Patent Grant
12365995
The present technology generally relates to CO2 electroreduction into multi-carbon products, and more particularly to a system and related process involving controlled CO2 reduction reactions (CO2RR) and organic oxidation reactions (OOR) to facilitate the capture of crossover CO2.
The electrochemical conversion of CO2 (CO2RR) to multi-carbon (C2+) chemicals is a promising approach to storing renewable energy and closing the carbon cycle, see the study of Verma S., et al., entitled “Co-electrolysis of CO2 and glycerol as a pathway to carbon chemicals with improved technoeconomics due to low electricity consumption” (Nat. Energy, 2019, 4, 466-474). State-of-art CO2RR flow cell systems-see the study of Garcia de Arquer, F. P., et al., entitled “CO2 electrolysis to multicarbon products at activities greater than 1 A cm−2” (Science, 2020, 367, 661-666)—, and zero-gap membrane electrode assembly (MEA) systems-see studies of Gabardo C. M., et al., entitled “Continuous Carbon Dioxide Electroreduction to Concentrated Multi-carbon Products Using a Membrane Electrode Assembly” (Joule, 2019, 3, 2777-2791), of Li F., et al., entitled “Molecular tuning of CO2-to-ethylene conversion” (Nature, 2020, 577, 509-513) and of Ozden A., et al., entitled “High-rate and efficient ethylene electrosynthesis using a catalyst/promoter/transport layer” (ACS Energy Lett., 2020, 5, 2811-2818)-achieve C2+ Faradaic efficiencies (FEs) exceeding 70% and C2+ partial current densities of 1 A cm−2 (flow cells) and 100 mA cm−2 (MEAs). These productivity levels are in the regime of interest on the path toward industrial application.
Industrial CO2 streams with 98%+ purity are being used for the electro-conversion of CO2, generated through selective capture of CO2 from anthropogenic or nature point sources. Significantly high cost and low energy efficiency associated with industrial CO2 capture negatively affect the techno-economic feasibility of CO2 electrolysis when a pure stream of CO2 is used as feed to the electrolyser. Additionally, the energy required for present-day CO2-to-C2+ electrolysis is too high—for example, when targeting ethylene, known electrosynthesis systems require 8× more energy to produce ethylene than is embodied in the product. Major energy costs are incurred in the electrolyser and the downstream separation steps. Established approaches to reducing the electrolysis energy requirements include increasing the selectivity for the target product and incorporating alternative anode reactions.
The major energy penalty associated with the downstream separation of CO2 remains a challenge. Downstream separation is required to isolate products and recover unconverted CO2 from the product streams and electrolytes. Recovering CO2 is particularly costly, requiring 25% and 70% of total energy input for neutral and alkaline media CO2-to-C2+ electrolysers, respectively.
Current CO2RR catalysts operate with highly alkaline local conditions (pH>12) to promote C2+ generation at the cathode, see the study of Garcia de Arquer, F. P., et al., entitled “CO2 electrolysis to multicarbon products at activities greater than 1 A cm−2” (Science, 2020, 367, 661-666). However, the carbonate-forming side reaction (CO2+OH−→CO32− or HCO3−) is favoured under alkaline conditions, consuming the majority of the CO2 injected by forming (bi)carbonates. Operating with neutral electrolytes (e.g., KHCO3) in a membrane electrode assembly cell can mitigate CO2 loss to (bi) carbonates. However, ˜ 70% of input CO2 crosses the anion exchange membrane (AEM) to the anode as (bi) carbonate ions, which combine with the protons generated from the anodic reaction to regenerate CO2 back (see
DE 10 2020 207 192 concerns a carbon dioxide reduction reaction/organic oxidation reaction (CO2RR/OOR) system, in which CO2 is reduced in a cathode compartment into CO, while acetic acid is oxidized into peroxyacetic acid in an anodic compartment. The cathode and the anode in the electrolytic system are separated by an anion exchange membrane (AEM). A catholyte is circulated through the cathode chamber and has a pH of about 10.5 to 11.5.
WO2014/046794 concerns a method wherein CO2 forms a CO2RR product at the cathode of an electrolytic system and wherein, simultaneously, an organic compound is oxidized into CO2 at the anode, the CO2 formed at the anode being included in the CO2 feed required at the cathode along with a catholyte.
There is thus a need for a technology that overcomes at least some of the drawbacks of what is known in the field, such as the above-mentioned drawbacks that may result. In particular, there is a need to provide a process and system to convert CO2 into multi-carbon products while optimizing the use of CO2 from the CO2 feedstream, such as minimizing CO2 loss.
In its first aspect, the present disclosure relates to a process for electrochemically converting a gaseous carbon dioxide stream to multi-carbon products having at least two carbon atoms in a carbon dioxide reduction reaction/organic oxidation reaction (CO2RR/OOR), the process is remarkable in that it comprises:
According to a second aspect, the present disclosure relates to a carbon dioxide reduction reaction/organic oxidation reaction (CO2RR/OOR) system to perform the process according to the first aspect, the system is remarkable in that it comprises:
With preference, the present disclosure relates to a carbon dioxide reduction reaction/organic oxidation reaction (CO2RR/OOR) system to perform the process according to the first aspect, the system is remarkable in that it comprises:
Particularly, the present disclosure relates to a CO2RR/OOR system utilizing a stream of CO2 (as only/major/minor component) as a feedstream to the cathode to produce a stream of pure CO2 at the anode outlet while electrochemically converting a portion of cathode-fed gaseous carbon dioxide (CO2) stream to multi-carbon products (C2+) being CO2RR products.
Surprisingly, the system and process of the present disclosure optimizes the CO2 utilization, by recovering it at the anodic compartment. There is for provide a CO2RR/OOR MEA electrolyser which allows the anodic reaction to being all liquid in nature—i.e., to avoid any O2 evolution from CO2-to avoid contamination of the anodic product stream (including CO2) with Oz. A CO2 stream of high purity (>99%), and referred to as a pure CO2 stream, can then be recovered by gas-liquid separation of the anodic product stream and can further be directly recycled to the cathodic to yield multi-carbon products (such as ethylene) as part of a cathodic product stream. Controlling the anodic reaction allows achieving higher CO2 utilization than the conventional 25% CO2 utilization threshold, to avoid an energy consumption penalty associated with supplemental anodic gas separation, without incurring penalties to a full-cell voltage or a selectivity to ethylene.
Advantageously, the organic oxidation reaction catalyst of the anode comprises carbon and a metal selected from platinum, nickel, iron, cobalt, palladium or lead.
For example, the CO2 concentration of the gaseous CO2-containing stream at the cathode is between 1 vol. % and 100 vol. % based on the total volume of said gaseous CO2 feedstream, or between 5 vol. % and 95 vol. %, or between 10 vol. % and 90 vol. %.
The electrolyser for electrochemically converting a gaseous carbon dioxide stream to multi-carbon products having at least two carbon atoms is catholyte-free. For example, the electrolyser for electrochemically converting a gaseous carbon dioxide stream to multi-carbon products having at least two carbon atoms is an anolyte-containing one-gap electrolyser. For example, the electrolyser for electrochemically converting a gaseous carbon dioxide stream to multi-carbon products having at least two carbon atoms is a zero-gap electrolyser, such as a membrane electrode assembly (MEA) electrolyser.
Particularly, the organic oxidation reaction catalyst can be a glucose oxidation reaction catalyst. Such oxidation reaction leads to liquid products, namely gluconate, glucuronate, glucarate or a mixture thereof. This favours therefore the implementation of the gas-liquid separation unit in a way to further optimize the recovery of the gaseous CO2. For example, the organic oxidation reaction (OOR) catalyst of the anode can include carbon and a metal selected from platinum, nickel, iron, cobalt, palladium or lead. For example, the OOR catalyst of the anode can include carbon and platinum. Optionally, the organic oxidation reaction catalyst of the anode can have a catalyst loading between 0.1 mg/cm2 and 10 mg/cm2, between 0.1 mg/cm2 and 4.0 mg/cm2, or between 0.3 mg/cm2 and 2.0 mg/cm2. For example, the anode can have a carbon loading between 0.5 mg/cm2 and 60 mg/cm2, or between 1 mg/cm2 and 50 mg/cm−2.
The anode can also include a hydrophilic porous support. For example, the hydrophilic porous support is a carbon fibre cloth substrate or a PTFE non-woven cloth pre-sputtered by metal. Optionally, the anode can further include an ionomer layer. For example, the ionomer of the ionomer layer can be a perfluorinated sulfonic acid ionomer such as a perfluorosulfonic acid (PFSA) ionomer.
For example, the CO2 reduction reaction catalyst of the cathode can be or include a transition metal selected from copper, silver, gold, tin, cobalt, zinc and their alloys. Optionally, the CO2 reduction reaction catalyst of the cathode can have a catalyst loading between 0.1 mg/cm−2 and 6.0 mg/cm2; between 0.5 mg/cm2 and 3.0 mg/cm2, or between 1.0 mg/cm2 and 2.0 mg/cm−2.
The cathode can further include a hydrophobic porous support. For example, the hydrophobic porous support is a polytetrafluoroethylene (PTFE) support. Optionally, the cathode can further include an ionomer layer. For example, the ionomer of said ionomer layer can be a perfluorinated sulfonic acid ionomer such as a perfluorosulfonic acid (PFSA), poly(aryl piperidinium) or polystyrene methyl methylimidazolium chloride ionomer.
Advantageously, the anodic compartment comprises a solution including an anolyte and an organic liquid-phase precursor of the organic oxidation reaction. For example, the anolyte can be selected from KHCO3, K2CO3, NaHCO3, Na2CO3, and any mixture thereof. With preference, the anolyte is or comprises KHCO3.
For example, the organic liquid-phase precursor can be or comprise one or more selected from glucose, glycerol, furfural, 5-hydroxymethylfurfural, starch, cellulose, lignin, alcohols (such as ethanol, n-propanol, iso-propanol, methanol or benzyl alcohol), and any combinations thereof. For example, the organic liquid-phase precursor is or comprises one or more selected from glucose, glycerol, furfural, 5-hydroxymethylfurfural, ethanol, n-propanol, iso-propanol, methanol, benzyl alcohol, starch, cellulose, lignin and any mixtures thereof. With preference, the liquid-phase precursor is or comprises glucose.
For example, the organic liquid-phase precursor of an organic oxidation reaction is a liquid-phase precursor of a glucose oxidation reaction.
For example, the organic liquid-phase precursor of the organic oxidation reaction has an active organic concentration ranging between 0.01 M and 1.5 M. For example, the active organic concentration is ranging between 0.1 M and 1.5 M in the solution; preferably between 0.2 M and 1.2 M; or between 0.5 M and 1.0 M; or between 0.5 M and 1.5 M.
Advantageously, the solution comprising the anolyte and the organic liquid-phase precursor can have a bulk pH between 4 and 9.
In some implementations, the ionic exchange membrane can be an anionic exchange membrane. With preference, said anionic exchange membrane comprises poly(aryl piperidinium) polymer.
The CO2RR/OOR system is a catholyte-free system. For example, the system can be an anolyte-containing one-gap electrolyser. In another example, the system can be a membrane electrode assembly electrolyser.
In some implementations, the CO2RR/OOR system can further include a recycle line in fluid communication with the gas-liquid separation unit to redirect the pure gaseous CO2 stream to the cathodic compartment as a portion of the gaseous CO2-containing stream.
For example, the process can be carried out at a temperature ranging between 30° C. and 50° C., or between 40° C. and 50° C.
For example, the gaseous CO2 stream can be a by-product CO2 stream produced from an industrial upstream process; with preference, from the fermentation of glucose to ethanol. In some implementations of the process, the CO2 concentration of the gaseous CO2-containing stream at the cathode can be between 1 vol. % and 100 vol. % based on the total volume of said gaseous CO2 feedstream, or between 5 vol. % and 95 vol. %, or between 10 vol. % and 90 vol. %.
For example, the anodic product stream further comprises one or more liquid products. The OOR liquid-phase products can include gluconate, glucuronate, glucarate, formate, tartarate, tratronate, or a mixture thereof.
In some implementations of the process, redirecting the recovered pure gaseous CO2 stream to the cathodic compartment as a portion of the gaseous CO2-containing stream can be performed to maximize CO2 utilization.
In some other implementations of the process, redirecting the recovered pure gaseous CO2 stream as a feedstream to another electrolyser can be performed, with the other electrolyser being a solid oxide electrolyser cell, a membrane electrode assembly electrolyser, an alkaline flow cell or any combination thereof.
It should be noted that all implementations herein with respect to the CO2RR-OOR system can be applied/combined with any implementations described in relation to the process.
For example, the multi-carbon products are or comprise ethylene.
While the disclosure will be described in conjunction with example embodiments and implementations, it will be understood that it is not intended to limit the scope of the disclosure to such embodiments or implementations. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the present description. The objects, advantages and other features of the present disclosure will become more apparent and be better understood upon reading the following non-restrictive description of the disclosure, given with reference to the accompanying drawings.
Implementations of the CO2RR-OOR system and related process are represented in and will be further understood in connection with the following figures.
For the disclosure, the following definitions are given:
As used herein, the term “C#hydrocarbons”, wherein “#” is a positive integer, is meant to describe all hydrocarbons having #carbon atoms. C#hydrocarbons are sometimes indicated as just C#. Moreover, the term “C#+ hydrocarbons” is meant to describe all hydrocarbon molecules having #or more carbon atoms. Accordingly, the expression “C2+ hydrocarbons” is meant to describe a mixture of hydrocarbons having 2 or more carbon atoms.
The term “transition metal” refers to an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell (IUPAC definition). According to this definition, the transition metals are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn. The metals Ga, In, Sn, TI, Pb and Bi are considered as “post-transition” metal.
The yield to particular chemical compounds is determined as the mathematical product between the selectivity to said particular chemical compounds and the conversion rate of the chemical reaction. The mathematical product is expressed as a percentage.
The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms “comprising”, “comprises” and “comprised of” also include the term “consisting of”.
The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g., 1 to 5 can include 1, 2, 3, 4, 5 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.
The particular features, structures, characteristics or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.
Electrochemical reduction of CO2 to multi-carbon products (C2+), when powered using renewable electricity, offers a route to valuable chemicals and fuels. In conventional zero-gap, neutral-media CO2-to-C2+ devices, over 70% of input CO2 crosses the cell to the anodic side where CO2 is mixed with produced oxygen at the anode to form a gaseous product mixture. This amount of CO2 that migrates to the anodic side can be referred to as the crossover CO2. Recovering CO2 from the formed gaseous product mixture (which contains CO2 and oxygen) incurs a significant energy penalty.
There is thus proposed herein a liquid-to-liquid anodic system and related processes that can be implemented to facilitate the capture of crossover CO2 without additional energy input. The techniques encompassed herein can be used to achieve a high carbon efficiency while being compatible with highly-performing CO2 reduction reaction catalysts and electrolysers that are already developed to work optimally in neutral and alkaline electrolytes. For example, the performance of the proposed system can be characterized by a low full-cell voltage of about 1.9 V and a total carbon efficiency of about 48%, for achieving production of about 259 GJ/tonne ethylene, with a 30% reduction in energy intensity compared to state-of-art CO2-to-C2+ systems.
More particularly, it is proposed herein to pair a CO2 reduction reaction (CO2RR) with an all-liquid anodic reaction (e.g., organic oxidation reaction (OOR)) in a neutral electrolyte to achieve high carbon efficiency and low energy input in the electrosynthesis of renewable chemicals and fuels. The present techniques enable recovery of the crossover CO2 as a stream of pure gaseous CO2 which can be used in various ways including (1) being stored, (2) being recycled to the cathode for utilization in the CO2RR-OOR electrolyser or (3) being fed into any other electrolyser for the production of CO, C1 products, C2+ products, or any combinations thereof. Examples of combinations of electrolysers are described further below with reference to
Referring to
For example, the CO2RR-OOR electrolyser can be a zero-gap CO2RR-OOR electrolyser or a one-gap CO2RR-OOR electrolyser (flow cell).
Experimentation in operating the proposed CO2RR-OOR electrolyser and related system implementations demonstrated a high carbon efficiency by returning the recovered crossover CO2 to the cathodic gaseous CO2-containing stream, thereby achieving a high CO2 conversion of up to 75%. It was further shown that the proposed CO2RR-OOR electrolyser can achieve a low full-cell potential of 1.90 V at a current density of 100 mA cm−2 and stable electrosynthesis of C2+ products for over 80 hours while maintaining a high CO2 conversion of 45%. Accounting for the total electricity and downstream separation energy costs, the present techniques achieve a total energy intensity of 259 GJ per ton of ethylene produced, approximately 30% lower than that of known CO2RR electrolysers.
Process and System Design to Facilitate Recovery of Crossover CO2
The techniques described herein facilitate direct recovery of pure CO2 from the anodic product mixture that is generated from a neutral/alkaline electrolyte media and can apply to a CO2RR-OOR electrolyser including a cathodic compartment comprising a cathode supporting CO2 reduction reactions, an anodic compartment comprising an anode supporting organic oxidation reactions in a neutral/alkaline media containing an organic liquid-phase precursor, and an anionic exchange membrane (AEM) ensuring anionic exchange between the two compartments.
For example, the present system can be a zero-gap CO2RR-OOR MEA electrolyser. Referring to
Other examples of near-neutral anolyte are anolytes selected from K2CO3, NaHCO3, Na2CO3 and any mixture thereof.
CO2RR products refer herein to multi-carbon products having at least 2 carbon atoms. CO2RR products for example include ethylene.
The AEM separates the cathode and the anode and further provides highly alkaline conditions favourable for CO2RR. Referring to
The process can include separating the anodic product mixture into a pure gaseous CO2 stream (purity >99%) and a CO2-depleted liquid stream (that can be recycled as liquid anolyte remainder). Referring to
All-Liquid-Phase Anodic Process
The present techniques allow all-liquid-phase anodic reactions that produce protons (or consume hydroxides) and operate in near-neutral media. Candidate anode reactions include water-to-hydrogen peroxide, chloride-to-hypochlorite, and a wide range of organic oxidation reactions (OORs). However, known catalysts for hydrogen peroxide and hypochlorite production can result in gaseous by-products.
Coupling electrochemical CO reduction with OOR has been demonstrated in an MEA electrolyser. However, prior systems that employed OOR as an anodic reaction did not focus on overall carbon efficiency: recent gas-CO2-fed CO2RR-OOR systems operated in strong alkaline electrolytes (pH>14), causing a severe energy penalty associated with the regeneration of (bi) carbonate back to alkaline and CO2.
The process thus includes controlling the anodic reaction to favour OORs at the anode at a neutral/alkaline pH. A neutral/alkaline anolyte/electrolyte/media refers herein to an anolyte/electrolyte/media having a neutral/alkaline pH, i.e., a pH between 4 and 9, optionally between 4 and 8, and further optionally between 4.5 and 7.5. The OORs that are encompassed herein include the oxidation of glucose, glycerol, furfural, 5-hydroxymethylfurfural, starch, cellulose, lignin, and alcohols.
In some implementations, controlling the anodic reaction can include favouring a glucose oxidation reaction (GOR) in a neutral/alkaline anolyte. Coupling the CO2RR with GOR is demonstrated herein as a suitable liquid-phase anodic process strategy for high-carbon efficiency and low-energy intensity in CO2-to-C2+ conversion. Favouring the GOR includes providing glucose as a liquid precursor in the anolyte.
Glucose is abundant in biomass, with an average market price of $400-500 ton-1, mainly produced from starch. In 2017, over 5 million tons of glucose were produced in the United States. Electrochemical oxidation of glucose mainly produces gluconate, glucuronate, and glucarate (
The GOR that is selected herein avoids gaseous products, thereby facilitating the recovery of pure gaseous CO2 from the anodic product mixture via direct gas-liquid separation. The selected GOR can outcompete the oxygen evolution reaction (OER) at industrially relevant reaction rates in electrolytes having a pH between 4 and 9, between 4 and 8, or between 4.5 and 7.5. The selected GOR also offers electrolysis energy savings, with a thermodynamic potential of 0.05 V, significantly lower than that of the OER (1.23 V). A large supply of each reactant, CO2 and glucose, is available and co-located in industrial bioethanol plants. In these operations, glucose ferments to ethanol and CO2 is emitted. A 2012 report estimated that 14.8 tons of CO2 is emitted in producing 1 ton of bioethanol. The CO2RR-GOR electrolyser can convert waste CO2 and available glucose to chemicals, providing additional product streams and reducing the overall/net carbon footprint of bioethanol production if it used low-carbon electricity.
Catalyst Characterization
The cathodic compartment of the system includes a cathode that catalyzes the CO2RR. The cathode comprises a catalyst that can be referred to as a CO2RR catalyst. The CO2RR catalyst comprises one or more transition metals, for example, Cu, Ag, Pb, Co, Sn, Zn, and alloys thereof, and/or any combinations thereof. The CO2RR catalyst comprises one or more transition metals in addition to copper, for example, Ag, Pb, Co, Sn, Zn, and alloys thereof, and/or any combinations thereof. For example, the CO2RR catalyst can comprise one or more phthalocyanines of said one or more transition metals. In some implementations, the cathode is a gas diffusion electrode (GDE) that includes hydrophobic porous support. For example, the hydrophobic porous support can comprise polytetrafluoroethylene (PTFE) and/or hydrophobic carbon paper.
Optionally, the cathode can further include an ionomer layer that comprises a perfluorinated sulfonic acid ionomer. The ionomer layer is co-sprayed with catalyst nanoparticles (e.g., copper nanoparticles).
For example, the perfluorinated sulfonic acid ionomer can be Fumion®, Sustainion®, Aquivion®, Pention, or PiperION. For example, the perfluorinated sulfonic acid ionomer can include perfluorosulfonic acid (PFSA), sulfonated tetrafluoroethylene based fluoropolymer-copolymer (such as Nafion® or 1,1,2,2-Tetrafluoroethene; 1,1,2,2-tetrafluoro-2-[1,1,1,2,3,3-hexafluoro-3-(1,2,2-trifluoroethenoxy) propan-2-yl]oxyethanesulfonic acid), SSC, Aciplex, Flemion, 3M-perfluorinated sulfonic acid ionomer, Aquivion, an ionene, or a combination thereof.
In some implementations, the cathode can be produced by depositing copper nanoparticles and a perfluorosulfonic acid (PFSA) ionomer on a hydrophobic porous polytetrafluoroethylene (PTFE) support, thereby being referred to as a PTFE gas diffusion electrode. Optionally, the production of the cathode can include pre-sputtering a layer of copper to improve the electrical conductivity thereof. For example, experimental results provided further below include experiments with a cathode being prepared by steps including pre-sputtering a 200 nm-thick polycrystalline Cu layer to improve electrical conductivity (see Experimental Results for details). Referring to the scanning and transmission electron microscopy (SEM and TEM, respectively) of
The anodic compartment of the system includes an anode that comprises a catalyst that can be referred to as an anodic catalyst. For example, the anodic catalyst can include Pt, IrO2, Pd, Au, Ni3P, Ni—Fe alloys or any combinations thereof. In some implementations, the anode can further include a hydrophilic and porous support. For example, the hydrophilic and porous support can include, without being limited to, a hydrophilic and highly porous carbon fiber cloth substrate, Ti felt, Ni mesh, Cu mesh, or any combination thereof. In some implementations, the anode can further include an ionomer provided as a layer or film to bond the catalyst particles. For example, the anode can be prepared in accordance with the details provided in the Experimental Results section, to comprise a homogeneous blend of Pt/C nanoparticles and PFSA ionomer on a hydrophilic and highly porous carbon fibre cloth substrate. As seen in the SEM image of
In some implementations, the cathode can be prepared by depositing copper nanoparticles and a perfluorosulfonic acid (PFSA) ionomer on a hydrophobic porous carbon paper.
In some implementations, the anode can be prepared by depositing metal nanoparticles onto above-mentioned hydrophilic and highly porous substrates via electrochemical deposition or solvent-thermal deposition.
On Engineering Cathode and Anode to Facilitate Ethylene Faradaic Efficiency (FE) and Reduce/Prevent Oxygen FE Simultaneously
In some implementations, controlling the anodic reaction can include favouring the OOR by selecting the organic liquid-phase precursor of the anolyte in the group consisting of glucose, glycerol, furfural, 5-hydroxymethylfurfural, alcohols, starch, cellulose lignin, and any mixtures thereof. The alcohols can include ethanol, n-propanol, iso-propanol, methanol or benzyl alcohol, or any mixtures thereof. For example, the liquid precursor of the anolyte can be glucose and controlling the anodic reaction includes favouring a glucose oxidation reaction (GOR). Optionally, the anodic reaction can be further controlled by adjusting an active organic concentration of glucose in the anolyte.
The present techniques allow maintaining a low OER FE to facilitate/maximize GOR FE, and thereby achieving recovery of an anodic gaseous stream being substantially pure CO2. In the present CO2RR-GOR system, the cathodic and anodic catalysts can be tailored to the CO2 recovery strategy.
In some implementations, controlling the anodic reaction to avoid production of gaseous O2 from the crossover CO2 can include at least one of adjusting a catalyst loading of the anode, and adjusting a catalyst loading of the cathode. For example, favouring OOR instead of OER at the anode can include balancing a catalyst loading between the anode and the cathode. For example, the catalyst loading can be a metal loading of the electrode.
In some implementations, controlling the anodic reaction to avoid O2 production by OER can include adjusting the catalyst loading of the anode. For example, the catalyst loading of the anode can be adjusted between 0.1 mg/cm2 and 10 mg/cm2, preferably between 0.2 mg/cm2 and 9.5 mg/cm2, more preferably between 0.4 mg/cm2 and 9 mg/cm2, or between 0.5 mg/cm2 and 5 mg/cm2. The catalyst loading thus depends on the surface area of the anode catalyst. The catalyst loading of the cathode can amount to a range between 20% and 30% of the catalyst loading of the anode, optionally between 22% and 28%. For example, the catalyst loading of the cathode can amount to 25% of the catalyst loading at the anode.
Referring to graphs of
Referring to the graphs of
Known catalysts have typical mass loadings that include a cathode Cu loading and an anode Pt loading of 1 mg cm−2 and 0.5 mg cm−2, respectively. Referring to the graph of
The techniques described herein include adjusting a catalyst mass loading on at least one of the cathode and anode to maximize CO2RR product selectivity and minimize anodic OER selectivity simultaneously. Consequently, upon separation of the anodic product mixture, an anodic gaseous stream can be directly recovered with a high purity of >99% in CO2.
Controlling the anodic reaction to avoid O2 production by OER can include adjusting the catalyst loading of the anode. For example, referring to
Controlling the anodic reaction to avoid O2 production by OER can further include adjusting the catalyst loading of the cathode. Still referring to
The anode can further have a carbon loading with the carbon serving as a conductor and/or substrate for the metal catalyst, such as Pt. For example, the carbon loading of the anode can be further adjusted between 0.5 mg/cm2 and 60 mg/cm2, preferably between 1 mg/cm2 and 50 mg/cm2. For example, the anodic carbon to catalyst ratio can be ranging between 2 and 10, between 3 and 9, or between 4 and 8.
Recycling CO2
The present techniques facilitate the use of a dilute stream of CO2 as the gaseous CO2-containing stream being the CO2RR-OOR electrolyser feedstream, and recovering the crossover CO2 as a stream of pure CO2. The stream of pure CO2 can be further fed to an electrolyser to produce CO and/or other multi-carbon products (C2+). A combination of electrolysers can be referred to herein as an assembly of electrolysers.
Referring to the combination of electrolysers as shown in
Referring to the combination of electrolysers as shown in
Referring to the combination of electrolysers as shown in
Referring to
The present CO2 recycling strategy requires a high CO2 recovery rate (defined as the fraction of the recovered CO2 flow rate to the rate of CO2 crossover). Referring to the graph of
Suppressing CO2RR liquid products and subsequent crossover.
Ethylene production via CO2RR is accompanied by cathodic liquid-phase products such as ethanol, acetate and propanol, much of which can cross the AEM to join the anodic product mixture. Cathode-to-anode crossover of liquid products remains a challenge in CO2RR systems as this liquid products risk oxidation and dilution in the anolyte.
In some implementations, adjusting the temperature of the electrolyser can control, e.g. reduce, the crossover of cathodic liquid products. Increasing the temperature from 20° C. to 50° C., the FEs toward the major gas products of CO2RR (C2H4 and CO) were found to be increased from 48% to 56% at a constant current density of 100 mA cm−2 (see
It should be understood that any one of the above-mentioned implementations of the CO2RR-OOR system and related process may be combined with any other of the aspects thereof unless two aspects clearly cannot be combined due to their mutual exclusivity.
Materials
Potassium bicarbonate (KHCO3, 99.7%), D-glucose (99.5%), copper nanoparticles (25 nm), Nafion™ 1100W (5 wt. % in a mixture of lower aliphatic alcohols and water) and Pt/C (40 wt. % Pt on Vulcan XC72) were purchased from Sigma Aldrich and used as received. Aquivion D79-25BS ionomer was purchased from Fuel Cell Store. Piperion (40 μm) was used as the anion-exchange membrane, purchased from W7Energy and stored in 0.5M KOH. The water used in this study was 18 MO Milli-Q deionized-(DI-)water.
Electrodes
For the CO2RR, we prepared the gas diffusion electrodes (GDEs) by spray-depositing a catalyst ink dispersing 1 mg mL-1 of Cu nanoparticles and 0.25 mg mL-1 of Nafion™ 1100W in methanol onto a PTFE substrate that pre-sputtered with a 200 nm thick polycrystalline Cu layer. The Cu sputtering procedure was described in detail in the previous reports. The mass loading of Cu NPs on the GDE was tuned between 0.5 to 1.0 mg/cm2. The GDEs were dried in the air overnight prior to experiments.
For the GOR anode electrodes, a commercially available Pt/C was first physically mixed with an ionomer (Aquivion D79-25BS) in a glass beaker and then sonicated for 1 h. The resulting catalyst ink was then spray-coated on both sides of the hydrophilic carbon cloth until the Pt loading of 0.5 to 2.0 mg cm−2 was achieved.
Characterizations
Scanning Electron Microscopy
Scanning electron microscopy (SEM) images of the cathode and anode were captured by an FEI Quanta FEG 250 environmental SEM.
Transition Electron Microscopy
Transition electron microscopy (TEM) images and elemental mappings were acquired by an FEI Titan 80-300 kV TEM microscope.
X-Ray Photoelectron Spectra
X-ray photoelectron spectra (XPS) of the electrodes were determined by a model 5600, PerkinElmer using a monochromatic aluminum X-ray source.
1H Nuclear Magnetic Resonance
1H NMR spectra were determined by the Agilent DD2 500 spectrometer.
High-Performance Liquid Chromatography (HPCL)
The by-products of the GOR were measured by high-performance liquid chromatography (UltiMate 3000 HPLC) equipped with an Aminex HPX-87H column (Bio-Rad) and a reflective index detector. The eluent was 0.05 M H2SO4, and the column was kept at 60° C.
Assembling of the CO2RR-GOR System
The MEA set (5 cm−2) was purchased from Dioxide Materials. A cathode was cut into a 2.5 cm×2.5 cm piece and placed onto the MEA cathode plate with a flow window with a dimension of 2.23 cm×2.23 cm. The four edges of the cathode were sealed by copper tapes and then Kapton tapes, and make sure the tapes did not cover the flow window. A Piperion AEM (3 cm×3 cm) was carefully placed onto the cathode. A gasket with a 2.23 cm×2.23 cm window was placed on the cathode. The Pt/C loaded carbon cloth anode (2 cm×2 cm) was placed onto the AEM.
Electrochemical Measurements
The cathode side of the MEA was fed with CO2 flow (0.18 to 10 sccm per cm2 of electrode area, 10 sccm cm−2 if not specified) that comes from both CO2 feedstock and anodic gas stream. The anode side was circulated with a solution containing 1M KHCO3 and glucose with various active organic concentrations (0 to 2M) at 10 mL/min by a peristaltic pump. A gas-tight glass bottle with four in/out channels (gas inlet, gas outlet, liquid inlet and liquid outlet) was used as the anolyte reservoir and gas-liquid separator. In typical CO2RR-GOR performance evaluations, the gas inlet channel was sealed, and the gas outlet channel was connected to a ‘Y’ shape tubing connector.
Since the anolyte reservoir/gas-liquid separator is gas tight, the CO2 pressure between the feedstock stream and the anodic stream will eventually balance and promote a steady flow rate from both sides. The electrochemical measurements were performed with a potentiostat (Autolab PGSTAT204 with 10A booster). All the performance metrics were recorded after at least 1000 seconds of stabilization at a specific condition. The full-cell voltages reported in this work are not iR corrected.
Product Analysis
The CO2RR gas products, oxygen, and CO2 were analyzed by injecting the gas samples into a gas chromatograph (Perkin Elmer Clarus 590) coupled with a thermal conductivity detector (TCD) and a flame ionization detector (FID). The gas chromatograph was equipped with a Molecular Sieve 5A Capillary Column and a packed Carboxen-1000 Column with argon as the carrier gas. The volumetric gas flow rates in and out of the cell were measured with a bubble column. The FE of a gas product is calculated as follows:
Where xi is the volume fraction of the gas product i, V is the outlet gas flow rate in L s−1, P is atmosphere pressure 101.325 kPa, R is the ideal gas constant 8.314 J mol−1 K−1, T is the room temperature in K, n; is the number of electrons required to produce one molecule of product F is the Faraday Constant 96485 C mol−1, and J is the total current in A. To analyze the anodic gas stream component, the gas outlet channel of the anolyte reservoir was disconnected from the tubing for circulating to the cathode. A 20 sccm argon flow was input from the ‘gas inlet’ channel of the anolyte reservoir as the carrier gas to promote the accurate analysis of CO2 and O2 components in the anode gas.
The liquid products from the cathode side of the SC-MEA were collected using a cold trap cooled to 0° C. The collected liquid from the cathode side and the anolyte were quantified separately by the proton nuclear magnetic resonance spectroscopy (1H NMR) on an Agilent DD2 500 spectrometer in D20 using water suppression mode and dimethyl sulfoxide (DMSO) as the internal standard. Typical 1H NMR spectra can be found in
When run at 100 mA cm−2 and 50° C., the CO2RR-GOR system provides a full-cell voltage of 1.80±0.1 V, representing a 1.6 V lower voltage than the conventional CO2RR-OER system at the same current density and temperature. This low full-cell voltage can be attributed to the lower thermodynamic potential of GOR than OER (0.05 vs. 1.23 V) and the anodic catalyst's high activity toward GOR. Such a low full-cell potential significantly reduces electricity demand (Table 1). At 100 mA cm−2, the system delivers ethylene FEs of 42%, 48%, and 44% at 20° C., 35° C., and 50° C. (see
a All the data sets from references are the ones that consume the least overall energy for producing one ton of ethylene.
b Recorded with the CO2 carbon efficiency indicated in the same column above.
c Recorded with a CO2 carbon efficiency of 20%.
d Recorded with a CO2 carbon efficiency of 1.8%.
e The sum of the GOR product FEs obtained from NMR (FIG. 37) and HPLC
b Recorded with the CO2 carbon efficiency indicated in the same column above.
eThe sum of the GOR product FEs obtained from NMR (FIG. 37) and HPLC
In addition, the selectivity of the GOR was investigated for a wide range of current densities (from 80 mA cm−2 to 160 mA cm−2) and operating temperatures (see
With the temperature increasing from 20° C. to 50° C., we detected a slight increase in anolyte pH (from pH 7.9 to 8.3,
Carbon efficiency upper limits in the proposed CO2RR-OOR system were studied. A common approach to determine carbon efficiency upper limits is restricting the CO2 availability at the cathodic stream and measuring a ratio between [CO2 converted to products] and [total CO2 feeding].
Decreasing an input CO2 flow rate increases the carbon efficiency (see Table 6 and
At an inlet CO2 flow rate of 0.18 sccm cm−2 (flow rates are normalized by electrode area), the system delivered a total C2+ FE of ˜44% at a constant current density of 100 mA cm−2 and a full-cell voltage of 1.90 V, corresponding to a carbon efficiency of 75% toward all CO2RR products (total carbon efficiency, see
A trade-off between carbon efficiency and ethylene FE is typical of CO2-to-ethylene electrolysis (
Compared to state-of-art conventional CO2-to-ethylene systems (i.e., MEAs based on AEM and neutral electrolyte), the present CO2RR-GOR system eliminates the anodic separation energy (>57 GJ per ton ethylene, see
Stability with High Carbon Efficiency
Stability is a prerequisite for the industrial application of CO2RR. However, long-term operation of CO2RR with a high carbon efficiency (e.g., CO2 carbon efficiency >40%) has not been achieved to date. The best CO2 carbon efficiency achieved for a run duration of 100 hours was <4%.
Extended CO2RR operation was performed under conditions that enable the lowest energy intensity of ethylene production. The CO2RR-GOR system achieved stable electrosynthesis of cathodic C2+ and anodic products for over 80 hours at a current density of 100 mA cm−2, comparable to the stability of conventional MEAs. The system maintained an average full-cell voltage of 1.90±0.1 V, an average total C2+FE of 42%, and an average carbon efficiency of about 45% toward all CO2RR products (see
Similarly, stable GOR productivity was detected throughout (See
Notably, the present CO2-to-C2+ system demonstrates high stability while maintaining high carbon efficiency.
The cathodic and anodic liquid-phase products were evaluated from the 1H NMR spectra of catholyte and anolyte, respectively. The typical 1H NMR spectra are shown in
Energy Assessment
Energy consumptions for electrolyser electricity, cathodic separation, and anodic separation were evaluated for ethylene—the world's most produced feedstock. State-of-the-art CO2RR systems, including alkaline flow-cell electrolysers, neutral MEA electrolysers, acidic flow-cell and acidic MEA electrolysers were considered. This consideration is based on the performance metrics including selectivity, productivity, and full-cell voltage-combination of them in turn reflect as energy intensity of producing multi-carbon products (i.e. ethylene). The proximity of these performance metrics will help refine the effect of anodic and cathodic separation on the energy requirement for producing ethylene. Input parameters to the model for all the systems are summarized. The energy assessment model as well as the assumptions are based on a previous work. The majority of these input parameters listed in Table 1 are from the literature. The model considers a production rate of 1 ton/day, with the assumptions of H2 and O2 are the only products at the anodic and cathodic streams. The details of calculations for the carbon regeneration (for alkaline flow cell), cathodic separation (for all the electrolysers), and anodic separation (for neutral MEA electrolyser) can be found in the previous work. For acidic flow-cell and MEA electrolysers, no energy cost was assumed to be associated with the anodic separation considering no CO2 availability at the anodic gas stream.
| Number | Date | Country | Kind |
|---|---|---|---|
| LU502158 | May 2022 | LU | national |
This application claims the benefit of PCT/EP2023/062389 filed May 10, 2023, which claims priority from U.S. 63/340,448 filed May 10, 2022, and LU502158 filed May 24, 2022 which are incorporated herein by reference in their entireties for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/062389 | 5/10/2023 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2023/217842 | 11/16/2023 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20190055656 | Kenis et al. | Feb 2019 | A1 |
| 20210079538 | Schmid | Mar 2021 | A1 |
| 20210292925 | Mikoshiba et al. | Sep 2021 | A1 |
| Number | Date | Country |
|---|---|---|
| 102020207192 | Dec 2021 | DE |
| 2014046794 | Mar 2014 | WO |
| Entry |
|---|
| International Search Report and Written Opinion issued in Application No. PCT/EP2023/062389, dated Sep. 19, 2023, 12 pages. |
| International Preliminary Report on Patentability issued in Application No. PCT/EP2023/062389, dated Apr. 3, 2024, 16 pages. |
| Novalin Timon et al., “Electrochemical performance of poly(arylene piperidinium) membranes and ionomers in anion exchange membrane fuel cells”, Journal of Power Sources, Elsevier, Amsterdam, NL, vol. 507, Jul. 22, 2021, 13 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20250109512 A1 | Apr 2025 | US |
| Number | Date | Country | |
|---|---|---|---|
| 63340448 | May 2022 | US |
