Photoelectrochemical reactor and method for carrying out a photoelectrochemical reaction

Abstract

The invention relates to a photoelectrochemical reactor, comprising at least one container (20) which is at least partially filled with an electrolyte (11), and comprising at least one solar cell (19) for converting electromagnetic input radiation (29) incident on the reactor into electrical power, wherein the solar cell (19) has an anode side and a cathode side opposite the anode side, and has one or more side faces, wherein a cathode-side catalyst layer (7) is arranged on the cathode side and an anode-side catalyst layer (6) is arranged on the anode side, and wherein the solar cell (19) is arranged in such a way that the cathode-side catalyst layer (7) and the anode-side catalyst layer (6) are in contact with the electrolyte (11). An essential aspect of the invention is that the reactor is designed in such a way that the input radiation is coupled into the solar cell substantially through one or more side faces of the solar cell, preferably substantially through one side face of the solar cell.

Description

[0001] title

[0002] Photoelectrochemical reactor and method for carrying out a photoelectrochemical reaction

[0003] Description

[0004] The invention relates to a photoelectrochemical reactor according to claim 1 and a method for carrying out a photoelectrochemical reaction according to claim 12.

[0005] Photoelectrochemical reactors are known for carrying out photoelectrochemical reactions. In these reactors, a solar cell is used to convert incident electromagnetic input radiation, typically sunlight, into electrical power. The poles of the solar cell are connected to catalysts arranged in an electrolyte within the reactor. The electric current generated by the solar cell is used to carry out the photoelectrochemical reaction at the interface between the catalysts and the electrolyte.

[0006] Such photoelectrochemical reactions are used for solar water splitting. A cell for such a reactor is described in DE 10 2016119634 Al.

[0007] The present invention is based on the objective of providing an improved photoelectrochemical reactor and an improved method for carrying out a photoelectrochemical reaction, which enable the reduction of ion transport losses in the electrolyte as well as an optimized removal of the reaction products.

[0008] 33937-P-DE Tue / co 01.10.2024 Solar cells are planar elements where the length and width are significantly greater than the thickness of the solar cell. Accordingly, typical solar cells have a large front surface and an opposing, large back surface, with the front surface facing the incident sunlight in typical terrestrial applications. The front and back surfaces thus represent the planar faces (large-area sides) of the solar cell, whereas the side surfaces, typically four and perpendicular to the planar faces, have a significantly smaller area compared to the planar faces, since one edge or height of the side surfaces corresponds to the thickness of the solar cell.

[0009] In previously known photoelectrochemical reactors, the solar cells are therefore arranged in such a way that, in the operating configuration, the input radiation strikes one of the surface sides of the solar cell at approximately a perpendicular angle.

[0010] The present invention is based on the knowledge that the previously known arrangements of solar cells in photoelectrochemical reactions have disadvantages with regard to the reduction of ion transport losses in the electrolyte, the avoidance of photocurrent losses through partially / intransparent catalysts, the minimization of catalytic overpotentials, and the separation of the reaction products.

[0011] This is particularly true for highly integrated photoelectrochemical reactors, in which a catalyst layer is arranged directly on the solar cell at both the anode and cathode sides.

[0012] According to the invention, a separation is achieved between the areas of the solar cell used for the reaction and the area or areas through which the light coupling into the solar cell essentially occurs. This separation allows for an independent and thus, compared to previously known reactors, a significantly greater degree of optimization with regard to minimizing [something].

[0013] 33937-P-DE Di / co 01.10.2024 ion transport losses, catalytic overpotentials and improved removal of reaction products.

[0014] The photoelectrochemical reactor according to the invention comprises at least one container which is at least partially filled with an electrolyte. The reactor comprises at least one solar cell for converting electromagnetic input radiation incident on the reactor into electrical power. The solar cell has an anode side and a cathode side opposite the anode side, and one or more side surfaces. The anode and cathode sides are surface surfaces of the solar cell, i.e., large-area surfaces of the solar cell. In contrast, the side surfaces preferably have a smaller area; in particular, the thickness of the solar cell preferably corresponds to an edge length or height of the side surfaces.

[0015] A catalyst layer is arranged on the cathode side and an anode side. The photoelectrochemical reactor is thus highly integrated and particularly suitable for highly integrated solar water splitting.

[0016] The solar cell is arranged in such a way that the cathode-side catalyst layer and the anode-side catalyst layer are in contact with the electrolyte, so that the reaction can be carried out at the interfaces of the catalyst layers to the electrolyte using the current generated by the solar cell as a reaction current.

[0017] It is essential that the reactor is designed in such a way that the input radiation is coupled into the solar cell essentially through one or more side surfaces of the solar cells, preferably essentially through one side surface of the solar cell.

[0018] As previously described, in the present invention, unlike in the prior art, the input radiation is not essentially transmitted via

[0019] 33937-P-DE Di / co 01.10.2024 one of the surface sides (in this case, the anode side or the cathode side) is coupled into the solar cell. Instead, the coupling occurs essentially via one or more of the side surfaces of the solar cell, preferably via exactly one side surface of the solar cell.

[0020] The coupling of the input radiation into the solar cell for conversion into electrical power takes place in a manner unusual compared to the prior art, in that the radiation occurs via a side surface which typically has a considerably smaller area compared to the anode side and the cathode side.

[0021] This allows for optimization of the design, particularly the dimensions, as well as the arrangement of the anode and cathode sides to minimize ion transport losses and catalytic overpotentials. Optimization is also possible with regard to the removal of reaction products, especially gaseous products such as hydrogen and oxygen, particularly in solar water splitting. Furthermore, the catalyst layer can be optimized for stability, as it does not need to be transparent.

[0022] The aforementioned problem is further solved by a method according to claim 12.

[0023] The inventive method for carrying out a photoelectrochemical reaction is preferably designed to be carried out using a reactor according to the invention, in particular a preferred embodiment thereof. The photoelectrochemical reactor according to the invention is preferably designed to carry out the inventive method, in particular a preferred embodiment thereof.

[0024] The inventive method for carrying out a photoelectrochemical

[0025] The response outlines the following procedural steps:

[0026] 33937-P-DE Di / co 01.10.2024 Providing at least one solar cell with an anode side, a cathode side and one or more side surfaces, wherein the anode side is electrically conductively connected to an anode-side catalyst and the cathode side is connected to a cathode-side catalyst and both catalysts are in contact with an electrolyte,

[0027] Coupling of electromagnetic input radiation, especially sunlight, to convert the input radiation into electrical power and to generate an electric current between the anode and cathode sides of the solar cell.

[0028] It is essential that the input radiation is coupled into the solar cell via one or more side surfaces of the solar cell, preferably essentially via one side surface of the solar cell.

[0029] This results in the advantages previously listed in the description of the photoelectrochemical reactor according to the invention.

[0030] According to the invention, the input radiation is coupled in essentially via one or more side surfaces of the solar cell. It is therefore within the scope of the invention that small proportions of the input radiation are coupled into the solar cell via other surfaces, in particular also via the anode or cathode side. It is advantageous to couple a large proportion of the input radiation into the solar cell via one or more side surfaces, and in particular that the input radiation is coupled into the solar cell exclusively via one or more side surfaces, preferably via exactly one side surface.

[0031] The proportion of input radiation coupled into the solar cell via one or more side surfaces can be quantified using the radiant energy E [J] :

[0032] 33937-P-DE Tue / co 01.10.2024 (Formula l), with the frequency / [s' 1], the number n( / ) of photons at frequency f and the Planck constant h [J s].

[0033] In an advantageous embodiment, the reactor is designed such that the radiant energy E of the radiation coupled into the solar cell through one or more side surfaces is at least 80%, preferably at least 90%, and in particular at least 95% of the total radiant energy of the input radiation coupled into the solar cell. In the method according to the invention, it is advantageous that the radiant energy of the radiation coupled into the solar cell through one or more side surfaces is at least 80%, preferably at least 90%, and in particular at least 95% of the total radiant energy of the input radiation coupled into the solar cell.

[0034] Due to the radiation coupling primarily via one or more side surfaces of the solar cell, it is advantageous to use a solar cell with high efficiency and / or high absorption of the input radiation. In an advantageous embodiment, the solar cell is therefore designed as a multi-junction solar cell with several sub-junctions. In particular, it is advantageous to design the multi-junction solar cell with sub-junctions connected in series in order to provide a higher reaction voltage.

[0035] Multi-junction solar cells are known per se and comprise several sub-solar cells, each sub-solar cell being configured for charge carrier separation by means of absorbed electromagnetic radiation. Advantageously, several of the sub-solar cells, in particular all sub-solar cells, have a pn junction.

[0036] Compared to silicon-based solar cells, solar cells with an absorber structure designed as a direct semiconductor exhibit higher absorption at the same thickness. It is within the scope of the invention that at least one of the partial solar cells can have an absorber based on a direct semiconductor.

[0037] 33937-P-DE Di / co 01.10.2024 Due to the coupling of radiation entirely or substantially through one or more side surfaces of the solar cell, the present invention has the advantage that a longer light path in the solar cell is favored, compared to the typical use of a solar cell with light coupling at the front. Therefore, solar cells based on indirect semiconductors, in particular silicon-based solar cells, are also particularly suitable for the present invention.

[0038] In an advantageous embodiment, the solar cell is therefore designed as a silicon solar cell, in particular preferably based on a silicon substrate.

[0039] In a further advantageous embodiment, the solar cell is designed as a multi-cell solar cell with several sub-cells, wherein at least one of the sub-cells, preferably several of the sub-cells, in particular all sub-cells are designed as a silicon sub-cell, in particular with a silicon layer as an absorber.

[0040] It is advantageous that the sub-solar cells of the multi-junction solar cell have absorber structures with essentially identical band gaps. This avoids or at least reduces the need for thickness adjustments of sub-cells with different thicknesses for stromal balancing.

[0041] This also applies when the input radiation is coupled in essentially via one or more side surfaces. Coupling in via one or more side surfaces has the advantage over coupling from a front surface of the solar cell that, in the majority, preferably all, sub-solar cells, the entire spectrum of the input radiation passes through the sub-solar cell, whereas in previously known configurations, the input radiation of a sub-solar cell must first pass through the sub-solar cells located between this sub-solar cell and the sub-solar cells located between the front surface and this sub-solar cell. With input radiation coupled in via one or more side surfaces, this is not the case, or only the case if the entire spectrum of the input radiation passes through the sub-solar cells located between the front surface and this sub-solar cell.

[0042] 33937-P-DE Di / co 01.10.2024 slightly disadvantageous if a subcell absorbs a part of the input radiation without charge carrier generation, since another sub-solar cell optimized for this part of the spectrum is supplied with the input radiation unaffected by the absorption of other sub-solar cells due to the lateral coupling.

[0043] In the method according to the invention, it is advantageous to use a multi-junction solar cell as described above, in particular an advantageous embodiment thereof.

[0044] The multi-junction solar cell can be configured in a manner known per se. In particular, it is advantageous to configure the multi-junction solar cell as a multi-junction solar cell from the following list:

[0045] Silicon / silicon dual or triple solar cell;

[0046] Multi-junction solar cell with a silicon sub-solar cell and one or more sub-cells based on a direct semiconductor, in particular with materials from main groups III and V, so-called 11V solar cells;

[0047] Multi-junction solar cell which includes a perovskite solar cell as a sub-junction.

[0048] The sub-solar cell configured as a multiple solar cell is preferably monolithic. In particular, it is advantageous that the multiple solar cell has monocrystalline layers.

[0049] An advantageous design of a solar cell as a multi-junction solar cell with a catalyst layer on the cathode side and a catalyst layer on the anode side is described in Wen-Hui Cheng et al, Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency, ACS Energy Lett. 2018, 3, 1795-1800, DOI : 10.1021 / acsenergylett.8b00920.

[0050] 33937-P-DE Tue / co 01.10.2024 As previously described, known photoelectrochemical reactors are designed such that incident radiation is coupled into the solar cell via a surface, typically a front side of the solar cell. In known devices, the solar cell is therefore typically arranged parallel to a horizontal, upper surface of the electrolyte in the operating position, in particular parallel to a top surface of the reactor. Accordingly, in known devices, it is desirable that the incident radiation strikes a surface perpendicularly, typically a front side of the solar cell. For this reason, in known devices, the solar cells are typically arranged perpendicular to an incident direction of the input radiation in the operating configuration.

[0051] In the present invention, however, it is advantageous that a side surface, via which the radiation coupling of the input radiation essentially takes place, faces the input radiation. This also simplifies the removal of reaction products, particularly gaseous ones.

[0052] In the reactor according to the invention, it is therefore advantageous that the solar cell is positioned at an angle in the range of 45° to 90°, in particular 60° to 90°, preferably 70° to 90° to a top surface of the electrolyte.

[0053] In an advantageous embodiment, the surface of the electrolyte is horizontally oriented in the operating configuration. This offers the advantage that no cover is necessary directly on the surface of the electrolyte for a non-horizontal arrangement. In this advantageous embodiment, the anode side and / or the cathode side of the solar cell thus forms an angle in the range of 45° to 90°, in particular 60° to 90°, preferably 70° to 90°, with a top surface of the electrolyte, in particular a horizontal surface of the electrolyte that is located on top in the operating configuration.

[0054] 33937-P-DE Di / co 01.10.2024 In an advantageous embodiment, the reactor has a cover. The cover is preferably designed and arranged such that escape of the electrolyte from the reactor, in particular escape upwards, especially from an opening at the top of the electrolyte container, is prevented.

[0055] In an advantageous embodiment, the top surface of the cover, onto which the input radiation preferably strikes, is designed parallel to the surface of the electrolyte. This results in a compact design.

[0056] When the input radiation is incident obliquely to the surface of the electrolyte in the operating configuration, particularly to the horizontal surface of the electrolyte, it is advantageous that the upper surface of the cover, onto which the input radiation preferably strikes, is not arranged parallel to the surface of the electrolyte. This allows the upper surface of the cover to be oriented perpendicular or approximately perpendicular to the input radiation. In an advantageous embodiment, the surface of the cover is therefore arranged at an angle of 10° to 60°, preferably 20° to 40°, and particularly 25° to 35°, to the surface of the electrolyte.

[0057] Accordingly, it is advantageous that one of the sides, the anode side or cathode side, or, in the typical configuration with parallel anode and cathode sides, both surfaces of the solar cell, is arranged at an angle of 45° to 90°, particularly 60° to 90°, to a top surface of the electrolyte, particularly to a top surface of the reactor, which, in the operating configuration, faces the input radiation. This top surface of the electrolyte is preferably an upper surface, preferably a horizontal surface of the electrolyte in the operating configuration.

[0058] The optical element described above is preferably arranged and designed such that the side surface of the solar cell is parallel to a surface of the

[0059] 33937-P-DE Di / co 01.10.2024 electrolytes and / or to a top surface of the cover facing the incident radiation during use. In an alternative advantageous embodiment, the optical element is designed and arranged such that maximum transmission into the solar cell occurs despite an angle between the top surface of the cover and the side surface of the solar cell (in particular up to max. 45 degrees).

[0060] The reactor and method according to the invention have the advantage that the surfaces of the solar cell, on which the anode-side catalyst layer and the cathode-side catalyst layer are preferably arranged, do not need to be transparent to the input radiation. In particular, optimization of the catalyst layers, especially with regard to their stability against corrosion, can be carried out without considering optical transparency.

[0061] In an advantageous embodiment, the reactor is designed such that the sum of the radiation energies coupled into the solar cell through the anode and cathode sides is less than 20%, preferably less than 10%, and particularly less than 5% of the total radiation energy coupled into the solar cell. This has the advantage of minimizing losses due to input radiation absorbed by the catalyst layers.

[0062] For efficient and robust execution of the reaction, it is advantageous that the anode-side catalyst layer and / or the cathode-side catalyst layer, preferably both catalyst layers including possible surface passivation layers (or chemically insulating layers [from the electrolyte]), have a thickness greater than 3 nm, preferably greater than 50 nm, and are preferably formed as a closed layer, in particular without holes towards the solar cell.

[0063] 33937-P-DE Tue / co 01.10.2024 Advantageously, the coupling of the input radiation into the solar cell occurs essentially through one or more side surfaces of the solar cell, preferably a side surface of the solar cell that is not in contact with the electrolyte. This has the advantage that the potentially changing optical properties of the electrolyte do not need to be taken into account when optimizing the radiation coupling. Furthermore, it has the advantage that the electronic properties, in particular the charge carrier recombination, are not impaired at the side surface by the electrolyte.

[0064] In an advantageous embodiment, a side surface of the solar cell, through which input radiation is coupled into the solar cell, is arranged on the surface of the electrolyte, so that the side surface is not in contact with the electrolyte.

[0065] In a preferred embodiment, an optical element transparent to the input radiation is arranged on a side surface of the solar cell where the input radiation is coupled into the solar cell, so that there is no contact between the side surface and the electrolyte. The optical element is preferably designed as a partition transparent to the input radiation. In particular, the optical element designed as a partition is preferably arranged such that it penetrates the surface of the electrolyte. This simplifies the separate removal of reaction products formed on the anode side and those formed on the cathode side.

[0066] To increase the efficiency of the solar cell, it is advantageous to arrange a reflective layer on at least one of the solar cell's side surfaces. The reflective layer is preferably designed to cause internal reflection of input radiation within the solar cell. The reflective layer is preferably arranged on a side surface which is one

[0067] 33937-P-DE Di / co 01.10.2024 Side surface through which input radiation is coupled into the solar cell, opposite.

[0068] In a preferred embodiment, input radiation is coupled into the solar cell via an upper side surface. Advantageously, in this embodiment, a reflective layer is arranged on a lower side surface of the solar cell.

[0069] The reactor and method according to the invention enable a compact design and, in particular, the minimization of ion transport losses in the electrolyte.

[0070] Advantageously, the reactor comprises a plurality of solar cells. Each solar cell is preferably designed and arranged according to the solar cell described above, in particular an advantageous embodiment thereof. In particular, each solar cell preferably has an anode side and a cathode side opposite the anode side, and one or more side surfaces, wherein a catalyst layer is arranged on the cathode side and an anode-side catalyst layer is arranged on the anode side. Each solar cell is preferably arranged such that the cathode-side catalyst layer and the anode-side catalyst layer are in contact with the electrolyte.The reactor and the method are preferably designed such that for each solar cell, the input radiation is coupled into the solar cell substantially through one or more side surfaces of the solar cell, preferably substantially through one side surface of the solar cell.

[0071] The reactor and the method are preferably designed such that one or more of the previously described advantageous features and configurations apply to each solar cell of the reactor.

[0072] 33937-P-DE Di / co 01.10.2024 The solar cells of the photoelectrochemical reactor are preferably arranged in a lamellar configuration. This allows for a compact design with minimized ion transport losses. In an advantageous embodiment, the solar cells are arranged parallel to each other. Advantageously, the distance between two adjacent lamellae is in the range of 0.5 mm to 4 mm.

[0073] In an alternative advantageous embodiment, the solar cells are arranged radially around a common center.

[0074] In an advantageous embodiment, the solar cells are arranged such that an anode side of one solar cell faces an anode side of an adjacent solar cell, and similarly, a cathode side of one solar cell faces a cathode side of an adjacent solar cell. This has the advantage that a single reaction product is generated between two solar cells, thereby simplifying the derivation of the reaction product.

[0075] In an alternative embodiment, the solar cells are arranged such that the anode side of one solar cell faces the cathode side of an adjacent solar cell. Advantageously, in this embodiment, a partition is arranged in the electrolyte between each pair of adjacent solar cells to separate the reaction products from the anode side of one solar cell and the cathode side of the adjacent solar cell. Advantageously, the partition has recesses and / or is spaced from the bottom of the electrolyte-containing chamber to allow ion exchange in the electrolyte between the anode and cathode sides of the two adjacent solar cells. Alternatively or additionally, the partition is preferably designed as a membrane. The membrane serves to conduct ions between the two halves of the reactor while blocking gas transport.The membrane is preferably configured as a proton-conducting membrane, particularly made of sodium. In an alternative advantageous embodiment, the membrane is configured as an anion-conducting membrane for alkaline electrolytes (anion-exchange membrane, AEM). In a further embodiment...

[0076] 33937-P-DE Di / co 01.10.2024 In an advantageous embodiment, the partition is designed as a porous partition, in particular as a diaphragm.

[0077] The photoelectrochemical reactor and the method according to the invention are preferably configured to carry out solar water splitting. Gaseous hydrogen and gaseous oxygen are produced in this process.

[0078] It is also within the scope of the invention to use the reactor and the process for CO2 reduction:

[0079] As an alternative reaction to water splitting, CO2 can also be reduced. For this, CO2 is dissolved in the electrolyte, and on the cathode side, instead of a catalyst for H2, a catalyst layer for CC reduction is arranged. On the anode, oxygen is still evolved with the aforementioned catalyst. The catalyst layer for CC reduction preferably comprises at least one layer from the group consisting of a copper layer, a copper oxide layer, a palladium layer, a cobalt layer, and a cobalt oxide layer, each preferably with a thickness of at least 50 nm.

[0080] The product of reduced CO2 can be gaseous (e.g., CO or CH4), in which case gas separation occurs analogously to water splitting. If the product is liquid and lighter than the electrolyte, the liquid product can be transported in the channels instead of hydrogen. If the product is heavier than the electrolyte, it can be collected at the bottom of the reactor and removed. If the product is highly soluble in the electrolyte, it can be separated from the electrolyte in a single post-processing step.

[0081] Other alternative reactions for water splitting can also be carried out with the present invention. The following table lists the electrolyte, materials, and other relevant components for further advantageous embodiments of the reactor and process according to the invention.

[0082] 33937-P-DE Di / co 01.10.2024 with preferred materials listed for the catalyst layer on the anode side and for the catalyst layer on the cathode side:

[0083] In the design of the reactor and the process for generating at least one gaseous reaction product, it is advantageous that the photoelectrochemical reactor has a cover on a surface of the electrolyte, which preferably has channels for removing the gaseous reaction product.

[0084] In an advantageous embodiment, the reactor has a cover arranged on the upper side of the electrolyte. Advantageously, the solar cells are

[0085] 33937-P-DE Di / co 01.10.2024, each with at least one side surface at which the input radiation is coupled into the solar cell, arranged directly or indirectly on the cover with an intermediate arrangement of optical transmission elements between the cover and the side surface of the solar cell. Advantageously, the cover is designed to guide the input radiation incident on the cover to the side surfaces of the solar cell; in particular, the cover preferably acts as a concentration unit for concentrating the input radiation incident on the cover onto the side surfaces of the solar cells, which are preferably arranged directly or indirectly on the cover.

[0086] The surfaces of the cover located between the solar cells are preferably designed to be reflective and / or optically scattering in order to achieve internal reflection and / or scattering of the input radiation within the cover. This concentrates the input radiation onto the side surfaces of the solar cells. Particularly in an advantageous embodiment where gas channels for removing gaseous reaction products are formed in the cover between the solar cells, it is advantageous for the side surfaces of the gas channels to be designed for internal reflection of the input radiation within the cover.

[0087] In an advantageous embodiment, the solar cells are arranged directly or indirectly with at least one side surface, preferably with exactly one side surface, on the cover. The reactor is preferably designed such that the coupling of the input radiation into each of the solar cells occurs essentially through the side surface of the solar cell arranged directly or indirectly on the cover. This results in a simple and easy-to-handle structure due to the mechanical support of the solar cells by the cover.

[0088] In an advantageous embodiment, the solar cells are each arranged directly on the cover with at least one side surface, preferably with exactly one side surface. This results in a simple manufacturing process.

[0089] 33937-P-DE Tue / co 01.10.2024 In an advantageous embodiment, the solar cells are each arranged indirectly on the cover with at least one side surface, preferably with exactly one side surface. An optical intermediate element is preferably arranged between the side surfaces of the solar cells and the cover, preferably such that these side surfaces of the solar cells arranged on the optical intermediate elements are not wetted by the electrolyte. This prevents damage to these side surfaces by the electrolyte.

[0090] Preferably, the optical intermediate elements for the input radiation are designed to be transparent in order to allow the input radiation to be coupled into the solar cells via the side surfaces arranged on the optical intermediate elements.

[0091] It is advantageous for the reactor to have an optical concentration unit, which is designed and arranged to concentrate the incident radiation onto one or more surfaces of the solar cell. This increases the overall efficiency.

[0092] In particular, it is advantageous that the concentration unit is designed and arranged in such a way that the input radiation is coupled into the solar cell essentially through one or more side surfaces of the solar cell, preferably essentially through one side surface of the solar cell.

[0093] In particular, it is advantageous that the concentration unit is designed and arranged such that the sum of the radiation energies of the radiation coupled into the solar cell through the anode side and through the cathode side is less than 20%, preferably less than 10%, and in particular less than 5% of the total radiation energy of the radiation coupled into the solar cell.

[0094] The optical concentration unit is preferably designed as a cover as described above and / or below.

[0095] 33937-P-DE Di / co 01.10.2024 In an advantageous embodiment, the cover between the partial solar cells has intermediate areas with a different optical refractive index compared to the optical refractive index outside the intermediate areas in order to achieve internal reflection of the input radiation at the interface to the intermediate areas within the cover.

[0096] Advantageously, the refractive index within the covering is at least 1.043 times greater than the refractive index of the intermediate regions, preferably at least for the relevant spectral ranges, particularly the relevant spectral range of the input radiation. This promotes reflection of the radiation within the covering at the interface with the intermediate regions.

[0097] In an advantageous embodiment, an antireflective layer is arranged between the solar cell and the cover, preferably between each solar cell and the cover. The antireflective layer serves to prevent optical reflections at the cover / solar cell interface, thus enabling efficient coupling of the input radiation into the solar cell. The antireflective layer can be configured in a known manner. The passivation layer can be a single layer or a multi-layer structure. The passivation layer preferably comprises one or more of the layers from the group consisting of TiC₂ layers and SiO₂ layers.

[0098] The sides of the gas channels facing the electrolyte are preferably hydrophobic.

[0099] When designing gas channels, it is advantageous to adapt the ratio of the cross-sectional areas of the gas channels to the expected volume ratios of the gaseous reaction products. In particular, when designing the reactor for solar water splitting, it is advantageous to use a ratio of 1:2.

[0100] 33937-P-DE Di / co 01.10.2024 (cross-sectional area of ​​the channel for the transport of oxygen : cross-sectional area of ​​the channel for the transport of hydrogen) to be formed.

[0101] To achieve a high efficiency of the solar cell, it is advantageous to passivate the cell's surface(s) by means of a passivation layer to reduce charge carrier recombination. Advantageously, a passivation layer is therefore arranged on the surface(s) where the input radiation is coupled into the solar cell. This passivation layer is preferably transparent to the input radiation. The passivation layer can be a single layer or a multi-layered structure. The passivation layer preferably comprises one or more layers from the group consisting of TiOj and SiOj materials.

[0102] In particular, it is advantageous to arrange a passivation layer between the solar cell and the cover on the side facing the solar cell and an antireflection layer on the side facing the cover.

[0103] In an advantageous embodiment, the reactor is mounted on a single- or dual-axis tracker to follow the position of the sun.

[0104] In an advantageous embodiment, the interface between the solar cell and the catalyst layer is designed such that it reflects as much light as possible back into the solar cell. In particular, it is advantageous that pyramids are formed at the interface between the solar cell and the catalyst layer (preferably at the interfaces with both catalyst layers) and / or that a reflector layer, especially made of gold, is arranged.

[0105] In an advantageous embodiment, the body of the cover is solid, in particular made of glass or transparent plastic.

[0106] 33937-P-DE Di / co 01.10.2024 In an advantageous embodiment, the body of the cover is hollow. The cover shell is preferably made of glass or transparent plastic.

[0107] Further advantageous features and designs are described below with reference to exemplary embodiments and the figures. These show:

[0108] Figure 1 shows a first embodiment of a photoelectrochemical reactor according to the invention,

[0109] Figure 2 shows a second embodiment of a photoelectrochemical reactor according to the invention.

[0110] Figure 3 shows a top view of the first embodiment,

[0111] Figure 4 shows a third embodiment of a photoelectrochemical reactor according to the invention and

[0112] Figure 5 shows a fourth embodiment of a photoelectrochemical reactor according to the invention.

[0113] All figures are schematic representations, not to scale.

[0114] Identical reference symbols in the figures denote identical or similarly functioning elements.

[0115] Figures 1, 2, 4 and 5 show cross-sections through exemplary embodiments of photoelectrochemical reactors, with the cutting plane intersecting solar cells of the reactors and being perpendicular to the surface sides of the solar cells.

[0116] The first embodiment of a photoelectrochemical reactor shown in Figure 1 has a container 20 which is filled with an electrolyte 11.

[0117] The reactor according to the exemplary embodiment has three solar cells 19 for

[0118] 33937-P-DE Di / co 01.10.2024 Conversion of electromagnetic input radiation 2 incident on the reactor into electrical power. Each solar cell 19 is designed as a multiple solar cell, in this case as a tandem solar cell with a first partial solar cell 12 and a second partial solar cell 14. A tunnel diode 13 is arranged between the partial solar cells 12 and 14.

[0119] The solar cells 19 are designed as planar elements, as is known per se, whereby in the schematic representations in Figures 1 and 2 the thicknesses of the solar cells are enlarged for better clarity, so that in particular the ratio of thickness to length of the solar cell is not to scale.

[0120] The solar cells 19 have a thickness Li of 1000 mm and are square in shape, with an edge length L2 of 0.5 to 5 mm, in this case 2.5 mm. The distance L4 between two solar cells is 1 to 5 mm, in this case 3 mm.

[0121] An anode-side catalyst layer 6 is arranged on each anode side of the solar cells 19. A cathode-side catalyst layer 7 is arranged on each cathode side of the solar cells 19. The catalyst layers completely cover the surfaces of the solar cells 19.

[0122] The solar cells 19 are arranged in the container 20 in such a way that the catalyst layers 6, 7 are completely in contact with the electrolyte.

[0123] The solar cells 19 are arranged in the container 20 such that a side surface of the solar cells, located at the top in Figures 1 and 2 and perpendicular to the plane of the drawing, is at the same level as the surface of the electrolyte. The solar cells 19 are arranged at an angle of 90° and thus perpendicular to the upper surface of the electrolyte 11.

[0124] 33937-P-DE Di / co 01.10.2024 The photoelectrochemical reactor is designed such that the input radiation 2 is essentially coupled into the solar cells through the upper side surfaces of the solar cells 19.

[0125] In contrast to previously known reactors, the radiation coupling thus does not occur essentially via a surface side, i.e. not via the anode side or the cathode side of the solar cells 19, but via a side surface which has a considerably smaller area compared to the surface sides.

[0126] The solar cell 19 and the catalyst layers are designed as described in Nature Communications 6, 8286 (2015), https: / / doi.org / 10.1038 / ncomms9286 and in particular as shown schematically in Figure 2 there.

[0127] In a variation of the exemplary embodiment, the solar cell 19 and the

[0128] Catalyst layers as described in Cell Reports Physical Science 4, 101606 (2023), .2023 101606 described trained.

[0129] In a further modification of the embodiment, the solar cell 19 and the catalyst layers are designed as described in Perales et al. SPI E proc. 2016 doi: 10.1117 / 12.2213886.

[0130] The photoelectrochemical reactor has a cover 1 which is located above the electrolyte 11 and the solar cells 19.

[0131] The cover 1 is made of (solar) glass or a transparent, UV-resistant polymer, in this case made of glass, and is therefore transparent to the incoming radiation 2. The upper side surfaces of the solar cells 19 are arranged directly against the cover 1, so that contact between the electrolyte 11 and the upper side surfaces is excluded.

[0132] Between the solar cells 19, the cover 1 has gas channels 5, which are in the present form in prism shape.

[0133] 33937-P-DE Tue / co 01.10.2024 The solar cells 19 are arranged such that the anode sides or the cathode sides of adjacent solar cells are opposite each other. Accordingly, a gaseous reaction product is generated between each pair of solar cells.

[0134] The photoelectrochemical reactor according to the first embodiment is designed for solar water splitting. The electrolyte is a dilute acid such as HClO4 or H2SO4, a neutral solution such as phosphate buffer, or a base such as NaOH, in this case a phosphate buffer.

[0135] When input radiation 2 in the form of sunlight strikes the cover 1, it is directed to the upper side surfaces of the solar cells 19 and coupled into them. The solar cells 19 convert the coupled input radiation 2 into electrical power, creating a reaction current between the anode and cathode sides. Oxygen gas is formed at the catalyst layers on the anode side, and hydrogen gas is formed at the catalyst layers on the cathode side.

[0136] Due to the mutually facing anode and cathode sides of the solar cells 19, hydrogen gas H2 (reference numeral 3) is formed in the left space between the solar cells in the embodiment shown in Figure 1. This gas rises in gas bubbles 15 and is collected and discharged in the left channel 5. In the right space, oxygen gas O2 (reference numeral 4) is generated, which also rises in gas bubbles and is collected and discharged in the right channel 5.

[0137] The arrangement shown in Figure 1 separates the two gaseous reaction products without the need for further separation devices. In an advantageous embodiment of the model shown in Figure 1, membranes 10 are attached at the lower ends between the solar cells 19. These membranes are permeable to ions of the electrolyte but impermeable to gas.

[0138] 33937-P-DE Di / co 01.10.2024. This further reduces the risk of the reaction gases mixing. As an example, a membrane 10 according to the described advantageous embodiment is shown between the middle and right solar cells 19 in Figure 1. The membranes are designed as Nation, AEM or diaphragm, in this case as Nation.

[0139] An insulating layer 8, made of SiC or TiC, in this case a silicon dioxide layer, is arranged on the lower side surfaces of each solar cell 19. The insulating layer reduces charge carrier recombination on the lower side surfaces of the solar cells 19, thereby increasing the electronic efficiency of the solar cells. Furthermore, it facilitates contact between the lower side surfaces and the electrolyte. Additionally, a reflective layer 9 is arranged on the lower side of the insulating layer 8 of each solar cell 19. The reflective layer 9 is a metallic reflective layer, in this case made of gold. The reflective layer achieves internal reflection at the lower side surfaces of the solar cells 19, resulting in multiple passes of the input radiation 2 into the solar cells 19 and thus increasing the efficiency of the solar cells.

[0140] The wall surfaces of the gas channels 5 are also coated with a reflective layer, in this case made of a vapor-deposited metal, in this case gold. This achieves internal reflection of the input radiation 2, which strikes the inner walls of the gas channels 5, and thus concentrates the input radiation 2 onto the upper side surfaces of the solar cells 19. The beam path of a reflection 16 is shown as an example. This can also be achieved instead of the reflective layer by using materials 1 and 5 with different refractive indices, which may also include any gases or liquids transported in 5. The cover 1 is therefore designed as a concentration unit, made of glass with a refractive index of 1.46.In a variation of this embodiment, in which the wall surfaces of the gas channels do not have reflective properties, the cover 1 is therefore not designed as a concentration unit.

[0141] 33937-P-DE Di / co 01.10.2024 Figure 2 shows a second embodiment of a photoelectrochemical reactor according to the invention. The structure essentially corresponds to the structure of the first embodiment shown in Figure 1. To avoid repetition, the essential differences are discussed below:

[0142] The solar cells 19 are arranged such that an anode side of one solar cell 19 is opposite a cathode side of an adjacent solar cell.

[0143] Accordingly, both gaseous reaction products, hydrogen gas and oxygen gas, are generated in the spaces between the solar cells. To prevent the reaction products from mixing, a membrane 10, made of Nation, AEM, or a diaphragm (in this case, Nation), is arranged centrally between the solar cells 19 and parallel to the solar cells in each space. The membrane 10 is permeable to ions of the electrolyte but not to the reaction products, hydrogen gas or oxygen gas. Extending from the membrane 10, a partition 17 is arranged centrally in each of the gas channels 5 of the cover 1. The gas channels 5 are thus each divided into two sub-gas channels. Accordingly, hydrogen gas 3 is collected and discharged in the left sub-channel of the gas channels 5, and oxygen gas 4 is collected and discharged in the right sub-channel.

[0144] In a modification of the embodiment shown in Figure 2, the membrane 10 and the partitions 17 are omitted. This creates a mixture between each of the solar cells 19, so that both reaction products, hydrogen gas and oxygen gas, are collected and discharged in the gas channel 5. In this further development, the reactor has a downstream device for separating gaseous hydrogen on the one hand and gaseous oxygen on the other.

[0145] 33937-P-DE Tue / co 01.10.2024 TI

[0146] Figure 3 shows a top view of the first embodiment shown in Figure 1, excluding the cover 1. The parallel arrangement of the solar cells 19 m is evident, each with its respective cathode-side catalyst layers 7 or anode-side catalyst layers 6 facing each other.

[0147] Figure 4 shows a third embodiment of a reactor according to the invention, which is a further development of the first embodiment shown in Figure 1. The further development consists of an arrangement of an antireflective layer 18 and an insulating layer 8 between the cover 1 and the solar cells 19.

[0148] The antireflective layers 18 are formed as a TiOj / MgFj layer with a thickness of 50 to 200 nm, in this case 100 nm. The insulating layers 8 are made of SiOz or TiC, in this case as a titanium oxide layer with a thickness of 5 to 100 nm, in this case 50 nm.

[0149] Figure 5 shows a fourth embodiment of a reactor according to the invention, which is a further development of the first embodiment shown in Figure 1. The fourth embodiment additionally has an insulating layer 8 between the cover 1 and the solar cells 19, as described above.

[0150] In the fourth embodiment, the prismatic gaps in the cover 1 according to the first embodiment are replaced by intermediate areas 21, which have a different refractive index than the cover outside the intermediate areas. In this case, the intermediate areas have a refractive index of 1.52 (glass with a refractive index of 1.52), while the cover outside the intermediate areas has a refractive index of 1.46 (glass with a refractive index of 1.46). This results in internal reflection of the incoming radiation at the interfaces with the intermediate areas within the cover.

[0151] 33937-P-DE Di / co 01.10.2024 In this embodiment, the gas channels 5 are designed as narrow, cuboid-shaped gas channels between the surface of the electrolyte 11 and the intermediate areas 21.

[0152] In a modification of the fourth embodiment shown in Figure 5, the reactor is configured for CO₂ reduction. For this purpose, the cathode-side catalyst layer can be made of one of the materials copper(oxide), palladium, or cobalt(oxide); in this case, it is a copper oxide layer with a thickness of approximately 50 nm, allowing for a hole-free covering of the photoelectrode. The anode-side catalyst layer remains unchanged. Accordingly, CO₂ is produced on the cathode side.

[0153] Specific information on the refractive index or the ratio of refractive indices refers, within the scope of this application, to the usual specification for the wavelength of the sodium D line (589 nm).

[0154] 33937-P-DE Di / co 01.10.2024 Characters

[0155] 1 cover

[0156] 2 Input radiation

[0157] 3 H2

[0158] 4 02

[0159] 5 Gas channel

[0160] 6 anode-side catalyst layer

[0161] 7 cathode-side catalyst layer

[0162] 8 Insulation layer

[0163] 9 Mirror layer

[0164] 10 Membran

[0165] 11 Electrolyte

[0166] 12, 14 partial solar cells

[0167] 13 Tunnel diode

[0168] 15 gas bubbles

[0169] 16 Reflection

[0170] 17 Partition wall

[0171] 18 Anti-reflective coating

[0172] 19 solar cells

[0173] 20 containers

[0174] 21 Intermediate areas

[0175] 33937-P-DE Tue / co 01.10.2024

Claims

Claims 1. Photoelectrochemical reactor, comprising at least one container which is at least partially filled with an electrolyte (11) and comprising at least one solar cell (19) for converting electromagnetic input radiation (2) incident on the reactor into electrical power, wherein the solar cell has an anode side and a cathode side opposite the anode side and one or more side surfaces, wherein a cathode-side catalyst layer (7) and an anode-side catalyst layer (6) are arranged on the cathode side and wherein the solar cell (19) is arranged such that the cathode-side catalyst layer (7) and the anode-side catalyst layer (6) are in contact with the electrolyte (11), characterized in that the reactor is designed such that the input radiation (2) is coupled into the solar cell (19) substantially through one or more side surfaces of the solar cell (19).preferably substantially through a side surface of the solar cell (19).

2. Reactor according to claim 1, characterized in that the reactor is designed such that the radiant energy of the radiation coupled into the solar cell (19) through one or more side surfaces is at least 80%, preferably at least 90%, in particular at least 95% of the total radiant energy of the input radiation (2) coupled into the solar cell (19).

3. Reactor according to one of the preceding claims, characterized in that 33937-P-DE Tue / co 01.10.2024 that the solar cell (19) is designed as a multiple solar cell with several sub-solar cells (12, 14), in particular that the sub-solar cells (12, 14) have absorber structures with substantially the same band gaps.

4. Reactor according to one of the preceding claims, characterized in that one of the sides, anode side or cathode side of the solar cell ( 19), is arranged at an angle in the range of 45° to 90°, in particular 60° to 90°, to a top side of the electrolyte (11).

5. Reactor according to one of the preceding claims, characterized in that the reactor is designed such that the sum of the radiation energies of the radiation coupled into the solar cell (19) through the anode side and through the cathode side is less than 20%, preferably less than 10%, in particular less than 5% of the total radiation energy of the radiation coupled into the solar cell (19).

6. Reactor according to one of the preceding claims, characterized in that the anode-side catalyst layer (6) and / or the cathode-side catalyst layer (7), preferably both catalyst layers, have a thickness greater than 3 nm, preferably greater than 50 nm and are preferably formed as a closed layer.

7. Reactor according to one of the preceding claims, characterized in that the radiative coupling of the input radiation (2) into the solar cell (19) is effected substantially by one or more side surfaces of the solar cell (19), preferably a side surface of the solar cell (19), which are not in contact with the electrolyte (11). 33937-P-DE Tue / co 01.10.2024 8. Reactor according to one of the preceding claims, characterized in that a mirror layer (9) is arranged on at least one of the side surfaces of the solar cell ( 19), in particular on a side surface which is opposite a side surface through which input radiation (2) is coupled into the solar cell (19).

9. Reactor according to one of the preceding claims, characterized in that the reactor has a plurality of solar cells ( 19 ), in particular that the solar cells (19 ) are arranged parallel to each other or radially around a common center.

10. Reactor according to one of the preceding claims, characterized in that the reactor has an optical concentration unit which is designed and arranged to concentrate input radiation (2) incident on the reactor onto one or more side surfaces of the solar cell (19), in particular that the concentration unit is designed and arranged such that the input radiation (2) is coupled into the solar cell (19) substantially through one or more side surfaces of the solar cell (19), preferably substantially through one side surface of the solar cell (19), in particular that the concentration unit is designed and arranged such that the sum of the radiation energies of the radiation coupled into the solar cell (19) through the anode side and through the cathode side is less than 20%, preferably less than 10%.in particular less than 5% of the total irradiance energy of the radiation coupled into the solar cell (19). 33937-P-DE Tue / co 01.10.2024 11. Reactor according to one of the preceding claims, characterized in that the reactor is designed for solar water splitting.

12. Method for carrying out a photoelectrochemical reaction, in particular by means of a reactor according to one of the preceding claims, comprising the process steps Providing at least one solar cell (19) with an anode side, a cathode side and one or more side surfaces, wherein the anode side is electrically connected to an anode-side catalyst (6) and the cathode side to a cathode-side catalyst (7) and both catalysts are in contact with an electrolyte (11), Coupling of electromagnetic input radiation (2), in particular sunlight, to convert the input radiation (2) into electrical power and to generate an electric current between the anode side and the cathode side of the solar cell (19), characterized in that the input radiation (2) is coupled into the solar cell (19) via one or more side surfaces of the solar cell (19), preferably substantially via one side surface of the solar cell (19).

13. Method according to claim 12, characterized in that the radiant energy of the radiation coupled into the solar cell (19) through one or more side surfaces is at least 80%, preferably at least 90%, in particular at least 95% of the total radiant energy of the input radiation (2) coupled into the solar cell (19).

14. Method according to one of claims 12 to 13, characterized in that, 33937-P-DE Tue / co 01.10.2024 that the input radiation (2) is concentrated onto one or more side surfaces of the solar cell (19), preferably onto one side surface of the solar cell (19), by means of an optical concentration device.

15. Method according to one of the preceding claims, characterized in that the electrolyte (11) comprises water and solar water splitting takes place by means of the electric current formed between the anode side and the cathode side of the solar cell (19). 33937-P-DE Tue / co 01.10.2024

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