NOVEL CATHODE CONFIGURATION FOR ENHANCED ELECTROCHEMICAL CONVERSION OF CARBON DIOXIDE INTO REDUCED PRODUCTS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Application Nos. 63/569,830, filed Mar. 26, 2024, which is hereby incorporated by reference in its entirety.

STATEMENT OF GOVERNMENTAL SUPPORT

This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the United States Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

This invention relates generally to electrochemical conversion of carbon dioxide into reduced products.

BACKGROUND OF THE INVENTION

Integrating electrochemical CO₂ reduction to a C1 substrate (i.e., formic acid) with its biological upgrade in one pot allows one to efficiently supply energy to microorganisms using electricity and CO₂ while reducing capital costs and diluting the microbial broth. The integration in 1 pot requires using the right biocompatible electrochemical operational environment so that C1 substrates can be produced and consumed simultaneously. One of the main challenges of this integration is maintaining high electrocatalysis performance (selectivity and reaction rates) and lifespan when electrodes are used in a biocompatible electrolyte.

SUMMARY OF THE INVENTION

The present invention provides for a system comprising a cathode configuration for enhanced electrochemical conversion of carbon dioxide into reduced products. In some embodiments, the system is encompassed in a device configured to operate the system. In some embodiments, the system or device comprises (a) an electrode, wherein the electrode optionally comprises a plurality of microparticles on a surface of the electrode, wherein the microparticles comprise tin (Sn), indium (In), and/or bismuth (Bi), and (b) an electrolyte solution comprising a plurality of microparticles wherein the microparticles comprise tin (Sn), indium (In), and/or bismuth (Bi). In some embodiments, the microparticles are free floating or suspended in the electrolyte solution.

The device comprises an anode and a cathode. In some embodiments, the cathode is a fluidized bed cathode. In some embodiments, the device is configured to have a carbon dioxide bubbling through the electrolyte solution. In some embodiments, the electrolyte solution is under agitation when the device is in operation. In some embodiments, the cathode comprises a mesh. In some embodiments, the cathode comprises an electroconductive metal, such as stainless steel. In some embodiments, the mesh is a SS316 mesh. In some embodiments, the cathode has an about 5% to 10% particle load each of Sn microparticle, In microparticle, and/or Bi microparticle, or any combination thereof. In some embodiments, the cathode is a fluidized bed cathode having an about 5% to 10% particle load each of Sn microparticle, In microparticle, and/or Bi microparticle, or any combination thereof.

In some embodiments, the device comprises a reactor configuration comprising a sandwich-type electrosynthesis cell comprising of two compartments (anodic and cathodic) interconnected with an ionic exchange membrane.

In some embodiments, the electrolyte solution comprises a Sn microparticle, an In microparticle, and/or a Bi microparticle, or any combination thereof. In some embodiments, the electrolyte solution comprises a Sn microparticle and an In microparticle. In some embodiments, the electrolyte solution comprises a Sn microparticle and a Bi microparticle. In some embodiments, the electrolyte solution comprises an In microparticle and a Bi microparticle.

The present invention provides for a method of culturing a bacterium capable of utilizing formic acid comprising: (a) providing a device of the present invention and a power source in electrical communication with the device, (b) running a current through the electrode of the device by the power source, (c) producing formic acid through reacting carbon dioxide with electrons from the cathode, and (d) a bacterium capable of utilizing formic acid utilizes or metabolizing the formic acid produced to growth.

In some embodiments, the bacterium is capable of utilizing formic acid as a sole carbon source. In some embodiments, the bacterium is a Cupriavidus species. In some embodiments, the bacterium is a Cupriavidus necator. In some embodiments, the bacterium is naturally capable of utilizing or metabolizing formic acid. In some embodiments, the bacterium is naturally capable of utilizing or metabolizing formic acid as a sole carbon source. Examples of naturally capable of utilizing or metabolizing formic acid are disclosed by Jiang et al., 2021 (Wei Jiang et al., “Metabolic engineering strategies to enable microbial utilization of C1 feedstocks,” Nature Chem. Biol . . . 17:845-855, 2021). In some embodiments, the bacterium is engineered or constructed to be capable of utilizing or metabolizing formic acid. An example of Escherichia coli engineered or constructed to be capable of utilizing or metabolizing formic acid is disclosed by Bang et al., 2020 (Junho Bang, Chang Hun Hwang, Jung Ho Ahn, Jong An Lee, Sang Yup Lee. “Escherichia coli is engineered to grow on CO₂ and formic acid,” Nature Microbiol., 5; 1459-1463, 2020).

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

FIG. 1. A configuration based on the use of fluidized bed electrodes to couple the bioconversion of electricity and CO₂ into chemicals.

FIG. 2. Screening of catalysis selective to CO₂ reduction to formic acid.

FIG. 3. Selecting and obtaining a biocompatible material to be used as fluidized bed cathode. All In, Tin and Bi microparticles showed great compatibility with Cupriavidus necator growth at 2.5% (v-bed/v-media) quantity and in a heterotrophic medium, and under shaking conditions. Tin at 10% levels showed to inhibit growth, however, cells were able to rapidly acclimate to grow in the presence of a 10% (v/v) of this electrocatalyst.

FIG. 4. Electrical connection between particles and collector. The experimental conditions were: 1 mM Hexaammineruthenium (III) Chloride as redox probe E=−0.8 V (vs Ag/AgCl 3M), T=30° C., Electrolyte: 50 mM NaCl. Cathode: mesh of SS316 (30 cm²)+5% In (bed/electrolyte, v/v).

FIG. 5. CO₂ electrolysis to formic acid by microparticles. The experimental conditions were: E=−1.5 V (vs Ag/AgCl 3M), T=30° C. Cathode: mesh of stainless steel+5% (bed/electrolyte, v/v). Electrolyte: 50 mM NaHCO₃, 0.5 g/L MgSO₄; 0.5 g/L K₂SO₄.

FIG. 6. Compatibility of electrochemical conditions with growth. Examined the growth of Cupriavidus necator at different cathodic compared with open circuit (OCP) mode as control using Sn and a minimal growth medium (minerals, 50 mM NaHCO₃, 0.5 g/L MgSO₄; 0.5 g/L K₂SO₄). Sn, In and Bi are biocompatible electrocatalysts with C. necator under nonpolarized conditions and heterotrophic growth. However, polarizations conditions for driving CO₂ reduction can significantly affect growth. The production of formic acid was highest with indium powder compared to Sn and Bi over 140 min. Without CO₂ injection (low CO₂ availability), growth of C. necator was slightly affected at the polarization of −1.5 V compared to −1 V and control. However, with CO₂ injection, growth under −1 V was significantly impacted compared to OCP conditions. CO₂ reduction to formic acid at −1.5 V and a minimal growth medium was significantly higher than at −1 V.

FIG. 7. Performance of the different fluidized bed cathodes (5% particle load) tested compared to the condition in which no particles, but only the gas diffusion current collector, are employed for the catalytical conversion of CO₂ to formic acid.

FIG. 8. Carbon balance (%) for the reactor inlet and outlet.

FIG. 9. Cupriavidus necator culture growth with different particle catalyst versus time.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings:

The terms “optional” or “optionally” as used herein mean that the subsequently described feature or structure may or may not be present, or that the subsequently described event or circumstance may or may not occur, and that the description includes instances where a particular feature or structure is present and instances where the feature or structure is absent, or instances where the event or circumstance occurs and instances where it does not.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

The term “about” refers to a value including 10% more than the stated value and 10% less than the stated value.

In our invention, we tested a novel configuration for CO₂ electrolysis comprising the use of electrocatalytical particles (Sn, In, and Bi) that are suspended, agitated and/or fluidized within an electrolyte solution in a two-chamber sandwich-type microbial electrosynthesis cell, where a flat and static cathode electrode serves as the current collector. We currently have a configuration that operates with a biocompatible electrolyte and directly converts CO₂ into formic acid with remarkable selectivity (90%), and high production rates. The use of suspended selective electrocatalyst in the microparticles form allowed for an enhancement of coulombic efficiency and product production as compared to when the system operated only with the flat current collector gas diffusion electrode with and without a coating of selective material (i.e. Bi) for CO₂ reduction. The enhanced performance of our configuration was observed at low potentials typically employed for CO₂ reduction, i.e. below-1V vs Ag/AgCl.

Current methods employ flat and/or static gas diffusion electrodes for electron delivery, leading to biocatalytic and electron transfer challenges associated with inadequate mass transfer, possible loss of electrocatalyst, and a limited surface electrocatalytic area, resulting in lower conversion rates of CO₂ to formic acid. This innovative approach offers a promising technological advancement for improving the efficiency of CO₂ reduction to value-added chemical species using electrical energy, overcoming challenges associated with conventional static cathode electrodes.

In some embodiments, the system comprises a configuration made of fluidized bed cathodes from CO₂ reduction to formic acid, in conjunction with microorganisms grown on the electrolyte.

Previous studies have explored electrochemical processes to transform CO₂ into chemical products, but achieving high efficiency has proven challenging. In addition, issues related to the electroconductive materials and electrode geometries significantly hinder the technology's expansion to pilot scale.

We are addressing these challenges by investigating the use of microbial electrochemical fluidized bed reactors (ME-FBR) to convert CO₂ into chemicals with direct and indirect electron transfer approaches. Utilizing fluidized bed electrodes enhances gas-liquid mass transport and electron transfer, facilitating the efficient coupling of electrochemical and biological conversions.

In our research, we have identified commercial electrocatalysts (Sn, In, and Bi) as potential candidates for the fluidized bed cathode. These catalysts enable the reduction of CO₂ to formic acid under highly selective and efficient conditions. We tested the biocompatibility of these materials with model microorganisms (Cupriavidus necator) capable of utilizing formic acid. Our findings demonstrated that these microorganisms can thrive in the presence of suspended particles of these electrocatalysts, adapting rapidly to the environment. Consequently, we established ME-FBR using fluidized particles (In, Sn, and Bi) for the indirect conversion of CO₂ to formate, and subsequent biological upgrading by C. necator. For the direct approach, we integrated fluidized particles (conductive glassy carbon and activated carbon) for the conversion of CO₂ to diverse chemical products with Clostridium ljungdahlii and mixed consortia. Our results indicated that microbial electrochemical fluidized bed reactors offer innovative approaches to efficiently couple CO₂ electrolysis with biological C1 upgrading.

Analysis showed that: microbial biocompatibility, electrical conductivity using a mesh of stainless steel current collector to evaluate whether they can be used as electrodes., and their capacity under that set-up to produce formic acid in an H-shape reactor when they are stirred with a magnetic bar and interacting with a stainless steel mesh.

In our innovative design, we conducted experiments to evaluate a novel cathode electrode configuration. This unique electrode comprises of microparticles made of selective electrocatalytical particles, namely tin (Sn), indium (In), and bismuth (Bi) into the electrolyte. These electrocatalysts are suspended and agitated within an electrolyte solution employing a CO₂ stream, a liquid or mechanical agitation and integrated into a sandwich-type microbial electrosynthesis cell, where a flat and static selective electrocatalytical cathode electrode serves as electrode and the current collector.

The particles remain suspended or fluidized within the electrolyte, which enhances mass transfer and particles-electrode interactions, addressing limitations associated with poor mass transfer and limited surface electrocatalytic area, often observed in traditional flat and static cathode electrodes.

This configuration can directly convert CO₂ into formic acid and potentially other CO₂ reduction products with an impressive 90% selectivity. Under a polarization of −2 V vs. Ag/AgCl, our innovative cathode electrode configuration exhibited a 2-fold increase in formic acid formation from CO₂ (0.2 mmol/h or 6.7 mmol/h/L and CE 90%) when contrasted with only the electrocatalytical static current collector electrode (0.1 mmol/h or 3.4 mmol/h/L and CE % 80%). This inventive approach offers a solution for improving the efficiency of CO₂ electrochemical reduction into products The incorporation of the electrocatalytic particles in motion enhances both the selectivity and rates of CO₂ conversion, for instance into formic acid, marking a significant advancement in the field of microbial electrosynthesis. It also eliminates the decrease in performance of the electrolyzer associated with the loss of electrocatalyst layer (nano or microparticles) coated or deposited on flat gas diffusion electrodes that many scientific studies report.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

It is to be understood that, while the invention has been described in conjunction with the preferred specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages, and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

All patents, patent applications, and publications mentioned herein are hereby incorporated by reference in their entireties.

The invention having been described, the following examples are offered to illustrate the subject invention by way of illustration, not by way of limitation.

Example 1

Interfacing Electrochemical Reduction of CO₂ and Biological Upgrading Using Fluidized Bed Cathodes

Gas fermentations are inexpensive and selective methods to fix carbon into desired products if reducing equivalents in the form of electrons are supplied. However, gas fermentations are constrained by the low solubility of gases in liquids and the inefficient delivery of electrons to microorganisms in bioreactors. Electricity has proven to effectively provide the energy source needed by microorganisms directly or via intermediates that are produced electrocatalytically (i.e., formate, H2). However, current approaches deliver electrons using flat and/or static electrodes, which poses (bio) catalytic and electron transfer limitations related to poor mass transfer and low electrocatalytic surface area. Thus, these processes do not achieve high enough production rates and energy conversion efficiencies to be scalable.

We propose to explore a configuration based on the use of fluidized bed electrodes to couple the bioconversion of electricity and CO₂ into chemicals (see FIG. 1).

Pre-Selection of Material and Methods

• • 1. Screening of catalysis selective to CO₂ reduction to formic acid: Commercially available as microparticles, and good selectivity to formic acid (see FIG. 2).

Materials selected (which are commercially available): (1) Indium (In), <150 μm (Atlantic Equipment Engineers (Upper Saddle River, NJ), 100 μm, 99.99% purity); (2) Tin (Sn), <150 μm (Thermo Fisher Scientific (Waltham, MA), 100 mesh, 99.85% purity); (3) Bismuth (Bi), <100 μm (Thermo Fisher Scientific (Waltham, MA), 100 mesh, 99.5% purity).

Preliminary Results

• • 1. Selecting and obtaining a biocompatible material to be used as fluidized bed cathode. All In, Tin and Bi microparticles showed great compatibility with Cupriavidus necator growth at 2.5% (v-bed/v-media) quantity and in a heterotrophic medium, and under shaking conditions. Tin at 10% levels showed to inhibit growth, however, cells were able to rapidly acclimate to grow in the presence of a 10% (v/v) of this electrocatalyst (see FIG. 3).
  • 2. Electrochemical conversion of CO₂ to formic acid with particles as electrocatalysts. Electrical connection between particles and collector. The experimental conditions were: 1 mM Hexaammineruthenium (III) Chloride as redox probe E=−0.8 V (vs Ag/AgCl 3M), T=30° C., Electrolyte: 50 mM NaCl. Cathode: mesh of SS316 (30 cm²)+5% In (bed/electrolyte, v/v) (see FIG. 4). CO₂ electrolysis to formic acid by microparticles. The experimental conditions were: E=−1.5 V (vs Ag/AgCl 3M), T=30° C. Cathode: mesh of stainless steel+5% (bed/electrolyte, v/v). Electrolyte: 50 mM NaHCO₃, 0.5 g/L MgSO₄; 0.5 g/L K₂SO₄ (see FIG. 5.)
  • 3. Compatibility of electrochemical conditions with growth. Examined the growth of Cupriavidus necator at different cathodic compared with open circuit (OCP) mode as control using Sn and a minimal growth medium (minerals, 50 mM NaHCO₃, 0.5 g/L MgSO₄; 0.5 g/L K₂SO₄) (see FIG. 6.). Sn, In and Bi are biocompatible electrocatalysts with C. necator under nonpolarized conditions and heterotrophic growth. However, polarizations conditions for driving CO₂ reduction can significantly affect growth. The production of formic acid was highest with indium powder compared to Sn and Bi over 140 min. Without CO₂ injection (low CO₂ availability), growth of C. necator was slightly affected at the polarization of −1.5 V compared to −1 V and control. However, with CO₂ injection, growth under −1 V was significantly impacted compared to OCP conditions. CO₂ reduction to formic acid at −1.5 V and a minimal growth medium was significantly higher than at −1 V.

Preliminary Conclusions

Selective electrocatalysis for CO₂ reduction to formic acid are biocompatible and have the potential to be used to couple CO₂ reduction and formic acid upgrading in one reactor. However, media composition, formic acid production and polarization will affect growth and the CO₂ evolution. Thus, it is critical to deeply examine the media, material, and operational conditions to evaluate viability of integration.

Example 2

Fluidized Bed Cathode for Enhanced Carbon Dioxide Electroreduction to Formic Acid

The present invention allows one to efficiently perform CO₂ electrolysis to formic acid with high surface and volumetric area electrocatalysts design in a 2-chamber configuration, and with compatible electrochemical and biological environments.

Our configuration employs microparticles (50-150 μm) made of selective electrocatalytical particles, namely tin (Sn), indium (In), and bismuth (Bi) into the electrolyte. Concentrations of between 2 and a 10% v-material/v-electrolyte were used. These electrocatalysts are used as suspended bed and agitated within an electrolyte solution in the cathodic compartment of a 2-chamber electrochemical cell by employing a CO₂ stream, and/or mechanical agitation. The reactor configuration is a sandwich-type electrosynthesis cell comprising of 2 compartments (anodic, cathodic), interconnected with an ionic exchange membrane. A flat and static selective electrocatalytical cathode electrode serves as electrode to connect the microparticles with the external power source and the current collector, and is placed in proximity to the membrane. This flat current collector is made of a carbon-based gas diffusion electrode with selective micro-particles of Bi, Tin or In, deposited on its surface to avoid side-products production. When the particles interact with the current collector, charge is transferred to the particles and the selective carbon dioxide reduction to formic acid occurs. A liquid electrolyte is used in both compartments. For the cathodic compartment, an electrolyte of biocompatible salts such as NaSO₂, Mg₂O₄, and NaHCO₃ at levels that are viable for microbial growth was employed.

The particles remain suspended or fluidized within the electrolyte, which enhances mass transfer and particles-electrode interactions, addressing limitations associated with poor mass transfer and limited surface, electrocatalytic area, often observed in traditional flat and static cathode electrodes.

In some embodiments: This configuration can directly convert CO₂ into formic acid (FA) and potentially other CO₂ reduction products with an impressive 92% selectivity under a polarization of −2 V vs. Ag/AgCl (FIG. 1). All the electrically conductive and selective particles tested of Tin, In and Bi, all commercially available, showed a greater performance than when no particles were added to the electrolyte. A significant increase in FA production rate was obtained under all the different potentials tested (−2V, −1.5V and −1.2 V), while a greater selectivity with the microparticles was observed for greater potentials than-1.2V. When using Tin microparticles, a cheap and widely available material, our innovative configuration exhibited up to a 2-fold increase in formic acid production from CO₂ (0.24 mmol/h/cm2—or 6.7 mmol/h/L and CE 92%) when contrasted with only the electrocatalytical static current collector electrode (0.12 mmol/h or 3.4 mmol/h/L and CE % 72%).

This novel configuration was also able to operate with consistent performance for at least 120 h using a biocompatible electrolyte (FIG. 7).

This inventive approach offers a promising solution for improving the efficiency of CO₂ electrochemical reduction into products. It provides a mean for expanding the CO₂-electrocataysis to C1 products volumetrically, and beyond the surface of a flat gas diffusion electrode, allowing thus to use higher volumes of electrolyte within an electrochemical cell. The incorporation of the electrocatalytic particles in motion also enhances both the selectivity and rates of CO₂ conversion into formic acid, marking a significant advancement in the field of microbial electrosynthesis. It can also eliminate the decrease in performance of the electrolyzer associated with the loss of electrocatalyst layer (nano or microparticles) coated or deposited on flat gas diffusion electrodes that many scientific reports.

This configuration can also minimize biofouling as the continuous movement of the particles reduces the likelihood of biofouling when microorganisms are used in the same chamber where CO₂ is reduced, preventing the accumulation of contaminants/bacteria on the electrode surface. This feature is crucial for maintaining consistent performance over time, which may be compromised by biofilm formation on static and flat cathode electrodes.

The adoption of the novel configuration for the conversion of CO₂ to chemicals, including but not limited to formic acid, hydrogen, carbon monoxide or methanol, has the potential to be embraced by various types of consumers, companies, and organizations with specific interests and needs. The products of CO₂ electrolysis, including carbon-based fuels and other value-added chemicals, can serve as green alternatives of fossil fuel-based products. For instance, the industrially relevant hots C. necator can be cultured in electrolytes that support CO₂-electrolysis and this host is also able to utilize formic acid as sole carbon source. Thus, with our innovation it would be possible to efficiently biomanufacture from carbon dioxide streams and electricity with the host C. necator in a 1 pot hybrid bioelectrochemical reactor. His can be extrapolated to other hosts that can utilize the CO₂-electrolysis products.

Since the reactor was supplied continuously with CO₂ at a fixed flow rate (15 mL/min), the overall carbon balance was assessed (FIG. 8). Notably, the use of a Tin microparticle catalyst at −2 V significantly improved the carbon conversion efficiency (CCE) to formic acid, achieving 41.4%, while the solid electrode without the catalyst only reached a CCE of 20.5%.

To assess the biocompatibility of microparticles with Cupriavidus necator, experiments were conducted using 5% and 10% concentrations of Tin, Indium, and Bismuth microparticles (FIG. 9). Additionally, a control group without particles was included for comparison. The biocompatibility was evaluated based on the microbial growth patterns observed under each condition. The results indicated that C. necator exhibits high biocompatibility with all tested particles at a 5% concentration. Microbial growth at this concentration was robust, closely matching the growth trend observed in the control group without particles. Among the tested metals, 5% Tin particles demonstrated a particularly interesting effect, enhancing microbial growth beyond that of the control group. This improvement in growth may be attributed to the catalytic activity of Tin, which possibly facilitates oxidation-reduction reactions beneficial for the bacterial metabolism. Therefore, Tin particles at lower concentrations not only do not hinder the growth of C. necator but may actively promote it through catalytic interactions. These results demonstrate that this system can effectively biomanufacture products from carbon dioxide streams and electricity using C. necator as the host organism in a one-pot hybrid bioelectrochemical reactor.

While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.