Catalyst System for Catalyzed Electrochemical Reactions and Preparation Thereof, Applications and Uses Thereof

Abstract

A catalyst system for catalyzed electrochemical reactions, in particular the electrochemical conversion of carbon dioxide into valuable chemical products, such as carboxylates and carboxylic acids, comprises a catalyst, wherein the catalyst comprises bismuth and indium. The catalyst system can be a component of a gas diffusion electrode, that can be used as the cathode electrode in an electrochemical cell.

Claims

1. A catalyst system for catalyzed electrochemical reactions, comprising a catalyst, wherein the catalyst comprises 5-94 wt. % bismuth and 6-95 wt. % indium, based on a total amount of bismuth and indium.

2. A catalyst system according to claim 1, further comprising an electrically conductive support.

3. A catalyst system according to claim 1, wherein the amount of bismuth is in a range of 10-90 wt. %, based on the total amount of bismuth and indium.

4. A catalyst system according to claim 1, wherein the amount of bismuth is in a the range of 40-60 wt. %, based on the total amount of bismuth and indium

5. A catalyst system according to claim 2, wherein the conductive support comprises a porous structure of carbon particles.

6. A gas-diffusion electrode comprising: a gas-diffusion layer on a conductive substrate, the gas-diffusion layer comprising a catalyst system for catalyzed electrochemical reactions, comprising a catalyst, wherein the catalyst comprises 5-94 wt. % bismuth and 6-95 wt. % indium, based on a total amount of bismuth and indium.

7. A gas-diffusion electrode according to claim 6, wherein the catalyst system is bonded to the conductive substrate by a hydrophobic binder.

8. An electrochemical cell comprising: at least one gas chamber and at least one liquid chamber, which chambers are separated by a gas-diffusion electrode, the gas-diffusion electrode including a gas-diffusion layer on a conductive substrate, the gas-diffusion layer comprising a catalyst system for catalyzed electrochemical reactions, the catalyst system comprising a catalyst, wherein the catalyst comprises 5-94 wt. % bismuth and 6-95 wt. % indium, based on a total amount of bismuth and indium.

9-10. (canceled)

11. A method of electrocatalytically reducing carbon dioxide, comprising introducing an anolyte to a first cell compartment of an electrochemical cell, the first cell compartment comprising an anode; introducing a catholyte and carbon dioxide to a second cell compartment of the electrochemical cell, the second cell compartment comprising a cathode, and applying an electrical potential between the anode and the cathode sufficient to reduce the carbon dioxide to a reduced reaction product, wherein the cathode comprises a catalyst system, the catalyst system for catalyzed electrochemical reactions, comprising a catalyst, wherein the catalyst comprises 5-94 wt. % bismuth and 6-95 wt. % indium, based on a total amount of bismuth and indium.

12. A method according to claim 11, wherein the cathode is a gas-diffusion electrode, the gas-diffusion electrode comprising: a gas-diffusion layer on a conductive substrate, the gas-diffusion layer including the catalyst system.

13. A method according to claim 11, wherein carbon dioxide is reduced to a reaction product selected from carboxylates and carboxylic acids.

14. A method according to claim 11, wherein carbon dioxide is reduced to formate or formic acid in an aqueous medium.

15. A method according to claim 11, wherein carbon dioxide is reduced to oxalate or oxalic acid in a non-aqueous medium.

Description

[0034] The invention is further illustrated by the attached drawings and examples. In the drawings

[0035] FIG. 1 shows an embodiment of an electrochemical cell according to the invention; and

[0036] FIG. 2 is an embodiment of a gas-diffusion electrode according to the invention.

[0037] In FIG. 1 a block diagram of a system 100 is shown in accordance with an embodiment of the present invention. System 100 may be utilized for electrochemical production of carboxylic acid intermediates, carboxylic acids, and glycols from carbon dioxide and water (and hydrogen for glycol production). The system 100 generally comprises an electrochemical cell 102, a liquid source 104, an energy source 106, a carbon dioxide source 108, a product extractor 110 and an extractor 112, the latter in this embodiment for the recovery of oxygen produced at the anode. In an embodiment the liquid source 104 is a water source. In another embodiment the liquid source is an organic solvent source. A product or product mixture may be obtained from the product extractor 110 after extraction. An output gas containing oxygen may be output from the oxygen extractor 112 after extraction.

[0038] In the embodiment shown the cell 102 is a divided electrochemical cell. The cell 102 reduces carbon dioxide into products or product intermediates. The reduction may take place by introducing such as bubbling carbon dioxide into an electrolyte solution in the cell 102. At the cathode 120 comprising the catalyst system according to the invention carbon dioxide is reduced into a carboxylic acid or a carboxylic acid intermediate.

[0039] The cell 102 generally comprises two or more or cell compartments 114a, 114b, a separator 116 e.g. a ion exchange membrane, an anode 118 in anode cell compartment 114a, and a cathode 120 in cathode cell compartment 114b on an opposite side of the separator 116. The cathode 120 includes a catalyst system according to the invention suitable for the reduction of carbon dioxide. An electrolyte solution e.g., anolyte 122a and catholyte 122b may fill the respective cell compartments 114a and 114b.

[0040] The liquid source 104 preferably includes a water source, such that the liquid source 104 may provide pure water to the cell 102. The liquid source 104 may provide other fluids to the cell 102, including an organic solvent, such as methanol, acetonitrile, and dimethylfuran. The liquid source 104 may also provide a mixture of an organic solvent and water to the cell 102.

[0041] The catholyte 122 may include an aromatic heterocyclic catalyst, e.g. in a concentration of about 10 mM to 1 M. The electrolyte may also include one or more suitable salts, such as KCl, NaNO.sub.3, Na.sub.2SO.sub.4, NaCL, NaF, NaClO.sub.4, KClO.sub.4, K.sub.2SiO.sub.3 or CaCl.sub.2, e.g. at a concentration of about 0.5 M.

[0042] Other additives may include Group I cations (H, Ii, Na, K, Rb and Cs except Fr), divalent cations (e.g., Ca.sup.2+, Mg.sup.2+, Zn.sup.2+) ammonium, alkylammonium cations and alkyl amines. Examples of anions comprise halides, carbonates, bicarbonates, nitrates, nitrites, perchlorates, phosphates, polyphosphates, silicates and sulfates. .Bicarbonate is a preferred anion.

[0043] The pH of the cathode compartment 114b is preferably between about 1 and 8.

[0044] The energy source 106 may include a variable voltage source. The energy source 106 may be operational to generate an electrical potential between the anode 118 and the cathode 120. The gas source 108 preferably includes a carbon dioxide source, such that the gas source 108 may provide carbon dioxide to the cell 102. E.g. the carbon dioxide is bubbled directly into the compartment 114b containing the cathode 120. For instance, the compartment 114b may include a carbon dioxide input, such as a port 126a configured to be coupled between the carbon dioxide source and the cathode 120.

[0045] The carbon dioxide may be obtained from any source, preferably a renewable source. The product extractor 110 may include an organic product and/or inorganic product extractor. The product extractor 110 generally facilitates extraction of one or more products e.g., carboxylic acid, and /or carboxylic acid intermediate from the electrolyte 122. The extraction may occur via one or more of a solid sorbent, carbon dioxide-assisted solid sorbent, liquid-liquid extraction, nanofiltration, crystallization and electrodialysis. The extracted products may be presented through a port 126b of the system 100 for subsequent storage, consumption, and/or processing by other devices and/or processes at A. In an embodiment the carboxylic acid or carboxylic acid intermediate is continuously removed from the cell 102, where cell 102 operates on a continuous basis, such as through a continuous flow-single pass reactor where fresh catholyte and carbon dioxide is fed continuously as the input, and where the output from the reactor is continuously removed. In other embodiments, the carboxylic acid or carboxylic acid intermediate is continuously removed from the catholyte 122 via one or more of adsorbing with a solid sorbent, liquid-liquid extraction, and electrodialysis.

[0046] The separated carboxylic acid or carboxylic acid intermediate may be placed in contact with a hydrogen stream at A, e.g. in an additional reactor, to produce a glycol or carboxylic acid, respectively.

[0047] Oxygen may be discharged from extractor 112 through port 128.

[0048] An embodiment of a gas-diffusion electrode according to the invention is shown in FIG. 2. FIG. 2 represents a schematic illustration of an electrochemical cell 200 utilizing an anode electrode 202 for the anode reaction, in this specific embodiment a hydrogen gas-diffusion electrode, and a carbon dioxide gas-diffusion electrode 204 for the cathode reaction of reducing carbon dioxide e.g. to formate. The cathode 204 may have a carbon dioxide internal gas plenum 206 in the current collector 208 of the electrode 204 to distribute carbon dioxide evenly into the gas-diffusion electrode. A cathode trickle bed solution distributor or percolator 210 is present in the catholyte cell compartment 212. The catholyte solution may be introduced at the top entry 214 of the catholyte compartment 212 and the catholyte solution is distributed evenly down the cell and is discharged via exit 216 at the bottom of the catholyte compartment 212. Alternatively, the flow may be reversed, so that the flow is in the upward vertical direction. The solution may be fed at specific rates, such as in the range of 0.001 to 10 liters per minute or more depending on the electrochemical cell dimensions, so that the cathode gas diffusion electrode 204 may not be flooded with the catholyte solution due to excessive pressure, and so as to maintain good ionic contact with the cathode gas diffusion electrode 204 for the transfer of electrons into the solution in the reduction of carbon dioxide. The flow and pressure of the catholyte flow are such that minimal amounts of catholyte solution pass through the gas diffusion electrode 204 into the carbon dioxide gas plenum 206 inside the cathode current collector 208, and that the carbon dioxide gas reduction within the gas diffusion electrode is sufficient, so as to obtain a reasonable cathode current density, e.g. in the range of 10 mA/cm.sup.2 to 1000 mA/cm.sup.2, or more preferably in a range of about 50 to 500 mA/cm.sup.2. An energy source (not shown) is operably coupled with the electrodes 202 and 204 to reduce carbon dioxide at the cathode 204. Carbon dioxide is fed to the gas-diffusion electrode 204 via entry 218 into the gas plenum 206. Micro-channels 220 may be provided to pass carbon dioxide from the plenum 206 to the gas-diffusion electrode 204 that comprises the bismuth indium catalyst system. Carbon dioxide leaves the cell through exit 222.

[0049] The anode side of the cell is similarly constructed. In this embodiment hydrogen gas is fed via entry 224 to gas plenum 226 provided with microchannels 228 and leaves the cell via exit 230. Anolyte is introduced at entry 232, flows through a distributor 234 down to the exit 236. A ion exchange membrane 238 is arranged between the anolyte and catholyte distributors 234 and 210.

[0050] The cathode trickle bed 210 may include a thin construction, e.g. made from non-conductive corrosion resistant polymer plastics, such as PTFE, polypropylene and the like, in the form of screen-like or convoluted forms so to distribute the catholyte solution evenly as it passes down the gas-diffusion electrode 204. Alternatively, the trickle bed material may include conductive carbon and graphite, or potentially be manufactured from metal. The entry and exit ports of the catholyte compartment are designed such that the flow distribution of liquid is uniform along the cross section of the trickle bed at the top and bottom. In another embodiment the GDE cathode may be able to be operated in a partially flooded or possibly fully flooded condition, and the flow conditions and electrolyte may be adjusted to operate the cathode in this mode.

EXAMPLE 1

Screening Catalyst

[0051] Various binary metal catalysts were screened for their formate Faradaic yield in a test set up. The test set up comprised a 3 chambered glass cell wherein the electrodes were positioned. 0.75M KHCO3 was used as elektrolyt. Potentiostatic (xV vs SCE) electrolysis for the electrochemical reduction of CO.sub.2 to formate was performed during 3.5-5 hrs. Tables 1 and 2 show the results. It has appeared that a 50 wt. % Bi sample showed the best results in this screening test, while a 10 wt. % Bi sample outperformed a 90 wt. % Bi sample.

TABLE-US-00001 TABLE 1 Screening test results Formate Faradaic Catalyst E1/2 (V) vs SCE) Yield (%) In/Bi 50/50 −1.90 79.88 In/Bi 90/10 −1.90 76.81 Anodized In −1.75 75.73 In/Bi 10/90 −1.90 71.97 Bi/Pb 55.5/44.5 −1.90 70.87 Sn/Zn 60/40 −1.90 57.81 In/Sn 70/30 −1.90 53.64 In/Zn 90/10 −1.90 51.81 Sn/Pb 50/50 −1.90 48.42 In/Sn 30/70 −1.90 45.00 In/Sn 50/50 −1.90 41.46 In/Sn 30/70 −1.60 30.24 In/Sn 96/4 −1.75 28.79 Au/Ni (82/18) −1.90  3.35 In −1.9  63.47

TABLE-US-00002 TABLE 2 Screening Test Results Formate Faradaic Alloy E1/2 (V) vs SCE Yield (%) In/Sn 50:50 rod −1.46  7.69 −1.60 16.91 −1.90 54.21 Sn/Zn 60/40 −1.90 57.81 Bi:Pb −1.60 18.25 −1.75 68.78 −1.90 70.87 Sn:Pb −1.75 41.97 −1.90 48.42 In/Sn 70/30 −1.60 19.39 −1.75 46.87 −1.90 53.64 In/Sn 30/70 −1.60 30.24 −1.75 51.88 −1.90 45.00 In/Sn 96/4 −1.60 27.28 −1.75 28.79 In/Sn 50/50 −1.90 41.46 In/Bi 90/10 −1.75 82.26 −1.80 68.83 −1.90 76.82 In/Bi 10/90 −1.75 57.53 −1.80 65.57 −1.90 71.97 In/Bi 50/50 −1.75 73.70 −1.80 82.13 −1.90 79.88 In/Zn 90/10 −1.70 52.30 −1.80 59.64 −1.90 51.81

EXAMPLE 2

Preparation of Binary Metal Catalyst System In/Bi on C

[0052] InCl.sub.3, Bi(NO.sub.3).sub.3*5H.sub.2O and tri-sodium citrate dehydrate were weighted as shown in Table 3 and put inside a two-neck round bottom flask containing 100 mL of tri-ethylene glycol and Vulcan carbon (available from Cabot). The round bottom flask was placed in an oil bath and fitted with a condenser. The system was continuously purged with N.sub.2 gas. The oil bath temperature was set to 100° C. The content of the flask was stirred. After the system reached the desired value of the temperature, it was allowed to stabilize for about 10 minutes, before rapidly injecting a water solution of NaBH.sub.4 using a syringe and needle. The NaBH.sub.4 was freshly prepared and sonicated in order to speed up the solubilization process. As soon as the NaBH.sub.4 was injected, a vigorous bubbling was observed in the mixture. The color of the suspension was black and no change in it was observed throughout the course of the reaction. After injecting NaBH.sub.4, the system was maintained at 100° C. under stirring for 15 minutes. Then the heater was turned off and the suspension was allowed to cool slowly. At room temperature the suspension was transferred into 4 centrifuge tubes and centrifuged at 8000 rpm for 30 min. The supernatant was poured out and ethanol was added into the tubes, followed by a thorough washing. The washing was performed by sonicating the suspension for 10 min. Then centrifugation at 8000 rpm for 30 minutes was performed. This process was repeated 3 times. At the end ethanol (90 mL) was added into the tubes and the overall content was transferred in a 100 mL glass jar. The resulting mixture was sonicated for 40 minutes at room temperature and then magnetically stirred for 15 minutes. The thus obtained emulsion (catalyst ink) was ready for spray application.

[0053] The In:Bi weight ratio in the thus prepared catalyst is 52.3:47.6.

TABLE-US-00003 TABLE 3 Material Mass (mg) InCl3 310 BiNO.sub.3 × H.sub.2O 340 Na.sub.3Citrate 441 Carbon 716 NaBH.sub.4 946

EXAMPLE 3

Preparation of Gas Diffusion Electrode (GDE)

[0054] A gas-diffusion electrode with a geometric surface area of about 172 cm.sup.2 was cut using a metallic blade. The GDE thus prepared was fixed on an aluminum panel using magnets and positioned at an angle of about 60° from the horizontal planed inside a ventilated fume hood. The catalyst ink was sprayed on the GDE using a manual air brusher at room temperature under atmospheric conditions.