Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/22—Inorganic acids
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/25—Reduction
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• the present invention relates to a reduction method and an electrolysis system for electrochemical carbon dioxide utilization. Carbon dioxide is introduced into an electrolyte cell and reduced at a cathode.
• Natural carbon dioxide degradation occurs, for example, through photosynthesis.
• carbon dioxide are reacted to form carbohydrates.
• This process is not easily adaptable on an industrial scale.
• a copy of the natural photosynthesis process with large-scale photocatalysis has not yet been sufficiently ef ⁇ efficient.
• An alternative is the electrochemical reduction of carbon dioxide.
• Systematic studies of the electrochemical reduction of carbon dioxide are still a relatively recent field of development. Only for a few years has there been an effort to develop an electrochemical system that can reduce an acceptable amount of carbon dioxide.
• Research in the laboratory scale have shown that are to be used for the electrolysis of carbon dioxide preferably metals as catalysts Kata ⁇ . From the publication
• Electrochemical CO 2 reduction on metal electrodes from Y Electrochemical CO 2 reduction on metal electrodes from Y.
• Gallium cathodes almost exclusively reduced to carbon monoxide, formed on a copper cathode, a variety of hydrocarbons as reaction products. For example, predominantly on a silver cathode
• the table shows Faraday efficiencies [%] of products produced by carbon dioxide reduction on various metal electrodes. The values given apply to a 0.1 M potassium bicarbonate solution as electrolyte and current densities below 10 mA / cm 2 .
• Electrolysis cells which are suitable for the electrochemical reduction of carbon dioxide, usually consist of an anode and a cathode compartment.
• FIGS. 2 to 4 show a schematic representation of examples of cell arrangements. The structure with gas diffusion electrode is shown in ⁇ example in Figure 3.
• an electrolytic cell the carbon dioxide is carried through a porous cathode placed directly from the cathode surface in the Ka ⁇ Thode space.
• FIG. 1 shows an example of a Hägg diagram of a 0.05 molar solution of carbon dioxide in order to illustrate the dependence on the concentration and pH parameters. Be in a medium pH range
• Carbon dioxide and its salts next to each other While in strongly basic carbon dioxide (CO2) preferred as Car ⁇ bonat (CO32-), in the middle pH range preferred as
• Hydrogen carbonate (HCO3-) is present, it comes at low pH values in an acidic medium to expel the hydrogencarbonate ions from the solution in the form of carbon dioxide. According to the Hägg diagram or equations 1 and 2, the carbon dioxide concentration in a bicarbonate-containing electrolyte can be very low despite the high hydrogen carbonate concentration in the range from 0.1 mol / 1 to well above 1 mol / 1 up to the solubility limit of the corresponding salt.
• the electrolysis system for carbon dioxide utilization comprises an electrolysis cell having an anode in an anode space, a cathode in a cathode space and at least one membrane, wherein the cathode space has a first access for carbon dioxide and is designed to bring the incoming carbon dioxide in contact with the cathode ,
• membrane is meant a mechanically separating layer, e.g. a diaphragm which separates at least the electrolysis products formed in the anode compartment and cathode compartment from one another.
• separator membrane or separating layer e.g. a diaphragm which separates at least the electrolysis products formed in the anode compartment and cathode compartment from one another.
• separator membrane or separating layer e.g. a diaphragm which separates at least the electrolysis products formed in the anode compartment and cathode compartment from one another.
• the electrolysis products can also be gaseous substances, preference is given to using a membrane having a high bubble point
• Carbon dioxide in chemically bonded form eg as carbonate or bicarbonate in the electrolyte
• carbon dioxide gas separately from the electrolyte or physically dissolved carbon dioxide in an electrolyte can be introduced into the cathode space via the first access , In particular, it is the electrolyte and educt inlet.
• the carbon dioxide enters ⁇ gaseous or dissolved in the cathode chamber, a portion of which is in accordance with the above-described equilibrium reactions with a chemical compound contained in the electrolyte substances, a, especially when a basic pH is present.
• the electrolysis system also has a proton donor unit and the cathode compartment is connected to the proton donor unit via a second access for protons.
• the second approach for protons is designed so that the protons are brought in the cathode chamber in contact with the Kathodenoberflä ⁇ che.
• the proton donor unit is as ⁇ defined by that fact, free protons are thus provided What ⁇ serstoffkationen. Hydrogen (H2) or other hydrogen bonds are not protons in the sense of the proton donor unit according to the invention.
• the proton donor unit By means of the proton donor unit can be effected a local pH decrease in the electrolysis ⁇ system, the surfactant forming physically dissolved carbon dioxide at the reaction promotes the cathode and thus significantly increases the metabolic rate.
• the electrolysis system comprises a proton donor unit having a proton reservoir and a proton transmissive membrane.
• the protonen vomläs ⁇ sige membrane acts as a second access to the cathode chamber for protons. While the proton reservoir provides the advantage of continuous replenishment of protons, the proton-permeable membrane is used to ensure the pure Io nenzulig or proton influx to the cathode compartment, while retaining other molecules, liquid ⁇ speeds or gases.
• the proton-permeable membrane preferably has sulfonated polytetrafluoroethylene. Alternatively, a cation exchange membrane can be used as a proton permeable membrane.
• the electrolysis system has an acid reservoir as proton reservoir, which in particular comprises a Brönsted acid.
• a Bronsted acid for example sulfuric acid, phosphoric acid, nitric acid, salt ⁇ acid or various organic acids such as formic acid, acetic acid or ⁇ game.
• the acidity definition according to Brönsted describes acids as so-called proton donors, ie particles that can give off protons, ie positively charged hydrogen ions.
• Brönsted acids are preferably used whose pKs value is correspondingly smaller than the pKa value of the aqueous carbonate, bicarbonate or dihydrogen carbonate solution. Smaller means in this case, the acid is stronger.
• An advantage of the acid reservoir is that it creates a relatively continuous proton source that does not rely on an additional external energy input.
• the electrolysis system comprises a second proton transmissive membrane comprising sulfonated polytetrafluoroethylene.
• Be ⁇ preferred is a proton permeable membrane a
• Nafion membrane used.
• This membrane can be designed, for example, multi-layered or porous.
• a separator membrane also a proton permeable membrane, such as the proton donor unit, can be used.
• the cathode compartment of the electrolysis system comprises a catholyte-carbon dioxide mixture, wherein the
• Katholyt carbonate and / or bicarbonate has anions.
• the catholyte in the cathode compartment of the electrolysis ⁇ system in particular alkali metal and / or ammonium ions (NHz [ + ].
• the alkali metals are the chemical elements lithium, sodium, potassium, rubidium, cesium and francium from the first main group of the periodic table.
• the carbonate and / or bicarbonate-containing electrolyte has the advantage of having chemically bonded carbon dioxide. Alternatively or additionally, carbon dioxide in dissolved or gaseous form can be introduced into the cathode compartment.
• the pH of the catholyte in the cathode compartment is preferably between 4 and 14.
• the electrolysis system comprises an anode space, which acts as a proton reservoir. It can be z.
• anode space which acts as a proton reservoir.
• the anode space which acts as a proton reservoir, is connected via the membrane and a porous anode to the cathode space.
• a compound of the proton reservoir is not absolutely necessary because in turn also pro ⁇ tone can be produced at the anode, which depends concentration of the Elektrolytkon-. For the release of carbon dioxide, the concentration must be correspondingly high.
• the electrolysis system has a first and a second membrane, wherein the first membrane between anode and cathode as
• the second membrane between the cathode and proton reservoir is arranged and at least this second membrane is proton permeable.
• This arrangement of the electrolysis system is advantageous because the connection of the proton reservoir via the proton permeable membrane to the cathode ensures that the protons are delivered directly to the reaction surface of the cathode.
• the cathode is preferably made porous, and in direct contact with the sur fa ⁇ speaking proton permeable membrane, which connects to the proton reservoir.
• anolyte, catholyte and proton source for example an acid or acid mixture, can be selected separately from each other and specially adapted.
• the cathode space of the electrolysis system is designed as Katholytspalt extending along the cathode and in its width, ie its extent perpendicular to the cathode surface extension, maximum 5 mm.
• a catholyte gap is therefore to be understood as meaning a thin, areally expanded cavity between the cathode and a membrane.
• the membrane limited the catholyte, for example, ge ⁇ genüber the proton reservoir or to the anode compartment or the anode.
• the described pH gradient in the cathode space plays a not insignificant role.
• the cathode space is designed as Katholytspalt, which cathode and proton ⁇ permeable membrane or cathode and first membrane separates, and these are each arranged at a distance of a maximum of 5 mm zueinan ⁇ .
• the cathode compartment can also comprise two catholyte gaps, which are arranged on both sides of the cathode and each bounded by a membrane, the cathode and the membranes being arranged at a distance of not more than 5 mm from each other.
• electrolysis products can be produced on both sides of the cathode electrolysis products.
• a solid cathode ie, for example, a Ka thodenblech
• Such a solid cathode preferably has a nanostructured surface.
• both membranes are made permeable to ensure proton corresponding to the proton ⁇ access.
• the electrolysis system comprises a proton donor cathode comprising the proton donor unit and an integrated therein proton ⁇ permeable cathode.
• the cathode is porous, eg as a perforated plate, as screening, as a grid, net or fabric electrode, or as a gas diffusion electrode ⁇ , from pressed nano- to micron particles gegebe ⁇ appropriate, carried out with additional membrane layers.
• the proto ⁇ permeable cathode is preferably directly connected to the proton permeable membrane, for example, applied to this or vice versa, and thus forms part of the second access to the cathode space for the protons.
• the protons enter from the proton reservoir over the entire cathode surface into the cathode chamber, so the exact spot in the cathode chamber, at the phase boundary between the cathode surface and catholyte to which they are to release the Koh ⁇ lenstoffdioxid from the catholyte.
• this variant was referred to as proto ⁇ nenspenderkathode.
• the proton donating membrane of the proto ⁇ nenspenderatti be in the immediate vicinity of the cathode angeord ⁇ net
• the cathode may be integrated into the proton donor unit with the proton donating membrane.
• a catholyte-carbon dioxide mixture is introduced into a cathode space and brought into contact with a cathode, in the Katho ⁇ denraum a local pH decrease of the Catholyte-carbon dioxide mixture in the additional protons complaintge ⁇ provides.
• the additional protons then serve to produce reducible, physically dissolved or gaseous, but no longer chemically bound, carbon dioxide, the generation or release of this carbon dioxide taking place directly at the cathode reaction interface. This local carbon dioxide concentration increase significantly increases its conversion.
• the local pH reduction of the catholyte-carbon dioxide mixture at the liquid-solid phase boundary surface of the catholyte-carbon dioxide mixture is made to the cathode in which the additional protons on the proton permeable membrane or via the proton-permeable cathode at the liquid-solid-phase interface of the
• Catholyte-carbon dioxide mixture are provided to the cathode.
• in-situ generation of carbon dioxide in the phase boundary region is effected from the anions hydrogen carbonate or carbonate present in the electrolyte.
• protons are taken from a proton reservoir, in particular an acid reservoir, which in particular has a Bronsted acid, e.g. Sulfuric acid, phosphoric acid or nitric acid, hydrochloric acid or an organic acid such as acetic acid and formic acid.
• a Bronsted acid e.g. Sulfuric acid, phosphoric acid or nitric acid, hydrochloric acid or an organic acid such as acetic acid and formic acid.
• the catholyte has carbonate and / or bicarbonate anions and / or dihydrogen carbonate.
• the catholyte to preferably alkali metal and / or Ammoniumio ⁇ NEN.
• the catholyte has sulfate and / or hydrogen sulphations, phosphate, hydrogen phosphate and / or dihydrogen phosphate ions.
• the pH of the catholyte is in a rich Be ⁇ 4 to 14
• a conductive porous catalogs lysatorkathode in the proton donor unit such inte ⁇ grated is that the protons on the proton-conducting Memb ⁇ ran and it incorporated in direct connection through the cathode itself into the cathode compartment, the proton- tende membrane, for example, backwashed by an acid who ⁇ .
• the acid strength is preferably adjusted so that just as much carbon dioxide from the catholyte is driven out ⁇ , can be reduced as at a given current density at the Ka Thode. This has the particular advantage that thereby the resulting product or the product mixture can be ensured very low in carbon dioxide.
• the cathode itself preferably has a large surface area.
• the cathode itself is made porous, which also means an increase or maximization of the reactive surface.
• the cathode is an RVC electrode
• a silver-gas diffusion electrode is placed a ⁇ as a cathode. It is important that this can be carried out without carbon ⁇ share.
• An inserted silver gas diffusion electrode comprises, for example, silver (Ag), silver oxide (Ag 2 O) and polytetrafluoroethylene (PTFE, eg Teflon).
• the invention described allows the conversion of chemically bound in carbonates and bicarbonates lenstoffdioxidanteils coal to physically dissolved Kohlenstoffdi ⁇ oxide or carbon dioxide, which is the desired from ⁇ transition component for the electrochemical production Kohlenstoffdioxidre-.
• a method and a system is described which allows high carbon dioxide conversion rates with current densities >> 100 mA / cm 2 , without the need for a cathode with a separate gassing as a cathode.
• a gas diffusion electrode as used hitherto could, in an embodiment according to the invention, be used as an additional be introduced component.
• phase boundary layer between the proton-conducting membrane of the Protonenspender- unit and the catholyte or the phase boundary layer Zvi ⁇ rule of the cathode surface and the catholytes quasi serves itself as carbon dioxide source.
• phase boundary ⁇ layer occurs a local pH change due to the migrating protons.
• the equilibrium reaction 1 is then influenced in such a way that finely distributed carbon dioxide gas bubbles are formed on the membrane surface or cathode surface by carbonate decomposition in an acidic medium.
• the locally acidic pH is also determined by the Brönsted acid surface of the proton-conducting membrane or by the acidic sulfonic acid groups present on the cathode surface.
• the sulfonic acid groups come from the sulfonated polytetrafluoroethylene of the membrane.
• this polymer swells into a kind of "solid” sulfuric acid, which is then transferred from the sulfonic acid group to the sulfonic acid group in a kind of hopping transport.
• “Protons can pass through the Nafion, tunnels, or bounce hang and are no longer transported, which is why we also speak of polymer ion exchangers.
• the cause of the formation of gaseous carbon dioxide is a neutralization of the passing Hydroniumionen due to existing carbonate or hydrogen carbonate ions.
• a strongly acidic electrolyte for example a strongly acidic anolyte, can additionally reinforce this effect.
• the anode space serves as a proton reservoir
• an increased proton pressure is produced on the membrane from the anode side and intensifies the concentration gradient in the cathode space.
• the anolyte, as described include a Bronsted acid for example sulfuric acid, phosphoric acid or nitric acid ⁇ .
• the catholyte are preferably alkali metal or Ammo ⁇ niumionen or bicarbonates or carbonates used.
• the starting composition of the catholyte in particular its hydrogen carbonate or. Carbonate concentration via the entry or
• Such a process can for example, as described, be realized by the additional use of a gas diffusion electrode.
• the process-intensifying method presented for the electrochemical reduction of carbon dioxide improves the conversion per electrode area and per current density.
• undesirably high carbonate and hydrogen phosphate are carbonate concentrations in the electrolyte, in particular prevents the catholyte which negatively affect the physi ⁇ cal solubility of carbon dioxide.
• the principle of a technically established gas diffusion electrode can be replaced by the described method. But the Gasdiffusi ⁇ onselektrode can continue to be used as an add-on of this new principle described, for example, for subsequent delivery of carbon dioxide in the electrolyte circuit. Particularly suitable is the method for use in the Elect ⁇ rolysezellen with external Kohlenstoffdioxidslitistist.
• a particularly suitable application of the process described is the work-up of the potassium bicarbonate solution obtained in the basic carbon dioxide washings in the context of an in situ electrochemical regeneration of the loaded absorbent. Compared to the classical thermal regeneration, the method offers an enormous energy saving potential.
• FIG. 1 shows a Hägg diagram for a 0.05 molar carbon dioxide solution
• FIG. 2 shows a schematic representation of a two-chamber structure of an electrolytic cell
• FIG. 3 shows a schematic representation of a three-chamber structure of an electrolysis cell
• FIG. 4 shows a schematic representation of a PEM structure of an electrolysis cell
• FIG. 5 shows an electrolysis cell in the two-chamber design and the characteristic increase in pH to the cathode
• FIG. 6 shows a schematic representation of a cell arrangement with additional acid reservoir and porous cathode
• FIG. 7 shows a cell arrangement with additional acid reservoir and two catholyte gaps
• Figure 8 shows a schematic representation of another
• Figure 9 shows a schematic representation of another
• Embodiment of a cell assembly with additional acid reservoir and electrolyte columns Embodiment of a cell assembly with additional acid reservoir and electrolyte columns.
• the Hägg diagram shown in FIG. 1 contains values for a 0.05 molar solution of carbon dioxide in water: the concentration C in the unit mol / l is plotted over the pH.
• the concentration of protons (H +) decreases a pH value> 0 from 1 to a value of 10 ⁇ 10 mol / 1 at a pH of 10, whereas the OH- ion concentration entspre ⁇ accordingly the pH definition increases.
• Is in the acidic milieu ie until pH still a virtually pH independent ⁇ carbon dioxide concentration in approximately 4 (CO2) of 0.05 mol / 1 before, this drops to a pH of 5 significantly in favor of an increase in Hydrogen carbonate ions (HCO3), which have their highest concentration in a pH range between 8 and 9.
• HCO3 Hydrogen carbonate ions
• the carbon dioxide predominantly exists in the form of carbonate ions (CC ⁇ -) in the solution.
• the common structures of electrolysis cells 2, 3, 4 shown schematically in FIGS. 2 to 4 comprise at least one anode A in an anode space AR and one cathode K in a cathode space KR.
• anode space AR and cathode space KR are separated from one another at least by a membrane Mi.
• This membrane Ml preferably provides for the separation of the gaseous products Gl and products PI or prevents mixing.
• a defining parameter for the membrane M1 is the so-called bubble point. This be ⁇ writes from which pressure difference ⁇ between the two sides of the membrane Ml a gas flow through the membrane Ml would take place.
• a membrane M1 is used with a high bubble point of 10 mbar or greater.
• the membrane may be an ion-conducting membrane Mi, for example, an anion conducting membrane or a cation conducting membrane ⁇ .
• the membrane may be a porous layer or a diaphragm.
• the term membrane M 1 can also be understood as meaning an ion-conducting spatial separator which separates electrolytes into anode and cathode chambers AR, KR. Depending on the electrolyte solution E used, a construction without membrane Mi would also be conceivable.
• Anode A and Ka ⁇ method K are each electrically connected to a power supply.
• the anode compartment AR of each of the electrolysis cells 2, 3, 4 shown is in each case equipped with an electrolyte inlet 21, 31, 41.
• each anode chamber AR shown comprises a electrolyte outlet 23, 33, 43 via the 2 may give off ⁇ the electrolyte E and formed at the anode A Elektrolysepro ⁇ Gl-products, for example, oxygen gas O out of the anode space AR.
• the respective cathode chambers KR each have at least one electrolyte and product outlet 24, 34, 44.
• the total electrolysis product PI can be composed of a large number of electrolysis products.
• the electrodes While in the two-chamber structure 2 anode A and cathode K are separated by the anode space AR and cathode space KR of the membrane Mi, the electrodes are in a so-called polymer electrolyte membrane assembly (PEM) 4 with porous electrodes directly to the membrane Mi on. As shown in Figure 4, it is then a porous anode A and a porous Katho ⁇ de K.
• PEM polymer electrolyte membrane assembly
• the electrolyte and the carbon dioxide CO 2 is preferably via a common Edukteinlass 22, 42 introduced into the cathode space KR.
• the cathode K in the Cathode space KR flowed.
• the porous cathode K is designed as a gas diffusion electrode GDE.
• a gas diffusion electrode GDE is because ⁇ characterized by that a liquid component, such as an electrolyte, and a gaseous component, such as a Elektrolyseedukt, can be brought together in a pore system of the electrode, for example, the cathode K in contact.
• the pore system of the electrode is designed so that the liquid and the gaseous phase can equally penetrate into the pore system and can be present in it at the same time.
• a reaction catalyst is designed to be porous and takes over the electrode function, or a porous electrode has catalytically active components.
• Catholyte cycle includes the gas diffusion electrode GDE ei ⁇ nen carbon dioxide inlet 320.
• the invention could, for example, in one of the previously ⁇ known electrolysis cell structures, such as. As shown in Figures 2 and 3, implemented, if they were provided with a corresponding proton donor unit.
• the structure shown in Figure 4 needed for the implementation of the invention more concrete modifications, such as
• Transport channels for the electrolyte through the cathode to produce a membrane-electrolyte contact Preferably, the carbon dioxide development or release would take place in these transport channels.
• transport channels for the anolyte to the membrane are required on the anode side in order to make the protons available.
• anode space can be embodied as a polymer electrolyte membrane half cell, while a cathode space consists of a half cell, with a cathode space between the membrane and the cathode, as shown in FIGS. 2 and 3.
• Figure 5 shows schematically the structure of an electrolytic cell 5 with an anode space AR between an anode A and a membrane Ml and a cathode space KR between the membrane Ml and the cathode K.
• Anode A and cathode K are connected to each other via a power supply.
• an arrow from the anode compartment AR in the cathode compartment KR through the membrane Ml therethrough is indicated that this is ionically conductive at least for a La ⁇ makers places, preferably at least for cations X +, where this different depending on the anolyte metal cations X may be the + and for protons H + .
• the cathode compartment KR has a width dj [ie ei ⁇ that a clearance between the membrane Ml and the cathode K.
• the membrane Ml and the cathode K so on ⁇ arranged that their located facing the cathode compartment KR surfaces plane-parallel in the electrolysis cell 5 to each other run.
• a slope triangle the pH gradient in the cathode compartment KR is displayed: The pH rises from a locally acidic environment na ⁇ height of the membrane Ml to a local basic environment near the cathode surface K to.
• the locally acidic region is denoted by I and represented by a dashed line parallel to Ml, correspondingly with II and the dashed line in front of the cathode K of the local basic area in the cathode space KR is shown.
• the anode space AR becomes equally acidic, as does the cathode space KR basic.
• the catholyte preferably comprises Alkalime ⁇ tallow and / or ammonium ions or their hydrogencarbonates or carbonates.
• the reaction of hydrogen HC03 ⁇ to carbon dioxide CO2 is known as the acidic Zerset ⁇ Zung bicarbonate HC03 ⁇ . In the basic medium, ie at a pH between 6 and 9, bicarbonate HC03 ⁇ is formed, ie then runs the equilibrium reaction
• FIGS. 6 to 9 show preferred embodiments of electrolysis cells according to the invention. These are basically in accordance with the polymer electrolyte membrane assembly (PEM) or polymer electrolyte membrane-type cell structure kon ⁇ zipiert.
• PEM polymer electrolyte membrane assembly
• the proton donating membrane of the proton donor unit can be in the immediate vicinity of the cathode to ⁇ arranged, as can be found in Figures 7 and 9, on the other hand, the cathode may be integrated in the proton donor unit with the proton donating membrane, such as by the figures 6 and 8 is shown by way of example.
• the polymer electrolyte membrane is often called the proton exchange membrane (proton exchange membrane) and is a semi-permeable membrane. These membranes are before Trains t ⁇ for cations, such as protons, H +, lithium Li +, sodium Na + or K + potassium cations permeable, during the transport of gases such as oxygen O2 or hydrogen is prevented H2.
• aqueous fluids can pass through the PEM, although capillary forces inhibit this transport.
• a polymer electrolyte membrane may be made of an ionomer, pure polymer or composite membranes in which other materials are embedded in a polymer matrix.
• An example of a commercially available polymer electrolyte membrane is Nafion from DuPont.
• Equal to all structures is the sequence of left side an anode compartment AR, which is separated from the cathode compartment KR by an anode A and, on the side facing away from the anode compartment AR side of the anode A membrane.
• the cathode K and the proton donor unit in different designs are connected to the cathode space KR.
• the educt and electrolyte inputs E in the anode compartment AR and cathode compartment KR and the outlets for electrolyte E and product mixtures PI, Gl are indicated.
• the membrane Ml is about ⁇ mainly as a separator, but can also be protonen press- casual, as required, for example, for the embodiment of anode-, additional acid reservoir PR1.
• the cathode-side acid or proton reservoir PR is separated from the cathode K in all cases by a proton-conducting membrane M2.
• the cathode K is located in the fi gures 7 and 9 between two Katholytspalten KS or as a product in the proton donor tonenspenderkathode PSK unit inte grated ⁇ .
• the porous cathode K is not only proton ⁇ permeable, but preferably carried out also electrolyte permeable, so that the carbon dioxide release on a very large cathode surface, for. B. within electro ⁇ lytkanälen, in the cathode K can be done.
• the cathode can K may be formed from a solid sheet, but may also have an advantageous nanostructuring for surface enlargement.
• the acid flowing past the cathode K can form the anolyte, since protons H + are then produced on the anode side, for example by water oxidation.
• the anode space AR is explicitly designed as an additional proton reservoir PR1, and an acid is used as the anolyte.
• the two proton or acid reservoirs PR, PR1 can be connected to one another via a circulatory system.
• the Katholytspalte KS shown in Figures 7 and 9 be a width, for example between 0 and 5 mm, advantageously ⁇ legally between 0.1 and 1 mm, preferably between 0.1 and 0.5 mm.
• the separator membrane M1 can be proton-conducting, at least least one membrane Ml is used, which ensures a Ladungsaus ⁇ same.
• Separator membrane Ml and cathode K would otherwise be converted at the catalyst interface primarily to hydrogen H2 and thus no carbon dioxide reduction could take place.
• the protons H + which have entered the cathode space KR must first ensure the formation of carbon dioxide and must not be converted directly to hydrogen H2.
• the Min ⁇ least distance bj (R for the cathode compartment KR at a cell North ⁇ voltage 6, 8 with proton donors cathode PSK is 1 mm. Before ⁇ preferably the distance b j ⁇ R is between Separatormembran- surface Ml and catalyst surface K between 1 and 10 mm, preferably not more than 5 mm, advantageously not more than 2 mm.
• the absolute carbon dioxide concentration of the liquid phase and, above all, the local availability of the physically dissolved carbon dioxide in the immediate vicinity of the electrode surface can be adjusted by means of the invention.
• Macrokinetic mass transfer processes play only a subordinate role in the arrangement according to the invention, since the carbon dioxide required for the electrochemical reduction from the anions of the electrolyte is made available, as it were, by in-situ protonation on the reaction surface.

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• 2015
  • 2015-05-22 DE DE102015209509.6A patent/DE102015209509A1/de not_active Withdrawn
• 2016
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