Modular electrolyzer stack and method for converting carbon dioxide into gaseous products at elevated pressure with high conversion rate

Abstract

The present invention relates to the field of converting gaseous carbon dioxide into gaseous products at high conversion rates at elevated pressures by electrolysis using a novel multi-cell CO2 electrolyser stack (100") having a novel gas and fluid flow architecture formed in the bipolar plate assemblies of the individual cells (40) used to construct the stack (100").

Description

Field of the Invention

[0001] The present invention relates to the field of generating gaseous products at elevated pressures with high conversion rates by electrolysis of gaseous carbon dioxide. The present invention therefore also relates to a novel modular electrolyser stack for carrying out the electrolysis and thus for converting carbon dioxide gas into various gaseous products, preferably ready for use as feedstock for further industrial processes. Background Art

[0002] Carbon dioxide (CO2) is a greenhouse gas; therefore, using renewable energy to convert it into transportation fuels and bulk chemicals is a value-added method for simultaneously generating products and environmentally repairing carbon emissions. The large number of chemicals produced worldwide that have the potential to be derived from the electrochemical reduction (and hydrogenation) of CO2 further highlights the importance of this strategy. The electrosynthesis of chemicals using renewable energy (such as solar or wind energy) contributes to a green and more sustainable chemical industry. Due to the various possible CO2-derived products, electrolyzers based on polymer-electrolyte membranes (PEMs) are particularly attractive. Some industrial entities are interested in such technologies, from energy / utilities companies to cement production and processing companies to oil and gas companies.

[0003] Similar to PEM-based water electrolyzers (i.e., H2 / O2 generators), the typical configuration of PEM-based CO2 electrolyzers consists of two flow paths, one for the anolyte and the other for the catholyte, separated by an ion exchange membrane in direct contact with the catalyst. The cathode electrocatalyst is fixed on a porous gas diffusion layer (GDL) that is usually in contact with the flowing liquid cathode electrolyte, while the CO2 gas is also fed through the GDL. This arrangement may overcome some of the known problems in the field, namely: (i) current limitations due to low CO2 concentrations at the electrodes; (ii) H + From the anode across the membrane, and with it acidification of the catholyte, resulting in increased selectivity for H2 evolution; (iii) the products diffuse to the anode where they are oxidized (product crossover). Although such an instrument is not currently commercially available on an industrial scale, most of its components (i.e., GDLs and catalysts) as well as laboratory-scale devices (~5 cm 2 However, in the case of CO2 electrolysis, the structure and operating conditions of PEM-based CO2 electrolyzers must be carefully optimized.

[0004] For example, a comprehensive review of PEM-based CO2 electrolysis is provided in Progress in Energy and Combustion Science 62(2017), pages 133 - 154, where the parameters affecting the performance of a flowing CO2 electrolyzer are discussed in detail. The analysis covers the basic design concepts of the electrochemical cell (microfluidic or membrane-based), the materials used (such as catalysts, supports, etc.), and the operating conditions (such as the type of electrolyte, the role of pressure, temperature, etc.).

[0005] European Patent Application Publication No. 3,375,907 A1 discloses a carbon dioxide electrolysis device in the form of a single-cell electrolyzer, which comprises: an anode part including an anode that oxidizes water or hydroxide ions to produce oxygen; a cathode part including a cathode that reduces carbon dioxide to produce carbon compounds, a cathode solution flow path for supplying a cathode solution to the cathode, and a gas flow path for supplying carbon dioxide to the cathode; a diaphragm that separates the anode part from the cathode part; and a differential pressure control unit that controls the differential pressure between the pressure of the cathode solution and the pressure of carbon dioxide to adjust the amount of carbon dioxide generated by the reduction reaction in the cathode part.

[0006] U.S. Patent Application Publication No. 2018 / 0274109 A1 relates to a single-cell carbon dioxide electrolysis device equipped with: a refresh material supply unit including a gas supply unit that supplies a gaseous substance to at least one of the anode and the cathode; and a refresh control unit that stops the supply of current from a power source, the supply of carbon dioxide and an electrolytic solution, and manipulates the refresh material supply unit based on request criteria of the cell output of the electrolytic cell.

[0007] U.S. Patent Application Publication No. 2013 / 0105304 A1 relates to methods and systems for electrochemically converting carbon dioxide into organic products (including formate and formic acid). One embodiment of the system includes a first electrochemical cell comprising a cathode chamber containing a high-surface-area cathode and a bicarbonate-based liquid cathode electrolyte saturated with carbon dioxide. The system further includes an anode chamber containing an anode and a liquid acidic anode electrolyte. The first electrochemical cell is configured to produce a product stream when a potential is applied between the anode and the cathode. Further embodiments of the system may include a separate second electrochemical cell similar to and fluidly connected to the first electrochemical cell.

[0008] U.S. Published Patent Application No. 2016 / 0369415 A1 discloses a catalyst layer for an electrochemical device, particularly an electrolyzer, the feed of which contains at least one of CO2 and H2O. The catalyst layer contains a catalytically active element and an ion-conductive polymer. The ion-conductive polymer contains a positively charged cyclic amine group. The ion-conductive polymer contains at least one of imidazolium, pyridinium, pyrazolium, pyrrolidinium, pyrrolium, pyrimidinium, piperidinium, indolium, triazinium, and their polymers. The catalytically active element contains at least one of V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd.

[0009] U.S. Published Patent Application No. 2017 / 0321334 A1 teaches a membrane electrode assembly (MEA) for a CO x reduction reactor. The MEA has a cathode layer containing a reduction catalyst and a first ion-conductive polymer, and an anode layer containing an oxidation catalyst and a second ion-conductive polymer. Between the anode layer and the cathode layer, a PEM containing a third ion-conductive polymer is disposed. The PEM provides ionic communication between the anode layer and the cathode layer. There is also a cathode buffer layer containing a fourth ion-conductive polymer, namely cathode buffer, between the cathode layer and the PEM. There are three types of ion-conductive polymers: anion conductors, cation conductors, and cation-anion conductors. At least two of the first, second, third, and fourth ion-conductive polymers are from different types of ion-conductive polymers.

[0010] International Publication Pamphlet No. WO2017 / 176600 A1 relates to an electrocatalytic method for CO2 conversion. The method uses a novel catalyst combination, which aims to overcome one or more limitations of low rate, high overpotential, and low electron conversion efficiency (i.e., selectivity), low rate of catalytic reaction, and high power requirement for sensors. The catalyst combination or mixture includes at least one catalytically active element in the form of supported or unsupported particles, wherein the average particle size of the particles is between about 0.6 nm and 100 nm, preferably between 0.6 nm and 40 nm, and most preferably between 0.6 nm and 10 nm. The catalyst combination also includes an auxiliary polymer, which may contain, for example, a positively charged cyclic amine group, such as imidazolium or pyridinium. The catalyst combination of the catalytically active element and the auxiliary polymer is very useful when used in the cathode catalyst layer of a single electrochemical cell for converting CO2 into various reaction products.

[0011] U.S. Patent No. 10,208,385 B2 discloses a carbon dioxide electrolysis device having a single electrolyzer cell for converting CO2 into various products, especially CO, wherein the cell includes a cathode, an anode, a carbon dioxide supply unit, an electrolytic solution supply unit, and a diaphragm separating the cathode and the anode from each other. In addition to the cell, the carbon dioxide electrolysis device further includes a power source; a reaction control unit that causes reduction and oxidation reactions by flowing current from the power source to the anode and the cathode. The cell is fed with gaseous CO2 on the cathode side and with liquid electrolyte on at least the anode side. The gas and the liquid are distributed in the cell through gas and liquid flow paths formed in the cathode and anode current collectors, respectively.

[0012] As is clear from the above, most of the prior art in the field of CO2 electrolysis has focused on developing new catalysts to enhance the activity and product selectivity using a single cell configuration. At the same time, in a simple batch-type electrochemical cell, the maximum achievable rate of the reaction is usually limited by the low solubility of CO2 in water (∼30 mM). Similar problems arise when feeding a solution (catholyte) to the cathode of a continuous flow electrolyzer, and thus a direct CO2 gas-fed (i.e., electrolyte-free) electrolyzer cell is preferred.

[0013] Therefore, there is a need to increase the CO2 conversion rate to a practically meaningful level. In other words, to overcome the mass transfer limitations, continuous flow, direct CO2 gas-fed devices and methods are needed to electrochemically reduce CO2 at a high conversion rate (e.g., at a current density of at least 150 mA cm -2 .

[0014] There is a broad consensus in the art that, in order to drive this method in an economically attractive manner, it is important to (i) produce any product as selectively as possible; (ii) produce a product of economic value; and (iii) produce a product that is easy to separate. To achieve these objectives, an electrolyzer cell / stack operating as follows is therefore needed:

[0015] · Operate at a high current density (which translates to a high reaction rate);

[0016] · Operate at a high Faradaic efficiency for the desired product (i.e., most of the total current input (∑ i j i ) is used for product formation (j 产物 ), and thus exhibits high selectivity for a given product), where

[0017]

[0018] · Operate at a low overpotential for the method (which determines the energy efficiency of the method), which is defined as

[0019]

[0020] where E 0 阳极 and E 0 阴极 are the standard redox potentials of the anodic and cathodic reactions, respectively, and V 池 is the measured cell voltage; and

[0021] · Operating at high conversion efficiency (which gives the ratio of converted CO2 to CO2 feed), which is defined as

[0022]

[0023] If the electrolyzer cell / stack does not meet any of these points, it cannot compete with other non-electrochemical technologies at a practical scale.

[0024] Therefore, there is also a need for a new type of CO2 electrolyzer stack and method that optimize the stack architecture and operating parameters to achieve the above goals in this case.

[0025] In addition, there is a need to provide large-sized and cell-based modular CO2 electrolyzer stacks, especially for industrial applications, i.e., multi-cell electrolyzer stacks composed of more than one, preferably several, electrolyzer cells, where the cells can be manufactured relatively simply and inexpensively.

[0026] In most cases, industrial CO2 sources provide gaseous CO2 at elevated pressures. In addition, industrial processes that utilize various gas-phase carbon-based substances, such as syngas, carbon monoxide, methane, ethane, ethylene, etc., as raw materials for producing other products require the raw materials to also be at elevated pressures; herein and hereinafter, the term "elevated pressure" refers to a pressure difference that falls within the range of approximately 0 bar to at most approximately 30 bar.

[0027] In view of this, there is clearly a need for a CO2 electrolyzer stack that can withstand elevated pressures, especially on its cathode side.

[0028] Another object of the present invention is to provide a CO2 electrolyzer stack that can be easily and simply reconfigured as needed if the required productivity or even the product type changes.

[0029] Other objects, aspects, features, and advantages of the present invention will be set forth in the following description. Summary of the Invention

[0031] The above object is achieved by means of a continuous flow multi-cell or multi-layer electrolyser stack according to claim 1. Further preferred embodiments of the stack according to the invention are set out in claims 2 to 14. The above object is also achieved by means of a CO2 electrolyser device according to claim 15 for converting starting gaseous carbon dioxide into a final gaseous phase product. Preferred embodiments of the CO2 electrolyser arrangement according to the invention are defined by claims 14 to 21. The above object is also achieved by means of a method according to claim 22 for converting gaseous carbon dioxide CO2 into at least one gaseous phase product. Claims 23 and 24 list preferred variants of the method.

[0032] In particular, the present invention relates to new components and new assemblies of a carbon dioxide electrolyser stack capable of operating at elevated pressure differences with high conversion rates. It is based on the electrochemical reduction of gaseous carbon dioxide to gaseous phase products (see Table 1 below) and oxidation reactions (such as the oxidation of water, H2O - 2e - = 2H + + 0.5O2) on the cathode side and the anode side respectively; the carbon dioxide used is preferably humidified before it is fed into the electrolyser stack.

[0033] Table 1. Some possible reactions for producing gaseous phase products in CO2 electrolysis

[0034]

[0035] Due to the proposed technical novelty and modular construction, the proposed electrolyser stack architecture is highly scalable and flexible. While maintaining the pressure tolerance, the stack can be easily scaled both in terms of its size / dimensions and the number of cells used. Thus, based on a new concept of a multi-layer configuration in the field of CO2 electrolysis, a CO2 electrolyser stack is constructed, where the number of cells is up to 10 or more, preferably 2 to 7, more preferably 3 to 6, and most preferably three, or four, or five or six.

[0036] Furthermore, the stack architecture allows the individual electrolyser cells to be connected in parallel or in series, or in a hybrid manner, with respect to gas management. It has surprisingly been found that by changing only one element of the electrolyser stack (and rearranging the other elements), the operation can be switched from series to parallel. Thus, the stack can be operated as required to achieve particularly high conversion rates or conversion efficiencies. The catalysts, gas diffusion layers and ion exchange membranes used allow the flexible generation of different gaseous phase products. This enables the CO2 electrolyser stack according to the invention to be applied to various industries, such as the chemical, petroleum and energy industries. It should be noted that the present invention is not limited to CO2 electrolyser stacks and, with appropriate conventional modifications, it can also be applied to other electrochemical devices (such as an N2 reduction stack for ammonia production).

[0037] In the present invention, several cells (electrocatalyst layer and membrane) are (electrically) connected in series, bounded by bipolar plate assemblies, which act as the anode of one cell on one side and as the cathode of the subsequent cell on the other side (similar to a PEM fuel cell or a water electrolyzer).

[0038] A specific multi-cell stack architecture is achieved by using two-component bipolar plate assemblies in the formation of the single electrolyzer cell. Here, the first component of a certain bipolar plate assembly forms the anode part of the cell, while the second component of the bipolar plate assembly forms the cathode part of the cell arranged immediately following said cell. In this way, a series of electrolyzer cells can be formed, where some of the flow structure elements of the cathode / anode flow paths within the stack, namely the cavities and channels for gas flow on the cathode part and the cavities and channels for liquid flow on the anode part of the stack, are prepared on / within and between the opposing side surfaces of the first and second components of the bipolar plate assembly.

[0039] Furthermore, by selectively forming annular spacer elements with through-channels, namely anode side distances (which actually support the subsequent bipolar plate assemblies in the electrolyzer stack when the stack is assembled), a series / parallel flow channel configuration is formed; in particular, in line with the modular construction, two different types of spacer elements are provided, the first type having a single internal gas transport channel in the outer peripheral part of the spacer element, and the second type having two gas transport channels diametrically opposed to the outer peripheral part of the spacer element. When assembling the electrolyzer stack, using the first type of spacer element between successive bipolar plate assemblies enables the formation of a continuous gas flow path within the stack (i.e., in terms of the gas management of the stack, the individual cells are connected in series), while using the second type of spacer element between successive bipolar plate assemblies results in the formation of a gas flow path with parallel segments within the stack (i.e., in terms of the gas management of the stack, the cell gas flow paths in the individual cells are connected in parallel). The use of said specific spacer elements also enables the establishment of a structured gas flow path within the multi-cell electrolyzer stack, which may equally contain series and parallel segments.

[0040] That is to say, the functions of the bipolar plate assembly and the end unit are complex: (i) they form a current collector in contact with the catalyst layer, (ii) when reactants are fed to the catalyst layer via channels formed in these plates, they are responsible for supplying the reactants to the active area of the stack and for the proper discharge of the products, and (iii) these contribute to the mechanical strength of the stack. In addition, they also play an important role in the thermal management of the electrolyzer stack. To achieve this, an in-plane flow channel system is formed on the surface of each of the said elements to increase the surface area and assist the transport process. The flow channels are organized into various flow field designs of specific geometries that are specifically optimized for the first time.

[0041] Another component used in the CO2 electrolyzer stack according to the present invention is a custom-designed and assembled anode-side structural element made of titanium (Ti) frit (Ti frit). The Ti frit is made of titanium powder of different average particle sizes. The Ti frit is actually made by pressing Ti particles. The anode catalyst is directly deposited on such Ti frit by, for example, a wet chemical synthesis method, or synthesized separately and then fixed on the Ti frit.

[0042] Regarding the cathode catalyst used in the CO2 electrolyzer stack according to the present invention, it is fixed on a high-surface-area carbon carrier (i.e., GDL) in direct contact with the bipolar plate assembly. The CO2 gas is fed to the catalyst through such GDL. At the same time, the catalyst is in direct contact with the PEM to facilitate ion transport.

[0043] Another component used within the CO2 electrolyzer stack according to the present invention is a pressure chamber formed within specific end units arranged at both ends of the stack, i.e., the cathode side and the anode side ends. The pressure chamber provides adaptive pressure control to the cell from both sides, thereby providing a uniform pressure distribution throughout the cell. This configuration inhibits deformation of the stack body and thus avoids a reduction in the contact area between internal components. This results in a stack resistance that is stable even under elevated pressures. Importantly, the application of the end unit eliminates the need for moving parts (such as pistons or valves) or elastic plastic elements as pressure control devices within the stack. In addition, different from any external pressure control, the use of the pressure chamber in the end unit is inherently safe because the pressure in the pressure chamber will never be higher than the pressure generated in the electrolyzer cell. To ensure pressure-independent electrochemical performance, the pressure chambers are applied in pairs, i.e., one on the cathode side of the electrolyzer stack according to the present invention and the other on the anode side. Brief Description of the Drawings

[0045] The present invention will be described in detail below with reference to the accompanying drawings, where

[0046] - Figure 1Illustrated is the simplified operation of a carbon dioxide electrolyzer device according to the present invention, where the cathode side of the electrolyzer stack used therein is fed with (humidified) CO2 gas and the anode side is fed with tempered anolyte;

[0047] - Figure 2A is Figure 1 a schematic cross-sectional view of a single-layer electrolyzer cell available in the carbon dioxide electrolyzer device shown in;

[0048] - Figure 2B is Figure 2A an exploded view of a part of the cell illustrated in;

[0049] - Figure 3A and 3B are respectively the complete upper and lower perspective views of a specific exemplary embodiment of an electrolyzer stack according to the present invention having three cells for converting carbon dioxide gas into various gas-phase products;

[0050] - Figure 4 is a partially exploded view of a multi-cell electrolyzer stack according to the present invention containing n cells, where one electrolyzer cell is exploded;

[0051] - Figure 5 is a bottom view of a preferred dual-component bipolar plate assembly that serves as the first (anode) component of the intermediate electrolyzer cell (cell i + 1) of the stack and the second (cathode) component of the adjacent intermediate electrolyzer cell (cell i) of the stack (here, 0 < i < n - 1, i, n are integers);

[0052] - Figure 5A is Figure 5 a cross-sectional view of the bipolar plate assembly shown in taken along the A-A section;

[0053] - Figure 5B is Figure 5 a cross-sectional view of the bipolar plate assembly shown in taken along the B-B section;

[0054] - Figure 6 is a cross-sectional view of a three-cell stack assembled for a parallel flow configuration in terms of CO2 supply to the stack along Figure 3A the A-A section shown in; here, the flow channel and cavity system shown in gray represents the path of the gas flow in the stack from the CO2 inlet to the CO2 and product outlet;

[0055] - Figure 7 is a cross-sectional view of a three-cell stack assembled for a serial configuration in terms of CO2 supply to the stack along Figure 3ACross-sectional view of the A-A section as shown; here, the flow channels and cavity system shown in grey represent the path of the gas flow within the stack from the CO2 inlet to the CO2 and product outlet;

[0056] - Figure 8 is a cross-sectional view of a three-cell stack in a serial / parallel configuration along Figure 3A the B-B section as shown; here, the flow channels and cavity system shown in grey represent the path of the fluid (i.e., the anolyte) flow within the stack from the anolyte inlet to the anolyte and anode product (especially O2 when using water as the anolyte) outlet;

[0057] - Figure 9 illustrates the various flow patterns formed in the surface of the cathode current collector used in the electrolyzer stack according to the present invention; here Figure 9 (a) to (c) show some exemplary designs where CO2 is fed into the cell at the center and collected from the cell along the peripheral ring, while figure (d) shows another exemplary design where CO2 is fed into the cell at the perimeter of the cathode current collector and also collected from the cell at the perimeter of the cathode current collector but at a position opposite the CO2 introduction point after passing through a double-helix pattern;

[0058] - Figure 10A illustrates a possible preferred embodiment of the anode-side spacer element for achieving a serial gas flow configuration between two adjacent cell / bipolar plate assemblies in an assembled multi-cell electrolyzer stack;

[0059] - Figure 10B illustrates a possible preferred embodiment of the anode-side spacer element for achieving a parallel gas flow configuration between two adjacent cell / bipolar plate assemblies in an assembled multi-cell electrolyzer stack;

[0060] - Figure 11A and 11B show the anode current collector, i.e., Figure 5 a possible preferred embodiment of the anode part of the bipolar plate assembly in

[0061] - Figure 12A and 12B respectively show the exploded views of a single cell in a multi-cell electrolyzer stack assembled in a serial or parallel gas flow configuration;

[0062] - Figure 13Illustrate the effect of increasing the number of individual electrolyzer cells used in an electrolyzer stack according to the present invention assembled in a serial or parallel gas flow configuration; in particular, in graph (a), plot the CO2 conversion during the electrolysis process at ΔU = -2.75 V / cell achievable with 1-cell and 3-cell series-connected electrolyzers at different CO2 feed rates, and in graph (b), show the CO2 conversion during the electrolysis process at different cell voltages achievable with an electrolyzer stack composed of one cell or three cells in parallel (with the gas feed standardized with the same cells);

[0063] - Figure 14 Show the current density vs. working cell voltage of a three-cell CO2 electrolyzer stack according to the present invention for the formation of syngas (H2 / CO mixture, on an Ag catalyst) or hydrocarbons (CH4 and C2H4, on a Cu catalyst), which is recorded by linear sweep voltammetry (LSV) at a scan rate of ν = 10 mV s -1 at a scan rate;

[0064] - Figure 15 Is a chronoamperometry curve obtained at ΔU = -3 V / cell for a three-cell CO2 electrolyzer stack according to the present invention using a cathode gas diffusion electrode (GDE) containing 1 mg cm -2 Ag fixed on Sigracet 39BC carbon paper by spraying;

[0065] - Figure 16 Show the gas chromatograms recorded during chronoamperometry measurements at ΔU = -2.75 V / cell using a three-cell CO2 electrolyzer stack according to the present invention using an Ag catalyst [graph (a)] or a Cu catalyst [graph (b)];

[0066] - Figure 17 Show the partial current density (left ordinate) for CO and H2 formation and the ratio of the partial current densities (right ordinate) at different stack voltages (obtained by chronoamperometry and gas chromatography measurements);

[0067] - Figure 18 Show the partial current density (left ordinate) for CO and H2 formation and the CO2 conversion (right ordinate) vs. the amount of Ag catalyst in the cathode GDE during the electrolysis process at ΔU = -2.75 V;

[0068] - Figure 19 Show the partial current density (left ordinate) for H2 and CO formation and the CO2 conversion (right ordinate) vs. the cathode spacing used during the electrolysis process at ΔU = -2.75 V;

[0069] - Figure 20Shown are the partial current densities for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) during electrolysis at ΔU = -2.75 V vs. the depth of the flow pattern used on the cathode side of the electrolyzer stack according to the invention;

[0070] - Figure 21 Graphically depicted are the partial current densities for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) during electrolysis at ΔU = -2.75 V vs. the carbon dioxide flow rate (normalized by surface area) in the cathode chamber of the electrolyzer stack according to the invention;

[0071] - Figure 22 Shown are the partial current densities for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) during electrolysis at ΔU = -2.75 V vs. the temperature of the anolyte (1 M KOH) present in the electrolyzer stack according to the invention (at a feed rate of ~9 cm 3 cm -2 min -1 feed rate);

[0072] - Figure 23 Shown are the LSV curves recorded at a scan rate of ν = 10 mV s during electrolysis in the electrolyzer stack according to the invention at various CO2 pressure differences; and -1 scan rate; and

[0073] - Figure 24 Shown are the current density (graph A) and the ratio of the partial current densities (graph B) at different stack voltages during electrolysis at ΔU = -2.75 V, both relative to the CO2 pressure difference.

[0074] Description of the Possible Embodiments

[0075] Figure 1FIG. illustrates an exemplary embodiment of a CO2 electrolyzer device 200 comprising a CO2 electrolyzer (electrochemical) stack 100 for generating a gaseous product at elevated pressure with high conversion by electrolysis of gaseous CO2 fed into the stack 100, said stack 100 comprising a cathode 101 on the cathode side, an anode 103 on the anode side, and a diaphragm 102 separating the cathode 101 from the anode 102; herein, the diaphragm 102 is preferably a PEM element (e.g., an anion exchange membrane or a cation exchange membrane or a bipolar membrane). The stack 100 is provided with at least one gas inlet 101a and at least one gas outlet 101b, both of which are gas-connected to the cathode side of the stack 100. The stack 100 is further provided with at least one fluid inlet 103a and at least one fluid outlet 103b, both of which are fluid-connected to the anode side of the stack 100. The device 200 further includes a gaseous CO2 source 201, a humidifier 203 for humidifying the gaseous CO2, a power supply 220 for energizing the electrochemical stack 100, an anolyte renewal unit 211 for regenerating the anolyte 213 used on the anode side of the stack 100, a water separator 208 for removing moisture from the gaseous product generated by electrolysis of gaseous CO2 passing through the cathode side of the stack 100, a back pressure regulator 209 for pressurizing the stack 100 to maintain the elevated pressure (up to 30 bar, preferably up to 20 bar) within the stack 100, and a gaseous product outlet 216 leading to a gaseous product container (not shown). As the CO2 source 201, a source of pure gaseous CO2 or a source supplying CO2 in the form of a gas mixture can be used. Optionally, the device 200 further includes any mass flow controller 202 for precisely controlling the mass flow rate of the gaseous CO2 fed into the cathode side of the stack 100, and suitable pressure gauges 210, 210' for characterizing the pressure present within the stack 100. The CO2 source 201 is connected via a suitable conduit 204 to the gas inlet 101a of the stack 100, while the product outlet 216 is connected via another conduit 207 to the gas outlet 101b of the stack 100. Thus, a continuous flow path is formed from the CO2 source 201 via the cathode side of the stack 100 to the product outlet 216. Preferably, the mass flow controller 202 is inserted into the conduit 204 downstream of the CO2 source 201. Preferably, the humidifier 203 is inserted into the conduit 204 downstream of the mass flow controller 202 to humidify the gaseous CO2 before it enters the stack 100. The humidifier 203 is preferably a temperature-controlled bubbler type humidifier, however, any other type of humidifier can also be used for this purpose. Optionally, a pressure gauge 210 is also inserted into the conduit 204 to continuously monitor the inlet pressure within the stack 100. The water separator 208 is inserted into the conduit 207 downstream of the stack 100. The back pressure regulator 209 is inserted into the conduit 207 downstream of the water separator 208. As the water separator 208 and the back pressure regulator 209, any kind of water separator and pressure regulator known to those skilled in the art can be used.Optionally, another pressure gauge 210' is inserted into the pipe 207 between the stack 100 and the back pressure regulator 209 to continuously monitor the outlet pressure in the stack 100. Thus, with the pressure gauges 210, 210', the pressure drop across the stack 100 can also be determined.

[0076] The anode side of the stack 100 is fluidly connected via its fluid outlet 103b and the pipe 205 to the inlet 211a of the anolyte renewal unit 211. In addition, the anode side of the stack 100 is fluidly connected via its fluid inlet 103a and the pipe 206 to the outlet 211b of the anolyte renewal unit 211. Thereby, a closed continuous flow path is formed on the anode side of the stack 100 between the anode side and the anolyte renewal unit 211. Through this closed flow path, the anolyte 213 is circulated by a pump 215 preferably inserted into the pipe 206 between the anode side (through a suitable system of fluid channels formed in the anode) and the renewal unit 211 to renew the spoilt anolyte generated in the electrochemical reaction on the anode side of the stack 100 (if required). In addition, in order to provide the possibility of venting in the anolyte renewal unit 211, the unit is also equipped with a venting device 214 - excess gas accumulating in the renewal unit 211, which is separated from the spoilt anolyte 213 during the renewal of the anolyte 213, can leave the unit via it. For the optimal operation of the CO2 electrolyzer device 200 and thus also for the optimal operation of the stack 100, the anolyte renewal unit 211 is thermally coupled to a suitable tempering device 212 to adjust the temperature of the anolyte 213, i.e., to cool / heat it. For this purpose, as is clear to a person skilled in the art, any kind of tempering device, i.e., a cooler / heater device, can be used.

[0077] Regarding the power supply for the stack 100, the negative pole of the power supply 220 is electrically connected to the cathode side of the stack 100, in particular to the cathode side contact plate, while the positive pole of the power supply 220 is electrically connected to the anode side of the stack 100, in particular to the anode side contact plate (which will be discussed in detail later). The power supply 220 can be the power grid itself or any local power source, i.e., a solar, wind, or nuclear power source. A battery - whether a primary battery or a secondary battery - can equally be used as the power supply 220.

[0078] During operation, carbon dioxide (pure or in a gas mixture) is first humidified at a controlled temperature (preferably in the range of about 20 °C to about 70 °C), and then fed to the cathode side of the stack 100. Here, no solution is fed to the cathode. When only the humidified CO2 gas is fed to the cathode side, a very high reactant concentration is maintained on the catalyst, and thus a high reaction rate (current) can be achieved. In addition, due to the lack of solution feed, there is no washing away of reactants that have not reacted with the feed stream. Since the type of reactants has an important and complex impact on the stack performance, this modification regarding the feed type represents a significant difference compared to most prior art solutions. In the proposed CO2 electrolyzer device 200, only gaseous products are formed in the electrolysis reaction occurring in the stack 100. Depending on the catalyst used in the stack 100 and the applied CO2 electrolysis reaction (see Table 1), various products are obtained; as examples, (i) syngas (a CO / H2 mixture with a controlled composition) and (ii) ethylene are mentioned here. In the cathode section, i.e., within the flow channel system made in the cathode-side member (discussed later), the gaseous products formed leave the stack 100 and are then introduced into the water separator 208 to remove moisture. The anolyte 213 (used as an aqueous solution, the type of which depends on the type of diaphragm 102 used, i.e., the ion exchange membrane used) is directly and continuously fed into the anode side of the stack 100 by the pump 215. The anolyte 213 then flows through the stack 100 in the flow channel system made in the anode-side member and collects the gaseous oxygen formed in the CO2 electrolysis reaction along its path. When the flow of the anolyte 213 leaves the stack 100 and before being recycled to the stack 100, the oxygen content in the anolyte 213 is released in the anolyte renewal unit 211 and then discharged through the exhaust device 214. Significantly, as is clear to those skilled in the art, other value-added anodic processes (in addition to water oxidation, such as chlorine formation or alcohol oxidation) can be combined with CO2 conversion; the architecture of the device 200 / stack 100 is not limited to water oxidation at all. In addition, during the operation of the device 200, the pressure in the stack 100 is continuously controlled by the backpressure regulator 209. Thus, contrary to most prior art solutions, the electrolyzer stack 100 actually operates under a continuous pressure difference.

[0079] Figure 2A is Figure 1 Schematic cross-sectional view of a single exemplary PEM electrolyzer cell available in the CO2 electrolyzer stack 100 / device 200 shown in Figure 2B is in Figure 2AAn exploded view of the cell portion taken near the b-b line shown in the figure. The cell contains a PEM, in particular an ion exchange membrane 7, 102, which is fixed in place by spacer elements 9(a, b) arranged on opposite sides (i.e., the cathode side and the anode side) of the membrane 7 along its peripheral portion. The membrane 7 acts as a diaphragm element that isolates the cathode 101 and the anode 103 (i.e., the cathode side and the anode side) of the cell from each other. On the cathode side, a (cathode) catalyst layer 6b is arranged adjacent to and in direct contact with the membrane 7. On the surface of the catalyst layer 6b facing away from the membrane 7, a gas diffusion layer 6a is arranged in direct contact with the catalyst layer 6b. On this gas diffusion layer 6a, a plate of the cathode current collector 5 is arranged in direct contact with the gas diffusion layer 6a.

[0080] Here, the membrane 7 is an anion exchange membrane that can be obtained, for example, under the trade names Fumasep, Selemion, and Sustanion (only a few examples are mentioned), which allows hydroxide ions (OH - ions; charge, and thus current) to migrate through its body between the cathode side and the anode side of the cell during operation, while the diffusion of water (H2O) from the anode side to the cathode side participates in the electrolytic reduction of CO2 on the cathode side. Since no electrons are transported through the membrane 7 in this case, the membrane 7 actually acts as an electrical insulation layer between the cathode side and the anode side of the cell. As will be clear to those skilled in the art, a cation exchange membrane or other bipolar membranes (such as Fumasep FBM) that can be obtained, for example, under the trade names Nafion and Aquivion can also be used as the membrane 7 according to the electrolytic reaction carried out on the cathode side.

[0081] The cathode current collector 5 acts as a current distribution element on the one hand, i.e., it uniformly distributes the current received from an external power source on the cathode side gas diffusion layer 6a via the cathode side contact plate (discussed below), and on the other hand provides a suitable space for compressing the cathode side gas diffusion layer 6a. The cathode current collector 5 contains an in-plane flow channel system 5” with a height of M formed on / within the surface of the cathode current collector 5 facing the membrane 7; the flow channel system 5” corresponds to various geometric patterns (see, for example Figure 9 ). The patterned formation of the flow channels 5” enables the uniform distribution of gaseous CO2 on the cathode side gas diffusion layer 6a. The cathode current collector 5 is also provided with an inlet in the form of a through hole for feeding gaseous CO2 to the gas diffusion layer 6a and an outlet for discharging the gaseous products formed on the cathode side of the cell during the electrolytic reaction (reduction) of CO2.

[0082] On the cathode side, the gas diffusion layer 6a can transport CO2 to the cathode catalyst layer 6b in contact with the membrane 7 during operation, where the reduction reaction of gaseous CO2 occurs and thus the desired products are formed. The gas diffusion layer 6a also allows the gaseous products (in the form of a mixture that also contains a certain amount of unreacted CO2) to be transported along the cathode flow channel structure towards the CO2 and product outlet of the cell. To provide effective transport properties, any one of carbon cloth, carbon felt, and carbon film can be used as the cathode side gas diffusion layer 6a, preferably modified with a microporous layer as known to those skilled in the art. As the cathode catalyst 6b, various catalysts can be used, and in this case, the cathode catalyst used is preferably an Ag / C and Cu / C catalyst. As Figure 2B shown, the gas diffusion layer 6a and the cathode catalyst layer 6b have a total thickness H, which represents the cathode chamber spacing.

[0083] Conversely, on the anode side, an anode catalyst layer 8b is arranged adjacent to and in direct contact with the membrane 7; here, IrO x 、RuO x 、NiO x and TiO x are highly preferred anode catalysts. On the surface of the anode catalyst layer 8b facing away from the membrane 7, the anode side gas diffusion layer 8a is arranged in direct contact with the anode catalyst layer 8b. The anode side gas diffusion layer 8a is formed by a layer of titanium frit (Ti frit) in the form of pressed Ti powder with different average particle sizes (in the range of preferably 50 - 200 μm) or a layer of nickel frit (Ni frit, Ni frit) in the form of pressed Ni powder with different average particle sizes (in the range of preferably 50 - 200 μm), a Ti mesh (Ti mesh) or a Ni mesh (Ni mesh) (both having a wire thickness and pore size preferably in the range of 50 - 200 μm), only to mention a few examples. On the anode side gas diffusion layer 8a, a plate of the anode current collector 10 is arranged in direct contact with the gas diffusion layer 8a. The anode current collector 10 also includes a flow channel system 5' formed in the surface of the anode current collector 10 facing the membrane 7.

[0084] The anode current collector 10 acts as a current distribution element on the one hand, that is, it uniformly distributes the current received from an external power source on the anode side gas diffusion layer 8a via the anode side contact plate (discussed below), and on the other hand provides an appropriate space for compressing the anode side gas diffusion layer 8a. The anode current collector 10 is also provided with an inlet in the form of through openings for feeding the liquid anode electrolyte to the anode side gas diffusion layer 8a and an outlet for discharging the mixture of the liquid anode electrolyte and the anode products (such as gaseous O2 if the anode electrolyte also contains water) that appear on the anode side of the cell during the electrolysis reaction (oxidation) of the anode electrolyte that occurs on the anode side.

[0085] As will be apparent to those skilled in the art, the cathode-side gas diffusion layer 6a, the cathode catalyst layer 6b, the membrane 7, the anode catalyst layer 8b, and the anode-side gas diffusion layer 8a can be combined into a single unit, namely, a membrane electrode assembly, and used in the form of such an assembly to construct a modular electrolyzer cell - by arranging such a membrane electrode assembly between the cathode current collector 5 and the anode current collector 10 and making electrical contact and gas / fluid communication with them, and properly positioning the assembly by the anode-side spacer elements 9a, 9b. It should also be noted here that the electrolyzer cell obtained and shown in FIG. 2, which is basically a zero-gap electrolyzer cell incorporated into the discussion below, can also be used to construct a multi-cell CO2 electrolyzer stack 100" of a modular structure.

[0086] FIGS. 3 and 4 illustrate exemplary multi-cell electrolyzer stacks 100', 100" having more than one electrolyzer cell module. In particular, Figure 3A and 3B are respectively the upper and lower perspective views of an electrolyzer stack 100' comprising three electrolyzer cells for converting gaseous CO2 into gaseous products at high conversion rates by electrolysis at elevated pressures. Figure 4 is a partially exploded view of a multi-cell electrolyzer stack 100" according to the present invention comprising n cells 40 (n is a positive integer), where one electrolyzer cell is exploded in a series of cells 40. However, for practical considerations, the number n is selected to be at least 1 to 10 or more; in particular, in an electrolyzer stack 100", the number n of cells used is preferably between 2 and 7, more preferably between 3 and 6, and most preferably 3, or 4, or 5, or 6.

[0087] As Figure 3A 、 3B and as can be seen in FIG. 4, the electrolyzer stacks 100', 100" are of modular construction, and the components for constructing the stacks 100', 100" are provided in the form of plate-like elements with different functions. The plate-like components can be of any planar shape; in the exemplary embodiments shown in Figure 3A 、 3B and FIG. 4, the components are substantially circular. In addition, to facilitate the rapid assembly and / or reassembly of the components into the stacks 100', 100", each plate-like component is provided with assembly-assist grooves 52 formed on its periphery. The assembly-assist grooves 52 thus clearly show how the components can be properly combined into a stack; in the correct arrangement / orientation of the components, the grooves 52 are aligned.

[0088] After assembling the components into a stack, the resulting stack contains individual electrolyzer cells arranged side by side longitudinally. Hereinafter, the term "longitudinal" refers to a direction substantially perpendicular to the surface plane of the plate-like component. Thus, as Figure 3A 、 3BAs shown in Figures 3 and 4, the plate-like assembly is provided with a plurality of through-holes along said longitudinal direction. A part of said holes serve as drilled holes 1a to receive screws 1 with shrink tubes and gaskets to assemble said assembly into stacks 100', 100", and then the assembly is hermetically connected by means of nuts 14 with gaskets screwed onto the screws 1 inserted into the respective drilled holes 1a. The remaining part of the holes formed in the plate-like assembly - which are configured to be properly aligned with each other and sealed by specific channel sealing tools (detailed below) that can be arranged around each hole and between the plate-like assemblies - are used to form the longitudinal flow-through portions of the cathode-side and anode-side transfer channel structures within stacks 100', 100". In particular, on the cathode side, one of said holes serves as a gas inlet 21 to introduce gaseous CO2 into the electrolyzer cells 40 assembled in series or parallel (or mixed) configuration with respect to CO2 supply and transfer within the stack, while the other two of said holes serve as (i) a fluid inlet 23 to introduce liquid anodic electrolyte into the electrolyzer cells 40 assembled in series / parallel configuration, and as (ii) a fluid outlet 24 to discharge the spent anodic electrolyte together with the gaseous anodic products (such as O2) formed in the respective cells 40 during the anodic-side electrolysis reaction. Conversely, on the anode side, one of said holes serves as a gas outlet 22 to discharge the excess unreacted CO2 supplied together with the gaseous cathodic products formed in the cells 40 during the cathodic-side electrolysis of CO2.

[0089] Now referring to Figure 4 , the multi-cell CO2 electrolyzer stack 100" according to the present invention is used to electrolytically decompose gaseous CO2 and thus, depending on the catalyst and anodic electrolyte used, generate various gaseous products. For this purpose, stack 100" comprises a certain number n of electrolyzer cells 40, which are arranged adjacent to each other and in hermetically fluid / gas communication with each other through the longitudinal portions of the cathode-side and anode-side transfer channel structures. In addition, the electrolyzer cells 40 are electrically coupled in series with each other and with the electrical terminals of stack 100", i.e., with the cathode-side and anode-side contact plates 4, 11. Thus, stack 100" contains a series of electrolyzer cells 40, consisting of interconnected intermediate cells sandwiched between a cathode-side end unit 26 and an anode-side end unit 27 arranged at opposite ends of the series along the longitudinal direction.

[0090] The cathode-side end unit 26 closes the series of electrolyzer cells 40 on the cathode side of the stack 100”. The inner surface of the cathode-side end unit 26 is in direct contact with the first cell 40 of the series, while the outer surface of the cathode-side end unit 26 is in practice exposed to the environment. The cathode-side end unit 26 itself has a modular structure; it includes a cathode-side contact plate 4 with the inner surface in question, a cathode-side insulator 3 arranged on the cathode-side contact plate 4, and a cathode-side end plate 2 with the outer surface arranged on the cathode-side insulator 3. The cathode-side end plate 2 is provided with openings that are in gas / fluid communication with the cathode and / or anode transport channel structures of the stack 100” via corresponding openings formed in the insulator 3 and the contact plate 4 that are appropriately aligned with the openings in question, namely, a gas inlet 21 for CO2 supply, a fluid inlet 23 for anode electrolyte supply, and a fluid outlet 24 for waste anode electrolyte (and anode products) discharge. In the assembled state of the stack 100”, the openings formed in the cathode-side end unit 26 in alignment with each other form continuous longitudinal sealed flow channels, each leading to a corresponding opening of the first electrolyzer cell 40. Here, sealing is achieved by appropriately sized sealing elements arranged between the end plate 2 and the insulator 3, between the insulator 3 and the contact plate 4, and between the contact plate 4 and the first cell around the respective openings, preferably in the form of O-rings 15, 16, 17 made of a corrosion-resistant plastic (e.g. ). The cathode-side end plate 2 acts as a mechanical reinforcement element and enhances the compaction of the stack 100” by means of through bolts 1. The cathode-side insulator 3 acts as an electrical insulator between the end plate 2 and the cathode-side contact plate 4. The cathode-side insulator 3 also houses a cathode-side pressure chamber to prevent possible displacement of the internal components of the stack 100” towards the cathode-side end plate 2 when the stack 100” is pressurized at the start of operation. The pressure chamber is formed as a hollow cavity in the body of the cathode-side insulator 3 and covers a given part of the cathode-side end plate 2 when the stack 100” is assembled. In this case, the cathode-side pressure chamber is sealed by an O-ring 15 in an annular groove around the cavity arranged in the cathode-side insulator 3 between the insulator 3 and the end plate 2. In addition, the cathode-side contact plate 4 acts as an electrical connection to an external power source and at the same time acts as a current distribution element to uniformly distribute the current received from the power source over the outermost surface of the first cell of the intermediate cells 40 of the series via the inner surface of the cathode-side end unit 26. The cathode-side contact plate 4 also helps gaseous CO2 to be fed into the first electrolyzer cell 40 of the stack 100” and helps liquid anode electrolyte and waste anode electrolyte to be introduced into and discharged from the first electrolyzer cell 40 of the stack 100” respectively.

[0091] The anode-side end unit 27 closes the series of electrolyzer cells 40 on the anode side of the stack 100". The inner surface of the anode-side end unit 27 is in direct contact with the last, i.e., the nth, cell 40 of the series, while the outer surface of the anode-side end unit 27 is in practice exposed to the environment. The anode-side end unit 27 itself has a modular structure; it includes an anode-side contact plate 11 with the inner surface in question, an anode-side insulator 12 arranged on the anode-side contact plate 11, and an anode-side end plate 13 with the outer surface arranged on the anode-side insulator 12. The anode-side end plate 13 is provided with openings that are in gas communication with the cathode transfer channel structure of the stack 100" via corresponding openings formed in the anode-side insulator 12 and the anode-side contact plate 11 that are properly aligned with the openings in question, i.e., the gas outlet 22 for the discharge of CO2 and cathode products. In the assembled state of the stack 100", the openings formed in alignment with each other in the anode-side end unit 27 form a continuous longitudinal sealed flow channel that leads to the corresponding opening of the last electrolyzer cell 40. Here, sealing is achieved by appropriately sized sealing elements arranged around the openings between the last cell and the anode-side contact plate 11, between the anode-side contact plate 11 and the anode-side insulator 12, and between the anode-side insulator 12 and the anode-side end plate 13, preferably in the form of O-rings; the O-rings in question are similar / equivalent to the O-rings used in the cathode-side end unit 26. Here, the anode-side contact plate 11 serves as an electrical connection to an external power source and at the same time serves as a current distribution element to uniformly distribute the current received from the power source over the outermost surface of the last cell of the intermediate cells 40 of the series via the inner surface of the anode-side end unit 27. The anode-side contact plate 11 also helps to discharge the gaseous CO2 mixed with the electrolysis products from the last electrolyzer cell 40 of the stack 100". The anode-side insulator 12 serves as an electrical insulator between the anode-side contact plate 11 and the anode-side end plate 13. The anode-side insulator 12 also houses an anode-side pressure chamber to prevent possible displacement of the internal components of the stack 100" towards the anode-side end plate 13 when the stack 100" is pressurized at the start of operation. The pressure chamber is formed as a hollow cavity in the body of the anode-side insulator 12 and covers a given part of the anode-side end plate 13 when the stack 100" is assembled. In this case, the anode-side pressure chamber is sealed by an O-ring 15 in an annular groove around the cavity arranged in the anode-side insulator 12 between the insulator 12 and the anode-side end plate 13. In addition, the anode-side end plate 13 serves as a mechanical strengthening element and enhances the compaction of the stack 100" by means of nuts 14 with washers screwed onto screws 1 that pass through the entire structure of the stack 100" from the cathode-side end plate 2 in the drill holes 1a. In accordance with the convention, the cathode-side contact plate 4 and the anode-side contact plate 11 are electrically connected to the negative and positive poles of an external power source, respectively.

[0092] Now refer to Figure 5 、 5AFigures 5A and 5B show the dual-component bipolar plate assembly 40' in a bottom view, a cross-sectional view taken along line A-A, and a cross-sectional view taken along line B-B, respectively. The first component 40a of the assembly 40' (i.e., the anode current collector 10 in a single cell) and the second component 40b of the assembly 40' (i.e., the cathode current collectors 5(a, b, c, d) in a single cell) are provided with certain elements of the cathode and anode side transfer channel structures on their opposing side surfaces. In particular, the first component 40a is provided with inlet / out orifices for the cathode side and anode side flow channel systems within the cell 40'. The orifices are: the cell inlet gas transfer channel 41 and the cell outlet gas transfer channel 42 for gas supply and transfer (i.e., CO2, desired products) on the cathode side of the bipolar plate assembly 40', and the cell anode electrolyte inlet channel 48, the cell anode electrolyte outlet channel 49, the cell anode electrolyte transfer channel 43, and the cell anode electrolyte and anode product transfer channel 44 for fluid supply and transfer (i.e., anode electrolyte; spent anode electrolyte together with anode products such as gaseous O2) on the anode side of the bipolar plate assembly 40'. The first component 40a further has an in-plane system 5' of fluid flow channels with a specific geometry on / within its side surface that faces the cathode side end unit when assembled into the stack. The orifices lead from the side surface to the opposing side surface of the second component 40b, where each of the orifices leads to a corresponding cavity that completely surrounds it, i.e., cavities 33a, 33b, 33c, 33d. The cavities and orifices provide fluid communication with the corresponding longitudinal fluid flow channels 41', 42', 43', 44' formed in the second component 40b. The second component 40b is also provided with the cell gas inlet channel 46 and the cell gas outlet channel 47 for gas supply and transfer (i.e., CO2, desired products) on the cathode side of the bipolar plate assembly 40', and an in-plane system 5'' of gas flow channels with a specific geometry (see Figure 9 ). The cavities are fitted with appropriate seals, in particular O-rings 16, 17, 17', 19 made of a corrosion-resistant plastic (e.g., ) to seal the flow channels when assembling the stack and to maintain the pressure present within the stack during operation.

[0093] The first and second components 40a, 40b of the assembly 40' are made of the same electrically conductive compound as the other electrically conductive components of the stack, such as titanium, stainless steel, different alloys, and composite materials. The orifices and cavities are formed by machining, in particular CNC milling.

[0094] As Figure 4As is obvious, after assembling the CO2 electrolyzer stack 100" according to the present invention, the cathode-side and anode-side end units 26, 27 sandwich n substantially identical intermediate electrolyzer cells 40 therebetween, where the electrolyzer cells 40 are (i) connected in series in terms of power (current) management of the stack 100", (ii) connected in parallel in terms of anolyte supply and transport within the stack 100", and (iii) connected to each other in series or in parallel or in a hybrid manner in terms of CO2 supply and transport within the stack 100". Each cell 40 is composed of a dual-component bipolar membrane assembly 40' (see Figure 5A and 5B ). In particular, each cell 40 includes a first (anode) component 40a of the i-th bipolar membrane assembly 40', an adjacent, i.e., the second (cathode) component 40b of the (i - 1)-th bipolar membrane assembly 40' (here, 1 < i < n, integer), the membrane electrode assembly arranged between the first and second components 40a, 40b as previously discussed, and anode-side spacer elements 9a, 9b inserted between the first and second components 40a, 40b of the bipolar membrane assembly 40' in its outer peripheral region. Feature (i) is the result of the electrical contact between successive cells 40 in the stack 100". Feature (ii) is the result of the physical construction, i.e., the number of longitudinal channels provided in the anode-side spacer elements 9a, 9b for gas transport to the cathode side, and the actual arrangement orientation of the specific spacer elements 9a, 9b in the stack 100". In particular, as Figure 10A shown, a single longitudinal channel 36 is provided in the spacer element 9A used when connecting two adjacent cells to form a serial gas flow path on the cathode side of the stack 100"; the corresponding construction of this cell is shown in exploded view in Figure 12A . In addition, as Figure 10B shown, two longitudinal channels 36 are provided in the spacer element 9b used when connecting two adjacent cells to form gas flow paths extending in parallel on the cathode side of the stack 100"; here, the longitudinal channels 36 are formed at diametrically opposite positions of the spacer element 9b. The corresponding construction of this cell is shown in exploded view in Figure 12B .

[0095] The preferred embodiment of a multi-cell electrolyzer stack 100" including three independent cells 40 or bipolar plate assemblies 40' is explained in more detail below for cathode-side gas management and anode-side fluid management. In particular, Figure 6 a cross-sectional view taken along the Figure 3A A-A line segment shown in Figure 7 shows the three-cell electrolyzer stack 100', where the gas flow paths of the stack are shown in gray; here, the stack 100' is assembled in a parallel configuration of the cell gas flow paths of each cell 40 in terms of CO2 supply and transport within the stack 100'. In addition, Figure 3AThe cross-sectional view taken along the line A-A shown in the figure shows the three-cell electrolyzer stack 100', where the gas flow paths of the stack are again shown in gray; here, the stack 100' is assembled in a serial configuration of the cell gas flow paths of the individual cells 40 with respect to the supply and transmission of CO2 within the stack 100'. In addition, Figure 8 The cross-sectional view taken along Figure 3A the line B-B shown in the figure shows the three-cell electrolyzer stack 100', where the fluid flow paths of the stack are shown in gray; here, the stack 100' is assembled in either a serial or parallel configuration of the individual cells 40 with respect to the supply and transmission of CO2 within the stack 100', and the cell fluid flow paths combine to form the fluid flow paths of the stack that are in a parallel configuration with respect to the supply and transmission of the anolyte within the stack 100'.

[0096] Figure 6 Illustrates the continuous stack gas flow path that extends from the gas inlet 21 to the gas outlet 22 - passing through the cathode-side pressure chamber 31 formed within the cathode-side end unit, particularly within the cathode-side insulator 3, then through the drilled holes formed in the cathode-side insulator 3 and the cathode-side contact plate 4, which lead to the cell gas inlet 46 formed in the cathode current collector, then through the cell gas inlet 46 into the groove 45 of the flow pattern 5" (see Figure 9 ) formed in the surface of the cathode current collector facing the cathode-side gas diffusion layer and thus into the first electrolyzer cell 40 of the series of cells 40 used. The stack gas flow path then further extends as an in-plane cell gas flow path of the first cell 40 formed between the cathode-side current collector and the cathode-side gas diffusion layer in partial contact with each other and exits the first cell 40 via the cell gas outlet 47 in gas communication with the sealed cavity 33b; the cavity 33b is formed in the surface of the anode current collector. The stack gas flow path then extends from the cavity 33b through the outlet gas transfer channel 35, then through the drilled holes formed in the anode-side contact plate 11 and the anode-side insulator 12 into the anode-side pressure chamber 32 formed within the anode-side end unit, particularly within the anode-side insulator 12, and then extends from the anode-side pressure chamber 32 to the gas outlet 22. Here, the outlet gas transfer channel 35 is formed by the cell outlet gas transfer channel 42' (see Figure 9 ) formed in the cathode current collector, the internal gas transfer channel 36 of the anode spacer element 9b (see Figure 10B ) and the cell outlet gas transfer channel 42 (e.g., see Figure 11A ) formed in the anode current collector.

[0097] In addition, in order to supply CO2 also to the second and any subsequent cells 40, the stacked flow paths extend from the cathode-side pressure chamber 31 through the inlet gas delivery channel 34 into the sealed cavities 33a formed in the surfaces of the anode current collectors of the respective cells 40, where each cavity 33a is connected to the cell gas inlet 46 of the cell 40. Thus, in operation, all cells 40 are in gas communication with the inlet gas transfer channel 34, which means a parallel gas transfer configuration of the electrolyzer stack 100'. The inlet gas transfer channel 34 formed by the cell inlet gas transfer channels 41 formed in the cathode current collector, another internal gas transfer channel 36 of the anode spacer element 9b, and the cell inlet gas channels 41 terminates at the inlet gas transfer channel end 34a, i.e., it is a dead-end channel.

[0098] Figure 7 Illustrates the continuous stacked gas flow path that extends from the gas inlet 21 to the gas outlet 22. Here, when assembling the multi-cell electrolyzer stack 100', due to (i) using an anode spacer element 9a with only a single internal gas transfer channel 36 (instead of two), and (ii) the fact that the anode spacer element 9a is arranged in adjacent cells in an orientation rotated 180° about an axis perpendicular to the spacer element 9a at its center, as a consequence of the segmentation of the inlet gas transfer channel 34 and the outlet gas transfer channel 35 (see Figure 6 ), the stacked flow path becomes a flow path of series-connected cell flow paths.

[0099] Figure 8 Illustrates the continuous stacked fluid flow path that extends from the fluid inlet 23 to the fluid outlet 24 - through the continuous inlet flow transfer channel formed by the through-channel 43' in the cathode current collector, the through-channel 38 in the spacer element, and the through-channel 43 in the anode current collector of the electrolyzer cell, then through the sealed cavity 33c in fluid communication with the cell fluid inlet 48, then through the flow pattern 5' and the through-channel 49 into the sealed cavity 33d, and then out of the cavity 33d, which is in fluid communication with the continuous outlet flow transfer channel formed by the through-channel 44 in the anode current collector, the through-channel 39 in the spacer element, and the through-channel 44' in the cathode current collector of the electrolyzer cell.

[0100] The following explains in more detail the construction components of a single electrolyzer cell 40 formed by a dual-component bipolar plate assembly 40', for example, the one shown as a decomposition cell in Figures 9 to 1 1, with reference to Figure 4 that one.

[0101] In particular, Figure 9Four possible embodiments of the display cathode current collectors 5a, 5b, 5c, 5d (forming the second component 40b of the dual-component bipolar plate assembly used), where each embodiment has a specific in-plane flow channel structure or flow pattern 5". The flow pattern 5" is a key part for achieving uniform CO2 feeding to the cathode side of the cell and efficient collection of products therefrom. Here, the CO2 feeding is carried out through the longitudinally extending cell gas inlet channel 46, and the product collection is carried out through the cell gas outlet channel 47 also extending longitudinally. Between the inlet and outlet channels 46 and 47, the gaseous CO2 is transported and continuously participates in the cathode electrolysis reaction, and thus is converted into gaseous products in the grooves 45 of the continuous flow pattern 5" in contact with the membrane electrode assembly (not shown). As Figure 9 can be seen, in the three exemplary flow designs, namely corresponding to the maze flow pattern, the offset circle flow pattern, and the radial double helix flow pattern respectively in Figure 5 (a) to 5(c), the gaseous CO2 is fed in the center, that is, the cell gas inlet channel 46 is located at the center of the cathode current collector, and collected along the outer ring, that is, the cell gas outlet channel 47 is arranged at the outer peripheral part of the cathode current collector. Figure 5 (d) illustrates another flow design. In this case, the CO2 is fed at the perimeter of the cathode current collector and collected at diametrically opposite positions of the cathode current collector, for example, after passing through a double helix pattern, that is, both the cell gas inlet channel 46 and the outlet channel 47 are located in the outer peripheral region of the cathode current collector. It is surprisingly found that, different from fuel cells, the best-performing flow patterns are always those with CO2 fed in the center of the flow pattern.

[0102] It should be noted here that, in order to use the cathode current collectors 5a, 5b, 5c, 5d with different flow patterns 5" together with the same anode current collector 10 in a multi-cell stack, or in other words, in order to use the various flow patterns 5" of the second component 40b of the dual-component bipolar plate 40' together with a single type of first component 40a (i.e., with a unique flow pattern 5'), the inlet gas transport channel 41 is specifically formed. In particular, the shape of the inlet gas transport channel 41 is circular on the side of the second component 40b with the flow pattern 5", while it has a narrow and elongated shape on the opposite side of the second component 40b to cover the cell gas inlet channel 46, regardless of the fact that it is formed in the central or outer peripheral region of the second component 40b.

[0103] Figure 10A and 10BShows possible embodiments of the anode-side spacer elements 9a, 9b between the cathode current collector and the anode current collector in each electrolyzer cell 40 of the multi-cell electrolyzer stacks 100’, 100” to achieve a serial or parallel cathode-side gas flow configuration, respectively. These two types of anode-side spacer elements 9a, 9b are almost identical except for the number of longitudinally extending internal gas transport channels 36. By means of this unique design choice, the anode-side spacer elements are spacer elements configured to act as means for selectively choosing the way in which two adjacent cell flow paths are connected to each other in the gas flow path of the electrolyzer stack. The anode-side spacer elements 9a, 9b are made of an electrical insulator, preferably plastic or Teflon. Thus, the anode-side spacer elements 9a, 9b can be manufactured simply and inexpensively, even on an industrial scale and in an automated manner.

[0104] Figure 11 shows the anode current collector 10 (which forms the first component 40a of the dual-component bipolar plate assembly) used in the CO2 electrolyzer stack according to the present invention, Figure 11A is a top view, while Figure 11B is a bottom view of the anode current collector 10, highlighting the cavities 33a, 33b, 33c, 33d provided for establishing sealed gas / fluid communication for gas / fluid management of the stack and for accommodating the required seals (i.e., various O-rings).

[0105] Finally, Figure 12A and 12B show, in exploded views, the individual cells 40 of the multi-cell electrolyzer stack assembled in serial and parallel cathode-side gas flow configurations, respectively. Figure 12A and 12B also show the advantages of the modular construction used. In particular, by replacing the anode spacer element 9a having only a single internal gas transport channel 36 with an anode spacer element 9b containing two internal gas transport channels 36, the flow configuration of the cell 40 involved is simply modified from a serial configuration to a parallel configuration, and vice versa. That is, by simply disassembling the electrolyzer stack into cells, then disassembling any cell into components, replacing the anode spacer element with the anode spacer element required for the desired cathode-side gas flow configuration, then reassembling each cell from the components, and then reassembling the stack from the cells, a multi-cell electrolyzer stack with the required gas flow management is obtained. Thus, the multi-cell electrolyzer stack according to the present invention can be simply and quickly matched to the operating requirements and is almost completed on-site.

[0106] The present invention and its advantages are further discussed below based on experimental measurements specifically carried out on a CO2 electrolyzer stack consisting of one cell or three cells, in the latter case with series / parallel connection.

[0107] As already discussed, the CO2 electrolyzer stack according to the invention has a configuration with at least one, preferably more than one cell, i.e., the core for performing CO2 electrolysis is constructed of individual electrolyzer cells that are electrically connected in series and are in series or parallel configuration with respect to the gas management of the stack; the number of cells used to construct the stack is up to 10 or more, preferably 2 to 7, more preferably 3 to 6, and most preferably three, or four, or five or six.

[0108] Example 1 - Operation

[0109] In this embodiment, some operating characteristics of a 3-cell stack assembled in series configuration and then in parallel configuration (with respect to the cathode-side gas management) are briefly compared with a 1-cell stack (i.e., one cell).

[0110] Figure 13 Illustrates the effect of increasing the number of individual electrolyzer cells used in possible embodiments of the stack according to the invention assembled in serial or parallel gas flow configurations. In particular, in graph (a), the CO2 conversion during the electrolysis process at ΔU = -2.75 V / cell achieved with a 1-cell and a 3-cell series stack at different CO2 feed rates is plotted. In graph (b), the CO2 conversion during the electrolysis process achieved with a stack consisting of one cell or three cells in parallel (with the gas feed normalized with the same cells) at different stack voltages is shown. Feed the anode with T = 50 °C 1 M KOH anode electrolyte (at a feed rate of 1.5 dm 3 min -1 for this series of measurements. Regarding the cathode catalyst layer, 3 mg cm -2 Ag is fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode catalyst, 1 mg cm -2 Ir black is fixed on porous titanium frit. Both of these catalyst layers contain 15 wt% Sustanion ion crosslinked polymer. The cathode chamber is purged with humidified (room temperature deionized water) CO2. In addition, the CO2 flow rate is set to 8.3 cm 3 cm -2 min -1 .

[0111] It is clearly seen from graph (a) that when three electrolyzer cells are connected in series (compared to a 1-cell stack under the same conditions):

[0112] · The CO2 conversion is improved;

[0113] · This effect is more pronounced at higher flow rates; and

[0114] · A conversion of approximately 40% is achieved.

[0115] As is clearly seen from graph (b), when three electrolyzer cells are connected in parallel (compared to a 1-cell stack under the same conditions):

[0116] · It is possible to increase the number of cells without changing the operating characteristics;

[0117] · Within the stack, the CO₂ feed flow is uniformly distributed; and

[0118] · The conversion rate and the CO partial current are similar in the 3-cell configuration, which is conclusive evidence of the scalability of this method.

[0119] Figure 14 Graph showing current density vs. operational stack-voltage for a three-cell CO₂ electrolyzer stack according to the invention for the formation of syngas (H₂ / CO mixture, on an Ag catalyst) or hydrocarbons (CH₄ and C₂H₄, on a Cu catalyst). The curves were recorded by linear sweep voltammetry (LSV) with a cathodic gas diffusion electrode (GDE) containing different catalysts at a scan rate of ν = 10 mV s -1 The anolyte (1 M KOH at T = 50 °C) was continuously fed to the anodic chamber at a feed rate of ~9 cm 3 cm -2 min -1 for this series of measurements, while the cathodic chamber was purged with humidified (room-temperature deionized water) CO₂ at a flow rate of u = 2.5 cm 3 cm -2 min -1 Regarding the cathodic catalyst layer, 1 mg cm -2 Ag was immobilized on Sigracet 39BC carbon paper by spraying. The Cu-containing GDE was formed by electrodeposition. Regarding the anodic catalyst layer, 1 mg cm -2 Ir black was immobilized on porous titanium frit. Both of these catalyst layers contain 15 wt% Sustanion ionomer cross-linked polymer. In addition, the stack was equipped with a spacer element with a thickness of 300 μm.

[0120] Electrochemical verification of the cells shows a low voltage requirement. Due to the enhanced excellent electrical coupling between the various components of the stack under pressure, the operating voltage of the stack is quite low (2.5 to 3.0 V). This translates into good energy efficiency (40 - 50%). The formation of syngas (H₂ / CO mixture) is shown on an Ag / C catalyst, while ethylene formation is shown on a Cu / C catalyst.

[0121] Figure 15 Verification of the stable operation of the electrolyzer stack. For use with 1 mg cm -2The three-cell CO2 electrolyzer stack of the cathode GDE with an Ag catalyst according to the present invention obtains the shown chronoamperometry curves at ΔU = -3 V / cell. Regarding the anode, 1 mg cm -2 Ir black is fixed on a porous titanium frit. Both of these catalyst layers contain 15 wt% Sustanion ionomer. The stack is equipped with a spacer element with a thickness of 270 μm. A T = 50 °C 1 M KOH anolyte is continuously fed to the anode chamber (at a feed rate of ~9 cm 3 cm -2 min -1 for measurement, while the cathode chamber is purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 2.5 cm 3 cm -2 min -1 .

[0122] Figure 16 Shows the formation of different gaseous CO2 reduction products generated using electrolyzer stacks with different catalysts. Shows the gas chromatogram recorded during chronoamperometry measurements at ΔU = -2.75 V / cell using a three-cell CO2 electrolyzer stack according to the present invention, which uses a spray-coated GDE with 3 mg cm -2 Ag catalyst [graph (a)] and a GDE with a Cu catalyst formed by electrodepositing copper nanocubes on Sigracet 39BC carbon paper [graph (b)]. Regarding the anode, 1 mg cm -2 Ir black is fixed on a porous titanium frit. The Ag-containing GDE and the anode catalyst layer contain 15 wt% Sustanion ionomer. The stack is equipped with a spacer element with a thickness of 270 μm. A T = 50 °C 1 M KOH anolyte is continuously fed to the anode chamber (at a feed rate of ~9 cm 3 cm -2 min -1 for measurement, while the cathode chamber is purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 2.5 cm 3 cm -2 min -1 .

[0123] Example 2 - Voltage - Dependent Product Distribution

[0124] This example demonstrates that the composition (H2 / CO ratio) of the product syngas can be simply adjusted by the voltage of the stack. The higher the stack voltage, the more H2 is generated.

[0125] Figure 17 Shows the use of a spray-coated 3 mg cm fixed on Sigracet 39BC carbon paper -2The cathodic GDE of Ag (obtained by chronoamperometry and gas chromatography) was used for the partial current density for CO and H2 formation (left ordinate) and the ratio of the partial current densities (right ordinate) at different stack voltages. For the anode, 1 mg cm -2 Ir black was fixed on porous titanium frit. Both of these catalyst layers contained 15 wt% Sustanion ionomer. The stack was equipped with a spacer element with a thickness of 300 μm. The anodic chamber was continuously fed with a 1 M KOH anolyte at T = 50 °C (at a feed rate of ~9 cm 3 cm -2 min -1 for measurements, while the cathodic chamber was purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 2.5 cm 3 cm -2 min -1 .

[0126] Example 3 - Influence of Catalyst Loading

[0127] This example confirmed that the carbon dioxide reduction rate depends strongly on the amount of immobilized cathodic catalyst. The partial current density for CO formation reached a maximum at an intermediate catalyst loading.

[0128] Figure 18 Shown are the partial current densities for H2 and CO formation (left ordinate) and the CO2 conversion (right ordinate) vs the amount of Ag catalyst in the cathodic GDE during electrolysis at ΔU = -2.75 V. The Ag cathodic catalyst layer was fixed on Sigracet 39BC carbon paper by spraying. For the anode, 1 mg cm -2 Ir black was fixed on porous titanium frit. Both of these catalyst layers contained 15 wt% Sustanion ionomer. The anodic chamber was continuously fed with a 1 M KOH anolyte at T = 50 °C (at a feed rate of ~9 cm 3 cm -2 min -1 for measurements, while the cathodic chamber was purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 2.5 cm 3 cm -2 min -1 .

[0129] Example 4 - Influence of Cathode Spacing ( GDL Compression)

[0130] This example presents additional benefits of the stack design according to the invention. By changing only one plastic element, the compression of the gas diffusion layer (GDL) can be altered. Apparently, both the product distribution and the conversion rate are affected by this parameter. Importantly, if different GDLs have to be used, the stack can be quickly and easily customized for them (unlike similar fuel cell arrangements, where the hermetic sealing and compression of the GDL are achieved by using gaskets of a given thickness, which have to be carefully customized for the GDEs involved).

[0131] Figure 19 Shows the partial current densities for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) vs the cathode spacing used during the electrolysis process at ΔU = -2.75 V. Regarding the cathode, 1 mg cm -2 Ag cathode catalyst layer was fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode, 1 mg cm -2 Ir black was fixed on porous titanium frit. Both of these catalyst layers contain 15 wt% Sustanion ionomer cross-linked polymer. The anode chamber was continuously fed with a 1 M KOH anode electrolyte at T = 50 °C (at a feed rate of ~9 cm 3 cm -2 min -1 for measurements, while the cathode chamber was purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 1.25 cm 3 cm -2 min -1 .

[0132] Example 5 - Influence of the Flow Pattern Used in the Cathode Current Collector

[0133] This example clearly shows the significant influence of the flow pattern design (see Figure 9 ) on the residence time of CO2 gas in the electrolyzer stack according to the invention and thus on the stack performance. Here, the influence of the groove depth M of the flow pattern for Figure 9 (a) is shown (see Figure 2B ). According to this example, there is an optimal groove depth and thus an optimal residence time to ensure a high conversion rate.

[0134] Figure 20 Shows the partial current densities for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) vs the groove depth M of the flow pattern used on the cathode side of the electrolyzer stack according to the invention during the electrolysis process at ΔU = -2.75 V. Regarding the cathode, 3 mg cm -2 Ag cathode catalyst layer was fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode, 1 mg cm -2Ir black is fixed on the porous titanium frit. Both of these catalyst layers contain 15 wt% Sustanion ion cross-linked polymer. Feed the anode chamber continuously with a 1M KOH anode electrolyte at T = 50 °C (at a feed rate of ~9 cm 3 cm -2 min -1 for measurement, while the cathode chamber is purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 2.5 cm 3 cm -2 min -1 .

[0135] Example 6 - Influence of Carbon Dioxide Flow Rate in the Electrolyzer Stack

[0136] This example confirms that an increased CO2 flow rate increases the conversion rate (current density) of the electrolyzer stack according to the present invention. At the same time, the relative ratio of the converted CO2 to the feed rate decreases (therefore, the optimal value of the CO2 flow rate must be found and used).

[0137] Figure 21 Graphical representation of the partial current density for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) vs the carbon dioxide flow rate (normalized by the surface area) in the cathode chamber of an electrolyzer stack according to the present invention during electrolysis at ΔU = -2.75 V. Regarding the cathode, a 3 mg cm -2 Ag cathode catalyst layer is fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode, 1 mg cm -2 Ir black is fixed on the porous titanium frit. Both of these catalyst layers contain 15 wt% Sustanion ion cross-linked polymer. Feed the anode chamber continuously with a 1M KOH anode electrolyte at T = 50 °C (at a feed rate of ~9 cm 3 cm -2 min -1 for measurement.

[0138] Example 7 - Influence of Anolyte (Stack) Temperature

[0139] This example confirms that high reaction rates and selectivities can be achieved at elevated temperatures, which can be easily adjusted by the temperature of the anode electrolyte. Importantly, as illustrated in this case, the components of the electrolyzer stack are designed to withstand exposure to hot (alkaline) solutions.

[0140] Figure 22 Shows the partial current density for H2 and CO formation (left ordinate) and the CO2 conversion rate (right ordinate) vs the temperature of the anode electrolyte (1M KOH) present in the electrolyzer stack according to the present invention during electrolysis at ΔU = -2.75 V (at ~9 cm 3 cm-2 min -1 at a feeding rate of). The cathode chamber was purged with humidified (room temperature deionized water) CO2 at u = 2.5 cm 3 cm -2 min -1 at a flow rate of. Regarding the cathode, 3 mg cm -2 of Ag cathode catalyst layer was fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode, 1 mg cm -2 of Ir black was fixed on porous titanium frit. Both of these catalyst layers contained 15 wt% Sustanion ionomer.

[0141] Example 8 - Influence of Pressure in the Electrolyzer Stack

[0142] This example demonstrates that CO2 reduction is the main cathode process at lower stack voltages, while water reduction is the main cathode process at larger stack voltages. The transition between these two processes was shifted towards larger current densities by increasing the CO2 pressure so that CO2 electroreduction proceeded at a higher rate. The slope of the LSV curve at lower stack voltages increased gradually with the CO2 pressure. Therefore, a lower stack voltage was required to achieve the same current density during the pressurized operation of the electrolyzer stack. This was further highlighted by tracing the LSV curves recorded at different CO2 pressures at a given stack voltage.

[0143] Figure 23 Shows the LSV curves recorded at a scan rate of ν = 10 mV s -1 during the electrolysis process carried out in the electrolyzer stack according to the present invention at various CO2 pressure differences from 1 bar to 10 bar. Regarding the cathode, 3 mg cm -2 of Ag cathode catalyst layer was fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode, 1 mg cm -2 of Ir black was fixed on porous titanium frit. The anode chamber was continuously fed with T = 50 °C 1 M KOH anode electrolyte (at a feeding rate of ~9 cm 3 cm -2 min -1 for measurement, while the cathode chamber was purged with humidified (room temperature deionized water) CO2 at u = 12.5 cm 3 cm -2 min -1 at a flow rate of.

[0144] In addition, Figure 24Shows the current density (graph A) and the ratio of partial current densities (graph B) at different stack voltages during the electrolysis process at ΔU = -2.75 V, both relative to the CO2 pressure difference present in the electrolyzer stack during continuous operation. Regarding the cathode, 3 mg cm -2 Ag cathode catalyst layer was fixed on Sigracet 39BC carbon paper by spraying. Regarding the anode, 1 mg cm -2 Ir black was fixed on a porous titanium frit. The anode chamber was continuously fed with a T = 50 °C 1 M KOH anode electrolyte (at a feed rate of ~9 cm 3 cm -2 min -1 for measurement, while the cathode chamber was purged with humidified (room temperature deionized water) CO2 at a flow rate of u = 12.5 cm 3 cm -2 min -1 .

[0145] Figure 24 It is shown that the selectivity for CO production is significantly increased by increased CO2 pressure. Thus, this further allows control of the syngas product composition (H2 / CO ratio).

[0146] Overview

[0147] As is clear from the above, the present invention provides / demonstrates

[0148] · An electrochemical stack architecture for the efficient electrochemical conversion of carbon dioxide

[0149] · Pressure treatment up to 30 bar (preferably 20 bar) through cathode-side and anode-side pressure chambers

[0150] · Pressure tolerance, i.e., the pressure applied to the electrolyzer stack improves the fit of various stack components, sealing elements, and electrical contact points by compensating for the negative effects of imperfect matching of component sizes caused by manufacturing, thus enhancing stack performance.

[0151] · High mechanical strength components (such as stainless steel, titanium, metal alloys, or composite frames)

[0152] · A specific sealing system including O-rings stuck in recesses / grooves and pressure chambers on the anode side and cathode side.

[0153] · A stack configuration that is highly scalable in terms of size or physical dimensions, number of cells, and product yield due to its modular construction.

[0154] · Multi-cell configuration in serial and parallel gas feeds (important for scale-up), meaning that the initial CO2 gas stream (i) is distributed within the stack and fed to all cells (parallel conversion occurs at various cells), or (ii) the entire CO2 feed passes through all cells one by one (serial design).

[0155] · The above two scenarios (i.e., serial or parallel gas management on the cathode side) are achieved with the same stack construction elements only through different assemblies, which is ensured by the modular construction and elements of the electrolyzer stack, especially the versatility of the anode-side spacer elements - the specific design of this element allows for serial or parallel gas management to be achieved within the same stack.

[0156] · The modularity of the stack allows for the combination of these two scenarios, so that some electrolyzer cells are in parallel while others are in series within the same stack.

[0157] · Modularity also ensures the use of different ion exchange membranes, gas diffusion layers, and catalysts without changing the overall architecture (while still maintaining pressure tolerance).

[0158] · High conversion rate, which is attributed to

[0159] ο Direct gas feed,

[0160] ο High-pressure capability,

[0161] ο Controlled residence time (by means of stack geometry),

[0162] ο Specific flow pattern (CO2 central feed, radial product collection)

[0163] · Novel design for connecting multiple independent cells to each other to facilitate gas and liquid transfer within the electrolyzer stack

[0164] · A wide variety of catalysts can be used in the electrolyzer, including but not limited to Sn, Pb, Ag, Cu, Au, C, Fe, Co, Ni, Zn, Ti, Mn, Mo, Cr, Nb, Pt, Ir, Rh, Ru, and different binary compositions and oxides formed therefrom.

[0165] · Multiple different products are formed with different compositions, including but not limited to hydrogen, carbon monoxide, ethylene, methane.

[0166] · The ability to produce, for example, syngas and ethylene using Ag / C catalyst and Cu / C catalyst respectively in a CO2 electrolyzer stack, also at an industrial scale,

[0167] · The possibility of optimizing operating parameters (input flow rate, humidification, pressure, stack temperature, flow pattern and its depth, GDL compression).

[0168] · An adjustable syngas composition can be achieved simply by changing the stack voltage.

[0169] Furthermore, it will be clear to those skilled in the art that the solution of the present invention, considered alone or in any combination, is not limited to the exemplified embodiments, namely an electrolyzer stack for the conversion of gaseous carbon dioxide, but can also be used in other electrochemical setups (e.g., N2 reduction to ammonia).

[0170] According to the above, from a technical perspective, instead of multiple single-cell stacks operating in parallel, assembling a multi-cell electrolyzer similarly to that shown in Figure 1 reduces the capital investment cost because the stack frame and the anolyte circulation loop only need to be built once, and the addition of further cells only requires additional bipolar plate assemblies, some sealing elements, and additional membrane electrode assemblies.

Claims

1. An electrolyzer stack (100’, 100”) for converting gaseous carbon dioxide CO2 into at least one gaseous-phase product exiting the electrolyzer stack (100’, 100”), comprising - a cathode-side end unit (26) having a gas inlet (21), a fluid inlet (23), a fluid outlet (24), and an electrical terminal; - an anode-side end unit (27) having a gas outlet (22) and an electrical terminal; - at least two electrolyzer cells (40) sandwiched between the cathode-side end unit (26) and the anode-side end unit (27), each electrolyzer cell (40) comprising a cathode current collector (5; 5a, 5b, 5c, 5d); an anode current collector (10); a membrane electrode assembly comprising an ion-exchange membrane (7) having a first side and a second side, a cathode catalyst layer (6b) arranged in contact with the membrane (7) on the first side, a cathode-side gas diffusion layer (6a) arranged in contact with the cathode catalyst (6b) on the cathode catalyst layer (6b), an anode catalyst layer (8b) arranged in contact with the membrane (7) on the second side, an anode-side gas diffusion layer (8a) arranged in contact with the anode catalyst (8b) on the anode catalyst layer (8b); spacer elements (9a, 9b) configured to fix the membrane electrode assembly sandwiched between the cathode current collector (5; 5a, 5b, 5c, 5d) and the anode current collector (10) between the cathode current collector (5; 5a, 5b, 5c, 5d) and the anode current collector (10), wherein the cathode-side gas diffusion layer (6a) is in partial contact with the cathode current collector (5; 5a, 5b, 5c, 5d), thereby forming an in-plane flow structure (5”) on the cathode side therebetween, and the anode-side gas diffusion layer (8a) is in partial contact with the anode current collector (10), thereby forming an in-plane flow structure (5’) on the anode side therebetween; separating the cathode current collector (5; 5a, 5b, 5c, 5d) and the anode current collector (10) from each other; a sealed continuous cell gas flow path extending between a cell gas inlet (46) and a cell gas outlet (47) within the cell (40) through the cathode-side flow structure (5”); a sealed continuous cell fluid flow path extending between a cell fluid inlet (48) and a cell fluid outlet (49) within the cell (40) through the anode-side flow structure (5’); wherein ● the electrical terminals of the cathode-side end unit (26), the at least two electrolyzer cells (40), and the electrical terminals of the anode-side end unit (27) are electrically connected in series; and ● An electrolyzer cell (40) having gas transport channels (34, 35) extending between adjacent cells (40) through a cathode current collector (5; 5a, 5b, 5c, 5d), spacer elements (9a, 9b), and an anode current collector (10) forms a continuous gas flow path extending from a gas inlet (21) to a gas outlet (22) to supply CO2 to each cathode-side gas diffusion layer (6a) to convert CO2 into a gas-phase product by at least one cathode electrolysis reaction occurring in a cathode-side flow structure (5”) of each electrolyzer cell (40), and to discharge the product via the gas outlet (22), and ● An electrolyzer cell (40) having fluid transport channels (38, 39) extending between adjacent cells (40) through a cathode current collector (5; 5a, 5b, 5c, 5d), spacer elements (9a, 9b), and an anode current collector (10) forms a continuous fluid flow path extending from a fluid inlet (23) to a fluid outlet (24) to supply a liquid anode electrolyte to each anode-side flow structure (5’) to complete the cathode electrolysis reaction with at least one anode electrolysis reaction occurring in the anode-side flow structure (5’) of each electrolyzer cell (40), and to discharge the liquid-phase anode electrolyte and reaction products formed in the anode electrolysis reaction via the fluid outlet (24).

2. The electrolyzer stack (100’, 100”) according to claim 1, wherein at least a portion of the gas flow paths of the electrolyzer cells (40) are connected in series with each other; or At least a portion of the gas flow paths of the electrolyzer cells (40) are connected in parallel with each other.

3. The electrolyzer stack (100’, 100”) according to claim 2, wherein the spacer elements (9a, 9b) include an internal gas transport channel (36) passing through a first outer peripheral region of the spacer elements (9a, 9b), the spacer elements (9a, 9b) further include a second outer peripheral region diametrically opposite the first outer peripheral region, and the second outer peripheral region is configured as a means for selectively selecting the manner in which two adjacent cell flow paths are connected to each other in the gas flow path of the electrolyzer stack (100’, 100”), and the means provides another internal gas transport channel (36) in the second outer peripheral region.

4. The electrolyzer stack (100’, 100”) according to claim 1, wherein assembly-assist grooves 52 are formed at the outer peripheral edges of each of the cathode-side end unit (26), the anode-side end unit (27), the cathode current collector (5; 5a, 5b, 5c, 5d), the spacer elements (9a, 9b), and the anode current collector (10) of each electrolyzer cell (40) of each electrolyzer stack (100’, 100”) to assist in fastening and properly assembling / reassembling the electrolyzer stack (100’, 100”).

5. The electrolyzer stack (100’, 100”) according to claim 2, wherein assembly - assisting grooves 52 are formed at the outer peripheral edges of each of the cathode - side end unit (26), the anode - side end unit (27), the cathode current collector (5; 5a, 5b, 5c, 5d), the spacer elements (9a, 9b), and the anode current collector (10) of each electrolyzer cell (40) of each electrolyzer stack (100’, 100”) to assist in fastening and proper assembly / reassembly of the electrolyzer stack (100’, 100”).

6. The electrolyzer stack (100’, 100”) according to claim 3, wherein assembly - assisting grooves 52 are formed at the outer peripheral edges of each of the cathode - side end unit (26), the anode - side end unit (27), the cathode current collector (5; 5a, 5b, 5c, 5d), the spacer elements (9a, 9b), and the anode current collector (10) of each electrolyzer cell (40) of each electrolyzer stack (100’, 100”) to assist in fastening and proper assembly / reassembly of the electrolyzer stack (100’, 100”).

7. The electrolyzer stack (100’, 100”) according to claim 1, wherein a cathode - side pressure chamber (31) is formed in the cathode - side end unit (26), and an anode - side pressure chamber (32) is formed in the anode - side end unit (27), wherein the gas flow path passes through the cathode - side pressure chamber (31) and the anode - side pressure chamber (32) to provide adaptive pressure control for the electrolyzer cells (40) and thus provide a uniform pressure distribution throughout the electrolyzer cells (40).

8. The electrolyzer stack (100’, 100”) according to claim 2, wherein a cathode - side pressure chamber (31) is formed in the cathode - side end unit (26), and an anode - side pressure chamber (32) is formed in the anode - side end unit (27), wherein the gas flow path passes through the cathode - side pressure chamber (31) and the anode - side pressure chamber (32) to provide adaptive pressure control for the electrolyzer cells (40) and thus provide a uniform pressure distribution throughout the electrolyzer cells (40).

9. The electrolyzer stack (100’, 100”) according to claim 3, wherein a cathode - side pressure chamber (31) is formed in the cathode - side end unit (26), and an anode - side pressure chamber (32) is formed in the anode - side end unit (27), wherein the gas flow path passes through the cathode - side pressure chamber (31) and the anode - side pressure chamber (32) to provide adaptive pressure control for the electrolyzer cells (40) and thus provide a uniform pressure distribution throughout the electrolyzer cells (40).

10. The electrolyzer stack (100’, 100”) according to claim 4, wherein a cathode - side pressure chamber (31) is formed in the cathode - side end unit (26), and an anode - side pressure chamber (32) is formed in the anode - side end unit (27), wherein the gas flow path passes through the cathode - side pressure chamber (31) and the anode - side pressure chamber (32) to provide adaptive pressure control for the electrolyzer cells (40) and thus provide a uniform pressure distribution throughout the electrolyzer cells (40).

11. The electrolyzer stack (100’, 100”) according to claim 5, wherein a cathode-side pressure chamber (31) is formed in the cathode-side end unit (26), and an anode-side pressure chamber (32) is formed in the anode-side end unit (27), wherein the gas flow path passes through the cathode-side pressure chamber (31) and the anode-side pressure chamber (32) to provide adaptive pressure control of the electrolyzer cell (40) and thus provide a uniform pressure distribution throughout the electrolyzer cell (40).

12. The electrolyzer stack (100’, 100”) according to claim 6, wherein a cathode-side pressure chamber (31) is formed in the cathode-side end unit (26), and an anode-side pressure chamber (32) is formed in the anode-side end unit (27), wherein the gas flow path passes through the cathode-side pressure chamber (31) and the anode-side pressure chamber (32) to provide adaptive pressure control of the electrolyzer cell (40) and thus provide a uniform pressure distribution throughout the electrolyzer cell (40).

13. The electrolyzer stack (100’, 100”) according to any one of claims 1 to 12, wherein the cathode current collector (5; 5a, 5b, 5c, 5d) of each electrolyzer cell (40) is formed as the second component (40b) of a dual-component bipolar plate assembly (40’), and the anode current collector (10) of each electrolyzer cell (40) is formed as the first component (40a) of a dual-component bipolar plate assembly (40’).

14. The electrolyzer stack (100’, 100”) according to claim 13, wherein the second component (40b) of the dual-component bipolar plate assembly (40’) includes a flow channel system (5”) in its surface facing the membrane (7), which is arranged to provide a uniform gas distribution on the cathode-side gas diffusion layer (6a).

15. The electrolyzer stack (100’, 100”) according to claim 13, wherein the first component (40a) of the dual-component bipolar plate assembly (40’) includes a flow channel system (5’) in its surface facing the membrane (7), which is arranged to provide a uniform fluid distribution on the anode-side gas diffusion layer (8a).

16. The electrolyzer stack (100’, 100”) according to claim 14, wherein the first component (40a) of the dual-component bipolar plate assembly (40’) includes a flow channel system (5’) in its surface facing the membrane (7), which is arranged to provide a uniform fluid distribution on the anode-side gas diffusion layer (8a).

17. The electrolyzer stack (100’, 100”) according to claim 13, wherein the first and second components (40a, 40b) of the dual-component bipolar plate assembly (40’) further include orifices (41, 42, 43, 44, 46, 47, 48, 49) and respective cavities (33a, 33b, 33c, 33d) completely surrounding the orifices, which are used for fluid / gas communication between opposite sides of the first and second components (40a, 40b).

18. The electrolyzer stack (100’, 100”) according to claim 14, wherein the first and second components (40a, 40b) of the dual-component bipolar plate assembly (40’) further comprise orifices (41, 42, 43, 44, 46, 47, 48, 49) and respective cavities (33a, 33b, 33c, 33d) completely surrounding the orifices for fluid / gas communication between opposite sides of the first and second components (40a, 40b).

19. The electrolyzer stack (100’, 100”) according to claim 15, wherein the first and second components (40a, 40b) of the dual-component bipolar plate assembly (40’) further comprise orifices (41, 42, 43, 44, 46, 47, 48, 49) and respective cavities (33a, 33b, 33c, 33d) completely surrounding the orifices for fluid / gas communication between opposite sides of the first and second components (40a, 40b).

20. The electrolyzer stack (100’, 100”) according to claim 16, wherein the first and second components (40a, 40b) of the dual-component bipolar plate assembly (40’) further comprise orifices (41, 42, 43, 44, 46, 47, 48, 49) and respective cavities (33a, 33b, 33c, 33d) completely surrounding the orifices for fluid / gas communication between opposite sides of the first and second components (40a, 40b).

21. The electrolyzer stack (100’, 100”) according to claim 17, wherein the cavities (33a, 33b, 33c, 33d) are respectively closed when assembling the stack (100’, 100”).

22. The electrolyzer stack (100’, 100”) according to any one of claims 1 to 12, wherein the anode side gas diffusion layer (8a) of each electrolyzer cell (40) is selected from Ti melts in the form of pressed Ti powders of different average particle sizes, Ni melts in the form of pressed Ni powders of different average particle sizes, Ti meshes, and Ni meshes.

23. The electrolyzer stack (100’, 100”) according to claim 13, wherein the anode side gas diffusion layer (8a) of each electrolyzer cell (40) is selected from Ti melts in the form of pressed Ti powders of different average particle sizes, Ni melts in the form of pressed Ni powders of different average particle sizes, Ti meshes, and Ni meshes.

24. The electrolyzer stack (100’, 100”) according to claim 14, wherein the anode side gas diffusion layer (8a) of each electrolyzer cell (40) is selected from Ti melts in the form of pressed Ti powders of different average particle sizes, Ni melts in the form of pressed Ni powders of different average particle sizes, Ti meshes, and Ni meshes.

25. The electrolyzer stack (100’, 100”) according to claim 15, wherein the anode-side gas diffusion layer (8a) of each electrolyzer cell (40) is selected from Ti melts in the form of pressed Ti powders with different average particle sizes, Ni melts in the form of pressed Ni powders with different average particle sizes, Ti meshes, and Ni meshes.

26. The electrolyzer stack (100’, 100”) according to claim 17, wherein the anode-side gas diffusion layer (8a) of each electrolyzer cell (40) is selected from Ti melts in the form of pressed Ti powders with different average particle sizes, Ni melts in the form of pressed Ni powders with different average particle sizes, Ti meshes, and Ni meshes.

27. The electrolyzer stack (100’, 100”) according to claim 21, wherein the anode-side gas diffusion layer (8a) of each electrolyzer cell (40) is selected from Ti melts in the form of pressed Ti powders with different average particle sizes, Ni melts in the form of pressed Ni powders with different average particle sizes, Ti meshes, and Ni meshes.

28. The electrolyzer stack according to any one of claims 1 to 12, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

29. The electrolyzer stack according to claim 13, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

30. The electrolyzer stack according to claim 14, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

31. The electrolyzer stack according to claim 15, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

32. The electrolyzer stack according to claim 17, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

33. The electrolyzer stack according to claim 21, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

34. The electrolyzer stack according to claim 22, wherein the cathode catalyst (6b) is selected from Ag / C catalysts and Cu / C catalysts.

35. The electrolyzer stack according to any one of claims 1 to 12, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

36. The electrolyzer stack according to claim 13, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

37. The electrolyzer stack according to claim 14, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

38. The electrolyzer stack according to claim 15, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

39. The electrolyzer stack according to claim 17, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

40. The electrolyzer stack according to claim 21, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

41. The electrolyzer stack according to claim 22, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

42. The electrolyzer stack according to claim 28, wherein the anode catalyst (8b) is selected from IrO x , RuO x , NiO x and TiO x .

43. The electrolyzer stack (100’, 100”) according to any one of claims 1 to 12, wherein the number of electrolyzer cells (40) is at most 10.

44. The electrolyzer stack (100’, 100”) according to claim 13, wherein the number of electrolyzer cells (40) is at most 10.

45. The electrolyzer stack (100’, 100”) according to claim 14, wherein the number of electrolyzer cells (40) is at most 10.

46. The electrolyzer stack (100’, 100”) according to claim 15, wherein the number of electrolyzer cells (40) is at most 10.

47. The electrolyzer stack (100’, 100”) according to claim 17, wherein the number of electrolyzer cells (40) is at most 10.

48. The electrolyzer stack (100’, 100”) according to claim 21, wherein the number of electrolyzer cells (40) is at most 10.

49. The electrolyzer stack (100’, 100”) according to claim 22, wherein the number of electrolyzer cells (40) is at most 10.

50. The electrolyzer stack (100’, 100”) according to claim 28, wherein the number of electrolyzer cells (40) is at most 10.

51. The electrolyzer stack (100’, 100”) according to claim 35, wherein the number of electrolyzer cells (40) is at most 10.

52. The electrolyzer stack (100’, 100”) according to claim 43, wherein the number of electrolyzer cells (40) is from 3 to 7.

53. The electrolyzer stack (100’, 100”) according to claim 52, wherein the number of electrolyzer cells (40) is from 3 to 6.

54. An electrolyzer device (200) for converting gaseous carbon dioxide CO2 into at least one gas-phase product, the device (200) comprising the electrolyzer stack (100’, 100”) according to any one of claims 1 to 51; a gaseous CO2 source (201); a liquid anolyte source (213); an external power supply (220) having a first pole of a first charge and a second pole of a second charge, the second charge being opposite in sign to the first charge; the first pole being electrically coupled to an electrical terminal of the cathode-side end unit (26) of the electrolyzer stack (100’, 100”), and the second pole being electrically coupled to an electrical terminal of the anode-side end unit (27) of the electrolyzer stack (100’, 100”); a cathode-side circulation assembly for circulating gaseous CO2 from the gaseous CO2 source (201) through a gas flow path of the electrolyzer stack (100’, 100”) to at least one product container; and an anode-side circulation assembly for circulating liquid anolyte (213) from the liquid anolyte source (213) through a fluid flow path of the electrolyzer stack (100’, 100”).

55. The electrolyzer device (200) according to claim 54, wherein the cathode-side circulation assembly further comprises a humidifier (203) disposed upstream of the electrolyzer stack for humidifying CO2 before supplying it to the electrolyzer stack (100’, 100”).

56. The electrolyzer device (200) according to claim 54, wherein the cathode-side circulation assembly further comprises a backpressure regulator (209) disposed downstream of the electrolyzer stack (100’, 100”) for increasing the pressure difference present in the electrolyzer stack (100’, 100”).

57. The electrolyzer device (200) according to claim 55, wherein the cathode-side circulation assembly further comprises a backpressure regulator (209) disposed downstream of the electrolyzer stack (100’, 100”) for increasing the pressure difference present in the electrolyzer stack (100’, 100”).

58. The electrolyzer device (200) according to claim 54, wherein the cathode-side circulation assembly further comprises a water separator (208) disposed downstream of the electrolyzer stack (100’, 100”) and upstream of the backpressure regulator (209) for removing moisture from the gaseous product.

59. The electrolyzer device (200) according to claim 55, wherein the cathode-side circulation assembly further comprises a water separator (208) arranged downstream of the electrolyzer stack (100’, 100”) and upstream of the back pressure regulator (209) to remove moisture from the gaseous product.

60. The electrolyzer device (200) according to claim 56, wherein the cathode-side circulation assembly further comprises a water separator (208) arranged downstream of the electrolyzer stack (100’, 100”) and upstream of the back pressure regulator (209) to remove moisture from the gaseous product.

61. The electrolyzer device (200) according to any one of claims 54 to 60, wherein the anode-side circulation assembly further comprises an anolyte renewal unit (211) to renew the anolyte (213) as needed and / or to separate reaction products formed in the anodic electrolysis reaction from the anolyte (213).

62. The electrolyzer device (200) according to claim 61, wherein the anolyte renewal unit (211) is thermally coupled to a tempering device (212) to regulate the temperature of the anolyte (213).

63. The electrolyzer device (200) according to any one of claims 54 to 60, wherein the anolyte is an aqueous KOH solution.

64. The electrolyzer device (200) according to claim 61, wherein the anolyte is an aqueous KOH solution.

65. The electrolyzer device (200) according to claim 62, wherein the anolyte is an aqueous KOH solution.

66. A method for converting gaseous carbon dioxide CO2 into at least one gas-phase product, comprising the following steps providing an electrolyzer stack (100’, 100”) according to any one of claims 1 to 53; assembling an electrolyzer device (200) according to any one of claims 54 to 65 by using the electrolyzer stack (100’, 100”); circulating gaseous CO2 through the electrolyzer stack (100’, 100”) of the electrolyzer device (200); while circulating CO2, circulating a liquid anolyte (213) through the electrolyzer stack (100’, 100”) of the electrolyzer device (200); and while keeping CO2 and the anolyte circulating, performing a cathodic electrolysis reaction and an anodic electrolysis reaction in the electrolyzer stack (100’, 100”) to convert gaseous CO2 into the at least one gas-phase product in a continuous flow; separating the at least one gas-phase product from the gaseous CO2; optionally, renewing the anolyte (213) if needed; and discharging the at least one gas-phase product from the electrolyzer device (200).

67. The method according to claim 66, wherein an Ag / C cathode catalyst is used to produce a mixture of hydrogen and carbon monoxide as the gas-phase product.

68. The method according to claim 66, wherein a Cu / C cathode catalyst is used to produce ethylene as the gas-phase product.

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