Patent Description:
The present invention relates to an electrolytic cell for the production of hydrogen (H<NUM>).

Some scientific research has long been committed to the production of energy that does not involve the use of fossil fuels. Such a need stems both from the progressive decrease in oil reserves and from an increased attention to environmental issues.

The use of renewable energy sources, increasingly widespread and distributed in the territory, has led to the need to develop energy storage systems. Renewable Energy Sources are, by their nature, non-programmable and their availability does not always coincide with our needs. It is, therefore, necessary to try to store that energy that is sold off cheaply and which could not be put into the electricity distribution network. One of the most promising solutions is to use this energy to produce the first of the energy carriers: hydrogen. The storage and the use of hydrogen will allow us to obtain energy when we need it.

This gas, in fact, is an energy carrier that can meet energy demands and, above all, has a very low environmental impact since it does not produce pollutants such as carbon dioxide or greenhouse gases. Hydrogen can be used to obtain both thermal energy, thanks to its combustion, and electrical energy, thanks to special electrochemical devices called fuel cells. In both cases, hydrogen binds to oxygen forming water as the only reaction product, which makes it extremely environmentally friendly. Hydrogen has the additional advantage of being able to be produced in a non-polluting manner, using a photovoltaic cell system to produce the current necessary for the dissociation by electrolysis of the water solution. Finally, hydrogen has the great advantage of being extremely light and of therefore possessing a high energy density per unit mass.

As is known, electrolysis can be used to break down water into oxygen and hydrogen gases.

In particular, at the cathode hydrogen ions acquire electrons in a reduction reaction leading to hydrogen gas, while at the anode hydroxide ions undergo oxidation leading to the formation of oxygen gas.

The device in which the electrolysis of the water solution takes place is called electrolytic cell. Usually, the electrolytic cell is composed of two half-elements, also called half-cells, kept separate by a semi-permeable membrane, or they are contained in separate containers and connected by a salt bridge. The function of the semi-permeable membrane and of the salt bridge is to allow the passage of an internal ionic current that is necessary so that in each of the half-elements the necessary conditions are maintained to favour the respective redox reaction.

In particular, the purpose of the semi-permeable membrane is to keep the two gases produced separate from each other, while still allowing the passage of ions. In fact, in the electrolysis of the water solution, an electrolytic cell must be used, whose components are able to guarantee the separation of the hydrogen and oxygen produced.

As may be immediately apparent to a person skilled in the art, the presence of the structural salt bridge or of the semi-permeable membrane constitutes a significant cost in the global economy of the electrolysers. This cost derives both from the energy consumptions linked to the activity of the salt bridge and from the intrinsic value of the semi-permeable membranes.

In the sector, there was a need for an electrolytic cell, whose technical characteristics are such as to guarantee both the separation from each other of hydrogen and oxygen produced during electrolysis, and the correct maintenance of the electrolytic solution without having to use either a salt bridge or a semi-permeable membrane.

Patent <CIT> in the name of the Applicant describes an electrolytic cell which does not require either a structural salt bridge or a semi-permeable membrane. In fact, the electrolytic cell described in <CIT> substantially provides for a double passage of the water solution through an electrode consisting of a metal sheet, wherein a plurality of holes are obtained and wherein the electrolysis takes place exclusively during the second crossing of the respective electrode. This characteristic and the continuous recirculation of the water solution guarantee an automatic separation of the two gases produced during the electrolysis and, at the same time, a passage of the ions between the two half-elements. In addition, the two gases produced during the electrolysis will not be able to mix with each other, since, after being produced exclusively inside the holes of the respective metal sheet, they are each pushed into a respective discharge tank to be then treated by a respective degasser.

Although the electrolytic cell subject-matter of patent <CIT> already entails important advantages in itself with respect to the prior art, nevertheless the Applicant has realized a new electrolytic cell that represents an advance in terms of efficiency and safety.

Basically, a series of technical characteristics have been added to the electrolytic cell described in <CIT> that with different relevance increase its effectiveness and safety.

Object of the present invention is an electrolytic cell for the electrolysis of a water solution, whose essential characteristics are reported in Claim <NUM> and whose auxiliary or preferred characteristics are reported in the dependent Claims.

In this document, any position indications, such as "vertical", "horizontal", "above", "below", "upper" and "lower", is relative to the operating position of the electrolytic cell as shown in the attached Figures. As may be immediately apparent to a person skilled in the art, for obvious functional reasons, the operating position of the electrolytic cell according to the present invention cannot be different from that shown.

Hereinafter an embodiment is reported for illustrative and non-limiting purposes with the aid of the accompanying Figures, wherein:.

In <FIG> denotes as a whole an electrolytic cell according to the present invention. The electrolytic cell <NUM> is composed of two separate units <NUM> and <NUM> coupled together to define internally an electrolysis chamber C (<FIG>), in which the water solution to be electrolyzed is housed as will be described below, and two water solution external recirculation circuits <NUM> each of which is connected to a respective degasser <NUM>. Both the external recirculation circuits <NUM> and the degassers <NUM> are shown in <FIG> in an extremely schematic form.

As will be described below, the electrolysis chamber C is internally subdivided into a plurality of compartments which are crossed by the water solution during the different steps of the electrolysis process to which it is subjected.

The two separate units <NUM> and <NUM> below will be called half-elements to recall the terminology of the electrolytic cells.

Each of the half-elements <NUM> and <NUM> comprises an inlet sleeve <NUM> for feeding the respective half-element with the water solution and an outlet sleeve <NUM> to allow the water solution and the gases produced by the respective half-element to outflow.

As shown in <FIG>, the external recirculation circuits <NUM> hydraulically connect the outlet sleeve <NUM> of the half-element <NUM> with the inlet sleeve <NUM> of the half-element <NUM>, and the outlet sleeve <NUM> of the half-element <NUM> with the inlet sleeve <NUM> of the half-element <NUM>. In this way, the water solution that together with the gas produced by the electrolysis comes out of one half-element, is introduced into the other half-element, after the passage through the degasser <NUM>. The two external recirculation circuits <NUM> are operated by two respective known pumps not shown nor described for simplicity's sake.

Contrary to what has been described above, the electrolytic cell of the present invention can provide that the external recirculation circuits hydraulically connect the outlet sleeve directly with the inlet sleeve of the same half-element.

As shown in <FIG> and <FIG>, each of the half-elements <NUM> or <NUM> comprises an electrode composed of a metal sheet <NUM>, one front surface 10a of which is covered by an insulating coating. In the metal sheet <NUM>, as well as in the insulating coating that covers the front surface 10a thereof, there are obtained a plurality of holes <NUM> and a plurality of vertical slits <NUM> parallel to each other.

As shown in <FIG>, each of the half-elements <NUM> and <NUM> comprises a feeding tank <NUM> and a discharge tank <NUM>, which is faced by the rear surface 10b of the metal sheet <NUM>.

The feeding tank <NUM> is hydraulically connected to the inlet sleeve <NUM> through a water solution inlet opening <NUM> and to the vertical slits <NUM> through hollow partitions <NUM> and made of insulating material. In particular, each of the hollow partitions <NUM> defines a hydraulic connection 16a between the feeding tank and the vertical slits <NUM>.

The discharge tank <NUM> is hydraulically connected to the outlet sleeve <NUM> through a water solution outlet opening <NUM> and receives directly from the holes <NUM> the water solution/gas mixture deriving from the electrolysis process.

As shown in <FIG> and <FIG>, both the feeding tank <NUM> and the discharge tank <NUM> are delimited by a same oblique wall <NUM> which determines a vertical narrowing thereof. In particular, the presence of the oblique wall <NUM> gives the tanks <NUM> and <NUM> a triangular vertical section. The inlet <NUM> and outlet <NUM> openings are obtained in the larger portion of the respective tanks <NUM> and <NUM>.

In other words, the feeding tank <NUM> has a large section in the lower part of the cell for the passage of the incoming fluid and then narrows down towards the upper part of the cell with gradually smaller sections. In contrast, the discharge tank has a narrow section in the lower part of the cell and then widens towards the upper part of the cell with gradually larger sections where, therefore, the flow rate of the outgoing electrolysis fluid and gas is maximum.

The narrowing/widening conformation of the tanks <NUM> and <NUM> ensures an improvement of the water solution speed distribution and the usage of all the surfaces of the metal sheet <NUM>, in which the electrolysis takes place and, therefore, the generation of the gases.

In particular, the discharge tank <NUM> is broken down into a plurality of vertical compartments defined by the hollow partitions <NUM> and by the oblique wall <NUM> and by an upper horizontal duct which is faced by the outlet opening <NUM>.

As shown in <FIG>, the electrolytic cell <NUM> comprises a plurality of conveying and stiffening cross members <NUM> housed inside the hollow partitions <NUM>, i.e. in the hydraulic connections 16a.

The presence of the cross members <NUM> guarantees a better distribution of the fluid and at the same time guarantees a stiffening of the walls of the hollow partitions <NUM>.

As shown in <FIG> the electrolytic cell <NUM> comprises a plurality of dividing partitions <NUM> housed vertically in the feeding tank <NUM>.

The presence of the dividing walls <NUM> leads to a further optimization of the flow of the water solution. In other words, the dividing partitions <NUM>, by realizing a sort of channels, allow to have, also along the entire vertical development of the metal sheet <NUM>, the maximum uniformity and correct distribution of the fluid flow rates.

Each of the dividing partition <NUM> comprises at a lower end thereof a curved conveying portion <NUM> facing said water solution inlet opening <NUM>. In particular, the conveying portions <NUM> have a staggered position relative to one another from the top to the bottom moving away from said inlet opening <NUM>. The conveying portions <NUM> deflect the incoming water solution (having a horizontal speed) upwards and have the further task of "sectioning" the incoming flow in equal parts, subdividing it and sending very similar flow rates to the various vertical channels realized by the dividing partitions <NUM>.

Again in <FIG>, there is shown a plurality of conveying deflectors <NUM> housed in the upper horizontal duct of the discharge tank <NUM> and each of which extends in the area of a dividing partition <NUM>. The conveying deflectors <NUM> have the function of effectively deflecting the flow of water solution and of gas from the vertical compartments towards the outlet opening <NUM>.

In particular, the conveying deflectors <NUM> have a staggered position relative to one another from the top to the bottom moving close to the outlet opening <NUM>.

Each of the electrodes comprises a hydraulic resistance layer <NUM>, whose task is to achieve a pressure drop of at least <NUM> Pa in the passage of the electrolyte from the electrolysis chamber C to the discharge tank <NUM> (second crossing of the metal sheet <NUM> by the water solution).

The hydraulic resistance layer <NUM> is an electrically insulating layer arranged to cover the holes <NUM> of the respective metal sheet <NUM> and having a mesh structure with a US mesh number ranging from <NUM> to <NUM> (<NUM> and <NUM>). The US mesh number is an Anglo-Saxon unit of measurement corresponding to the number of meshes per linear inch (US mesh). In particular, the mesh structure of the layer <NUM> is not shown in <FIG> and <FIG> for convenience.

Each of the layers <NUM> has a thickness of the order of one-tenth of a mm (approximately <NUM>-<NUM>) and adheres to the non-perforated portions of the metal sheet <NUM> to which it is coupled. After passing this layer <NUM>, in the perforated areas, the water solution comes into contact with the internal surface of the holes of the metal sheet <NUM> causing electrolysis. The internal surface of the holes is the only electrically active surface with which the water solution comes into contact.

The primary task of the layer <NUM> is to realize a hydraulic resistance to the flow of the water solution. The consequent pressure drop must have a sufficient value (≈ <NUM> Pa min) to guarantee a flow as uniform and unidirectional as possible inside the electrolysis holes <NUM>.

By way of example, it can be said that the front dimensions of the electrodes <NUM> are of the order of decimetres (<NUM>-<NUM>m) with a thickness of the order of millimetres (<NUM>-<NUM>m). In the current prototype the dimensions are about 3x4 dm with a thickness of <NUM>. The distance between the two electrodes must be as short as possible and in the current example it has been set at about <NUM>.

About the diameter of the set of holes <NUM>, their diameter is still of the order of millimetres and has been fixed as a first approximation at <NUM>.

The thickness of the electrical insulating coating deposited on the non-perforated parts of the electrode surfaces 10a is of the order of microns (<NUM>-<NUM> m). In particular, the layer shows a thickness of about <NUM>.

The pressure drop of the water solution leads to a more uniform distribution of the speeds of the water solution itself through all the holes in the horizontal sections. The uniformity of the speeds of the water solution (thanks to the presence of the layer <NUM>) that crosses the electrode is the first condition for (i) ensuring that there are no points where the water solution is stopped and that it can therefore not drag the produced gas towards the outlet; (ii) distributing the electrolysis current on the maximum surface of the holes, allowing the maximum yield of the electrode and a uniformly distributed generation of the gases; (iii) allowing a larger scale up of the electrolytic cell from the fluid-dynamic point of view.

Furthermore, each of the half-elements <NUM> and <NUM> comprises a plurality of flow deflectors <NUM> each of which is arranged in front of a respective slit <NUM> of the metal sheet <NUM>, and has the function of deflecting the flow of water solution coming from the feeding tank <NUM> onto the holes <NUM> of the same metal sheet <NUM>.

In use, the water solution enters from the inlet sleeve <NUM> and, through the opening <NUM>, is distributed in the feeding tank <NUM> in order to meet the conveying portions <NUM>, deflect upwards by flowing through the channels delimited by the dividing partition <NUM>, run along the hydraulic connections 16a and, then, outflow from the vertical slits <NUM> thus crossing the metal sheet <NUM> for the first time. Once the water solution outflows from the vertical slits <NUM>, it meets the flow deflectors <NUM> which deflect it against the front surface 10a. In this way, the water solution is forced to cross the metal sheet <NUM> a second time after undergoing the pressure drop by the layer <NUM>. In other words, while the first crossing of the metal sheet <NUM> takes place through the vertical slits <NUM>, the second crossing (in the opposite direction to the first one) takes place through the holes <NUM>.

In particular, the water solution, once the flow deflectors <NUM> have been met, passes through the hydraulic resistance layer <NUM> which achieves a pressure drop ranging from <NUM> Pa to <NUM> Pa.

As anticipated above, the above pressure drop leads to a more uniform distribution of the speed of the fluid through all the holes with the relative advantages in terms of safety and performance that this entails.

During the crossing of the holes <NUM> the water solution undergoes the electrolysis process as the metal sheet <NUM> is connected to a voltage generator. The electrolysis of the water solution takes place exclusively during the second crossing of the metal sheet <NUM> through the holes <NUM>. In fact, the first crossing of the metal sheet <NUM> takes place through the vertical slits <NUM> which are protected by the electrically insulated hollow partitions <NUM> and the front surface 10a is covered by the insulating coating, while the internal walls of the holes are the only electrically conductive portions with which the water solution comes into contact.

In other words, the hollow partitions <NUM> and the insulating coating arranged on the surface 10a ensure that the water solution coming from the feeding tank <NUM>, before crossing the metal sheet <NUM> for the second time, cannot come into contact with any electrically conductive surface.

The water solution and the gas produced by the electrolysis pass into the discharge tank <NUM> (firstly vertical compartments and then upper horizontal duct) and from here, helped by the action of the conveying deflectors <NUM>, exit from the opening <NUM>.

From the opening <NUM> the water solution and the produced gas cross the outlet sleeve <NUM> and pass into the external recirculation circuit <NUM> where they are separated by the respective degasser <NUM>. While the produced gas is collected, the water solution continues in the external recirculation circuit <NUM> to be introduced into the feeding tank <NUM> of the other half-element, or of the same half-element, through the inlet sleeve <NUM>.

Unlike what has been described above, the metal sheet <NUM>, instead of the holes <NUM>, may comprise equivalent lamellate portions consisting of a plurality of mutually parallel lamellae, the extended surfaces of which constitute the active electrolysis surfaces. In this case, each of the lamellate portions will be arranged side-by-side to a vertical slit <NUM>, such that the water solution outflowing from the vertical slit <NUM> will be deflected by the relative flow deflector <NUM> towards the lamellate portion itself. The water solution will then be forced to cross backwards firstly the layer <NUM> and then the metal sheet in the area of the lamellate portion undergoing, during its crossing, the electrolysis process by means of the active surfaces of the lamellae.

As can be easily understood by a person skilled in the art, the technical characteristics of the cell of the present invention with respect to the electrolytic cell described and claimed in patent <CIT>, guarantee a greater uniformity of the speeds of the water solution that crosses the electrode with the advantages in terms of efficiency and safety that this entails.

Claim 1:
An electrolytic cell (<NUM>) for the electrolysis of a water solution comprising two half-elements (<NUM>, <NUM>), each of which comprising a respective electrode comprising a metal sheet (<NUM>) connected to a voltage generator and housed in an electrolysis chamber (C) defined between the two half-elements (<NUM>, <NUM>), and means (<NUM>) for the continuous recirculation of the water solution inside said electrolysis chamber (C); in each one of said metal sheets (<NUM>) there being obtained (i) a plurality of electrolysis openings (<NUM>) having side walls defining sole active electrolysis surfaces and designed to allow a water solution to flow from a front surface (10a) to a rear surface (10b) of said metal sheet (<NUM>) and (ii) a plurality of vertical slits (<NUM>) designed to allow a water solution to flow from the rear surface (10b) to the front surface (10a) of said metal sheet (<NUM>); each one of said half-elements (<NUM>, <NUM>) comprising (a) a feeding tank (<NUM>), where an inlet opening (<NUM>) for the water solution is obtained, (b) a discharge tank (<NUM>), where an outlet opening (<NUM>) for the water solution is obtained and which is faced by said rear surface (10b) of said metal sheet (<NUM>), (c) a plurality of hydraulic connections (16a) made of an electrically insulating material and arranged so as to connect said feeding tank (<NUM>) to said vertical slits (<NUM>), and (d) a plurality of flow deflectors (<NUM>) arranged in front of the vertical slits (<NUM>) on the front surface (10a) of the metal sheet (<NUM>) in order to deflect the water solution flowing out of the vertical slits (<NUM>) towards said electrolysis openings (<NUM>) so as to allow it to flow through the metal sheet (<NUM>) a second time; said electrolytic cell being characterized in that each one of said electrodes comprises a hydraulic resistance layer (<NUM>) designed to achieve a pressure drop ranging from <NUM> Pa to <NUM> Pa of the water solution in the passage from the electrolysis chamber (C) to the discharge tank (<NUM>); said hydraulic resistance layer being an electrically insulating layer (<NUM>) arranged on said front surface (10a) to cover the electrolysis openings (<NUM>) of the metal sheet (<NUM>) and having a mesh structure with a US mesh number ranging from <NUM> to <NUM>, which corresponds to <NUM>-<NUM> micrometers.