U.S. patent application number 16/778772 was filed with the patent office on 2020-08-06 for metal-carbon nanostructures and method of manufacturing thereof.
This patent application is currently assigned to DIMARTECH FABRICATION INC.. The applicant listed for this patent is DIMARTECH FABRICATION INC.. Invention is credited to Richard Boudreault, Ulrich Legrand.
Application Number | 20200248324 16/778772 |
Document ID | / |
Family ID | 1000004732930 |
Filed Date | 2020-08-06 |
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United States Patent
Application |
20200248324 |
Kind Code |
A1 |
Legrand; Ulrich ; et
al. |
August 6, 2020 |
METAL-CARBON NANOSTRUCTURES AND METHOD OF MANUFACTURING THEREOF
Abstract
A method of producing a fuel from carbon dioxide comprising
performing a carbon dioxide electroreduction using a cathode
comprising carbon powder, the carbon powder composed of carbon
particles with metallic particles deposited on the carbon
particles, wherein a product of the carbon dioxide electroreduction
is the fuel.
Inventors: |
Legrand; Ulrich; (Verdun,
CA) ; Boudreault; Richard; (St-Laurent, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DIMARTECH FABRICATION INC. |
Montreal |
|
CA |
|
|
Assignee: |
DIMARTECH FABRICATION INC.
Montreal
CA
|
Family ID: |
1000004732930 |
Appl. No.: |
16/778772 |
Filed: |
January 31, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62799191 |
Jan 31, 2019 |
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16778772 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 3/04 20130101; C25B
11/0478 20130101 |
International
Class: |
C25B 11/04 20060101
C25B011/04; C25B 3/04 20060101 C25B003/04 |
Claims
1. Graphene powder composed of graphene nanoflakes comprising
metallic particles deposited thereon, wherein said metallic
particles comprise at least one of: copper; copper oxide; copper
sulfide; tin; tin sulfide; tin oxide; iridium dihydride; iron
carbonyl; one or more manganese complexes; one or more rhodium
complexes; one or more iron complexes; one or more copper
complexes; bismuth; one or more bismuth complexes; cobalt oxide;
one or more ruthenium complexes; one or more rhenium complexes; one
or more osmium complexes; lead; lead oxide; mercury; and an alloy
of one or more metals selected from copper, tin, bismuth, lead,
mercury and iron.
2. The graphene powder as defined in claim 1, wherein said metallic
particles are at least one of: copper; copper oxide; copper
sulfide; tin; tin sulfide; tin oxide; iridium dihydride; iron
carbonyl; one or more manganese complexes; one or more rhodium
complexes; one or more copper complexes; bismuth; one or more
bismuth complexes; cobalt oxide; one or more ruthenium complexes;
one or more rhenium complexes; one or more osmium complexes; lead;
lead oxide; mercury; and an alloy of one or more metals selected
from copper, tin, bismuth, lead, mercury and iron.
3. The graphene powder as defined in claim 1, wherein said metallic
particles comprise at least one of: copper; copper oxide; copper
sulfide; tin; tin sulfide; tin oxide; and alloy of copper and
tin.
4. The graphene powder as defined in claim 3, wherein said metallic
particles comprise metallic nanoparticles.
5. The graphene powder as defined in claim 4, wherein said graphene
nanoflakes are composed of five to twenty stacked layers of
graphene.
6. The graphene powder as defined in claim 5, wherein copper
composes at least 15% wt of said graphene nanoflakes.
7. An electrode comprising said graphene powder as defined in claim
6.
8. The electrode as defined in claim 7, wherein said electrode
comprises a gas diffusion layer and a binding polymer, said binding
polymer binding said graphene powder to said gas diffusion
layer.
9. A method of manufacturing carbon particles with metallic
particle deposits, comprising: introducing carbon particles into a
hydrophilic solvent, resulting in a mixture; dissolving a metal
salt in said mixture; drying said mixture containing said dissolved
metal salt; and pyrolyzing said dried mixture containing said
dissolved metal salt to yield said carbon particles with metal
particle deposits.
10. The method as defined in claim 9, wherein said metal salt
comprises one or more of: copper salt and tin salt.
11. The method as defined in claim 10, wherein said metal salt is
copper salt.
12. The method as defined in claim 11, wherein said copper salt is
CuSO.sub.4 and said copper particle deposits comprise at least one
of copper sulfide and copper oxide.
13. The method as defined in claim 12, wherein the mass of copper
introduced into the hydrophilic solvent is at least 20 wt %.
14. The method as defined in claim 13, wherein said carbon
particles are graphene nanoflakes, and said introduced carbon
particles are introduced graphene nanoflakes composed of stacked
layers of graphene.
15. The method as defined in claim 14, wherein said introduced
graphene nanoflakes are composed of five to twenty stacked layers
of graphene.
16. The method as defined in claim 15, wherein said hydrophilic
solvent is a mixture of water and ethanol.
17. The method as defined in claim 16, wherein said pyrolysis is
performed at a temperature above 500.degree. C.
18. Carbon particles with metal particle deposits manufactured in
accordance with the method as defined in claim 17.
19. A method of producing a fuel from carbon dioxide comprising
performing a carbon dioxide electroreduction using a cathode
comprising carbon powder, said carbon powder composed of carbon
particles with metallic particles deposited on said carbon
particles, wherein a product of said carbon dioxide
electroreduction is said fuel.
20. The method as defined in claim 19, wherein said metallic
particles comprise at least one of: copper; copper oxide; copper
sulfide; tin; tin sulfide; tin oxide; iridium dihydride; iron
carbonyl; one or more manganese complexes; one or more rhodium
complexes; one or more iron complexes; one or more copper
complexes; bismuth; one or more bismuth complexes; cobalt oxide;
one or more ruthenium complexes; one or more rhenium complexes; one
or more osmium complexes; lead; lead oxide; mercury; and an alloy
of one or more metals selected from copper, tin, bismuth, lead,
mercury and iron.
Description
[0001] The present patent application claims priority from the U.S.
provisional patent application No. 62/680,200 filed on Jun. 4,
2018, that is incorporated by reference herein, and U.S.
provisional patent application No. 62/799,191 filed on Jan. 31,
2019 that is incorporated by reference herein.
TECHNICAL FIELD
[0002] The present application relates to the field of
nanotechnology, and more specifically to carbon nanostructures.
BACKGROUND
[0003] Carbon dioxide is massively emitted into the atmosphere
since the industrial era. Human-made CO.sub.2 is linked with global
warming and its consequences. Reducing the emissions of this
greenhouse gas is a challenge that can be achieved through several
strategies. These strategies include, but are not limited to: the
energy transition, to switch from fossil fuels to renewable energy
sources [1]; associating energy storage systems to renewables to
make them more reliable [2]; promoting collective transportation
and electric vehicles [3]; protecting and multiplying the number of
green spaces, natural carbon storage systems [4]; making systems
and processes more energy efficient [5].
[0004] These strategies take time, money and political willingness
to be fully implemented in the world. [6] [7] [8] [9].
SUMMARY
[0005] Extensive research has been done in the last decades on the
CO.sub.2 conversion toward valuable products. CO.sub.2 is a highly
stable and poorly reactive molecule. The process of converting it
may thus be energy intensive. Different methods to convert CO.sub.2
exist, such as plasma [10] or photocatalytic [11] based techniques,
but the electrocatalytic reduction of CO.sub.2 may be the most
promising technology [12]. A catalyst is required to lower the
energy intake to convert CO.sub.2. Most of the transition metals
used in the CO.sub.2 electroreduction have a tendency to produce
carbon monoxide, CO [31]. CO has to be associated with dihydrogen
to form syngas and go through the Fischer-Tropsch process before
obtaining hydrocarbons, re-used as fuels [13]. Copper is an element
able to directly produce complex hydrocarbons through the
electrochemical process. However, copper as a catalyst may produce
a large variety of hydrocarbons with low efficiency and low
selectivity for each [14].
[0006] A recent study realized by Song et al. [15] presented a
catalyst based on copper nanoparticles dispersed on a graphitic
material where graphene was grown on a substrate, resulting in a
single carbon structure once grown and not carbon particles or
carbon powder that can be dispersed, producing ethanol with
faradaic efficiency of 61% and a selectivity of 62% toward the
carbon-based products (value extrapolated from the article's data).
The synergistic effect between the carbon-based material and the
copper nanoparticles is apparently responsible for the high
electrocatalytic performance of the catalyst described in the
research article. Despite the high efficiency of their catalyst,
the reported current density is relatively low, around 2
mAcm.sup.-2 at -1.2 V vs RHE, making the catalyst not suitable for
a commercial application. Commercial catalysts for CO.sub.2
reduction are expected to have current densities higher that 100
mAcm.sup.-2 for faradaic efficiencies reaching at least 50%
[32].
[0007] The present study is using graphene nanoflakes (GNFs)[16].
GNFs have been proven to be an interesting material as carbon
support for catalytic applications, thanks to outstanding
crystallinity properties [17]. Different methods of
functionalization and nanoparticles decoration have been developed
and applied to the GNFs [18]-[20]. The wet chemistry method
initially developed by Yeager et al. [21] is chosen in this study
to disperse copper nanoparticles on the surface of the GNFs
(Cu-GNFs) and thus synthesize an active catalyst toward the
CO.sub.2 electroreduction.
[0008] Catalysts with various amount of copper and various chemical
composition are synthesized and characterized in this study.
Physical characterization aims to understand the structure and
composition of the samples. The electrochemical characterization
provides an insight on the electrocatalytic performance of the
Cu-GNFs.
[0009] A broad aspect is a graphene powder composed of graphene
nanoflakes including copper sulfide nanoparticles deposited
thereon.
[0010] In some embodiments, the graphene nanoflakes may be composed
of five to twenty stacked layers of graphene.
[0011] In some embodiments, the copper may compose at least 15% wt
of the graphene nanoflakes.
[0012] Another broad aspect is an electrode at least partially
coated with graphene nanoflakes, the graphene nanoflakes comprising
copper sulfide nanoparticle deposits.
[0013] Another broad aspect is a method of manufacturing graphene
nanoflakes with copper nanoparticle deposits. The method includes
introducing graphene nanoflakes composed of stacked layers of
graphene into a hydrophilic solvent, resulting in a mixture. The
method includes dissolving a copper salt in the mixture. The method
includes drying the mixture containing the dissolved copper salt.
The method includes pyrolyzing the dried mixture containing the
dissolved copper salt to yield the graphene nanoflakes with copper
nanoparticle deposits.
[0014] In some embodiments, the introduced graphene nanoflakes may
be composed of five to twenty stacked layers of graphene.
[0015] In some embodiments, the hydrophilic solvent may be a
mixture of water and ethanol.
[0016] In some embodiments, the pyrolysis may be performed at a
temperature above 500.degree. C.
[0017] In some embodiments, the mass of copper introduced to the
hydrophilic solvent may be at least 20 wt %.
[0018] In some embodiments, the copper salt may be CuSO.sub.4 and
the copper nanoparticle deposits may include copper sulfide.
[0019] Another broad aspect are graphene nanoflakes with copper
nanoparticle deposits manufactured in accordance with the method as
defined herein.
[0020] In some embodiments, the graphene particles may be graphene
nanoflakes.
[0021] A broad aspect is carbon powder composed of carbon particles
comprising metallic particles deposited thereon, wherein said
metallic particles include, but not limited to copper; copper
oxide; copper sulfide; tin; tin sulfide; tin oxide; iridium
dihydride; iron carbonyl; one or more manganese complexes; one or
more rhodium complexes; one or more iron complexes; one or more
copper complexes; bismuth; one or more bismuth complexes; cobalt
oxide; platinum, one or more platinum complexes; one or more
ruthenium complexes; one or more rhenium complexes; one or more
osmium complexes; lead; lead oxide; mercury; and/or an alloy of one
or more metals selected from copper, tin, bismuth, lead, mercury
and iron.
[0022] A broad aspect is a graphene powder composed of graphene
nanoflakes comprising metallic particles deposited thereon, wherein
the metallic particles include at least one of copper; copper
oxide; copper sulfide; tin; tin sulfide; tin oxide; iridium
dihydride; iron carbonyl; one or more manganese complexes; one or
more rhodium complexes; one or more iron complexes; one or more
copper complexes; bismuth; one or more bismuth complexes; cobalt
oxide; one or more ruthenium complexes; one or more rhenium
complexes; one or more osmium complexes; lead; lead oxide; mercury;
and an alloy of one or more metals selected from copper, tin,
bismuth, lead, mercury and iron.
[0023] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; iridium dihydride; iron carbonyl; one or more
manganese complexes; one or more rhodium complexes; one or more
copper complexes; bismuth; one or more bismuth complexes; cobalt
oxide; one or more ruthenium complexes; one or more rhenium
complexes; one or more osmium complexes; lead; lead oxide; mercury;
and an alloy of one or more metals selected from copper, tin,
bismuth, lead, mercury and iron.
[0024] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; and alloy of copper and tin.
[0025] In some embodiments, the metallic particles may include
metallic nanoparticles.
[0026] In some embodiments, the graphene nanoflakes may be composed
of five to twenty stacked layers of graphene.
[0027] In some embodiments, the copper may compose at least 15% wt
of the graphene nanoflakes.
[0028] Another In some embodiments, the electrode may include a gas
diffusion layer and a binding polymer, the binding polymer binding
the graphene powder to the gas diffusion layer.
[0029] Another broad aspect is a method of manufacturing carbon
particles with metallic particle deposits. The method includes
introducing carbon particles into a hydrophilic solvent, resulting
in a mixture; dissolving a metal salt in the mixture; drying the
mixture containing the dissolved metal salt; and pyrolyzing the
dried mixture containing the dissolved metal salt to yield the
carbon particles with metal particle deposits.
[0030] In some embodiments, the metal salt may include one or more
of copper salt and tin salt.
[0031] In some embodiments, the metal salt may be copper salt.
[0032] In some embodiments, the copper salt may be CuSO4 and the
copper particle deposits may include copper sulfide, copper oxide
and/or metallic copper.
[0033] In some embodiments, the mass of copper introduced into the
hydrophilic solvent may be at least 20 wt %.
[0034] In some embodiments, the carbon particles may be graphene
nanoflakes, and the introduced carbon particles may be introduced
graphene nanoflakes composed of stacked layers of graphene.
[0035] In some embodiments, the introduced graphene nanoflakes may
be composed of five to twenty stacked layers of graphene.
[0036] In some embodiments, the hydrophilic solvent may be a
mixture of water and ethanol.
[0037] In some embodiments, the pyrolysis may be performed at a
temperature above 500.degree. C.
[0038] Another broad aspect are carbon particles with metal
particle deposits manufactured in accordance with the method as
defined herein.
[0039] Another broad aspect is a method of producing a fuel from
carbon dioxide comprising performing a carbon dioxide
electroreduction using a cathode comprising carbon powder, the
carbon powder composed of carbon particles with metallic particles
deposited on the carbon particles, wherein a product of the carbon
dioxide electroreduction is the fuel.
[0040] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; iridium dihydride; iron carbonyl; one or more
manganese complexes; one or more rhodium complexes; one or more
iron complexes; one or more copper complexes; bismuth; one or more
bismuth complexes; cobalt oxide; one or more ruthenium complexes;
one or more rhenium complexes; one or more osmium complexes; lead;
lead oxide; mercury; and an alloy of one or more metals selected
from copper, tin, bismuth, lead, mercury and iron.
[0041] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; iridium dihydride; iron carbonyl; one or more
manganese complexes; one or more rhodium complexes; one or more
copper complexes; bismuth; one or more bismuth complexes; cobalt
oxide; one or more ruthenium complexes; one or more rhenium
complexes; one or more osmium complexes; lead; lead oxide; mercury;
and an alloy of one or more metals selected from copper, tin,
bismuth, lead, mercury and iron.
[0042] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; and alloy of copper and tin.
[0043] In some embodiments, the metallic particles may include
metallic nanoparticles.
[0044] In some embodiments, the fuel that is produced from the
electroreduction may include at least one of: formic acid,
n-propanol and acetate.
[0045] In some embodiments, water may act as a proton or hydroxide
donor during the electroreduction.
[0046] In some embodiments, the cathode may include a liquid
comprising the graphene powder, a solvent and a binding polymer,
the liquid deposited on a gas diffusion layer.
[0047] In some embodiments, the carbon particles may be graphene
nanoflakes.
[0048] In some embodiments, the method further includes collecting
the fuel following the electroreduction.
[0049] Another broad aspect is an electrolytic cell for producing a
fuel by electro-reducing carbon dioxide. The cell includes a carbon
dioxide inlet; a proton or hydroxide donor inlet; a cathode
connected to the carbon dioxide inlet, wherein the cathode
comprises a gas diffusion layer, a binding polymer and carbon
powder, the carbon powder comprising carbon particles with metallic
particles deposited on the carbon particles, wherein the binding
polymer binds the carbon powder to the gas diffusion layer; an
anode comprising a gas diffusion layer, the anode connected to the
proton or hydroxide donor inlet; a first current collector plate
that is positioned closer to the cathode than to the anode; a
second current collector plate that is positioned closer to the
anode than to the cathode; a first separator plate in proximity
with the first current collector plate; a second separator plate in
proximity with the second current collector plate; an ion exchange
medium between the cathode and the anode; a by-product outlet in
communication with the anode; and a fuel outlet in communication
with the cathode.
[0050] In some embodiments, the proton or hydroxide donor may be
water or an organic solvent.
[0051] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; iridium dihydride; iron carbonyl; one or more
manganese complexes; one or more rhodium complexes; one or more
iron complexes; one or more copper complexes; bismuth; one or more
bismuth complexes; cobalt oxide; one or more ruthenium complexes;
one or more rhenium complexes; one or more osmium complexes; lead;
lead oxide; mercury; and an alloy of one or more metals selected
from copper, tin, bismuth, lead, mercury and iron.
[0052] In some embodiments, the metallic particles of the graphene
powder may include at least one of copper; copper oxide; copper
sulfide; tin; tin sulfide; tin oxide; iridium dihydride; iron
carbonyl; one or more manganese complexes; one or more rhodium
complexes; one or more copper complexes; bismuth; one or more
bismuth complexes; cobalt oxide; one or more ruthenium complexes;
one or more rhenium complexes; one or more osmium complexes; lead;
lead oxide; mercury; and an alloy of one or more metals selected
from copper, tin, bismuth, lead, mercury and iron.
[0053] In some embodiments, the metallic particles may include at
least one of copper; copper oxide; copper sulfide; tin; tin
sulfide; tin oxide; and alloy of copper and tin.
[0054] In some embodiments, the carbon powder may be graphene
power, and the carbon particles may be graphene nanoflakes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] The invention will be better understood by way of the
following detailed description of embodiments of the invention with
reference to the appended drawings, in which:
[0056] FIG. 1 are images taken by a TEM micrograph of Cu-GNF2 with
a scale of 200 nm (left) and 5 nm (right);
[0057] FIG. 2 is a graph of an EDS spectrum on area containing
copper nanoparticles and area containing only GNFs;
[0058] FIG. 3 is a graph of an XPS Survey for Cu-GNF2;
[0059] FIG. 4 are graphs of high-resolution XPS peaks of Carbon
C1s, Nitrogen N1s, Oxygen O1s and Copper Cu2p for Cu-GNF2;
[0060] FIG. 5 is an X-ray diffractogram of Cu-GNF3;
[0061] FIG. 6 is a graph of LSVs of Cu-GNF2 under N2 bubbling and
CO2 bubbling;
[0062] FIG. 7 is a graph of faradaic efficiency toward formate and
n-propanol at -0.6 and -0.9 V vs RHE for the Cu-GNFs;
[0063] FIG. 8 is a graph of faradaic efficiency toward formate and
n-propanol at -0.6, -0.7, -0.8 and -0.9 V vs RHE for Cu-GNF30;
[0064] FIG. 9 is a drawing of the molecular structure of graphitic
material showing exemplary different nitrogen species found in
graphitic material by X-Ray Photoelectron Spectroscopy;
[0065] FIG. 10 is a graph showing the Faradaic Efficiency of iron
decorated graphene nanoflakes, prepared using an exemplary thermal
plasma technique;
[0066] FIG. 11 is a graph showing the Faradaic Efficiency of copper
decorated graphene nanoflakes, prepared using an exemplary thermal
plasma technique;
[0067] FIG. 12 is a graph showing the Faradaic Efficiency of copper
decorated commercial graphene, prepared using an exemplary wet
chemistry method;
[0068] FIG. 13 is a graph showing the Faradaic Efficiency of tin
decorated graphene nanoflakes, prepared using an exemplary wet
chemistry method;
[0069] FIG. 14 is a graph showing the Faradaic Efficiency of bare
graphene nanoflakes;
[0070] FIG. 15 is a drawing of a cross-sectional rendering of an
exemplary electrolyser cell; and
[0071] FIG. 16 is a drawing of an exemplary system for
electro-reducing carbon dioxide.
DETAILED DESCRIPTION
[0072] The present disclosure relates to carbon powder composed of
carbon particles with metallic particles deposited thereon that act
as a catalyst in the electroreduction of carbon dioxide into a
fuel, such as formic acid, acetate and/or n-propanol. Exemplary
carbon particles may be graphene nanoflakes. Exemplary metallic
particles may be copper, tin, copper sulfate, an alloy of copper
and tin, or a metal, metal oxide, metal sulfide or metal alloy that
can be used as a catalyst to produce formic acid from carbon
dioxide as described herein. The disclosure also relates to an
electroreduction cell, where the cathode of the cell includes the
carbon powder as described herein.
[0073] The carbon powder are small particles (e.g. micro or nano
particles) that can then be bound to, e.g., a porous substrate, to
form an electrode used, e.g., for the electroreduction of carbon
dioxide.
[0074] The disclosure further relates to graphene powder composed
of graphene nanoflakes with metal particle deposits as explained
herein. Moreover, an electrode may include the graphene powder.
[0075] The disclosure further relates to a method of manufacturing
carbon particles with metallic particles deposited thereon through
pyrolysis as explained herein.
[0076] As such, the carbon powder can be used as a cost-effective,
power-effective, efficient solution to transform carbon dioxide
into a usable fuel, therefore reducing carbon dioxide
emissions.
[0077] The cells and system described herein can be employed or
added to machines, factories or installations that emit carbon
dioxide. After the capture of the emissions and, in some cases, the
isolating of the carbon dioxide, the cells and the system can be
used to convert the carbon dioxide emissions into a fuel that can
be used by the same machines, factories or installations, or stored
and/or transported for later use.
[0078] In some examples, the cells and system can be used as
standalone equipment, where reserves of carbon dioxide (e.g. stored
in liquid, solid or gaseous form) can be provided for
transformation by the cell or system.
Definitions
[0079] Transmission Electron Microscopy (TEM): TEM is a technique
based on the interaction between electrons and the samples to
create a picture, with a resolution down to the atom. An electron
beam is generated and focused on the sample, thin enough to allow
electrons being transmitted. The transmitted electrons are detected
and create the picture based on the difference of thickness of the
sample. The energy of the transmitted being low, the operation is
realized under an ultra-high vacuum (10-7 to 10-9 kPa). The
analyzed sample has to be thin enough, at most hundreds of
nanometers thick, without any volatile products degassing in the
chamber and support the ultra-high vacuum. The sample is generally
mounted on a 5 mm copper grid covered by an ultra-thin carbon
film.
[0080] X-Ray Photoelectron Spectroscopy (XPS): XPS is a technique
to determine the elemental composition at the surface of a sample.
Samples are placed under ultra-high vacuum (10-9 to 10-10 kPa) and
are irradiated by monochromatic x-rays. Under the energy of the
x-ray photons, electrons from the core shells of surface atoms are
extracted. These photoelectrons are typically coming from the first
10 nanometers of the sample thickness, but most of them are
actually extracted from the first atomic layers. The binding energy
of these photoelectrons is then measured to establish a spectrum of
energies. The peak position is specific for each element while the
peak intensity is used to calculate the atomic percentage of the
elements. Closer analysis of the peaks can also help determine the
local bonding of one element.
[0081] Neutron Activation Analysis (NAA): NAA is used to determine
the bulk composition of a sample. Samples are irradiated with
thermal neutrons, generated by enriched uranium in a water-cooled
nuclear reactor. A small fraction of the atoms in the sample
capture a thermal neutron to generate an unstable isotope, or
radioisotope, which will decay rapidly. The decay of the
radioisotope to a ground state emits specific gamma rays, whose
energy depends on the nature of the element. The intensity of the
peaks also enables the determination of the bulk composition in
weight percentage. Some elements are not detected at all by NAA for
several reasons (H, He, Li, Be, B, C, N, O). The samples do not
need any particular preparation and can be activated in solid or
liquid state.
[0082] X-Ray Diffraction (XRD): X-rays can be diffracted by the
crystalline structure of a sample when their wavelength is close to
the interspacing of the crystalline planes. This property is used
to determine the unknown crystalline structure of a sample by
analyzing its diffraction scan. Monochromatic x-rays are focused
and irradiate the sample at a varying angle. A constructive
interference is created, and thus detected, with specific
conditions described by Bragg's law:
n.lamda.=2d sin .theta.
where .lamda. is the wavelength of the incident x-ray beam, d Is
the interspacing of the crystalline planes and .theta. is the
diffraction angle. The sample can be analyzed under the form of a
powder, packed to provide a flat surface to the x-ray beam.
[0083] Gas Chromatography (GC): GC is used to determine the
composition of a gas in volume percentage. A sample of the analyzed
gas is injected in a column containing a solid stationary phase and
flushed by a carrier gas, typically an inert gas such as helium.
The different components of the analyzed gas have different rates
of progression due to molecular interaction with the stationary
phase, and thus come out of the column at different times. For
gases overlapping at the exit, it is possible to vary the carrier
gas flow rate, column length, or temperature of the operation. Many
different detectors can be used at the exit of the column to
quantify the different gaseous components, including flame
ionization or thermal conductivity detectors. The GC is usually
calibrated with gases of interest which have a known
concentration.
[0084] Nuclear Magnetic Resonance (NMR): NMR is a technique to
determine molecular structures which can be used for
quantification. The molecules are placed in an intense magnetic
field, where the protons nuclei absorb the radiofrequencies (RF).
The RF frequency is shifted during the absorption, and this shift
is dependent on the chemical environment of the protons. The
chemical environment includes the molecules themselves as well as
the solvent used for the analysis. The measurement of the
difference between the initial and shifted frequency provides the
identification of the molecules, while the area under the peaks
gives information on the quantification. For quantification
purposes, calibration curves are produced from products with known
concentration.
[0085] In the present application, by "carbon particles", it is
meant small graphene carbon structures, such as graphene
nanoflakes, carbon nanotubes, black carbon, graphene oxide, reduced
graphene oxide, etc.
[0086] In the present application, by "carbon powder", it is meant
a powder that includes carbon particles with metallic particles
deposited thereon.
[0087] In the pre sent application, by "graphene powder", it is
meant a carbon powder with metallic particles deposited thereon,
where the carbon particles are or include graphene nanoflakes.
EXPERIMENTAL METHODS
[0088] The present exemplary method relates to the preparation and
testing of an exemplary catalyst of graphene powder that is
composed of graphene nanoflakes with metal particles deposited
thereon. The exemplary graphene powder may be used for the
electroreduction of carbon dioxide into a fuel, such as formic
acid. However, it will be understood that the graphene powder may
have other applications that acting as a catalyst in the
electroreduction of carbon dioxide such that a fuel (e.g. formic
acid) be produced.
[0089] Even though the present study is directed to graphene
nanoflakes, it will be understood that, in some examples, other
carbon particles (e.g. carbon nanotubes, graphene oxide, etc.) with
metal particles deposited thereon may also be used to
electro-reduce carbon dioxide to produce a fuel without departing
from the present teachings.
Experiment 1
[0090] Catalyst Preparation
[0091] The exemplary catalysts consist of copper nanoparticles
dispersed on stacked-graphene nanoparticles, the graphene
nanoflakes (GNFs) and are referred to as Cu-GNFs. GNFs are grown by
thermal plasma method, following Pristavita's procedure [22].
Methane is injected in an ICP torch where molecules are decomposed
into carbon and hydrogen atoms by the argon thermal plasma (10,000
K). The ICP torch is connected to a water-cooled axisymmetric
reactor with conical expansion. The well controlled flow lines of
the plasma allow the homogeneous nucleation and growth of the
well-crystallized GNFs downstream of the ICP torch in a temperature
window from 3,700 to 4,900 K [23]. The GNFs are then deposited on
the walls and bottom plate of the reactor due to the thermophoretic
forces. A small flow of nitrogen (0.1 slpm) is also added during
the growth procedure along with methane, leading to a nitrogen
content up to 2 at % on the surface of the GNFs. The argon thermal
plasma is shut down and the nanoparticles are collected from the
reactor. The GNFs consist of 5 to 20 layers of stacked graphene
typically measuring 100 by 100 nm.
[0092] The addition of the copper nanoparticles to the GNFs is done
by wet chemistry method. GNFs are dispersed in a 1:1 mixture of
water and ethanol. Various amounts of copper sulfate salt
(CuSO.sub.4) purchased from Sigma Aldrich .COPYRGT. is dissolved in
the water-ethanol solvent. The amount of salt added to the mixture
is calculated for the final catalyst to contain copper amount from
20 to 50 wt %. The mixture is stirred until complete dissolution of
the copper sulfate salt, and then dried in an oven at 80.degree. C.
for 24 h. The dried solid is collected before undergoing in a
pyrolysis step. The pyrolysis step is performed in a tubular quartz
furnace at 700.degree. C. for an hour under a flow of 542 sccm of
argon. The mass of the catalysts is controlled before and after
pyrolysis. It can be noted that the GNFs do not go under
decomposition at the temperature used during the pyrolysis due to
their good crystallinity. The experimental conditions of the
different batches are summarized in Table 1.
TABLE-US-00001 TABLE 1 Experimental conditions of the wet chemistry
method for catalyst synthesis. 1:1 Expected mass Catalyst Catalyst
Name of GNFs CuSO.sub.4 Water-Ethanol content of Cu mass before
mass after sample mass (mg) mass (mg) volume (mL) in catalyst (wt
%) pyrolysis (mg) pyrolysis (mg) Cu-GNF1 50 31 100 20 83.3 54.5
Cu-GNF2 50 54 100 30 115.0 70.5 Cu-GNF3 50 84 100 40 141.8 73.6
Cu-GNF4 50 126 100 50 182.3 84.4
[0093] Physical Characterization
[0094] The catalysts are also analyzed in terms of their structure
and composition. Transmission Electron Microscopy (TEM) is used for
observing the catalysts at an atomic level and especially the
copper nanoparticles for size distribution determination. The TEM
is a FEI Tecnai G2 F20 200 kV Cryo-STEM. The overall copper content
in the different catalysts is determined by Neutron Activation
Analysis (NAA) on the SLOWPOKE nuclear reactor. The SLOWPOKE
nuclear reactor is coupled with an Ortec GEM30185-P germanium
semiconductor gamma-ray detector, an Ortec DSPEC Pro.TM.
multichannel analyzer, a Sartorius precision balance and the EPAA
analysis software [24]. The elemental composition of the samples is
analyzed by X-ray Photoelectron Spectroscopy (XPS) on a Scientific
K-Alpha XPS from Thermo Scientific. An aluminum x-ray source is
used on 400 .mu.m size area. X-Ray Diffraction (XRD) is employed to
determine the crystalline phase of the copper nanoparticles in the
samples and performed on a Brucker D8 Discovery X-Ray
Diffractometer with a VANTEC detector, and having a copper K.alpha.
source.
[0095] Electrochemical Characterization
[0096] The electrochemical characterization of the Cu-GNFs
catalysts is realized in a custom made three-electrode set-up with
different configurations for gas and electrolyte sampling. The
counter electrode is a platinum wire separated to the other two
electrodes by a Nafion membrane, to avoid the oxidation of the
products generated at the cathode. The reference electrode is
silver/silver chloride (Ag/AgCl) containing saturated solution. The
working electrode is a 1 cm by 1 cm carbon cloth piece covered by 1
mgcm.sup.-2 catalyst. Nitrogen and carbon dioxide gases are bubbled
through a sintered quartz sparger in the electrolyte, a 0.1 M
potassium bicarbonate (KHCO.sub.3) solution. The electrolyte is
prepared by dissolving the KHCO.sub.3 salt purchased at Sigma
Aldrich O into deionized water. Potentials are converted from
Ag/AgCl to the reverse hydrogen electrode (RHE) using Nernst
equation (eq. 1):
E.sub.RHE=E.sub.Ag/AgCl+E.sub.Ag/AgCl.sup.0+0.059pH (eq. 1)
where E.sub./AgCl.sup.0 is the standard potential for Ag/AgCl
electrode and is equal to 0.1976 V. The pH of the potassium
bicarbonate solution is 6.8.
[0097] The catalysts are dispersed into an ink prior deposition on
the working electrode. The catalyst ink consists of 5 mg of
catalyst, 1 mL of ethanol and 4 .mu.L Nafion 5 wt % solution
purchased at Sigma Aldrich O. The ink is sonicated before series of
4 deposition of 50 .mu.L, for a total volume of 200 .mu.L, is
deposited on the electrodes. The electrodes are dried for 24 h in
an oven at 80.degree. C.
[0098] Linear Sweep Voltammetry (LSV) and Chrono-Amperometry (CA)
are used to characterize the catalysts. LSV consists in recording
the current density for a range of potential, while CA consist in
holding a potential for a certain duration and measuring the
current density. For both electrochemical analysis, the catalysts
go through a conditioning step under nitrogen bubbling in order to
remove impurities on the catalyst surface. The conditioning step
consists of repeated sweeps from 0.0 to -1.4 V vs RHE at a scan
rate of 100 mVs.sup.-1 until there is no variation from a
voltammogram to the next one. LSVs are then recorded in
electrolytes saturated with nitrogen and then carbon dioxide from
0.0 to -1.4 V vs RHE at a scan rate of 20 mVs.sup.-1. Carbon
dioxide is bubbled for 30 min in order to reach the saturation
concentration in the electrolyte, estimated at 2.66.times.10.sup.-2
molkg-1, using Henry's law (eq. 2) with Sechenov equation (eq. 3)
[25].
e.sup.p=e.sup.k.sup.HC (eq. 2)
where p is the partial pressure of the gas, k.sub.H is the Henry's
constant at 20.degree. C. and C is the gas concentration in pure
water.
ln ( z B * z B ) = k s y y ( eq . 3 ) ##EQU00001##
where z.sub.B* and z.sub.B correspond to either the concentration,
molarity or molality among other parameters of CO.sub.2 in pure
water and electrolyte, respectively.
[0099] CA is performed by holding potentials of -0.6 and -0.9 V vs
RHE for 2 hours whereas the current density is recorded. Gas and
liquid products are generated during the CA and are quantified by
Nuclear Magnetic Resonance (NMR) and Gas Chromatography (GC). NMR
is performed on a Bruker Advance III HD 600 MHz machine. NMR
samples were prepared by mixing 500 .mu.L of liquid analyte, 50
.mu.L of a 12 mM DMSO solution in a 0.1 M KHCO.sub.3 solution and
100 .mu.L of D.sub.2O. A preliminary calibration is performed on
the following five products: formate, methanol, acetate, ethanol
and n-propanol. A calibration is done on hydrogen, methane, carbon
monoxide, carbon dioxide, ethylene and ethene standard gases.
[0100] The quantification of the gaseous and liquids products
generated during the CO.sub.2 electroreduction is used to calculate
the Faradaic Efficiency (FE) shown in eq. 4.
F E i = n i z i F It ( eq . 4 ) ##EQU00002##
where n.sub.i is the number of moles of the product i, z.sub.i the
number of electrons necessary to produce one molecule of the
product i, F the Faraday constant, I the current passed through the
working electrode and t the duration of the CA.
[0101] Results and Discussion
[0102] Structure and Composition of the Cu-GNFs
[0103] The Cu-GNFs are analysed by TEM, where both GNFs and copper
nanoparticles are observed, appearing as the darkest particles on
FIG. 1. The flake shape of the stacked graphene is typical for
these nanoparticles. Copper nanoparticles seem to have a wide size
distribution, from a few tens of nanometers to several hundreds of
nanometers for the largest particles. They are not homogenously
dispersed on the GNFs, with areas containing more copper than
others. The composition of areas containing copper and areas
containing only the GNFs is analyzed by Energy Dispersive
Spectrometry (EDS). The analysis reveals the presence of Carbon,
Oxygen, Copper and Sulfur. Areas containing only GNFs are mostly
composed of carbon, with traces of copper, due to the TEM support
grid, made in copper and covered by a thin layer of carbon. The
copper nanoparticles are thus composed of copper and sulfur,
suggesting the presence of copper sulfide.
[0104] The elemental composition of the surface of the Cu-GNFs
reveal the presence of carbon, nitrogen, oxygen and copper as seen
on the XPS survey from FIG. 1. High-resolution peaks of the
different elements are recorded and analyzed to determine the
chemical state of the elements through deconvolution (FIG. 2).
Carbon is mostly in sp2 orbital configuration, corresponding to the
graphitic form of carbon, with small amounts of carbon bonded to
nitrogen and oxygen. Nitrogen is found is small amounts under the
four different forms typically found in graphitic structure:
pyridinic, pyrrolic, quaternary and oxidized nitrogen. Additional
information of these chemical states for nitrogen are provided in
the Annexe. Nitrogen is coming from the small flow of nitrogen
added during the GNF growth in the thermal plasma reactor. It has
been proved in the literature that nitrogen in its pyridinic form
promotes the CO2 reduction [26]. Oxygen is present in the samples
for several reasons: contamination in the thermal plasma reactor
during the GNFs growth, contact of the powder with air, the wet
chemistry method and the oxidation of the copper nanoparticles. It
can also be noted that Cu-GNF1 contains some adsorbed humidity on
its surface.
[0105] Sulfur was detected by EDS during the TEM analysis but no
signal is detected by XPS at the typical binding energy of 162 eV
for sulfur S 2p. XPS is a characterization technique analyzing the
extreme surface of samples. The absence of sulfur detected by XPS
can mainly be explained by the presence of sulfur in the core of
the nanoparticles. The copper nanoparticles are synthesized from
CuSO.sub.4. During the pyrolysis step, while the SO.sub.4 groups
are evaporated by the temperature of 700.degree. C., some sulfur
may be trapped inside the core of the nanoparticles to form copper
sulfide.
[0106] The actual copper content in the bulk of the samples is
determined by NAA. The amount of copper in the catalysts is 17.6,
26.6, 41.4 and 52.6 for Cu-GNF1, 2, 3 and 4 respectively. These
values show that the synthesis process delivers the expected amount
of copper with an error between -12% and +5%.
TABLE-US-00002 Element peak Cu-GNF1 Cu-GNF2 Cu-GNF3 Cu-GNF4 C 1 s
94.6 95.0 96.3 86.3 N 1 s 0.7 1.6 0.7 0.2 O 1 s 4.1 2.5 2.3 9.5 Cu
2p 0.6 0.9 0.7 4.0
[0107] XPS is used to determine the elemental composition at the
surface of the Cu-GNF catalysts. Copper in the catalyst samples
have two chemical states which are located at 954.0 and 952.0 eV.
The peak located at 954.0 eV corresponds without any doubt to
copper oxide CuO due to its peak location and satellite shape [27].
The identification of the chemical state from the peak at 952.0 eV
can be more difficult, because metallic copper, copper oxide
Cu.sub.2O and copper sulfide Cu.sub.2S present very similar signal
in XPS. However, the presence of sulfur in the core of the
nanoparticles, the analysis of the elemental composition (Table 2)
and the relative amounts (Table 3) from copper and oxygen tend to
support the presence of metallic copper in the samples. It can be
noted that the samples Cu-GNF2 and 3 contain nearly half of the
overall surfacic copper in metallic form while Cu-GNF1 and 4 have
mostly oxidized copper. XPS being a surface analysis, it is
possible that the copper nanoparticles in Cu-GNF2 and 3 have a
thinner oxide layer compared to the ones in Cu-GNF1 and 4.
TABLE-US-00003 TABLE 2 Relative amounts of Carbon, Nitrogen, Oxygen
and Copper states from deconvolution of the high-resolution peaks.
Element peak Cu-GNF1 Cu-GNF2 Cu-GNF3 Cu-GNF4 C 1s 284.4 .+-. 0.1 eV
Carbon sp2 76.8 91.8 89.9 91.3 286.0 .+-. 0.1 eV C--O 3.9 6.4 7.3
7.5 286.9 .+-. 0.1 eV C--N 3.9 1.8 2.7 1.2 288.5 .+-. 0.1 eV
O--C.dbd.O 15.4 0.0 0.0 0.0 N 1s 398.3 .+-. 0.3 eV Pyridinic 14.3
44.4 36.4 22.7 399.6 .+-. 0.2 eV Pyrrolic 21.4 11.1 24.2 45.5 400.9
.+-. 0.3 eV Quaternary 28.6 33.3 27.3 22.7 402.3 .+-. 0.3 eV N--O
35.7 11.1 12.1 9.1 O 1s 529.7 .+-. 0.1 eV Cu--O 14.9 11.2 9.1 44.2
531.2 .+-. 0.1 eV C.dbd.O 23.6 68.7 56.6 43.2 533.0 .+-. 0.2 eV
C--O 14.8 16.5 22.9 10.4 534.4 .+-. 0.1 eV N--O 46.7 3.6 11.4 2.3
535.3 .+-. 0.1 eV OH/H.sub.2O 42.3 0.0 0.0 0.0 Cu 2p 932.4 .+-. 0.1
eV Cu(0)/Cu(I) 19.6 46.9 45.5 13.0 3/2 934.2 .+-. 0.2 eV Cu(II)
80.4 53.1 54.5 87.0 Cu 2p 952.0 .+-. 0.2 eV Cu(0)/Cu(I) 19.8 46.4
43.5 25.6 1/2 954.0 .+-. 0.2 eV Cu(II) 80.2 53.6 56.5 74.4
[0108] The Cu-GNFs are analyzed by XRD to investigate the
crystalline structure of the copper nanoparticles as seen on FIG.
3. Indeed, the previous techniques used (TEM, EDS and XPS) show the
possibility to have metallic copper, copper oxide and/or copper
sulfide in the samples. The typical peaks for the GNFs are observed
on the diffractograms, with a broad peak at 25.degree. and peaks
located at 42.degree., 72.degree. and 88.degree. [16] which are
overlapping with the peaks associated to copper. The most intense
peaks observed on the diffractograms are from metallic copper,
located at 43.degree., 50.degree., 74.degree., and 90.degree. [28].
The least intense peaks include phases of copper oxide and sulfide,
whose relative amounts are depicted in Table 3.
TABLE-US-00004 TABLE 3 Percentage of crystalline phase containing
copper in the Cu-GNF samples. Samples Cu metal (%) Cu.sub.2S (%)
CuO (%) Cu.sub.2O (%) Cu-GNF1 43.1 -- 40.5 16.4 Cu-GNF2 53.6 46.4
-- -- Cu-GNF3 70.4 29.6 -- -- Cu-GNF4 88.3 -- 11.7 --
[0109] It can be noted that the samples Cu-GNF2 and 3 contain
copper sulfide while Cu-GNF1 and 4 contain copper oxide while
metallic copper is present in all the samples, with increasing
percentage. Comparing with XPS results, the samples containing
solely copper sulfide also contained the lowest amount of oxygen,
and the lowest amount of copper bonded to oxygen. The presence of
copper oxide by XPS on samples Cu-GNF2 and 3 which was not detected
by XRD can be explained by a thin and amorphous oxide layer on
these samples. XRD also show an increasing amount of metallic
copper in the samples synthesized with increasing amount of copper
sulfate. This analysis suggests that changing the amount of copper
sulfate while keeping the other synthesis parameters constant has a
great impact on the composition of the samples, and possibly on the
performance of the catalysts.
[0110] Electrochemical Characterization of the Catalysts
[0111] The Cu-GNF samples are tested through the electroreduction
of CO.sub.2 by linear sweep voltammetry (LSV) first, under nitrogen
and CO.sub.2 bubbling, as seen on FIG. 6. The onset potential and
current density for each catalyst is reported in Table 4. The onset
potential is typically defined as the potential where the corrected
current density is no longer null. In this case, the onset
potential is defined as the potential where the current density is
reaching a value more negative with CO.sub.2 bubbling compared to
nitrogen bubbling. The current density reported in Table 4 is
measured at -0.6 and -0.9 V vs RHE, potential at which
chronoamperometry (CA) is ran.
[0112] The catalysts all have a higher current density under the
CO.sub.2 bubbling compared to nitrogen bubbling, suggesting an
activity toward the CO.sub.2 reduction. The analysis of the LSVs
provides a screening technique to compare the electrochemical
performance of the different catalysts, and thus selecting the best
one. Cu-GNF2 has the less negative onset potential among the
catalysts, with the highest values of current density at -0.6 and
-0.9 V vs RHE.
TABLE-US-00005 TABLE 4 Onset potential and Current density values
from LSVs at -0.6 and -0.9 V vs RHE for the catalysts. j (mA
cm.sup.-2) from LSV Onset potential @ -0.6 V @ -0.9 V Catalyst (V
vs RHE) vs RHE vs RHE Cu-GNF1 -0.44 -5.5 -14.6 Cu-GNF2 -0.40 -5.4
-15.9 Cu-GNF3 -0.53 -3.1 -9.4 Cu-GNF4 -0.48 -5.1 -12.9
[0113] Each catalyst undergoes CA for the two potentials of -0.6
and -0.9 V vs RHE during two hours. The liquid products are
identified and quantified by NMR. Among the different products
tested, formate and n-propanol were the major products detected,
with a few traces of the other products, close to the detection
limits. Due to the low amount of these products, they are not
counted for the calculation of the faradaic efficiency, represented
on FIG. 7 for the different catalysts. In all of the conditions,
formate is generated with more than 99% selectivity among liquid
products, while Cu-GNF2 exhibits the best performance in terms of
faradaic efficiency. The efficiency is reaching up to 40% toward
formate at the potential of -0.6 V vs RHE.
[0114] It appears that increasing the overall amount of copper in
the catalysts is not linked to an improvement in the
electrocatalytic activity toward the CO.sub.2 reduction. Similarly,
the increasing amount of metallic copper does not have any
correlation with the catalyst's performance. Cu-GNF2 is the
catalyst containing the highest amount of copper sulfide.
Literature suggests that copper nanoparticles doped with sulfur are
more selective toward formate generation [29], [30].
[0115] Cu-GNF2 is studied in more details due to its better
performance compared to the other samples. CA is performed at -0.6,
-0.7, -0.8 and -0.9 V vs RHE in order to find the potential where
both faradaic efficiency and current density are maximized, as seen
on FIG. 8. The highest efficiency toward formate generation is
observed at -0.6 V vs RHE, representing a low overpotential of 0.38
V compared to the redox potential of the couple CO.sub.2/HCOO--
(-0.225 V). Hydrogen, CO.sub.2 and air are detected as gases, but
H.sub.2 is the only gas produced through electrochemistry and
counted for the calculation of the Faradaic Efficiency (FE).
Hydrogen formation is a competitive process to the CO.sub.2
reduction and has to be minimized to favor formate generation. The
overall Faradaic efficiency varies between 91% at -0.9V vs RHE and
96% at -0.6 V vs RHE. The FE is lower than 100% because of traces
of products that are not counted in the calculation as well as
electrical losses in the set-up.
[0116] Conclusion
[0117] Catalysts made of metallic copper and copper sulphide
nanoparticles deposited on graphene nanoflakes are produced with an
easy and scalable wet-chemistry method followed by pyrolysis step.
One of the catalysts, Cu-GNF2, offers interesting electrochemical
properties, with low overpotential, high current densities and
faradaic efficiencies going up to 40% toward formate production.
This specific catalyst is characterized by a high amount of copper
sulphide amount in its composition. Industrial CO.sub.2
electrolyzer requires catalyst with higher current densities and
lower energy consumption, which can be achieved by several
strategies. These strategies include the optimization of the
catalyst in a real electrolyzer instead of a three-electrode set-up
with parameters such as catalyst loading, pressure of the gas,
temperature of the electrolyte, the addition of ionic liquids to
the catalysts.
Experiment 2
[0118] The second exemplary relates to a graphene powder that is
composed of graphene nanoflakes with metal particles deposited
thereon, where the metal particles are composed at least of copper,
iron or tin.
[0119] The catalysts prepared in this exemplary study contain
either copper, iron or tin metal, added to a carbon support, the
graphene nanoflakes made in the laboratory or commercial graphene,
with varying metal weight content. The catalysts are prepared
through wet chemistry method, as described herein, and thermal
plasma technique (see J.-L. Meunier, U. Legrand, D. Berk
"Decoration of graphene nanoflakes with metal nanoparticles in a
thermal plasma jet environment" ROI 2018-021 or U. Legrand, J.-L.
Meunier, D. Berk, Iron functionalization on graphene nanoflakes
using thermal plasma for catalyst applications, Applied Catalysis
A, 528, 36-43, 2016). The electrochemical characterization and
determination of the faradaic efficiency is performed as detailed
herein.
TABLE-US-00006 TABLE 6 Experimental conditions for the different
metal - graphene support catalysts. Preparation Catalyst name
Technique Metal content Notes Fe.sub.p-GNF Thermal plasma 10 to 40
wt % -- Cu.sub.p-GNF Thermal Plasma 10 to 40 wt % -- Cu-GNF Wet
chemistry 20 to 50 wt % From initial report Cu-G Wet chemistry 20
to 40 wt % G = commercial graphene Sn-GNF Wet chemistry 10 to 40 wt
% -- GNF No preparation No metal Bare graphene powder used to
prepare other catalysts
[0120] Results:
[0121] The results are presented in FIGS. 10 to 14, illustrating
the faradaic efficiency of different electrodes comprising graphene
powder composed of graphene nanoflakes with metal particles
deposited thereon.
[0122] Discussion:
[0123] Bare graphene nanoflakes have been tested as catalysts and
appear to have an overall faradaic efficiency of about 17% but with
low current density (see FIG. 14). The addition of metal
nanoparticles on the surface of the GNFs increases both faradaic
efficiency and current density, in exception of iron.
[0124] The nature of the metal has an important influence on the
overall performance of the catalysts. It appears that tin is
related to a high faradaic efficiency with high current density and
high selectivity. On the contrary, iron is relatively poorly active
with respect to CO.sub.2 electroreduction, with a faradaic
efficiency lower than 10%.
[0125] The method synthesis the catalyst may also impact the
overall performance of the electrocatalytic CO.sub.2 reduction. For
instance, catalysts containing copper nanoparticles prepared using
a wet chemistry method have been observed to show a higher faradaic
efficiency, current density and selectivity toward formic acid
generation compared to the ones prepared through thermal plasma
technique. This can be explained by a better control in the metal
concentration with the wet chemistry method. Indeed, the addition
of metal nanoparticles with the thermal plasma technique tends to
provide lower metal concentration than expected, probably due to a
higher metal loss rate during the process.
[0126] Commercial graphene has been tested as a carbon support in
replacement of graphene nanoflakes. Both have very similar
structures due to similar reactors used for the carbon
nanoparticles synthesis. The main difference between these
structures remain in the size of the nanoparticles (commercial
graphene nanoparticles larger than GNFs) and in the composition at
their surface. Indeed, a small amount of 2% of nitrogen is present
on the surface of the GNFs. It can be seen that GNFs as carbon
support offer higher faradaic efficiency, higher selectivity and
lower current density for same copper concentration compared to the
commercial graphene.
[0127] Other Metal Particles:
[0128] Even though Experiments 1 and 2 pertained to studying the
effects of graphene with metal particle deposits, where the metal
particle is selected from copper, tin and iron, it will be
understood that other metals, metal oxides, metal sulfides, and
metal alloys may be used without departing from the present
teachings.
[0129] Namely, metals, metal oxides, metal sulfides, and metal
alloys that have been known to act as a catalyst to transform
carbon dioxide to formic acid may be used. Examples may include but
not limited to, for instance, copper, copper oxide, copper sulfide,
tin, tin sulfide, tin oxide, iridium dihydride, iron carbonyl, one
or more manganese complexes, one or more rhodium complexes, one or
more iron complexes, one or more copper complexes, bismuth, one or
more bismuth complexes, cobalt oxide, one or more ruthenium
complexes, one or more rhenium complexes, one or more osmium
complexes, lead, lead oxide, mercury, and or an alloy of one or
more metals selected from copper, tin, bismuth, lead, mercury and
iron.
[0130] Exemplary System for Performing Electroreduction of Carbon
Dioxide:
[0131] Reference is now made to FIG. 15, illustrating an exemplary
electrolysis cell 100 for performing the electroreduction of carbon
dioxide into a fuel.
[0132] The exemplary cell 100 has two current collector plates 1,
two separator plates 2, a sealant on each end (e.g. sealant gasket
3), an ion exchange medium (e.g. proton or anion exchange membrane
4), one or more gas diffusion layers 5, a first catalyst layer 6
laid on a first gas diffusion layer 5 that forms part of the
cathode (5 and 6) and a second catalyst layer 7 laid on a second
gas diffusion layer 5 that forms part of the anode (5 and 7).
[0133] The cell 100 has a carbon dioxide inlet 101 that is in
communication with the cathode. The carbon dioxide inlet 101 may
output carbon dioxide into a gas diffusion layer 5 that diffuses
gas across the first catalyst layer 6.
[0134] The cell 100 has an ion donor inlet 102. In some examples,
the proton or hydroxide donor may be water, but it will be
understood that other substances may be used as a proton or ion
donor (e.g. H.sub.2, hydroxide salts). The ion donor inlet 102 is
in communication with the anode. In some examples, the ion donor
inlet 102 may lead to the second gas diffusion layer 5 that is in
contact with the second catalyst layer 7.
[0135] The cell 100 also has a fuel outlet 103 which is directly or
indirectly in communication with the cathode. The fuel (e.g.
hydrogen, formic acid, acetate, n-propanol, etc.) is evacuated by
the fuel outlet 103 once the fuel is produced. In some examples,
the fuel travels through the gas diffusion layer 5 before reaching
the fuel outlet 103.
[0136] The cell 100 has a by-product outlet 104 that is directly or
indirectly in communication with the anode. The by-product outlet
104 is for evacuating the by-products of the reaction taking place
with respect to the anode. Examples of by-products may be water and
oxygen. In some examples, the by-products may travel through the
gas diffusion layer 5 before reaching the by-product outlet
104.
[0137] In some examples, on the cathode side, the catalyst of
metal-graphene nanoflakes (M-GNFs) is dispersed into an ink (e.g.
powder, water/ethanol solvent and binding polymer such as
Nafion.TM.) which is deposited on the gas diffusion layer (GDL) 5
made of porous carbon paper and then dried out.
[0138] In some examples, the gas diffusion layer 5 may be made out
of a porous material other than carbon paper, such as out of porous
stainless steel or titanium. In some examples, a thin protective
layer may be added over the gas diffusion layer 5, such as a thin
protective layer of metal.
[0139] On the anode side, similar procedure is followed with a
catalyst designed to break water molecules into hydrogen protons,
electrons and oxygen. Exemplary catalysts on the anode side may be
a precious metal/metal oxide, pure or dispersed onto a carbon
support (e.g. iridium oxide (IrO.sub.2), nickel, etc.)
[0140] The two GDLs with the catalyst may be hot pressed with an
ion exchange membrane (e.g. polymer membrane 4) between the two. In
some embodiments, a gap may be present between the GDL and the ion
exchange membrane, with electrolyte flowing in this gap. The ion
exchange membrane 4 allows ions to go through while electrically
insulating the anode from the cathode and preventing products to
diffuse between the two electrodes. The ion exchange membrane 4 can
include Nafion.TM., or another proton or ion exchange membrane. The
GDLs 5 with the catalyst layers and the ion exchange membrane 5 may
represent a membrane electrode assembly (MEA).
[0141] The MEA may be pressed between two separator plates 2 and
surrounded by a sealer (e.g. sealing gaskets 3) on both sides. The
separator plates 2 have a flow pattern engraved on their surface in
contact with the MEA for gas and liquid management in the
electrolyser. The sealing gaskets 3 prevent leakage from the
cell.
[0142] The current collector plates 1 deliver electricity to the
electrolyzer cell 100. They allow electrons to go from the anode to
the cathode.
[0143] In one example, at the anode, water, in liquid or vapor
form, is injected at the inlet 102. Water molecules diffuse into
the catalyst layer through the GDL 5 and produce dioxygen gas,
hydrogen protons and electrons. The hydrogen protons migrate from
the anode to the cathode 6 through the ion exchange membrane 4. At
the cathode, pure or diluted CO.sub.2 (preferably pure CO.sub.2)
may be injected in the presence of water, enabling membrane
humidification, electric conduction and liquid product
transportation at the outlet of the electrolyser. The CO.sub.2
molecules diffuse to the catalyst layer and react with hydrogen
protons and electrons to form fuel products (e.g. formic acid,
n-propanol, acetic acid). A side reaction that may be competing
with the CO.sub.2 electroreduction may result in the production of
dihydrogen gas.
[0144] Reference is now made to FIG. 16, illustrating a
three-dimensional rendering of a system 200 for electro-reducing
carbon dioxide.
[0145] The electrolyzer cells 100 are connected in series and
electrically insulated one from each other. The cells are pressed
together between two end plates and form a stack, represented on
FIG. 2 (middle part). The right part of the 3D drawing of FIG. 16
shows CO.sub.2 and water being stored in tanks before being
injected inside the stack. The left part shows a separation unit at
the outlet of the stack. Liquid and gas products may be separated
and stored. CO.sub.2 and water at the outlet of the separation unit
may be recirculated in the electrolyzer. The separation process
unit may consist non-exclusively of a distillation column, gas
separation membranes and compressors to eventually store gases
products.
[0146] Although the invention has been described with reference to
preferred embodiments, it is to be understood that modifications
may be resorted to as will be apparent to those skilled in the art.
Such modifications and variations are to be considered within the
purview and scope of the present invention.
[0147] Representative, non-limiting examples of the present
invention were described above in detail with reference to the
attached drawing. This detailed description is merely intended to
teach a person of skill in the art further details for practicing
preferred aspects of the present teachings and is not intended to
limit the scope of the invention. Furthermore, each of the
additional features and teachings disclosed above and below may be
utilized separately or in conjunction with other features and
teachings.
[0148] Moreover, combinations of features and steps disclosed in
the above detailed description, as well as in the experimental
examples, may not be necessary to practice the invention in the
broadest sense, and are instead taught merely to particularly
describe representative examples of the invention. Furthermore,
various features of the above-described representative examples, as
well as the various independent and dependent claims below, may be
combined in ways that are not specifically and explicitly
enumerated in order to provide additional useful embodiments of the
present teachings.
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