KR20150055033A - Process and high surface area electrodes for the electrochemical reduction of carbon dioxide - Google Patents

Abstract

Methods and systems are provided for electrochemically converting carbon dioxide to organic products including formate salts and formic acid. The method may include, but is not limited to, steps (A) through (C). Step (A) may introduce the acidic anolyte into the first compartment of the electrochemical cell. The first compartment may comprise an anode. Step (B) can introduce the bicarbonate-based cathode liquid saturated with carbon dioxide into the second compartment of the electrochemical cell. The second compartment may comprise indium and may include a high surface area cathode having a pore volume of about 30% to 98%. At least a part of the bicarbonate-based cathode liquid is recycled. Step (C) may apply a sufficient electric potential between the anode and the cathode to reduce the carbon dioxide to at least one of the single-carbon based product or the multi-carbon based product.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for electrochemical reduction of carbon dioxide and a high surface area electrode,

FIELD OF THE INVENTION The present invention relates generally to the field of electrochemical reactions, and more particularly to methods and / or systems for electrochemical reduction of carbon dioxide using high surface area electrodes.

 By burning fossil fuels in activities such as power generation, transportation and manufacturing, billions of tons of carbon dioxide are generated annually. Studies since the 1970s indicate that increasing concentrations of carbon dioxide in the atmosphere may be responsible for global climate change, ocean pH changes, and other potential destructive effects. Countries around the world, including the United States, are looking for ways to alleviate carbon dioxide emissions.

The mechanism to mitigate emissions is to convert carbon dioxide into economically valuable materials such as fuels and industrial chemicals. Conversion of carbon dioxide using energy from renewable resources makes it possible to both mitigate carbon dioxide emissions and convert renewable energy into a chemical form that can be stored for later use.

The present invention relates to a process for the production of a single carbon (C1) chemical comprising formic acid and a multi-carbon (C2 +) chemical (i. E., A chemical having two or more carbon atoms in the compound) using a high surface area electrode and a particular electrolyte solution Quot; The present invention includes processes, systems, and various components thereof.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the scope of the claims. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Many of the advantages herein will be better understood by one of ordinary skill in the art with reference to the accompanying drawings.
1 is a flow diagram of a preferred electrolyzer system for carbon dioxide reduction in accordance with an embodiment of the present invention.
2 is a flow chart of a preferred electrochemical acidification system.
Figure 3 is a flow diagram of another preferred system for electrochemical reduction of carbon dioxide.
Figure 4 is a flow diagram of another preferred electrochemical acidification system comprising a bipolar membrane.
Figure 5 is a flow chart of another preferred electrochemical electrolysis system comprising an ion exchange section for the reduction of carbon dioxide.
6 is a flow diagram of a nano-filtration system in accordance with an aspect of the present invention.
Figure 7 is a chart showing the cumulative yield of formate salt versus time according to an embodiment disclosed with reference to Example 1 of the present invention.
Figure 8 is a chart showing the cumulative yield of formate salt versus time according to an embodiment disclosed with reference to Example 2 of the present invention.
9 is a chart showing the cumulative yield of formate salt versus time according to an embodiment disclosed with reference to Example 3 of the present invention.
10 is a chart showing the cumulative yield of formate salt versus time according to an embodiment disclosed with reference to Example 4 of the present invention.
11 is a chart showing the cumulative yield of formate salt versus time according to an embodiment disclosed with reference to Example 9 of the present invention.
FIG. 12 is a chart showing the concentration of the fosate salt over time according to an embodiment disclosed with reference to Example 9 of the present invention. FIG.
13 is a chart showing the cumulative fomate yield versus time according to an embodiment disclosed with reference to Example 10 of the present invention.
Figure 14 is a chart showing the concentration of the fosate salt over time according to an embodiment disclosed with reference to Example 10 of the present invention.
15 is a chart showing the operating battery voltage over time according to an embodiment disclosed with reference to Embodiment 11 of the present invention.
16 is a chart depicting the catholyte fomate salt concentration versus time according to an embodiment disclosed with reference to Example 11 of the present invention.
17 is a chart showing the foam acid current efficiency versus time according to an embodiment disclosed with reference to Example 11 of the present invention.
18 is a chart depicting catholyte pH versus time according to an embodiment disclosed with reference to Example 11 of the present invention.
19 is a chart showing the foam acid current efficiency versus time according to an embodiment disclosed with reference to Example 12 of the present invention.
20 is a chart depicting the concentration of the catholyte fosfomate salt over time according to an embodiment disclosed with reference to Example 12 of the present invention.
21 is a chart depicting catholyte pH versus time according to an embodiment disclosed with reference to Example 12 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail, and examples thereof are shown in the accompanying drawings.

According to some aspects of the present invention, an electrochemical system is provided for converting carbon dioxide to an organic product including a formate salt and formic acid. The use of high surface area three-dimensional materials, acidic anolyte and catholyte containing bicarbonate promotes the process.

Before any aspect of the invention is described in detail, it should be understood that the embodiments described below do not limit the scope of the claims. It is also to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. In the present invention, the use of terms such as " comprising ", "containing ", or" having ", and variations thereof, generally encompasses the items listed below and their equivalents as well as additional items. Also, unless stated otherwise, technical terms may be used in accordance with conventional usage.

Referring to Figure 1, a flow diagram of an electrolyzer system 100 in accordance with an aspect of the present invention is shown. The electrolyzer system 100 can be used to electrochemically reduce carbon dioxide to organic or organic product intermediates. Preferably, the electrolyzer system 100 converts the carbon dioxide to an alkali metal formate salt, such as potassium formate salt. The electrolyzer system 100 generally includes an electrolytic cell 102, an anode fluid recycle loop 104, and a catholyte recycle loop 106. The electrolytic cell system 100 includes a cathode fluid comprising carbon dioxide, bicarbonate (preferably potassium bicarbonate, but also other bicarbonate-based compounds in addition to or instead of potassium bicarbonate) as the process feed / An acidic anolyte solution (which is preferably sulfuric acid, but may include other acids in addition to or instead of sulfuric acid). The product of the electrolyzer system 100 is generally an alkali metal formate such as potassium formate and may contain excess amounts of catholyte, carbon dioxide, hydrogen, oxygen, and / or other unreacted process impurities.

The electrolytic cell 102 generally includes an anode compartment 108 and a cathode compartment 110 and may further include a cation exchange membrane 112 that separates the anode compartment 108 from the cathode compartment 110 have. The anode compartment 108 includes an anode 114 sufficient to oxidize the water. In a preferred embodiment, the anode 114 is a titanium anode having an anode electrochemical catalyst coating opposite the cation exchange membrane 112. For example, the anode 114 may include an anode mesh screen 116 having an anode electrochemical catalyst coating and including a folded and expanded titanium screen. The anode mash screen 116 may provide a gap and an earth pressure between the anode 114 and the cation exchange membrane 112. The anode 114 may also include one or more current contact posts (not shown) on the back surface of the anode 114.

The cathode compartment 110 generally includes a cathode 118 mounted within the cathode compartment 110. The cathode compartment 110 includes a cathode 118, The cathode 118 preferably includes a metal electrode having an active electrochemical catalyst layer on the front side of the cathode 118 opposite the cation exchange membrane 112 and one or more Current conduction posts (not shown). The cathode 118 preferably includes a high surface area cathode structure 120. A high surface area cathode structure 120 may be mounted between the cation exchange membrane 112 and the cathode 118 to conduct current in the high surface area cathode structure 120. The interface between the high surface area cathode structure 120 and the cation exchange membrane 112 minimizes direct contact between the insulation screen (not shown), e.g., the high surface area cathode structure 120 and the cation exchange membrane 112 And may include a thin expanded plastic mesh insulation screen.

The anode compartment 108 includes an anode feed stream 122 that typically includes a diluted acidic anolyte solution. The anode feed stream 122 is introduced into the lower portion of the anode compartment 108 and flows through the anode mash screen 116 past the surface of the anode 114. The reaction in the anode compartment 108 can include obtaining oxygen (O ₂ , i.e., gaseous oxygen) and hydrogen ions (H ⁺ ) or protons from the oxidation of water at the applied current and voltage potentials. Hydrogen ions or protons are generally available for reaction in the cathode compartment 110 through the cation exchange membrane 112. Gaseous oxygen and other liquid leaving the anode compartment 108 of the electrolytic cell 102 leave as the anode effluent stream 124. The anode effluent stream 124 can be monitored by the temperature sensor 126a and flow to the anode liquid freezer 128 suitable for separating oxygen from the anode effluent stream 124. Anode liquor freezer 128 may process the anode effluent stream 124 into an oxygen stream 130, an anolyte recycle stream 132 and an anolyte overflow stream 134. Oxygen stream 130 may be evacuated from anode liquid freezer 128. The anode liquid stream 132 can be combined with water (preferably deionized water) from the water source 136 and combined with acid (preferably sulfuric acid) from the acid source 138. The water source 136 and the acid source 138 in the anode fluid recycle loop 104 can maintain the anode liquid acid strength and volume for the anode feed stream 122. [ The temperature of the anode feed stream 122 may be controlled by a heat exchanger 140a associated with a coolant supply source 142a prior to introduction into the anode compartment 108 of the electrolyzer 102.

The cathode compartment 110 generally comprises a cathode feed stream 144 comprising carbon dioxide and catholyte. In a preferred embodiment, the catholyte is bicarbonate saturated with carbon dioxide, such as potassium bicarbonate (KHCO ₃ ). The cathode feed stream 144 is introduced into the bottom of the cathode compartment 110 and flows through the high surface area cathode structure 120 past the surface of the cathode 118. The reaction in the cathode compartment 110 reduces the carbon dioxide to the formate salt at the applied current and voltage potential. The reaction product and any unreacted material (e. G., An excess of the catholyte solution) is discharged from the cathode compartment 110 as a cathode discharge stream 146. The cathode exhaust stream 146 may be monitored by a pH sensor 148a and a temperature sensor 126b and may be a cathode solution suitable for separating gas components (e.g., hydrogen) from the cathode exhaust stream 146 And can flow to the freezer 150. The catholyte freezer 150 may treat the cathode discharge stream 146 with a hydrogen stream 152, a product stream 154 and a catholyte recycle stream 156. The hydrogen stream 152 may be evacuated from the catholyte freezer 150. The product stream 154 may preferably comprise an alkali metal formate salt (e.g., a potassium formate salt in which the electrolyte comprises potassium bicarbonate) and may comprise an excess of the catholyte. The catholyte fluid stream 156 may be processed by a heat exchanger 140b associated with a catholyte recycle pump 158 and a coolant source 142b. The temperature sensor 126c may monitor the catholyte stream 156 downstream from the heat exchanger 140b with the cooling water supply 142b. The new catholyte electrolyte feed 160 can be metered into the catholyte liquid stream 156 and the new catholyte electrolyte feed 160 can be adjusted to adjust the pH of the cathode feed stream 144 to the cathode of the electrolyzer 102 Can be adjusted to compartment 110, which can control the final product overflow rate and set the foam acid product concentration. The pH can be monitored by the pH sensor 148b. The carbon dioxide stream 162 can be metered into the cathode feed stream 144 that is directed downstream from the cathode liquid electrolyte feed 160 prior to entering the cathode compartment 110 of the electrolyzer 102. Preferably, the carbon dioxide saturates the cathode liquid entering the cathode compartment.

When an acidic anolyte is used, the protons pass through the membrane into the cathode compartment, and the pH of the electrolyzer 102 is maintained or controlled through the use of carbonate and / or alkali metal bicarbonate combined with water to adjust the pH of the catholyte Can be controlled. By controlling the pH of the catholyte to an optimum value, the cell can convert carbon dioxide to the C1 and C2 products more efficiently at higher conversions than when the non-conforming pH value is maintained or the pH control mechanism is not applied . In a preferred process, the catholyte is continuously recycled to maintain a suitable and uniform carbon dioxide concentration at the cathode surface coated with the electrochemical catalyst. The new catholyte feed stream can be used to control the pH of the catholyte and to control the product concentration in the product overflow stream. The mass flow rate of the catholyte feed (e. G., The mass flow of potassium bicarbonate) to the cathode compartment is preferably controlled such that the introduction of the proton into the catholyte, and the ineffective by- The formation of hydroxides can be balanced. The concentration of potassium bicarbonate provides a volume in the catholyte, which is important because it can dilute the product in the catholyte.

For pH control of the catholyte, potassium bicarbonate in the range of 5 to 600 gm / L, or more preferably 10 to 500 gm / L, is preferred. When the feed concentration of bicarbonate to the catholyte liquid is fixed, a separate feed of water is used as the catholyte to control the final product concentration. In another embodiment, potassium carbonate may be used as a feed for pH control. Potassium carbonate has a higher solubility in water than potassium bicarbonate and is preferably used in a concentration range of 5 to 1,500 gm / L.

Referring to FIG. 2, a block diagram of an electrochemical acidification system 200 according to an embodiment of the present invention is shown. The electrochemical acidification system 200 may be used to acidify the product stream 154 from the electrolyzer system 100. Preferably, the electrochemical acidification system 200 acidifies an alkali metal formate salt, such as, for example, potassium formate salt to produce an organic acid such as formic acid and co-produces an alkali metal hydroxide such as potassium hydroxide. The electrochemical acidification system 200 generally comprises an electrochemical acidification unit 202, an anolyte recycle loop 204 and a catholyte recycle loop 206. The electrochemical acidification system 200 includes a product stream 154 (preferably comprising an alkali metal formate salt) from the electrolyzer system 100 as the process feed / feed, an anode fluid recycle loop 204 and a cathode fluid recycle Each of the loops 206, and an acidic anolyte (which may include sulfuric acid, but in addition to or instead of sulfuric acid, another acid). The products of the electrochemical acidification system 200 are generally organic acids and alkali metal hydroxides, such as, for example, formic acid, and the remaining alkali metal formate salts, bicarbonate catholyte, carbon dioxide, hydrogen, oxygen and / Water.

The electrochemical acidification unit 202 is preferably a three-compartment electrochemical acidification unit or cell. The electrochemical acidification unit 202 generally comprises an anode compartment 208, a cathode compartment 210 and a central ion exchange compartment 212 abutting the cation exchange membranes 214a and 214b on each side. The anode compartment 208 includes an anode 216 suitable for oxidizing water. In a preferred embodiment, the anode 216 is a titanium anode having an anode electrochemical catalyst coating opposite the cation exchange membrane 214a. The cathode compartment 210 includes a cathode 218 suitable for reducing water and generating an alkali metal hydroxide. In a preferred embodiment, hydrogen ions (H ⁺ ) or protons are produced in the anode compartment 208 when potentials and currents are applied to the electrochemical acidification unit 202. Hydrogen ions (H ⁺ ) or protons pass through the cation exchange membrane 214a into the central ion exchange section 212. The product stream 154 from the electrolyzer system 100 is preferably introduced into the electrochemical acidification unit 202 through the central ion exchange section 212 where the hydrogen ion H ⁺ (E. G., Potassium ions) in the stream to produce a product stream 260 comprising an organic acid product, preferably formic acid. The substituted alkali metal ions pass through the cation exchange membrane 214b to the cathode compartment 210 and combine with hydroxide ions (OH <"& gt ^; ) resulting from the reduction of water in the cathode 218 and form alkali metal hydroxides, Hydroxide.

The central ion exchange section 212 may include a plastic mesh spacer (not shown) to maintain dimensional space within the central ion exchange section 212 between the ion exchange membranes 214a and 214b. In one embodiment, the cation exchange material 220 can be included in the central ion exchange section 212 between the cation exchange membranes 214a and 214b. The cation exchange material 220 may include beads, fibers, and ion exchange resins of such a shape. The cation exchange material 220 can increase the electrolyte conductivity in the ion exchange section solution and reduce the potential effect of the carbon dioxide gas on the cell voltage as bubbles are produced and passed through the central ion exchange section 212 .

The anode compartment 208 generally comprises an anode feed stream 222 comprising an acidic anolyte solution (preferably a sulfuric acid solution). Gaseous oxygen and other liquid leaving the anode compartment 208 of the electrochemical acidification unit 202 leaves as the anode effluent stream 224. The anode effluent stream 224 may be monitored by a temperature sensor 226a and may flow to an anode liquid freezer 228 suitable for separating oxygen from the anode effluent stream 224. Anode liquor freezer 228 may process anode discharge stream 224 into an oxygen stream 230, an anode liquid recycle stream 232, and an anolyte overflow stream 234. The oxygen stream 23 can be exhausted from the anode liquid freezer 228. The anode liquid stream 232 can be combined with water (preferably deionized water) from the water source 236 and acid (preferably sulfuric acid) from the acid source 238. The water source 236 and the acid source 238 in the anode fluid recycle loop 204 can maintain the anode liquid acid strength and volume for the anode feed stream 222. [ The temperature of the anode feed stream 222 may be controlled by a heat exchanger 240a associated with the cooling water source 242a before entering the anode compartment 208 of the electrochemical acidification unit 202. [

The cathode compartment 210 generally includes a catholyte feed stream 244 that includes water and may include an alkali metal hydroxide that is circulated through the catholyte recycle loop 206. The reaction product comprising the alkali metal hydroxide and the hydrogen gas leaves the cathode compartment 210 as the cathode exhaust stream 246. The cathode exhaust stream 246 can be monitored by the temperature sensor 226b and flow to the cathode freezer 248 suitable for separating the gas element (e.g., hydrogen) from the cathode exhaust stream 246 . The catholyte freezer 248 may process the cathode discharge stream 246 into a hydrogen stream 250, a catholyte liquid stream 252 and a catholyte overflow stream 254, which may comprise KOH. The hydrogen stream 250 may be evacuated from the catholyte freezer 248. Cathode liquid stream 252 preferably comprises an alkali metal hydroxide (e.g., potassium hydroxide, wherein product stream 154 comprises a potassium formate salt). Cathodic liquid stream 252 may be processed by a heat exchanger 240b associated with a catholyte recycle pump 256 and a coolant source 242b. A temperature sensor 226c may monitor the catholyte stream 242 flowing downward from the heat exchanger 240b. The catholyte liquid stream 252 can be combined with water (preferably deionized water) from a water source 258 where the concentration of alkali metal hydroxide in the catholyte feed stream 244 entering the cathode compartment 210 Water can be metered to control.

Referring to FIG. 3, a flow diagram of a preferred system 300 for electrochemically reducing carbon dioxide to organic acid products is presented. The system 300 can include an electrolyzer system 100 (described with reference to FIG. 1) and an electrochemical acidification system 200 (as described with reference to FIG. 2), and is preferably formed from potassium hydroxide and carbon dioxide, And a potassium hydroxide recycle loop 302 suitable for the production of bicarbonate. The system 300 may also include carbon dioxide processing components for separating carbon dioxide from the process stream (e.g., gas separation units 304a, 304b, 304c, and 304d).

The system 300 generally includes carbon dioxide, alkali metal hydroxides (preferably potassium hydroxides), acids (preferably sulfuric acid) and water (preferably deionized water) as process injectables and is generally an organic acid , Oxygen gas, and hydrogen gas as process emissions. The organic acid may be subjected to further processing to provide the desired shape and concentration. Such processes may include evaporation, distillation or other suitable physical separation / concentration processes.

The reduction reaction of carbon dioxide in the system 300 is as follows.

As shown in formula (1), hydrogen atoms are adsorbed to the electrode from the reduction of water.

H ⁺ + e ^- → H _ad (1)

Carbon dioxide is adsorbed on the surface according to Eq. (2), with the adsorbed hydrogen atoms and the surface of the cathode reduced to form the formate.

CO₂ + H_name → HCOO_name (2)

The adsorbed formate on the surface then reacts with other adsorbed hydrogen atoms to form formic acid, which is then released into solution according to equation (3).

HCOO _ad + H _ad ? HCOOH (3)

The competitive reaction in the cathode is the reduction of water in which hydrogen gas is formed as well as hydroxide ion as in equation (4).

2H ₂ O + 2e ^- ? H ₂ + 2OH ^- ????? (4)

The anode reaction is reduction of water to oxygen and hydrogen ions as shown in equation (5).

2H ₂ O → 4H ⁺ + 4e ^- + O ₂ (5)

High surface area Cathode

As shown with reference to FIG. 1, the cathode 118 preferably includes a high surface area cathode structure 120. The high surface area cathode structure 120 preferably has a pore volume of 30% to 98%. The specific surface area of the high surface area cathode structure 120 is preferably from 2 cm ² / cm ³ to 500 cm ² / cm ³ or higher. The surface area can also be defined as the total area as compared to the current distributor / conductor back plate and is preferably in the range of 2x to 1000x or more.

The cathode 118 may preferably comprise tin-coated copper woven mesh, copper screen, bronze as well as electroless indium on copper fibers, and others copper-tin alloy, nickel and stainless steel . The metal may be precoated with other metals, for example, to suitably form a suitable substrate for the application of indium and other desirable cathode coatings. The cathode may also comprise copper fibers, meshed copper foams or indium-copper alloys formed on the surface of the copper screen. Alloys are generally harder than soft indium metal and can provide desirable mechanical properties in addition to the catalytic properties that are available. The cathode may also include, but is not limited to, metal structures and / or coatings including Pb, Sn, Hg, Ti, In, Bi and Cd, alloys thereof and combinations thereof. Metals including Ti, Nb, Cr, Mo, Ag, Cd, Hg, Tl, An and Pb as well as Cr-Ni-Mo steel alloys may be incorporated in various things. The cathode 118 may comprise a single or multi-layered electrode coating, such that the electrochemical catalyst coating on the cathode substrate may include one or more metal and alloy layers. A preferred electrochemical catalyst coating on the cathode comprises a tin coating on a high surface area copper substrate with a top layer / coating of indium. The indium coating range is preferably in the range of 5% to 100% as indium.

In the use of an indium alloy on the exposed catalytic surface of the electrode, the indium composition is used in an alloy with other metals including Sn, Pb, Hg, Tl, Bi, Cu and Cd and their mixed alloys and combinations thereof The indium preferably ranges from 5% to 99%. It is also considered that Au, Ag, Zn and Pd are contained in the coating in the range of 1% to 95%.

Additionally, the metal oxide may be used or produced as an electrochemical catalyst on the surface of the substrate cathode structure. For example, lead oxide may be produced as an electrochemical catalyst on the surface of the substrate cathode structure. The metal oxide coating may be formed by a thermal oxidation process or by electrodeposition followed by subsequent chemical or thermal oxidation.

In addition, the cathode substrate structure has a gradient such that the density of the cathode may vary vertically or horizontally (e.g., at various fiber sizes) in terms of density, void volume, or specific surface area. The cathode structure may also consist of two or more different electrochemical catalyst compositions that are located or mixed in separate regions of the cathode structure in the catholyte compartment.

During normal operation of the electrolytic cell 102, the performance of the system may be reduced with respect to the yield of the foam salt, such as by catalytic loss or overcoating of the catalyst, along with other metals that may be plated on the cathode 118, can do. The surface of the cathode 118 may be updated in situ by periodic addition of a mixture of indium salts or indium / tin salts during operation of the electrolytic cell 102. Depending on the composition of the cathode 118, it is believed that other or additional metal salts can be added in situ, including Ag, Au, Mo, Cd, Sn, and other suitable metals singly or in combination. The electrolyzer 102 can be operated at full speed during operation or temporarily operated at low current densities with or without the addition of any carbon dioxide during the injection of the metal salt. The conditions for updating the cathode surface with the addition of such salts may vary depending on the required update result. During electrochemical cell operation, the use of a simple reverse current can also be used to potentially update the cathode surface.

In certain embodiments, the electrolyzer 102 is operated at a pressure in excess of atmospheric pressure, which allows the electrolyzer 102 to operate at a higher current density than when the electrolyzer 102 is operated below atmospheric pressure, You can.

In the preparation of the preferred cathode material for the production of organic compounds, addition of a metal salt which can be reduced on the surface of the cathode structure, such as addition of Ag, Au, Mo, Cd, Sn and other suitable metals may also be used. The addition of such a metal salt can provide a catalyst surface which is difficult to manufacture directly during cathode preparation or for updating the catalyst surface.

A preferred method for the manufacture of the high surface area cathode structure 120 is to use an electroless plating solution that may include an indium salt, one or more complexing agents, a reducing agent, a pH adjusting agent, and a surfactant. A preferred procedure for forming an electroless indium coating on a high surface area cathode may involve combining stirred deionized water with the following: trisodium citrate dihydrate (100 g / L), EDTA-disodium salt (15 g / L), sodium acetate (10 g / L), InCl ₃ (anhydrous, 10 g / L) and thiodiglycolic acid (0.3 g / L, for example 3 mL of a 100 mg / mL solution). Stirred pre-mixed stock depositing solution (preferably for several hours, for example overnight) may also be used. The procedure also includes heating the mixture to about < RTI ID = 0.0 > 40 C. < / RTI > The procedure is also repeated until the pH of the mixture is about 7 (about 15 mL ammonia solution / liter) at a point where ammonium hydroxide (28% ammonia solution) is used to adjust the pH to between about 9.0 and 9.2, Of TiCl ₃ (20% by weight in 2% HCl) [0.05 mM] and adding 7 M ammonia in methanol. The procedure then involves heating the mixture to about < RTI ID = 0.0 > 60 C. < / RTI > When the pH drops, adjust the pH to about 9.0 with ammonium hydroxide solution. The procedure then involves heating the mixture to about < RTI ID = 0.0 > 75 C, < / RTI > The procedure involves maintaining the mixture at 75 DEG C for about one hour.

A preferred procedure for the metal coating of the copper substrate is to clean the bare copper substrate with acetone to clean the copper surface (e.g., to remove any residual oil or grease that may be present on the copper surface) And cleaning the treated copper substrate with deionized water. The procedure may also include dipping the bare copper substrate in a 10% sulfuric acid bath for approximately 5 minutes and then rinsing with deionized water. The procedure also includes depositing approximately 25 [mu] m of tin on the copper surface. Deposition can be performed using a commercial electroless tin plating bath (Caswell, Inc.) that is conducted at 60 占 폚 for 15 minutes. After tin deposition, a portion is thoroughly rinsed with deionized water. The procedure also involves depositing approximately 1 [mu] m of indium on the tinned copper surface. Deposition can be performed using an electroless bath operated at < RTI ID = 0.0 > 90 C < / RTI > for 60 minutes. After the indium deposition, a portion is thoroughly cleaned with deionized water. The procedure may also include treating the copper / tin / indium electrode with a 5 wt% nitric acid bath for 5 minutes. This treatment can improve electrode stability compared to untreated copper / tin / indium electrodes. In other implementations, the electrolessly tinned copper substrate may be immersed in molten indium for coating.

In certain implementations, the cathode substrate may be treated with a catalytic material for carbon dioxide reduction. The four exemplary processes are as follows.

The first treatment may include coating a conductive substrate (e.g., glassy carbon or metal) with a conductive sol-gel containing sufficient catalytic material to produce a high active surface area. The conductive component of the sol-gel may be catalytically active. After the substrate is coated with the catalytic sol-gel, the sol-gel allows for a high degree of polymerization / crosslinking-bonding. The combined substrate / sol-gel structure can then be pyrolized at high temperatures to convert organic materials to amorphous (and potentially conductive) carbon. The pyrolysed structure can also be introduced into a chemical treatment to selectively remove organic material or silica phase, leading to a high catalyst content coating.

The second treatment involves bonding relatively small particles (e.g., micron or nanometer scale) to the substrate using a binder such as an amine, a thiol, or other suitable binder. The binder is preferably conductive so as to pass an electric current between the substrate and the catalyst particles. The catalyst particles preferably comprise conjugated organic molecules, such as diphenylbenzene. When the substrate is also made of catalytic material, the binder may comprise a symmetrical linker, or a binder with two other linkers may be used.

The third treatment may include coating the substrate with a slurry containing a catalytic material (which may be in the form of a salt) and a binder. The slurry may also contain conductive additives such as carbon black, carbon nanotubes, or other suitable conductive additives. The slurry coating may then be dried to form a conformal coating over the substrate. The substrate and dried slurry coating can be heated to fuse the various constituents to a mechanically good, conductive and catalytic material. In certain embodiments, heating of the substrate and dried slurry coating is performed in a reducing environment.

The fourth treatment involves applying the precursor to the substrate, removing the solvent, and baking the substrate to convert the precursor material to a monolithic semiconductor metal chalcogenide coating, ≪ / RTI > Coating material is _{Na 4 SnS 4, Na 4 Sn} 2 S 6, K 4 SnTe 4, Na 3 AsS 3, (NH 4) 4 Sn 2 S 6, (NH 4) 3 AsS 3 and (NH _{4) 2} MoS ₄ But are not limited thereto.

Other coating and electrochemical catalyst manufacturing techniques include applying a thermal oxide on a substrate, forming an alloy with the substrate, and applying the semiconductor material onto the substrate. In one aspect, thermal oxidation of various metal salts painted on various metal and ceramic substrates is desirable to form a high surface area material suitable for electrochemical reduction of carbon dioxide. Thermal oxidation may be similar to that for preparing an electrochemical catalyst on titanium materials used as an anode material, e.g., iridium oxide and ruthenium oxide, in an electrochemical chlorine cell. In another embodiment, indium is electrodeposited on a copper foil, and then the copper foil is heated to 40 DEG C above the melting point of indium until the indium melts on the foil surface, forming a copper and gold alloy and then cooling. The preparation of the alloys can be carried out in air or in an inert gas atmosphere (e.g. argon or helium) or under full or partial vacuum. The electrodeposition material preferably provides a Faradaic conversion efficiency of approximately 50% and can be used as a coating on a flat metal backplate or on copper fibers. The alloy may also be formed from a tin-coated copper substrate. In a further aspect, the semiconductor material may be applied to the substrate by gas deposition, sputtering or other suitable application methods. The substrate is preferably a metal substrate. The semiconductor material may be doped to P-type or N-type, if desired.

In the fourth process described above and other coating techniques, certain measurements may be performed to improve the bond quality (mechanical, electrical, etc.) between the substrate and the catalyst. Such measurements may involve chemically bonding the catalyst or binder with the generation of functional groups on the surface of the substrate, or may involve generating geometrical features at the substrate surface that promote bonding with the applied catalyst coating.

Substrates for the high surface area cathodes described herein may include RVC materials such as carbon and graphite, metal foams, meshes, metal wool made from fibers, sintered powder metal films and plates, metal and ceramic beads, pellets, Metal columns and trickle bed fillers, metal and inorganic powder forms, metal fibers and wool or other suitable substrate materials. The specific surface area of the physical form preferably includes a specific surface area of about 2 to 2,000 cm ² / cm ³ or more.

The high surface area structure of the electrodes or electrodes may comprise alloys as fibers or wool and may be coated with a variety of compounds and then heated in air or in a reducing atmosphere oven to produce stable oxides on the surface of the electrocatalyst in the reduction of carbon dioxide . Other cathode materials may include metal glasses and amorphous metals.

Referring to FIG. 4, a specific implementation of the acid acidification system 200 of FIG. 2 using a bipolar membrane in an electrochemical acidification unit 402 is shown. As the bipolar membrane is used in the electrochemical acidification unit 402, in addition to the recovery of potassium hydroxide, the alkali metal formate salt (e.g., potassium formate salt) may be oxidized. The use of bipolar membranes can reduce the voltage required for acidification of the alkali metal formate salt and reduce the number of actual anodes and cathodes needed for the electrochemical stack. The bipolar membrane is preferably composed of a cation membrane and an anion membrane bonded to each other and separates water from the two membrane interfaces to form hydrogen ions (H ⁺ ) from the cation membrane and hydroxide ions (OH ^- ) from the anion membrane .

Referring to FIG. 5, an alternative embodiment of the electrochemical system 100 of FIG. 1 is presented. The electrolyzer 502 of FIG. 5 includes an ion-exchange compartment 504 in addition to the anode compartment 506 and the cathode compartment 508. The ion exchange section 504 functions similarly to the acid acidification section 212 in the electrochemical acidification unit 202 shown in FIG. The alkali metal formate salt product (e.g., potassium formate salt) from the cathode compartment and the unreacted KHCO ₃ pass through the ion exchange compartment 504 to provide the formate product and residual KHCO ₃ with CO ₂ . The hydrogen ions (H ⁺ ) passing through the adjacent membrane 510a on the anode compartment may be replaced by alkali metal ions (e.g., K ⁺ ) in the stream passing through the central ion exchange section 504, The acid salt is acidified and the alkali metal ions and residual hydrogen ions pass through the adjacent membrane 510b on the cathode compartment 508 to the cathode liquid. This enables the operation of the catholyte at high pH conditions if required to achieve high Faraday current efficiency with the selected cathode for the process.

In indium-based cathode systems, preferred catholyte solutions include alkali metal bicarbonates, carbonates, sulphates, phosphates, and the like. Other preferred catholyte solutions include borates, ammonium and hydroxides. Other catholyte fluids may include chloride, bromide, and other organic and inorganic salts. Non-aqueous electrolytes such as propylene carbonate, methanesulfonic acid, methanol, and other ionic conductive liquids may be used, and they may be present in the catholyte as a non-aqueous mixture or in an aqueous mixture. Introducing microbubbles of carbon dioxide into the canister liquid stream improves the transfer of carbon dioxide to the cathode surface.

Referring to FIG. 6, a nano-filtration system may be used between the electrolyzer system 100 shown in FIG. 1 and the electrochemical acidification system 200 shown in FIG. The nano-filtration system preferably separates the alkali metal formate salt (e.g., potassium formate salt) from the bicarbonate (e.g., stream 154) leaving the electrolyzer system 100 to form an electrochemical acidification unit 202 ) ≪ / RTI > The nano-filtration system preferably uses a nano-filtration filter / membrane under pressure for selective separation of the bicarbonate from the alkali metal formate salt. The nano-filtration filter / membrane separates a monovalent anion (e.g., a formate salt) from a divalent anion (e.g., carbonate) using a membrane that is suitably selected for high pressure pumps and separation. In order to efficiently separate the foam salt from the carbonate with the nano-filtration filter / membrane when using the nano-filtration system as a separation tool between the electrolyzer system 100 and the electrochemical acidification system 200, the foam salt / bicarbonate product (E. G., Stream 154) is preferably converted to a carbonate. The nano-filtration system may include a mixer, such as a mixer tank, to mix the foamed salt / bicarbonate product stream with a potassium hydroxide (KOH) stream. The mixer facilitates the conversion of potassium bicarbonate to potassium carbonate to enable the separation of the formate salt from the carbonate. The high pressure pump then sends the potassium formate / carbonate stream to the nano-filtration unit containing the nano-filtration filter / membrane. The nano-filtration unit produces a low-carbonate-containing potassium formate salt permeate stream which is then sent to the electrochemical acidification system 200, as indicated by stream 154 in FIG. 2, and the electrochemical acidification unit 202 ). The potassium carbonate containing the reject stream leaving the nano-filtration unit is preferably sent to the KHCO ₃ block of FIG. 3 where the potassium carbonate is mixed with KOH and CO _{2 for} conversion to potassium bicarbonate. Potassium bicarbonate is preferably used as a feed to the cathode compartment of the electrolytic cell 102 of the electrolyzer system 100. The nano-filtration separation system may consist of multiple units connected in a series flow arrangement to increase the total separation efficiency of the carbonate from the phosphate salt separation. The system can also use the recycle stream to recycle the effluent stream from one unit to the infusion of the other unit and to maintain the flow and pressure as well as increase the recovery of the foam salt.

Depending on the reaction of the electrochemical system disclosed herein, the pH of the catholyte preferably ranges from 3 to 12. The preferred pH of the catholyte may be a function of the catalyst and catholyte operating conditions used in the cathode compartment and thus does not limit or inhibit corrosion in the electrochemical cell.

Preferably, with a flow rate in the range of 0.002 to 20 ft / sec (0.0006 to 6.1 m / sec), the cross-sectional flow rate of the catholyte is in the range of 2 to 3,000 gpm / ft ² (0.0076 to 11.36 m ³ / m ² ) .

Homogeneous heterocyclic catalysts can preferably be used in the catholyte. Homogeneous heterocyclic catalysts include, for example, one or more of 4-hydroxypyridine, adenine, sulfur containing heterocyclic amines, oxygen containing heterocyclic amines, azoles, benzimidazoles, bipyridines, furans, imidazoles An imidazole-related species having at least one 5-membered ring, indoline, lutidine, methylimidazole, oxazole, phenanthroline, fterine, pteridine, pyridine, pyridine-related pyridine having at least one 6-membered ring Species, pyrrole, quinoline or thiazole, and mixtures thereof.

Preferred anolyte solutions for systems include alkali metal hydroxides such as KOH, NaOH and LiOH; Ammonium hydroxide; Sulfuric acid, phosphoric acid and the like; Organic acids such as methanesulfonic acid; Nonaqueous solutions and aqueous solutions; Alkali halide salts such as chloride, bromide and iodine types such as NaCl, NaBr, LiBr and NaI; And halide acids such as HCl, HBr, and HI. The halide acid and alkali halide salts produce, for example, chlorine, bromine or iodine as halide gas or dissolved aqueous products from the anode liquid compartment. Methanol or other hydrocarbon non-aqueous liquids may be used and form some oxidized organic products from the anolyte. The selection of the anode liquid is determined by the requirements for lowering the process reaction and the total operating cell voltage. For example, the formation of bromine at the anode requires a significantly lower anode voltage potential than chlorine formation, and iodine requires a lower voltage potential than bromine. This allows significant operating cost savings in the operation of both electrochemical units when bromine is produced in the anode liquid. The formation of a halogen, such as bromine, in the anolyte may then be used in an external reaction to produce another compound, for example, reacting with an alkane to form bromoethane, followed by reaction with an alcohol such as ethanol or an alkene such as ethylene And the halogen acid by-products from the reaction can be recycled back to the electrochemical cell anode solution.

The operation of the electrolytic cell catholyte at high operating pressures allows the carbon dioxide to be more soluble in the water-based electrolyte than at low pressures (e.g., atmospheric pressure). The electrochemical cell can operate at a pressure of up to about 20 to 30 psig with a multi-cell stack design and can operate up to 100 psig although it is accompanied by a modification. The electrolytic cell anode liquid can be operated in the same pressure range to minimize the pressure difference on the membrane separating the two electrode compartments. Particular electrochemical designs are required to operate the electrochemical unit at high operating pressures up to about 60 to 100 atmospheres or more in liquid CO ₂ and supercritical CO ₂ operating range.

In certain implementations, a portion of the catholyte recycle stream may be separately pressurized, with a CO ₂ injection, using a pump, or using reverse flow pressure control, whereby the pressurized stream is then injected into the catholyte compartment of the electrolyzer do. Such a structure can increase the amount of dissolved CO _{2 in} the aqueous solution to improve the yield.

The operating temperatures of the catholyte and the anolyte are preferably in the range of about -10 to 95 ° C, more preferably 5 to 60 ° C. The lowest operating temperature is limited to the electrolyte used and their freezing point. Generally, the lower the temperature, the higher the solubility of CO ₂ in the aqueous solution of the electrolyte and helps to obtain higher conversion and current efficiency. A consideration for low operating temperatures is that the operating electrolyser cell voltage is high and optimization may be required to manufacture compounds at low operating costs.

The electrochemical cell may include a zero gap, which is a flow-through design with a recirculating cathode liquid electrolyte having a variety of high surface area cathode materials. Other designs include a flooded co-current packed and trickle bed design with a variety of high surface area cathode materials, a bipolar stack cell design, and a high pressure cell design.

Anodes for use in electrochemical systems may depend on various system conditions. In order to oxidize the acidic anode liquid and water to produce oxygen and hydrogen ions, the anode may comprise a coating, preferably an electrocatalyst coating comprising a noble metal oxide, examples of noble metals include metals deposited on the valve metal substrate, Ruthenium and iridium oxides as well as platinum, rhodium and gold as oxides, and combinations thereof, such as titanium, tantalum, zirconium and niobium. For other anode liquids such as alkaline or hydroxide electrolytes, the anode may comprise stable carbon, cobalt oxide, stainless steel, nickel and alloys and combinations thereof as an anode suitable for alkaline conditions.

In the present invention, the electrochemical system may use a film deposited between the anode compartment and the cathode compartment. A cation exchange membrane, particularly a cation exchange type with a high exclusion (rejection) efficiency for the anion membrane, such as the nasal cavity to burn the perfluoro sulfuric acid-based ion exchange film, for example under the trade name DuPont Nafion ^® (DuPont Nafion ^®) N117 and N120 series, and is more preferably a PTEE film is preferably a fiber-reinforced type N324 and N424 type, and for example, play lukewarm ^® supply of (Flemion ^®) brand name related to a similarly produced by Japanese company. Another multi-layered perfluorinated ion exchange membrane used in the chlorine-alkali industry has a bilayer structure of a sulfonic acid-based membrane layer bonded to a carboxylic acid-based membrane layer, which operates efficiently in anolyte and catholyte solutions above about pH 2 . These membranes have much higher negative ion removal efficiency. It is sold by DuPont under the trademark of N900 series, such as N90209, N966, N982 and 2000 series, for example, N2010, N2020 and N2030, and as all of these types and their subtypes of Nafion ^®. If the anion exclusion does not matter, will be sold by the hydrocarbon layer, for example, of the things that can get in the market, bitter loans under the tradename of Iowa Octopus ^® (Ionac ^®) (Sybron) is manufactured from a variety of cation exchange material, Selena is lukewarm ^® (Selemion ^®) brand names that are to be sold by Tokuyama soda and sold by AGC engineering (Asahi glass) may also be used.

example Electrolytic bath  design

The electrolyzer design used in laboratory experiments may include a high surface area cathode structure of varying thicknesses with additional spacer frames and may also provide a physical voltage for electrical contact to the cathode current conductor backplate.

An electrochemical bench scale cell having an electrode projected area of about 108 cm ² was used for a number of bench scale experiments. The electrochemical cell was designed to consist of two electrode compartments fabricated with 1.0 inch (2.54 cm) thick natural polypropylene. The exterior dimensions of the anode and cathode compartments are 8 inches (20.32 cm) by 5 inches (12.70 cm), 0.375 inches (0.9525 cm) deep, 3.0 inches (7.62 cm) wide, and 6 inches (15.24 cm) It has a machined recess and a 1.0 inch (2.52 cm) wide flat gasket sealing area surface. Two holes are drilled at the same distance in the recessed portion to accommodate two electrode conductor posts passing through the compartment thickness and two 0.25 inch (0.635 cm) drilled holes pass through a 0.25 inch (0.635 cm) conductor post And seals the periphery so that liquid does not leak out of the electrode compartment. The electrode frame has a plastic joint that is drilled through the top and bottom flow distribution holes with 0.25 inch tubing threaded holes and is mounted on the outside of the cell frame at the top and bottom of the cell to provide a flow in and out of the cell frame, Twelve 0.125 inch (0.3175 cm) holes through the 45 degree slope at the edge of the seth region pierce the upper and lower flow distribution holes to provide equal flow distribution across the flat electrode surface and through the high surface area electrode thickness of the compartment .

For the anode compartment battery frame, a thickness of 0.060 inches (0.1524 cm), a width of 2.875 inches (7.3025 cm) and a width of 5.875 inches (14.9225 cm) with two 0.25 inch (0.635 cm) titanium diameter conductor posts, cm < / RTI > of the anode was mounted through the two apertures in the electrode compartment recess region. The positioning depth of the anode at the recess depth was adjusted by adding a plastic spacer behind the anode and the anode edge to the battery frame recess was sealed with a medical epoxy. The electrochemical catalytic coating on the anode was Water Star WS-32, an iridium oxide-based coating on a 0.060 inch (0.1524 cm) thick titanium substrate suitable for oxygen release in acid. In addition, the anode compartment is also 0.010 inches (0.0254 inches) from DeNora North America (EC626) with an iridium oxide-based oxygen-releasing coating, which is an anode folded screen (folded three times) cm < / RTI > thick titanium expanded metal material was used and was used to provide a zero gap anode structure (anode in contact with the membrane) and to provide pressure to the membrane from the anode surface with a voltage from the cathode surface Respectively.

For the cathode segment cell frame, a 0.080 inch (0.2032 cm) thick, 2.875 inch (7.3025 cm) wide, and 5.875 inch (0.2032 cm) wide opening with two 0.25 inch (0.635 cm) diameter 316L SS conductor posts welded on the backside A 316L stainless steel cathode having a length of 14.9225 cm was mounted through the two holes drilled in the electrode compartment recess area. The position depth of the cathode at the recess depth was adjusted by adding a plastic spacer behind the cathode, and the anode edge to the cell frame recess was sealed with a fast curing medical epoxy.

A copper bar was connected between the two anode posts and the cathode posts to distribute current to the electrode backplate. The cell was assembled and compressed using 0.25 inch (0.635 cm) bolts and nuts at a compressive force of about 60 in-lbs force. A neoprene elastomer gasket (0.0625 inch (0.159 cm) thick) was used as a sealing gasket between the cell frame, the frame spacers and the membrane.

Example 1

The cell was assembled with a 0.010 inch (0.0254 cm) thick indium foil mounted on a 316L SS back conductor plate using conductive silver epoxy. The multi-laminated high surface area cathode included an approximately 1 micron thick electrolessly applied indium layer deposited on a electroless tin layer previously applied to a thickness of about 25 microns on a meshed copper fiber substrate. The base copper fiber structure was a copper net mesh obtained from PestMall.com, an online Internet sales office, Anteater Pest Control Inc. The copper fiber dimensions in the mesh mesh were 0.0025 inches (0.00635 cm) thick and 0.010 inches The fabricated high surface area cathode material was folded into pads having a thickness of 1.25 inches (3.175 cm) and a height of 6 inches (15.24 cm) and a width of 3 inches (7.62 cm) This filled the cathode compartment dimensions and exceeded the adjusted compartment thickness (spacer addition), which was 0.875 inches (2.225 cm) x about 0.25 inches (0.635 cm). The manufactured cathode had an area of about 31 times the area of the flat cathode plate Had a calculated surface area of about 3,171 cm ² , a 91% pore volume, and a specific surface area of 12.3 cm ² / cm ^3. The cathode pad was compressible and provided spring force to contact the cathode plate and membrane. 0.125 inches (0.3175 very thin with very large hole in cm) (two layers of plastic screens 0.002 inch thick) was placed between the cathode mesh and Nafion ^® 324 membrane. neoprene gasket (0.0625 inches (0.159 cm) thick) The battery frame The electrochemical catalytic coating on the anode in the anolyte compartment was Waterstar WS-32, which is an iridium oxide-based coating suitable for oxygen release in acid. The anode compartment also contains iridium oxide-based oxygen A triple folded screen between the anode and the membrane, 0.010 inch (0.0254 cm) thick titanium expanded metal material available from Dinora North America (EC626) was used with the release coating, and a zero gap anode structure To provide pressure on the membrane from the anode side having an earth pressure from the cathode side, Respectively.

The battery assembly was tightened with stainless steel bolts and mounted into a battery station, which was shown in Figure 1 with a cathode liquid freezer, an efferent cathode liquid circulation pump, an injected battery pH and an outlet battery pH sensor, a temperature sensor on the effluent solution stream And have the same structure. A 5 micron stainless steel frit filter is used to spray carbon dioxide into the solution in the volume of the catholyte free radical to provide dissolved carbon dioxide into the recycle stream returning to the catholyte cell infusion.

The anode liquid used was a diluted 5 vol% sulfuric acid solution made from 98% sulfuric acid and deionized water reagent.

In this experimental run, the system was operated with a catholyte liquid composition containing 0.4 moles of potassium sulfate aqueous solution with 2 gm / L potassium bicarbonate added and sparged with carbon dioxide to a final pH of 6.60.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 0.4 MK ₂ SO ₄ , 0.14 mM KHCO ₃

Cathode liquid flow rate: 2.5 LPM

Cathodic Liquid Flow Rate: 0.08 ft / sec

Applied Current: 6 amps (6,000 mA)

Cathodic liquid pH range: 5.5-6.6, controlled by periodic addition of potassium bicarbonate to the catholyte solution recycle loop. The catholyte pH decreases with time and is controlled by the addition of potassium bicarbonate.

result:

Battery voltage range: 3.39-3.55 volts (slightly reduced voltage when catholyte pH drops)

Operating time: 6 hours

Foam Faraday yield: stable at 32-35%, calculated periodically by sampling the sample. See FIG.

Final formate concentration: 9,845 ppm

Example  2

With the same cathode, the same cell as in Example 1 was used, which was rinsed with water while in the electrochemical cell after the operation was completed, and was then used for such operation.

In this experimental run, the system was operated with a catholyte liquid composition containing 0.375 moles potassium sulfate aqueous solution with 40 gm / L potassium bicarbonate and was sparged with carbon dioxide to a final pH of 7.05.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 0.4 MK ₂ SO ₄ , 0.4 M KHCO ₃

Cathode liquid flow rate: 2.5 LPM

Cathodic Liquid Flow Rate: 0.08 ft / sec

Applied Current: 6 amps (6,000 mA)

Cathodic Fluid pH Range: Decrease linearly from 7.5 to 6.75 over time during operation.

result:

Battery voltage range: 3.40-3.45 volts

Operating time: 5.5 hours

Foam Faraday yield: Stable to 52%, slowly decreasing to 44% over time as the catholyte pH decreases. See FIG.

Final formate concentration: 13,078 ppm

Example  3

Along with the same cathode, the same cell as in Examples 1 and 2 was used, which was rinsed with water while in the electrochemical cell after the operation was completed and was then used for such operation.

In this experimental run, the system was operated with a catholyte liquid composition containing 0.200 moles of aqueous potassium sulfate solution with 40 gm / L potassium bicarbonate and was sparged with carbon dioxide to a final pH of 7.10.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 0.2 MK ₂ SO ₄ , 0.4 M KHCO ₃

Cathode liquid flow rate: 2.5 LPM

Cathodic Liquid Flow Rate: 0.08 ft / sec

Applied Current: 9 amps (9,000 mA)

Catholyte pH range: linearly decreases from 7.5 to 6.65 over time during operation, and additional solid KHCO ₃ is added to the catholyte loop in 10 gm increments at 210, 252, and 290 min to a pH of about 7 The pH was returned.

result:

Battery voltage range: 3.98-3.80 volts

Operating time: 6.2 hours

Foam Faraday yield was reduced from 75% to 60% at pH 6.65 and increased to 75% when solid potassium bicarbonate was added to the catholyte loop at 10 gm increments at 210, 252, and 290 min, and the pH of the catholyte Decreases to 68% as time decreases to 6.90. See FIG.

Final formate concentration: 31,809 ppm.

Example  4

With the same cathode, the same cells as in Examples 1, 2 and 3 were used, which was rinsed with water while in the electrochemical cell after the operation was completed and then used for such operation.

In this experimental run, the system was run with a catholyte liquid composition containing 1.40 moles of potassium bicarbonate (120 gm / L KHCO ₃ ) and sparged with carbon dioxide to a final pH of 7.8.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 1.4 M KHCO ₃

Cathode liquid flow rate: 2.6 LPM

Cathodic Liquid Flow Rate: 0.09 ft / sec

Applied Current: 11 amps (11,000 mA)

Cathode liquid pH range: linearly decreases from 7.8 to the final pH of 7.48 over time during operation.

result:

Battery voltage range: 3.98-3.82 volts

Operating time: 6 hours

Foam Faraday yield: 63%, and is fixed at about 54-55%. See FIG.

Final formate concentration: 29,987 ppm.

Prophetic Example  5

This experiment considered separation of the product potassium formate salt from the potassium carbonate / bicarbonate supporting electrolyte by membrane nano-filtration (NF) (see FIG. 10). The experiment included two commercial NF membranes. The feed solution contained 1.2 M KHCO ³ + 0.6 M K-formate, and its pH was adjusted to 7, 9, and 11 (for each membrane) for three separate runs.

All NF experiments were carried out at an applied pressure of 40 bar (580 psig) and a GE-OsmonicSepapermeator (active membrane portion of 0.0137 m ² ) at 50 ° C. During each operation, 3 liters of feed solution was passed, and permeate was collected in the measuring cylinder (to measure the volume) and the flow time was recorded. The permeate was then analyzed for total carbonates (HCO ₃ ^- + CO ₃ ^{2 -} ) and the formate salt. From these data, the permeability (L / m ² h bar) and solute exclusion (%) were calculated by the following formula:

[S] represents the molar concentration of the solute, which may be a formate salt or a total carbonate.

Expected results are summarized as follows:

GE - Desar ( GE - Desal ) DK  membrane

Dow - DOW-Filmtec NF270  membrane

Prophetic Example  6

Single permeation experiments were performed with a DK membrane using a foam acid rich feed solution containing 1.2 M KHCO ₃ + 1.2 M K-formate. The experiment can be performed at pH 11 and all other conditions are the same as in Example 1 above.

These experiments showed exclusion of 79.9% and -33.8% for the total carbonate and the formate salt, respectively. The permeability was 0.32 L / m ² h bar.

Example  7

The same cells as in Examples 1, 2 and 3 were used, except that a 701 gm tin shot (0.3-0.6 mm diameter) medium with an electrolessly plated indium coating was used as the cathode. The thickness of the cathode compartment was 0.875 inches.

In this experimental run, the system was operated with a catholyte liquid composition containing 1.40 moles of potassium bicarbonate (120 gm / L KHCO ₃ ) and sparged with carbon dioxide to a final pH of 8.0.

The cell was operated under batch conditions for the first 7.3 hours without overflow, after which 1.40 moles of potassium bicarbonate feed was introduced into the catholyte at a rate of about 1.4 mL / min, resulting in an overflow and a sample of the loop Were collected for analysis of formate salt concentration.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 1.4 M KHCO ₃

Cathode liquid flow rate: 3.2 LPM

Applied Current: 6 amps (6,000 mA)

Cathode liquid pH range: During operation, it linearly decreased from a pH of about 8.0 to a final pH of 7.50 over time.

result:

Battery voltage range: 3.98-3.82 volts

Operating time: Batch mode: 7.3 hours

Feed and product overflow: 7.3 hours from 47 hours to the end of operation.

During the batch operation, the foam acid ferrate efficiency was 42% to 52% and the foam acid concentration rose to 10,490 ppm. During the feed and overflow periods, the periodically calculated efficiency varied from 32% to 49%. The average conversion efficiency was about 44%. The feedrate and the concentration of formate during the overflow period varied from 10,490 to 48,000 ppm. The battery voltage started at about 4.05 volts and ended at 3.80 volts.

Example  8

The electrolysis was carried out using a 3-compartment glass cell of approximately 80 mL total volume. The cell was designed with a gas fixed with a Teflon bushing. The compartment was separated by two glass frit. A three-electrode assembly was used. One compartment included a reference electrode (Accumet / silver chloride) with a water-based electrolyte and a catalyst, and a working electrode, as described. As described, the central compartment also contained an electrolyte and a catalyst solution. The third compartment was filled with a 0.5 molar K ₂ SO ₄ electrolyte aqueous solution sparged with CO _{2 at} a pH of about 4.5 and a counter electrode (TELPRO (Stafford, TX)) - Mixed metal oxide electrode). During the experiment, the working electrode compartment was purged with carbon dioxide. The solution for formic acid was determined by ion chromatography, and the solution was analyzed before and after electrolysis (blank). Experiments were performed on SCE reference electrodes at -1.46 or -1.90 volts for about 1.5 hours using 6 channel Arbin Instruments MSTAT under potential difference conditions.

Example  9

The same cells as in Examples 1, 2 and 3 were used, except that a tin foil coating was used as the cathode and a tin shot (3 mm diameter) medium of 890.5 gm was used. The thickness of the cathode compartment was 1.25 inches, and the system was run in batch mode with no feed injection. Carbon dioxide was sprayed to saturate the solution in the catholyte free radical.

Tin packed bed casters Details:

Weight: 890.5 gm tin shots

Annotation shot: Average size of 3 mm

Total compartment volume: 369 cm ³

Calculated tin bead surface area: 4,498 cm ²

Calculated packed bed cathode Specific surface area: 12.2 cm ² / cm ³

Calculated packed bed void volume: 34.6%

In this experimental run, the system was run with a catholyte composition containing 1.40 moles of potassium bicarbonate (120 gm / L KHCO ₃ ) and sparged with carbon dioxide to a final pH of about 8.0.

The cell was operated under batch conditions without overflow, and the catholyte loop samples were periodically collected for analysis of the formate concentration.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 1.4 M KHCO ₃

Cathode liquid flow rate: 3.2 LPM (upward flow)

Cathodic Liquid Flow Rate: 0.068 ft / sec

Applied Current: 6 amps (6,000 mA)

Cathodic Fluid pH Range: Slowly linearly increasing over time from a pH of about 7.62 to a final pH of 7.73 during operation.

result:

Battery voltage range: Starting at 3.84 volts, slowly decreasing to 3.42 volts.

Operating time: batch mode, 19 hours

The fomate paraday efficiency started at about 65% and decreased to 36% after 10 hours and to 18.3% after 19 hours. The final formate concentration ended at 20,500 ppm after 19 hours of operation. 11 and 12.

Example  10

Conductivity using a cathode as cathode was 0.010 inch (0.0254 cm) thick indium foil mounted on a 316L SS back conductor plate, except for using 805 gm of indium coated tin shot (3 mm diameter) media. The same cells as in Examples 1, 2 and 3 were used. The thickness of the cathode compartment was 1.25 inches, and the system was run in batch mode with no feed injection. Carbon dioxide was sprayed to saturate the solution in the catholyte free radical. The annotation shots were electroless plated with indium on the tin-coated copper mesh in the same manner as described in Examples 1-4. The indium coating was about 0.5-1.0 microns in thickness.

Indium coated tin shots Packed bed cathode Detail:

Weight: 890.5 gm, Indium coating on tin shots

Indium coated tin shots: Average size of 3 mm

Total compartment volume: 369 cm ³

Calculated tin bead surface area: 4,498 cm ²

Packed bed cathode Specific surface area: 12.2 cm ² / cm ³

Packed bed void volume: 34.6%

In this experimental run, the system was run with a catholyte composition containing 1.40 moles of potassium bicarbonate (120 gm / L KHCO ₃ ) and sparged with carbon dioxide to a final pH of about 8.0.

The cell was operated under batch conditions without overflow, and the catholyte loop samples were periodically collected for analysis of the formate concentration.

Operating conditions:

Batch catholyte recirculation operation

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 1.4 M KHCO ₃

Cathode liquid flow rate: 3.0 LPM (upward flow)

Cathodic Liquid Flow Rate: 0.068 ft / sec

Applied Current: 6 amps (6,000 mA)

Cathode liquid pH range: Slowly linearly decreasing over time from a pH of about 7.86 to a final pH of 5.51 during operation.

result:

Battery voltage range: Starting at 3.68 volts, slowly decreasing to 3.18 volts.

Operating time: batch mode, 24 hours

The fomate paradise efficiency started at about 100%, varied between 60% and 85%, and ended at about 60% after 24 hours. The final formate concentration ended at about 60,000 ppm after 24 hours of operation. The dilution error of the sample at high concentrations of the phosphate salt provides the variability shown in the yield number. 13 and 14.

Example  11

The same cell as Examples 1, 2 and 3 with freshly prepared indium on a tin electrochemical catalyst coating on a copper mesh cathode was used. The prepared cathode had a calculated surface area of about 3,171 cm ^2, an area of about 31 times that of a flat cathode plate area, a 91% pore volume, and a specific surface area of 12.3 cm ² / cm ³ .

In this experimental run, the system was run with a catholyte liquid composition containing 1.40 moles of potassium bicarbonate (120 gm / L KHCO ₃ ) and sparged with carbon dioxide to a final pH of 7.8.

The cell was operated in a recirculation batch mode for 8 hours of initial operation to obtain a caustic liquid formate ion concentration of up to about 20,000 ppm and then a fresh feed of 1.4 M potassium bicarbonate was fed at a feed rate of about 1.2 mL / . Overflow volumes were obtained and volumes were collected, and overflow and catholyte loop samples were sampled and analyzed by ion chromatography for the formate salt.

Operating conditions:

Cathode: tin-phase electroluminescent indium on a copper mesh substrate

Continuous supply with cathodic liquid recycle operation - 11.5 days

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 1.4 M KHCO ₃

Cathode liquid flow rate: 3.2 LPM

Cathodic Liquid Flow Rate: 0.09 ft / sec

Applied Current: 6 amps (6,000 mA)

result:

Battery Voltage versus Time: Figure 15 shows the result of electrical voltage versus time, showing a stable operating voltage of about 3.45 volts over 11.5 days after initial startup.

Continuous operation time: 11.5 days

Foamate concentration vs. time: Figure 16 shows the results of the foam acid concentration versus time.

Foamate Faraday Yield: Figure 17 shows calculated formate current efficiency versus time, from which the yield of the foam acid was measured.

Final formate concentration: about 28,000 ppm

Cathode liquid pH: Figure 18 shows a change in catholyte pH over 11.5 days, gradually decreasing from pH 7.8 to pH 7.5. The feed rate during operation does not change, but it can slowly increase or decrease to maintain a constant catholyte pH at any optimum operating pH range.

Example  12

The same cell as Examples 1, 2 and 3 with freshly prepared indium on a tin electrochemical catalyst coating on a copper mesh cathode was used. The prepared cathode had a calculated surface area of about 3,171 cm ^2, an area of about 31 times that of a flat cathode plate area, a 91% pore volume, and a specific surface area of 12.3 cm ² / cm ³ .

In this experimental run, the system was run with a catholyte composition containing 1.40 moles of potassium bicarbonate (120 gm / L KHCO ₃ ) and sparged with carbon dioxide to a final pH of 7.8 before use.

The cell was operated in a recirculation batch mode for 8 hours of initial operation to obtain a caustic liquid formate ion concentration of up to about 20,000 ppm and then a fresh feed of 1.4 M potassium bicarbonate was fed at a feed rate of about 1.2 mL / . Overflow volumes were collected and volumetrically measured, and overflow and catholyte loop samples were sampled and analyzed by ion chromatography for the formate salt.

Operating conditions:

Cathode: tin-phase electroless indium on copper mesh substrate

Continuous supply with cathodic liquid recycle operation - 21 days

Anode liquid solution: 0.92 MH ₂ SO ₄

Cathode liquid solution: 1.4 M KHCO ₃

Cathode liquid flow rate: 3.2 LPM

Cathodic Liquid Flow Rate: 0.09 ft / sec

Applied Current: 6 amps (6,000 mA)

result:

Battery Voltage vs. Time: The battery exhibited a higher operating voltage, about 4.40 volts, than other batteries, due to insufficient electrical voltage of the cathode to the indium foil conductor backplate. The battery maintained its drive for extended operation.

Continuous operation time: 21 days

Foamate Faraday Yield: Figure 19 shows calculated formate current efficiency versus time, from which the yield of the foam acid was measured. Foam Faraday current efficiency decreased to 20% after 16 days.

Foamate concentration versus time: Figure 20 shows the results of the foam acid concentration versus time. On the 21st day, 0.5 gm of indium (III) carbonate was added to the catholyte during battery operation at a 6 amp operating speed. The formate concentration in the catholyte working loop before addition of indium was 11,330 ppm and increased to 13,400 ppm after 8 hours and to 14,100 ppm after 16 hours when the unit stopped after 21 days of operation.

Cathodic Fluid pH: Figure 21 shows the change in catholyte pH over a continuous drive period and was driven to a pH of 7.6 to 7.7, except for the off-datum point near 16 days when the feed pump stopped pumping. The feed rate did not change during operation, but could be increased or decreased to maintain constant pH drive to the optimum range.

The present disclosure and many of the attendant advantages thereof are believed to be understood by those skilled in the art and do not depart from the spirit and scope of the present disclosure or make all variations of the materials thereof without departing from the scope of the present invention, It is clear that this can be done. It is to be understood that the above-described forms described herein are merely exemplary embodiments thereof, and the following claims are intended to cover and include the changes.

Claims (30)

As a method for electrochemically reducing carbon dioxide to a product,
(A) introducing an acidic anolyte into a first compartment of an electrochemical cell;
(B) introducing a bicarbonate-based caustic solution saturated with carbon dioxide into the second compartment of the electrochemical cell; And
(C) applying between the anode and the cathode a potential sufficient to reduce the carbon dioxide to at least one of the single-carbon or multi-carbon based products
, ≪ / RTI &
The first compartment comprising an anode,
Wherein the second compartment comprises a high surface area cathode, wherein the high surface area cathode comprises an indium coating and has a void volume of about 30% to 98%, at least a portion of the bicarbonate based cathode liquid being recycled. The method according to claim 1,
The step of applying a potential between the anode and the cathode sufficient to reduce the carbon dioxide to at least one of the single-carbon or multi-carbon based products comprises reducing the carbon dioxide to a single-carbon based product comprising an alkali metal formate salt Lt; RTI ID = 0.0 > between < / RTI > the anode and the cathode. 3. The method of claim 2,
Introducing an alkali metal formate into a second electrochemical cell; And
Converting the alkali metal formate salt to at least formic acid by applying an electric potential to the second electrochemical cell
≪ / RTI > The method according to claim 1,
Wherein the cathode compartment further comprises a homogeneous heterocyclic amine catalyst. 5. The method of claim 4,
Wherein the homogeneous heterocyclic amine catalyst is selected from the group consisting of 4-hydroxypyridine, adenine, sulfur containing heterocyclic amines, oxygen containing heterocyclic amines, azoles, benzimidazoles, bipyridines, furans, imidazoles, Pyridine, pyridine-related species having at least one six-membered ring, pyrrole, quinoline, or pyrimidine ring having at least one six-membered ring, Thiazole, and mixtures thereof. The method according to claim 1,
Wherein the high surface area cathode comprises indium deposited on tin. The method according to claim 6,
Wherein the high surface area cathode further comprises tin deposited on the copper substrate and the copper substrate. The method according to claim 1,
Further comprising operating the electrochemical cell at a pressure above atmospheric pressure. The method according to claim 1,
Wherein the anode comprises an electrocatalyst coating comprising at least one of ruthenium oxide, iridium oxide, platinum, platinum oxide, gold and gold oxide. The method according to claim 1,
Wherein the electrochemical cell comprises a membrane designed to selectively control the flow of ions between the first compartment and the second compartment. A method of controlling pH in a cathode compartment of an electrochemical system having an acidic anolyte,
(A) introducing an acidic anode liquid into a first compartment of an electrochemical cell;
(B) introducing a carbon dioxide saturated catholyte into the second compartment of the electrochemical cell;
(C) removing at least a portion of the catholyte from the second compartment;
(D) recirculating at least a portion of the catholyte back into the second compartment; And
(E) introducing a new catholyte liquid stream into at least one of at least a portion of the catholyte or second compartment, or (ii) introducing water into the second compartment, controlling the
Lt; / RTI >
The first compartment comprising an anode,
Wherein the catholyte comprises at least one alkali metal bicarbonate, an alkali metal carbonate, an alkali metal sulfate, an alkali metal chloride and mixtures thereof, the second compartment comprising a high surface area cathode, the high surface area cathode comprising an indium coating And has a void volume of about 30% to 98%. 12. The method of claim 11,
Wherein the catholyte comprises an alkali metal bicarbonate. 13. The method of claim 12,
Wherein the alkali metal bicarbonate is potassium bicarbonate. 14. The method of claim 13,
Wherein the potassium bicarbonate has a concentration range of about 5 to 600 g / l. 12. The method of claim 11,
Wherein the catholyte comprises an alkali metal carbonate. 16. The method of claim 15,
Wherein the alkali metal carbonate is potassium carbonate. 17. The method of claim 16,
Wherein the potassium carbonate has a concentration range of about 5 to 1500 g / l. As a method for electrochemically reducing carbon dioxide to a product,
(A) introducing an acidic anolyte into a first compartment of a first electrochemical cell;
(B) introducing a catholyte comprising an alkali metal bicarbonate into a second compartment of a first electrochemical cell;
(C) applying a potential between the anode and the cathode sufficient to reduce carbon dioxide to the alkali metal formate salt;
(D) introducing an alkali metal formate into an ion exchange section of a second electrochemical cell;
(E) applying a potential between the anode of the second electrochemical cell and the cathode of the second electrochemical cell sufficient to produce at least formic acid and an alkali metal hydroxide; And
(F) introducing an alkali metal hydroxide together with carbon dioxide to produce at least a portion of the alkali metal bicarbonate introduced into the second compartment of the first electrochemical cell
Lt; / RTI >
The first compartment comprising an anode,
Wherein the catholyte is saturated with carbon dioxide and the second compartment comprises a high surface area cathode, the high surface area cathode comprising an indium coating and having a void volume of about 30% to 98%, the bicarbonate based catholyte Is recycled. 19. The method of claim 18,
Further comprising the step of separating the alkali metal formate salt from the alkali metal bicarbonate of the catholyte of the first electrochemical cell using a nano-filtration system. 20. The method of claim 19,
Separating the alkali metal formate salt from the alkali metal bicarbonate of the catholyte of the first electrochemical cell using a nano-filtration system,
Introducing an alkali metal bicarbonate of a catholyte into an alkali metal hydroxide to convert at least a portion of the alkali metal bicarbonate to an alkali metal carbonate; And
Separating the alkali metal carbonate from the alkali metal formate salt using a nano-filtration unit. 21. The method of claim 20,
Further comprising introducing an alkali metal carbonate together with an alkali metal hydroxide and carbon dioxide to produce at least a portion of the alkali metal bicarbonate introduced into the second compartment of the first electrochemical cell. 19. The method of claim 18,
Wherein at least a portion of the alkali metal hydroxide is from at least one of the first electrochemical cell and the second electrochemical cell. 19. The method of claim 18,
Wherein formic acid is produced in an ion exchange section of a second electrochemical cell. 19. The method of claim 18,
Wherein an alkali metal hydroxide is produced in the cathode compartment of the second electrochemical cell. 19. The method of claim 18,
Wherein the high surface area cathode has a specific surface area greater than 2 cm < ² > / cm < ³ >. 19. The method of claim 18,
Wherein the acidic anolyte solution comprises sulfuric acid. 19. The method of claim 18,
Further comprising the step of producing a halogen selected from the group consisting of F ₂ , Cl ₂ , Br _2, and I ₂ in at least one of the first compartment of the first electrochemical cell and the first compartment of the second electrochemical cell How to. 28. The method of claim 27,
Further comprising reacting the halogen with an organic compound to produce a halogenated product. 28. The method of claim 27,
Wherein the halogen is bromine. 29. The method of claim 28,
Wherein the halogen is bromine.

Images