ELECTRODE CONFIGURATIONS FOR FLOW-THROUGH MEMBRANE-FREE ELECTROLYZERS

Abstract

An electrolytic device including a housing and at least one electrolytic cell disposed in the housing. The electrolytic cell includes a plurality of porous cathodes, a plurality of porous anodes, with each of the plurality of porous anodes disposed directly adjacent to a respective one of the plurality of cathodes so as to form a plurality of anode-cathode pairs, and a plurality of walls with each wall disposed between the porous anode and the porous cathode within each respective one of the plurality of anode-cathode pairs. At least one inlet delivers electrolyte to the porous cathodes and the porous anodes. The porous anodes and cathodes include at least partially folded portions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/IB2024/000497, filed September 10, 2024, which claims priority to and the benefit of U.S. Provisional Patent Application No. 63/537,611, filed September 11, 2023 and entitled ELECTRODE CONFIGURATIONS FOR FLOW-THROUGH MEMBRANE-FREE ELECTROLYZERS, the contents of each of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to electrochemical devices, and in particular to electrochemical devices that use flow-based product separation instead of membrane-based separation.

BACKGROUND

Electrolysis is a very important industrial process used to produce a variety of vital chemical building blocks. Processes such as the chlor-alkali process, electro-synthesis of anthraquinone, and electro-fluoridation all play essential roles in the production of chemicals used in our everyday lives. Electrolysis can be an energy efficient process with a significantly lower carbon footprint compared to traditional thermal catalysis processes if the input electricity is derived from a renewable resource such as wind or solar. As of 2006, chemical production by electrochemical processes made up more than 6% of the total electrical generating capacity of the United States, with the most energy intensive process as being performed by the chlor-alkali industry. These processes are used to produce hydrogen gas, caustic soda (sodium hydroxide), and chlorine gas. For the chlor-alkali processes, and most electrolysis processes, the economics are dominated by the cost of electricity, which accounts for a significant fraction of the total manufacturing cost. However, the decreasing costs of electricity from renewable resources and the continued adoption of time-of-use pricing schemes are likely to change the economics of electrochemical processes, shifting importance towards decreasing the capital cost of the electrolyzer system itself.

The process chemistry of the chlor-alkali process is relatively simple but the operational and reactor design issues are vastly complex. The most energy efficient electrolyzer in the chlor-alkali industry is the membrane electrolyzer. The membrane electrolyzer functions by separating anolyte and catholyte streams by means of an ion selective membrane and that only allows cationic species (e.g., Na+, K+, H+) and small amounts of water to pass through it. Diaphragm electrolyzers and mercury electrolytic cells are also used to produce bases, although these technologies are being phased out in favor of membrane reactors. This is due to health and environmental concerns relating to the use of asbestos and mercury, respectively. Key challenges with membrane electrolyzers include the high cost of the ion-selective membranes and their susceptibility to fouling. Various approaches have been pursued in order to improve the yield, energy efficiency, economics, and environmental impacts of the membrane process.

Efforts have been made to address the problems with membrane electrolyzers by introducing so-called “membrane-free” electrolyzers. These electrolyzers operate without membranes due to the use of porous electrodes combined with flow-induced separation of products before they can cross over between anolyte and catholyte effluent streams. The simplicity of such designs allows them to be fabricated by low-cost manufacturing techniques (e.g., injection molding) and thereby offers great promise for decreasing the capital costs associated with electrolysis processes. Membrane-free electrolyzers are described in U.S. Patent No. 10/844,494, U.S. Patent Application Publication No. 2022-0194823, U.S. Patent Application Publication No. 2021-0188711, PCT Application Publication No. WO2020/198350 and PCT Application Publication No. WO2022/104242, the contents of which are incorporated herein by reference in their entirety.

Present membrane-free water electrolysis devices use electrodes that trap hydrogen or oxygen bubbles produced at the electrode due to the liquid flow being normal to the electrode orientation resulting in poor gas purity.

The flat orientation of electrodes causes large potential and current density gradients across the electrode, resulting in efficiency loss. In addition, the two-dimensional nature of these electrodes results in a lower electrically active surface area per geometric area, which also results in efficiency loss.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of positioning and shaping metal mesh electrodes for membrane-free alkaline seawater electrolyzers that improve the fluid flow profiles and efficiency of these devices.

In exemplary embodiments, the present invention provides (i) possible electrode morphologies and (ii) positioning of the electrodes in the membrane-free electrolyzer device that achieve improvements in fluid flow profiles and device efficiency.

An electrolytic device according to an exemplary embodiment of the present invention comprises: a housing; and at least one electrolytic cell disposed in the housing and comprising:

a plurality of porous cathodes; a plurality of porous anodes, each of the plurality of porous anodes disposed directly adjacent to a respective one of the plurality of cathodes so as to form a plurality of anode-cathode pairs, at least one of: a) at least one of the plurality of porous cathodes comprising at least one partially folded portion or b) at least one of the plurality of porous anodes comprising at least one partially folded portion; and a plurality of walls with each wall disposed between the porous anode and the porous cathode within each respective one of the plurality of anode-cathode pairs; and at least one inlet for delivery of electrolyte to the porous cathodes and the porous anodes.

In an exemplary embodiment, at least one of the plurality of porous cathodes comprises at least one partially folded portion.

In an exemplary embodiment, the at least one partially folded portion of the at least one of the plurality of porous cathodes comprises a plurality of partially folded portions.

In an exemplary embodiment, at least one of the plurality of porous anodes comprises at least one partially folded portion.

In an exemplary embodiment, the at least one partially folded portion of the at least one of the plurality of porous anodes comprises a plurality of partially folded portions.

In an exemplary embodiment, all of the porous cathodes and all of the porous anodes comprise partially folded portions

In an exemplary embodiment, at least one of the plurality of porous cathodes is fully folded along a length of the porous cathode.

In an exemplary embodiment, at least one of the plurality of porous anodes is fully folded along a length of the porous anode.

In an exemplary embodiment, all of the porous cathodes and all of the porous anodes are fully folded along their lengths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 show an electrochemical scheme for the alkaline water splitting reaction to produce H₂ and O₂;

FIG. 2 illustrates a single cell electrolytic device according to an exemplary embodiment of the present invention;

FIG. 3A and 3B illustrate an anode and cathode finger array according to an exemplary embodiment of the present invention;

FIGS. 4A, 4B and 4C illustrate top views of electrodes according to exemplary embodiments of the present invention;

FIGS. 4D, 4E and 4F illustrate cross-sections of electrodes according to exemplary embodiments of the present invention;

FIG. 5A is a photograph of an electrolytic cell with partially folded electrodes according to an exemplary embodiment of the present invention;

FIG. 5B is a photograph of an electrolytic cell with fully folded electrodes according to an exemplary embodiment of the present invention;

FIG. 6 illustrates a folded electrode within a chamber of an electrolytic cell according to an exemplary embodiment of the present invention;

FIGS. 7A, 7B and 7C illustrate different configurations of an electrolytic cell according to an exemplary embodiment of the present invention;

FIGS. 8A and 8B illustrate a surface area comparison between a flat electrode finger and an electrode finger intended for folding according to an exemplary embodiment of the present invention;

FIG. 9A illustrates a woven mesh electrode;

FIG. 9B illustrates an expanded mesh electrode;

FIG. 10 is a graph of cell voltage vs. current density showing performance of an electrolytic cell according to an exemplary embodiment of the present invention;

FIGS. 11A and 11B are graphs of cell voltage vs. current density showing performance of electrolytic cells according to exemplary embodiments of the present invention;

FIGS. 12A and 12B are graphs of current density vs. gas purity exhibited by an electrolytic cell according to an exemplary embodiment of the present invention;

FIGS. 13A and 13B are graphs of current density vs. gas purity exhibited by an electrolytic cell according to an exemplary embodiment of the present invention;

FIG. 14 is a graph of cell voltage vs. current density showing comparison of performance between electrolytic cells according to exemplary embodiments of the present invention;

FIGS. 15A and 15B are graphs of time vs. cell voltage for electrolytic cells according to exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description relates to various exemplary embodiments of an electrolyzer used with H₂ electrochemistry. However, it should be appreciated that the inventive electrolyzer described herein may also be used with O₂ electrochemistry. An exemplary electrochemical scheme is shown in FIG. 1, and is based on H₂ electrochemistry for which H₂ is oxidized at the anode through the hydrogen oxidation reaction (HOR) and H₂ is generated at the cathode through the hydrogen evolution reaction (HER). In this scheme, it is assumed the reaction is happening in a salty, alkaline environment. The overall reaction involves converting the inlet brine solution into one effluent that is more alkaline and another effluent that is more acidic than the inlet brine, without net generation or consumption of H₂. Without being bound by theory, this scheme is the most desirable for applications in seawater or brine since the HOR can be used to generate acid without competing with the chlorine evolution reaction (CER) due to its lower standard reduction potential, and can be implemented in the most energy efficient manner due to the relatively fast kinetics for the HER/HOR

In exemplary embodiments, the systems and methods described herein may be applicable to a number of chemistries, such as, for example, water electrolysis, acid-base production, CO₂ electroreduction, chloralkali process, organic electrosynthesis, waste water purification, sodium chlorate production and hydrogen peroxide production, to name a few.

Referring to FIG. 2, a single membrane-free electrolysis cell 1 according to an exemplary embodiment of the present invention is made up of a porous cathode 10 (where HER occurs), a porous anode 20 (where OER occurs) adjacent to the cathode, and a solid dividing wall 30 placed between them. This electrode-wall configuration can be made into a device that involves (i) the flow of a liquid brine vertically past/through the porous electrodes 10, 20, (ii) the collection of hydrogen gas and remaining liquid in a hydrogen collection chamber 40 above the cathode 10 (iii) the collection of oxygen gas and remaining liquid in an oxygen collection chamber 50 above the anode 20, and (iv) separation of the hydrogen and oxygen gas by means of electrode configuration and the relative placement of the dividing wall.

This single electrode-wall configuration can be increased to any number of electrode pairs to increase the amount of hydrogen production per cell by placing the next electrode pair adjacent to the previous cell. This results in an array of anodic and cathodic electrode fingers, as shown in FIG. 3A. Specifically, FIG. 3A shows a cathode 110 having a cathode base portion 112 and cathode elongated portions 114 extending from the cathode base portion 112, and an anode 120 having an anode base portion 122 and anode elongated portions 124 extending from the anode base portion 122. In an exemplary embodiment, the cathode elongated portions 114 and the anode elongated portions 124 extend across the electrolysis cell so that liquid brine can flow vertically past/through the cathode elongated portions 114 and the anode elongated portions 124 to thereby generate oxygen and hydrogen gas.

Without being bound by theory, the electrode finger configuration not only increases the hydrogen production per cell, but it also may improve the efficiency of the device compared to a single electrode pair. In a single electrode pair, the outer edges of each electrode are far away from the other electrode, resulting in a large solution resistance. However, when electrode pairs are placed next to each other, the “middle” electrodes experience lower solution resistance (see FIG. 3B), improving the cell efficiency.

In exemplary embodiments, the cathode elongated portions 114 and anode elongated portions 124 may have varying shapes. In this regard, FIGS. 4A-4C show examples of the possible shapes of the electrode elongated portions.

A horizontal electrode finger configuration is shown in FIG. 4A, in which all of the electrode fingers are in the same plane and positioned across the entire gas collection chambers. FIG. 4D shows the cross-section of the FIG. 4A configuration taken along the line A-A. In this configuration, the parts of the electrodes that are closest to the adjacent electrode will have a higher local current density due to the lower solution resistance between the electrodes.

A partially folded electrode finger configuration is shown in FIG. 4B. FIG. 4E shows the cross-section of the FIG. 4B configuration taken along the line B-B. With this shape, the outside of the electrode finger is folded upward to create a U-shape at various locations along the length of the electrode finger. This shape allows for the produced gas to flow around the folded parts of the electrode, reducing the possibility of gas bubbles getting trapped below the electrodes and therefore reducing the ionic conductivity. The locations of the folded parts along the length of the electrode finger can be optimized to maximize bubble separation and minimize cell resistance.

A third example of an electrode finger configuration is shown in FIG. 4C, in which the entire electrode finger is folded into a U-shape. FIG. 4F shows the cross-section of the FIG. 4C configuration taken along the line C-C. This configuration allows for the fluid to pass around the electrode fingers and maintain hydrogen and oxygen separation. In addition, the U-shape of the electrode fingers results in the hydrogen or oxygen being located in the center of the gas collection chambers, reducing the possibility of gas crossover to an adjacent chamber.

FIGS. 5A and 5B show electrodes with partial U-shape configurations and electrode with full U-shape configurations, respectively, disposed within a membrane-free electrolysis cell.

In exemplary embodiments, the angle of the folded electrode and the overall folded width can play important roles in fluid dynamics around the electrode and in the gas crossover. FIG. 6 shows how these parameters affect the electrode morphology.

Referring to FIGS. 7A-7C, the positions of the electrodes relative to the bottom of the dividing wall can affect the gas collection purity. Generally, if the electrodes are placed above the bottom of the dividing wall (FIGS. 7B and 7C), there would be little gas crossover. However, this may lead to higher cell resistance, as the ions involved in completing the electrochemical circuit would need to travel a further distance. Because of this phenomenon, there is an optimum position of the electrodes relative to the bottom of the wall that balances the gas purity and the cell resistance.

The electrode configurations described above can be modified further to improve cell efficiency. FIGS. 8A and 8B show how electrode fingers could have a larger surface area, improving the cell efficiency further. When the electrodes are placed horizontally (FIG. 8A), the maximum electrode width is the width of the gas collection chambers. However, with the folded electrodes, the initial width of the electrode finger can be much wider (FIG. 8B), as long as the folded width is smaller than the gas collection chambers. The dimensions shown in FIGS. 8A and 8B and merely exemplary, and not intended to be limiting.

In exemplary embodiments, any porous, flow-through electrode can be used in the configurations described herein. FIGS. 9A and 9B show examples of woven mesh and expanded mesh, respectively. Metal foam electrodes can also be used. The porosity and pore size of the electrode can affect the fluid dynamics and gas removal from the surface of the electrodes. The thickness of the electrode may also affect the ability of the electrode finger to be folded. In order to fold the electrodes into the desired shape, the electrode needs to be malleable enough for the folding process. In exemplary embodiments, the electrodes may be made of materials, such as, for example, nickel mesh, nickel foam, stainless steel mesh, stainless steel foam, titanium mesh, carbon foam, and any catalyst material coated on the metal mesh substrate, to name a few.

FIG. 10 provides a graph of cell voltage vs. current density of an electrolysis cell with a conventional flat electrode operating under the conditions listed in the figure. As shown in the graph, performance of the cell diminished as more experiments were run, indicating that bubbles or air pockets were getting stuck on the electrodes.

FIGS. 11A and 11B are graphs of cell voltage vs. current density of an electrolysis cell with a conventional flat electrode and the same electrolysis cell with partly pinched electrodes (as shown in FIGS. 4B and 4E), respectively, operating under the same conditions. The graphs indicate the partly pinched electrodes provided a reduction in bubble induced losses over time.

FIGS. 12A and 12B are graphs of current density vs. gas purity of H₂ and O₂, respectively, showing comparison of results between fully pinched electrodes (as shown in FIGS. 4C and 4F) and partly pinched electrodes. The results were obtained using an electrolysis cell in which electrodes are positioned above the bottom of the dividing wall. The graphs indicate higher O₂ purity was achieved using fully pinched electrodes as compared to partially pinched electrodes, with mixed results for H₂ purity. In this example, the brine flow rate was 50 mL/min and the flow velocity past the electrodes was 0.03 cm/s (50mL/min) and 0.067 cm/s (100mL/min).

FIGS. 13A and 13B are graphs of current density vs. gas purity of H₂ and O₂, respectively, showing comparison of results between fully pinched electrodes (as shown in FIGS. 4C and 4F) and partly pinched electrodes with a brine flow of 100 mL/min. The results were obtained using an electrolysis cell in which electrodes are positioned above the bottom of the dividing wall. The graphs indicate O2 and H2 purities achieved with fully pinched electrodes were about the same as the purities achieved with partially pinched electrodes.

FIG. 14 is a graph of cell voltage vs. current density of an electrolysis cell showing comparison of results between fully pinched electrodes and partially pinched electrodes. The fully pinched electrodes exhibited improved efficiency as compared to the partially pinched electrodes. As shown in the time vs. cell voltage graphs of FIG. 15A and 15B, the fully pinched electrodes exhibited less bubble-induced efficiency losses as compared to partially pinched electrodes.

Now that embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon can become readily apparent to those skilled in the art. Accordingly, the exemplary embodiments of the present invention, as set forth above, are intended to be illustrative, not limiting. The spirit and scope of the present invention is to be construed broadly.

Claims

1. An electrolytic device comprising:

a housing; and

at least one electrolytic cell disposed in the housing and comprising: a plurality of porous cathodes; a plurality of porous anodes, each of the plurality of porous anodes disposed directly adjacent to a respective one of the plurality of cathodes so as to form a plurality of anode-cathode pairs, at least one of: a) at least one of the plurality of porous cathodes comprising at least one partially folded portion or b) at least one of the plurality of porous anodes comprising at least one partially folded portion; and a plurality of walls with each wall disposed between the porous anode and the porous cathode within each respective one of the plurality of anode-cathode pairs; and at least one inlet for delivery of electrolyte to the porous cathodes and the porous anodes.

2. The electrolytic device of claim 1, wherein at least one of the plurality of porous cathodes comprises at least one partially folded portion.

3. The electrolytic device of claim 2, wherein the at least one partially folded portion comprises a plurality of partially folded portions.

4. The electrolytic device of claim 1, wherein at least one of the plurality of porous anodes comprises at least one partially folded portion.

5. The electrolytic device of claim 4, wherein the at least one partially folded portion comprises a plurality of partially folded portions.

6. The electrolytic device of claim 1, wherein all of the porous cathodes and all of the porous anodes comprise partially folded portions

7. The electrolytic device of claim 1, wherein at least one of the plurality of porous cathodes is fully folded along a length of the porous cathode.

8. The electrolytic device of claim 1, wherein at least one of the plurality of porous anodes is fully folded along a length of the porous anode.

9. The electrolytic device of claim 1, wherein all of the porous cathodes and all of the porous anodes are fully folded along their lengths.