WO2020005482A1

WO2020005482A1 - Transition metal mxene catalysts for conversion of carbon dioxide to hydrocarbons

Info

Publication number: WO2020005482A1
Application number: PCT/US2019/035577
Authority: WO
Inventors: Mohammad ASADI; Alireza KONDORI; Mohammadreza ESMAEILIRAD; Andres RUIZ BELMONTE
Original assignee: Illinois Institute Of Technology
Priority date: 2018-06-29
Filing date: 2019-06-05
Publication date: 2020-01-02

Abstract

Transition metal MXene catalysts and methods for using with electrochemical cells for reduction of carbon dioxide and production of hydrocarbons. The transition metal catalysts include nanostructured transition metal carbides, nitrides, or carbonitrides. The method includes electrochemically reducing carbon dioxide in an electrochemical cell, by contacting the carbon dioxide with at least one transition metal carbide, nitride, or carbonitride catalyst in the electrochemical cell and applying a potential to the electrochemical cell.

Description

TRANSITION METAL MXENE CATALYSTS FOR CONVERSION OF CARBON DIOXIDE TO HYDROCARBONS CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S Application, Serial No. 62/691,726, filed on 29 June 2018. The co-pending parent application is hereby incorporated by reference herein in its entirety and is made a part hereof, including but not limited to those portions which specifically appear hereinafter.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates generally to photoelectrochemical cells, and more particularly, methods for using cells for reduction of carbon dioxide and/or production of hydrocarbons.

Description of Related Art

Today, the rapid growth of the population is draining the finite resources of the Earth’s crust, i.e., fossil fuels, coals, and minerals, to supply their energy needs. Although fossil fuels have been widely used as the energy resource, when burnt, are the primary cause of global warming due to the released C0₂. Therefore, developing a net zero carbon cycle, in which the released C0₂ can be transformed into valuable products and fuels using renewable and sustainable energy is quite desirable.

Electrocatalytic reduction of carbon dioxide to value-added chemicals using renewable energy sources is one of the promising approaches to reach to this goal. Thus far, most of the efforts have been focused to reduce C0₂ into CO as a final product in a electrocatalysis process. However, CO is known as an intermediate product and must be mixed with hydrogen (H₂) in the desired ratio to produce syngas. The produced syngas also has to feed into a less efficient thermal process (Fischer-Tropsch) to produce value-added chemicals such as methanol. Therefore, reaching to the goal of the net-zero carbon emission process by producing syngas is not economically feasible.

Among various possible products of a C0₂ reduction reaction, hydrocarbon fuels, such as methane (CH₄), ethylene (C₂H₄) and ethane (C₂H6), that have much higher energy density compared with carbon monoxide (CO), a common gas phase product of this reaction. The energy densities of CH₄ (891.1 kJ mol ¹), C₂H₄ (1411.2 kJ mol ¹) and C₂H₆ (1554 kJ mol ¹) are three, five and about six times higher than CO (283.4 kJ mol ¹), respectively. Moreover, these gases can be utilized directly as fuels or fed into various petrochemical/chemical processes to produce other valuable chemicals. To date, numerous types of copper catalysts such as oxide drive copper, copper nanoparticles, and nanorods have been used to reduce CO2 into hydrocarbon fuels such as CH₄, C2H4_, and C2H6. However, despite enormous efforts, none of them are capable of efficiently producing hydrocarbon fuels directly from carbon dioxide. Therefore, developing catalysts that can directly result in hydrocarbon formation is highly desirable.

Metals such as copper, silver, nickel, etc., have also been employed in the catalytic conversion of CO2 into high-value products. However, none of them show a reasonable faradaic efficiency for CH₄, C₂H_4, and C2H6 formation with respect to the applied overpotential. Therefore, an economical methane formation system cannot be obtained because of the low energy efficiency of the conventional metal catalysts.

SUMMARY OF THE INVENTION

A general object of the invention is to provide an improved method and system for carbon dioxide reduction into valuable end products such as hydrocarbons. Embodiments of this invention incorporate a catalyst that can selectively produce, for example, CH₄ (natural gas) with 100-fold higher turnover frequency, 40 times higher selectivity at four times less energy compared to state of the art catalysts (e.g., copper). Other exemplary hydrocarbon fuels possible by this invention include, without limitation, ethylene (C2H₄) and ethane (C₂H₆) with 1411.2 and 1554 kJ mol ¹ energy density, respectively. The type of hydrocarbon can depend on the stoichiometric ratio of the catalyst used.

The invention includes a catalyst composition for carbon dioxide reduction, including at least one transition metal MXene catalyst. The transition metal catalyst comprises a nanostructured MXene carbide, nitride, or carbonitride, such as M_yX_z, wherein M is a transition metal, X is carbon, nitrogen or carbonitride (e.g., M_xC_yN_z), and y and z are stoichiometric ratio integers. The transition metal can be, for example, molybdenum, tungsten, titanium, or cobalt. In embodiments of this invention, the transition metal MXene catalyst comprises a nanoparticle form, such as having an average size between about 1 nm and 400 nm. The transition metal MXene catalyst can further be a nanoflake, nanosheet, or nanoribbon form.

The invention further includes an electrochemical cell having a cathode with at least one transition metal catalyst, and in contact with an electrolyte. The electrolyte, such as a solution of 1M KHCO3, is saturated with the carbon dioxide to be treated, which can be fed into the electrolyte through any known manner.

The invention further includes a method of electrochemically reducing carbon dioxide, including: introducing the carbon dioxide to a catalyst comprising a transition metal catalyst in an electrochemical cell; applying a potential to the electrochemical cell; and converting the carbon dioxide to a hydrocarbon. Embodiments of the invention further include steps of providing the electrochemical cell including a cathode coated with the catalyst, and an electrolyte in contact with the cathode and the catalyst; providing carbon dioxide to the electrochemical cell; and applying the potential to the electrochemical cell in the presence of the carbon dioxide to reduce the carbon dioxide to the hydrocarbon.

Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an electrochemical device according to one embodiment of this invention.

FIG. 2 representatively illustrates a two-compartment three-electrode electrochemical cell according to one embodiment of this invention.

DESCRIPTION OF THE INVENTION

This invention relates generally to reduction of carbon dioxide (C0₂) to hydrocarbons such as methane (CH₄) and, more particularly, to MXene materials as catalysts for this reduction.

The invention provides transition metal catalysts and method of using the catalysts to reduce carbon dioxide, such as to hydrocarbons for use as fuel. Exemplary catalysts include nanostructured MXenes, such as typically in one of the following structures: M₂X (e.g., M₂N, M₂C, or M₂CN), M₃X₂ (e.g., M₃N₂, M₃C₂, or M₃C₂N), and M₄X₃ (e.g., M₄C₃N), wherein M is a transition metal and X is carbon, nitrogen, or a carbonitride. One presently preferred transition metal is molybdenum, such as in the form of Mo₂C or Mo₂CN nanoparticles or nanoflakes. Other exemplary MXenes include, without limitation, carbides, nitrides, or carbonitrides of cobalt, titanium, tungsten, etc. Multiple metals and/or multiple stoichiometries are also possible for the MXene catalysts.

Two ultimate goals in the electrochemical reduction of carbon dioxide can be addressed by using the transition metal MXene catalysts of this invention. First, it tackles the amount of required energy to reduce the C0₂ into useful products. The observed onset overpotential for the CH₄ fonnation (-0.15 V vs. RHE) using Mo₂C is the lowest reported to date which shows its superior catalytic activity among commonly used catalysts. Second, employing MO₂C catalysts provides production of CH₄ having two orders of magnitude higher numbers of product formation compared to typical state of the art metal catalysts (e.g., copper).

FIG. 1 is a schematic sectional view of an electrochemical device 20 (e.g., electrochemical cell) with a first compartment 22 including at least one transition metal MXene 24 disposed on a cathode 26. Device 20 includes a second compartment 32 including at least one water oxidizing catalyst 34 disposed on an anode 36. Compartments 22 and 32 include a first electrolyte 28 and a second electrolyte 38, respectively, and are in ionic contact through an ion-conductive membrane 40. An electrical potential source 50 is included. In embodiments of this invention, the electrical potential source is a photovoltaic cell. The device 20 further includes a carbon dioxide inlet and a suitable hydrocarbon outlet, and a corresponding anode side inlet and outlet.

The transition metal MXene catalysts of embodiments of this invention have a general chemical formula of M_yX_z, wherein M is a transition metal, X is carbon and/or nitrogen, and y and z are stoichiometric ratio integers (generally each one of 1-4, with y and z being equal or y one whole number greater than z; e.g., M₂X, M₃X₂, and/or M4X3)· In embodiments of this invention, the catalyst is or includes M_n+iX_n, wherein M is a transition metal, X is carbon and/or nitrogen, and n is zero or an integer. In additional embodiments of this invention, the catalyst is or includes M_xC_yN_z wherein M is a transition metal, C is carbon, N is nitrogen, and x, y and z are each an stoichiometric ratio integer (e.g., with each of y and z being independently one of 0 to 3, with at least one of y and z not zero, and x, y and/or z being equal or x being one whole number greater than y or z (e.g., MC, MN, M₂C, M₂N, M₃C₂, M4C3, M₂CN, M₃C₂N, and/or M₄C₃N). Presently preferred transition metals include molybdenum, tungsten, titanium, or cobalt. Exemplary catalyst materials include, without limitation, WC, TiC, Co₂C, and/or M02C.

The transition metal MXene catalysts can be provided in a variety of forms, for example, as a bulk material, in nanostructure form, as a collection of particles, and/or as a collection of supported particles. The MXene catalyst in bulk form can have a layered structure as is typical for such compounds. The MXene catalyst may have a nanostructure morphology, including but not limited to monolayers, nanotubes, nanoparticles, nanoflakes (e.g., multilayer nanoflakes), nanosheets, nanoribbons, nanoporous solids, etc. As used herein, the term “nanostructure” refers to a material with a dimension (e.g., of a pore, a thickness, a diameter, as appropriate for the structure) in the nanometer range.

In some embodiments, the catalyst is a layer-stacked bulk MXene with metal atom-terminated edges. In other embodiments, MXene nanoparticles may be used in the devices and methods of the disclosure. In other embodiments, al MXene nanoflakes may be used in the devices and methods of the disclosure. Nanoflakes can be made, for example, via liquid exfoliation, as described in Coleman, J. N. et al., “Two-dimensional nanosheets produced by liquid exfoliation of layered materials.” Science 331, 568-71 (201 1) and Yasaei, P. et al.,“High-Quality Black Phosphorus Atomic Layers by Liquid-Phase Exfoliation.” Adv. Mater. (2015) (doi: 10.1002/adma.201405150), each of which is hereby incorporated herein by reference in its entirety. In other embodiments, transition metal MXene nanoribbons may be used in the devices and methods of the disclosure. In other embodiments, transition metal MXene nanosheets may be used in the devices and methods of the disclosure. The person of ordinary skill in the art can select the appropriate morphology for a particular device.

In some embodiments of the methods and devices as otherwise described herein, the transition metal MXene nanostructures (e.g., nanoflakes, nanoparticles, nanoribbons, etc.) have an average size between about 1 nm and 1000 nm. The relevant size for a nanoparticle is its largest diameter. The relevant size for a nanoflake is its largest width along its major surface. The relevant size for a nanoribbon is its width across the ribbon. The relevant size for a nanosheet is its thickness. In some embodiments, the transition metal MXene nanostructures have an average size between from about 1 nm to about 400 nm, or about 1 nm to about 350 nm, or about 1 nm to about 300 nm, or about 1 nm to about 250 nm, or about 1 nm to about 200 nm, or about 1 nm to about 150 nm, or about 1 nm to about 100 nm, or about 1 nm to about 80 nm, or about 1 nm to about 70 nm, or about 1 nm to about 50 nm, or 50 nm to about 400 nm, or about 50 nm to about 350 nm, or about 50 nm to about 300 nm, or about 50 nm to about 250 nm, or about 50 nm to about 200 nm, or about 50 nm to about 150 nm, or about 50 nm to about 100 nm, or about 10 nm to about 70 nm, or about 10 nm to about 80 n , or about 10 nm to about 100 nm, or about 100 nm to about 500 nm, or about 100 nm to about 600 nm, or about 100 nm to about 700 nm, or about 100 nm to about 800 nm, or about 100 nm to about 900 nm, or about 100 nm to about 1000 nm, or about 400 nm to about 500 nm, or about 400 nm to about 600 nm, or about 400 nm to about 700 nm, or about 400 nm to about 800 nm, or about 400 nm to about 900 nm, or about 400 nm to about 1000 nm.

In certain embodiments of the methods and devices as otherwise described herein, transition metal MXene nanoflakes have an average thickness between about 1 nm and about 100 pm (e.g., about 1 nm to about 10 pm, or about 1 nm to about 1 pm, or about 1 nm to about 1000 nm, or about 1 nm to about 400 nm, or about 1 nm to about 350 nm, or about 1 nm to about 300 nm, or about 1 nm to about 250 nm, or about 1 nm to about 200 nm, or about 1 nm to about 150 nm, or about 1 nm to about 100 nm, or about 1 nm to about 80 nm, or about 1 nm to about 70 nm, or about 1 nm to about 50 nm, or about 50 nm to about 400 nm, or about 50 nm to about 350 nm, or about 50 nm to about 300 nm, or about 50 nm to about 250 nm, or about 50 nm to about 200 nm, or about 50 nm to about 150 nm, or about 50 nm to about 100 nm, or about 10 nm to about 70 nm, or about 10 nm to about 80 nm, or about 10 nm to about 100 nm, or about 100 ran to about 500 ran, or about 100 nm to about 600 ran, or about 100 ran to about 700 nm, or about 100 nm to about 800 nm, or about 100 nm to about 900 ran, or about 100 nm to about 1000 nm, or about 400 nm to about 500 ran, or about 400 nm to about 600 nm, or about 400 nm to about 700 nm, or about 400 nm to about 800 nm, or about 400 ran to about 900 nm, or about 400 nm to about 1000 nm); and average dimensions along the major surface of about 20 nm to about 100 gm (e.g., about 20 nm to about 50 gm, or about 20 nm to about 10 gm, or about 20 nm to about 1 gm, or about 50 nm to about 100 gm, or about 50 ran to about 50 gm, or about 50 nm to about 10 gm, or about 50 nm to about 1 gm, or about 100 nm to about 100 gm, or about 100 nm to about 50 gm, or about 100 nm to about 10 gm, or about 100 nm to about 1 gm), The aspect ratio (largest major dimension: thickness) of the nanoflakes can be on average, for example, at least about 5: 1, at least about 10: 1 or at least about 20:1. For example, in certain embodiments the transition metal MXene nanoflakes have an average thickness in the range of about 1 nm to about 1000 nm (e.g., about 1 nm to about 100 nm), average dimensions along the major surface of about 50 nm to about 10 gm, and an aspect ratio of at least about 5: 1.

The invention includes methods of electrochemically reducing carbon dioxide by introducing the carbon dioxide to a transition metal MXene catalyst in an electrochemical cell. Embodiments of this invention utilize nanostructured transition metal MXenes as catalysts in the electrocatalytic conversion of carbon dioxide (C0₂) to produce hydrocarbon, such methane (CH₄), the main component of natural gas, at remarkably low overpotentials.

The nanostructured transition metal MXenes can be synthesized using liquid exfoliation techniques, and were tested in a two-compartment three-electrode electrochemical cell as a working electrode, as shown in FIG. 2. FIG. 2 representatively illustrates the two- compartment three-electrode electrochemical cell according to embodiments of this invention used for testing. Transition metal carbides were drop-cast onto a glassy carbon substrate to form the working electrode 124. Platinum gauze or other suitable material can be used as the counter and reference electrodes 136 and 126, respectively. The working electrode 124, reference electrode 126, and counter electrode 136 are immersed in an aqueous electrolyte solution 128 and 138, respectively. The cathode and anode are separated by an ion-conductive membrane 140 to eliminate potential product oxidation at the anode 136 surface.

Testing results indicated that Mo₂C exhibited an onset potential of -0.15 V vs. RHE, which is a potential where the reduction reaction begins in a buffer electrolyte of 1 M KHC0₃. The recorded onset potential for Mo₂C is the lowest overpotential (-0.15 V), excess energy beyond thermodynamic potential, for CH₄ formation reported so far, which is 650 mV less than that of copper (- 0.8 V). Mo₂C also exhibits significantly higher faradaic efficiency at a potential range of -0.15 to -0.8 V. For instance, at a potential of -0.4 V, methane formation F.E. for MO₂C nanoflake is 44% while copper has a negligible faradaic efficiency of less than 1%. Moreover, the calculated turnover frequency (TOF), the number of product (CH₄) formation per active sites, for Mo₂C indicated approximately two orders of magnitude higher CH₄ formation than that of copper at a potential range of -0.15 to -0.8 V vs. RHE.

Thus, the invention a method and system to recycle C0₂ into hydrocarbons, such as CH₄ (natural gas) in an energy efficient and economically feasible electrochemical process. A scale-up of the invention coupled with solar energy cells can develop a carbon-zero electrochemical system in which C0₂ from the air, wastes of the big industries, etc. can be reduced to a profitable product (natural gas) that can directly be used as a fuel.

The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.

While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.

Claims

What is claimed is:

1. A method of electrochemically reducing carbon dioxide, comprising: introducing the carbon dioxide to a catalyst comprising a transition metal carbide, nitride, or carbonitride in an electrochemical cell;

applying a potential to the electrochemical cell; and

converting the carbon dioxide to a hydrocarbon, preferably methane.

2. A method of claim 1, wherein the electrochemical cell comprises a cathode, wherein the cathode is coated with the catalyst.

3. A method of claim 1, further comprising:

providing the electrochemical cell including a cathode coated with the catalyst, and an electrolyte in contact with the cathode and the catalyst;

providing carbon dioxide to the electrochemical cell; and

applying the potential to the electrochemical cell in the presence of the carbon dioxide to reduce the carbon dioxide to the hydrocarbon.

4. The method of any one of claim 3, wherein the electrolyte, such as a solution of 1M KHC0₃, is saturated with the carbon dioxide.

5. A method of any one of claims 1 to 4, wherein the catalyst comprises a nanostructured MXene.

6. A method of any one of claims 1 to 5, wherein the catalyst comprises M_yX_z, wherein M is a transition metal, X is carbon and/or nitrogen, and y and z are stoichiometric ratio integers.

7. A method of any one of claims 1 to 6, wherein the transition metal comprises molybdenum, tungsten, titanium, or cobalt.

8. A method of any one of claims 1 to 7, wherein the catalyst comprises a nanoparticle form.

9. A method of claim 8, wherein the catalyst nanoparticles have an average size between about 1 nm and 400 nm.

10. A method of any of claims 1 to 9, wherein the catalyst comprises a nanoflake, nanosheet, or nanoribbon form.

11. An electrochemical cell having a cathode with at least one MXene catalyst, and in contact with an electrolyte.

12. An electrochemical cell of claim 11, wherein the MXene catalyst comprises a nanostructured transition metal carbide, nitride and/or carbonitride.

13. An electrochemical cell of claim 11, wherein the MXene catalyst comprises M_yX_z, wherein M is a transition metal, X is carbon and/or nitrogen, and y and z are stoichiometric ratio integers.

14. An electrochemical cell of any one of claims 11 to 13, wherein the MXene catalyst comprises molybdenum, tungsten, titanium, or cobalt.

15. An electrochemical cell of any one of claims 1 1 to 14, wherein the MXene catalyst comprises a nanoparticle form.

16. An electrochemical cell of claim 15, wherein the MXene catalyst nanoparticles have an average size between about 1 nm and 400 nm.

17. An electrochemical cell of any one of claims 11 to 16, wherein the MXene catalyst comprises a nanoflake, nanosheet, or nanoribbon form.

18. An electrochemical cell according to any one of claims 11 to 17 for use in reducing carbon dioxide.

19. A catalyst composition for carbon dioxide reduction, comprising at least one transition metal MXene.

20. A composition of claim 19, wherein the transition metal MXene comprises a nanostructured carbide, nitride, and/or carbonitride.

21. A composition of claim 19 or 20, wherein the transition metal MXene comprises M_yX_z, wherein M is a transition metal, X is carbon and/or nitrogen, and y and z are stoichiometric ratio integers.

22. A composition of any one of claims 19 to 21, wherein the transition metal MXene comprises molybdenum, tungsten, titanium, or cobalt.

23. A composition of any one of claims 19 to 22, wherein the transition metal MXene comprises a nanoparticle form.

24. A composition of claim 23, wherein the transition metal MXene nanoparticles have an average size between about 1 nm and 400 nm.

25. A composition of any one of claims 19-24, wherein the transition metal MXene comprises a nanoflake, nanosheet, or nanoribbon form.