Electrochemical Conversion of Carbon Dioxide

This application is a divisional of and claims the benefit of priority to U.S. application Ser. No. 17/684,891, filed Mar. 2, 2022, which claims the benefit of priority to Greek application Ser. No. 20/210,100132, filed on Mar. 4, 2021, the entire contents of which are incorporated by reference herein.

This disclosure relates to electrochemical conversion of carbon dioxide into chemicals.

Carbon dioxide is the primary greenhouse gas emitted through human activities. Carbon dioxide (CO) may be generated in various industrial and chemical plant facilities. At such facilities, the utilization of COas a feedstock may reduce COemissions at the facility and therefore decrease the COfootprint of the facility. The conversion of the greenhouse gas COinto value-added feedstocks or products may be beneficial.

An aspect relates to a method including feeding carbon dioxide to a first cathode cavity of a first electrochemical cell, electrochemically reducing the carbon dioxide at a first cathode in the first electrochemical cell to carbon monoxide (CO), flowing the CO from the first cathode cavity to a second cathode cavity of a second electrochemical cell, and forming at least one of ethanol or ethylene from the CO at a second cathode in the second electrochemical cell.

Another aspect relates to a method including feeding carbon dioxide to a first cathode cavity of a first electrochemical cell of an electrochemical two-cell apparatus, and electrochemically reducing the carbon dioxide at a first cathode in the first electrochemical cell to carbon monoxide (CO), wherein electrochemically reducing the carbon dioxide generates oxygen ions. The method includes flowing the CO from the first cathode cavity to a second cathode cavity of a second electrochemical cell of the electrochemical two-cell apparatus, and forming a product including at least one of ethanol or ethylene from the CO via a catalyst at a second cathode in the second electrochemical cell.

Yet another aspect relates to a system including an electrochemical two-cell apparatus to electrochemically reduce carbon dioxide into carbon monoxide at a first cathode and convert the carbon monoxide into at least one of ethanol or ethylene at a second cathode. The electrochemical two-cell apparatus includes a first electrochemical cell including a first cathode cavity, the first cathode, a first catalyst disposed along the first cathode, a first anode, a first electrolyte to conduct oxygen ions from the first cathode to the first anode, and a first anode cavity to collect and discharge oxygen gas formed from the oxygen ions. The electrochemical apparatus includes a second electrochemical cell including a second cathode cavity to receive the carbon monoxide from the first cathode cavity, the second cathode, a second catalyst disposed along the second cathode, a second anode to generate hydrogen ions, a second anode cavity, a second electrolyte disposed between the second anode and the second cathode to diffuse the hydrogen ions from the second anode to the second cathode, wherein the second electrolyte is a proton conductor. The system includes a first conduit to supply the carbon dioxide to the first cathode cavity, and a second conduit to discharge the at least one of ethanol or ethylene from the second cathode cavity.

Yet another aspect relates to an electrochemical two-cell apparatus including a first electrochemical cell including a first cathode cavity to receive carbon dioxide, a first cathode to electrochemically reduce the carbon dioxide into carbon monoxide and generate oxygen ions, a first anode to receive the oxygen ions, a first anode cavity to collect and discharge oxygen gas formed from the oxygen ions, a first electrolyte disposed between the first cathode and the first anode to conduct the oxygen ions, and a first catalyst disposed along the first cathode. The electrochemical two-cell apparatus includes a second electrochemical cell including a second cathode cavity to receive the carbon monoxide, a second cathode to convert the carbon monoxide into at least one of ethanol or ethylene, a second anode to generate hydrogen ions, a second anode cavity, a second electrolyte to diffuse the hydrogen ions from the second anode to the second cathode, and a second catalyst disposed along the second cathode.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

Some aspects of the present disclosure are directed to electrochemical conversion of carbon dioxide (CO) into chemicals that have value, such as ethanol, ethylene, etc. A multi-cell (e.g., two-cell) arrangement may be employed for conversion (e.g., direct conversion) of COinto ethanol or ethylene. The setup may include two connected electrochemical cells, where COis reduced on the cathode of the first cell to carbon monoxide (CO). This CO may go through dimerization and hydrogenation on the second cell to produce ethanol and/or ethylene.

The research community and industry are progressively converging to a conclusion that COsequestration has limitations for the value proposition. Alternatively, creating diverse demand markets and revenue streams for the recovered almost-pure COmay prevail over COsequestration options and improve the economic feasibility of this mitigation approach for climate change. As such, research in the carbon capture and management field is seen to be shifting towards COutilization, directly and indirectly, in energy and chemical industries.

Electrochemical reduction of COto value-added chemicals and fuels offers a potential platform to store renewable energy in chemical bonds and thus a route to carbon recycling. Among many possible reaction pathways, and due to relatively high efficiency and reasonable economic feasibility, COconversion to CO can be an action in the synthesis of more complex carbon-based fuels and feedstocks, and may hold significance for the chemical industry.

Embodiments herein produce hydrocarbons (e.g. ethanol, ethylene, etc.) through the electrochemical reduction of CO. This COconversion may be implemented in a two-cell setup (dual cell arrangement) of electrochemical cells including, for instance, in which the two cells are coupled to one another and may share a housing.

is a techniqueto convert COin an electrochemical two-cell arrangement or apparatus. The COis electrochemically reduced into COvia electrons at the cathode of the first electrochemical cell. Oxygen (O) ions flows from the cathode through an electrolyte (high-temperature Oconductor) to the anode.

At the cathode of the second electrochemical cell, the COundergoes dimerization via electrocatalyst to give CO dimer(OCCO or OCCO*) that is hydrogenated via Hions into compounds. The CO dimerization may be via electrochemical reduction. Electrochemical reduction or the electrons may be involved in the dimerization of CO. The compoundsmay be, for example, ethanol (EtOH) or ethylene (C2H4). The hydrogenation may be electrochemical hydrogenation. Electrochemical reduction or electrons may be involved in the hydrogenation of the CO dimer. The Hions flow from the anode through an electrolyte (proton conductor) to the cathode. This electrolyte may be a high-temperature proton conductor and/or low-temperature proton conductor. The Hions may hydrogenate the CO dimer directly from the cathode. The intermediate OCCO* may be hydrogenated by the Hions. The Hions may form Hgas in the cathode side cavity for the hydrogenation of the CO dimer. The asterisk (*) notation for dimer OCCO* means that the dimer is an excimer (excited dimer) that can be temporary or short-lived.

In summary, the electrochemical two-cell setup or apparatus may be utilized for COconversion to ethanol and/or ethylene through CO dimerization. Therefore, embodiments may enhance COutilization by electrochemically reducing COinto CO and then the CO dimerized and converted to ethanol and/or ethylene. The COconversion may be characterized as a direct conversion in at least the sense that the conversion of COto ethanol or ethylene occurs within the arrangement of two coupled electrochemical cells. The sequence may be the reduction of COto CO, followed by the dimerization of the CO, and then hydrogenation of the CO dimer to ethanol and/or ethylene. These actions in the sequence may occur simultaneously in a continuous operation of the two coupled electrochemical cells.

is a systemhaving an electrochemical two-cell apparatusthat can be labeled as an electrochemical two-cell device. The electrochemical two-cell apparatusincludes a first electrochemical cell(labeled as cell (A)) and a second electrochemical cell(labeled as cell (B)) that are coupled. In the illustrated embodiment, the electrochemical cells,share a housing. The housingmay be, for example, metal such as stainless steel. In other embodiments, the two cells,do not share a housing but are otherwise fluidically coupled (e.g., via a conduit), for example, on the cathode sides.

The first cellhas a cathode cavity, a cathode, an anode, and an anode cavity. Likewise, the second cellhas a cathode cavity, a cathode, an anode, and an anode cavity.

The cathodes,and the anodes,as electrodes may each be a ceramic or metal (or metal oxide). An example metallurgy is a nickel alloy to give nickel-based electrodes. The cathodes,and the anodes,may be electrodes based on ceramic materials that exhibit stability through reduction-oxidation (redox) cycles, electrocatalytic activity and mixed ionic/electronic conductivity in reducing atmospheres are applicable. In implementations, the electrode material may be ceramic oxides of perovskite structure. Other materials are applicable.

Respective catalyst,(e.g., electrocatalyst) may be disposed along the cathodes,in the cathode cavities,. In examples for the first cell, the catalyst(first catalyst) in the cathode cavitymay be coated on the surface of the cathode. Likewise, in examples for the second cell, the catalyst(second catalyst) in the cathode cavitymay be coated on the surface of the cathode.

The first catalyst(e.g., electrocatalyst) associated with the cathodefor the reduction of COmay be, for example, metals, metal oxides, tetrahedral oxide structures, or ceramic oxides of perovskite structure and alloys. The first catalystmay include, for example, LiMSiO(LMS), LiCoSiO(LCS), LiNiSiO(LNS), LiNiCoMnO, (La,Sr)CoO(LSC) with different La—Sr ratios, LaSrxCrMO(M=Mn, Fe, Co, Ni), (La,Sr)(Fe,Co)O(LSCF), (Sm,Sr)CoO(SSC), and (Ba,Sr)(Co,Fe)O(BSCF).

The second catalyst(e.g., electrocatalyst) associated with the cathodefor the CO dimerization may be a metal or metal oxide. In some examples, the second catalystis copper (Cu) or includes copper. The metal catalyst may have a specified facet cut. The facets may be, for example, (111), (110), or (100), which are Miller indices. The principal difference between (111), (110), and (100) facets in materials may be the surface energy. Each facet can have a characteristic surface energy with the value depending, for example, on the number of broken chemical bonds in the surface.

The catalyst metal and facet may be specified to promote the CO dimerization. In examples, the facet specified for the catalyst metal is (100). In one example, the catalystis Cu(100) catalyst, which is copper catalyst having a cut at (100) facet. This Cu(100) catalyst [copper (100) facet] has been utilized, for instance, in the production of methanol and can be utilized for CO dimerization to CO dimer 2CO. The dimer mechanism may take place on the Cu(100) surface followed by hydrogenation of the CO dimer to ethylene or ethanol.

The anodes,may be an electrocatalytic anode or an electrocatalyst may be employed at the anodes,. An example of electrocatalyst for the anodes,is silver (Ag) and Ag-containing materials. Other materials for an electrocatalyst (if employed) at the anodes,are applicable.

The first electrochemical cellhas an electrolyte(first electrolyte) disposed between the cathodeand the anode. Likewise, the second chemical cellhas an electrolyte(second electrolyte) disposed between the cathodeand the anode. The electrolytes,may be a solid electrolyte. The solid electrolyte may be a solid oxide or ceramic, or other material, for the high-temperature regime. The solid electrolyte may be a polymer, or other material, for the low-temperature regime. In implementations, the first cellor the second cell, or both, may be a solid oxide electrolysis cell (SOEC) or a reversible polymer electrolyte membrane fuel cell (R-PEM).

The electrolyteof the first cellmay be a high-temperature Oconductor that conducts Oions. The first electrolytemay be, for example, yttria-stabilized zirconia (YSZ), cerium (IV) oxide (CeO), or other material that conducts Oions. The YSZ material if employed may be prepared by doping yttrium oxide (YO) into zirconium dioxide (ZrO). In one example, the electrolyteis YO-stabilized ZrO(YSZ) having at least 6 mole percent (mol %) Yor at least 8 mol % YO.

The electrolyteof the second electrochemical cellmay be a high-temperature proton conductor that conducts Hions. The second electrolytematerial may be, for example, material of the perovskite family that conducts Hions. The second electrolytemay be other material that conducts Hions. In some examples, the second electrolyteis SrCeYbOor CaInZrO, where Sr is strontium, Ce is Cerium, Yb is Ytterbium, O is elemental oxygen, Ca is calcium, In is indium, and Zr is zirconium. Also, the second electrolytematerial may be polymer electrolyte membrane. In one example, the second electrolyteis a sulfonated tetrafluoroethylene (a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer), such as Nafion® commercially available from DuPont de Nemours, Inc. having headquarters in Wilmington, Delaware USA.

In the illustrated embodiment, the first celland the second cellshare the housing, and with the first cathode cavityand the second cathode cavitysharing a space in the housing. The first cathode cavityis a portion (about half) of the space that is adjacent to the first cathode. The second cathode cavityis a portion (about half) of the space that is adjacent the second cathode. A partial barrierin the shared space generally divides the first cathode cavityand the second cathode cavity. The partial barrierallows for flow of gas (e.g., CO) from the first cathode cavityto the second cathode cavity. In other embodiments, there is no partial barrier. Instead, the COformed by the electrochemical reduction of carbon dioxide at the first cathodeflows from the first cathode cavityto the second cavity(and second cathode) without a partial barrier between the cavities,. In yet other embodiments, the first celland the second cellhave separate housings and the cavities,do not share a space. Instead, the first cathode cavityis fluidically coupled to the second cathode cavityvia a conduit, such as metal tubing (e.g., stainless steel), for flow of gas (e.g., CO).

In implementations, the electrochemical cells,share the partial barrier(e.g., stainless steel plate) as depicted positioned to divide the cathode cavityof the first cellfrom the cathode cavityof the second cell. The partial barriermay be a metal plate (e.g., stainless steel) as a solid wall. The partial barrierhas a gap or opening to allow for flow of gas (e.g., CO) from the cathode cavityof the first cellto the cathode cavityof the second cell.

A power sourcesupplies electric current (electrons) to the cathodeof the first cellfor the electrochemical reduction of COinto CO to occur. A power sourcesupplies electric current (electrons) to the cathodeof the second cellfor the dimerization of CO and hydrogenation of the CO dimer into ethanol or ethylene. In implementations, the first power sourceand the second power sourcemay be the same power source. The power source,may be a battery, a power generator, an electrical grid, a renewable source of power, etc. The applied electric current may be modulated or regulated. The desired amount of current (or set point of the amount of current supplied) may be determine correlative with reaction requirements at the cathodes,or anodes,. In implementations, the amount of current input may be based at least in part on the oxidation reaction requirement at the anode. The amount of current supplied by the power source,may be modulated via a variable resistor or potentiometer, or by varying voltage, and the like. The amount of current supplied by the power source,may be modulated (adjusted and maintained) via a controller directing or including the variable resistor or potentiometer, or directing the varying of the voltage, and the like.

While only one dual-cell arrangement (one electrochemical two-cell apparatus) is depicted for clarity, more than one dual-cell arrangement (more than one electrochemical two-cell apparatus) may be employed. The systemmay include an electrochemical cell stack having multiple dual-cells (multiple electrochemical two-cell apparatuses) operationally in parallel.

Operating conditions for the electrochemical two-cell apparatus as a dual-cell arrangement (two-cell setup) may include an operating pressure at less than 2 bar gauge (barg). The operating temperature may be, for example, in the range of 500° C. and 950° C. (or 700° C. to 900° C.) for the high-temperature regime. The operating temperature may be, for example, in the range of 25° C. to 200° C. for the low-temperature regime associated with the second cell.

In operation, COis fed via a supply conduit to the cathode cavityof the first electrochemical cell. In certain embodiments, the COstream fed to the cathode cavitymay be primarily CO, such as greater than 50 volume percent (vol %) CO, greater than 80 vol % CO, or greater than 90 wt % CO. The housinghas an inlet to receive the COinto the cathode cavityadjacent the cathodeand catalyst. The inlets and outlets of the electrochemical two-cell apparatus including for the cathode cavities,and anode cavities,may be formed through the housing.

In operation, the COis electrochemically reduced at the cathodeinto CO via the electrons provided from the power source. The COflows from the first cathode cavityto the second cathode cavity. In the reduction of the COinto CO at the cathode, Oions are generated and diffuse (conduct, migrate, transmit) through the electrolyteto the anode. The reaction or half reaction that takes place at the cathodein the cathode cavitymay be CO+2e→CO+O. This reaction or half reaction (electrochemical reduction) is endothermic.

With respect to the Oions that diffuse from the cathodethrough the electrolyteto the anode, the half reaction that takes place at the anodeside is 2O→O+4e. This reaction is generally exothermic. The anodedischarges electrons to the power source. The oxygen (O) gasat the anodeside that forms in the anode cavitymay discharge through an outlet of the anode cavityinto a discharge conduit. The Ogas can be utilized for different applications. In implementations, a displacement gas (e.g., air) may be provided via a supply conduit through an inlet to the anode cavityto displace the Ogas.

As mentioned, the COgenerated via the electrochemical reduction of the COon the cathodeside of the first cellflows to the cathode cavityof the second cell. On the cathodeside of the second cell, the COis dimerized and the resulting CO dimer is hydrogenated into ethanol or ethylene, or both. Half reactions that may take place at the cathodeinclude 2CO+8H+8eHOH+Hand/or 2CO+8H+8e→CH+2HO. The “2CO” notation in these two reactions is the CO dimer. These two half reactions generate water (HO) in addition to the desired ethanol (CHOH) or ethylene (CH).

To provide Hions for the hydrogenation, a streamis fed via a supply conduit through an inlet of the anode cavityinto the anode cavity. The streammay be or include hydrogen (H) gas or water (HO), or both. Thus, the streammay be or include at least one of Hor HO.

For the streambeing or including hydrogen (H) gas, Hions are generated at the anode, for example, per the half reaction 4H→8H+8e. This half reaction could be expressed as H→2H+2ebut the general balance of the system is with respect to 8 electrons. The electrons flow to the power source. The Hions diffuse from the anodethrough the electrolyteto the cathodefor the hydrogenation in the second cell.

For the streambeing or including water (HO) fed to the anode cavityand utilized on the anodeas a source of Hions, Hions may be generated, for example, per the reaction 4HO→2O+8H+8e. This half reaction could be expressed as 2HO→O+4H+4ebut the general balance of the system is with respect to 8 electrons. The streammay include HO in addition to or in lieu of H.

As indicated, Cu(100) may be utilized as the catalystin the reduction of COto OCCO* formed by CO dimerization and followed by hydrogenation into ethanol or ethylene. The first step of forming OCCO* by CO dimerization is generally a more favorable pathway than the further hydrogenation of CO. This explains why only two-carbon (C2) species and generally not single carbon (C1) species are observed experimentally on Cu(100). For the formation of C2H4 or EtOH on Cu(100), the hydrogenation of OCCO* to the OCCHO* intermediate is the most likely reaction path, followed by the formation of intermediate OHCCHO* through further hydrogenation of the OCCHO* intermediate. The formation of OCCO* may be the rate-determining step in the reduction mechanism of the CO dimer.

The productdischarges through an outlet from the cathode cavityof the second electrochemical cellinto a discharge conduit. The productmay include ethanol or ethylene, or both. The productmay also include generated HO, unreacted CO, and unreacted CO. There may be unreacted Hin the product. The target may be electrochemical hydrogenation via the Hions. Yet, the Hions could form Hin the cathode cavityfor the hydrogenation. The productdischarged may be further processed. The motive force for discharge of the productfrom the second cathode cavitymay be the incoming supply pressure of the COfed to the first cathode cavity. The supply pressure of the COmay be by an upstream mechanical compressor or by a COsupply header pressure, and the like.

A control valvemay be disposed along the supply conduit conveying the COto the first cellto modulate (adjust and maintain at set point) the flow rate of the COinto the cathode cavityof the first cell. The control valvemay instead be disposed on the discharge conduit conveying the productdischarged from the cathode cavityof the second cell. The amount of COfed to the cathode cavitymay depend, for example, on the specified production rate of the product, which can be affected by the electrochemical two-cell apparatuscapacity and other factors. The control valvemay be a flow control valve that controls mass rate (mass per time) or volumetric rate (volume per time) of the COstream. The control valvemay be a pressure control valve that controls pressure by modulating (adjusting, altering) the flow rate of the COstream or the productstream. For example, pressure may be controlled upstream or downstream of the control valve. In one example, the control valveis disposed along the discharge conduit conveying the productand acts as a backpressure regulator to control pressure in the cathode cavities,. In other examples, an upstream mechanical compressor controls the flow rate of the COstream.

As for supply of the streamas H, the amount (rate) of Hfed to the anode cavityof the second cellmay be set or modulated (adjusted and maintained) to generate a specified amount (rate) of Hions to migrate to the cathode. The amount (flow rate) of Hmay be modulated by a control valve (not shown) disposed on the supply conduit conveying the Hor modulated (adjusted, altered, maintained) by an upstream Hmechanical compressor, and the like. Similarly, for implementations in which HO is fed as the stream, the amount (rate) of HO fed to the anode cavityof the second cellmay be set or modulated (adjusted and maintained) to generate a specified amount (rate) of Hions to migrate to the cathode. The amount (flow rate) of supplied HO may be modulated by a control valve (not shown) disposed on the supply conduit conveying the water or modulated by an upstream HO supply pump (e.g., by controlling the speed and/or length of strokes of the pump) or steam mechanical compressor, and the like.

An adequate number of Hions are generated at the anodefor the hydrogenation on the cathodeside. This migration of the Hions from anodeto the cathodemay be affected by the anodematerial, proton conductivity of the electrolyte, and the electrochemical dual-cell operating conditions, such as temperature and applied electric potential by the power source.

The systemmay include a control systemhaving a processor and memory storing code (e.g., instructions, logic, etc.) executed by the processor. The control systemmay be or include one or more controllers. The control systemmay direct operation of the system. In certain implementations, the control systemor controller regulates the amount of electric current provided to the cathodes,from the power source,. The control system, via calculation or user-input, may direct and specify the set point of the control valveand also the control valve on the H(or water) supply.

The processor may be one or more processors and each processor may have one or more cores. The hardware processor(s) may include a microprocessor, a central processing unit (CPU), a graphic processing unit (GPU), a controller card, or other circuitry. The memory may include volatile memory (for example, cache and random access memory (RAM)), nonvolatile memory (for example, hard drive, solid-state drive, and read-only memory (ROM)), and firmware. The control systemmay include a desktop computer, laptop computer, computer server, programmable logic controller (PLC), distributed computing system (DSC), controllers, actuators, or control cards. In operation, the control systemmay facilitate processes of the systemincluding to direct operation of the electrochemical two-cell system. The control systemmay receive user input or computer input that specifies the set points of control components in the system. The control systemmay determine, calculate, and specify the set point of control devices. The determination can be based at least in part on the operating conditions of the systemincluding feedback information from sensors and transmitters, and the like.

As can be appreciated, derivation of beneficial or applicable operating conditions (including optimization of operating conditions) can be implemented. Operating conditions can include temperature, pressure, oxygen-to-ethylene ratio, and flow rates, and so forth. In implementations, the oxygen in the oxygen-to-ethylene ratio may include the oxygen ions controlled electrochemically to meet the reaction requirements in the first electrochemical cell. The operating conditions may be adjusted to favor production of ethanol or ethylene. Such may include changing the reaction parameters, including the reactant ratios and partial pressures. To force the reaction toward a specific direction (to give ethanol or ethylene) may involve a combination of at least three factors: optimized parameters, catalysis, and electrochemical effect. The dominant influence may be electrochemically because the different intermediate species required specific activation energy and a goal can be to stabilize the ethoxy intermediate. To force the reaction into one direction (ethanol or ethylene) can involve applied electric-potential numerical ranges with a combination of decided parameters.

In implementation, two CO molecules may go through dimerization to form active OCCO*. The following electrochemical hydrogenation steps may produce CHCHO, which upon further electrochemical hydrogenation may take the two following possible reaction paths:

The selection of either of the two paths may be determined electrochemically by controlling the potential, in addition to other parameters such as the catalyst type and cut shape. Surface structure may control the coverage of CO, leading to the reduction of CO dimer to Cproducts (ethylene and ethanol) at a voltage range, for example of 0.4V-1.3V versus reversible hydrogen electrode (RHE) as reference electrode. Ethanol may present a plateau peak, for example at potential range [1.0V-1.2V] vs. RHE, while ethylene may present a plateau peak at slightly lower potential (e.g., [0.8V-1.0V]) vs. RHE. This can be changed if the electrocatalyst surface structure and/or composition are changed.

Lastly, the nomenclature of the systemmay be expressed as follows. The systemincludes the electrochemical two-cell apparatus, supply conduits, discharge conduits, control valve(s), the control system, and so on. The electrochemical two-cell apparatusmay be characterized as a two-cell setup or a dual cell arrangement. The electrochemical two-cell apparatusincludes the first electrochemical celland the second electrochemical cell. The first electrochemical cellincludes the first cathode cavity, the first cathode, the first anode, the first anode cavity, the first electrolytedisposed between the first cathodeand the first anode, the first catalystdisposed along the first cathode, and so forth. The second electrochemical cellincludes the second cathode cavity, the second cathode, the second anode, the second anode cavity, the second electrolyte(e.g., proton conductor) disposed between the second cathodeand the second anode, the second catalystdisposed along the second cathode, and the like.