DE102022107895A1 - Process for the light-induced production of gaseous fuel - Google Patents

Abstract

The invention relates to a method for the light-induced production of gaseous fuel, wherein at least one starting material is introduced into a reactor, gas formed in the reactor is discharged, the gas is converted into the gaseous fuel and the reactor has a porous structural material in and/or on it located semiconductor material.

Description

The invention relates to a method for the light-induced production of gaseous fuel.

As industrial processes and other technical systems such as motor vehicles are converted to an operating mode that produces as little carbon dioxide or other greenhouse gases as possible, gaseous fuel such as hydrogen or methane is becoming particularly important. Such gaseous fuel can in particular be stored much more easily than electrical power can be stored, and it typically produces no or at least little carbon dioxide during combustion. If the gaseous fuel is not taken from fossil energy sources, but is produced using environmentally friendly electricity and/or produced in a way that removes as much carbon dioxide from the atmosphere as is later released during combustion, it is called gaseous fuel a climate-neutral energy source.

Known approaches to producing gaseous fuels that are as climate-neutral as possible are based in particular on the idea of generating the fuel using electricity, which is fed into the grid in excess from renewable energy sources. This occurs in particular when environmentally dependent power generators such as wind turbines or solar cells generate a lot of electricity due to high wind strength or high solar radiation, but this is not currently needed by the consumers connected to the grid. In such situations, it is essential for grid stability to dissipate excess electricity appropriately. Since storing electricity in chemical energy storage systems is complex and expensive and requires a lot of space, the selective production of gaseous fuel using the excess electricity can be used to relieve the electricity grid of excess electricity. The disadvantage of this approach, however, is that in this case the gaseous fuel cannot be produced in a predictable manner over the long term, since the availability of excess electricity depends on both the consumption behavior of other consumers and weather conditions. Furthermore, the overall efficiency is currently still relatively low.

As gaseous fuels are increasingly introduced as energy sources in systems that have so far been supplied by fossil fuels, the need for gaseous fuels such as hydrogen and methane in particular will increase significantly, so that independent, efficient production of such gaseous fuels independently of the power grid appears to make sense.

It is therefore an object of the invention to provide a method for the light-induced production of gaseous fuel, which is designed alternatively or better, or more cheaply, compared to known designs. This is achieved according to the invention by a method according to claim 1. Advantageous refinements can be found, for example, in the subclaims. The content of the claims is made the content of the description by express reference.

• - Einleiten mindestens eines Edukts in einen Reaktor,
• - Ableiten von im Reaktor entstandenem Gas, und
• - Umsetzen des Gases in den gasförmigen Brennstoff;
• - wobei der Reaktor ein vollständig oder teilweise poröses Strukturmaterial mit darin und/oder darauf befindlichem Halbleitermaterial aufweist.

The invention relates to a method for the light-induced production of gaseous fuel. The procedure has the following steps:

• - introducing at least one reactant into a reactor,
• - Discharging gas produced in the reactor, and
• - converting the gas into the gaseous fuel;
• - wherein the reactor has a completely or partially porous structural material with semiconductor material located therein and/or thereon.

By means of such a process it is possible to produce gaseous fuel directly using light, in particular sunlight. For this purpose, a reactor is used, onto which light typically shines and into which at least one reactant is passed. The gaseous fuel is produced from this starting material. In this way, a detour in which light is first converted into electricity and then a gaseous fuel is produced with this electricity is avoided. The efficiency of producing gaseous fuel using the energy contained in light is thus significantly improved.

According to one embodiment, the structural material can be completely porous. This can mean that the structural material is completely traversed by small channels and/or pores. The structural material can also be partially porous. This can mean that there is a porous area in the structural material, which is traversed by small channels and/or pores. This porous area can in particular be surrounded by a non-porous area, for example completely or partially.

In particular, the structural material can be completely or partially translucent. On the Reference is made to any related description provided elsewhere herein.

The starting material can be, for example, water. The water can be split in the reactor, producing hydrogen and oxygen. Hydrogen or the combination of hydrogen and oxygen, which is also known as oxyhydrogen, can then be used as a gaseous fuel. However, other starting materials are also possible.

The reactor can be, for example, a reactor as described elsewhere herein. In particular, the reactor may have been manufactured using a method described herein. All of the features described in this regard can be used. In particular, all of the features described with respect to the method of manufacturing a reactor may constitute structural features of the reactor which may be used for the light-induced production of gaseous fuel method described herein. An arrangement described here can also be used, and all of the described designs and variants can also be used.

A reactor is typically a component into which at least one educt is introduced and onto which light shines, with at least one product, in particular gaseous fuel, being produced from the educt in a light-induced manner. Chemical processes are used that are stimulated directly by light. Gaseous fuel is therefore produced directly.

To generate gas, in particular a chemical reaction or a sequence of chemical reactions can take place in the reactor. In particular, it can involve electrochemical reactions. These can be triggered or amplified in particular by the semiconductor material. In particular, electron-hole pairs can be generated in the semiconductor material upon irradiation with light, with the electrons and/or the holes then recombining with ions that arise from the starting material to form gaseous fuel and/or another product.

The structural material can in particular have a three-dimensional porous structure. This can apply in particular to a porous area or to the entire structural material. Such a structure allows light to pass through a three-dimensional area of the reactor in which chemical reactions can take place. The porous structure can therefore be designed in particular in three dimensions. This means that the volume in which light can achieve its desired effect can be significantly increased compared to flat versions with a thin layer. The use of the energy contained in light can be significantly improved in this way. Reference is made to the explanations given elsewhere regarding a porous structure.

The structural material can in particular have a sponge-like structure, in particular an open-pore sponge-like structure. This can apply in particular to a porous area or to the entire structural material. This can mean in particular that there are numerous three-dimensional connections between small spaces in the structural material, with predominantly continuous small spaces being formed in the structural material. The starting material can typically flow through these gaps from one side of the structural material to the opposite side, with at least part of it being converted into a product.

The reactor can in particular be arranged entirely or partially between a first mirror and a second mirror. At least one of the mirrors is typically semi-transparent. This can ensure that light can first penetrate the reactor through the semi-transparent mirror and have its desired effect, whereby it does not then leave the reactor unused, but is reflected by the other mirror and penetrates the active area again. By reflecting again on the semi-transparent mirror, a further pass through the relevant area of the reactor can be carried out, and this process can be carried out practically as often as you like. The semi-transparent mirror ensures that light reaches the reactor. The other mirror can in particular not be transparent, so that light is completely reflected. However, it can also be semi-transparent to allow some light to pass through. This can be used, for example, when the reactor is positioned over an agricultural area so that some of the sunlight is used to produce gaseous fuel, but the other part of the sunlight is used to grow agricultural crops. It can be provided that only part of the agricultural area is covered by the mirrors and/or reactors. This can in particular ensure that sufficient sunlight and/or precipitation reaches the usable area. Reference is made to the description given elsewhere herein regarding mirrors. In particular, only one mirror can be used, especially below the reactor.

Concentrator mirrors or concentrator elements can also be used. These can focus sunlight onto a reactor. They can have a light concentrating effect. For example, several mirrors can be arranged on a surface, which focus sunlight on a centrally arranged reactor. Mirrors can also be used that are trough-shaped, whereby the reactor can extend elongated, in particular at the focal point or a line of focal points.

The reactor can in particular be illuminated by sunlight and/or focused sunlight. Sunlight is specifically the light that is emitted by the sun and hits the earth's surface during the day. It doesn't necessarily have to be full sun. Light that has penetrated clouds, for example, can also be used for the method described here. To produce focused sunlight, a special focusing device can typically be used. This can, for example, have one or more lenses and/or one or more mirrors. This allows sunlight to be collected from a larger area and directed to a reactor in a focused manner.

According to an advantageous embodiment, the reactor is designed without a glass substrate. This means that the use of a glass substrate can be dispensed with. In particular, glass substrates can be used for units for converting educts into products which only have a thin layer thickness, i.e. are in fact two-dimensional. In the embodiments of the reactor described herein, a three-dimensional structure is used, which offers a significantly better yield of the energy contained in the light.

The educt can in particular be at least partially derived again from the reactor. This is the educt which has not reacted to form the product, i.e. in particular not to form the gaseous fuel and possibly other gases formed in the process. The educt can then, for example, be fed back into the reactor, whereby a completely or at least partially closed circuit of the educt can be achieved.

The educt can in particular be completely or partially liquid. This allows the educt to be passed through the reactor easily. However, the starting material can alternatively also be gaseous or have a certain viscosity.

In particular, the starting material can be water or contain water. In particular, water can be decomposed, producing hydrogen and/or oxygen. This combination is also known as oxyhydrogen. The water can, for example, also be provided with additives which can, for example, improve the chemical reaction and/or prevent corrosion.

The gaseous fuel can in particular be hydrogen. This can be obtained, for example, by separation from a mixture of hydrogen and oxygen.

According to one embodiment, the educt is wholly or partly gaseous. For example, the starting material can be air or contain air. This can be the typical ambient air. The starting material can also be a gas mixture of carbon dioxide and hydrogen, or can be a gas mixture that contains carbon dioxide and hydrogen. By using carbon dioxide and hydrogen as starting material, it can be achieved in particular that a light-induced reaction leads to the production of methane. This means that methane can be produced in particular from hydrogen and carbon dioxide, which is either contained in the air that is passed through or has been taken from the air. In terms of climate protection, this has the advantage that the combustion of methane only produces a quantity of CO ₂ that was previously removed from the atmosphere. The use of methane is therefore climate-neutral despite the combustion of a hydrocarbon.

The gaseous fuel can be, for example, methane, another hydrocarbon or a mixture of hydrocarbons. Such hydrocarbons, for example methane, can be produced in particular from carbon dioxide taken from the air, as already mentioned. Methane or other gaseous hydrocarbons can be stored, transported and converted into energy through combustion relatively easily. When burned cleanly, hardly any harmful exhaust gases are produced.

The gas produced in the reactor can be a mixture of hydrogen and oxygen. During the reaction, hydrogen in particular can be separated from oxygen. The hydrogen then forms, in particular, the gaseous fuel. The oxygen can also be used or it can be released into the environment. For example, swing adsorption (vacuum pressure swing adsorption), metal-based semipermeable membranes or ceramic semipermeable membranes can be used as separation techniques. Such separation techniques are basically known in the prior art.

The gas formed in the reactor can be a mixture of oxygen with methane and/or one or more other hydrocarbons. During the reaction, methane, another hydrocarbon and/or several other hydrocarbons or a mixture of hydrocarbons can be separated from oxygen. The separation techniques already mentioned can also be used here. The gaseous fuel is then typically methane or the hydrocarbon or a mixture of hydrocarbons.

However, the reaction can also mean that gas produced in the reactor is used directly as gaseous fuel, i.e. without further process steps and/or without separation steps. This can be the case in particular if oxyhydrogen gas is produced in the reactor, i.e. a mixture of hydrogen and oxygen, which can be used directly, for example, to generate energy. It can also be the case when methane is produced, which, for example, may already have a purity sufficient for use.

It should be mentioned that the resulting gaseous fuel does not necessarily have to be used as an energy source. For example, it can also be used as a raw material, for example as a raw material for chemical processes to produce products such as plastics.

In particular, the reactor can form an inherently stable unit. This allows for easy handling. Reference is made to the information provided elsewhere.

The structural material can in particular have a pore size of at least 5 μm and/or a pore size of at most 1 mm. This has proven useful for typical designs because water can flow through easily and a large internal surface is created in the structural material on which reactions can take place to produce gaseous fuel. Additional typical or preferred pore size ranges are provided elsewhere herein and reference is made to these.

In particular, a material that is completely or at least partially transparent to light in the visible spectrum and/or in the ultraviolet spectrum can be used as the structural material. This allows advantageous transparency to visible light and/or ultraviolet radiation, whereby such radiation can induce the processes relevant here.

Polydimethylsiloxane in particular can be used as a structural material. However, other materials are also possible.

At least one support material can also be located in the structural material. Multiple support materials can also be used. Reference is made to the description of support materials provided elsewhere herein.

The support material can at least partially contact the semiconductor material. This allows the support material to exchange electrons and/or holes with the semiconductor material. Reference is made to the description given elsewhere.

In particular, at least one support material can be a noble metal, gold, silver, platinum, aluminum, cobalt, iridium, ruthenium, cobalt oxide, iridium oxide, ruthenium oxide, an organic cobalt compound, an organic ruthenium compound and/or a metal-free catalyst based on boron, carbon, phosphorus, Be sulfur, silicon and/or selenium and/or a non-metal oxide. Such support materials have proven to be advantageous for typical applications. In particular, they can have a catalytic effect. Any combinations can be used. Other support materials can also be used alternatively or additionally.

In particular, exactly two or at least two different support materials can be located in the reactor. In particular, gold and platinum can be used as support materials. One, some or all of the support materials can in particular be formed as nanoparticles and/or as crystals. Typically, support materials such as gold or platinum are arranged within the reactor in such a way that individual particles, at least predominantly, do not touch each other. Thus, even though such support materials may be conductive, electrical conductivity of the reactor is not typically produced.

One, some or all of the support materials in the reactor may in particular have a particle size of at least 1 nm, 5 nm or at least 10 nm and/or at most 250 nm or at most 300 nm.

The description of support materials provided elsewhere herein can be fully applied to the gaseous fuel production process described.

For example, titanium dioxide, silicon dioxide, indium oxide, iron (III) oxide, tungsten oxide, an alloyed oxide, a mixed oxide, strontium titanium oxide and / or bismuth vanadium oxide can be used as semiconductor material. Such semiconductor materials have proven to be advantageous for typical applications. However, others can also be used. Any combinations can also be used. The semiconductor material can in particular be doped. This allows the properties of the semiconductor material to be optimized. For example, phosphorus, arsenic, antimony, boron, aluminum, gallium and/or indium can be used for doping.

The semiconductor material can in particular be particulate. In particular, it can have a particle size of at least 1 nm, at least 5 nm, at least 10 nm, at least 50 nm, at least 75 nm or at least 100 nm. It may have a particle size of at most 200 nm, at most 225 nm, at most 250 nm, at most 500 nm, at most 1 µm or at most 5 µm. Such particle sizes have proven to be advantageous for typical applications. Reference is made to the description given elsewhere herein. However, other particle sizes can also be used.

The gas or the gaseous fuel formed in the reactor can in particular be used as starting material in a further process as described herein. Thus, the method described herein can be carried out twice in succession. For example, a mixture of hydrogen and oxygen can be produced in a first reactor. The oxygen can be separated and used for other purposes. The hydrogen can be used as a starting material for a second reactor, in which a process as described herein is again carried out. In this case, additional carbon dioxide is supplied, which has been removed from the air, or alternatively, additional air is supplied, which typically contains carbon dioxide. In the second reactor, the hydrogen reacts with the carbon dioxide, producing methane. Overall, a simple coupling of two reactors enables a process in which methane is produced from water and carbon dioxide. This can in particular be methane produced in a climate-neutral manner, since water as a starting material is not harmful to the climate, sunlight is used as an energy source and the carbon dioxide that is later produced when methane is burned has already been removed from the atmosphere.

In particular, hydrogen can initially be produced as a gaseous fuel, and the hydrogen can be used together with carbon dioxide or air as a starting material in the further process. Overall, this allows an advantageous process for producing methane using sunlight as an energy source.

Further aspects of the invention are described below. These relate in particular to the hearth position of a reactor. They are also relevant individually, and can be combined in any way with each other and with other aspects described herein. In particular, the process for producing gaseous fuel may be carried out using a reactor described herein or using a reactor manufactured as described herein.

• - Einbringen eines porösen Opfermaterials in eine Form,
• - Einbringen eines Strukturmaterials in die Form, so dass das Opfermaterial ganz oder teilweise bedeckt ist,
• - Einbringen eines Halbleitermaterials in das Strukturmaterial,
• - Aushärten des Strukturmaterials, und dann
• - Entfernen des Opfermaterials.

The invention relates to a method for producing a reactor for the light-induced production of gaseous fuel. The procedure has the following steps:

• - introducing a porous sacrificial material into a mold,
• - introducing a structural material into the mold so that the sacrificial material is completely or partially covered,
• - introducing a semiconductor material into the structural material,
• - curing the structural material, and then
• - Removal of the sacrificial material.

Using such a reactor, gaseous fuel such as hydrogen or methane can be produced directly using sunlight and one or more reactants. For example, water can be broken down into hydrogen and oxygen using light, whereby, for example, the resulting hydrogen can be separated off and used as a gaseous fuel. Due to the use of a porous sacrificial material, the formation of a three-dimensional structure is possible, which enables significantly better utilization of the energy present in sunlight compared to two-dimensional thin layers. Gaseous fuel can be produced particularly efficiently from one or more educts and the energy contained in sunlight without taking a loss-prone detour through electricity generation and use.

The steps of the method can in particular be carried out in the order specified. However, other orders can also be selected.

In particular, the introduction of the porous sacrificial material can begin.

According to one embodiment, the structural material is then introduced and then the semiconductor material is introduced. However, the semiconductor material can also be introduced into the structural material first, and this combination made of semiconductor material and structural material are then introduced into the sacrificial material. It is also possible to carry out these steps at the same time.

The structural material may be cured before, after and/or during removal of the sacrificial material.

Manufacturing is understood here to mean, in particular, the production of an object such as a reactor. In this context, production is understood to mean, in particular, the production of a gaseous fuel. This distinction is only for conceptual clarity.

Gaseous fuel can in particular be hydrogen or methane. These fuels are expected to be of greatest importance in converting industrial processes or other energy-consuming units to climate-neutral operation. In principle, however, depending on the design, the reactor can also be used to produce other gaseous fuels, such as other hydrocarbons. The gaseous fuel can also be a mixture, for example a mixture of hydrogen and oxygen formed when water decomposes, which is also referred to as oxyhydrogen.

The sacrificial material is in particular a material which is used in the course of the process, but is at least largely removed again before the reactor is used for the light-induced production of gaseous fuel. The sacrificial material is used in particular to bring the structural material into a defined shape. Since the sacrificial material is porous, it is ensured in particular that the structural material is also porous after hardening, which applies to at least a region or part of the structural material. This can be understood in particular to mean that there are channels in the structural material, which are typically connected to one another and/or branched, so that, for example, a liquid can move three-dimensionally through the structural material. The shape typically specifies at least a rough extent of the reactor to be manufactured. The shape can, for example, be designed at least approximately as a shell, which is enclosed at the bottom and sides, but is open at the top. Other versions are also possible. The sacrificial material can be placed in such a form that it remains in place after insertion.

The structural material is typically the material that at least essentially determines the structure of the reactor produced after the method has been carried out. In particular, the structural material defines an inner surface on which chemical, in particular electrochemical, processes for the reaction of one or more educts in the gaseous fuel can take place. Due to the porous structure, this inner surface is typically three-dimensional, so that compared to layered versions, a significantly larger surface area in the reactor and thus also a significantly better utilization of the light shining on the reactor is achieved. When the structural material is placed in the mold, the sacrificial material is already in the mold. The structural material essentially occupies those areas within the mold that are not filled by the sacrificial material. The sacrificial material appears, for example, as a lost form. Since the sacrificial material is porous, the structural material also has a porous structure. Preferably, the structural material is wholly or at least partially translucent, in particular in the visible spectral range and/or in the ultraviolet spectral range. This can happen especially after hardening at the latest, but it can also happen earlier.

The semiconductor material is typically introduced into the structural material in such a way that it covers the already mentioned inner surface of the structural material or at least a part or a significant part thereof. The semiconductor material therefore has a large reactive surface on which chemical processes can take place, so that particularly good utilization of the sunlight irradiating the reactor is achieved. Accordingly, instead of introducing the structural material, one can also speak of applying it. In another formulation, introducing the structural material may include applying.

Before curing, the structural material is typically liquid or at least essentially liquid, in particular at room temperature, i.e. at a temperature of approximately 20 ° C. In particular, it can be flowable, so that it can be introduced into the mold and distributed there essentially automatically . Support, for example with ultrasound, is possible. In particular, the structural material can be distributed in free spaces left by the sacrificial material due to its porous structure. Typically, pressure exerted by gravity and/or support from ultrasound is sufficient. When hardening, the structural material changes to a state in which it is no longer flowable. This may mean that Structural material assumes a hard state, which no longer allows non-destructive bending or compression of the structural material. However, it can also mean that the structural material hardens into a state in which it is soft or at least has a certain softness, so that, for example, the structural material can be bent and/or compressed using pressure. This is typically not a disadvantage for the functionality of a reactor. During curing, in particular a chemical reaction and/or a physical transformation can take place in the structural material, so that in particular the structural material subsequently has a higher strength and/or stiffness at room temperature.

When removing the sacrificial material, the sacrificial material is typically removed in whole or in part, so that cavities remain in the structural material, which define a porous structure of the structural material. When using the reactor for the light-induced production of gaseous fuel, these cavities typically serve to pass one or more reactants through and to produce gaseous fuel upon contact with the semiconductor material or other materials.

The semiconductor material typically has a band gap, which allows electron-hole pairs to be created by light irradiation. This can be done directly in the semiconductor material, or it can be done through the use of additional materials, for example the support materials mentioned below, such as catalysts. For example, gold can be used to generate light-induced electron-hole pairs particularly efficiently. The electrons and holes generated can then be released to surrounding atoms, molecules and/or ions, for example to convert them into a more stable state.

It is known, for example, that water (H ₂ O) undergoes autodissociation, that is, it automatically breaks down into ions and then immediately recombines into water molecules. This recombination can be prevented by the presence of electrons and holes in the semiconductor material, resulting in other stable products such as hydrogen molecules and oxygen molecules. A similar process can also be used to produce other gaseous fuels.

The reactor can in particular be manufactured as an inherently stable unit. This can mean, in particular, that the reactor has internal stability after completion of the manufacturing process, so that the individual components no longer disintegrate during normal use and/or transport. The possible bendability or compressibility already mentioned above does not stand in the way of this. The reactor can thus be brought to a site and used there without the need for special measures to ensure the integrity of the reactor.

For example, stability can be achieved by the structural material, whereby, as already mentioned, flexibility or compressibility can remain. The stability can also be achieved through the shape, which in at least one embodiment can remain completely or partially in the finished reactor. Alternatively, it can also be removed.

The hardened structural material can in particular stabilize the reactor as an independently manageable unit. This can mean in particular that the hardened structural material represents an essential part of the reactor and ensures that the reactor does not independently disassemble into its components and cannot be held and/or transported by gripping the structural material or another component. The reactor can thus be moved to its place of use and/or can be maintained at its place of use so that it fulfills its intended purpose.

According to one embodiment, the reactor is bordered on the outside by hardened structural material and/or another solid or flexible material. A limitation through hardened structural material can occur in particular in those places where the mold already mentioned above was removed or was not present at all from the beginning. The mold can also be left entirely or partially on the reactor so that it can form a material that at least partially delimits the outside of the reactor. The shape is typically solid. Alternatively, a flexible material can in principle also be used for the shape.

• - Anwenden von Ultraschall auf das Strukturmaterial nach dem Einbringen des Strukturmaterials in die Form und vor dem Aushärten des Strukturmaterials.

According to one embodiment, the method further comprises the following step:

• - Applying ultrasound to the structural material after placing the structural material into the mold and before curing the structural material.

In particular, the ultrasound can be applied before the introduction of the semiconductor material and/or after the introduction of the semiconductor material. By using ultrasound, the distribution of the structural material in the sacrificial material is further improved. Through this The process can be accelerated, allowing the reactor to be manufactured more quickly. In addition, depending on the structural material and the sacrificial material, it can be achieved that the structural material even better fills the cavities left by the sacrificial material due to its porosity.

The ultrasound can, for example, be applied for at least 5 minutes and/or for a maximum of 15 minutes.

• - Einbringen von einem oder mehreren Platzhaltern in die Form vor dem Einbringen des Strukturmaterials, wobei sich der oder die Platzhalter bis zum Opfermaterial erstrecken, und
• - Entfernen des Platzhalters oder der Platzhalter nach dem Aushärten des Strukturmaterials.

According to one embodiment, the method further comprises the following steps:

• - Introducing one or more placeholders into the mold before introducing the structural material, the placeholder(s) extending to the sacrificial material, and
• - Removal of the placeholder or placeholders after the structural material has hardened.

Using such placeholders, the structural material can be deliberately kept away from certain areas. In particular, the respective placeholder can define a space in which the structural material cannot spread. This makes it possible, for example, to create channels for educts and/or products.

In particular, the placeholder(s) can define one or more fluidic connections of the reactor.

For example, a first placeholder and a second placeholder can be introduced on opposite sides of the sacrificial material and/or the mold and/or at mutually opposite vertical and/or horizontal positions. Such placeholders can serve in particular to form a connection for introducing educts and a connection for discharging products and/or unreacted educts. However, more or fewer placeholders can also be used.

The sacrificial material can in particular be formed from one or more carbohydrates, one or more sugars, glucose, salt, polymer and/or as a 3D printed object. Such procedures have proven to be advantageous for typical applications. For example, when using carbohydrates or sugars, a granular structure of the sacrificial material can be used, which can be filled into the mold like ordinary household sugar, for example. Table sugar or another form of sugar, which can be handled in a similar way, can also be used as sacrificial material. Similarly, granular salt or polymer can be used. By using 3D printing, the structure of the sacrificial material, especially the porous structure, can be specified very precisely, which enables the pore structure to be optimized. A granular sacrificial material is particularly considered a porous sacrificial material.

According to one embodiment, the sacrificial material has a pore size of at least 5 μm. This has proven to be advantageous in ensuring a flow of educts and a discharge of products. For example, at least 40 µm or at least 50 µm can also be used as a pore size, with powdered sugar crystals, for example, which can be used as sacrificial material, having a typical pore size of around 50 µm. The sacrificial material advantageously has a pore size of at most 1 mm, at most 5 mm or at most 10 mm. For example, a range between 5 mm and 10 mm can be used. This corresponds to the size of a Styrofoam ball. The use of the specified dimensions ensures that a large internal surface is created within the porous structure of the structural material on which chemical reactions can take place. The utilization of irradiated light is thereby improved.

The sacrificial material can be introduced into the mold in whole or in part as a solid body. For example, the sacrificial material can be a granular sacrificial material, whereby the respective grains can be designed as solid bodies. This gives the sacrificial material a solid structure before the structural material is introduced, which is not changed or at least not significantly changed by the introduction of the structural material. The solid can in particular be cuboid, cube-shaped, cylindrical, spherical and/or ellipsoid. This can refer to individual bodies of the sacrificial material as well as to the entire spatial structure of the sacrificial material.

In particular, the sacrificial material can be introduced into the mold in whole or in part as a powder. This allows the sacrificial material to be easily handled and a porous structure to be formed automatically. Such a powder can be, for example, table sugar or a material with similar properties. In particular, a sacrificial material can be used that is soluble in a substance or chemical in which the structural material is not soluble. For example, water can be such a substance.

However, the sacrificial material can also be introduced into the mold as a body. For example It can be one or more sugar cubes.

A material that is completely or at least partially transparent to light in the visible spectrum and/or in the ultraviolet spectrum is preferably used as the structural material. This can ensure that sunlight can penetrate through the structural material and reach those places where it can trigger chemical reactions. In this way, absorption of sunlight in the structural material, which would only lead to an increase in temperature without any further benefit, is prevented as much as possible.

In particular, a water-insoluble material and/or a hydrophobic material can be used as the structural material. This allows water to be passed through as a starting material without having an impact on the structural material. A hydrophobic material can in particular ensure that the water is not absorbed into the structural material and thus does not lead to a chemical change in the structural material in the long term.

In particular, polydimethylsiloxane can be used as a structural material. This has proven to be an advantageous structural material, which is in particular water-insoluble and can be easily used together with a suitable sacrificial material such as sugar in the context of the method described herein. In principle, however, the use of other structural materials is also possible.

The structural material can in particular be introduced into the mold in liquid and/or particle form. This allows a completely or at least partially automatic distribution of the structural material in the mold, in particular penetration into pores left by the sacrificial material.

The structural material can be hardened in particular by heating. This allows the structural material to harden easily and reliably.

According to one embodiment, the mold is removed after the structural material has hardened. This can mean complete or partial removal. When the mold is no longer needed for the finished reactor, this can save space and weight. Alternatively, the mold can also be left in the finished reactor, for example to create an external structure and/or to increase general stability.

• - Einbringen mindestens eines Unterstützungsmaterials in das Strukturmaterial.

According to one embodiment, the method further comprises the following step:

• - Introducing at least one support material into the structural material.

This allows another material to be introduced into the reactor, which can in particular support the desired chemical reactions for the production of gaseous fuel. That's why this is called support material. Typically, the support material is a catalyst and/or a material for supplying additional energy and/or increasing efficiency. For example, it can be a material on which desired chemical processes can take place better and/or faster than on the semiconductor material. It can also be a material that can absorb light and thereby generate electrons and/or holes that are released to the semiconductor material. In particular, the support material is different from the semiconductor material.

The support material can at least partially contact the semiconductor material. In particular, these can be particles of the support material, which can adhere to the semiconductor material. The semiconductor material can be contained in the structural material, for example, flatly or in sections, for example cylindrically or in particle form. Contact between the support material and the semiconductor material enables an advantageous exchange of electrons and/or holes.

At least one support material can, for example, be a noble metal, gold, silver, platinum, aluminum, cobalt, iridium, ruthenium, cobalt oxide, iridium oxide, ruthenium oxide, an organic cobalt compound, an organic ruthenium compound and/or a metal-free catalyst based on boron, carbon, phosphorus, Sulfur, silicon, silicon dioxide, and / or selenium and / or a non-metal oxide and / or be designed as carbon nanotubes. In particular, full-surface silicon dioxide can be used as a catalyst, which can, for example, completely cover pores on the inside. Such support materials can advantageously support desired chemical processes for the production of gaseous fuel. One such support material may be used, but two, three or more such support materials may also be used. Any combinations and sub-combinations of the specified materials and the use of other, not specified materials are possible.

According to an advantageous embodiment, exactly two support materials will be introduced. At least two, i.e. two or more, different support materials can also be introduced. It has proven to be particularly advantageous in typical cases when gold and platinum are introduced as support materials. Gold can in particular absorb light in the visible spectrum and generate electron-hole pairs, with the electrons generated in particular being able to pass into the conduction band of the semiconductor material. Platinum can advantageously catalyze the formation of hydrogen molecules from protons and electrons from the conduction band.

For example, one, some or all of the support materials may be introduced as nanoparticles or may be grown as nanoparticles. They can also be grown more generally as crystals. Growing can also occur in the structural material. The nanoparticles can also be present as agglomerates. They can be produced, for example, by flame spray pyrolysis.

In particular, one, some or all of the support materials in the finished reactor may have a particle size of at least 5 nm or at least 10 nm and/or at most 250 nm or at most 300 nm or at most 500 nm. This can in particular provide a suitable large surface area on which chemical processes can take place. Higher particle sizes of, for example, 250 nm or 300 nm correspond at least approximately to the wavelength of UV light, which facilitates its absorption.

One, some or all of the support materials can be introduced, for example, by introducing a solution containing the respective support material or a starting material of the support material into the mold before introducing the structural material so that it completely or partially covers the sacrificial material. The solution is therefore already present when the structural material is introduced, so that the support material is arranged in a suitable manner on an inner surface of the structural material. An alcohol, for example, can be used as the solvent for the respective solution. In particular, ethylene glycol can be used. The use of other solvents is also possible.

• - Erwärmen der jeweiligen Lösung, die das Unterstützungsmaterial oder einen Ausgangsstoff des Unterstützungsmaterials enthält, dabei vorteilhaft Einbringen des Unterstützungsmaterials oder des Ausgangsstoffs in das Opfermaterial und/oder Wachsen des Unterstützungsmaterials in dem Opfermaterial.

According to one embodiment, the method further comprises the following step:

• - Heating the respective solution containing the support material or a starting material of the support material, advantageously introducing the support material or the starting material into the sacrificial material and/or growing the support material in the sacrificial material.

Heating can improve the distribution of the support material or its starting material in the sacrificial material. In addition, a growth process can be promoted so that, for example, particles of the support material are created. For this purpose, for example, temperatures between 20° C or room temperature and 100° C can be used. In particular, a temperature range of at least 80° C. and/or at most 90° C. can be used.

• - Einbringen einer Schicht Strukturmaterial am Boden der Form, und
• - Aushärten der Schicht Strukturmaterial.

According to one embodiment, the method further comprises the following steps before introducing the sacrificial material:

• - Introducing a layer of structural material at the bottom of the mold, and
• - Hardening of the layer of structural material.

This allows a non-porous layer of structural material to be created on the bottom, which can form, for example, a bottom plate or other bottom unit in the finished reactor. This can be used to prevent introduced educts or manufactured products from escaping from the bottom of the reactor. The subsequently applied structural material, which is to be made porous, typically combines with the previously applied layer of structural material on the bottom during curing, so that a completely or at least largely continuous block of structural material is created.

• - Anbringen einer Deckschicht über dem ausgehärteten Strukturmaterial.

According to one embodiment, the method further comprises the following step after the structural material has hardened:

• - Applying a top layer over the cured structural material.

This can, for example, prevent educts and/or products from escaping from the top of the reactor. The cover layer can, for example, be formed from structural material that has already hardened. This allows the same material to be used and the parts of the structural material introduced at different times to be connected.

• - Aufbringen von nicht ausgehärtetem Strukturmaterial zwischen dem ausgehärteten Strukturmaterial und der Deckschicht, und
• - Aushärten des aufgebrachten Strukturmaterials.

According to one embodiment, the method further comprises the following steps:

• - Application of uncured structural material between the cured structural material and the cover layer, and
• - Hardening of the applied structural material.

This means that a cover layer that has already hardened outside the mold or independently of the other components of the reactor can be used and connected to the rest of the structural material in a suitable manner. Typically, adjacent areas of already hardened structural material melt to such an extent that, after cooling, a cohesive connection or a uniform, continuous formation of the structural material is created.

• - Ausbilden eines Gasabführkanals obenseitig im Reaktor und/oder in einer Deckschicht.

According to one embodiment, the method further comprises the following step after the structural material has hardened:

• - Forming a gas discharge channel at the top of the reactor and/or in a cover layer.

The formation in a cover layer can be carried out in particular if such a cover layer is present. The gas discharge channel can be formed, for example, by drilling, machining or laser processing. The gas discharge channel can in particular be used to discharge gaseous fuel produced upwards. Since the gaseous fuel is typically lighter than the liquid educts used and is also typically lighter than air, it typically rises upwards so that it can be easily removed through the gas discharge channel. Several gas discharge channels can also be designed accordingly.

Alternatively or additionally, it is also possible to form one or more gas discharge channels using placeholders, as described elsewhere herein.

• - Durchspülen des Strukturmaterials.

According to one embodiment, the method further comprises the following step after removing the sacrificial material:

• - Flushing the structural material.

This can be done in particular with deionized water. This allows any remaining sacrificial material or other contaminants still contained in the reactor to be flushed out.

For example, titanium oxide, silicon dioxide, indium oxide, iron (III) oxide, tungsten oxide, an alloyed oxide, a mixed oxide, strontium titanium oxide and / or bismuth vanadium oxide can be used as semiconductor material. A combination of such materials is also possible. Such semiconductor materials have proven to be advantageous for a typical application, in particular for the production of hydrogen or methane. Other materials, such as non-metallic materials, can also be used. Any combinations are possible.

According to an advantageous embodiment, the semiconductor material is doped. This allows its effect to support gaseous fuel production to be improved. For example, phosphorus, arsenic, antimony, boron, aluminum, gallium and/or indium can be used as doping materials.

• - Verbringen des Halbleitermaterials in die Form, und
• - Verteilen des Halbleitermaterials in dem Opfermaterial.

According to one embodiment, the introduction of the semiconductor material has the following steps before the introduction of the structural material:

• - Placing the semiconductor material in the mold, and
• - Distributing the semiconductor material in the sacrificial material.

The semiconductor material can be distributed in the sacrificial material by indiffusion. It can be supported, for example, by shaking and/or tapping. This can lead to a faster procedure.

The semiconductor material can also be introduced via channels created. These can be of any type, for example as connections between pores and/or as channels that were created by machining or placeholders.

The semiconductor material can be introduced into the mold in particular in powder and/or liquid form. This allows for easy insertion. In particular, the semiconductor material can be bonded to the sacrificial material by applying steam to the sacrificial material. In particular, the steam causes a typical sacrificial material such as sugar, but also other sacrificial materials, to become somewhat sticky and thus combine with the semiconductor material. The semiconductor material later combines with the structural material when the structural material is introduced or remains at least partially on the inner surface of the structural material that is being formed. The procedure described can ensure a simple and reliable introduction of the semiconductor material, so that a sufficient or ideal amount of semiconductor material is available within the structural material for the intended function.

In particular, it can be provided that the semiconductor material is only introduced or picked up when the structural material has already been completed.

The semiconductor material can in particular be particulate and/or liquid. The particle size can be, for example, at least 10 nm, at least 50 nm, at least 75 nm or at least 100 nm. The particle size can also be at most 200 nm, at most 225 nm, at most 250 nm, at most 500 nm, at most 1 µm or at most 5 µm. Such particle sizes are in particular in a typical wavelength of visible light, which facilitates the capture of visible light photons or UV radiation. Such photons can typically lead to the creation of electron-hole pairs in the semiconductor material, which can be used for desired chemical processes to produce gaseous fuel.

The sacrificial material can be removed in particular by dissolving it in a solvent. Water, for example, can be used as a solvent for dissolving the sacrificial material. This can be used particularly when a water-soluble sacrificial material is used. For example, water is particularly suitable as a solvent for dissolving the sacrificial material if sugar or another readily water-soluble material is used as the sacrificial material. In principle, however, other solvents can also be used, in particular a solvent can be used in which the sacrificial material used is readily soluble.

• - Trocknen des Reaktors nach dem Aushärten des Strukturmaterials.

The method advantageously also has the following step:

• - Drying the reactor after the structural material has hardened.

Drying can be done, for example, by heating or heating. This allows any remaining water or other solvent to be removed from the reactor.

The reactor can in particular be designed to produce hydrogen and/or methane. How such production can occur will be explained elsewhere herein. However, training to produce other gaseous fuels is also possible.

• - Anbringen mindestens eines Spiegels derart, dass durch den Reaktor transmittiertes Licht ganz oder teilweise auf den Spiegel trifft und der Spiegel dieses Licht ganz oder teilweise zum Reaktor zurück reflektiert.

According to one embodiment, the method further comprises the following step, in particular after the structural material has hardened:

• - Attaching at least one mirror in such a way that light transmitted through the reactor hits the mirror in whole or in part and the mirror reflects this light in whole or in part back to the reactor.

Such a mirror can, for example, be arranged below the reactor. Sunlight can shine onto the reactor from above and partially leave the reactor at the bottom. Then it hits the mirror and is fully or partially reflected. As a result, it hits the reactor again and can lead to light-induced reactions again. The mentioned mirror can be completely reflective. It can also be semi-transparent, especially if an area under the reactor or under the mirror is to be illuminated, for example for agricultural or human use.

• - Anbringen eines ersten Spiegels und eines zweiten Spiegels derart, dass der Reaktor sich zwischen den Spiegeln befindet,
• - wobei vorzugsweise mindestens einer der Spiegel halbtransparent ist.

According to one embodiment, the method further comprises the following step, in particular after the structural material has hardened:

• - attaching a first mirror and a second mirror such that the reactor is between the mirrors,
• - Preferably at least one of the mirrors is semi-transparent.

Through such a process, additional mirrors are attached to the reactor, which can ensure that incident light does not only pass through the part of the reactor in which chemical reactions can take place. Rather, the mirrors can ensure that the light passes through the relevant part of the reactor several times, i.e. in particular through that part of the reactor in which the semiconductor material is located. By making one of the mirrors semi-transparent, it can be ensured that sunlight can enter. After passing through the semi-transparent mirror, this typically first passes through that part of the reactor with semiconductor material, is then reflected on the other mirror and returns to the semi-transparent mirror. There it is at least partially reflected again and can release energy again. This is ultimately repeated until the light emerges again or has the desired effect in the reactor, namely the production of gaseous fuel, or is absorbed in some other way.

It can also be provided that both mirrors are semi-transparent, so that, for example, a process can take place below the reactor, which also requires light. This allows, for example, the reactor to be located over an agricultural field, with some of the sunlight in the reactor being used to produce gaseous fuel and another portion of the sunlight being used to grow plants in the agricultural field .

More than the first and second mirrors mentioned can also be attached or used. For example, the reactor can be surrounded on all sides by mirrors. For example, a total of six mirrors can be used for this, in particular corresponding to the side surfaces of a cuboid. Each of these mirrors can be semi-transparent or non-transparent.

• - Anbringen von Spiegeln, welche den Reaktor teilweise oder vollständig umschließen.

Accordingly, the method, in particular after the structural material has hardened, can have the following further step:

• - Attaching mirrors that partially or completely enclose the reactor.

At least one of the mirrors can be semi-transparent. This can be the case in particular if the mirrors completely enclose the reactor. Light can then enter and/or exit through the semi-transparent mirror. Completely reflecting mirrors can also be provided, which enclose the reactor on all but one side, the latter side being able to remain free. Light can enter through this side. This can in particular be an upper side, which can, for example, be aligned so that sunlight can enter.

Semi-transparent mirrors typically allow part of the incident light to pass through and reflect the other part. The two parts do not necessarily have to account for half of the light. If a mirror is not semi-transparent, it is typically completely or at least almost completely reflective.

The invention further relates to a reactor for the light-induced production of gaseous fuel, which was produced by a method as described herein. With regard to the method, all versions and variants described herein can be used. In particular, all features described with reference to the process can lead to corresponding structural features of the reactor produced. These can be combined with each other as desired. In this regard, reference is made to the description given with reference to the process.

The invention further relates to a reactor for the light-induced production of gaseous fuel. The reactor has a structural material in which a porous region is formed. It has a semiconductor material which is arranged in the porous region. It has an inlet connection for supplying an educt to the porous area. It has one or more gas discharge channels for discharging gaseous fuel from the porous area. This means that light-induced gaseous fuel can be produced in the manner already described.

The reactor just described, or a reactor in general, can be produced or have been produced in particular by means of a method as described herein. All described versions and variants of the method can be used. In particular, all features and variants described with reference to the method, which lead to features in the reactor, can be applied to the reactor accordingly.

In particular, a support material can also be arranged in the porous area, which, for example, reduces at least one activation energy and/or captures light and thereby generates free charge carriers. These can be, for example, the catalysts already described above. These can in particular have such properties.

The invention further relates to an arrangement for the light-induced production of gaseous fuel, namely methane. The arrangement has a first reactor as described herein, with all of the described designs and variants being available. The arrangement has a device for supplying water to the first reactor. It has a separation device for separating hydrogen, which is connected on the input side to a gas discharge channel of the first reactor, the separation device having at least one first connection for discharging hydrogen. The arrangement has a second reactor as described herein, with all of the described embodiments and variants being available, the second reactor being connected on the input side to the first connection and to a device for supplying carbon dioxide.

Using such an arrangement, methane can be produced in a simple and reliable manner. Reference is made to the information provided elsewhere.

The invention further relates to an arrangement for the light-induced production of gaseous fuel. The arrangement has a reactor as described herein, with all described embodiments and variants being possible, and it has one or more supports for holding the reactor above a floor.

This allows advantageous open-space assembly, with large areas being used for the production of gaseous fuel can be used, similar to what is known from solar fields. The floor can, but does not have to, be understood as part of the arrangement.

According to one embodiment, the arrangement can further have a first mirror, which is semi-transparent and expediently completely or partially covers the reactor above, and / or it can further have a second mirror, which expediently completely or partially covers the reactor below. This allows the light to be passed through the reactor several times and the yield can be increased.

If only the second mirror is present, it can also simply be referred to as a mirror or as a first mirror.

According to one embodiment, the second mirror can be semi-transparent. This enables light to be passed through in a targeted manner into an area below the reactor. This means that this area can be used, for example, for plant growth or for people to stay. The other versions with mirrors described elsewhere herein can also be used accordingly.

The floor can be part of the arrangement. In particular, the soil can be agriculturally usable soil. This can be, for example, a field or field or another agricultural area. Agricultural crops such as grains and vegetables can grow on this soil. In particular, the floor can be completely or at least partially or predominantly covered with earth. In particular, the reactor can be arranged so high above the ground and/or the supports can be so high that it is possible for agricultural vehicles to drive underneath the reactor. This can mean, for example, a height of at least 0.5 m, 1 m, 2 m, 3 m or 5 m. In particular, sufficient height can be provided for the passage of agricultural machines.

The invention also relates to use of a reactor or arrangement as described herein over an agricultural area. All versions and variants described can be used.

The procedures described herein are not limited to the splitting of water. By choosing suitable materials, such as nanostructures, they can also be used for other plasmon-assisted chemical processes or other processes. For example, it is possible to convert hydrogen into methane with the addition of carbon dioxide.

The porosity of the sacrificial material can be influenced, for example, by the choice of sacrificial material. For example, sugar cubes, salt, powdered sugar, silicon dioxide and/or polystyrene balls can be used as sacrificial material. The geometry of a resulting sponge-like structure, especially in the structural material, can be varied by changing the expansion of the sacrificial material, for example from a few millimeters to several meters or even larger systems. In the case of structural material, any material can typically be selected, such as transparent polymers, which are castable and do not dissolve the selected sacrificial material. For example, PMMA or silicones can be used. Plasmonic materials of the nanostructures can be, for example, gold, silver, platinum and/or aluminum. In addition, photocatalytic materials such as titanium oxide and/or indium oxide can be used as semiconductor materials. Other materials are also possible. Particle sizes can fundamentally be varied. The size of plasmonic nanoparticles can in particular be between 10 nm and 200 nm. The size of photocatalytic particles can vary in particular between 10 nm and several micrometers.

In particular, the reactor described herein can be understood as a flow cell in which water in a transparent polymer sponge is split into hydrogen and oxygen by plasmonic nanostructures under illumination by sunlight. However, the reactor can also be designed differently or used differently.

Special plasmonic nanoantennas (e.g. photocatalytic metallic nanoparticles) can, when excited by photons, split water into hydrogen and oxygen. They typically serve as moderators between the photons of (sun) light and the water molecules. For this purpose, the water molecules should typically be close to the nanostructures. The more nanostructures involved in water splitting in a system, the higher the hydrogen yield.

In particular, transparent polymer sponges are considered here, namely those that are structured with plasmonic nanoparticles that split water when exposed to sunlight. The large surface area and the three-dimensional extent of the sponge or the porous structure can be exploited, in particular to incorporate as many nanostructures as possible into the water splitting process. In particular, nanoparticles made of two materials, namely gold and titanium dioxide, can be applied to the surface of the sponge, as this combination of materials has proven particularly useful in experiments on plasmonic water splitting. However, other materials or combinations of materials can also be used. Nanoparticles can, for example, exist as agglomerates. They can be produced, for example, using flame spray pyrolysis.

For example, gold nanostructures can be grown from a solution (for example gold chloride dissolved in ethylene glycol) on the surface of the sponge under the influence of heat. The sponge is soaked in the solution and then heated. The size of the nanostructures is defined by temperature and time. Titanium dioxide particles can also be applied to the sponges from a solution or suspension. These processes enable the structuring of otherwise difficult to access areas in the sponges. This allows full use of the existing surface. In addition, they are passive processes that typically require only a small amount of working time. In addition, they are largely independent of the size of the sponge. The polymer sponges can be produced using a casting process that is largely independent of the size and geometry of the casting template. For example, sugar cubes can be used as a mold or sacrificial material. This results in open sponges in which all pores are connected to one another. To use the structured sponges, they can be integrated into flow cells. Water is supplied and removed from the sponge through channels. Gaseous hydrogen and oxygen, which are produced when the nanostructures in the sponge are illuminated, rise and are discharged via a separate outlet or several separate outlets. For example, separate outlets can be provided for hydrogen and oxygen.

The procedure described here enables high scalability and simple and time-efficient production of reactors or plasmonic sponges, particularly in comparison to other approaches to plasmonic water splitting. The large structured surface of the sponges compared to the base area is an advantage. The usual production of nanostructures using lithographic and/or 3D printing methods limits the number of nanostructures that can be produced. This is particularly because lithography is time-consuming, expensive, and requires flat surfaces to work effectively.

Another advantage is the expansion in three dimensions. This creates a multi-layer system from the perspective of the incident photons. This makes the interaction of photons with a nanostructure more likely.

Compared to electrolysis, which is carried out using electricity from renewable energies, the procedure described here has the advantage that solar energy is converted directly into hydrogen or another gaseous energy source. This saves the efficiency of energy production from wind, water or solar energy. Compared to steam reforming or electrolysis, which is carried out using non-renewable energies, it is particularly advantageous that no fossil raw materials are used and no carbon dioxide is released.

• 1: eine Illustration plasmonischer Wasserspaltung,
• 2: eine weitere Illustration plasmonischer Wasserspaltung,
• 3: mehrere Schritte eines Verfahrens zur Herstellung eines Reaktors,
• 4: einen Reaktor in einer Verwendungssituation,
• 5: eine Anordnung zur Erzeugung von gasförmigem Brennstoff, und
• 6: eine weitere Anordnung zur Erzeugung von gasförmigem Brennstoff.

A person skilled in the art will find further features and advantages in the exemplary embodiment described below with reference to the accompanying drawing. Show:

• 1 : an illustration of plasmonic water splitting,
• 2 : another illustration of plasmonic water splitting,
• 3 : several steps of a process for producing a reactor,
• 4 : a reactor in a situation of use,
• 5 : an arrangement for producing gaseous fuel, and
• 6 : another arrangement for producing gaseous fuel.

Solar plasmonic water splitting is considered a promising source of green hydrogen. Sunlight can be converted directly into hydrogen, which enables carbon dioxide-free and low-loss hydrogen production. Other gaseous fuels can also be produced accordingly.

In particular, the procedure described here can result in a transparent and porous medium with an irregular surface. The surface is then coated with water-splitting nanostructures, particularly via direct growth. The entire surface is thus structured at the same time. A stochastically layered system of nanostructures is created. This increases the probability of interaction between photons and plasmonic particles.

Plasmonic water splitting can be understood in particular as a process in which optical properties of materials on the nanometer scale are used to support the splitting of water molecules into H ⁺ ions and O ^- ions. The energy threshold for such a fission is 1.23 eV. Light with a wavelength of 1,000 nm and below has enough energy to carry out water splitting. However, a further reaction of ions to form molecules, especially hydrogen and oxygen molecules, can also be achieved. Therefore, electrons as well as holes and energy are needed. Holes take part in the further reaction of oxygen, that is, the formation of O ₂ molecules from O ^- ions. Electrons ensure that H ₂ molecules are formed from H ⁺ ions. The formation of gas occurs in particular at catalytic sites at interfaces between, for example, a semiconductor material and water. The energy of the valence band of the semiconductor material should in particular be smaller than the energy required for the further reaction to oxygen gas. The conduction band should in particular be higher than the energy required for further reaction to hydrogen gas. Titanium oxide, for example, meets these criteria. The efficiency can be further increased by doping the titanium oxide. Exciton generation in semiconductors with wide band gaps typically requires energy from the ultraviolet region of the electromagnetic spectrum. Sunlight typically only has about 5% of its energy in the relevant spectrum. To increase efficiency, plasmonic nanoparticles can be used.

Plasmonic nanoparticles are, in particular, metal particles with dimensions that are smaller than the wavelength of visible light. The depth of entry of visible light into metals is large compared to the size of the particles. Therefore, a free electron gas can be set into collective oscillation by absorbing incident light. One effect of the collective oscillation is a periodic accumulation of electrons and holes on the surface of the particles that act as nanoantennas. This leads to an increased near field near the particles and the generation of hot charge carriers that are able to leave the metal particles.

A nanoantenna-semiconductor system can form a heterojunction with a Schottky barrier in between. If the hot charge carriers have sufficient energy, they can pass through and enter the conduction band of the semiconductor material. The Schottky barrier can advantageously prevent backward migration. In the case of gold and titanium oxide, the Schottky barrier is 0.23 eV, which is high enough to largely prevent re-emission. The hot charge carriers generated in the gold nanoparticles typically have an energy of 1 to 2 eV. They are passed on to the conduction band of the semiconductor material.

A possible system for plasmonic water splitting is in 1 shown. A semiconductor material 200 is shown, which in the present case has a particle shape and is made of titanium oxide (TiO ₂ ). Ultraviolet light hµ (UV) is absorbed in it, which leads to the excitation of electrons from the valence band VB to the conduction band LB. This creates electron-hole pairs.

In addition, next to the semiconductor material 200 there is a support material 210 in the form of a gold nanoparticle. Visible and infrared light hµ (Vis-NIR) is absorbed there, which also leads to the creation of electron-hole pairs. The electrons enter the conduction band LB of the semiconductor material 200, namely via the Schottky barrier already mentioned above.

An electrochemical reaction of H ⁺ ions into hydrogen molecules (H ₂ ) takes place on the semiconductor material 200 with the absorption of two electrons from the conduction band LB. This produces hydrogen. Likewise, an electrochemical reaction of water molecules (H ₂ O) into oxygen molecules (O ₂ ) takes place on the support material 210, releasing H ⁺ ions. The holes in the support material 210 are used to balance the load.

The process can be further supported. This is in 2 shown. There is also another supporting material 212 in the form of an organic cobalt compound (Co-OEC). It has been shown that this makes it easier to produce oxygen from water. Furthermore, there is another support material 214 in the form of a platinum nanoparticle, which has proven to be advantageous for the combination of H ⁺ ions to form hydrogen, including the electrons present in the conduction band LB. This can further increase the efficiency of plasmonic water splitting into hydrogen and oxygen.

3 shows an example of a method for producing a reactor.

In step 1, a mold 300 is first provided, in which a first opening 302 and a second opening 304 are formed. As shown, the first opening 302 is arranged on the left side and further down, whereas the second opening 304 is arranged on the right side and further up is. Liquid structural material 110 is filled into the mold 300, and only enough to form a lower layer. This is hardened, for example by applying heat. This creates a hardened soil layer 116, as can be seen in the illustration for step 2. A sacrificial material 310 is placed thereon, a cuboid piece of sugar being used as the sacrificial material 310 in the present case. However, other materials can also be used. In the embodiment described here, titanium dioxide particles, which represent a semiconductor material 200, are already introduced at this point. For this purpose, titanium dioxide particles are scattered over the sacrificial material 310 and steam is applied to the sacrificial material 310 for a certain time. This causes the sugar to become sticky and the titanium dioxide particles are distributed throughout the sacrificial material 310 and bond with it. The titanium dioxide particles can, for example, have a diameter of 100 nm to 200 nm, but other diameters can also be used.

As can be further seen in step 3, a first placeholder 320 and a second placeholder 325 are inserted through the openings 302, 304. These extend from outside the mold 300 to the sacrificial material 310. The mold 300 is then filled with structural material 110. The structural material 110 is still in liquid form. It is therefore distributed both next to the sacrificial material 310 and in spaces left between particles of the sacrificial material 310.

As shown, in the present embodiment the sacrificial material 310 is completely covered by the structural material 110.

Ultrasound is then applied to the structural material 110 in step 4. As a result, the structural material 110 is distributed better and faster in the spaces between the sacrificial material 310.

Subsequently, in step 5, the structural material 110 is hardened, which creates a porous area 112 in which the sacrificial material 310 is still located, with a non-porous area 114 also created surrounding the porous area 112. The placeholders 320, 325 are removed, so that a first fluidic connection in the form of an inlet connection 120 and a second fluidic connection in the form of an outlet connection 125 are created. These are used in the later finished reactor 100 to feed in educts and to discharge unreacted educts.

The reactor 100 can already be seen here as block 105.

Subsequently, in step 6, the mold 300 is removed and the sacrificial material 310 is removed in a water bath 330. In other words, the sugar is triggered. This leaves cavities in the porous area 112.

In step 7, the reactor 100 is then dried and a cover layer 118 is applied. By applying a further thermal curing step, bottom layer 116, porous region 112, non-porous region 114 and top layer 118 combine to form a single block 105 of structural material 110.

A solution containing dissolved gold is then introduced. This is shown in step 8. In particular, a solution containing HAuCl ₄ can be used. Such a solution can be heated so that gold precipitates. After the solution has been introduced, gold can harden or precipitate, for example for 2.5 hours at 80 °C. The gold thereby combines with the semiconductor material 200 and grows as particles to form a support material 210.

In step 9, the porous area 112 is blown out with compressed air so that it is finally cleaned. Furthermore, a gas discharge channel 130 is formed on the top side of the reactor 100 by drilling.

Polydimethylsiloxane (PDMS) in particular can be used as a structural material. This is particularly suitable for the application relevant here. It is highly transparent throughout the visible and infrared spectrum, as well as the ultraviolet spectrum. It is also inert to most organic solvents and is non-toxic. The polydimethylsiloxane or another structural material 110 can be introduced into the sacrificial material 310 more quickly and more uniformly, in particular by means of ultrasound. For example, ultrasound can be applied for about 5 minutes to 15 minutes. The structural material 110 can be hardened, for example, by applying a temperature of 120 ° C for approximately 25 minutes. When washing out the sacrificial material 310, the water bath 330 can be heated to achieve better washing out. Final drying, for example after rinsing with deionized water, can take place, for example, in an oven at 150 ° C. This makes the surface accessible.

For example, a solution of gold chloride (HAuCl ₂ ) in ethylene glycol can be used to coat the surface of the porous structural material 110 with gold nanostructures. Other solutions and/or solvents are also available however possible. The solution is added to the porous medium. The porous medium is filled with the solution and is then dried out, for example on a hot plate at 80 ° C, preferably covered. A color change from white to red typically occurs over the next 2.5 hours. This indicates that growth of gold nanoparticles is occurring in sizes between 10 nm and 200 nm. Remaining solution of gold chloride is then typically rinsed out, for example with water, in particular with ultrapure water or deionized water.

The formation of platinum nanostructures can be done in the same way as with gold, but for example a solution of platinum chloride (PtCl ₂ /Pt ₂ Cl ₄ ) can be used. Ethylene glycol, for example, can also be used as a solvent. The growth process is typically slower than gold. For the same temperature and time, smaller particles are observed.

The shape 300 already mentioned above can in particular specify the later expansion of the reactor 100.

The water bath 330 can, for example, be used for a period of at least 30 minutes and/or at most 1.5 hours. It has been shown that the sacrificial material 310 is sufficiently washed out during this period.

4 shows the reactor 100 with further components. The reactor 100 is, as shown, formed as a block 105 in which the porous region 112 and the surrounding non-porous region 114 of the structural material 110 are located. An inlet connection 120 is formed on the bottom left side, to which a pump 122 is connected for supplying water as educt. The pump 122 thus represents a device for supplying water. The outlet connection 125 is formed on the top right, to which a return line 150 is connected. Excess water that has not reacted in the reactor 100 is directed back to the inlet port 120 via a valve 156. A heat exchanger 160 for cooling the returned water is attached to the return line 150. Any excess water can be drained off via a valve 152 and a drain 154.

Light 102 shines onto the reactor 100. This is typically sunlight. The chemical processes mentioned above take place so that some of the water passed through decomposes into hydrogen and oxygen. The resulting oxyhydrogen gas is drained off at the top via the already mentioned gas discharge channel 130 and fed to a separating device 140. This can, for example, be based on membranes. The separation device 140 has a first connection 142 and a second connection 144. In the present implementation, hydrogen is drained at the first port 142 and oxygen is drained at the second port 144. This means that hydrogen is available in pure form as a gaseous fuel.

5 shows an arrangement 400 for producing gaseous fuel, with a reactor 100 being shown purely schematically above a base 410. The reactor 100 is held above the floor 410 by a first support 420 and a second support 425. The reactor 100 is predominantly arranged between two semi-transparent mirrors, namely an upper semi-transparent mirror 170 and a lower semi-transparent mirror 175. This results in sunlight first passing through the upper semi-transparent mirror 170, passing through the reactor 100 and being partially reflected by the lower semi-transparent mirror 175. Part of the sunlight thus leads to the already mentioned processes in the reactor 100 to produce gaseous fuel. However, some also reaches the ground 410 and can be used there to enable plant growth. The reactor 100 can thus be used over a large area over agricultural land, whereby both hydrogen is produced and agricultural crops can grow underneath. In contrast to known open-field solar systems, this means that the area does not have to be used for agricultural purposes.

6 shows another arrangement 500 for producing gaseous fuel, in this case for producing methane. Regarding the left part of it, ie the reactor 100, please refer to the description already given above 4 referred. A hydrogen line 510 is connected to the first connection 142 of the separation device 140, which supplies the resulting hydrogen to a second reactor 100a. Directly in front of an inlet port 120a of the second reactor 100a, a carbon dioxide line 515 is additionally connected to the hydrogen line 510, which supplies carbon dioxide to the inlet port 120a of the second reactor 100a and thus represents a device for supplying carbon dioxide. A mixture of hydrogen and carbon dioxide thus enters the second reactor 100a.

The second reactor 100a does not have an outlet port. Instead, it only has a gas discharge channel 130a on the top side. Through the described supply of the educts hydrogen and carbon dioxide, methane is generated in the second reactor 100a when light hits. This methane is discharged from the top via the gas discharge channel 130a and can be used as gaseous fuel. If the carbon dioxide used is previously removed from the atmosphere, the resulting methane is climate-neutral because its combustion only produces as much carbon dioxide as was previously removed from the atmosphere.

Overall, the procedures described herein enable very efficient and cost-effective production of gaseous fuel, for which a reactor that is easy to manufacture can be used. In contrast to known procedures, the detour via generated electricity can be dispensed with and large-scale use can take place under the condition that areas used for the production of solar hydrogen can also be used for agriculture.

Mentioned steps of the method according to the invention can be carried out in the order specified. However, they can also be executed in a different order if this makes technical sense. The method according to the invention can be carried out in one of its embodiments, for example with a specific combination of steps, in such a way that no further steps are carried out. However, in principle, further steps can also be carried out, including those not mentioned.

It should be noted that in the claims and the description features may be described in combination, for example to facilitate understanding, although they may also be used separately. The person skilled in the art will recognize that such features can also be combined independently of one another with other features or combinations of features.

References in subclaims can indicate preferred combinations of the respective features, but do not exclude other combinations of features.

Reference symbol list

100

reactor

105

block

110

Structural material

112

porous area

114

non-porous area

116

soil layer

118

top layer

120

Inlet port

122

pump

125

Outlet port

130

Gas discharge channel

140

Separating device

142

first connection

144

second connection

150

return line

152

Valve

154

Sequence

156

Valve

160

Heat exchanger

170

Mirror

175

Mirror

200

Semiconductor material

210

Support material

212

Support material

214

Support material

300

shape

302

opening

304

opening

310

Sacrificial material

320

placeholder

325

placeholder

330

water bath

400

arrangement

410

Floor

420

support

425

support

500

arrangement

510

Hydrogen pipe

515

Carbon dioxide pipe

Claims (36)

Process for the light-induced production of gaseous fuel, the process having the following steps: - introducing at least one starting material into a reactor (100), - discharging gas formed in the reactor (100), and - converting the gas into the gaseous fuel; - wherein the reactor (100) has a completely or partially porous structural material (110) with semiconductor material (200) located therein and/or thereon. Procedure according to Claim 1 , - wherein the structural material (110) has a three-dimensional porous structure. Method according to one of the preceding claims, - Wherein the structural material (110) has an open-pore sponge-like structure. Method according to one of the preceding claims, - wherein the reactor (100) is arranged entirely or partially between a first mirror (170) and a second mirror (175), at least one of the mirrors (170, 175) being semi-transparent. Method according to one of the preceding claims, - Wherein the reactor (100) is illuminated by sunlight and/or focused sunlight. Method according to one of the preceding claims, - Wherein the reactor (100) is designed without a glass substrate. Method according to one of the preceding claims, - The educt is at least partially derived again from the reactor (100). Method according to one of the preceding claims, - where the educt is wholly or partly liquid. Method according to one of the preceding claims, - where the starting material is water or contains water. Method according to one of the preceding claims, - where the gaseous fuel is hydrogen. Method according to one of the preceding claims, - where the educt is wholly or partly gaseous. Method according to one of the preceding claims, - where the starting material is air or contains air. Method according to one of the preceding claims, - where the starting material is a gas mixture of carbon dioxide and hydrogen, or is a gas mixture that contains carbon dioxide and hydrogen. Method according to one of the preceding claims, - where the gaseous fuel is methane, another hydrocarbon or a mixture of hydrocarbons. Method according to one of the preceding claims, - Wherein the gas formed in the reactor (100) is a mixture of hydrogen and oxygen and hydrogen is separated from oxygen during the reaction. Method according to one of the preceding claims, - Wherein the gas formed in the reactor (100) is a mixture of oxygen with methane and/or one or more other hydrocarbons and during the reaction methane, another hydrocarbon and/or several other hydrocarbons or a mixture of hydrocarbons are separated from the oxygen. Method according to one of the preceding claims, - The reactor (100) forms an inherently stable unit. Method according to one of the preceding claims, - Wherein the structural material (110) has a pore size of at least 5 µm. Method according to one of the preceding claims, - Wherein the structural material (110) has a pore size of at most 1 mm. Method according to one of the preceding claims, - A material that is completely or at least partially translucent in the visible spectrum and/or in the ultraviolet spectrum is used as the structural material (110). Method according to one of the preceding claims, - Polydimethylsiloxane being used as the structural material (110). Method according to one of the preceding claims, - wherein at least one support material (210, 212, 214) is also located in the structural material (110). Procedure according to Claim 22 , - wherein the support material (210, 212, 214) at least partially contacts the semiconductor material (200). Procedure according to one of the Claims 22 or 23 , - wherein at least one support material (210, 212, 214) comprises a noble metal, gold, silver, platinum, aluminum, cobalt, iridium, ruthenium, cobalt oxide, iridium oxide, ruthenium oxide, an organic cobalt compound, an organic ruthenium compound and/or a metal-free catalyst Base of boron, carbon, phosphorus, sulfur, silicon and/or selenium and/or a non-metal oxide. Procedure according to one of the Claims 22 until 24 , - whereby there are exactly two or at least two different support materials (210, 212, 214) in the reactor (100). Procedure according to one of the Claims 22 until 25 , - where gold and platinum are used as support materials (210, 212, 214). Procedure according to one of the Claims 22 until 26 , - where one, some or all of the support materials (210, 212, 214) are formed as nanoparticles and/or as crystals. Procedure according to Claim 27 , - wherein one, some or all of the support materials (210, 212, 214) in the reactor (100) have a particle size of at least 1 nm, 5 nm or at least 10 nm and / or at most 250 nm or at most 300 nm. Method according to one of the preceding claims, - Titanium dioxide, silicon dioxide, indium oxide, iron (III) oxide, tungsten oxide, an alloyed oxide, a mixed oxide, strontium titanium oxide and / or bismuth vanadium oxide being used as the semiconductor material (200). Method according to one of the preceding claims, - Wherein the semiconductor material (200) is doped. Method according to one of the preceding claims, - Wherein the semiconductor material (200) is doped with phosphorus, arsenic, antimony, boron, aluminum, gallium and/or indium. Method according to one of the preceding claims, - Wherein the semiconductor material (200) is particulate. Procedure according to Claim 32 , - wherein the semiconductor material (200) has a particle size of at least 1 nm, at least 5 nm, at least 10 nm, at least 50 nm, at least 75 nm or at least 100 nm. Procedure according to one of the Claims 32 or 33 , - wherein the semiconductor material (200) has a particle size of at most 200 nm, at most 225 nm, at most 250 nm, at most 500 nm, at most 1 mm or at most 5 mm. Method according to one of the preceding claims, - wherein the gas or the gaseous fuel formed in the reactor (100) is used as starting material in a further process according to one of the preceding claims. Procedure according to Claim 35 , - where hydrogen is initially produced as a gaseous fuel, and - where the hydrogen is used together with carbon dioxide or air as a starting material in the further process.

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