A METHOD FOR PRODUCING ELECTRODES FOR ELECTROLYSIS

Abstract

The present invention relates to a method for producing an electrode for alkaline electrolysis based on a composition of metal sulfides on a Ni foam substrate. The metal can be Mo, Ni, Co, Fe and/or W. In a first step S1), there is performed a metal deposition, e.g. by electroplating, the metal, Me1/Me2, being Mo, Ni, Co, Fe, and/or W, on a Ni foam substrate resulting in a metal-Ni compound being formed on and/or in the Ni foam substrate. In a second step, S2) there is performed a sulfiding on the metal-Ni compound from the first step S1). The third step S3) is an optional repetition of S1 and/or S2 at least one time. The step S1) and step S2) thereby result in the formation of electrocatalytic active nano-sites with Me1-Me2-SNi compounds. It is found that these nano-sites are capable of reducing the so-called overpotential of the electrodes during alkaline water electrolysis, and the production of electrodes may be significantly simplified.

Claims

1. A method for producing an electrode for alkaline electrolysis based on a composition of metal sulfides on a Ni foam substrate, the metal being Mo, Ni, Co, Fe and/or W, the method comprising initially providing a nickel (Ni) foam substrate, the method comprising the separate steps of: S1) performing a metal deposition, preferably by electroplating, the metal being Mo, Ni, Co, Fe, and/or W, on said Ni foam substrate resulting in a metal-Ni compound being formed on and/or in the Ni foam substrate, and S2) performing a sulfiding on said metal-Ni compound, and S3) optionally repeating, at least one time, said step S1) and/or said step S2), thereby resulting in the formation of electrocatalytic active nano-sites comprising Me1-Me2-SNi compounds capable of reducing the overpotential of the electrode during alkaline water electrolysis, wherein Me1 is a metal chosen from the group consisting of Mo, Ni, Co, Fe, and/or W, and wherein Me2 is a metal chosen from the group consisting of Mo, Ni, Co, Fe, and/or W.

2. The method for producing an electrode according to claim 1, wherein step S1) and step S2) are performed as separate and distinct steps in a production line for manufacturing the electrode.

3. The method for producing an electrode according to claim 1, wherein the Me1 metal is different from the Me2 metal.

4. The method for producing an electrode according to claim 3, where said Me1 metal and said Me2 metal are being deposited in separate and distinct steps S1) of metal deposition.

5. The method for producing an electrode according to claim 3, wherein said Me1 metal and said Me2 metal depositions are performed in separate and distinct places in a production line for manufacturing the electrode.

6. The method for producing an electrode according to claim 1, wherein the Me1 metal is different from the Me2 metal, and where said Me1 metal and said Me2 metal are being deposited in the same step S1) of metal deposition.

7. The method for producing an electrode according to claim 1, where the metal deposition step S1) is performed by electroplating, preferably DC electroplating, pulse electroplating or ionic electroplating, or any combinations thereof.

8. The method for producing an electrode according to claim 1, where the step S2) of sulfiding on said metal-Ni compound is performed with a sulfiding medium comprising hydrogen sulfide, H.sub.2S, alternatively dimethyl sulfide (DMS), dimethyl sulfoxide (DMSO, (CH.sub.3).sub.2SO), Ethyl Mercaptan (CH.sub.3CH.sub.2SH), Butyl Mercaptan (C.sub.4H.sub.10S), thiourea, C.sub.2S.sub.2 or H.sub.2S.sub.2.

9. The method for producing an electrode according to claim 1, wherein the Ni foam is replaced by a foam from any of the metals chosen from the group consisting of Fe, Co, Cr, and Cu.

10. The method for producing an electrode according to claim 1, wherein an additional heating step is performed: S_Pre) before step S1) metal deposition, S_Inter) between S1) metal deposition and S2) sulfiding, and/or S_Post) after S2) sulfiding, and any combinations thereof.

11. The method for producing an electrode according to claim 1, wherein the electrocatalytic active nano-sites comprising Me1-Me2-SNi compounds capable of reducing the overpotential of the electrode during alkaline water electrolysis comprises primarily edge sites situated on the edge of the said nano-sites.

12. The method for producing an electrode according to claim 1, wherein the electrocatalytic active nano-sites comprising Me1-Me2-SNi compounds capable of reducing the overpotential of the electrode during alkaline water electrolysis comprises primarily sulfur deficient sites with near metallic properties.

13. The method for producing an electrode according to claim 1, wherein the electrocatalytic active nano-sites comprising Me1-Me2-SNi compounds are capable of reducing the overpotential of the electrode during alkaline water electrolysis at least 0.2 V, preferably at least 0.3 V, more preferably at least 0.4 V.

14. The method for producing an electrode according to claim 1, wherein the Ni foam is replaced by a Ni woven structure, a Ni plate, or a Ni mesh.

15. The method for producing an electrode according to claim 1, wherein the step S2) of sulfiding of said Ni foam substrate is performed with a gas, preferably with a H.sub.2S gas, optionally with a composition of 1-10 vol. % H.sub.2S, preferably 2-4 vol. % H.sub.2S, more preferably around 3 vol. % H.sub.2S.

16. The method for producing an electrode according to claim 1, wherein the step S2) of sulfiding of said Ni foam substrate is performed only on a surface part of the Ni foam substrate.

17. An electrode manufactured according the method of claim 1.

18. An electrolysis system comprising one or more electrodes manufactured according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0028] FIG. 1 shows an example of reduced overvoltage for hydrogen formation as compared to an untreated Ni reference at pilot scale level 10 m.sup.3/h at 30 bar,

[0029] FIG. 2 shows a Pourbaix diagram for NiTe.sub.2 in the entire pH range from 0 to 14,

[0030] FIG. 3 shows a flow chart of the present invention for a method for producing an electrode for alkaline electrolysis,

[0031] FIG. 4 shows another flow chart of the present invention for a method for producing an electrode for alkaline electrolysis having preliminary treatment with heating and post-treatment with heating,

[0032] FIG. 5 shows a principle drawing of electrolytic deposition of metal in an electrolytic cell where the metal layer is deposited on the cathode,

[0033] FIG. 6 shows a principle drawing of an oven heating a nickel foam in a H.sub.2S containing gas to perform sulfiding of the substrate,

[0034] FIG. 7 shows three different levels of an electrolysis system according to the present invention; in A) a photograph of an electrolysis configuration is shown based on Ni foam electrodes, where in the enlargement B) the Ni foam on both the anode and the cathode side is schematically illustrated, and the additional enlargement C) shows a schematic illustration of these electrocatalytic active nano-sites on a part of the Ni foam according to the present invention,

[0035] FIG. 8 shows the effect of sulfiding a Ni foam in 3% H.sub.2S at 75 deg. C., where the two left SEM images (high and low magnification) shows the pure Ni surface before sulfiding, whereas the middle and right set of SEM images shows the effect of 1 hours and 2 hours sulfiding, respectively, and

[0036] FIG. 9 shows three polarisation curves for the necessary voltage for hydrogen/oxygen formation as a function of the applied current density in 30% KOH at 90 deg. C. for various treatment of Ni foam.

[0037] The present invention will now be described in more detail in the following.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Prior to discussing the present invention in further details, the following terms and conventions will first be defined:

[0039] In context of the present application, it may be understood that the term electrodes is to be interpreted broadly as the skilled person in electrochemistry will readily understand. Thus, electrodes according to the present invention may form part of one, or more, electrolytic cell(s), for example a single electrolytic cell, stacked electrolytic cells, low pressure electrolytic cells, high pressure electrolytic cell, a traditional electrolytic cell, a zero gap electrolytic cell, an electrolytic cell with gas diffusion layers in between, etc.

[0040] In context of the present application, it may be understood that the term metal is to be interpreted broadly as the skilled person will readily understand, in particular that a metal may comprise impurities to a certain extent under realistic working conditions in production facilities for electrodes, and in particular that some metals may have a certain degree of metal oxide formation, on the surface and/or in the bulk, e.g. iron oxide formation like Fe.sub.2O.sub.3, etc.

[0041] In context of the present application, it may be understood that the term metal compounds of the type Me1-Me2-SNi is to be interpreted broadly as the skilled person will readily understand, in particular that various stoichiometry relations between the Me1 and Me2 and sulfur are possible on the Ni foam substrate. Thus, Me1-Me2-SNi is to be interpreted as Me1.sub.A-Me2.sub.B-S.sub.CNi, where stoichiometric coefficients A, B and C may vary over a range over meta-stable and/or thermodynamically stabile compounds depending on the specific metals of Me1 and/or Me2 used in the electrodes and being highly dependent on the degree of sulfiding, sulfiding partial pressure as well as the temperature during sulfiding, as the skilled person will readily understand from the below explanations and examples. It is also contemplated that Me1 and/or Me2, both being a metal chosen from the group consisting of Mo, Ni, Co, Fe, and/or W, mayto some extentform various metal oxides in the Me1-Me2-SNi compounds according to the present invention. Thus, if Me1 is iron, a certain amount of the iron may form Fe.sub.2O.sub.3-oxides (Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, Fe(OH).sub.2 and, Fe(OH).sub.3) in the electrodes. Similar oxidation or partial oxidation may be seen for other involved metals.

[0042] In context of the present application, it may be understood that the term sulfiding is generally to be interpreted broadly and refer to any chemical reaction with sulfur to form sulfides, also know as a sulfidation. In US English, the corresponding spelling is sulphiding to form sulphides, etc.

[0043] Since the sulfiding step may be based on a sulfur diffusion, e.g. via H.sub.2S gas, and subsequent reaction, it will be possible to document a diffusion-based production process by analysing the sulfur depth profile. If the sulfiding process is based on diffusion, there will be a decreasing sulfur concentration upon going deeper into the electrode incl. the Ni foam implying deeper into the structure of the Ni foam or deeper into a deposited metal overlayer. In advantageous embodiments, only on the surface part of the Ni substrate there is performed a sulfidation, which has the advantage of maintaining, at least to a substantial extent, the bulk properties of the Ni substrate, such as strong/flexible mechanical properties and relatively high conductivity. Thus, in the context of the present application, it is to be understood that a surface constitutes an upper boundary volume or region of the Ni substrate, such as a surface having a depth of about 200, 300, 400, 500 or 1000 nm. Therefore, the concept of performing a sulfiding only of the surface will be readily understood by a skilled person in this technical field.

[0044] Alternatively, sulfur may be added through co-deposition and there will be a relatively more abrupt change in the sulfur concentration profile as a function depth into the electrode coating. A co-deposition will not go into the substrate except if it involves a subsequent heating process where again the S-profile will be more abruptly going down to zero as compare to a diffusional sulfiding process.

[0045] Suitable analysis techniques for probing the sulfur depth profile is Rutherford Backscattering Spectrometry (RBS), Focused Ion Beam Scanning Electron Microscope (FIB-SEM) equipped with Energy-dispersive X-ray spectroscopy (EDX/EDS), Glow Discharge Optical Emission Spectroscopy (GDOES) or similar depth resolved elemental analysis techniques as the skilled person will readily understand.

[0046] In context of the present application, it may be understood that the term nano-sites is to be interpreted broadly as the skilled person in surface physics and/or surface chemistry will understand. Thus, the Me1-Me2-SNi compounds may form electrocatalytic nano-sites having a characteristic dimension, such as (average) diameter or length scale, of 1-1000 nm, preferably 10-500 nm, more preferably, 20-200 nm. Clearly, if electroplating thicker layers (in step1 S1) the active layer may be even thicker after sulfiding in step S2.

EMBODIMENTS

[0047] In one advantageous embodiment, the method for producing an electrode according to the first aspect may comprise that step S1) and step S2) are performed as separate and distinct steps in a production line for producing or manufacturing the electrode. In this particular embodiment, in the method for producing an electrode according to the first aspect, the Me1 metal may be different from the Me2 metal, and the metal deposition results in the metal Me1 being deposited, and second and sequent metal deposition results in the metal Me2 being deposited. Thus, beneficially S1 and S2 are performed at different locations in a production line facilitating a significant simplification of the production process.

[0048] In embodiments, where the metals Me1 and Me2 may be one and the same metal, the resulting Me1-SNi compound is also part of the present invention, and it may be the result of a single metal deposition by step S1), or repeated step of metal deposition; S1), S1), S1), etc., either at the same place in a production line, or at several positions in a production line depositing the same kind of metal, either by an identical metal deposition technique or by different metal deposition techniques. Alternatively, though it may also not form part of the present invention that the first Me1 and second Me2 are one and the same metal.

[0049] In another embodiment, where the method for producing an electrode is according to the first aspect, the Me1 metal may be different from the Me2 metal, and where said Me1 metal and said Me2 metal are being deposited in the same step S1) of metal deposition. Thus, for example combination of some metal compounds like CoMo may be performed at the same time, e.g. by electroplating at the same time.

[0050] According to literature, there are potential improvements by different steps in the catalyst formulation. The impregnation of Ni prior to Co results in higher dispersion of molybdenum. The tri-metallic catalyst CoNiMo/?-Al.sub.2O.sub.3 synthesized has been observed to have a higher hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activity as compared to that shown by bimetallic catalysts. The higher activity shown by tri-metallic CoNiMo catalysts may be ascribed to the double promotional effect of Co and Ni and formation of three types of active phases NiMOS, CoMOS and NiCoMOS, cf. Effect of synthesis technique on the activity of CoNiMo tri-metallic catalyst for hydrotreating of heavy gas oil, Catalysis Today, Volume 291, 1 Aug. 2017, Pages 160-171.

[0051] In another embodiment, the method for producing an electrode according to the first aspect relates to a metal deposition, where step S1) is performed by electroplating, preferably DC electroplating, pulse electroplating or ionic electroplating, or any combinations thereof. Other alternatives contemplated: PVD (DC sputtering, RF sputtering, HiPIMS, pulse DC, etc.), CVD processes, various types of thermal spraying, electroplating (DC, pulse plating or ionic plating). Liquid infiltration followed by calcination, etc., as will readily be understood by the skilled person once the teaching and principle of the present invention is fully comprehended. In FIG. 5, a conventional electroplating is schematically indicated. The metal source for the coating is supplied by the two anodes (+) as well as by the metal ions in the bath. The energy is supplied by an external power supply (not shown). The metal layer is then deposited at the cathode (?).

[0052] In another embodiment, the method for producing an electrode according to the first aspect, a step S2) of sulfiding on said metal-Ni compound may be performed with a sulfiding medium comprising hydrogen sulfide, H.sub.2S, alternatively dimethyl sulfide (DMS), dimethyl sulfoxide (DMSO, (CH.sub.3)2SO), Ethyl Mercaptan (CH.sub.3CH.sub.2SH), Butyl Mercaptan (C.sub.4H.sub.10S), thiourea, C.sub.2S.sub.2 or H.sub.2S.sub.2. It is also contemplated that heating in packed bed with S-containing granulates or elemental sulfur may be beneficially applied in the present invention.

[0053] In advantageous embodiments, the method for producing an electrode according to the first aspect may relate to the Ni foam being replaced by a foam from any of the metals chosen from the group consisting of Fe, Co, Cr, and Cu.

[0054] In useful embodiments, the method for producing an electrode according to the first aspect may relate to an additional heating step being performed at various positions in the overall process according to the present invention: [0055] S_Pre) before step S1) metal deposition, [0056] S_Inter) between S1) metal deposition and S2) sulfiding, and/or [0057] S_Post) after S2) sulfiding, and any combinations thereof.
as will be explained in more detail below, cf. FIG. 4.

[0058] In advantageous embodiments, the method for producing an electrode according to the first aspect may relate to step S1), in an initial execution, being omitted thereby resulting in step S2 being a pre-sulfiding step of the Ni foam substrate.

[0059] In advantageous embodiments, the electrocatalytic active nano-sites may comprise Me1-Me2-SNi compounds capable of reducing the overpotential of the electrode during alkaline water electrolysis comprises primarily edge sites situated on the edge of the said nano-sites. Thus, the Haldor Tops?e research team has together with Aarhus university and DTU in Denmark verified both experimentally and theoretically the existence of very active BRIM? sites, at the edges of the molybdenum disulfide nanocrystals. These edge sites with and without the presence of Ni/Co-edge atoms are believed to highly catalytic active sites for HDN and HDS. These sites interact with hydrogen and may also be very active in connection with alkaline electrolysis, cf. Atomic-Scale Structure of CoMoS Nanoclusters in Hydrotreating Catalysts, J. V. Lauritsen, S. Helveg, E. L?gsgaard, I. Stensgaard, B. S. Clausen, H. Tops?e, F. Besenbacher, Journal of Catalysis, Volume 197, Issue 1, 1 Jan. 2001, Pages 1-5.

[0060] In other advantageous embodiments, the electrocatalytic active nano-sites may comprise Me1-Me2-SNi compounds capable of reducing the overpotential of the electrode during alkaline water electrolysis comprising primarily sulfur deficient sites with near metallic properties. Thus, the reactivity and the ability to lower the voltage for hydrogen formation might be related to the degree of sulfur vacancies (sulfur deficient sites).

[0061] In some advantageous embodiments, the Ni foam may be replaced by a Ni woven structure, a Ni plate, or a Ni mesh, or any combination of such substrates as the skilled person will readily understand is within the scope and general principle of the present invention.

[0062] In still other advantageous embodiments, where the step S2) of sulfiding of said Ni foam substrate may performed with a gas or a gas composition having the advantage of relatively quick and easy application to the electrodes during manufacturing. This may preferably be with a H.sub.2S gas, optionally with a composition of 1-10 vol. % H.sub.2S, preferably 2-4 vol. % H.sub.2S, more preferably around 3 vol. % H.sub.2S. It may alternatively be around 20, 30, 40, 50, 60, 70, 80, 90 or 100 vol. % of H.sub.2S.

[0063] Advantageously, the step S2) of sulfiding of said Ni foam substrate may be performed only on a surface part of the Ni foam substrate in order to maintain to a substantially extent the beneficial bulk properties, e.g. mechanical and electrical properties, while modifying the electrocatalytic surface properties.

[0064] In advantageous embodiments of the invention according to the second aspect in a step S1), metal deposition is performed prior to the sulfiding step S2), preferably by electroplating, the metal being Mo, Ni, Co, Fe, and/or W, on said Ni foam substrate resulting in a metal-Ni compound being formed on and/or in the Ni foam substrate.

[0065] It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention. Thus, the skilled person in electrochemistry will readily understand that the various steps for producing a new and advantage electrode may swiftly be implemented in an electrode.

[0066] All patent and non-patent references cited in the present application are hereby incorporated by reference in their entirety.

[0067] The invention will now be described in further details in the following non-limiting examples.

Example 1: Lowering of the Overpotential for Hydrogen Formation in Alkaline Electrolysis

[0068] EP 0 235 860 covers a method for manufacturing an electrode for making H.sub.2 and O.sub.2 in an alkaline media, which comprises electro-deposition a catalytic layer which contains at least Ni and S, on an electrical-conducting substrate. Following the ideas outlined in EP 0 235 860 electroplating with suitable Ni-salts and suitable sulfur-releasing agents the present inventors fabricated and assembled 54 electrodes ?60 in an alkaline pilot electrolysis unit. As seen in FIG. 1, the voltage for hydrogen formation was on the average lowered by 0.3V as compared to an untreated Ni reference. The best performing electrode lowered the voltage for hydrogen formation with 0.33V.

[0069] FIG. 1 shows on the left a histogram over 54 ?60 cm electrodes showing the number of electrodes generating hydrogen in a specific voltage interval. Each interval is 0.005V. On the average, the voltage for hydrogen formation is lowered by 0.3V as compared to the red untreated nickel reference, which generates hydrogen at 1.95V. The best electrode needs only 1.62V for hydrogen formation corresponding to a decrease of 0.33V for hydrogen formation.

Example 2: Thermodynamic Stability of Different Metal Sulfides Under Alkaline Electrolysis Conditions

[0070] Table 1 and Table 2 below shows the calculated delta G value for the following two reactions:

[00002]$\begin{array}{cc}{\mathrm{MoS}}_2+4\mathrm{KOH}={\mathrm{MoO}}_2+2H_{2}O+2K_{2}S& \left(i\right)\end{array}$$\begin{array}{cc}{\mathrm{WS}}_2+4\mathrm{KOH}={\mathrm{WO}}_2+2H_{2}O+2K_{2}S& \left(\mathrm{ii}\right)\end{array}$

TABLE-US-00001 TABLE 1 MoS.sub.2 + 4KOH = MoO.sub.2 + 2H.sub.2O + 2K.sub.2S T(? C.) Delta G (kcal) 0 12,539 10 12,473 20 12,405 30 12,335 40 12,265 50 12,194 60 12,121 70 12,048 80 11,974 90 11,899 100 11,824

[0071] The predicted stability of MoS.sub.2 under KOH conditions. As evident from the calculated positive Delta G value, it is not possible to decompose MoS.sub.2 in a KOH solution below 100? C.

TABLE-US-00002 TABLE 2 WS.sub.2 + 4KOH = WO.sub.2 + 2H.sub.2O + 2K.sub.2S T(? C.) Delta G (kcal) 0 8,266 10 8,195 20 8,123 30 8,049 40 7,975 50 7,899 60 7,823 70 7,745 80 7,667 90 7,588 100 7,508

[0072] The predicted stability of WS.sub.2 under KOH conditions. As evident from the calculated positive Delta G value, it is not possible to decompose WS.sub.2 in a KOH solution below 100? C.

[0073] From the calculated positive delta G values, it can be concluded that it is not thermodynamically possible below 100? C. to transform MoS.sub.2 or WS.sub.2 to the corresponding oxides (MoO.sub.2 or WO2) in the presence of KOH. Hence, it can be concluded that MoS.sub.2 and WS.sub.2 are thermodynamically stable under typical conditions used in alkaline electrolysis (20-30% KOH and 90? C.).

Example 3: Calculated Stability of Metal Tellurides

[0074] FIG. 2 shows a Pourbaix diagram indicating that NiTe.sub.2 is stable under the hydrogen formation line in the entire pH range from 0 to 14 which makes it very suitable as electrode material on the cathode side.

[0075] As can be seen from the Pourbaix diagram in FIG. 2, NiTe.sub.2 is stable in the entire pH-range, below the stability area of water where water is forming hydrogen (the lower dashed line). This implies that NiTe.sub.2 is stable in the environment relevant for alkaline electrolysis as a hydrogen-forming cathode. Thus, in one aspect of the invention sulfur may be replaced with tellur.

Example 4: Stable CoMoS, NiMoS, CoNiMoS, CoWS, NiWS and/or CoNiWS-Sites for Hydrogen Formation

[0076] Nan Tops?e and Henrik Tops?e were the first to identify the active CoMoS, NiMoS and CoNiMoS-sites on sulfided catalysts for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) [A, B]. Over the years the Tops?e group has shown that the density of these active CoMoS, NiMoS and CoNiMoS-sites can be quantified by NO or CO adsorption, and furthermore, that the concentration of these edge sites on sulfided Co/NiMoS.sub.2 catalysts can be correlated with the overall catalytic activity [C]. The catalysts are often made by pore filling of ?-Al.sub.2O.sub.3 or a suitable zeolite system with Mo, W, Ni and/or Co, in one or more steps, followed by calcination forming ?-Al.sub.2O.sub.3 or zeolite supported mixed oxide systems. The mixed oxides are subsequently sulfided in e.g. H.sub.2S to obtain active HDN/HDS catalysts.

[0077] The uniqueness of the CoMoS, NiMoS, CoNiMoS, CoWS, NiWS, CoNiWS-sites formed at the edges of MoS.sub.2/W.sub.S2 clusters has been further supported by Density-functional theory (DFT) calculations [D, E]. Tops?e et al. has suggested that these sites are promoting good hydrogenation properties with unique hydrogen interaction.

[0078] Hence, the present patent application suggests to synthesis CoMoS, NiMoS, CoNiMoS, CoWS, NiWS and/or CoNiWS-sites on nickel foam substrate by the suggested step1/step2 procedure or combination of several step1's/step2's forming active electrodes for alkaline electrolysis.

[0079] Especially as the unique activity is associated with sulfur deficient sites approaching a metallic nature which is expected to be highly active/beneficial for the formation of hydrogen at a lower voltage in alkaline environments [E, F].

[0080] FIG. 7 C) shows a schematic illustration of these proposed unique electrocatalytic sites on a section of Ni foam according to the invention for hydrogen formation in the lower third section. The suggested electrodes may also be used on the anode side. In the middle B) section, the Ni foam on both the anode and the cathode side is schematically illustrated with a membrane where OH? can be transported. In section A), a photograph of an electrolysis configuration is shown based on Ni foam electrodes.

Example 5: Direct Heating of Ni Foam in H.SUB.2.S

[0081] In one embodiment of the present invention, a nickel foam may be heated in a H.sub.2S containing atmosphere converting the Ni-substrate (+surface oxidized substrate (NiO)) into a NiS phase. Depending on how extensive the sulfiding process should be, it may be necessary to heat to higher temperatures. It could be enough to heat to between 200-600? C. However, some experiments suggest that maximum temperatures of about 75, 90, 100, 150, 200 degrees C. may be sufficient for performing the sulfiding process step S2, which is favorable for practical implementation, saves energy, and minimizes the possible negative impact of heating the electrode unnecessary. Time is of course also a relevant factor as the skilled person in surface chemistry will readily understand, such process time of sulfiding may be 5, 10, 15, 20, 30, or 40 hours of maximum treatment time, though it naturally also depends on the flow of H.sub.2S and the concentration. Also, lower temperatures are beneficial preserving the mechanical and stable properties of the Ni foam.

Example 6: Coating of Nickel Foam with e.g. Mo Followed by Heating in H.SUB.2.S

[0082] In one embodiment of the invention, a nickel foam may be electroplated by e.g. Mo (or other metals) followed be heated in a H.sub.2S containing atmosphere converting part of the Ni-substrate (+surface oxidized substrate (NiO)) and the plated Mo into a MoS/NiMOS phase. Depending on how extensive the sulfiding process should be, it will be necessary to heat to higher temperatures. It could be enough to heat to between 200-600? C. However, some experiments suggest that maximum temperatures of about 75, 90, 100, 150, 200 degrees C. may be sufficient for performing the sulfiding process step S2 as mentioned above. Also, lower temperatures are beneficial preserving the mechanical and stable properties of the Ni foam.

Example 7: Example 6 Followed by Ni and/or Co Coating and Heating in H.SUB.2.S

[0083] Examples 6 might also be followed by electroplating with Ni and/or Co after Mo coating or after Mo coating and heating in H.sub.2S to create CoMOS and NiMOS sites. Depending on how extensive the sulfiding process should be, it will be necessary to heat to higher temperatures. It could be enough to heat to between 200-600? C. However, some experiments suggest that maximum temperatures of about 75, 90, 100, 150, 200 degrees C. may be sufficient for performing the sulfiding process step S2 as mentioned above. Also, lower temperatures are beneficial preserving the mechanical and stable properties of the Ni foam.

Example 8: Example 5-7 Involving Pre- and/or Post-Treatments

[0084] Example 5-7 might be combined with any pre- and/or post-treatments involve e.g. heating in air converting metal to metal oxides before sulfiding in H.sub.2S. Depending on the degree of oxidation, it will be necessary to heat to higher temperatures. It could be enough to heat to between 200-600? C. However, some experiments suggest that maximum temperatures of about 75, 90, 100, 150, 200 degrees C. may be sufficient for performing the sulfiding process step S2 as mentioned above. Also, lower temperatures are beneficial preserving the mechanical and stable properties of the Ni foam. For example, FIG. 4 shows pre-treatment S_Pre with heating following by S1 (for example metal electroplating) and S2 (for example sulfiding by H.sub.2S treatment shown in FIG. 6), where post-treatment S_Post with heating is followed by a first repeating of S1 and S2, the repeating being name S3.

[0085] In FIG. 6, a sulfiding is performed in a heated oven, where a flow of H.sub.2S containing gas in various concentration, such as 1-10%, is flowing through the Ni foam substrate. The sulfiding may be considered completed from a practical point of view when the gas is flowing through the Ni foam as schematically indicated to the right in FIG. 6 end there is no longer any H.sub.2S consumption.

Example 9: Example 5-8 Including Additional Steps of the Step1 and/or Step2 Types

[0086] In another embodiment of the proposed production of electrodes one might combine example 5-9 with any other number of Step 1 (S1) and/or Step 2 (S2) including one or more post-/pre-treatments/intermediate treatments and permutations hereof, as for example shown in FIG. 4.

Example 10: Example 5-9 Including Other Metals

[0087] Other metals such as Cr, Fe, and/or Cu could be applied, and instead of sulfiding step2 could involve Se or Te as explained above.

Example 11: Sulfiding of Ni FoamSEM Images and Polarization Curves

[0088] FIG. 8 shows the effect of sulfiding a Ni foam in 3% H.sub.2S at 75 deg. C., where the two left SEM images (high and low magnification) shows the pure Ni surface before sulfiding, whereas the middle and right SEM images show the effect of 1 hours and 2 hours sulfiding, respectfully. The sulfiding effect is clearly seen on the surface and the interpretation is that the sulfiding is creating new surface morphology, higher surface area and a new types of active nano sites.

[0089] FIG. 9 shows three polarisation curves for the necessary voltage for hydrogen/oxygen formation as a function of the applied current density in 30% KOH at 90 deg. C. for various treatment of Ni foam. The upper, solid curve is for Ni foam at the cathode (C) and Ni foam at the anode (A). The lower, dotted curve is the needed voltage for hydrogen formation at the cathode (C) (ex situ sulfided in a furnace) and pure Ni foam at the anode (A). Clearly, a significantly lower voltage is needed for hydrogen formation. The middle, hashed curve shows the performance of a H.sub.2S treated (ex situ in a furnace) Ni foam at the cathode (C) and pure Ni foam at the anode (A). This clearly show that sulfiding has an impact on both the anode (oxygen formation) and cathode (hydrogen formation). Measured data are shown as points whereas the three fitted curves are based on average values.

REFERENCES

[0090] [A] N. Y. Tops?e & H. Tops?e, Adsorption studies on hydrodesulfurization catalysts. Infrared and volumetric study of NO adsorption on alumina-supported Co, Mo, and CoMo catalysts in their calcined state. Journal of Catalysis 75(1982), 354-374. [0091] [B] N. Y. Tops?e & H. Tops?e, Characterization of the structures and active-sites in sulfided CoMo/Al.sub.2O.sub.3 and NiMo/Al.sub.2O.sub.3 catalysts by No chemisorption. Journal of Catalysis 84(1983)386-401. [0092] [C] H. Tops?e, B. S. Clausen & F. E. Massoth, Hydrotreating Catalysis Vol. 11 (Springer Verlag, 1996). [0093] [D] Poul Georg Moses, Berit Hinnemann, Henrik Tops?e, Jens K. N?rskov, Spectroscopy, microscopy and theoretical study of NO adsorption on MoS.sub.2, Journal of Catalysis Volume 268(2009)201-208. [0094] [E] H. Tops?e, The role of CoMoS type structures in hydrotreating catalysts, Applied Catalysis A: Volume 322(2007), 3-8. [0095] [F] Nan-Yu Tops?e, Anders Tuxen, Berit Hinnemann, Jeppe V. Lauritsen, Kim G. Knudsen, Flemming Besenbacher, Henrik Tops?e, Spectroscopy, microscopy and theoretical study of NO adsorption on MoS.sub.2 and CoMoS hydrotreating catalysts, Journal of Catalysis, 279(2011)337-351.

[0096] In short, the present invention relates to a method for producing an electrode for alkaline electrolysis based on a composition of metal sulfides on a Ni foam substrate. The metal can be Mo, Ni, Co, Fe and/or W. In a first step S1), there is performed a metal deposition, e.g. by electroplating, the metal, Me1/Me2, being Mo, Ni, Co, Fe, and/or W, on a Ni foam substrate resulting in a metal-Ni compound being formed on and/or in the Ni foam substrate. In a second step, S2) there is performed a sulfiding on the metal-Ni compound from the first step S1). The third step S3) is an optional repetition of S1 and/or S2 at least one time. The step S1) and step S2) thereby results in the formation of electrocatalytic active nano-sites with Me1-Me2-SNi compounds. It is found that these nano-sites are capable of reducing the so-called overpotential of the electrodes during alkaline water electrolysis, and the production of electrodes may be significantly simplified.