U.S. patent application number 17/251785 was filed with the patent office on 2021-07-08 for gas diffusion electrode for carbon dioxide utilization, method for producing same, and electrolytic cell having a gas diffusion electrode.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Martin Kalmar Hansen, Christian Reller, Kasper Tipsmark Therkildsen.
Application Number | 20210207276 17/251785 |
Document ID | / |
Family ID | 1000005509606 |
Filed Date | 2021-07-08 |
United States Patent
Application |
20210207276 |
Kind Code |
A1 |
Hansen; Martin Kalmar ; et
al. |
July 8, 2021 |
GAS DIFFUSION ELECTRODE FOR CARBON DIOXIDE UTILIZATION, METHOD FOR
PRODUCING SAME, AND ELECTROLYTIC CELL HAVING A GAS DIFFUSION
ELECTRODE
Abstract
A gas diffusion electrode for carbon dioxide utilization,
including a metal substrate and an electrically conductive catalyst
layer, which is applied to the metal substrate and has hydrophilic
pores and/or channels and hydrophobic pores and/or channels,
wherein the catalyst layer includes metal particles and a first
polymeric binding material; and a porous gas diffusion layer
containing the first polymeric binding material is formed on the
surface of the catalyst layer. A method produces a gas diffusion
electrode for CO2 utilization and an electrolytic cell has a
corresponding gas diffusion electrode.
Inventors: |
Hansen; Martin Kalmar;
(Vanlose, DK) ; Reller; Christian; (Minden,
DE) ; Therkildsen; Kasper Tipsmark; (Lille-Skensved,
DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
1000005509606 |
Appl. No.: |
17/251785 |
Filed: |
June 5, 2019 |
PCT Filed: |
June 5, 2019 |
PCT NO: |
PCT/EP2019/064572 |
371 Date: |
December 12, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 11/032 20210101;
C25B 1/00 20130101; C25B 11/095 20210101; C25B 11/075 20210101;
C25B 11/061 20210101 |
International
Class: |
C25B 11/032 20060101
C25B011/032; C25B 11/095 20060101 C25B011/095; C25B 1/00 20060101
C25B001/00; C25B 11/061 20060101 C25B011/061; C25B 11/075 20060101
C25B011/075 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2018 |
DE |
10 2018 210 457.3 |
Claims
1. A gas diffusion electrode for the utilization of carbon dioxide,
comprising: a metallic support, and an electrically conductive
catalyst layer which has been applied to the metallic support and
has hydrophilic pores and/or channels and hydrophobic pores and/or
channels, wherein the catalyst layer comprises metallic particles
and a first polymeric binder material and a porous gas diffusion
layer containing the first polymeric binder material has been
formed on the surface of the catalyst layer.
2. The gas diffusion electrode as claimed in claim 1, wherein the
gas diffusion layer has a porosity of more than 70%.
3. The gas diffusion electrode as claimed in claim 1, wherein a
fluoropolymer is used as first polymeric binder material.
4. The gas diffusion electrode as claimed claim 1, wherein the
thickness of the catalyst layer is in the range from 5 nm to 500
nm.
5. The gas diffusion electrode as claimed in claim 1, wherein the
first polymeric binder material is embedded partly within the pores
and/or channels of the catalyst layer.
6. The gas diffusion electrode as claimed in claim 1, wherein the
differential pressure based on the passage of a fluid medium
through the gas diffusion layer is in the range from 20 mbar to 220
mbar.
7. The gas diffusion electrode as claimed in claim 1, wherein the
hydrostatic pressure based on passage of a fluid medium through the
gas diffusion layer is in the range from 20 mbar to 1000 mbar.
8. The gas diffusion electrode as claimed in claim 1, wherein the
metallic particles are precoated at least in subregions with a
second polymeric binder material.
9. A process for producing a gas diffusion electrode for
utilization of CO.sub.2, comprising: mixing of metallic particles
with a first binder material to form a suspension, applying the
suspension to a metallic support, and introducing the metallic
support loaded with the suspension into a precipitation bath to
form an electrically conductive catalyst layer, wherein a porous
gas diffusion layer containing the first polymeric binder material
is formed on the surface of the catalyst layer within the
precipitation bath.
10. The process as claimed in claim 9, wherein a mixture of water
and isopropanol is used as precipitation bath.
11. An electrolysis cell comprising: a gas diffusion electrode as
claimed in claim 1.
12. The gas diffusion electrode as claimed in claim 6, wherein the
differential pressure based on the passage of a fluid medium
through the gas diffusion layer is in the range from 60 mbar to 200
mbar.
13. The gas diffusion electrode as claimed in claim 7, wherein the
hydrostatic pressure based on passage of a fluid medium through the
gas diffusion layer is in the range from 200 mbar to 1000 mbar.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2019/064572 filed 5 Jun. 2019, and claims the
benefit thereof. The International Application claims the benefit
of German Application No. DE 10 2018 210 457.3 filed 27 Jun. 2018.
All of the applications are incorporated by reference herein in
their entirety.
FIELD OF INVENTION
[0002] The present invention relates to a gas diffusion electrode
for utilization of carbon dioxide and also a process for producing
a gas diffusion electrode. The invention further relates to an
electrolysis system having a corresponding gas diffusion
electrode.
BACKGROUND OF INVENTION
[0003] At present, about 80% of worldwide energy consumption is
covered by the combustion of fossil fuels. About 34000 million
metric tons of the greenhouse gas carbon dioxide (CO.sub.2) are
emitted into the atmosphere via these combustion processes every
year worldwide. The major part of carbon dioxide is disposed of via
this liberation into the atmosphere (in the case of large brown
coal power stations more than 50000 t per day).
[0004] Owing to the increasing scarcity of fossil fuel resources
and the volatile availability of renewable energy sources, research
into the reduction of CO.sub.2 is becoming of ever greater
interest. Here, CO.sub.2 emissions are decreased and the CO.sub.2
could be utilized as inexpensive carbon source.
[0005] The discussion regarding the adverse effects of CO.sub.2 on
the climate has led to reutilization of CO.sub.2 being considered.
However, CO.sub.2 is thermodynamically in a very low position and
can therefore be reduced again to give usable products only with
difficulty.
[0006] A natural degradation of carbon dioxide occurs, for example,
by means of photosynthesis. Here, carbon dioxide is converted into
carbohydrates in a process divided into many substeps over time and
spatially on a molecular level. However, this process cannot
readily be carried over to an industrial scale. A copy of the
natural photosynthesis process using industrial photocatalysis has
hitherto not been sufficiently efficient.
[0007] A further method is the electrochemical reduction of carbon
dioxide. Systematic studies on the electrochemical reduction of
carbon dioxide are still a relatively young field of development.
Only since a few years ago have efforts been made to develop an
electrochemical system which can reduce an acceptable amount of
carbon dioxide.
[0008] Electrolysis systems having gas diffusion electrodes have
now been used to an increased extent for this purpose. These
systems usually consist of a cathode space and an anode space. To
achieve an effective conversion of the CO.sub.2 used, the cathode
is ideally configured as porous gas diffusion electrode. Gas
diffusion electrodes (GDE) are porous electrodes in which liquid,
solid and gaseous phases are present and the electrically
conductive catalyst catalyzes the electrochemical reaction between
the liquid phase and the gaseous phase.
[0009] A typical problem occurring in the case of gas diffusion
electrodes used for CO.sub.2 reduction which are in contact with an
electrolyte (for example KHCO.sub.3, K.sub.2SO.sub.4, KOH or
mixtures thereof) is that of avoiding undesirable secondary
reactions in the electrolyte-side region of the gas diffusion
electrode. Here, the gas diffusion electrode has to ensure
sufficient supply of CO.sub.2 and the respective electrolyte to the
catalytically active sites by means of gas and ion transport.
[0010] Gas diffusion electrodes are frequently produced by means of
a roller calendering process as is also disclosed in U.S. Pat. No.
2,013,010 190 6 A1. Here, the catalytically active metallic
particles used for forming the gas diffusion electrode are mixed
with hydrophobic particles such as PTFE, the resulting mixture is
applied to a metallic support and arranged between two PTFE films
before being calendered. The shear force enables the PTFE to flow
and a network of PTFE binds the catalytically active particles
together. The porosity and to a certain extent also the pore size
can be modified via the compression force and the particle
size.
[0011] However, gas diffusion electrodes produced in this way tend
to have the limiting pore diameter only within the gas diffusion
electrode but not on the surface. The pore size diameter facing the
electrolyte side is comparatively large compared to gas diffusion
electrodes having a gas diffusion layer, so that undesirable
flooding behavior of the pore system is observed. Furthermore, gas
diffusion electrodes having large pore openings or a low
hydrophobicity display strong electrolyte permeation through the
respective gas diffusion electrode. The permeation is controlled by
the electric field gradient, i.e. electroosmosis. This effect leads
to an undesirable decrease in the Faraday efficiency of the gaseous
products CO or ethylene.
SUMMARY OF INVENTION
[0012] It is therefore an object of the invention to provide a
possibility for electrochemical utilization of CO.sub.2 which is
more efficient compared to the prior art.
[0013] This object is achieved according to the invention by the
features of the independent claims. Advantageous embodiments of the
invention are set forth in the dependent claims and the following
description.
[0014] The gas diffusion electrode of the invention is used for the
utilization of carbon dioxide and comprises a metallic support and
an electrically conductive catalyst layer which has been applied to
this metallic support and has hydrophilic pores and/or channels and
hydrophobic pores and/or channels. The catalyst layer comprises
metallic particles and a first polymeric binder material, wherein a
porous gas diffusion layer containing the first polymeric binder
material has been formed on the surface of the catalyst layer.
[0015] The polymeric gas diffusion layer formed on the surface (the
side of the catalyst layer or the gas electrode facing the
electrolyte in an electrolysis cell) of the catalyst layer
represents the reaction zone outside the gas diffusion electrode
which is in contact with the reactants, in particular CO.sub.2 and
the electrolyte.
[0016] The gas diffusion layer here sets the limiting pore diameter
for the total gas diffusion electrode. Both the degree of
hydrophobicity and the pore size of the gas diffusion layer can be
controlled via targeted selection of the binder material used, the
size of the metallic, catalytically active particles and the
parameters in the production process for the gas diffusion
electrode.
[0017] The gas diffusion layer advantageously has a porosity of
more than 70%. The thickness of the gas diffusion layer is
advantageously in the range from 150 .mu.m to 500 .mu.m.
[0018] The thickness of the catalyst layer is advantageously in the
range from 5 nm to 500 nm. The differential pressure based on
passage of a fluid medium through the catalyst layer and also the
hydrostatic pressure based on passage of a fluid medium through the
outer layer can be influenced or set via such a catalyst layer.
[0019] A fluoropolymer is advantageously used as first polymeric
binder material. In particular, from 3% by weight to 15% by weight
of the first polymeric binder material is used. The use of
polyvinylidene fluoride (PVDF) is particularly advantageous here.
This polymer allows formation of the desired outer layer in the
production of the gas diffusion electrode.
[0020] In addition, the first polymeric binder material is
advantageously embedded partly within the pores and/or channels of
the catalyst layer. In this way, a hydrophobic "subnetwork" is
additionally formed within the pores of the catalyst layer, which
increases the hydrophobicity of the catalyst layer and thus the gas
diffusion electrode overall.
[0021] The differential pressure based on passage of a fluid medium
through the gas diffusion layer and also the hydrostatic pressure
based on passage of a fluid medium through the gas diffusion layer
can be influenced or set via such a gas diffusion layer. The
differential pressure based on passage of a fluid medium through
the gas diffusion layer is in the range from 20 mbar to 220 mbar,
in particular in the range from 60 mbar to 200 mbar. The
hydrostatic pressure based on passage of a fluid medium through the
gas diffusion layer is advantageously in the range from 20 mbar to
1000 mbar and in particular in the range from 200 mbar to 1000
mbar.
[0022] The pore size of the catalyst layer is advantageously in the
range from 0.3 .mu.m to 5 .mu.m. The pore size of the catalyst
layer is particularly advantageously in the range from 2 .mu.m to 3
.mu.m. The particle size of the metallic particles is
advantageously in the range from 500 nm to 5 .mu.m and particularly
advantageously in the range from 2 .mu.m to 3 .mu.m.
[0023] The metallic particles are advantageously precoated at least
in subregions with a second polymeric binder material. This
increases the hydrophobicity of the gas diffusion electrode
further. As second polymeric binder material (binder polymer),
advantage is given to using PTFE (polytetrafluoroethylene). As
metallic particles, advantage is given to using silver particles.
The use of copper particles or other catalytically active particles
is also possible. The metallic particles used are advantageously
coated at least in subregions with the first polymeric binder
material.
[0024] The metallic support is advantageously configured as a
metallic gauze (or a corresponding sheet-like structure made of
wire). Here, the material of the support is advantageously matched
to the metallic particles used. A silver gauze is advantageously
used as metallic support.
[0025] The gas diffusion electrode is particularly advantageously
made by means of an extraction process. This process makes growth
of the desired thin gas diffusion layer on the surface of the
catalyst layer of the gas diffusion electrode possible.
[0026] The process of the invention serves to produce a gas
diffusion electrode for utilization of CO.sub.2. The process
comprises mixing of metallic particles with a first binder material
to form a suspension, application of the suspension to a metallic
support and introduction of the metallic support loaded with the
suspension into a precipitation bath to form an electrically
conductive catalyst layer. A porous gas diffusion layer containing
the first polymeric binder material is formed on the surface of the
catalyst layer within the precipitation bath.
[0027] The above-described process is an extraction process
("inversion casting" process, phase inversion). Manufacture of the
gas diffusion electrode by means of this process makes it possible
for a thin gas diffusion layer whose pore diameter is limiting for
the total gas diffusion electrode to be produced on the surface of
the catalyst layer. Here, the first binder material, the size of
the metallic, catalytically active particles and the parameters in
the production process for the gas diffusion electrode influence
the degree of hydrophobicity and also the pore size of the gas
diffusion layer.
[0028] Furthermore, an intensive connection between the metallic
particles and the binder materials used is achieved by means of the
extraction process, as a result of which the mechanical stability
of the gas diffusion electrode is improved compared to conventional
gas diffusion electrodes.
[0029] The production of "tailored" gas diffusion layers on the
surface of the catalyst layer of gas diffusion electrodes is
particularly advantageous because the Faraday efficiency is
improved as a result of the reduced risk of flooding of the gas
diffusion electrode and thus two-phase secondary reactions such as
evolution of hydrogen are reduced.
[0030] Furthermore, the gas diffusion electrode can be made smaller
since a greater differential pressure through the gas diffusion
electrode is less sensitive to the hydrostatic pressure of the
electrolyte.
[0031] In addition, the production of the gas diffusion electrode
is associated with a smaller outlay since one process step, namely
activation of the electrode (oxidation of additional metal oxides),
can be omitted. The metallic particles can be used directly.
[0032] A further advantage is that the gas diffusion electrode is
simpler to integrate into electrolysis systems because of the
decreased passage of electrolyte compared to conventional
electrodes.
[0033] A mixture of water and isopropanol is advantageously used as
precipitation bath. This mixture represents a "nonsolvent" for the
polymeric binder materials and as a result of diffusion brings
about exchange of solvent and nonsolvent and thus phase
separation.
[0034] The first polymeric binder material solidifies here and
forms the gas diffusion layer on the surface of the catalyst
layer.
[0035] The advantages and advantageous embodiments described for
the gas diffusion electrode of the invention apply equally to the
process of the invention and can accordingly be carried over
analogously to this.
[0036] The electrolysis cell of the invention comprises a gas
diffusion electrode as per one of the above-described embodiments.
The gas diffusion electrode is advantageously used as cathode here.
The electrolysis cell is advantageously configured on the cathode
side for the reduction of carbon dioxide.
[0037] The further constituents of the electrolysis cell, for
instance the anode, optionally one or more membranes, feed
conduit(s) and discharge conduit(s), the voltage source and further
optional facilities such as cooling or heating devices, are
essentially variable for the purposes of the invention. The same
applies to the anolytes and/or catholytes which are used in such an
electrolysis cell.
[0038] Overall, the use of a gas diffusion electrode according to
the invention in an appropriate electrolysis system or in an
electrolysis cell leads to greater efficiency of the
electrochemical system and thus makes the end product more
competitive. This is additionally supported by the corresponding
process according to the invention for producing the gas diffusion
electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Working examples of the invention are explained in more
detail below with the aid of a drawing. The drawing shows:
[0040] FIG. 1 a schematic depiction of a section of a gas diffusion
electrode made by means of an extraction process,
[0041] FIG. 2 a schematic depiction of a section of a gas diffusion
electrode made by means of a calendering process,
[0042] FIG. 3 a section of the gas diffusion electrode of FIG. 2,
and
[0043] FIG. 4 a further section of the gas diffusion electrode of
FIG. 2.
DETAILED DESCRIPTION OF INVENTION
[0044] FIG. 1 shows a schematic depiction of a section of a gas
diffusion electrode 1 produced by means of an extraction process.
To this end, a suspension comprising metallic particles 3 and a
first polymeric binder material 5 is applied to a metallic support
7 (merely indicated by an arrow). As a result of phase inversion
(dipping of the coated metallic support 7 into a "non" solvent),
the first binder material 5 solidifies and forms a gas diffusion
layer 9 on the surface 11 of the catalyst layer 13 of the gas
diffusion electrode 1.
[0045] The reaction between a gaseous reactant 15, in the present
case CO.sub.2, and the electrolyte 17 then takes place at the
metallic particles 3 in this gas diffusion layer 9. This is in the
present case a 3-phase reaction in which a conversion of CO.sub.2
into CO occurs at the phase boundary 19 between the metallic
particles 3 in the gas diffusion layer 9, the CO.sub.2 and the
electrolyte 17 (see also FIG. 4).
[0046] In a likewise schematic depiction, FIG. 2 shows a section of
a gas diffusion electrode 21 produced by means of a calendering
process. Here, the reaction of the CO.sub.2 additionally takes
place in the electrolyte 17, which leads to undesirable secondary
reactions. Owing to the production process, the gas diffusion
electrode 21 has larger pores in the surface, so that there is a
risk of undesirable flooding of the gas diffusion electrode 21.
[0047] FIGS. 3 and 4 each show corresponding sections 25, 27 of the
2-phase reactions (section 25) and the 3-phase reactions (section
27) as per FIG. 2. FIG. 3 shows a 2-phase reaction. This takes
place within the electrolyte 17 and leads, as indicated above, to
undesirable secondary products. FIG. 3 shows a 3-phase reaction in
which a reaction of CO.sub.2 occurs within the gas diffusion layer
9 of the gas diffusion electrode 1.
[0048] The advantages and particular embodiments described for the
gas diffusion electrode of the invention and the process of the
invention apply equally to the electrolysis cell of the invention
and can accordingly be carried over analogously to this.
LIST OF REFERENCE NUMERALS
[0049] 1 Gas diffusion electrode [0050] 3 Metallic particles [0051]
5 Polymeric binder material [0052] 7 Metallic support [0053] 9
Outer layer [0054] 11 Catalyst surface [0055] 13 Catalyst layer
[0056] 15 Reactant [0057] 17 Electrolyte [0058] 18 Outer layer
[0059] 19 Phase boundary [0060] 21 Gas diffusion electrode [0061]
25 Section of gas diffusion electrode [0062] 27 Section of gas
diffusion electrode
* * * * *