The present disclosure relates to a porous metal plate material , such as a sieve , screen or a plate electrode , and to an electrodeposition process of producing such a porous metal plate material .

Hitherto , such porous plates can for example be made by connecting an electroconductive perforated substrate , such as a flat sheet or drum, as a cathode in an electroplating bath containing an electrolyte liquid . During the electrodeposition process , conditions are maintained for preferential growth, i . e . , the metal deposition does not grow evenly in every direction but mainly in flow direction of the electrolyte flow . The metal plate material has apertures of the same si ze and shape in the same pattern as the perforated substrate , resulting in the desired porosity of the metal plate material . The porous metal plate material can for example be used as a filter or sieve or as a flow-through plate electrode . The porous plate material can be plane or non-planar .

Preferential growth can for example be achieved by maintaining an electrolyte flow in through the apertures of the perforated plate in the desired growth direction, and/or by adding an ef fective amount of a brightener to the electrolyte , and/or by using a pulse plating electric current .

NL1021096 discloses such a process using a perforated substrate with slit-shaped perforations with short material bridges bordering the short sides of the slits , and longitudinal material bridges at the long sides of the slits . During the electrodeposition process , deposition of the metal takes place predominantly on the short material bridges at the short ends of the slits . This results in pin-shaped protrusions at the short ends of the slits and, consequently, in an enhanced speci fic surface area ( total m ² /m ² of mesh surface ) .

Due to the enhanced speci fic surface area, such metal plate materials are particularly suitable as gas permeable flow- through plate electrodes , e . g . , for electrolysis of water . Electrolysis of water is a process for the production of hydrogen . In alkaline water electrolysis , the two electrodes are immersed in a highly concentrated aqueous alkali solution, e . g . , a KOH solution . Hydrogen is produced in the cathode compartment by reduction of hydrogen cations , while in the anode compartment oxygen is produced by oxidation of hydroxide anions . Since the oxidation and reduction reactions take place at the surface of the electrodes , the speci fic surface area of the electrodes should preferably be maximi zed . On the other hand, the generated hydrogen and oxygen gases should swi ftly be released and discharged from the electrode surface and blockage of the pores of the electrode by gas bubbles should be prevented .

It is therefore desirable to provide a porous metal plate material which can be made with substantially enhanced speci fic surface area .

To this end, the invention provides a porous metal plate material comprising a perforated metal base plate and an electrodeposited layer with protrusions on at least one side of the perforated metal base plate made by electrodeposition while conditions are maintained for preferential growth . The perforated metal base plate has a pattern of apertures spaced by material bridges . The apertures include apertures bordered by bridges of varying width .

According to the teachings of NL1021095 , protrusions are grown on the material bridges only at the outer ends of the slit-shaped apertures . It has now been found that protrusions can also be obtained by varying the shortest distance between adj acent apertures , e . g . , by varying the width of the material bridges and/or the width of nodal points , also with non-slit shaped apertures. Patterns can be used with a high density of bridges, which offers a very effective way to optimize specific surface area and porosity of the produced porous plate material, The individual bridges can for example each have a constant width with some bridges being wider than other bridges. For example, the bridges in length direction of a row of apertures can have a larger or smaller width than the bridges between adjacent rows of apertures. Alternatively, or additionally, the individual bridges can each have a varying width, e.g., at a side where the apertures do not have a straight outline. This will for instance be the case with circular or star shaped apertures or the like.

In a particular embodiment, the ratio Rbri ge of the width Ww of the widest bridge adjacent an aperture and the width Wn of the narrowest bridge adjacent the same aperture is R > 1,0.

The apertures can be slit-shaped but can also be polygonal, e.g., triangular or square, or circular, oval, elliptical, or star-shaped. Combinations of apertures with different outlines and/or sizes can also be used. Hence, the disclosure also pertains to a porous metal plate material comprising a perforated metal base plate and an electrodeposited layer with pin-shaped protrusions on at least one side of the perforated metal base plate made by electrodeposition while conditions are maintained for preferential growth, wherein the perforated metal base plate has a pattern of apertures spaced by material bridges, and wherein the apertures are non-split shaped, e.g., triangular or square, or circular, oval, elliptical, or star-shaped. In this respect, pin-shaped protrusions are deposition peaks of electrodeposited material.

Good results are achieved if the ratio Rbridge > 1,1, e.g., > 1,4.

The apertures are generally arranged in a regular pattern, e.g., in rows and columns. A high density of pin-shaped protrusions can be obtained i f positions with the largest distance to the nearest aperture are of fset from the nearest center line of a row including said aperture . In that case , a twin pair of protrusions can be obtained on a single bridge or a protrusion with two peaks .

The apertures in the perforated metal base plate can for example have a width or diameter of about 5 - 500 micrometer . The apertures can be aligned, parallel , equidistant and uni form, but other patterns can also be used .

In the context of the present disclosure , a bridge is the material between two adj acent apertures . Apertures of a pair are considered adj acent i f the shortest line between the two does not cross another aperture or a bridge between another pair of apertures that are closer to each other . The width of a bridge at a given point on that bridge is the shortest distance at that point between two adj acent apertures .

The porous metal plate material can for example be made by an electrodeposition process using an electroconductive perforated metal base plate as a cathode in an electroplating bath containing an electrolyte liquid comprising at least one reduction inhibitor, such as a brightener or levelling agent , wherein the perforated metal base plate has a pattern of apertures spaced by material bridges , wherein a flow of the electrolyte liquid is maintained through the apertures from an upstream side of the porous plate material to a downstream side ; wherein the apertures include apertures bordered by bridges of varying width . In this respect , the width is considered varying i f the width variations exceed engineering tolerances or measurement margins .

The width per individual bridge may vary and/or the ratio Rbridge of the width Ww of the widest bridge adj acent an aperture and the width Wn of the narrowest bridge adj acent the same aperture is R > 1 , 0 . The average flow velocity V is defined as the ratio between the volume flow rate and the j oint cross sectional flow- through area of all apertures , the so-called open area . The average flow velocity V may for example be at least 2 cm/ s .

I f the average flow velocity is at least 10 cm/ s , a very irregular structure of protrusions is obtained, which was found to be particularly useful for the production of gas permeable plate electrodes . Therefore , the invention also relates to an electrodeposition process using an electroconductive perforated metal base plate as a cathode in an electroplating bath containing an electrolyte liquid comprising at least one reduction inhibitor, such as a brightener or levelling agent , wherein the perforated metal base plate has a pattern of apertures , wherein a flow of the electrolyte liquid is maintained through the apertures from an upstream side of the porous plate material to a downstream side with an average flow velocity of at least 10 cm/ s , e . g . , at least 12 cm/ s .

Alternatively, or additionally, positioning of peak deposition can also be controlled by varying the width of nodal points linking adj acent material bridges . Therefore , the invention also relates to a process of producing a porous metal plate material by electrodeposition using an electroconductive perforated metal base plate as a cathode in an electroplating bath containing an electrolyte liquid comprising at least one reduction inhibitor, such as a brightener or levelling agent , wherein the perforated metal base plate has a pattern of apertures spaced by material bridges , wherein a flow of the electrolyte liquid is maintained through the apertures from an upstream side of the perforated metal base plate material to a downstream side , wherein said bridges include at least two groups of parallel rows of bridges , the rows being uninterrupted by said apertures, the rows of one of the groups crossing another one of the groups of rows. This way, different rows of bridges cross each other at nodal points which are at least 1,4 times wider than the bridges themselves if the bridges are of equal width.

In a particular embodiment, the pattern of apertures and bridges may have a rotational symmetry at least of the order 3, e.g., at least 4. The "order of rotational symmetry" is the number of times a pattern coincides with itself when rotated through 360°. A higher order or rotational symmetry results in larger nodal points.

The reduction inhibitor inhibits reduction of the cations and hinders deposition of the metal. It was found that the local geometry of apertures and bridges, e.g., by varying the shortest distance between adjacent apertures, in particular by varying the width of the bridges and/or nodal points, can be used to control variations along the outline of each aperture of local concentrations of reduction inhibitor resulting in a desired texture and pattern of deposition peaks or protrusions.

Suitable reduction inhibitors include brighteners and leveling agents. During the electrodeposition process, such compounds are easier reduced than the metal cations, so they inhibit deposition of the metal. Specific examples include carrier brighteners (e.g. paratoluene sulfonamide, benzene sulphonic acid) in a concentration of about 0.75-23 g/1, levelers, second class brighteners (e.g. allyl sulfonic acid, formaldehyde chloral hydrate) , and auxiliary brighteners, e.g., sodium allyl sulfonate, pyridinium propyl sulfonate, e.g., in concentrations of 0.075-3.8 g/1. Alternatively, or additionally, inorganic brighteners, such as cobalt or zinc can be used in concentration 0.075-3.8 g/1. Particular examples of suitable brighteners include for example 1- (2-hydroxy-3-sulfopropyl) - pyridinium betaine, 1- ( 3-sulfopropyl ) -pyridinium betaine (PPS) , propionitrile, hydroxy propionitril (HPN) , 2-butyn-l, 4-diol, 1,4 butyndiol, 3-butyn-l-ol, 3-pentyn-l-ol, 1- ( 3-sulfopropyl ) , 2- vinylpyridinium betaine, thio ureum, fumaronitrile, propargyl alcohol, amino-acetonitril-hydrogen chloride, diallyl amine, 2- propyn-l-ol, chinoxaline, 3-amino propionitril fumarate, 1,4- butyndiol diethoxylaat , ethylene cyanohydrine, 1- ( 2-hydroxy-3- sulfopropyl) pyridine and 4-benzyl-l- ( 3-sulfopropyl ) -pyridinium betaine .

In general, higher concentrations of reduction inhibitors result in larger protrusions. Suitable concentrations are for example 250 mg/1 or more. During the electrodeposition process, the reduction inhibitor is consumed. The average concentration of reduction inhibitor in the electrolyte can be maintained at a constant level, e.g., by means of an in-line system for measurement and dosing.

The process is particularly useful for the production of porous material based on, e.g., nickel or copper. Suitable electrolytes include nickel sulfamate, nickel sulfate or nickel chloride baths, e.g., in a concentration of 50 - 800 g/1, preferably 300 - 450 g/1.

During the electrodeposition process, the electric current through the perforated metal base plate can for example be maintained at about 5 - 20 A/ dm ² . Other parameters, such as pH and temperature can be kept at the usual levels for electrodeposition, e.g., with a pH below 6, and a temperature above 50°C.

Good results are obtained if the perforated metal base plate, used as a starting material, is made of nickel or a nickel alloy. Other electroconductive materials, such as steel, copper, or brass can also be used.

The perforated metal base plate used as a starting material for the disclosed process can for example be plate shaped or be a rotating drum, e.g., enabling to configure the electrodeposition process as a continuous roll-to-roll process. The perforated metal base plate can for example be made by electrodeposition . The produced porous metal plate material can be a flat, plane plate or sheet. Alternatively, it can be formed as a cylinder or have any other suitable configuration. The porous metal plate material can have any desired thickness. If it used as an electrode, it can for instance have a thickness of up to about 5 mm (including the height of the pin-shaped protrusions) , e.g., at least about 0,01 mm, e.g., 0,8 - 1,3 mm, e.g., up to 1 mm.

The pin-shaped protrusions can extend from one side or from both sides. To obtain protrusions at both sides of the perforated metal base plate, the flow direction of the electrolyte can be reversed during the process.

The pin-shaped protrusions may all have substantially the same length or may be of different lengths, if so desired. The pin-shaped protrusions can for example have length of up to about 1000 pm. The pin-shaped protrusions may for example have a maximum diameter of about 120 - 180 pm. The core-to-core distance between adjacent pin-shaped protrusions can for example be about 150 - 350 pm.

The effective surface area of the resulting porous metal plate can for example be at least 4 times, e.g., at least 6 times the gross surface area (width times height) of the perforated metal base plate. Optionally, the specific surface area of the porous metal plate can be enhanced further, e.g., by means of a surface area enhancing coating. Examples of such surface area enhancing coatings, particularly for alkaline electrolysis, are disclosed in WO 2010/063695 and EP 3 159 433 Al. In the thesis of Kraglund, M. R., & Christensen, E. (2017) , Alkaline membrane water electrolysis with non-noble catalysts, Department of Energy Conversion and Storage, Technical University of Denmark, electrodes are disclosed having Raney nickel coating for enhancing the specific surface area.

The porous metal plate material can for example be used as a sieve, filter or screen, or as a catalyser, as a textured roller, or as a flow-through plate electrode , such as an anode or cathode in an electrolysis cell or a fuel cell . Such an electrode is particularly useful in cells for the electrolysis of water, more particularly as a cathode in alkaline electrolysis .

The electrode can be used in an electrolysis cell comprising :

- an electrolyte reservoir ;

- a membrane or separator, separating the electrolyte reservoir into an oxygen producing section and a hydrogen producing section;

- a gas di f fusion anode on a first surface of the separator in the oxygen evolution reaction ( OER) section;

- a gas di f fusion cathode on a second surface of the separator in the hydrogen evolution reaction (HER) section; wherein the gas di f fusion cathode and/or cathode is an electrode according to the present disclosure .

Very good results are obtained, when the pin-shaped protrusions of the gas di f fusion cathode point towards the separator . This results in higher current densities at lower voltages . In a zero gap arrangement , the tips of the pin-shaped protrusions may for example abut the separator .

The electrode can for example be made of a non-noble metal or its alloy . Alloys showing high catalytic activity in hydrogen evolution reactions (HER) include alloys of hypo-d- electronic metals , such as nickel or iron, with hyper-d- electronic elements , such as molybdenum wol fram, titanium, niobium or rhodium . Very good results are achieved with nickel . Among non-noble metals , nickel is one of the most stable in strong alkaline solutions and is also a good catalyst for hydrogen and oxygen formation . Nickel alloys can also be used . For example , a nickel iron alloy, e . g . , comprising up to about 10% of iron, was found to be particularly suitable as an anode . Nickel alloys comprising vanadium, molybdenum and/or manganese were found te be particularly suitable for use as a cathode .

The above-described aspects will hereafter be more explained with further details and benefits with reference to the drawings showing a number of embodiments by way of example .

Figure 1A: shows an exemplary embodiment of a perforated substrate in top view for use in the process of the present invention;

Figure IB : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 1A;

Figure 2A: shows a second exemplary embodiment of a perforated substrate in top view;

Figure 2B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 2A;

Figure 3A: shows a third exemplary embodiment of a perforated substrate in top view;

Figure 3B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 3A;

Figure 4A: shows a fourth exemplary embodiment of a perforated substrate in top view;

Figure 4B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 4A;

Figure 5A: shows a fi fth exemplary embodiment of a perforated substrate in top view;

Figure 5B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 5A;

Figure 6A: shows a sixth exemplary embodiment of a perforated substrate in top view;

Figure 6B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 6A;

Figure 7A: shows a seventh exemplary embodiment of a perforated substrate in top view; Figure 7B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 7A;

Figure 8A: shows an eighth exemplary embodiment of a perforated substrate in top view;

Figure 8B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 8A;

Figure 9A: shows a ninth exemplary embodiment of a perforated substrate in top view;

Figure 9B : shows a photograph of a detail of a porous metal plate produced with the substrate of Figure 9A;

Figure 10 : shows an electrolysis cell with an electrode according to the invention .

Example 1

A perforated metal base plate 1 was provided with a pattern of apertures 2 and bridges 3 as shown in Figure 1A. The perforated metal base plate 1 was made by electrodeposition of nickel .

The apertures 2 are slits with rounded edges having a length of 0 , 44 mm and a width of 0 , 22 mm .

The bridges 3 between the outer ends of the oval slits have a varying width . The apertures 2 are arranged in lines along a central axis LI . Positions P with the largest distance to the nearest aperture 2 are of fset from the center line LI in the wider nodal points . The apertures 2 of each line are staggered from the apertures 2 of an adj acent line . The material bridges 3 include three groups of parallel rows Rl , R2 , R3 of bridges , the rows being uninterrupted by the apertures .

The perforated metal base plate 1 was activated with a Wood' s nickel strike bath and rinsed . The perforated metal base plate was then positioned as a flow-through cathode in an electrolyte bath of a nickel sul famate solution comprising more than 250 mg/ 1 of 1- ( 3-sul fopropyl ) -pyridinium betaine as a reduction inhibitor . Deposition took place at 13 A/ dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate with an average flow velocity of 7 cm/ s . The pH was below 5 . The temperature was above 50 ° C .

The resulting texture is shown in Figure IB . Protrusions 4 grow predominantly on the positions P and curve back to the outer ends of the respective apertures to form lipshaped edges .

Example 2

A perforated metal base plate 1A was provided with a pattern of apertures 2A and bridges 3A as shown in Figure 2A. The apertures 2A are rather similar to the apertures 2 in Figure 1A, except in that the straight longitudinal sides are somewhat longer . The ratio Rbridge between the shortest width Ww between the longitudinal sides and the shortest width Wn between the outer ends is Rbridge = 1 , 1 .

The perforated metal base plate 1A was made by electrodeposition of nickel .

The perforated metal base plate 1A was activated with a Wood' s nickel strike bath and rinsed . The perforated metal base plate 1A was then positioned as a flow-through cathode in an electrolyte bath of a nickel sul famate solution comprising more than 250 mg/ 1 of 1- ( 3-sul fopropyl ) -pyridinium betaine as a reduction inhibitor . Deposition took place at 13 A/ dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate 1A with an average flow velocity of 4 cm/ s . The pH was below 5 . The temperature was above 50 ° C .

The resulting texture is shown in Figure 2B . Protrusions 4A grow predominantly on the positions P . The bridges at the rounded ends have two of such protrusions , which fuse at the base due to the short distance . This results in twin peak protrusions .

Example 3

A perforated metal base plate IB was provided with a pattern of apertures 2B and bridges 3B as shown in Figure 3A. The apertures 2B were diamond shaped and had a length of 0,31 mm and a width of 0,23 mm. The material bridges 3B include three groups of parallel rows Rib, R2b, R3b of bridges 3, the rows being uninterrupted by the apertures 2B.

The bridges 3B at the outer points of the diamond shaped apertures 2B have a width Wn of 0,11 mm. The bridges 3B between the lateral sides of the apertures have a width Ww of 0,18 mm.

Hence, the ratio Rbridge of the width Ww of the widest bridge adjacent an aperture and the width Wn of the narrowest bridge is Rbridge = 1, 7. The apertures 2B are arranged in lines along a central axis L2. The apertures 2B of each line are offset from the apertures 2B of an adjacent line, in a staggered arrangement .

The perforated metal base plate IB was activated with a Wood's nickel strike bath and rinsed. The perforated metal base plate IB was then positioned as a flow-through cathode in an electrolyte bath of a nickel sulfamate solution comprising more than 250 mg/1 of 1- ( 3-sulfopropyl ) -pyridinium betaine as a reduction inhibitor. Deposition took place at 13A/dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate with an average flow velocity of 4,3 cm/s .

The resulting texture is shown in Figure 3B. Protrusions 4B grow predominantly on nodes between three adjacent apertures and fuse at the base, particularly on the wider bridges.

Example 4

A perforated metal base plate 1C was provided with a pattern of apertures 2C and bridges 3C as shown in Figure 4A. The apertures 2C were diamond shaped and had a length of 0,21 mm and a width of 0,11 mm. The material bridges 3C include three groups of parallel rows Rlc, R2c, R3c of bridges 3C, the rows being uninterrupted by the apertures 2C. The bridges 3C at the outer points of the diamond shaped apertures have a width Wn of 0,11 mm which is equal to the width Ww of the bridges 3C between the lateral sides of the apertures, so the ratio Rbridge = 1- The apertures 2C are arranged in lines along a central axis L3. The apertures 2C of each line are offset from the apertures of an adjacent line.

The perforated metal base plate 1C was activated with a Wood's nickel strike bath and rinsed. The perforated metal base 1C plate was then positioned as a flow-through cathode in an electrolyte bath of a nickel sulfamate solution comprising more than 250 mg/1 of 1- ( 3-sulfopropyl ) -pyridinium betaine as a reduction inhibitor. Deposition took place at 13A/dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate 1C with an average flow velocity of 4,7 cm/s .

The resulting texture is shown in Figure 4B. Protrusions 4C grow predominantly on nodes between three adjacent apertures. Example 5 A perforated metal base plate ID was provided with a pattern of apertures 2D and bridges 3D as shown in Figure 5A. The apertures 2D were slit-shaped and had a length of 0,44 mm and a width of 0,03 mm.

The bridges 3D at the outer points of the apertures 2D have a width Wn of 0,19 mm. The bridges 3D between the lateral sides of the apertures 2D have a width Ww of 0,13 mm.

Hence, the ratio Rbridge of the width Ww of the widest bridge adjacent an aperture 2D and the width Wn of the narrowest bridge is Rbridge = 1,5. The apertures 2D are arranged in lines along a central axis L4. The apertures 2D of each line are offset from the apertures 2D of an adjacent line in a staggered arrangement .

The perforated metal base plate ID was made by electrodeposition of nickel. The perforated metal base plate ID was activated with a Wood' s nickel strike bath and rinsed . The perforated metal base plate ID was then positioned as a flow-through cathode in an electrolyte bath of a nickel sul famate solution comprising more than 250 mg/ 1 of 1- ( 3-sul fopropyl ) -pyridinium betaine as a reduction inhibitor . Deposition took place at 13A/dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate ID with an average flow velocity of 10 cm/ s .

The resulting texture is shown in Figure 5B . The protrusions 4D grow predominantly on the wider bridges between the outer ends of the apertures 2D in a very regular pattern . Example 6 A perforated metal base plate IE was provided with a pattern of apertures 2E and bridges 3E as shown in Figure 6A. The apertures 2E were triangular with three sides of equal length of 0 , 07 mm .

Each triangular aperture 2E is surrounded by four triangular apertures 2E of the same si ze but pointing in an opposite direction, resulting in varying widths of the bridges 3E . The material bridges 3E include three groups of parallel rows Rle , R2e , R3e of bridges 3E , the rows being uninterrupted by the apertures 2E .

The perforated metal base plate IE was made by electrodeposition of nickel .

The perforated metal base plate IE was activated with a Wood' s nickel strike bath and rinsed . The perforated metal base plate IE was then positioned as a flow-through cathode in an electrolyte bath of a nickel sul famate solution comprising more than 250 mg/ 1 of 1- ( 3-sul fopropyl ) -pyridinium betaine as a reduction inhibitor . Deposition took place at 13A/dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate IE with an average flow velocity of 17 cm/ s . The resulting texture is shown in Figure 6B . The protrusions 4E grow predominantly between the tips of the triangular apertures 2E.

Example 7

A perforated metal base plate IF was provided with a pattern of apertures 2F and bridges 3F as shown in Figure 7A. The apertures 2F were circular with a diameter of 0,06 mm.

The shortest distance between two adjacent apertures was 0,10 mm.

Each circular aperture 2F is equidistantly surrounded by six circular apertures 2F of the same size, resulting in a varying widths of the bridges 3F. The material bridges 3F include three groups of parallel rows Rif, R2f, R3f of bridges 3F, the rows being uninterrupted by the apertures 2F. Hence, three rows of bridges 3F cross each other at every nodal point. The pattern of apertures 2F and bridges 3F has a rotational symmetry of the order 6.

The perforated metal base plate IF was made by electrodeposition of nickel.

The perforated metal base plate IF was activated with a Wood's nickel strike bath and rinsed. The perforated metal base plate IF was then positioned as a flow-through cathode in an electrolyte bath of a nickel sulfamate solution comprising more than 250 mg/1 of 1- ( 3-sulfopropyl ) -pyridinium betaine as a reduction inhibitor. Deposition took place at 13A/dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate IF with an average flow velocity of 10, 6 cm/s .

The resulting texture is shown in Figure 7B. The protrusions 4F grow predominantly on the nodes between three adjacent circular apertures.

Example 8 A perforated metal base plate 1G was provided with a pattern of apertures 2G and bridges 3G as shown in Figure 8A. The apertures 2G were star-shaped with a largest width of 0 , 14 mm .

Each star-shaped aperture 2G is surrounded by six apertures 2G of the same shape and si ze , resulting in a varying widths of the bridges 3G . The material bridges 3G include three groups of parallel rows Rig, R2g, R3g of bridges 3G, the rows being uninterrupted by the apertures 2G .

The perforated metal base plate 1G was made by electrodeposition of nickel .

The perforated metal base plate 1G was activated with a Wood' s nickel strike bath and rinsed . The perforated metal base plate 1G was then positioned as a flow-through cathode in an electrolyte bath of a nickel sul famate solution comprising more than 250 mg/ 1 of 1- ( 3-sul fopropyl ) -pyridinium betaine as a reduction inhibitor . Deposition took place at 13 A/ dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate 1G with an average flow velocity of 9 , 3 cm/ s .

The resulting texture is shown in Figure 8B . The protrusions 4G grow in an irregular pattern .

Example 9

A perforated metal base plate 1H was provided with a pattern of apertures 2H and bridges 3H as shown in Figure 8A. The apertures 2H were square with a largest width of 0 , 14 mm . Each square aperture 2H is surrounded by eight apertures 2H of the same shape and si ze . The material bridges 3H include two groups Rih, R2h of parallel rows of bridges 3H, the rows being uninterrupted by the apertures 2H . The bridges 3H of the first group of rows are under right angles with the second group of rows of bridges 3H, resulting in nodes 5H having a width of about 1 , 4 times the width of the adj acent material bridges 3H . The pattern of apertures 2H and bridges 3H has a rotational symmetry of the order 4 .

The perforated metal base plate 1H was made by electrodeposition of nickel .

The perforated metal base plate 1H was activated with a Wood' s nickel strike bath and rinsed . The perforated metal base plate was then positioned as a flow-through cathode in an electrolyte bath of a nickel sul famate solution comprising more than 250 mg/ 1 of 1- ( 3-sul fopropyl ) -pyridinium betaine as a reduction inhibitor . Deposition took place at 13 A/ dm ² / 17 Ah/dm ² . A flow of electrolyte was maintained through the perforated metal plate with an average flow velocity of 9 , 3 cm/ s .

The resulting texture is shown in Figure 9B . The protrusions 4H grow in a very regular pattern .

Figure 10 shows an electrolysis cell 21 for the alkaline electrolysis of water to produce oxygen and hydrogen gases . The electrolysis cell 21 comprises an electrolyte reservoir 22 filled with an alkaline electrolyte liquid . A membrane or separator 23 separates the electrolyte reservoir 22 into an oxygen evolution reaction ( OER) section 24 and a hydrogen evolution reaction (HER) section 25 . A gas di f fusion anode 26 is mounted to a first surface of the separator 23 in the OER section 24 . A gas di f fusion cathode 27 is mounted to the opposite surface of the separator 23 in the HER section 25 .

The gas di f fusion cathode 27 is a porous metal plate as shown in Figure IB or 2B, and has pin-shaped protrusions 29 . The pin-shaped protrusions 29 extend into the direction of the separator 23 . In the zero-gap arrangement of Figure 3 , the pinshaped protrusions 29 abut the separator 23 . The gas di f fusion anode 26 can for example be a regular mesh electrode . The electrolysis cell 21 is bordered by bipolar plates

28 conducting electric current from or to further cells (not shown) of a stack .