulfone fibers comprising nickel salt, preferably nickel salt clusters and / or nickel salt particles; b) stabilizing one or more of the polysulfone fibers obtained in step a); c) reducing at least a part of the nickel salt to form metallic nickel, preferably metallic nickel clusters and / or nickel particles; and d) electroless plating of the one or more polymer fibers obtained in step c), using a plating solution, the one or more polysulfone fibers to form one or more nickel coated polysulfone fibers, wherein step c) is performed after step b); and wherein the porous structure is a microporous and / or nanoporous structure.

[0066] In one or more embodiments, step b) comprises keeping the polysulfone fibers in step a) at a temperature between 100 and 350°C, preferably, between 150 and 300°C, more preferably between 170 and 250°C.

[0067] In one or more embodiments, step b) comprises keeping the polysulfone fibers in step a) at a temperature T within the range of transition temperature (Tg) of said polysulfone fibers ± 100°C.

[0068] In one or more embodiments, step b) is performed for 0.5 to 2 hours, more preferably for 1 to 2 hours. aera ref. P6549WOOO

[0069] In one embodiment the one or more polymer fibers, preferably the polymer mat, obtained in step a) is subjected to a cleaning step before step b). In such an optional cleaning step the one or more polymer fibers, preferably the polymer mat, is immersed in a solvent, preferably in an organic solvent and more preferably in ethanol.

[0070] In one embodiment the one or more polymer fibers, preferably the polymer mat, is immersed in a solvent in an ultrasonic bath, preferably for 1 to 60 minutes. By that cleaning step oil, grease and dirt are removed from the surface of the one or more polymer fibers.

[0071] According to another embodiment, step d) takes less than 60 min, preferably 0.5 to 60 min, more preferably less than 20 min and even more preferably 0.5 to 20 min.

[0072] In a further embodiment step d) is performed with the plating solution having a temperature between 10 to 100°C, preferably between 30 to 95°C and more preferably between 50 to 90°C.

[0073] In an embodiment the plating solution in step d) comprises, or consists of, at least one nickel compound, preferably a nickel cation source, more preferably a nickel salt, and a further reducing agent different from the reducing agent in step c), preferably a hypophosphite, a chelating agent, preferably an organic chelating agent, and / or a stabilizer. The nickel compound provides nickel ions in the solution, the further reducing agent provides the catalytic active hydrogen atoms to reduce the nickel compound into metal, the chelating agent complexes the nickel ions and prevents a rapid decrease in pH, and the stabilizer prevents the decomposition of the solution (Fabianne Delaunois, Veronique Vitry, Luiza Bonin (2020), Electroless Nickel Plating: Fundamentals to Applications).

[0074] Further additives to enhance the rate of nickel deposition by activating hypophosphite anions, pH buffers such as sulfuric acid for acids (H+ions) and sodium carbonate for alkalines (OH‘ ions) to regulate the solution pH during the process and, a wetting agent, such as sulfated alcohols to decrease the surface tension and therefore increase the wettability, can be present in the plating solution as well. Further stabilizers can be present as well.

[0075] Preferably the further reducing agent is a phosphorus containing reducing agent, more preferably it is sodium hypophosphite. Phosphorus containing reducing agents supply the aera ref. P6549WOOO phosphorus in a NiP alloy. Preferably the chelating agent is selected from the group consisting of hydroxy acetic acid, hydroxy propionic acid, citric acid, malic acid or combinations thereof. Preferably the stabilizer is thiourea. Preferably the additive to enhance the rate of nickel deposition by activating the hypophosphite anions is succinic anions.

[0076] It is preferred that the nickel salt in step c) is selected from the group consisting of nickel (II) chloride, nickel (II) sulfate, nickel (II) carbonate, nickel (II) nitrate, nickel (II) bromide, nickel (II) iodide, nickel (II) phosphate, or mixtures thereof. It is preferred that the further reducing agent in step d) is a hypophosphite, preferably sodium hypophosphite.

[0077] Further compounds to be used can be selected from the group consisting of sodium citrate, sodium acetate, lactic acid, propionic acid, ammonium chloride, thiourea or combinations thereof.

[0078] In a further embodiment step d) is performed at a temperature between 50 to 120°C, preferably between 75 to 100°C, and more preferably between 80 to 95°C.

[0079] In another embodiment step d) is performed at a pH in the range from 2 - 12, preferably in the range from 3 - 11 , and more preferably in the range from 4 - 10.

[0080] It is preferred that the electroless plating in step d) is electroless nickel plating (ENP). Conductivity is imparted to the nickel coated polymer fibers through the electroless plating technique, preferably the electroless nickel plating technique (ENP). This method ensures a uniform nickel coating over the polymer matrix, promoting excellent corrosion resistance. To facilitate the deposition of a Ni, preferably NiP, nickel salt is added into the solution before electrospinning the polymer fibers. This approach aims to help the coating process, utilizing Ni particles as nucleation sites for Ni growth during ENP.

[0081] According to an embodiment at least 85%, preferably at least 90%, more preferably at least 95% or at least 99%, and most preferred 100% of the surface of the porous structure are covered by the coating after step d).

[0082] The polymer fibers can be subjected to further processing steps such as hot pressing or solvent vapor treatment. These steps can be performed after stabilizing in step b) and aera ref. P6549WOOO before reducing step with NaBFU in step c). Hot pressing involves the application of pressure and heat on two metal blocks keeping the polymer fibers or polymer mats between these. Hot pressing can be performed in either an inert or a typical atmosphere. The hot pressing aims to improve the polymer fibers mechanical properties. This occurs when the polymer fibers or the polymer mat is pressed at a temperature that is marginally above the glass transition temperature (Tg), which causes the softening of the polymer fibers and therefore at the junction points of the different polymer fibers will form a cross-link between them. Another process for cross-linking is solvent vapor treatment. Solvent vapor treatment affects the polymer fiber morphology by producing solvent-induced fusion at fiber junction points, which forms physical cross-links in polymer fibers or polymer mats, thereby increasing the mechanical properties of the mat.

[0083] In a second aspect, the present invention relates to a nickel coated porous structure comprising, or consisting of, one or more polymer fibers, preferably one or more electrospun polymer fibers, coated with a layer of metallic nickel, wherein the layer of metallic nickel has a thickness in the range from 50 nm to 10,000 nm, preferably in the range from 100 nm to 5,000 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

[0084] In a further aspect, the present invention relates to a nickel coated porous structure comprising, or consisting of, one or more polymer fibers, preferably one or more electrospun polymer fibers, wherein the polymer fibers are stable to degradation at temperatures between 350 and 700°C, and wherein the polymer fibers are coated with a layer of metallic nickel, wherein the layer of metallic nickel has a thickness in the range from 50 nm to 10,000 nm, preferably in the range from 100 nm to 5,000 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

[0085] In one or more embodiments, the one or more polymer fibers of the nickel coated porous structure comprise polysufone and / or a copolymer of polysulfone.

[0086] In one embodiment, the nickel coated porous structure comprising, or consisting of, one or more polymer fibers, preferably one or more electrospun polymer fibers, wherein the polymer fibers are stable to degradation at temperatures between 350 and 500°C, and wherein the polymer fibers are coated with a layer of metallic nickel, wherein the layer of metallic nickel has a thickness in the range from 50 nm to 10,000 nm, preferably in the aera ref. P6549WOOO range from 100 nm to 5,000 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

[0087] In one or more embodiments, the one or more polymer fibers of the nickel coated porous structure comprise polysufone and / or a copolymer of polysulfone.

[0088] It should be understood that any feature and / or aspect discussed above in connections with the method for manufacturing a nickel coated porous structure according to the invention apply by analogy to the nickel porous structure described herein.

[0089] It is preferred that the porous structure is made of a multitude of polymer fibers. The polymer fibres may be woven, non-woven and / or a collection of polymer fibres. In a preferred embodiment the polymer fibres are non-woven. The non-woven polymer fibres may form a polymer mat.

[0090] In one embodiment the average diameter of the one or more polymer fibers, preferably electrospun polymer fibers, is in the range from 20nm to 10pm, preferably 50nm to 5pm, and more preferably 75nm to 1 pm.

[0091] According to one embodiment at least 85%, preferably at least 90%, more preferably at least 95% or at least 99%, and most preferred 100% of the surface of the porous structure are covered by the coating.

[0092] In another embodiment the nickel coating of the nickel coated porous structure comprises, or consists of, 85 to 100 wt.% of nickel, and 0 to 15 wt.% residuals based on the overall amount of the coating. Residuals may stem from the plating solution. Residuals are for example phosphorous, boron, sodium etc. Preferably the residuals comprise, or consist of, phosporus. Phosphorus has a positive influence on the mechanical strength of the coating.

[0093] It is preferred that the nickel coating of the nickel coated porous structure comprises, or consists of, 85 to 100 wt.% of nickel, 2 to 14 wt.% of phosphorus, preferably 4 to 12 wt.% phosphorous, and 0 to 15 wt.% further residuals based on the overall amount of the coating.

[0094] According to another embodiment the outer surface of the layer of metallic nickel coating has a roughness parameter in the range from 5 to 500, preferably in the range from 50 to aera ref. P6549WOOO

[0095] 500, determined by double-layer capacitance by performing cyclic voltammetry. The roughness parameter provides an indication of the surface area available for the electrochemical reaction. A roughness parameter greater than 50 is preferred as a higher roughness parameter provides for a higher electrochemical performance of the nickel coated porous structure when used as an electrode.

[0096] In an embodiment the nickel coated porous structure has a BET surface area in the range from 5 to 50 m2 / g. In a further embodiment the nickel coated porous structure has a surface area per mass ratio in the range from 5 to 100 m2 / g, preferably in the range from 10 to 75 m2 / g, and more preferably in the range from 15 to 50 m2 / g. A BET surface area in the range from 5 to 50 m2 / g and / or a surface area per mass ratio in the range from 5 to 100 m2 / g of the nickel coated porous structure is advantageous for application as an electrode. Such a high surface area provides for higher electrochemical performance of the nickel coated porous structure when used as an electrode. Furthermore, the electrodes can be thinner while maintaining a higher surface area which helps avoid commonly labelled bubble resistance and leads to less mass transport losses since the path length for the evolved gasses is reduced

[0097] In another embodiment the nickel coated porous structure has a surface area to volume ratio in the range from 1 to 20 m2 / cm3, preferably in the range from 2 to 15 m2 / cm3, and more preferably in the range from 3 to 10 m2 / cm3.

[0098] In an embodiment the one or more polymer fibers comprise, or consist of, a polymer selected from the group consisting of polyolefines such as polypropylene, polyethylene or polybutene, polyacrylates such as poly(methyl methacrylate), polyesters such as polyethylene therephtahalate, polyvinylidene fluoride, polyamide, polylactic acid, polyglycolic acid, poly(lactic-co-glycolic) acid, polycyprolactone, polyurethane, polyvinylalcohol, polyhydroxyalkanoates, poly(butylene succinate), polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof, preferably are selected from the group consisting of polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof.

[0099] The aforementioned list comprises homopolymers and copolymers. The list also covers copolymers having the respective homopolymers as component, preferably as main component. aera ref. P6549WOOO

[0100] In a further embodiment the one or more polymer fibers comprise, or consist of, a polymer selected from the group of polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof.

[0101] In a third aspect the present invention relates to a nickel coated porous structure obtained by the method according to the invention.

[0102] It should be understood that any feature and / or aspect discussed above in connections with the method for manufacturing a nickel coated porous structure according to the invention and the nickel porous structure according to the invention apply by analogy to the nickel porous structure obtainable by the inventive method as described herein.

[0103] In a fourth aspect the present invention relates to a porous structure comprising, or consisting of, one or more polymer fibers, preferably one or more electrospun polymer fibers, wherein the one or more polymer fibers comprise metallic nickel, preferably metallic nickel clusters with a diameter in the range from 10 nm to 1000 nm, preferably in the range from 10 nm to 100 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

[0104] It should be understood that any feature and / or aspect discussed above in connections with the method for manufacturing a nickel coated porous structure according to the invention and the nickel porous structure according to the invention apply by analogy to the porous structure as described herein.

[0105] In a fifth aspect the present invention relates to an article made from a nickel coated porous structure according to the invention or a porous structure according to the invention, wherein the article is preferably an electrode, a membrane, a filter, or a mask.

[0106] It should be understood that any feature and / or aspect discussed above in connections with the method for manufacturing a nickel coated porous structure according to the invention, the nickel porous structure according to the invention as well as the porous structure according to the invention apply by analogy to the article as described herein. aera ref. P6549WOOO

[0107] In a sixth aspect the present invention relates to the use of a nickel coated porous structure according to the invention or a porous structure according to the invention as an electrode, a membrane, or a filter, preferably electrode.

[0108] It should be understood that any feature and / or aspect discussed above in connections with the method for manufacturing a nickel coated porous structure according to the invention, the nickel porous structure according to the invention as well as the porous structure and the article according to the invention apply by analogy to the uses as described herein.

[0109] In a seventh aspect the present invention relates to the use of a nickel coated porous structure according to the invention or a porous structure according to the invention in electrolysis, in air treatment, in water treatment, in a supercapacitor, in a fuel cell, in hydrogen production or in a flow battery.

[0110] It should be understood that any feature and / or aspect discussed above in connections with the method for manufacturing a nickel coated porous structure according to the invention, the nickel porous structure according to the invention as well as the porous structure and the article according to the invention apply by analogy to the uses as described herein.

[0111] In an eighth aspect the present invention relates to an electrochemical cell comprising the nickel coated structure according to the invention.

[0112] It should be understood that any feature and / or aspect discussed above in connection with the method for manufacturing a nickel coated porous structure according to the invention, the nickel porous structure according to the invention as well as the porous structure and the article according to the invention apply by analogy to the electrochemical cell as described herein.

[0113] In a preferred embodiment the electrochemical cell is an electrolyzer or a fuel cell.

[0114] It is preferred the at least one electrode of the electrochemical cell comprises the nickel coated structure according to the invention. aera ref. P6549WOOO

[0115] The following figures and examples are provided below to illustrate the present invention.

[0116] They are intended to be illustrative and are not to be construed as limiting in any way.

[0117] BRIEF DESCRIPTION OF FIGURES

[0118] Figs. 1 a) - f) SEM images of PAN nanofibers mats with NiCh before NaBF reduction: (a) 50,000 magnification, (b) 30,000 magnification, (c) macro visual mats appearance - and after NaBFU reduction: (d) 50,000 magnification, (e) 30,000 magnification, (f) macro visual mats appearance (Magnifications stated are those defined by the microscope, and will not adjust to the eventual rescaling of the figures).

[0119] Figs. 2 a) - b) SEM images of sample 1 PAN nanofibers NiP electroless plated: (a) 5,000 magnification, (b) Nickel EDS mapping images of SEM image, cf. Fig. 2a).

[0120] Figs. 3 a) - d) (a) SEM images of a cut PAN nanofiber NiP electroless plated - 1 pm scale bar, (b) nickel EDS mapping image of Figure 3(a), and (c) phosphorus EDS mapping image of Figure 3(a), and (d) oxygen EDS mapping image of Figure 3(a).

[0121] Figs. 4 a) - b) (a) SEM images (sample 1 ) of a full PAN nanofibers cross-section NiP electroless plated and (b) nickel EDS mapping image of Fig. 4(a).

[0122] Fig. 5 a) - c) (a) Picture of Polyacrylonitrile nanofibers after Nickel-Phosphorus electroless plating, and (b),(c) SEM image at different magnifications (1 pm, 1 pm, and 1 cm scale bar) to show the uniformity of the coating.

[0123] Figs. 6 a) - d) XPS spectra recorded on NiP PAN nanofibers after Ar etching, displaying a) C 1s, b) O 1s, c) Ni 2p, and d) P 2p regions.

[0124] Fig. 7 Cyclic voltammetry (CV) of sample 1 performed at different scan rates (0.1 , 0.2, 0.3, and 0.5 V / s).

[0125] Fig. 8 Polarization curves of: Sample 1 (anode) VS Sample 1 (cathode) both Ni perforate plate supported - 80°C - 30% KOH (circles) and commercial Ni foam (anode) VS commercial Ni foam (cathode) - 80°C - 30% KOH (squares).

[0126] Fig. 9 ai) - bi) macro visual mats appearance of: a) PSU nanofiber mat pristine, and b) PSU nanofiber mat stabilized in air at 190°C for 1 h. a?) - b?) SEM images at the same magnification of: a) PSU nanofiber mat pristine, and aera ref. P6549WOOO b) PSU nanofiber mat stabilized in air at 190°C for 1 h. b3) Cross-section of PSU nanofiber mat stabilized in air at 190°C for 1 h.

[0127] Fig. 10 Tensile strength analysis of: Pristine nanofibers mat PSU / DMAC 20 % wt.

[0128] I 1 wt.% NiCh'6 H2O, and nanofiber mat PSU / DMAC 20 % wt. I 1 wt.% NiCh'6 H2O stabilized in air at 190°C for 1 h (sample 2).

[0129] Fig. 11 Thermogravimetric Analysis (TGA) of: Pristine nanofibers mat

[0130] PSU / DMAC 20 % wt. 1 1 wt.% N iCI2- 6 H2O, and nanofiber mat PSU / DMAC 20 % wt. I 1 wt.% NiCh-6 H2O stabilized in air at 190°C for 1 h (sample 2).

[0131] Fig. 12 a) - b) SEM images of the NiP layer grow on PSU nanofibers at different magnifications, c) - d) EDS mapping image of Figure 12 a) of: c) Nickel and Phosphorus, and d) Sulfur.

[0132] Fig. 13 Rendered illustration of the growing process of the NiP coating on a single polymer nanofiber, madewith the software Render.

[0133] Figs. 14 a) - e) SEM images of PSU nanofibers mats after NiP electroless plating at 83°C for 10 minutes (sample 4): (a) 5,000 magnification, (b) 3,000 magnification, (c) 2,000 magnification, (d) 1 ,000 magnification and (e) macro visual mats appearance of sample 4 (4.5 x 4.5 cm).

[0134] Fig. 15 Mechanical stretching of the NiP-coated PSU nanofiber in the configuration of a flat initial starting point, bent, and a flat final point.

[0135] Fig. 16 Plot of NiP loading (mg / cm2) versus time of deposition.

[0136] Figs. 17 a-i ) — ei) Macro visual mats appearance of: a) sample 2 (PSU fiber mats stabilized in air at 190°C for 1 h), b) sample 3 (5 min NiP coating), c) sample 4 (10 min NiP coating - same fig.9), d) sample 5 (20 min NiP coating), and e) sample 6 (30 min NiP coating),

[0137] 82) - 62) SEM images with all 20,000 magnification of: sample 2 (PSU fiber mats stabilized in air at 190°C for 1 h), sample 3 (5 min NiP coating), sample 4 (10 min NiP coating - same fig.9), sample 5 (20 min NiP coating), and sample 6 (30 min NiP coating), as) - e3) Nanofibers diameter elaborated with the Imaged program for a number of 100 nanofibers of: sample 2 (PSU fiber mats stabilized in air at 190°C for 1 h), sample 3 (5 min NiP coating), sample 4 (10 min NiP coating - same fig.9), sample 5 (20 min NiP coating), and sample 6 (30 min NiP coating).

[0138] Fig. 18 HER (Hydrogen Evolution Reaction) polarization curves for different uncatalyzed substrates: nickel perforated plate (CS1 ) (Fig. 18a), nickel aera ref. P6549WOOO foam ALANTUM (CS2) (Fig. 18b), and PSU nanofibers NiP ENP coated - sample 4 (Fig. 18c)

[0139] Fig. 19 Substrates used as electrodes: nickel perforated plate (CS1 ) macro visual appearance (Fig. 19a), nickel foam ALANTUM (CS2) macro visual appearance (Fig. 19b) I nickel foam ALANTUM higher magnification (Fig. 19bi), and PSU nanofibers NiP ENP coated - sample 4 macro visual appearance (Fig. 19c) I PSU nanofibers NiP ENP coated - sample 4 higher magnification (19ci).

[0140] EXAMPLES

[0141] Materials

[0142] Nickel (II) chloride hexahydrate (NiCh ■ 6H2O, > 98%), sodium hypophosphite (NaPCkhh, 99%), trisodium citrate dihydrate (CeHgNasOg, > 99 %) and polyacrylonitrile (PAN) were supplied by Merck.

[0143] Ammonium chloride (NH4CI, > 99%) was purchased by Thermo Scientific Chemicals. Udel® polysulfone (PSU) was purchased by Solvay Advanced Polymer.

[0144] Dimethylacetamide (DMAc, 99%) was obtained from Sigma-Aldrich.

[0145] Nickel (II) chloride hexahydrate used in the electrospinning solution was dried for 1 hour between 80 °C and 100 °C, meanwhile, the other chemicals were used as received.

[0146] Nickel perforated plate (CS1 ) and nickel foam (CS2) for the comparative tests were purchased by VECO Precision and Alantum.

[0147] Measurement Methods

[0148] SEM and EDS

[0149] The surface morphology of the samples was characterized by Scanning Electron Microscopy (SEM) and Electron Dispersive X-ray Spectroscopy (EDS) using a Zeiss Merlin device, with an accelerating voltage of 15 kV. Moreover, using a Leica EM ACE600 Sputter Coater, gold was deposited at a thickness of 4.4 nm on the pristine nanofibers to have a conductive surface, so that their structure could be examined.

[0150] Morphological characterization

[0151] The nanofiber's thickness was qualitatively measured using SEM images (range 10 to 50 pm). The thickness of the samples was measured using a micrometer gauge (± 0.01 mm). The Brunauer-Emmett-Teller (BET) method was used for the determination of specific surface areas of NiP polymer mats (electrodes). A 3Flex by Micromeritics instrument was aera ref. P6549WOOO used. The BET equation describes a linear plot vs. correlating the weight of adsorbed nitrogen (N2) and relative pressure, from a pressure range = 0.05 - 0.3 (Katie A. Cychosz, Matthias Thomme (2018), Progress in the Physisorption Characterization of Nanoporous Gas Storage Materials) . Degassing was carried out at 80 °C for more than 12 hours to not have any structural changes due to the high temperature.

[0152] Electrochemical characterization

[0153] The electrochemical tests were conducted in a standard three-electrode cell in half cell configuration, in a non-zero-gap configuration using a VersaSTAT4 (Princeton Applied Research). Pristine 300 pm thick nickel foam and a reversible hydrogen electrode (RHE, Mini-Hydro Flex, Gaskatel) were used as counter and reference electrodes, respectively. Linear Scan Voltammetry (LSV) at a scan rate of 5 mV / s with a starting potential of 0.1 V and a final of -0.6 V was performed to analyze the HER performances of the studied electrodes.

[0154] The roughness factor was estimated by non-faradaic cyclic voltammetry (CV) scan rates of 0.1 , 0.2, 0.3, and 0.5 V / s to calculate the double-layer capacitance (CDL). The CDL was estimated to assume a nominal value of 40 pF / cm2(C. L. McCrory et aL, Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. Journal of the American Chemical Society, vol. 137, no. 13, pp. 4347-57, (2015).

[0155] It was advantageous to test the samples in a flow cell test after these had been tested in a half-cell test. This is essentially a smaller, lab-scale replica of an actual industrial electrolyzer, operating under the same conditions. The electrodes' cell performance was evaluated for this purpose using a proprietary new alkaline flow electrolysis testing zerogap apparatus developed by DTU Energy (cf. Kraglund, M. R. (2017), PhD Thesis, Alkaline membrane water electrolysis with non-noble catalysts. Department of Energy Conversion and Storage, Technical University of Denmark (DTU)).

[0156] Example 1 : Preparation and results of Sample 1 (PAN)

[0157] Electrospinning

[0158] The solution used to make the polymer mat was PAN / DMAC 8 wt.% + 0.5 wt.% nickel chloride hexahydrate (NiCl2’6 H2O). aera ref. P6549WOOO

[0159] Initially, the solvent and the polymer were mixed. Once a solution was formed, nickel salt was added. The nickel salt was dehydrated before addition to the solution by placing it in the oven between 80°C and 100°C for 1 hour. This dehydration step resulted in a color change in the nickel salt from green to deep yellow, facilitating the homogenization of the salt within the solution.

[0160] In a high-voltage electrostatic field (20 kV), a polymer solution was sprayed into fibers. These fibers were then drawn and refined by the electric field force, along with solvent volatilization, and solidified into fibers with a diameter of 50nm to 2pm. These pristine fibers (polymer mats) were deposited and collected on a drum collector device.

[0161] Pre-treatment Processes: Surface Activation

[0162] The above prepared polymer mat was airbrushed with 2 ml of 0.3 M sodium borohydride (NaBFk) in a 30% v / v ethanol / water solution. A fixed pressure of the airbrush of 3 bars was applied to prevent the sample from breaking. The activated polymer mat was then washed with distilled water. This procedure was repeated four times, with the waiting time between each step determined by the time needed for the solution to evaporate. After the last spraying step, the fibers were immediately inserted into the ENP solution while still wet.

[0163] Electroless Nickel Phosphorus (ENP) Plating

[0164] A beaker containing the plating solution was immersed in a water bath on a hotplate. A magnetic bar was used to stir the plating solution. The plating solution was heated to the required temperature, and the sample was inserted for 10 min. Table 1 shows the composition of the solution along with further plating parameters.

[0165] Table 1. The following solution was used for electroless nickel plating. aera ref. P6549WOOO

[0166] Physical characterization

[0167] The microstructure of the polymer mat (sample 1 ) prepared according to the process described above, before and after activation, can be seen in the SEM images in Figures 1 a-d. It is shown that the activation does not influence fiber morphology, which here is exemplified with fiber diameters in the range of 50 to 200 nm. Figures 1 e-f show images of the visual appearance of the mats before and after activation, indicating important visual changes on the surface of the fibers.

[0168] The pre-treatment step with a reducing agent is essential for the following nickel-plating process, as it activates the fibers, likely by improving hydrophilicity and by forming small nickel particles that can act as seeds or nucleation sites for the chemical precipitation process. Although the nickel seeds are not visible with the available magnification, the pretreatment step is essential for a homogeneous and successful coating in the following step. Figure 2 shows nickel-plated polymer mats. The fiber is predominantly homogenously coated with nickel, with some spots showing spots of increased thickness, or with the appearance of particle inclusion and growth in the coating. EDS analysis reveals a homogeneous distribution of Ni across the entire sampled area. In Fig. 2b) nickel EDS mapping images of SEM Fig. 2a) are shown. The coloring in Fig. 2b) clearly shows the even distribution of the nickel.

[0169] Figures 3a) and 3b) show a cut nanofiber, as well as cross-section SEM images. The nanofibers in the shown inventive sample 1 have an average diameter of 2 pm, with the polymer core being approximately 500 nm, and the nickel coating about 750 nm. The coating layer present is not completely smooth, but protrusions with a diameter ranging from 200 to 500 nm can be seen. Coating thickness can be controlled between 50 and 1000 nm by varying process time and temperature. In Fig. 3b), nickel EDS mapping images of SEM Fig. 3a) are shown. The coloring in Fig. 3b) also shows the even distribution of the nickel.

[0170] The amount of NiP deposited was around 2 to 2.5 mg / cm2. EDS spectrum shows that the NiP had a composition with a 68:17:15 atomic ratio of Ni:P:O. BET was used for the determination of specific surface areas of NiP-coated electrodes. A surface area per mass ratio equal to 6.0 m2 / g and a surface area to volume ratio equal to 4.6 m21 1 cm3were calculated. aera ref. P6549WOOO

[0171] A full cross-section and the relative nickel EDS analysis are shown in Figure 4a) and Figure 4b). The sample thickness can be tuned by modifying the amount of solution electrospun. Some cavities in the structure can be seen, demonstrating that the different layers are not perfectly attached to each other. This process can be promoted by the previous coating process, where the hydrogen evolution during the nickel reduction is too aggressive. In Fig. 4b), nickel EDS mapping images of SEM Fig. 4a) are shown. The coloring in Fig. 4b) also demonstrates the even distribution of the nickel.

[0172] The thickness of sample 1 of 80.7 pm is significantly less than that of electrodes typically used in lab settings, such as Ni foam or Ni mesh, which typically have a thickness of more than 250 pm. Moreover, the process can be easily tuned to have even thinner electrodes. The advantage of using thin electrodes instead of thick ones allows for better activity with a low overpotential, by facilitating a reduced reactant transfer resistance and decreased ohmic drop within the electrode. It is simple to adjust the final thickness, tuning the amount of solution electrospun, to achieve the desired result.

[0173] Optimizing the porous structure of electrodes is crucial for effective gas removal during the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER). A thinner electrode design is considered beneficial for gas removal and overall HER and OER performance.

[0174] Figure 5 (a) shows the macroscale image of polyacrylonitrile nanofibers after Nickel- Phosphorus electroplating with Figures 5 (b) and (c) showing the SEM image at different magnifications to illustrate the uniformity of the coating.

[0175] XPS analysis of the NiP nanofibers is presented in Figure 6, confirming the formation of nickel phosphide at the surface of the coatings. The lower binding energy (BE) feature in the P 2p spectrum (6d) at -129.5 eV is characteristic of phosphides such as Ni^Ps, Ni2P, and Ni5P4. The higher BE feature indicates oxidized forms, for example, (P-O-P) and (O- P=O) bonds, PO43", Ni3(PO4)2, HPOsH' and P2O5, where the BE can occur in the range 131 .5 - 134.5 eV. The binding energy increases with increasing oxygen content, and in this case, the BE around 133.5 eV indicates formation of Nis(PO4)2. Oxidized forms of Ni and P are expected at the surface, since they are susceptible to oxidation by atmospheric oxygen. Indeed, turning to the Ni 2p spectrum (6c), high spectral intensity around -856 eV is aera ref. P6549WOOO commonly attributed to Ni2+species in mixed NxPycompounds exhibiting oxidized surfaces such as Ni(OH)2, and Ni3(PO4)2.XPS studies on phosphides such as Ni^Ps, Ni2P, and Ni5P4 locate these species at around -853 eV, which is very close to the binding energy (BE) of metallic Ni, situated at 852.6 eV. The broad feature centered around -860.2 eV is consistent with satellite structure observed in Ni compounds.

[0176] Deconvolution of the Ni 2p spectra was performed using empirical models based on reference spectra following previously reported methodology. As can be seen from Figure 6, the Ni 2p spectrum is modelled well by a mixture of NixPy, Ni3(PC>4)2, Ni(OH)2 and NiO species and has good correlation to the fitted O 1 s and P 2p spectra. The O 1s spectra also contain a broad peak corresponding to the adventitious organic oxygen species that remained after Ar cleaning, which can be seen in the C 1 s spectrum.

[0177] Electrochemical characteristics

[0178] To analyze the roughness factor (RF) of sample 1 , cyclic voltammetry (CV) was performed to obtain the double-layer capacitance, cf. Fig. 7.

[0179] Running a CV in a non-Faradaic potential range is extremely important. In this instance, a 50 mV window around the Open Circuit Potential (OCP) was selected, specifically between 0 V and 0.05 V versus OCP. The formula to calculate the charging current (ic) is ic = v x Cdi, where Cdi represents the electrochemical double-layer capacitance and v is the scan rate. The scan rates of 0.1 , 0.2, 0.3, and 0.5 V / s were used in this test. The Cdi is the slope of the linear plot of the correlated values of icand v.

[0180] The electrochemical active surface area (ECSA) can be found by dividing the Cdi by the specific capacitance (Cs), parameters that vary with the different materials. In this case, 40 pF / cm2was used, as reported by McCrory et al. Finally, the RF can be found by dividing ECSA by the electrode geometrical area.

[0181] Sample 1 showed an RF equal to 65.9. Other electrode structures that are commonly used have lower RF, such as nickel perforated plate (2.3) and nickel foam (11 .4).

[0182] Higher RF identifies a higher area where the electrochemical reaction can take place.

[0183] Nanofibers NiP-coated electrodes, according to sample 1 , were used in a lab-scale electrolyzer to analyze performance and durability. aera ref. P6549WOOO

[0184] The polarization curves of the two tests performed are shown in Fig. 8.

[0185] In the first test, 300 pm pristine nickel foam (3D porous commercial material; comparative sample) on both the cathode and anode was used to establish an overall performance baseline.

[0186] In the second test, Sample 1 electrodes were used on both sides, cathode and anode. To stabilize the structure, a nickel-perforated plate supported the nanofiber electrodes with a thickness of 300 pm. The support was used only for these preliminary tests and will not be needed anymore once the polymeric structure is optimized. Two pumps set to 100 ml / min were used to circulate 30% KOH electrolyte at 80°C. It was utilized a PERL Zirfon 220 pm separator. No iR correction was performed in order to show the exact performance of an electrolyzer, considering all the ohmic losses as well.

[0187] The electrodes from Sample 1 (circles) are shown to be more efficient than Ni foam (squares) at a rate of 1 A / cm2with a voltage of 2.25 V. Meanwhile, the cell with Ni foam electrodes operates at 2.35 V. Thus, there is a 100 mV difference between these two electrode setups. Regarding the Sample 1 setup, the cathode side shows no signs of degradation at all. Meanwhile, the structure's anode side deteriorates. The primary cause might be that KOH got inside the structure and disintegrated the polymer.

[0188] Conclusion

[0189] Example 1 describes the development of Polyacrylonitrile nanofiber-based electrodes using electroless nickel-phosphorus (NiP) plating. The incorporation of nickel salts into the nanofibers promotes uniform plating. A 10-minute plating achieved a consistent NiP coating. Lab-scale electrolyzers using NiP-coated PAN electrodes performed better than Ni foam, requiring 2.25 V at 1 A / cm2versus 2.35 V, though durability issues on the anode side led to exploration of alternative polymer backbones. Moreover, the roughness factor was calculated electrochemically and found to have a value of 65.9, definitely higher than materials such as nickel perforated plate (2.3) and nickel foam (11.4).

[0190] Example 2: Preparation of Samples 2 to 6 (PSU)

[0191] Electrospinning

[0192] Nanofiber mats were electrospun using a solution of Udel® PSU / DMAC 20 wt.% and 1 wt.% NiCl2’6H2O. The electrospinning conditions include a voltage of 25 kV, a flow rate of 1 ml / h, a humidity level of 25%, and a temperature of 25 °C. To form the solution, the solvent and aera ref. P6549WOOO the polymer were mixed. Once a solution was formed, nickel salt was added. The nickel salt was dehydrated before addition to the solution by placing it in the oven between 80°C and 100°C for 1 hour. This dehydration step resulted in a color change in the nickel salt from green to deep yellow, facilitating the homogenization of the salt within the solution.

[0193] In a high-voltage electrostatic field, a polymer solution was sprayed into fibers. These fibers were then drawn and refined by the electric field force, along with solvent volatilization, and solidified into fibers with a diameter of 50 nm to 1 pm. These pristine fibers were deposited and collected on a flat collector forming a polymer mat.

[0194] Pre-treatment Process: stabilization

[0195] Before the surface activation procedure, a stabilization process was carried out with sample 2. This was performed by keeping the mat in between two glass discs in a furnace (in air) set at 190 °C for an hour. The temperature was chosen because it is slightly above Udel® PSU transition temperature (Tg), which is 187 °C. This was done to obtain a more relaxed structure of the nanofibers mat, and this process is crucial.

[0196] The mechanical strength rose notably. Furthermore, it is thought that the nanofibers form a kind of junction link, where they have crossing points, as a result of this treatment, and could be one of the causes why the mechanical strength increases. Moreover, the importance of this can be seen during electroless NiP plating. PSU is well-known for its hydrophobic characteristics, making it less suitable to be coated with a water-based solution. Without the stabilization treatment, during the reaction where the hypophosphite ions react with water to produce molecular hydrogen as an undesired side reaction, a “bubbling phenomenon” can be observed between the layers of the nanofiber mat, resulting in layer detachments with an unusable sample. Instead, since the stabilized mat has a more compact and stable structure, it can handle the hydrogen evolution reaction while maintaining its original form and being successfully then NiP coated.

[0197] Figure 9 shows the PSU nanofibers mat before a-ij-a?) and after b-ij-bs) the stabilization process was carried out. From the macro images (9ai and 9bi), there was significant shrinkage of the polymer mat, with no bending observed. Looking at the SEM planar images (9a? and 9b2), it can be seen that after the PSU nanofiber mat was stabilized in air at 190°C for 1 hour, nanoparticles were uniformly distributed and observed on its surface. These nanoparticles acted as nucleation sites for the formation of the NiP coating. As the coating aera ref. P6549WOOO grew on each site, it expanded until it merged with neighboring coatings, developing a hilllike structure around the starting point. It is hypothesized that these nanoparticles grew and coalesced during stabilization, leading to an increase in their size. A cross-section SEM image is shown after the stabilization process in Figure 9bs), where the measured thickness was 96 pm, whereas before the treatment it was 41 pm.

[0198] A Thermogravimetric Analysis (TGA) was done as a first step to verify the thermal stability before and after the process was performed. Both the pristine mat (not stabilized) and the one stabilized in air at 190°C for an hour (sample 2) were tested as shown in Figure 11 .

[0199] The pristine mat already exhibited extremely high stability (nearly no degradation up to 410 °C). Sample 2 was shown to be slightly more stable before degradation and noticeably more stable during degradation at high temperatures, above 650 °C. Furthermore, Sample 2 was shown to be as stable as the pristine mat before the onset of degradation at 410°C. The standard electrolyzer operates at 80°C, while advanced lab systems can reach up to 250°C; thus, the thermal stability of the pristine and stabilized mats is sufficient for these applications.

[0200] A tensile strength analysis was also done, as shown in Figure 10. It can be seen how the stabilized mat (sample 2) outperformed the pristine one regarding mechanical strength.

[0201] Pre-treatment Process: Surface Activation

[0202] The above-prepared polymer mat was airbrushed with 2 ml of 0.3 M sodium borohydride (NaBFk) in a 30% v / v ethanol / water solution. The activated polymer mat was then washed with distilled water. This procedure was repeated four times, with the waiting time between each step determined by the time needed for the solution to evaporate. After the last spraying step, the fibers were immediately inserted into the ENP solution while still wet.

[0203] Electroless Nickel Phosphorus (ENP) Plating

[0204] A beaker containing the plating solution was immersed in a water bath on a hot plate. A magnetic bar was used to stir the plating solution. The plating solution was heated to the required temperature, and the sample was inserted for 10 min. Table 1 shows the composition of the solution along with further plating parameters.

[0205] Table 1. The following solution was used for electroless nickel plating. aera ref. P6549WOOO

[0206] Table 2. NiP ENP performed with stabilized mats (samples 2 to 6) at different deposition times and average nanofiber diameters

[0207] To understand how the time influenced the NiP deposition, different coating times of 5 min (sample 3), 10 min (sample 4), 20 min (sample 5), and 30 min (sample 6) were chosen, keeping a fixed plating temperature of 83 °C, cf. Table 2. Figure 17 (a-e) illustrates this process.

[0208] The first column shows the sample's macro visual appearance from the stabilized mats (sample 2, ai) to the one coated for 30 minutes (sample 6, e-i), from top to bottom. It is clear to see how the coating is shinier increasing the NiP deposition time. The SEM images are displayed in the second column, Fig. 17a2-e2. Each image is at the same magnification, and the diameter increases over the deposition time is higher. The distribution of the various diameter sizes and the average diameter for each step are displayed in the third column, Fig. 17a3-e3. The Imaged program was used to perform it, averaging 100 nanofibers. The Gaussian method is used for the fitting line. The average diameters are displayed in Table 2. aera ref. P6549WOOO

[0209] After 5 minutes of deposition (sample 3), considering only the coating layer, an average of 148 nm of NiP thickness has grown on the pristine nanofibers. As observed in the SEM image (Fig. 17b?), this coating does not uniformly cover the entire nanofiber surface but appears as clusters where the nucleation started.

[0210] After 10 minutes of deposition (sample 4), an average of 364 nm of NiP layer is present on the nanofibers. This indicates close alignment with the desired result, as the coating layer is homogeneous across all nanofibers without filling the pores (Fig. 17c2). Subsequently, after 20 (sample 5; Fig. 17d2) and 30 minutes (sample 6; Fig. 17e2) of deposition, average NiP layer thicknesses of 951 nm and 1451 nm, respectively, were observed on the nanofibers.

[0211] The trendline of the diameter over time can be seen in Fig. 16, which also shows the NiP coating deposition (samples 3-6) per weight (mg / cm2) over time. The trendline initially displays almost linear deposition over time. Towards the end, though, the deposition rate decreases. This happens as a result of the material starting to fill the pores, which lowers the surface area that is available for additional coating growth.

[0212] Fig. 14 shows SEM images of sample 4 at various magnifications. Everywhere, the coating is homogeneous. Moreover, Fig. 14e) presents a macro-visual appearance of it. The sample has mechanical properties similar to a nickel foam sample, and it is bendable and highly resistant. Sample 4 exhibits mechanical properties similar to those of nickel foam in terms of high resistance, as shown in Figure 15. Unlike Ni foam, it is also elastic, returning to its original position after deformation.

[0213] How nickel nanoparticles grow on PSU nanofibers

[0214] A systematic study was conducted on the growth of nickel-phosphorus (NiP) nanoparticles on polysulfone nanofibers. Different samples were plated for varying durations, and the formation of a growing layer of nickel was observed. Figures 12a) and b) illustrate the nanofiber structure at high and low magnification, with the NiP nanoparticles visible. Initially, a layer of nanoparticles forms on the fibers, providing a foundation for further growth. To confirm the presence of the nickel-phosphorus coating, two EDS analyses were performed. Figure 12c) presents the spectrum of nickel and phosphorus, showing no presence of these elements in the visually bare fiber, where nanoparticle growth was not possible due to the stopping of the coating process after the nanofiber mat was removed from the coating aera ref. P6549WOOO solution. In contrast, the EDS spectrum shown in Figure 12d) presents an EDS map of sulfur, demonstrating its presence throughout the entire nanofiber, even in the central part, thereby confirming that it is indeed a pure nanofiber. Additionally, a 3D representation of a single polymer nanofiber with NiP coating was created using Render to visually illustrate the growth process, as shown in Figure 13.

[0215] Electrochemical characteristics

[0216] Sample 4 was tested in a standard three-electrode cell in a non-zero-gap configuration using a VersaSTAT4 (Princeton Applied Research). Pressed 300 pm-thick nickel foam and a reversible hydrogen electrode (RHE, Mini-Hydro Flex, Gaskatel) were used as counter and reference electrodes, respectively. These tests were conducted for the hydrogen evolution reaction (HER), using sample 4 as a cathode.

[0217] In Figure 18, HER polarization curves are shown, iR corrected for different substrates. These substrates are shown in Fig. 19, with macro and micro-scale images. Those are: nickel perforated plate (Comparative Sample 1 , CS1 ), (Fig. 19a), nickel foam ALANTUM (CS2) (Fig. 19b), and PSU nanofibers NiP ENP coated - sample 4 (Fig. 19c). All three samples were tested in their pristine form, without any catalyst applied.

[0218] The nickel perforated plate sample is typically used in commercial applications and can be considered a 2-dimensional structure. In contrast, the nickel foam and the NiP-coated PSU nanofibers (sample 4) developed in this work are 3-dimensional structures. These types of structures are characterized by their high surface area and enhanced gas transport properties, both beneficial for electrode applications.

[0219] Sample 4 exhibits higher performance compared to the other commercial substrates. At - 100 mA / cm2, the perforated plate substrate has an overpotential of 416 mV, the foam 374 mV, and sample 4 has the lowest value of 314 mV. After the entire cycle of characterization, sample 4 showed no signs of degradation.

[0220] Conclusion

[0221] Example 2 describes electrodes made using polysulfone as the backbone polymer. The nanofibers were thermally stabilized and uniformly coated with NiP. A 10-minute deposition yielded a 182 nm thick coating with 6.40 mg / cm2loading and good flexibility. This sample achieved a low overpotential of 314 mV at -100 mA / cm2in HER, outperforming commercial aera ref. P6549WOOO

[0222] Ni foam (374 mV) and Ni plate (416 mV). The surface area per unit volume was 6581 cm-1vs. 881 cm-1(foam) and 242 cm-1(plate). Long-term testing (400 h, 30% KOH, 80°C) showed structural stability.

[0223] EMBODIMENTS

[0224] Embodiment 1 :

[0225] A method for manufacturing a nickel coated porous structure, the method comprising the following steps: i) obtaining one or more polymer fibers comprising nickel salt, preferably nickel salt clusters and / or nickel salt particles; ii) reducing at least a part of the nickel salt to form metallic nickel, preferably metallic nickel clusters and / or nickel particles; and ill) electroless plating of the one or more polymer fibers obtained in step ii), using a plating solution, the one or more polymer fibers to form one or more nickel coated polymer fibers, wherein step iii) is performed after step ii); and wherein the porous structure is a microporous and / or nanoporous structure.

[0226] Embodiment 2:

[0227] The method according to embodiment 1 , wherein step i) comprises the following steps: drying, preferably heating, the nickel salt; and adding the dried nickel salt to a polymeric solution; and preparing one or more polymer fibers from the polymeric solution.

[0228] Embodiment 3

[0229] The method according to any of embodiments 1 and 2, wherein the polymer fibers obtained in step i) comprise a polymer and / or copolymer selected from the group consisting of polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof; and / or wherein the nickel salt in step i) is selected from the group consisting of nickel (II) chloride, nickel (II) sulfate, nickel (II) carbonate, nickel (II) nitrate, nickel (II) bromide, nickel (II) iodide, nickel (II) phosphate or mixtures thereof; and / or wherein step ii) comprises applying a reducing agent to the one or more polymer fibers, preferably spraying a reducing agent onto the one or more polymer fibers; and / or aera ref. P6549WOOO wherein the reducing agent in step ii) is a solution comprising an organic or inorganic reducing agent, preferably an inorganic reducing agent.

[0230] Embodiment 4:

[0231] The method according to embodiment 3, wherein the reducing agent is selected from the group consisting of sodium borohydride, potassium borohydride, lithium borohydride, sodium bis(2-methoxyethoxy) aluminum hydride, hydrogen or combinations thereof, preferably the reducing agent is sodium borohydride.

[0232] Embodiment 5:

[0233] The method according to any of the previous embodiments, wherein step iii) takes less than 60 min, preferably less than 20 min, more preferably 0.5 to 60 min and even more preferably 0.5 to 20 min; and / or wherein step iii) is performed with the plating solution having a temperature between 10 to 100°C, preferably between 30 to 95°C and more preferably between 50 to 90°C; and / or wherein the plating solution in step iii) comprises at least one nickel compound, preferably a nickel salt, and a further reducing agent different from the reducing agent in step ii), preferably a hypophosphite, a chelating agent, and / or a stabilizer.

[0234] Embodiment 6:

[0235] A nickel coated porous structure comprising one or more polymer fibers, preferably one or more electrospun polymer fibers, coated with a layer of metallic nickel, wherein the layer of metallic nickel has a thickness in the range from 50 nm to 10000 nm, preferably in the range of 100 nm to 5000 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

[0236] Embodiment 7:

[0237] The nickel coated porous structure according to embodiment 6, wherein the average diameter of the one or more polymer fibers, preferably electrospun polymer fibers, is in the range from 20 nm to 10 pm, preferably from 50 nm to 5 pm, and more preferably from 75 nm to 1 pm; and / or wherein the outer surface of the layer of metallic nickel coating has a roughness parameter in the range from 5 to 500, determined by double-layer capacitance performing cyclic voltammetry. aera ref. P6549WOOO

[0238] Embodiment 8:

[0239] The nickel coated porous structure according to any of embodiments 6-7, wherein the nickel coated porous structure has a BET surface area in the range from 5 to 50 m2 / g; and / or wherein the nickel coated porous structure has a surface area per mass ratio in the range from 5 to 100 m2 / g, preferably from 10 to 75 m2 / g, and more preferably from 15 to 50 m2 / g; and / or wherein the nickel coated porous structure has a surface area to volume ratio in the range from 1 to 20 m2 / cm3.

[0240] Embodiment 9:

[0241] The nickel coated porous structure according to any of embodiments 6-8, wherein the one or more polymer fibers comprise a polymer selected from the group of polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof.

[0242] Embodiment 10:

[0243] A nickel coated porous structure obtainable by the method according to any of embodiments 1 to 5.

[0244] Embodiment 11 :

[0245] A porous structure comprising one or more polymer fibers, preferably one or more electrospun polymer fibers, wherein the one or more polymer fibers comprise metallic nickel, preferably metallic nickel clusters with a diameter in the range from 10 nm to 1000 nm, preferably in the range from 10 nm to 100 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

[0246] Embodiment 12

[0247] Article made from a nickel coated porous structure according to any of embodiments 6 to 10, wherein the article is preferably an electrode, a membrane, a filter, or a mask.

[0248] Embodiment 13

[0249] Use of a nickel coated porous structure according to any of embodiments 6 to 10 as an electrode, a membrane, or a filter, preferably electrode. aera ref. P6549WOOO

[0250] Embodiment 14:

[0251] Use of a nickel coated porous structure according to any of embodiments 6 to 10 in electrolysis, in air treatment, in water treatment, in a super capacitor, in a fuel cell, in hydrogen production or in a flow battery.

[0252] Embodiment 15:

[0253] An electrochemical cell comprising the nickel coated structure according to embodiments 6 to 10.

Claims

aera ref. P6549WOOOCLAIMS1. A method for manufacturing a nickel coated porous structure, the method comprising the following steps: a) obtaining one or more polymer fibers comprising nickel salt, preferably nickel salt clusters and / or nickel salt particles; b) stabilizing the one or more polymer fibers obtained in step a) c) reducing at least a part of the nickel salt to form metallic nickel, preferably metallic nickel clusters and / or nickel particles; and d) electroless plating of the one or more polymer fibers obtained in step c), using a plating solution, the one or more polymer fibers to form one or more nickel coated polymer fibers, wherein step c) is performed after step b); and wherein the porous structure is a microporous and / or nanoporous structure.

2. The method according to any one of the previous claims, wherein step a) comprises the following steps: drying, preferably heating, the nickel salt; and adding the dried nickel salt to a polymeric solution; and preparing one or more polymer fibers from the polymeric solution.

3. The method according to any one of the previous claims, wherein the polymer fibers obtained in step a) comprise a polymer and / or copolymer selected from the group consisting of polyacrylonitrile, polysulfone, polybenzimidazole, polystyrene, polyvinylpyrrolidone, or mixtures thereof; and / or wherein the nickel salt in step a) is selected from the group consisting of nickel (II) chloride, nickel (II) sulfate, nickel (II) carbonate, nickel (II) nitrate, nickel (II) bromide, nickel (II) iodide, nickel (II) phosphate or mixtures thereof; and / or wherein step b) comprises keeping the one or more polymer fibers obtained in step a) at a temperature between 100 and 350°C, preferably between 150 and 300°C, and / or wherein step c) comprises applying a reducing agent to the one or more polymer fibers, preferably spraying a reducing agent onto the one or more polymer fibers; and / or wherein the reducing agent in step c) is a solution comprising an organic or inorganic reducing agent, preferably an inorganic reducing agent.36aera ref. P6549WOOO4. The method according to claim any one of the previous claims, wherein the polymer fibers obtained in step a) comprise polysulfone and / or a copolymer of polysulfone.

5. The method according to any one of the previous claims, wherein the reducing agent is selected from the group consisting of sodium borohydride, potassium borohydride, lithium borohydride, sodium bis(2-methoxyethoxy) aluminum hydride, hydrogen or combinations thereof, preferably the reducing agent is sodium borohydride.

6. The method according to any one of the previous claims, wherein step d) takes less than 60 min, preferably 0.5 to 60 min, more preferably less than 20 min and even more preferably 0.5 to 20 min; and / or wherein step d) is performed with the plating solution having a temperature between 10 to 100°C, preferably between 30 to 95°C and more preferably between 50 to 90°C; and / or wherein the plating solution in step d) comprises at least one nickel compound, preferably a nickel salt, and a further reducing agent different from the reducing agent in step c), preferably a hypophosphite, a chelating agent, and / or a stabilizer.

7. A nickel coated porous structure comprising one or more polymer fibers, preferably one or more electrospun polymer fibers, wherein the polymer fibers are stable to degradation at temperatures between 350 and 700°C, and wherein the polymer fibers are coated with a layer of metallic nickel, wherein the layer of metallic nickel has a thickness in the range from 50 nm to 10000 nm, preferably in the range of 100 nm to 5000 nm; and wherein the porous structure is a microporous and / or nanoporous structure.

8. The nickel coated porous structure according to claim 7, wherein the one or more polymer fibers comprise polysulfone and / or a copolymer of polysulfone.

9. The nickel coated porous structure according to any one of claims 7 or 8, wherein the average diameter of the one or more polymer fibers, preferably electrospun polymer fibers, is in the range from 20 nm to 10 pm, preferably from 50 nm to 5 pm, and more preferably from 75 nm to 1 pm; and / or wherein the outer surface of the layer of metallic nickel coating has a roughness parameter in the range from 5 to 500, determined by double-layer capacitance performing cyclic voltammetry.37aera ref. P6549WOOO10. The nickel coated porous structure according to any one of claims 7 to 9, wherein the nickel coated porous structure has a BET surface area in the range from 5 to 50 m2 / g; and / or wherein the nickel coated porous structure has a surface area per mass ratio in the range from 5 to 100 m2 / g, preferably from 10 to 75 m2 / g, and more preferably from 15 to 50 m2 / g; and / or wherein the nickel coated porous structure has a surface area to volume ratio in the range from 1 to 20 m2 / cm3.

11. A nickel coated porous structure obtained by the method according to any one of claims 1 to 6.

12. An article comprising the nickel coated porous structure according to any one of claims 7 to 11 , wherein the article is preferably an electrode, a membrane, a filter, or a mask.

13. Use of a nickel coated porous structure according to any of claims 7 to 11 as an electrode, a membrane, or a filter, preferably electrode.

14. Use of a nickel coated porous structure according to any of claims 7 to 11 in electrolysis, in air treatment, in water treatment, in a super capacitor, in a fuel cell, in hydrogen production or in a flow battery.

15. An electrochemical cell comprising the nickel coated structure according to claims 7 to 11.

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