Electrolyte Solution for Reversible CO2 Capture and Electrochemical Conversion

Abstract

The electrochemical reduction of CO2 in nonaqueous systems presents a promising avenue for carbon capture and utilization. The role of Fe-based anionic species (FeCl4− and Fe2Cl7−) in mediating CO2 activation and conversion within a quaternary amine-based eutectic electrolyte is accomplished using FTIR spectroscopy and electrochemical techniques, while confirming the formation of Fe—CO2 adducts upon CO2 purging. The electrolyte offers high carbon capture efficiency (14.3 g / L) with a diffusion coefficient of ~1×10−7 cm2 / s. The CO2 integrated electrochemical cell delivers a high discharge capacity of 0.3 mAh / cm2 and cycling efficiency reaching >20 cycles. During electrochemical discharge, the Fe—CO2 adducts undergo electron-driven transformations, producing CO2 reduction products such as formate, and carbonate. The triethylammonium cation in the electrolyte forms a neutral triethylamine, releasing CO2 radicals.

Description

STATEMENT OF GOVERNMENT INTEREST

[0001] This invention was made with government support under grant no. 2119688 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0002] The present teachings relate generally to electrochemical capture and conversion of carbon dioxide and, more particularly, to the use of tetrachloroferrate and heptachloroferrate ions for reduction of carbon dioxide in a nonaqueous eutectic electrolyte.BACKGROUND

[0003] CO2 emissions from the energy production have driven anthropogenic climate change, with total emissions projected to reach 41.6 billion tonnes in 2024—an increase of 645.92% since the first Kyoto protocol. The fraction of CO2 in the atmosphere has remained relatively stable, meaning changes in cumulative emissions are proportional to atmospheric CO2 levels. According to the Paris Agreement, to limit the global warming to 1.5° C. to 2.0° C., total human-caused CO2 emissions must be reduced to below 20 gigatons per year by 2050 and continue toward near-zero or negative emissions by the century. Failing to account for climate variability and extremes underestimates economic damage and increases risks for vulnerable populations, in addition to worsening environmental issues. Two key carbon capture and storage technologies, oxy-fuel combustion and post-combustion scrubbing, are well-established and commercially implemented in many power plants and industries. While both technologies are promising, their high energy consumption and the low CO2 concentration in flue gas create challenges, necessitating the development of alternative technologies for wider deployment.

[0004] Electrochemical carbon dioxide capture and conversion techniques are still in development within the broader field of carbon management technologies. These approaches utilize redox-active carriers to bind CO2 in a selective manner, then transform them into value-added products through applied potentials. Conventional capture and conversion technologies face considerable challenges. Post-combustion scrubbing with amine-based solvents requires substantial heating for regeneration, leading to high energy usage and solvent degradation over time. Ionic liquids and aqueous redox carriers have demonstrated selective CO2 binding, but often suffer from limited mass transport, low electrical conductivity, or expensive material costs. Gas diffusion electrodes can alleviate some mass-transfer constraints, yet long-term stability under repeated redox cycles remains elusive.

[0005] Therefore, methods and systems providing solutions that overcome these barriers could be beneficial for delivering a streamlined route to sustainable carbon recycling.SUMMARY

[0006] The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more embodiments of the present teachings. This summary is not an extensive overview, nor is it intended to identify key or critical elements of the present teachings, nor to delineate the scope of the disclosure. Rather, its primary purpose is merely to present one or more concepts in simplified form as a prelude to the detailed description presented later.

[0007] A method for fabricating an electrochemical cell is disclosed. The method includes adding an anode which may include iron, to an enclosure, adding a separator to the enclosure adjacent to the anode. The method also includes adding a eutectic electrolyte to the enclosure adjacent to the separator. The method also includes connecting an input line to deliver carbon dioxide at a rate of from about 10 to about 12 L / min. The method also includes setting an output valve such that an internal pressure of the electrochemical cell is pressurized with carbon dioxide to about 10 PSI. Implementations of the method for fabricating an electrochemical cell include where the fabrication is conducted in an inert environment. A redox activity of the electrochemical cell operates in a range of about 0.0 V to about 2.5 V vs. Fe / Fe3+. The electrochemical cell delivers an areal capacity of at least 0.3 mAh / cm2 at 0.1 mA / cm2.

[0008] An electrochemical cell is disclosed. The electrochemical cell includes an anode including iron. The cell also includes a cathode, which may include nickel. The cell also includes a separator disposed between the anode and the cathode. The cell includes an electrolyte in contact with the anode and the cathode, the electrolyte may include a nonaqueous deep eutectic electrolyte. Implementations of the electrochemical cell include where the electrolyte may include triethylamine, FeCl3, and AlCl3. The electrolyte may include triethylamine:FeCl3 in a ratio of 1.7:1. The electrolyte may include 1M AlCl3. A redox activity of the electrochemical cell operates in a range of about 0.0 V to about 2.5 V vs. Fe / Fe3+. The electrochemical cell delivers an areal capacity of at least 0.3 mAh / cm2 at 0.1 mA / cm2. The cathode may include a nickel foam. The anode may include polyvinylidene fluoride and conductive carbon.

[0009] A method for carbon dioxide capture and conversion is disclosed. The method for carbon dioxide capture and conversion includes introducing carbon dioxide into an electrochemical cell, where the electrochemical cell may include an anode including iron, a cathode including nickel, a separator disposed between the anode and the cathode, and an electrolyte in contact with the anode and the cathode, the electrolyte may include a nonaqueous deep eutectic electrolyte, scanning via cyclic voltammetry at a scan rate of 0.5 mV / s. The method also includes measuring reaction kinetics of carbon dioxide conversion using fourier transform infrared (FTIR) spectroscopy. Implementations of the method for carbon dioxide capture and conversion include where there is no separate carbon dioxide desorption step. A redox activity of the electrochemical cell operates in a range of about 0.0 V to about 2.5 V vs. Fe / Fe3+. The electrochemical cell delivers an areal capacity of at least 0.3 mAh / cm2 at 0.1 mA / cm2. The method for carbon dioxide capture and conversion may include maintaining a constant temperature and uniform carbon dioxide diffusion throughout operation. The electrolyte may include triethylamine, FeCl3, and AlCl3. The electrolyte may include triethylamine:FeCl3 in a ratio of 1.7:1. The electrolyte may include 1M AlCl3.

[0010] The features, functions, and advantages that have been discussed can be achieved independently in various implementations or can be combined in yet other implementations further details of which can be seen with reference to the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and together with the description, serve to explain the principles of the disclosure. In the figures:

[0012] FIG. 1 is a reaction scheme for an electrochemical reduction of CO2-bound quinone- and amine-based species, in accordance with the present disclosure.

[0013] FIG. 2 is a schematic illustration of CO2 capture by the eutectic electrolyte, forming adducts via chemical complexation, in accordance with the present disclosure.

[0014] FIGS. 3A-3D are a series of graphs depicting a mid-FTIR spectra displaying characteristic CO2 peaks at various time intervals within a 1M AlCl3 in 1.7:1 [(C2H5)3NH]Cl:FeCl3 eutectic electrolyte, time-dependent CO2 saturation levels in the electrolyte, dynamics of CO2 absorption by the eutectic electrolyte, and linear fitting of the pressure decay data using the ω=f−mt method, respectively, in accordance with the present disclosure.

[0015] FIGS. 4A-4D depict several graphs displaying representative cyclic voltammograms recorded in Ar and CO2 atmospheres within a 0.0-2.5V vs. Fe / Fe3+ potential range, GCD profile of Fe—CO2 cell at a current density of 0.1 mA / cm2, GCD profiles at varying current densities: (i) 0.01 mA / cm2, (ii) 0.1 mA / cm2 and (iii) 0.2 mA / cm2, and cycling performance of the Fe—CO2 cell at 0.1 mA / cm2, within the 0.0-2.5V vs. Fe / Fe3+ voltage range, respectively, in accordance with the present disclosure.

[0016] FIGS. 5A-5H depict FTIR spectra recorded for (i) as-synthesized eutectic electrolyte, (ii) CO2-purged electrolyte, and (iii) electrolyte retained from the cycled cell, highlighting spectral changes across different regions, high-resolution XPS spectra of C1s, O1s, and Fe2p, respectively, deconvoluted into multiple peaks representing different oxidation states of each element, and gas chromatography data for CO2, CO, and H2 detection, respectively, and a plot of XRD patterns, in accordance with the present disclosure.

[0017] FIG. 6 is a drawing illustrating the structural assembly of an electrochemical cell, in accordance with the present disclosure.

[0018] It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the present teachings rather than to maintain strict structural accuracy, detail, and scale.DETAILED DESCRIPTION

[0019] Reference will now be made in detail to exemplary embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same, similar, or like parts.

[0020] The present disclosure provides a method and system related to electrochemical carbon dioxide (CO2) capture and conversion methods. Specifically, the present teachings describe the use of nonaqueous deep eutectic electrolytes containing iron-based chloroferrate species and quaternary ammonium ions to facilitate CO2 activation, binding, and electrochemical reduction. This approach addresses significant challenges in sustainable carbon management, offering a streamlined pathway for integrated CO2 capture and conversion processes while utilizing cost-effective and scalable materials.

[0021] The systems of the present disclosure addresses challenges in CO2 capture and conversion by utilizing an integrated approach for CO2 capture and electrochemical conversion including a nonaqueous deep eutectic electrolyte (DEE) containing iron-based chloroferrate species and quaternary ammonium ions. This electrolyte composition, comprising triethylamine hydrochloride, FeCl3, and AlCl3, demonstrates advantageous physicochemical properties, including high CO2 solubility, low volatility, and a broad electrochemical stability window. The present system utilizes the ion-exchange and electrostatic interaction mechanisms of chloroferrate anions (FeCl4− and Fe2Cl7−) and quaternary ammonium ions to enable efficient CO2 binding, activation, and reduction. Unlike conventional systems, this approach eliminates the need for separate CO2 desorption steps, optimizing the process by directly supplying absorbed CO2 to the electrochemical cell for conversion into value-added products such as formate and carbonate. The use of cost-effective iron and nickel electrodes further supports the scalability and economic feasibility of the system.

[0022] By integrating CO2 capture and conversion into a single process, the system of the present disclosure addresses the limitations of prior technologies, offering improved energy efficiency, long-term stability, and selective conversion capabilities. The system, in examples, achieves a CO2 capture capacity of 14.3 g / L, with a diffusion coefficient of approximately 1×10−7 cm2 / s, validated through spectrochemical and pressure-decay analyses. Electrochemical testing demonstrates stable cycling performance, delivering an areal capacity of 0.3 mAh / cm2 at 0.1 mA / cm2, with efficient utilization of active materials and enhanced charge transfer kinetics. This approach represents a notable advancement in sustainable carbon management technologies, providing a scalable and cost-effective solution for mitigating CO2 emissions and promoting carbon recycling.

[0023] FIG. 1 is a reaction scheme for an electrochemical reduction of CO2-bound quinone- and amine-based species, enabling selective conversion through electron and proton transfer. Amine- and quinone-based systems are among the most widely studied and effective CO2 capture moieties. The following typical CO2 reduction reaction is observed for both organic moieties, as presented in FIG. 1. CO2 readily reacts with amines via a nucleophilic reaction to form carbamates, following an acid-base equilibrium. These carbamates can be decomposed with an energy input to regenerate the amines. Previous work has demonstrated that primary amines exhibit high CO2 adsorption via carbamate formation but slow desorption due to strong binding, whereas tertiary amines, lacking a proton for direct interaction, show low CO2 adsorption but rapid desorption due to weaker binding affinity. While the enthalpy of carbamate formation (ΔH0f) trends to increase slightly with increasing carbon chain length due to electronic effects, a similar trend is not observed in the regeneration of amines and CO2 from carbamate species. Instead, steric hindrance and solvation effects primarily influence the decomposition enthalpies of carbamates. Quaternary amine-based materials capture CO2 through an ion-exchange mechanism and exhibit higher CO2 uptake due to electrostatic interactions, along with faster adsorption kinetics in low-humidity environments.

[0024] Electrochemical carbon capture and CO2 reduction are gaining attention as energy-efficient and renewable-powered alternatives to traditional CO2 capture methods. One of the processes involves activating the redox-active carriers to facilitate rapid and efficient CO2 binding and release through redox cycles. An integrated approach of CO2 capture and conversion using electrolyte media eliminates the need for separate CO2 desorption, enhancing process efficiency by directly supplying absorbed CO2 to the electrolyzer at high concentrations. Few studies have explored the direct integration of CO2 capture media with electrochemical conversion processes. Recent work has investigated CO2 capture and electrochemical conversion system using a tetraethylammonium chloride / propylene carbonate / 2-amino-2-methyl-1-propanol electrolyte. The electrolyte exhibited a high CO2 absorption capacity of 22 g / L through carbamate formation in a nonaqueous medium, achieving a Faradic efficiency of ~45% for formate production. However, these and other studies face challenges related to the long-term stability of the electrolyte solution and lacks efficiency in generating high-value multi-carbon products. Other studies have demonstrated that the 1,3-diaminopropane / KCl / H2O electrolyte effectively captures CO2 via carbamate / bicarbonate mechanisms (absorption of 58.1 g / L), facilitating CO2 desorption under mild electrochemical conditions and enhancing conversion to formate and CO. Despite its promising carbon capture and electrochemical performance, the system faces challenges in long-term stability, mass transfer limitations, competitive hydrogen evolution, and selective conversion efficiency for multi-carbon products.

[0025] Deep eutectic solvents (DESs) are a class of environmentally friendly liquid media formed by mixing two or more components, leading to a depression in melting points due to strong intermolecular interactions. DESs exhibit physicochemical properties comparable to ionic liquids, including low vapor pressure (<100 Pa at 373 K), high thermal and chemical stability, nonflammability, and a wide electrochemical stability window. Additionally, they offer ease of preparation, cost-effectiveness, and compositional tunability, making them promising medium for carbon capture and electrochemical CO2 conversion. Recent studies have increasingly focused on investigating DESs for CO2 capture and conversion, emphasizing the fundamental interaction mechanisms. For example, the use of tetrapropylammonium bromide:formic DES has been investigated for CO2 capture, revealing that CO2 interacts with the eutectic medium through multiple interaction sites, including hydrogen bonding, dipole-quadrapole interactions, and Van der Waals forces. This interaction mechanism facilitated a CO2 solubility of 0.218 mole fraction (xCO2) at 25° C. and 35.2 bar pressure. Shala et al. demonstrated that the DES cholin chloride:ethylene glycol exhibits strong CO2 binding activity, effectively stabilizing CO2 intermediates and enhancing the selectivity of CO production. Their study highlights the superior electrochemical performance of DEEs, including reduced overpotential, faster charge transfer kinetics, and enhanced CO2 reduction efficiency, compared to conventional electrolyte solutions. Nevertheless, research on carbon capture using DESs and their integration with energy storage technologies gaining momentum, aiming to develop sustainable, dual-functional systems that not only capture CO2 but also convert it into value added products through electrochemical reduction or other catalytic processes.

[0026] In the present teachings eutectic electrolyte systems are investigated for sustainable carbon capture and conversion, integrated with energy storage in an iron-based electrochemical cell. The CO2 absorption capacity and diffusion kinetics of the electrolyte were systematically evaluated using spectrochemical techniques and in-situ pressure-decay analysis, revealing a 50% higher CO2 solubility than water. The electrolyte is coupled with cost-effective iron and nickel electrodes, facilitating redox activity within a potential range of 0.0-2.5V vs. Fe / Fe3+. and delivering a high areal capacity of 0.3 mAh / cm2 at 0.1 mA / cm2. Electrochemical reduction of CO2 in the electrolyte results in the formation of formate, CO, and H2, as confirmed by XPS, FTIR and gas-chromatographic analysis. The present disclosure highlights the potential of eutectic electrolytes in advancing integrated carbon capture and electrochemical conversion technologies.

[0027] FIG. 2 is a schematic illustration of CO2 capture by the eutectic electrolyte, forming adducts via chemical complexation. FIG. 2 shows a schematic representation of the CO2 capture and conversion process facilitated by the eutectic electrolyte system. The process begins with a flue gas source 202, which emits CO2 as a byproduct of industrial or energy production activities. The CO2 is directed into a CO2 container 204, where the carbon dioxide is stored or prepared for subsequent processing.

[0028] The captured CO2 is introduced into the eutectic electrolyte 206, which serves as the medium for chemical complexation and electrochemical conversion. The eutectic electrolyte 206, in examples, is composed of triethylamine hydrochloride, FeCl3, and AlCl3, forming a nonaqueous deep eutectic solvent with distinct physicochemical properties, including high CO2 solubility, low volatility, and a wide electrochemical stability window. Within the electrolyte 206, CO2 interacts with redox-active species, including chloroferrate anions (FeCl4− and Fe2Cl7−) and quaternary ammonium ions, resulting in the formation of CO2 adducts. Alternative electrolyte compositions can be simplified as R1R2R3NHX which comprises an organic ammonium halide, and imidazolium salts of formula R1R2ImX, wherein R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups, and X is a halide such as F, Cl, Br, I.

[0029] The chemical complexation of CO2 within the eutectic electrolyte 206 leads to the generation of intermediates, including R3NCOO−, [FeCl4·CO2]−, and [Fe2Cl7·CO2]−208. These intermediates are formed through ion-exchange mechanisms and electrostatic interactions, enabling efficient CO2 binding and activation. The R3NCOO− species are derived from the interaction of CO2 with quaternary ammonium ions, while [FeCl4·CO2]− and [Fe2Cl7·CO2]−208 result from the coordination of CO2 with chloroferrate anions. These intermediates are subsequently utilized in electrochemical reactions to produce value-added products such as formate and carbonate, contributing to sustainable carbon recycling and energy storage applications.

[0030] The potential of DESs for rechargeable multivalent batteries based on iron and aluminum has been previously described. A DES was selected, composed of triethylamine hydrochloride, FeCl3, and AlCl3, which retains key ionic complexes, including [C2H5)3NH]+, FeCl4−, Fe2Cl7− and AlCl4−. The key attributes of this electrolyte include a wide electrochemical stability window (3.2V vs. Fe / Fe3+) required for CO2 conversion, the presence of ionic complexes suitable for high CO2 sorption, cost-effectiveness, low volatility and nonflammability.

[0031] FIGS. 3A-3D are a series of graphs depicting a mid-FTIR spectra displaying characteristic CO2 peaks at various time intervals within a 1M AlCl3 in 1.7:1 [(C2H5)3NH]Cl:FeCl3 eutectic electrolyte, time-dependent CO2 saturation levels in the electrolyte, dynamics of CO2 absorption by the eutectic electrolyte, and linear fitting of the pressure decay data using the ω=f−mt method, respectively, in accordance with the present disclosure. FIG. 3A shows mid-FTIR spectra displaying characteristic CO2 peaks at various time intervals within a 1M AlCl3 in 1.7:1 [(C2H5)3NH]Cl:FeCl3 eutectic electrolyte, recorded in the range of 2370-2320 cm−1. The observed CO2 vibrational peaks provide insights into its solubility and suggest varying coordination environments within the electrolyte. FIG. 3B includes time-dependent CO2 saturation levels in the electrolyte, showing peak saturation after 12 hours under CO2 atmosphere. FIG. 3C includes dynamics of CO2 absorption by the eutectic electrolyte. FIG. 3D shows a linear fitting of the pressure decay data using the ω=f−mt method. The extracted slope and intercept were used to calculate the D, demonstrating the applicability of the linear approach for CO2 diffusion analysis in the eutectic electrolyte.

[0032] Fourier Transform Infrared (FTIR) spectroscopy was employed to determine the CO2 saturation time and diffusion coefficients in the proposed DES, as shown in FIG. 3A. The pure electrolyte exhibited no significant peaks in the 2370-2320 cm−1 range, confirming the absence of CO2 traces during sample transfer for FTIR measurements. To assess CO2 sorption kinetics, the electrolyte was purged with CO2 at 0.69 bar for varying durations, followed by FTIR analysis to determine the CO2 saturation limit under given pressure and time conditions. Upon CO2 exposure, the electrolyte displayed a characteristic CO2 asymmetric stretching peak within 2368-2318 cm−1. A small but distinct peak at 2325 cm−1, alongside a broad band spanning 2368-2330 cm−1 with multiple shoulder peaks centered at 2338 cm−1, 2344 cm−1, 2351 cm−1, 2358 cm−1, and 2361 cm−1 indicates a heterogeneous CO2 environment within the electrolyte. These shifts confirm that anions with higher charge density (Fe2Cl7−, FeCl4−) strongly interact with CO2, reducing its electron density and shifting peaks to lower frequencies, while smaller cations contribute to dipole-quadrupole stabilization. Furthermore, the integrated peak area analysis of the CO2 asymmetric stretch, as shown in FIG. 3B, reveals a maximum saturation occurs after 12 hours of purging. A slight decrease in saturation at 24 and 72 hours suggests a possible dynamic equilibrium in the electrolyte, leading to minor fluctuations in CO2 uptake.

[0033] Furthermore, the diffusion coefficient (D, cm2 / s) of CO2 in the eutectic electrolyte is estimated using the FTIR data. The concentration dynamics of dissolved CO2 within the electrolyte, both temporally and spatially, are governed by Fick's second law of diffusion:∂c∂t=D⁢∂2c∂x2(1)where c represents the concentration of CO2 in the eutectic electrolyte at a given time t. Assuming a constant diffusion, the mobility of CO2 molecules within the liquid medium remains stable over time and is not influenced by local CO2 concentration or other electrolyte conditions. Under this assumption, one possible solution to the above equation is given by:c=At1 / 2⁢e-x24⁢Dt(2)By applying the complementary Gaussian error function, Fick's second law can be rearranged under the specified boundary and initial conditions. Specifically, the boundary condition c=c0 at x=0 is imposed for all t>0, which represents a constant concentration c0 at the interface where CO2 begins to diffuse into the medium. This condition models a sustained source of CO2 at the boundary due to a constant partial pressure of CO2 at the surface. Additionally, we define the initial condition c=0 for x>0 is defined at t=0, representing the absence of CO2 within the medium at the start of the experiment. This initial state reflects a scenario where the medium is initially CO2-free and allows us to track the diffusion process as CO2 enters and spreads into the medium over time. With these boundary and initial conditions, equation-(2) can be transformed into the form:c⁡(x,t)=c0⁢ erfc⁢ (x2⁢Dt)(3)where erfc is the complementary error function. This solution describes the concentration profile c(x, t) as a function of both position x and time t, governed by the diffusion coefficient, D. Rearranging the equation-(3) provides diffusion coefficient.D=x2t⁢1[2·erf⁢c⁡(x,t)c0]2(4)The values for c(x, t), representing the CO2 concentration at specific times, were derived from the recorded FTIR spectra of CO2 peaks in the electrolyte purged with CO2 at different time intervals, as shown in FIG. 3A. It is assumed that the surface layer of the electrolyte was fully saturated with CO2, i.e. it had reached a stable, balanced concentration over time. Thus, the maximum saturation concentration, c0, was determined based on the relationship between dissolved CO2 and time under constant pressure. The concentration values c(x, t) were selected from 1-hour and 6-hour datasets, representing 35% and 52% of the maximum saturation concentration, respectively, as these intervals displayed a linear trend in CO2 uptake. At the 12-hour interval, CO2 reached a maximum saturation level. Therefore, only the first two datasets (1-hour and 6-hour) were used to calculate the diffusion coefficient of CO2 in the electrolyte. We used a fixed x value of 1 mm, representing the thickness of the electrolyte layer or the distance from the CO2 interface to the measurement point. The average diffusion coefficient of CO2 was determined to be 1.08×10−7 cm2 / s.To quantify the total CO2 sorption in the eutectic electrolyte and validate the diffusion coefficient obtained from FTIR measurements, a linear method was employed based on pressure-decay data (FIG. 3C), assuming a known equilibrium pressure. A total of 0.2 mL of eutectic electrolyte was placed in a 3 mL Swagelok cell equipped with a pressure gauge transducer, and CO2 was pressurized to 0.69 bar. Several assumptions were made before determining the diffusion coefficient of CO2 in the eutectic mixture. This method assumes a constant temperature and uniform CO2 diffusion throughout the measurement, with the eutectic electrolyte considered non-volatile. Density induced convection and swelling effects were deemed negligible. Additionally, the gas-liquid interface concentration was assumed to follow Henry's law, while gas compressibility (Z) was considered constant, with an average Z value of 0.39786 calculated from the recorded pressure decay data. The diffusion coefficient, D, was estimated using the following equation:Pc-PeqPi=2⁢λ1+λ+λ2⁢a12⁢e-Da12⁢tl2(5)Where Pc is the gas partial pressure, Peq is the equilibrium pressure, Pi is the initial pressure, λ is the ratio of equilibrium pressure to the pressure change of the gas phase, 1 is the thickness of the liquid, and a1 satisfies the equation tan (a1)=−λa1. Rearranging the equation provides the linear form,ω=f-mt(6)where ω, f, and m are defined as follows:ω=ln⁢ (Pc-PeqPi)(7)The intercept from the straight line is:f=ln⁢ (2⁢λ1+λ+a12⁢λ2)(8)The slope from the straight line is:m=Da12l2(9)The intercept and slope determined from the straight-line fit, as shown in FIG. 3D, are −0.33442 and 9.1847×10−6, respectively. The value of a1 deduced from equation-(8) is 0.8934. The diffusion coefficient recorded is, D=1.15×10−7 cm2 / s. The diffusion coefficients measured using the FTIR studies and the pressure-decay method show good correlation. The pressure decay method also determines the total number of moles of CO2 that can be absorbed by eutectic i.e. 6.5×10−5 moles (equivalent to 14.30 g / L).Electrochemical AnalysisFIGS. 4A-4D depict (FIG. 4A) Representative cyclic voltammograms recorded in Ar and CO2 atmospheres within a 0.0-2.5V vs. Fe / Fe3+ potential range, (FIG. 4B) GCD profile of Fe—CO2 cell at a current density of 0.1 mA / cm2, (FIG. 4C) GCD profiles at varying current densities: (i) 0.01 mA / cm2, (ii) 0.1 mA / cm2 and (iii) 0.2 mA / cm2, and (FIG. 4D) Cycling performance of the Fe—CO2 cell at 0.1 mA / cm2, within the 0.0-2.5V vs. Fe / Fe3+ voltage range. In the present study, all electrochemical cells were fabricated using carbonyl iron as the anode, Ni foam as the gas diffusion layer (GDL), and 1M AlCl3 in 1.7:1 molar ratio of [C2H5)3NH]Cl to FeCl3 as the electrolyte medium, assembled in a custom-made Swagelok cell purged with an ultra-high-purity CO2 at 10 PSI (~0.69 bar). Post fabrication, all cells were rested for at least 24 hours before performing electrochemical analysis. The electrochemical performance of Fe—CO2 batteries was initially evaluated using cyclic voltammetry (CV) within a potential range of 0.0-2.5V vs. Fe / Fe3+, at a scan rate of 0.5 mV / s, as shown in FIG. 4A. Under the Ar atmosphere, as shown in FIG. 3(a), the Ni electrode exhibits no distinct peaks throughout the full voltage sweep. In contrast, the cell in the CO2 atmosphere displays redox peaks, indicating CO2 conversion (FIG. 4(a)). FIG. 4(b) presents galvanostatic charge-discharge (GCD) analyses performed at 0.1 mA / cm2, revealing a progressive increase in discharge capacity, reaching 0.24 mAh / cm2 by the 10th cycle, accompanied by the rise in Coulombic efficiency to 102%. The progressive increase in discharge capacity with cycling correlates with the increasing peak current densities observed in the CV profiles. This suggests efficient CO2 diffusion, adsorption, and convection on the gas diffusion electrode (GDE), as well as improved utilization of active materials and enhanced charge transfer kinetics. The Fe—CO2 cell exhibited a capacity retention of 0.1 mAh / cm2 at a high current density of 0.2 mA / cm2, as shown in FIG. 4(c), whereas a lower current density of 0.01 mA / cm2 resulted in a capacity retention of 0.3 mAh / cm2. The cell maintained stability for >21 cycles, as shown in FIG. 4(d).Understanding CO2 Reaction Kinetics in Eutectic Systems

[0045] FIGS. 5A-5H depict FTIR spectra recorded for (i) as-synthesized eutectic electrolyte, (ii) CO2-purged electrolyte, and (iii) electrolyte retained from the cycled cell, highlighting spectral changes across different regions. FIGS. 5B, 5C, and 5D show the high-resolution XPS spectra of C1s, O1s, and Fe2p, respectively, deconvoluted into multiple peaks representing different oxidation states of each element. FIGS. 5E, 5F, and 5G, display gas chromatography data for CO2, CO, and H2 detection, respectively. FTIR spectroscopy was employed, as shown in FIG. 5A, to analyze the pure electrolyte, CO2-purged electrolyte, and the electrolyte recovered after cycling the Fe—Ni cell to elucidate the chemical interactions of CO2 within the electrolyte before and after electrochemical cycling. The FTIR spectra of the CO2-purged electrolyte exhibit distinct spectral modifications in two key regions: (i) the emergence of new absorption bands in the 2365-2320 cm−1 range, characteristic of CO2 asymmetric stretching, indicative of its coordination within the electrolyte; (ii) a shift in the N—H stretching mode from 3130 cm−1 to 3137.5 cm−1, suggesting CO2 interaction via hydrogen bonding or proton transfer within the triethylammonium cation, potentially facilitating the formation of carbamate (R—N—COO−) species. The presence of multiple peaks within the CO2 stretching region suggests the existence of diverse CO2 coordination environments within the electrolyte matrix. The cycled electrolyte retained from the Fe—Ni cell after GCD cycles exhibits noticeable peak shifts and intensity variations, indicating significant chemical transformations. (i) Hydrogen bonding and structural reorganization (3210-2830 cm−1): A broad absorption band in this region corresponds to C—H, N—H, and O—H stretching modes, indicative of changes in the electrolyte environment. The increased intensity and broadening in the range of 3210-2830 cm−1 imply enhanced hydrogen bonding, forming carbamate like structures. Additionally, a shift to a lower frequency in the range of 1690-1590 cm−1 also suggests the formation of carbamate species. (ii) CO2 complexation and carbonate formation (2360-2320 cm−1): Shifts and intensity variations in the CO2 asymmetric stretching mode suggest dynamic rearrangement of CO2 coordination within the electrolyte. These spectral modifications can be attributed to CO2 complexation with electrolyte species, including chloroferrate anions (FeCl4−, Fe2Cl7−) and amines. (iii) Carbamate formation and CO2 reduction products (1220-860 cm−1): A broad absorption feature in this region, with a distinct C—N stretching band near 1200 cm−1, confirms the formation of carbamate species (R3NCOO−) via CO2 interaction with amines. Additionally, the presence of C—O stretching bands between 1100-1000 cm−1 and 900-860 cm−1 supports the formation of formate (HCOO−) and bicarbonate (HCO3−) species, providing further evidence for electrochemical CO2 reduction pathways occurring in the system. (iv) Fe—CO2 complexation and Fe coordination changes (745-545 cm−1): Peak shifts observed in this range confirm the formation of Fe—CO2 adducts, specifically involving chloroferrate species (FeCl4−, Fe2Cl7−). The spectral variations in the range of 700-500 cm−1 involves the Fe—CO stretching vibrations, suggest modifications in Fe coordination chemistry, likely due to interactions with CO2-containing intermediates or formation of Fe products. (v) Fe redox processes and carbonate formation (547-414 cm−1): A broad, distinct absorption pattern in this region is attributed to Fe—Cl vibrational modes, confirming iron reduction processes occurring during cycling. Additionally, these spectral changes suggest the formation of Fe-carbonate complexes, supporting the conversion of CO2 into carbonate (CO32-) species as part of the electrochemical reaction sequence. These spectral observations collectively provide strong evidence for CO2 activation, complexation, and electrochemical reduction in the cycled electrolyte.

[0046] To further characterize the reaction products, X-ray photoelectron spectroscopy (XPS) was conducted on the cycled Ni electrode, focusing on identifying products resulting from the Fe—CO2 cell's redox reactions. A wide-scan XPS spectrum of the cycled electrode, reveals characteristic peaks corresponding to C1s, N1s, O1s, Fe2p, Ni2p, C12p and C12s. The high-resolution C1s spectrum (282-292 eV) showed three primary peaks (FIG. 5B): C—C or C═C (~284.9 eV), likely from residual carbonaceous species such as the electrolyte, C—N (~286.4 eV), indicating the presence of amines, and C═O (~288.7 eV), strongly suggesting the formation of carbamate or metal-carbonate species, which aligns with CO2 electrochemical reduction pathways. Similarly, FIG. 5C displays the Ols spectrum (530-534 eV) revealed multiple oxidation states, with O2— (~530.5 eV) corresponding to lattice oxygen or Fe oxide phases, oxygen bonded to Fe3+ (~533.9 eV) suggesting carbonate species, and physiosorbed CO2 or hydroxyl-related oxygen (~536.3 eV). FIG. 5D shows the high-resolution XPS spectra of Fe 2p (708-740 eV) were deconvoluted into multiple peaks, indicating the presence of Fe complexes. Further supporting these findings, gas chromatography analysis of gases from the electrochemical cell chamber identified CO2, CO and H2, as shown in FIGS. 5E, 5F, and 5G. The detection of H2 implies partial reduction of the electrolyte, possibly involving the triethylammonium cation, while the presence of CO provides direct evidence of CO2 electrochemical reduction occurring within the Fe—Ni cell. X-ray diffraction (XRD) analysis of the cycled Ni electrode was conducted to examine structural changes and product formation during the GCD cycles of the Fe—CO2 cell. As depicted in FIG. 5H, new diffraction peaks emerged within the 20 range of 5-50°. The XRD patterns suggest the formation of carbonate species and / or a mixed organic / inorganic phases, which is consistent with the observed XPS signals. Collectively, these findings indicate a CO2 conversion mechanism coupled with energy storage, involving electrochemical CO2 reduction to metal carbonates, the formation of carbonates and oxide intermediates, and electrolyte degradation contributing to structural and compositional changes in the cycled electrode.

[0047] The proposed reaction mechanism is:

[0048] At the anode is:

[0049] At the cathode:CONCLUSIONS

[0050] In summary, a chloroferrate-based eutectic electrolyte with quaternary ammonium ions was investigated, demonstrating efficient CO2 capture via an ion-exchange mechanism and subsequent electrochemical reduction using cost-effective and sustainable materials. The electrolyte achieves a CO2 capture capacity of 14.3 g / L, with a diffusion coefficient of ~1×10−7 cm2 / s, validated through FTIR spectroscopy and pressure-decay measurements. The system employs a Fe metal anode, delivering a high electrochemical capacity of 0.3 mAh / cm2 and demonstrating stable cycling performance of >20 cycles. During discharge, CO2 adducts of chloroferrate and amine species undergo electron-driven transformations, yielding formate (HCOO−) and carbonate (CO32-) species as primary reduction products. The present disclosure highlights the potential of eutectic Fe-based electrolytes as a scalable and cost-effective alternative for integrated CO2 capture and electrochemical conversion, offering a promising route toward sustainable carbon recycling technologies.Materials

[0051] Ultra-high purity CO2 (≥99.99%) was purchased from AirGas. Triethylamine hydrochloride ([(C2H5)3N]HCl, ≥99%), Iron chloride (FeCl3, ≥97% reagent grade), carbonyl iron (≥97% Fe basis), poly(vinylidene fluoride) (PVDF powder), glass microfiber filters (Whatman Grade 934-AH) were procured from Sigma-Aldrich. Aluminum (III) chloride (AlCl3, anhydrous, 99.985% metal basis) purchased from Thermo Scientific, Nickel form (>99.99%, Ni anti-corrosive) from MTI corporation, Toray carbon paper 030 (CP, wet proofed, 110 μm thickness) from FuelCell Store and 1-methyl-2-pyrrolidinone (C5H9NO, 99.5%) from Spectrum chemical manufacturing corporation.Electrolyte Preparation

[0052] The electrolyte preparation followed the methodology known in the art. All procedures were carried out in an argon-filled glovebox (<1 ppm O2, <1 ppm H2O, manufactured by vacuum Technologies Inc.). The eutectic electrolyte synthesis proceeded in two phases. First, a 1.7:1 molar ratio of triethylamine hydrochloride to FeCl3 was prepared by gradually adding FeCl3 to triethylamine hydrochloride. In the second phase, a predetermined amount of AlCl3 was introduced into the binary electrolyte, resulting in a final composition of 1M AlCl3 in 1.7:1 triethylamine hydroichloride:FeCl3.Electrode Fabrication

[0053] Carbonyl iron electrodes were fabricated by ball-milling a precise weight ratio of carbonyl iron, Super P conductive carbon, and PVDF (90:5:5 weight %) for 3 hours at 300 rotations per minute. The resulting mixture was then combined with 1-methyl-2-pyrrolidinone to form a homogeneous slurry, which was cast onto a carbon-paper current collector and dried vacuum at 100° C. for 12 hours. The dried electrodes were used as the anode in Fe—CO2 cell fabrication. Pristine nickel foam, as received from the manufacturer, served as the gas diffusion layer and current collector.Electrochemical CO2 Cell Fabrication

[0054] CO2 containing batteries and their corresponding controls were assembled within custom-made battery holders designated to regulate gas flow across the battery and fabricated inside an Ar-filled glove box (≤1 ppm O2 and ≤1 ppm H2O, vacuum technologies). Battery assembly involved sequentially adding the carbonyl Fe anode, a separator, 1-500 μL electrolyte, Ni foam cathode into the battery chamber, followed by sealing and removal from the glove box. To introduce CO2, the input line was loosely connected to a CO2 gas source, and CO2 was then directed over the closed inlet valve at a rate of 0<P≤50 mL / min for 1-30 minutes. Subsequently, the inlet and outlet valves are opened, allowing CO2 to flow through the battery chamber for 1-30 minutes. Finally, the outlet valve was closed, and the chamber was pressurized with CO2 to a pressure of ~1-50 PSI. The Swagelok cell was then rested for 24 hours before conducting electrochemical characterizations.

[0055] FIG. 6 is a drawing illustrating the structural assembly of an electrochemical cell, in accordance with the present disclosure. FIG. 6 represents a mechanical assembly of an electrochemical cell 600, showing the structural components and their arrangement. The electrochemical cell 600 is designed to execute processes for capturing carbon dioxide and performing electrochemical conversion, as described herein.

[0056] The electrochemical cell 600 includes an anode 602 and a cathode 604, which are positioned within separate chambers, the anode chamber 624 and the cathode chamber 626, respectively. These chambers are separated by a cell chamber 618, which houses the electrolyte and facilitates ionic contact between the anode 602 and cathode 604. The cell chamber 618 is sealed using fluoropolymer seals 616 to ensure containment of the electrolyte and prevent leakage during operation.

[0057] A gas inlet 608 is connected to the inlet valve 606, allowing controlled introduction of carbon dioxide into the cell chamber 618. The gas outlet 620, connected to the outlet valve 622, enables the removal of gases or reaction byproducts from the cell chamber 618. The inlet valve 606 and outlet valve 622 are further configured to regulate the flow and pressure of gases within the electrochemical cell 600, providing optimal conditions for carbon dioxide capture and conversion.

[0058] The electrochemical cell 600 incorporates a fluoropolymer tube 612, which provides a durable and chemically resistant pathway for gas flow. A spring 610 is included to maintain mechanical stability and ensure proper alignment of the internal components during operation. Screw holes 614 are provided for securing the assembly and enabling integration into larger systems or experimental setups. The structural design of the electrochemical cell 600 ensures efficient gas flow, containment, and mechanical stability, supporting the integrated carbon dioxide capture and electrochemical conversion processes described in the present disclosure.Electrochemical Testing

[0059] Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were performed using a multi-channel Biologic VSP potentiostat (EC-Lab v11.30 software). Galvanostatic charge-discharge (GCD) studies were conducted on a multi-channel Neware Battery Testing System (BTS v8 software). EIS studies were performed on a Fe—CO2 cells over a frequency range of 50 mHz to 1 MHz at open-circuit potential with an amplitude of 10 mV. CV measurements were conducted within the potential window of 0.0-2.5V versus Fe / Fe3+ at a scan rate of 0.5 mV / s. GCD analysis was performed under CO2 or Ar atmospheres within the same potential window of 0.0-2.5V vs. Fe / Fe3+.Materials Characterization

[0060] The CO2 absorption and diffusion kinetics were measured using a Pressure Gauge Transducer equipped with Track-It DataLogger Software. Fourier Transform Infrared (FTIR) spectroscopy (Nicolet 6700 FTIR Spectrometer) was performed on the CO2 purged electrolytes to determine the diffusion coefficients and the cycled electrodes to investigate charge storage kinetics within the spectral range of 400-4000 cm−1, with data acquired by averaging 64 scans. X-ray diffraction (XRD) analysis was performed using a Rigaku smartLab X-ray diffractometer. Scanning Electron Microscopy (SEM) (TESCAN VEGA, operating at an accelerating voltage of 20 kV) was employed to examine the morphology of discharge products or precipitates formed on Ni foam after cycling. Additionally, X-ray Photoelectron Spectroscopy (XPS) was conducted on a Kratos AXIS ULTRA spectrometer to determine the binding energies of the electrode materials.

[0061] In some examples of the present disclosure, a method for fabricating an electrochemical cell includes adding an anode to an enclosure, adding a conductive electrode to the enclosure, adding an electrolyte to the enclosure such that the anode and the conductive electrode are in contact with the electrolyte, and pressurizing the electrochemical cell with a gas. In some examples, the enclosure is a custom-made battery holder or a Swagelok-type cell configured to regulate gas flow across the cell chamber. In some examples, assembly is performed by sequentially placing the anode, a separator, the electrolyte, and the conductive electrode into the enclosure, followed by sealing of the enclosure and introduction of the gas. In some examples, the gas is introduced through an inlet line and the electrochemical cell is pressurized after a purge or flow-through step. In some aspects, the anode includes iron, an iron-based alloy, or an iron-containing composite with a conductive material. In some examples, the anode is a carbonyl iron electrode. In some examples, the anode is formed from carbonyl iron combined with conductive carbon and a polymeric binder to form a slurry-coated electrode on a current collector. In some examples, the iron-containing composite can include carbonyl iron, Super P conductive carbon, and poly(vinylidene fluoride).

[0062] In examples, the conductive electrode includes an electronically conductive substrate selected from a metal including nickel or zinc, a metal alloy, or a conductive carbon-based material including carbon cloth, carbon foam, graphite foam, or combinations thereof. In some examples, the conductive electrode comprises a nickel foam that serves as a gas diffusion layer and current collector. In some aspects, the conductive electrode is carbon cloth or another conductive porous substrate configured to provide gas access and electrical conductivity at the cathode side of the cell.

[0063] In some examples, the electrolyte includes a eutectic electrolyte composition. In examples, the eutectic electrolyte composition is a nonaqueous deep eutectic electrolyte having high carbon dioxide solubility, low volatility, and a broad electrochemical stability window. In some aspects, the eutectic electrolyte is introduced in an amount sufficient to wet the electrodes and separator and provide ionic contact therebetween.

[0064] In examples, the eutectic electrolyte composition includes a trialkyl amine halide or a trialkyl ammonium halide having the general formula R1R2R3NHX, where R1, R2, and R3 are independently selected from alkyl groups including methyl, ethyl, propyl, or butyl, and X is a halide including F, Cl, Br, or I. In aspects of the present disclosure, the ammonium halide provides a cationic species that participates in ion-exchange and electrostatic interactions with carbon dioxide. The electrolyte can include an organic ammonium halide selected to support carbon dioxide binding and electrochemical conversion in the eutectic medium. The eutectic electrolyte composition can include triethylamine hydrochloride and iron chloride. In some examples, triethylamine hydrochloride is combined with FeCl3 to form a binary eutectic electrolyte containing chloroferrate species. In some examples, the resulting electrolyte includes iron-based anionic species such as FeCl4− and Fe2C7− that facilitate carbon dioxide activation, binding, and electrochemical reduction.

[0065] In examples, the eutectic electrolyte composition further includes one or more halide salts including aluminum chloride, magnesium chloride, zinc chloride, or phosphorous pentachloride. In some examples, the additional halide salt adjusts ionic speciation, Lewis acidity, conductivity, and carbon dioxide interaction within the electrolyte. In some working examples, AlCl3 is added to the binary triethylamine hydrochloride and iron chloride eutectic to provide a final composition including 1 M AlCl3.

[0066] In some examples, the eutectic electrolyte composition includes triethylamine hydrochloride and iron chloride in a ratio of about 1.7:1. In some examples, FeCl3 is gradually added to triethylamine hydrochloride to prepare the binary eutectic. In some examples, the 1.7:1 ratio provides a liquid eutectic composition that retains chloroferrate species suitable for carbon dioxide sorption and electrochemical conversion.

[0067] The gas can include carbon dioxide or a mixture of carbon dioxide with one or more additional gases. In some examples, the gas is ultra-high-purity carbon dioxide. In some examples, the gas is a carbon dioxide-containing gas stream derived from an industrial or energy production source, including a flue gas source. In some examples, the gas is introduced into the enclosure and retained under pressure to promote dissolution of carbon dioxide into the electrolyte.

[0068] The electrochemical cell can include an iron anode disposed in the enclosure, a conductive electrode including nickel or carbon cloth disposed in the enclosure, and a eutectic electrolyte including triethylamine hydrochloride, iron chloride, and aluminum chloride, where the anode and the conductive electrode are in contact with the electrolyte, and carbon dioxide is introduced into the enclosure and the electrochemical cell is pressurized with carbon dioxide. In some working examples, the iron anode is a carbonyl iron anode, the conductive electrode is nickel foam, and the electrolyte is 1 M AlCl3 in a 1.7:1 molar ratio of triethylamine hydrochloride to FeCl3. In some examples, the cell is assembled in a custom-made Swagelok cell and pressurized with carbon dioxide to about 10 PSI.

[0069] Examples include where the conductive electrode comprises a substrate in a pure form or a substrate having one or more materials deposited thereon by mechanical, electrochemical, or chemical deposition methods, where the deposited materials include metal oxides, carbon-based materials, sulfides, or metal sulfides. In some examples, the substrate is used in a pristine form, such as a pristine nickel foam current collector and gas diffusion layer. In other examples, the substrate can carry deposited surface materials selected to modify conductivity, interfacial chemistry, catalytic activity, or gas transport behavior within the electrochemical cell.

[0070] In examples, the eutectic electrolyte composition can be configured to dissolve carbon dioxide or carbon dioxide-containing gases. In some examples, carbon dioxide uptake is confirmed by Fourier Transform Infrared spectroscopy through appearance of characteristic asymmetric stretching peaks in the 2368-2318 cm−1 region. In some examples, the eutectic electrolyte exhibits a carbon dioxide absorption capacity of about 14.3 g / L and a diffusion coefficient of about 1×10−1 cm2 / s, as determined by FTIR analysis and pressure-decay measurements. In some examples, the electrolyte reaches peak carbon dioxide saturation after about 12 hours under a carbon dioxide atmosphere.

[0071] The method of the present disclosure can further include converting carbon dioxide electrochemically within the electrochemical cell. For example, electrochemical conversion can be carried out after the cell is assembled and pressurized with carbon dioxide. In examples, cyclic voltammetry is performed within a potential window of about 0.0 V to about 2.5 V versus Fe / Fe3+ to evaluate redox activity associated with carbon dioxide conversion. The cell can be rested after fabrication and before electrochemical testing to permit gas dissolution and interfacial equilibration.

[0072] In aspects, electrochemical conversion of carbon dioxide within the electrochemical cell produces one or more carbon-containing products. In some examples, the products include formate, carbonate, bicarbonate, carbon monoxide, carbamate-containing species, or combinations thereof. These products can be identified by FTIR spectroscopy, X-ray photoelectron spectroscopy, gas chromatography, X-ray diffraction, or combinations thereof.

[0073] In some examples, electrochemical conversion of carbon dioxide within the electrochemical cell produces carbonate or bicarbonate species. This carbonate and bicarbonate formation is supported by FTIR absorption bands associated with C—O stretching and by spectroscopic and diffraction evidence consistent with carbonate-containing products or complexes. Carbonate can also be formed according to a reaction pathway in which two carbon dioxide molecules react electrochemically to yield carbonate and carbon monoxide, followed by protonation of carbonate to bicarbonate.

[0074] Alternatively, electrochemical conversion of carbon dioxide within the electrochemical cell produces formate species. Formate is produced through reduction of carbon dioxide-derived radical intermediates generated from chloroferrate-carbon dioxide adducts or amine-associated intermediates. In some examples, the proposed mechanism includes formation of CO2′−, followed by proton-coupled electron transfer to yield HCOO—. Electrochemical conversion of carbon dioxide also produces carbon monoxide. Carbon monoxide can be detected by gas chromatography of gases present in the electrochemical cell chamber. In examples, carbon monoxide is generated together with carbonate species during electrochemical reduction of carbon dioxide. Hydrogen gas can also be generated during operation of the electrochemical cell, and detected by gas chromatography from the electrochemical cell chamber. The hydrogen formation occurs through proton reduction within the electrolyte and may involve proton-containing species associated with the triethylammonium cation.

[0075] Carbon dioxide capture and electrochemical energy storage can occur simultaneously within the electrochemical cell. In examples, the eutectic electrolyte captures carbon dioxide through ion-exchange and electrostatic interactions involving chloroferrate species and ammonium-containing species, while the iron-based electrochemical cell stores and releases charge during cycling. In these examples, the integrated system delivers an areal capacity of about 0.3 mAh / cm2 at about 0.1 mA / cm2 while also supporting carbon dioxide conversion. In aspects, there may be no separate carbon dioxide desorption step, such as, for example, where carbon dioxide absorbed in the eutectic electrolyte is supplied directly to the electrochemical cell for conversion without thermal regeneration of a separate capture medium. The elimination of a separate desorption step reduces process complexity and improves overall energy efficiency of the integrated carbon dioxide capture and conversion system.

[0076] While the present teachings have been illustrated with respect to one or more implementations, alterations and / or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, it may be appreciated that while the process is described as a series of acts or events, the present teachings are not limited by the ordering of such acts or events. Some acts may occur in different orders and / or concurrently with other acts or events apart from those described herein. Also, not all process stages may be required to implement a methodology in accordance with one or more aspects or embodiments of the present teachings. It may be appreciated that structural objects and / or processing stages may be added, or existing structural objects and / or processing stages may be removed or modified. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and / or phases. Furthermore, to the extent that the terms “including,”“includes,”“having,”“has,”“with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” The term “at least one of” is used to mean one or more of the listed items may be selected. Further, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein. The term “conformal” describes a coating material in which angles of the underlying material are preserved by the conformal material. The term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated embodiment. The terms “couple,”“coupled,”“connect,”“connection,”“connected,”“in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via one or more intermediate elements or members.” Finally, the terms “exemplary” or “illustrative” indicate the description is used as an example, rather than implying that it is an ideal. Other embodiments of the present teachings may be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present teachings being indicated by the following claims.

Examples

Embodiment Construction

[0019]Reference will now be made in detail to exemplary embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same, similar, or like parts.

[0020]The present disclosure provides a method and system related to electrochemical carbon dioxide (CO2) capture and conversion methods. Specifically, the present teachings describe the use of nonaqueous deep eutectic electrolytes containing iron-based chloroferrate species and quaternary ammonium ions to facilitate CO2 activation, binding, and electrochemical reduction. This approach addresses significant challenges in sustainable carbon management, offering a streamlined pathway for integrated CO2 capture and conversion processes while utilizing cost-effective and scalable materials.

[0021]The systems of the present disclosure addresses challenges in CO2 capture and conversion by utilizing an integra...

STATEMENT OF GOVERNMENT INTEREST

[0001] This invention was made with government support under grant no. 2119688 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0002] The present teachings relate generally to electrochemical capture and conversion of carbon dioxide and, more particularly, to the use of tetrachloroferrate and heptachloroferrate ions for reduction of carbon dioxide in a nonaqueous eutectic electrolyte.BACKGROUND

[0003] CO2 emissions from the energy production have driven anthropogenic climate change, with total emissions projected to reach 41.6 billion tonnes in 2024—an increase of 645.92% since the first Kyoto protocol. The fraction of CO2 in the atmosphere has remained relatively stable, meaning changes in cumulative emissions are proportional to atmospheric CO2 levels. According to the Paris Agreement, to limit the global warming to 1.5° C. to 2.0° C., total human-caused CO2 emissions must be reduced to below 20 gigatons per year by 2050 and continue toward near-zero or negative emissions by the century. Failing to account for climate variability and extremes underestimates economic damage and increases risks for vulnerable populations, in addition to worsening environmental issues. Two key carbon capture and storage technologies, oxy-fuel combustion and post-combustion scrubbing, are well-established and commercially implemented in many power plants and industries. While both technologies are promising, their high energy consumption and the low CO2 concentration in flue gas create challenges, necessitating the development of alternative technologies for wider deployment.

[0004] Electrochemical carbon dioxide capture and conversion techniques are still in development within the broader field of carbon management technologies. These approaches utilize redox-active carriers to bind CO2 in a selective manner, then transform them into value-added products through applied potentials. Conventional capture and conversion technologies face considerable challenges. Post-combustion scrubbing with amine-based solvents requires substantial heating for regeneration, leading to high energy usage and solvent degradation over time. Ionic liquids and aqueous redox carriers have demonstrated selective CO2 binding, but often suffer from limited mass transport, low electrical conductivity, or expensive material costs. Gas diffusion electrodes can alleviate some mass-transfer constraints, yet long-term stability under repeated redox cycles remains elusive.

[0005] Therefore, methods and systems providing solutions that overcome these barriers could be beneficial for delivering a streamlined route to sustainable carbon recycling.SUMMARY

[0006] The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more embodiments of the present teachings. This summary is not an extensive overview, nor is it intended to identify key or critical elements of the present teachings, nor to delineate the scope of the disclosure. Rather, its primary purpose is merely to present one or more concepts in simplified form as a prelude to the detailed description presented later.

[0007] A method for fabricating an electrochemical cell is disclosed. The method includes adding an anode which may include iron, to an enclosure, adding a separator to the enclosure adjacent to the anode. The method also includes adding a eutectic electrolyte to the enclosure adjacent to the separator. The method also includes connecting an input line to deliver carbon dioxide at a rate of from about 10 to about 12 L / min. The method also includes setting an output valve such that an internal pressure of the electrochemical cell is pressurized with carbon dioxide to about 10 PSI. Implementations of the method for fabricating an electrochemical cell include where the fabrication is conducted in an inert environment. A redox activity of the electrochemical cell operates in a range of about 0.0 V to about 2.5 V vs. Fe / Fe3+. The electrochemical cell delivers an areal capacity of at least 0.3 mAh / cm2 at 0.1 mA / cm2.

[0008] An electrochemical cell is disclosed. The electrochemical cell includes an anode including iron. The cell also includes a cathode, which may include nickel. The cell also includes a separator disposed between the anode and the cathode. The cell includes an electrolyte in contact with the anode and the cathode, the electrolyte may include a nonaqueous deep eutectic electrolyte. Implementations of the electrochemical cell include where the electrolyte may include triethylamine, FeCl3, and AlCl3. The electrolyte may include triethylamine:FeCl3 in a ratio of 1.7:1. The electrolyte may include 1M AlCl3. A redox activity of the electrochemical cell operates in a range of about 0.0 V to about 2.5 V vs. Fe / Fe3+. The electrochemical cell delivers an areal capacity of at least 0.3 mAh / cm2 at 0.1 mA / cm2. The cathode may include a nickel foam. The anode may include polyvinylidene fluoride and conductive carbon.

[0009] A method for carbon dioxide capture and conversion is disclosed. The method for carbon dioxide capture and conversion includes introducing carbon dioxide into an electrochemical cell, where the electrochemical cell may include an anode including iron, a cathode including nickel, a separator disposed between the anode and the cathode, and an electrolyte in contact with the anode and the cathode, the electrolyte may include a nonaqueous deep eutectic electrolyte, scanning via cyclic voltammetry at a scan rate of 0.5 mV / s. The method also includes measuring reaction kinetics of carbon dioxide conversion using fourier transform infrared (FTIR) spectroscopy. Implementations of the method for carbon dioxide capture and conversion include where there is no separate carbon dioxide desorption step. A redox activity of the electrochemical cell operates in a range of about 0.0 V to about 2.5 V vs. Fe / Fe3+. The electrochemical cell delivers an areal capacity of at least 0.3 mAh / cm2 at 0.1 mA / cm2. The method for carbon dioxide capture and conversion may include maintaining a constant temperature and uniform carbon dioxide diffusion throughout operation. The electrolyte may include triethylamine, FeCl3, and AlCl3. The electrolyte may include triethylamine:FeCl3 in a ratio of 1.7:1. The electrolyte may include 1M AlCl3.

[0010] The features, functions, and advantages that have been discussed can be achieved independently in various implementations or can be combined in yet other implementations further details of which can be seen with reference to the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and together with the description, serve to explain the principles of the disclosure. In the figures:

[0012] FIG. 1 is a reaction scheme for an electrochemical reduction of CO2-bound quinone- and amine-based species, in accordance with the present disclosure.

[0013] FIG. 2 is a schematic illustration of CO2 capture by the eutectic electrolyte, forming adducts via chemical complexation, in accordance with the present disclosure.

[0014] FIGS. 3A-3D are a series of graphs depicting a mid-FTIR spectra displaying characteristic CO2 peaks at various time intervals within a 1M AlCl3 in 1.7:1 [(C2H5)3NH]Cl:FeCl3 eutectic electrolyte, time-dependent CO2 saturation levels in the electrolyte, dynamics of CO2 absorption by the eutectic electrolyte, and linear fitting of the pressure decay data using the ω=f−mt method, respectively, in accordance with the present disclosure.

[0015] FIGS. 4A-4D depict several graphs displaying representative cyclic voltammograms recorded in Ar and CO2 atmospheres within a 0.0-2.5V vs. Fe / Fe3+ potential range, GCD profile of Fe—CO2 cell at a current density of 0.1 mA / cm2, GCD profiles at varying current densities: (i) 0.01 mA / cm2, (ii) 0.1 mA / cm2 and (iii) 0.2 mA / cm2, and cycling performance of the Fe—CO2 cell at 0.1 mA / cm2, within the 0.0-2.5V vs. Fe / Fe3+ voltage range, respectively, in accordance with the present disclosure.

[0016] FIGS. 5A-5H depict FTIR spectra recorded for (i) as-synthesized eutectic electrolyte, (ii) CO2-purged electrolyte, and (iii) electrolyte retained from the cycled cell, highlighting spectral changes across different regions, high-resolution XPS spectra of C1s, O1s, and Fe2p, respectively, deconvoluted into multiple peaks representing different oxidation states of each element, and gas chromatography data for CO2, CO, and H2 detection, respectively, and a plot of XRD patterns, in accordance with the present disclosure.

[0017] FIG. 6 is a drawing illustrating the structural assembly of an electrochemical cell, in accordance with the present disclosure.

[0018] It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the present teachings rather than to maintain strict structural accuracy, detail, and scale.DETAILED DESCRIPTION

[0019] Reference will now be made in detail to exemplary embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same, similar, or like parts.

[0020] The present disclosure provides a method and system related to electrochemical carbon dioxide (CO2) capture and conversion methods. Specifically, the present teachings describe the use of nonaqueous deep eutectic electrolytes containing iron-based chloroferrate species and quaternary ammonium ions to facilitate CO2 activation, binding, and electrochemical reduction. This approach addresses significant challenges in sustainable carbon management, offering a streamlined pathway for integrated CO2 capture and conversion processes while utilizing cost-effective and scalable materials.

[0021] The systems of the present disclosure addresses challenges in CO2 capture and conversion by utilizing an integrated approach for CO2 capture and electrochemical conversion including a nonaqueous deep eutectic electrolyte (DEE) containing iron-based chloroferrate species and quaternary ammonium ions. This electrolyte composition, comprising triethylamine hydrochloride, FeCl3, and AlCl3, demonstrates advantageous physicochemical properties, including high CO2 solubility, low volatility, and a broad electrochemical stability window. The present system utilizes the ion-exchange and electrostatic interaction mechanisms of chloroferrate anions (FeCl4− and Fe2Cl7−) and quaternary ammonium ions to enable efficient CO2 binding, activation, and reduction. Unlike conventional systems, this approach eliminates the need for separate CO2 desorption steps, optimizing the process by directly supplying absorbed CO2 to the electrochemical cell for conversion into value-added products such as formate and carbonate. The use of cost-effective iron and nickel electrodes further supports the scalability and economic feasibility of the system.

[0022] By integrating CO2 capture and conversion into a single process, the system of the present disclosure addresses the limitations of prior technologies, offering improved energy efficiency, long-term stability, and selective conversion capabilities. The system, in examples, achieves a CO2 capture capacity of 14.3 g / L, with a diffusion coefficient of approximately 1×10−7 cm2 / s, validated through spectrochemical and pressure-decay analyses. Electrochemical testing demonstrates stable cycling performance, delivering an areal capacity of 0.3 mAh / cm2 at 0.1 mA / cm2, with efficient utilization of active materials and enhanced charge transfer kinetics. This approach represents a notable advancement in sustainable carbon management technologies, providing a scalable and cost-effective solution for mitigating CO2 emissions and promoting carbon recycling.

[0023] FIG. 1 is a reaction scheme for an electrochemical reduction of CO2-bound quinone- and amine-based species, enabling selective conversion through electron and proton transfer. Amine- and quinone-based systems are among the most widely studied and effective CO2 capture moieties. The following typical CO2 reduction reaction is observed for both organic moieties, as presented in FIG. 1. CO2 readily reacts with amines via a nucleophilic reaction to form carbamates, following an acid-base equilibrium. These carbamates can be decomposed with an energy input to regenerate the amines. Previous work has demonstrated that primary amines exhibit high CO2 adsorption via carbamate formation but slow desorption due to strong binding, whereas tertiary amines, lacking a proton for direct interaction, show low CO2 adsorption but rapid desorption due to weaker binding affinity. While the enthalpy of carbamate formation (ΔH0f) trends to increase slightly with increasing carbon chain length due to electronic effects, a similar trend is not observed in the regeneration of amines and CO2 from carbamate species. Instead, steric hindrance and solvation effects primarily influence the decomposition enthalpies of carbamates. Quaternary amine-based materials capture CO2 through an ion-exchange mechanism and exhibit higher CO2 uptake due to electrostatic interactions, along with faster adsorption kinetics in low-humidity environments.

[0024] Electrochemical carbon capture and CO2 reduction are gaining attention as energy-efficient and renewable-powered alternatives to traditional CO2 capture methods. One of the processes involves activating the redox-active carriers to facilitate rapid and efficient CO2 binding and release through redox cycles. An integrated approach of CO2 capture and conversion using electrolyte media eliminates the need for separate CO2 desorption, enhancing process efficiency by directly supplying absorbed CO2 to the electrolyzer at high concentrations. Few studies have explored the direct integration of CO2 capture media with electrochemical conversion processes. Recent work has investigated CO2 capture and electrochemical conversion system using a tetraethylammonium chloride / propylene carbonate / 2-amino-2-methyl-1-propanol electrolyte. The electrolyte exhibited a high CO2 absorption capacity of 22 g / L through carbamate formation in a nonaqueous medium, achieving a Faradic efficiency of ~45% for formate production. However, these and other studies face challenges related to the long-term stability of the electrolyte solution and lacks efficiency in generating high-value multi-carbon products. Other studies have demonstrated that the 1,3-diaminopropane / KCl / H2O electrolyte effectively captures CO2 via carbamate / bicarbonate mechanisms (absorption of 58.1 g / L), facilitating CO2 desorption under mild electrochemical conditions and enhancing conversion to formate and CO. Despite its promising carbon capture and electrochemical performance, the system faces challenges in long-term stability, mass transfer limitations, competitive hydrogen evolution, and selective conversion efficiency for multi-carbon products.

[0025] Deep eutectic solvents (DESs) are a class of environmentally friendly liquid media formed by mixing two or more components, leading to a depression in melting points due to strong intermolecular interactions. DESs exhibit physicochemical properties comparable to ionic liquids, including low vapor pressure (<100 Pa at 373 K), high thermal and chemical stability, nonflammability, and a wide electrochemical stability window. Additionally, they offer ease of preparation, cost-effectiveness, and compositional tunability, making them promising medium for carbon capture and electrochemical CO2 conversion. Recent studies have increasingly focused on investigating DESs for CO2 capture and conversion, emphasizing the fundamental interaction mechanisms. For example, the use of tetrapropylammonium bromide:formic DES has been investigated for CO2 capture, revealing that CO2 interacts with the eutectic medium through multiple interaction sites, including hydrogen bonding, dipole-quadrapole interactions, and Van der Waals forces. This interaction mechanism facilitated a CO2 solubility of 0.218 mole fraction (xCO2) at 25° C. and 35.2 bar pressure. Shala et al. demonstrated that the DES cholin chloride:ethylene glycol exhibits strong CO2 binding activity, effectively stabilizing CO2 intermediates and enhancing the selectivity of CO production. Their study highlights the superior electrochemical performance of DEEs, including reduced overpotential, faster charge transfer kinetics, and enhanced CO2 reduction efficiency, compared to conventional electrolyte solutions. Nevertheless, research on carbon capture using DESs and their integration with energy storage technologies gaining momentum, aiming to develop sustainable, dual-functional systems that not only capture CO2 but also convert it into value added products through electrochemical reduction or other catalytic processes.

[0026] In the present teachings eutectic electrolyte systems are investigated for sustainable carbon capture and conversion, integrated with energy storage in an iron-based electrochemical cell. The CO2 absorption capacity and diffusion kinetics of the electrolyte were systematically evaluated using spectrochemical techniques and in-situ pressure-decay analysis, revealing a 50% higher CO2 solubility than water. The electrolyte is coupled with cost-effective iron and nickel electrodes, facilitating redox activity within a potential range of 0.0-2.5V vs. Fe / Fe3+. and delivering a high areal capacity of 0.3 mAh / cm2 at 0.1 mA / cm2. Electrochemical reduction of CO2 in the electrolyte results in the formation of formate, CO, and H2, as confirmed by XPS, FTIR and gas-chromatographic analysis. The present disclosure highlights the potential of eutectic electrolytes in advancing integrated carbon capture and electrochemical conversion technologies.

[0027] FIG. 2 is a schematic illustration of CO2 capture by the eutectic electrolyte, forming adducts via chemical complexation. FIG. 2 shows a schematic representation of the CO2 capture and conversion process facilitated by the eutectic electrolyte system. The process begins with a flue gas source 202, which emits CO2 as a byproduct of industrial or energy production activities. The CO2 is directed into a CO2 container 204, where the carbon dioxide is stored or prepared for subsequent processing.

[0028] The captured CO2 is introduced into the eutectic electrolyte 206, which serves as the medium for chemical complexation and electrochemical conversion. The eutectic electrolyte 206, in examples, is composed of triethylamine hydrochloride, FeCl3, and AlCl3, forming a nonaqueous deep eutectic solvent with distinct physicochemical properties, including high CO2 solubility, low volatility, and a wide electrochemical stability window. Within the electrolyte 206, CO2 interacts with redox-active species, including chloroferrate anions (FeCl4− and Fe2Cl7−) and quaternary ammonium ions, resulting in the formation of CO2 adducts. Alternative electrolyte compositions can be simplified as R1R2R3NHX which comprises an organic ammonium halide, and imidazolium salts of formula R1R2ImX, wherein R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups, and X is a halide such as F, Cl, Br, I.

[0029] The chemical complexation of CO2 within the eutectic electrolyte 206 leads to the generation of intermediates, including R3NCOO−, [FeCl4·CO2]−, and [Fe2Cl7·CO2]−208. These intermediates are formed through ion-exchange mechanisms and electrostatic interactions, enabling efficient CO2 binding and activation. The R3NCOO− species are derived from the interaction of CO2 with quaternary ammonium ions, while [FeCl4·CO2]− and [Fe2Cl7·CO2]−208 result from the coordination of CO2 with chloroferrate anions. These intermediates are subsequently utilized in electrochemical reactions to produce value-added products such as formate and carbonate, contributing to sustainable carbon recycling and energy storage applications.

[0030] The potential of DESs for rechargeable multivalent batteries based on iron and aluminum has been previously described. A DES was selected, composed of triethylamine hydrochloride, FeCl3, and AlCl3, which retains key ionic complexes, including [C2H5)3NH]+, FeCl4−, Fe2Cl7− and AlCl4−. The key attributes of this electrolyte include a wide electrochemical stability window (3.2V vs. Fe / Fe3+) required for CO2 conversion, the presence of ionic complexes suitable for high CO2 sorption, cost-effectiveness, low volatility and nonflammability.

[0031] FIGS. 3A-3D are a series of graphs depicting a mid-FTIR spectra displaying characteristic CO2 peaks at various time intervals within a 1M AlCl3 in 1.7:1 [(C2H5)3NH]Cl:FeCl3 eutectic electrolyte, time-dependent CO2 saturation levels in the electrolyte, dynamics of CO2 absorption by the eutectic electrolyte, and linear fitting of the pressure decay data using the ω=f−mt method, respectively, in accordance with the present disclosure. FIG. 3A shows mid-FTIR spectra displaying characteristic CO2 peaks at various time intervals within a 1M AlCl3 in 1.7:1 [(C2H5)3NH]Cl:FeCl3 eutectic electrolyte, recorded in the range of 2370-2320 cm−1. The observed CO2 vibrational peaks provide insights into its solubility and suggest varying coordination environments within the electrolyte. FIG. 3B includes time-dependent CO2 saturation levels in the electrolyte, showing peak saturation after 12 hours under CO2 atmosphere. FIG. 3C includes dynamics of CO2 absorption by the eutectic electrolyte. FIG. 3D shows a linear fitting of the pressure decay data using the ω=f−mt method. The extracted slope and intercept were used to calculate the D, demonstrating the applicability of the linear approach for CO2 diffusion analysis in the eutectic electrolyte.

[0032] Fourier Transform Infrared (FTIR) spectroscopy was employed to determine the CO2 saturation time and diffusion coefficients in the proposed DES, as shown in FIG. 3A. The pure electrolyte exhibited no significant peaks in the 2370-2320 cm−1 range, confirming the absence of CO2 traces during sample transfer for FTIR measurements. To assess CO2 sorption kinetics, the electrolyte was purged with CO2 at 0.69 bar for varying durations, followed by FTIR analysis to determine the CO2 saturation limit under given pressure and time conditions. Upon CO2 exposure, the electrolyte displayed a characteristic CO2 asymmetric stretching peak within 2368-2318 cm−1. A small but distinct peak at 2325 cm−1, alongside a broad band spanning 2368-2330 cm−1 with multiple shoulder peaks centered at 2338 cm−1, 2344 cm−1, 2351 cm−1, 2358 cm−1, and 2361 cm−1 indicates a heterogeneous CO2 environment within the electrolyte. These shifts confirm that anions with higher charge density (Fe2Cl7−, FeCl4−) strongly interact with CO2, reducing its electron density and shifting peaks to lower frequencies, while smaller cations contribute to dipole-quadrupole stabilization. Furthermore, the integrated peak area analysis of the CO2 asymmetric stretch, as shown in FIG. 3B, reveals a maximum saturation occurs after 12 hours of purging. A slight decrease in saturation at 24 and 72 hours suggests a possible dynamic equilibrium in the electrolyte, leading to minor fluctuations in CO2 uptake.

[0033] Furthermore, the diffusion coefficient (D, cm2 / s) of CO2 in the eutectic electrolyte is estimated using the FTIR data. The concentration dynamics of dissolved CO2 within the electrolyte, both temporally and spatially, are governed by Fick's second law of diffusion:∂c∂t=D⁢∂2c∂x2(1)where c represents the concentration of CO2 in the eutectic electrolyte at a given time t. Assuming a constant diffusion, the mobility of CO2 molecules within the liquid medium remains stable over time and is not influenced by local CO2 concentration or other electrolyte conditions. Under this assumption, one possible solution to the above equation is given by:c=At1 / 2⁢e-x24⁢Dt(2)By applying the complementary Gaussian error function, Fick's second law can be rearranged under the specified boundary and initial conditions. Specifically, the boundary condition c=c0 at x=0 is imposed for all t>0, which represents a constant concentration c0 at the interface where CO2 begins to diffuse into the medium. This condition models a sustained source of CO2 at the boundary due to a constant partial pressure of CO2 at the surface. Additionally, we define the initial condition c=0 for x>0 is defined at t=0, representing the absence of CO2 within the medium at the start of the experiment. This initial state reflects a scenario where the medium is initially CO2-free and allows us to track the diffusion process as CO2 enters and spreads into the medium over time. With these boundary and initial conditions, equation-(2) can be transformed into the form:c⁡(x,t)=c0⁢ erfc⁢ (x2⁢Dt)(3)where erfc is the complementary error function. This solution describes the concentration profile c(x, t) as a function of both position x and time t, governed by the diffusion coefficient, D. Rearranging the equation-(3) provides diffusion coefficient.D=x2t⁢1[2·erf⁢c⁡(x,t)c0]2(4)The values for c(x, t), representing the CO2 concentration at specific times, were derived from the recorded FTIR spectra of CO2 peaks in the electrolyte purged with CO2 at different time intervals, as shown in FIG. 3A. It is assumed that the surface layer of the electrolyte was fully saturated with CO2, i.e. it had reached a stable, balanced concentration over time. Thus, the maximum saturation concentration, c0, was determined based on the relationship between dissolved CO2 and time under constant pressure. The concentration values c(x, t) were selected from 1-hour and 6-hour datasets, representing 35% and 52% of the maximum saturation concentration, respectively, as these intervals displayed a linear trend in CO2 uptake. At the 12-hour interval, CO2 reached a maximum saturation level. Therefore, only the first two datasets (1-hour and 6-hour) were used to calculate the diffusion coefficient of CO2 in the electrolyte. We used a fixed x value of 1 mm, representing the thickness of the electrolyte layer or the distance from the CO2 interface to the measurement point. The average diffusion coefficient of CO2 was determined to be 1.08×10−7 cm2 / s.To quantify the total CO2 sorption in the eutectic electrolyte and validate the diffusion coefficient obtained from FTIR measurements, a linear method was employed based on pressure-decay data (FIG. 3C), assuming a known equilibrium pressure. A total of 0.2 mL of eutectic electrolyte was placed in a 3 mL Swagelok cell equipped with a pressure gauge transducer, and CO2 was pressurized to 0.69 bar. Several assumptions were made before determining the diffusion coefficient of CO2 in the eutectic mixture. This method assumes a constant temperature and uniform CO2 diffusion throughout the measurement, with the eutectic electrolyte considered non-volatile. Density induced convection and swelling effects were deemed negligible. Additionally, the gas-liquid interface concentration was assumed to follow Henry's law, while gas compressibility (Z) was considered constant, with an average Z value of 0.39786 calculated from the recorded pressure decay data. The diffusion coefficient, D, was estimated using the following equation:Pc-PeqPi=2⁢λ1+λ+λ2⁢a12⁢e-Da12⁢tl2(5)Where Pc is the gas partial pressure, Peq is the equilibrium pressure, Pi is the initial pressure, λ is the ratio of equilibrium pressure to the pressure change of the gas phase, 1 is the thickness of the liquid, and a1 satisfies the equation tan (a1)=−λa1. Rearranging the equation provides the linear form,ω=f-mt(6)where ω, f, and m are defined as follows:ω=ln⁢ (Pc-PeqPi)(7)The intercept from the straight line is:f=ln⁢ (2⁢λ1+λ+a12⁢λ2)(8)The slope from the straight line is:m=Da12l2(9)The intercept and slope determined from the straight-line fit, as shown in FIG. 3D, are −0.33442 and 9.1847×10−6, respectively. The value of a1 deduced from equation-(8) is 0.8934. The diffusion coefficient recorded is, D=1.15×10−7 cm2 / s. The diffusion coefficients measured using the FTIR studies and the pressure-decay method show good correlation. The pressure decay method also determines the total number of moles of CO2 that can be absorbed by eutectic i.e. 6.5×10−5 moles (equivalent to 14.30 g / L).Electrochemical AnalysisFIGS. 4A-4D depict (FIG. 4A) Representative cyclic voltammograms recorded in Ar and CO2 atmospheres within a 0.0-2.5V vs. Fe / Fe3+ potential range, (FIG. 4B) GCD profile of Fe—CO2 cell at a current density of 0.1 mA / cm2, (FIG. 4C) GCD profiles at varying current densities: (i) 0.01 mA / cm2, (ii) 0.1 mA / cm2 and (iii) 0.2 mA / cm2, and (FIG. 4D) Cycling performance of the Fe—CO2 cell at 0.1 mA / cm2, within the 0.0-2.5V vs. Fe / Fe3+ voltage range. In the present study, all electrochemical cells were fabricated using carbonyl iron as the anode, Ni foam as the gas diffusion layer (GDL), and 1M AlCl3 in 1.7:1 molar ratio of [C2H5)3NH]Cl to FeCl3 as the electrolyte medium, assembled in a custom-made Swagelok cell purged with an ultra-high-purity CO2 at 10 PSI (~0.69 bar). Post fabrication, all cells were rested for at least 24 hours before performing electrochemical analysis. The electrochemical performance of Fe—CO2 batteries was initially evaluated using cyclic voltammetry (CV) within a potential range of 0.0-2.5V vs. Fe / Fe3+, at a scan rate of 0.5 mV / s, as shown in FIG. 4A. Under the Ar atmosphere, as shown in FIG. 3(a), the Ni electrode exhibits no distinct peaks throughout the full voltage sweep. In contrast, the cell in the CO2 atmosphere displays redox peaks, indicating CO2 conversion (FIG. 4(a)). FIG. 4(b) presents galvanostatic charge-discharge (GCD) analyses performed at 0.1 mA / cm2, revealing a progressive increase in discharge capacity, reaching 0.24 mAh / cm2 by the 10th cycle, accompanied by the rise in Coulombic efficiency to 102%. The progressive increase in discharge capacity with cycling correlates with the increasing peak current densities observed in the CV profiles. This suggests efficient CO2 diffusion, adsorption, and convection on the gas diffusion electrode (GDE), as well as improved utilization of active materials and enhanced charge transfer kinetics. The Fe—CO2 cell exhibited a capacity retention of 0.1 mAh / cm2 at a high current density of 0.2 mA / cm2, as shown in FIG. 4(c), whereas a lower current density of 0.01 mA / cm2 resulted in a capacity retention of 0.3 mAh / cm2. The cell maintained stability for >21 cycles, as shown in FIG. 4(d).Understanding CO2 Reaction Kinetics in Eutectic Systems

[0045] FIGS. 5A-5H depict FTIR spectra recorded for (i) as-synthesized eutectic electrolyte, (ii) CO2-purged electrolyte, and (iii) electrolyte retained from the cycled cell, highlighting spectral changes across different regions. FIGS. 5B, 5C, and 5D show the high-resolution XPS spectra of C1s, O1s, and Fe2p, respectively, deconvoluted into multiple peaks representing different oxidation states of each element. FIGS. 5E, 5F, and 5G, display gas chromatography data for CO2, CO, and H2 detection, respectively. FTIR spectroscopy was employed, as shown in FIG. 5A, to analyze the pure electrolyte, CO2-purged electrolyte, and the electrolyte recovered after cycling the Fe—Ni cell to elucidate the chemical interactions of CO2 within the electrolyte before and after electrochemical cycling. The FTIR spectra of the CO2-purged electrolyte exhibit distinct spectral modifications in two key regions: (i) the emergence of new absorption bands in the 2365-2320 cm−1 range, characteristic of CO2 asymmetric stretching, indicative of its coordination within the electrolyte; (ii) a shift in the N—H stretching mode from 3130 cm−1 to 3137.5 cm−1, suggesting CO2 interaction via hydrogen bonding or proton transfer within the triethylammonium cation, potentially facilitating the formation of carbamate (R—N—COO−) species. The presence of multiple peaks within the CO2 stretching region suggests the existence of diverse CO2 coordination environments within the electrolyte matrix. The cycled electrolyte retained from the Fe—Ni cell after GCD cycles exhibits noticeable peak shifts and intensity variations, indicating significant chemical transformations. (i) Hydrogen bonding and structural reorganization (3210-2830 cm−1): A broad absorption band in this region corresponds to C—H, N—H, and O—H stretching modes, indicative of changes in the electrolyte environment. The increased intensity and broadening in the range of 3210-2830 cm−1 imply enhanced hydrogen bonding, forming carbamate like structures. Additionally, a shift to a lower frequency in the range of 1690-1590 cm−1 also suggests the formation of carbamate species. (ii) CO2 complexation and carbonate formation (2360-2320 cm−1): Shifts and intensity variations in the CO2 asymmetric stretching mode suggest dynamic rearrangement of CO2 coordination within the electrolyte. These spectral modifications can be attributed to CO2 complexation with electrolyte species, including chloroferrate anions (FeCl4−, Fe2Cl7−) and amines. (iii) Carbamate formation and CO2 reduction products (1220-860 cm−1): A broad absorption feature in this region, with a distinct C—N stretching band near 1200 cm−1, confirms the formation of carbamate species (R3NCOO−) via CO2 interaction with amines. Additionally, the presence of C—O stretching bands between 1100-1000 cm−1 and 900-860 cm−1 supports the formation of formate (HCOO−) and bicarbonate (HCO3−) species, providing further evidence for electrochemical CO2 reduction pathways occurring in the system. (iv) Fe—CO2 complexation and Fe coordination changes (745-545 cm−1): Peak shifts observed in this range confirm the formation of Fe—CO2 adducts, specifically involving chloroferrate species (FeCl4−, Fe2Cl7−). The spectral variations in the range of 700-500 cm−1 involves the Fe—CO stretching vibrations, suggest modifications in Fe coordination chemistry, likely due to interactions with CO2-containing intermediates or formation of Fe products. (v) Fe redox processes and carbonate formation (547-414 cm−1): A broad, distinct absorption pattern in this region is attributed to Fe—Cl vibrational modes, confirming iron reduction processes occurring during cycling. Additionally, these spectral changes suggest the formation of Fe-carbonate complexes, supporting the conversion of CO2 into carbonate (CO32-) species as part of the electrochemical reaction sequence. These spectral observations collectively provide strong evidence for CO2 activation, complexation, and electrochemical reduction in the cycled electrolyte.

[0046] To further characterize the reaction products, X-ray photoelectron spectroscopy (XPS) was conducted on the cycled Ni electrode, focusing on identifying products resulting from the Fe—CO2 cell's redox reactions. A wide-scan XPS spectrum of the cycled electrode, reveals characteristic peaks corresponding to C1s, N1s, O1s, Fe2p, Ni2p, C12p and C12s. The high-resolution C1s spectrum (282-292 eV) showed three primary peaks (FIG. 5B): C—C or C═C (~284.9 eV), likely from residual carbonaceous species such as the electrolyte, C—N (~286.4 eV), indicating the presence of amines, and C═O (~288.7 eV), strongly suggesting the formation of carbamate or metal-carbonate species, which aligns with CO2 electrochemical reduction pathways. Similarly, FIG. 5C displays the Ols spectrum (530-534 eV) revealed multiple oxidation states, with O2— (~530.5 eV) corresponding to lattice oxygen or Fe oxide phases, oxygen bonded to Fe3+ (~533.9 eV) suggesting carbonate species, and physiosorbed CO2 or hydroxyl-related oxygen (~536.3 eV). FIG. 5D shows the high-resolution XPS spectra of Fe 2p (708-740 eV) were deconvoluted into multiple peaks, indicating the presence of Fe complexes. Further supporting these findings, gas chromatography analysis of gases from the electrochemical cell chamber identified CO2, CO and H2, as shown in FIGS. 5E, 5F, and 5G. The detection of H2 implies partial reduction of the electrolyte, possibly involving the triethylammonium cation, while the presence of CO provides direct evidence of CO2 electrochemical reduction occurring within the Fe—Ni cell. X-ray diffraction (XRD) analysis of the cycled Ni electrode was conducted to examine structural changes and product formation during the GCD cycles of the Fe—CO2 cell. As depicted in FIG. 5H, new diffraction peaks emerged within the 20 range of 5-50°. The XRD patterns suggest the formation of carbonate species and / or a mixed organic / inorganic phases, which is consistent with the observed XPS signals. Collectively, these findings indicate a CO2 conversion mechanism coupled with energy storage, involving electrochemical CO2 reduction to metal carbonates, the formation of carbonates and oxide intermediates, and electrolyte degradation contributing to structural and compositional changes in the cycled electrode.

[0047] The proposed reaction mechanism is:

[0048] At the anode is:

[0049] At the cathode:CONCLUSIONS

[0050] In summary, a chloroferrate-based eutectic electrolyte with quaternary ammonium ions was investigated, demonstrating efficient CO2 capture via an ion-exchange mechanism and subsequent electrochemical reduction using cost-effective and sustainable materials. The electrolyte achieves a CO2 capture capacity of 14.3 g / L, with a diffusion coefficient of ~1×10−7 cm2 / s, validated through FTIR spectroscopy and pressure-decay measurements. The system employs a Fe metal anode, delivering a high electrochemical capacity of 0.3 mAh / cm2 and demonstrating stable cycling performance of >20 cycles. During discharge, CO2 adducts of chloroferrate and amine species undergo electron-driven transformations, yielding formate (HCOO−) and carbonate (CO32-) species as primary reduction products. The present disclosure highlights the potential of eutectic Fe-based electrolytes as a scalable and cost-effective alternative for integrated CO2 capture and electrochemical conversion, offering a promising route toward sustainable carbon recycling technologies.Materials

[0051] Ultra-high purity CO2 (≥99.99%) was purchased from AirGas. Triethylamine hydrochloride ([(C2H5)3N]HCl, ≥99%), Iron chloride (FeCl3, ≥97% reagent grade), carbonyl iron (≥97% Fe basis), poly(vinylidene fluoride) (PVDF powder), glass microfiber filters (Whatman Grade 934-AH) were procured from Sigma-Aldrich. Aluminum (III) chloride (AlCl3, anhydrous, 99.985% metal basis) purchased from Thermo Scientific, Nickel form (>99.99%, Ni anti-corrosive) from MTI corporation, Toray carbon paper 030 (CP, wet proofed, 110 μm thickness) from FuelCell Store and 1-methyl-2-pyrrolidinone (C5H9NO, 99.5%) from Spectrum chemical manufacturing corporation.Electrolyte Preparation

[0052] The electrolyte preparation followed the methodology known in the art. All procedures were carried out in an argon-filled glovebox (<1 ppm O2, <1 ppm H2O, manufactured by vacuum Technologies Inc.). The eutectic electrolyte synthesis proceeded in two phases. First, a 1.7:1 molar ratio of triethylamine hydrochloride to FeCl3 was prepared by gradually adding FeCl3 to triethylamine hydrochloride. In the second phase, a predetermined amount of AlCl3 was introduced into the binary electrolyte, resulting in a final composition of 1M AlCl3 in 1.7:1 triethylamine hydroichloride:FeCl3.Electrode Fabrication

[0053] Carbonyl iron electrodes were fabricated by ball-milling a precise weight ratio of carbonyl iron, Super P conductive carbon, and PVDF (90:5:5 weight %) for 3 hours at 300 rotations per minute. The resulting mixture was then combined with 1-methyl-2-pyrrolidinone to form a homogeneous slurry, which was cast onto a carbon-paper current collector and dried vacuum at 100° C. for 12 hours. The dried electrodes were used as the anode in Fe—CO2 cell fabrication. Pristine nickel foam, as received from the manufacturer, served as the gas diffusion layer and current collector.Electrochemical CO2 Cell Fabrication

[0054] CO2 containing batteries and their corresponding controls were assembled within custom-made battery holders designated to regulate gas flow across the battery and fabricated inside an Ar-filled glove box (≤1 ppm O2 and ≤1 ppm H2O, vacuum technologies). Battery assembly involved sequentially adding the carbonyl Fe anode, a separator, 1-500 μL electrolyte, Ni foam cathode into the battery chamber, followed by sealing and removal from the glove box. To introduce CO2, the input line was loosely connected to a CO2 gas source, and CO2 was then directed over the closed inlet valve at a rate of 0<P≤50 mL / min for 1-30 minutes. Subsequently, the inlet and outlet valves are opened, allowing CO2 to flow through the battery chamber for 1-30 minutes. Finally, the outlet valve was closed, and the chamber was pressurized with CO2 to a pressure of ~1-50 PSI. The Swagelok cell was then rested for 24 hours before conducting electrochemical characterizations.

[0055] FIG. 6 is a drawing illustrating the structural assembly of an electrochemical cell, in accordance with the present disclosure. FIG. 6 represents a mechanical assembly of an electrochemical cell 600, showing the structural components and their arrangement. The electrochemical cell 600 is designed to execute processes for capturing carbon dioxide and performing electrochemical conversion, as described herein.

[0056] The electrochemical cell 600 includes an anode 602 and a cathode 604, which are positioned within separate chambers, the anode chamber 624 and the cathode chamber 626, respectively. These chambers are separated by a cell chamber 618, which houses the electrolyte and facilitates ionic contact between the anode 602 and cathode 604. The cell chamber 618 is sealed using fluoropolymer seals 616 to ensure containment of the electrolyte and prevent leakage during operation.

[0057] A gas inlet 608 is connected to the inlet valve 606, allowing controlled introduction of carbon dioxide into the cell chamber 618. The gas outlet 620, connected to the outlet valve 622, enables the removal of gases or reaction byproducts from the cell chamber 618. The inlet valve 606 and outlet valve 622 are further configured to regulate the flow and pressure of gases within the electrochemical cell 600, providing optimal conditions for carbon dioxide capture and conversion.

[0058] The electrochemical cell 600 incorporates a fluoropolymer tube 612, which provides a durable and chemically resistant pathway for gas flow. A spring 610 is included to maintain mechanical stability and ensure proper alignment of the internal components during operation. Screw holes 614 are provided for securing the assembly and enabling integration into larger systems or experimental setups. The structural design of the electrochemical cell 600 ensures efficient gas flow, containment, and mechanical stability, supporting the integrated carbon dioxide capture and electrochemical conversion processes described in the present disclosure.Electrochemical Testing

[0059] Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were performed using a multi-channel Biologic VSP potentiostat (EC-Lab v11.30 software). Galvanostatic charge-discharge (GCD) studies were conducted on a multi-channel Neware Battery Testing System (BTS v8 software). EIS studies were performed on a Fe—CO2 cells over a frequency range of 50 mHz to 1 MHz at open-circuit potential with an amplitude of 10 mV. CV measurements were conducted within the potential window of 0.0-2.5V versus Fe / Fe3+ at a scan rate of 0.5 mV / s. GCD analysis was performed under CO2 or Ar atmospheres within the same potential window of 0.0-2.5V vs. Fe / Fe3+.Materials Characterization

[0060] The CO2 absorption and diffusion kinetics were measured using a Pressure Gauge Transducer equipped with Track-It DataLogger Software. Fourier Transform Infrared (FTIR) spectroscopy (Nicolet 6700 FTIR Spectrometer) was performed on the CO2 purged electrolytes to determine the diffusion coefficients and the cycled electrodes to investigate charge storage kinetics within the spectral range of 400-4000 cm−1, with data acquired by averaging 64 scans. X-ray diffraction (XRD) analysis was performed using a Rigaku smartLab X-ray diffractometer. Scanning Electron Microscopy (SEM) (TESCAN VEGA, operating at an accelerating voltage of 20 kV) was employed to examine the morphology of discharge products or precipitates formed on Ni foam after cycling. Additionally, X-ray Photoelectron Spectroscopy (XPS) was conducted on a Kratos AXIS ULTRA spectrometer to determine the binding energies of the electrode materials.

[0061] In some examples of the present disclosure, a method for fabricating an electrochemical cell includes adding an anode to an enclosure, adding a conductive electrode to the enclosure, adding an electrolyte to the enclosure such that the anode and the conductive electrode are in contact with the electrolyte, and pressurizing the electrochemical cell with a gas. In some examples, the enclosure is a custom-made battery holder or a Swagelok-type cell configured to regulate gas flow across the cell chamber. In some examples, assembly is performed by sequentially placing the anode, a separator, the electrolyte, and the conductive electrode into the enclosure, followed by sealing of the enclosure and introduction of the gas. In some examples, the gas is introduced through an inlet line and the electrochemical cell is pressurized after a purge or flow-through step. In some aspects, the anode includes iron, an iron-based alloy, or an iron-containing composite with a conductive material. In some examples, the anode is a carbonyl iron electrode. In some examples, the anode is formed from carbonyl iron combined with conductive carbon and a polymeric binder to form a slurry-coated electrode on a current collector. In some examples, the iron-containing composite can include carbonyl iron, Super P conductive carbon, and poly(vinylidene fluoride).

[0062] In examples, the conductive electrode includes an electronically conductive substrate selected from a metal including nickel or zinc, a metal alloy, or a conductive carbon-based material including carbon cloth, carbon foam, graphite foam, or combinations thereof. In some examples, the conductive electrode comprises a nickel foam that serves as a gas diffusion layer and current collector. In some aspects, the conductive electrode is carbon cloth or another conductive porous substrate configured to provide gas access and electrical conductivity at the cathode side of the cell.

[0063] In some examples, the electrolyte includes a eutectic electrolyte composition. In examples, the eutectic electrolyte composition is a nonaqueous deep eutectic electrolyte having high carbon dioxide solubility, low volatility, and a broad electrochemical stability window. In some aspects, the eutectic electrolyte is introduced in an amount sufficient to wet the electrodes and separator and provide ionic contact therebetween.

[0064] In examples, the eutectic electrolyte composition includes a trialkyl amine halide or a trialkyl ammonium halide having the general formula R1R2R3NHX, where R1, R2, and R3 are independently selected from alkyl groups including methyl, ethyl, propyl, or butyl, and X is a halide including F, Cl, Br, or I. In aspects of the present disclosure, the ammonium halide provides a cationic species that participates in ion-exchange and electrostatic interactions with carbon dioxide. The electrolyte can include an organic ammonium halide selected to support carbon dioxide binding and electrochemical conversion in the eutectic medium. The eutectic electrolyte composition can include triethylamine hydrochloride and iron chloride. In some examples, triethylamine hydrochloride is combined with FeCl3 to form a binary eutectic electrolyte containing chloroferrate species. In some examples, the resulting electrolyte includes iron-based anionic species such as FeCl4− and Fe2C7− that facilitate carbon dioxide activation, binding, and electrochemical reduction.

[0065] In examples, the eutectic electrolyte composition further includes one or more halide salts including aluminum chloride, magnesium chloride, zinc chloride, or phosphorous pentachloride. In some examples, the additional halide salt adjusts ionic speciation, Lewis acidity, conductivity, and carbon dioxide interaction within the electrolyte. In some working examples, AlCl3 is added to the binary triethylamine hydrochloride and iron chloride eutectic to provide a final composition including 1 M AlCl3.

[0066] In some examples, the eutectic electrolyte composition includes triethylamine hydrochloride and iron chloride in a ratio of about 1.7:1. In some examples, FeCl3 is gradually added to triethylamine hydrochloride to prepare the binary eutectic. In some examples, the 1.7:1 ratio provides a liquid eutectic composition that retains chloroferrate species suitable for carbon dioxide sorption and electrochemical conversion.

[0067] The gas can include carbon dioxide or a mixture of carbon dioxide with one or more additional gases. In some examples, the gas is ultra-high-purity carbon dioxide. In some examples, the gas is a carbon dioxide-containing gas stream derived from an industrial or energy production source, including a flue gas source. In some examples, the gas is introduced into the enclosure and retained under pressure to promote dissolution of carbon dioxide into the electrolyte.

[0068] The electrochemical cell can include an iron anode disposed in the enclosure, a conductive electrode including nickel or carbon cloth disposed in the enclosure, and a eutectic electrolyte including triethylamine hydrochloride, iron chloride, and aluminum chloride, where the anode and the conductive electrode are in contact with the electrolyte, and carbon dioxide is introduced into the enclosure and the electrochemical cell is pressurized with carbon dioxide. In some working examples, the iron anode is a carbonyl iron anode, the conductive electrode is nickel foam, and the electrolyte is 1 M AlCl3 in a 1.7:1 molar ratio of triethylamine hydrochloride to FeCl3. In some examples, the cell is assembled in a custom-made Swagelok cell and pressurized with carbon dioxide to about 10 PSI.

[0069] Examples include where the conductive electrode comprises a substrate in a pure form or a substrate having one or more materials deposited thereon by mechanical, electrochemical, or chemical deposition methods, where the deposited materials include metal oxides, carbon-based materials, sulfides, or metal sulfides. In some examples, the substrate is used in a pristine form, such as a pristine nickel foam current collector and gas diffusion layer. In other examples, the substrate can carry deposited surface materials selected to modify conductivity, interfacial chemistry, catalytic activity, or gas transport behavior within the electrochemical cell.

[0070] In examples, the eutectic electrolyte composition can be configured to dissolve carbon dioxide or carbon dioxide-containing gases. In some examples, carbon dioxide uptake is confirmed by Fourier Transform Infrared spectroscopy through appearance of characteristic asymmetric stretching peaks in the 2368-2318 cm−1 region. In some examples, the eutectic electrolyte exhibits a carbon dioxide absorption capacity of about 14.3 g / L and a diffusion coefficient of about 1×10−1 cm2 / s, as determined by FTIR analysis and pressure-decay measurements. In some examples, the electrolyte reaches peak carbon dioxide saturation after about 12 hours under a carbon dioxide atmosphere.

[0071] The method of the present disclosure can further include converting carbon dioxide electrochemically within the electrochemical cell. For example, electrochemical conversion can be carried out after the cell is assembled and pressurized with carbon dioxide. In examples, cyclic voltammetry is performed within a potential window of about 0.0 V to about 2.5 V versus Fe / Fe3+ to evaluate redox activity associated with carbon dioxide conversion. The cell can be rested after fabrication and before electrochemical testing to permit gas dissolution and interfacial equilibration.

[0072] In aspects, electrochemical conversion of carbon dioxide within the electrochemical cell produces one or more carbon-containing products. In some examples, the products include formate, carbonate, bicarbonate, carbon monoxide, carbamate-containing species, or combinations thereof. These products can be identified by FTIR spectroscopy, X-ray photoelectron spectroscopy, gas chromatography, X-ray diffraction, or combinations thereof.

[0073] In some examples, electrochemical conversion of carbon dioxide within the electrochemical cell produces carbonate or bicarbonate species. This carbonate and bicarbonate formation is supported by FTIR absorption bands associated with C—O stretching and by spectroscopic and diffraction evidence consistent with carbonate-containing products or complexes. Carbonate can also be formed according to a reaction pathway in which two carbon dioxide molecules react electrochemically to yield carbonate and carbon monoxide, followed by protonation of carbonate to bicarbonate.

[0074] Alternatively, electrochemical conversion of carbon dioxide within the electrochemical cell produces formate species. Formate is produced through reduction of carbon dioxide-derived radical intermediates generated from chloroferrate-carbon dioxide adducts or amine-associated intermediates. In some examples, the proposed mechanism includes formation of CO2′−, followed by proton-coupled electron transfer to yield HCOO—. Electrochemical conversion of carbon dioxide also produces carbon monoxide. Carbon monoxide can be detected by gas chromatography of gases present in the electrochemical cell chamber. In examples, carbon monoxide is generated together with carbonate species during electrochemical reduction of carbon dioxide. Hydrogen gas can also be generated during operation of the electrochemical cell, and detected by gas chromatography from the electrochemical cell chamber. The hydrogen formation occurs through proton reduction within the electrolyte and may involve proton-containing species associated with the triethylammonium cation.

[0075] Carbon dioxide capture and electrochemical energy storage can occur simultaneously within the electrochemical cell. In examples, the eutectic electrolyte captures carbon dioxide through ion-exchange and electrostatic interactions involving chloroferrate species and ammonium-containing species, while the iron-based electrochemical cell stores and releases charge during cycling. In these examples, the integrated system delivers an areal capacity of about 0.3 mAh / cm2 at about 0.1 mA / cm2 while also supporting carbon dioxide conversion. In aspects, there may be no separate carbon dioxide desorption step, such as, for example, where carbon dioxide absorbed in the eutectic electrolyte is supplied directly to the electrochemical cell for conversion without thermal regeneration of a separate capture medium. The elimination of a separate desorption step reduces process complexity and improves overall energy efficiency of the integrated carbon dioxide capture and conversion system.

[0076] While the present teachings have been illustrated with respect to one or more implementations, alterations and / or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, it may be appreciated that while the process is described as a series of acts or events, the present teachings are not limited by the ordering of such acts or events. Some acts may occur in different orders and / or concurrently with other acts or events apart from those described herein. Also, not all process stages may be required to implement a methodology in accordance with one or more aspects or embodiments of the present teachings. It may be appreciated that structural objects and / or processing stages may be added, or existing structural objects and / or processing stages may be removed or modified. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and / or phases. Furthermore, to the extent that the terms “including,”“includes,”“having,”“has,”“with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” The term “at least one of” is used to mean one or more of the listed items may be selected. Further, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein. The term “conformal” describes a coating material in which angles of the underlying material are preserved by the conformal material. The term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated embodiment. The terms “couple,”“coupled,”“connect,”“connection,”“connected,”“in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via one or more intermediate elements or members.” Finally, the terms “exemplary” or “illustrative” indicate the description is used as an example, rather than implying that it is an ideal. Other embodiments of the present teachings may be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present teachings being indicated by the following claims.

Examples

Embodiment Construction

[0019]Reference will now be made in detail to exemplary embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same, similar, or like parts.

[0020]The present disclosure provides a method and system related to electrochemical carbon dioxide (CO2) capture and conversion methods. Specifically, the present teachings describe the use of nonaqueous deep eutectic electrolytes containing iron-based chloroferrate species and quaternary ammonium ions to facilitate CO2 activation, binding, and electrochemical reduction. This approach addresses significant challenges in sustainable carbon management, offering a streamlined pathway for integrated CO2 capture and conversion processes while utilizing cost-effective and scalable materials.

[0021]The systems of the present disclosure addresses challenges in CO2 capture and conversion by utilizing an integra...

Claims

1. A method for fabricating an electrochemical cell, comprising:adding an anode to an enclosure;adding a conductive electrode to the enclosure;adding an electrolyte to the enclosure such that the anode and the conductive electrode are in contact with the electrolyte; andpressurizing the electrochemical cell with a gas.

2. The method of claim 1, wherein the anode comprises iron, an iron-based alloy, or an iron-containing composite with a conductive material.

3. The method of claim 1, wherein the conductive electrode comprises an electronically conductive substrate selected from a metal including nickel, zinc, a metal alloy, or a conductive carbon-based material, including carbon cloth, carbon foam, graphite foam, or combinations thereof.

4. The method of claim 1, wherein the electrolyte comprises a eutectic electrolyte composition.

5. The method of claim 4, wherein the eutectic electrolyte composition comprises a trialkyl amine halide, trialkyl ammonium halide having a general formula R1R2R3NHX, wherein R1, R2, R3 are independently selected from alkyl groups including methyl, ethyl, propyl, or butyl, and X is a halide including F, Cl, Br, and I.

6. The method of claim 4, wherein the eutectic electrolyte composition comprises triethylamine hydrochloride and iron chloride.

7. The method of claim 4, wherein the eutectic electrolyte composition further comprises one or more halide salts including aluminum chloride, magnesium chloride, zinc chloride or phosphorous pentachloride.

8. The method of claim 4, wherein the eutectic electrolyte composition comprises triethylamine hydrochloride:iron chloride in a ratio of 1.7:1.

9. The method of claim 1, wherein the gas comprises carbon dioxide or a mixture of carbon dioxide with one or more additional gases.

10. The method of claim 1, wherein the electrochemical cell comprises:an iron anode disposed in the enclosure;a conductive electrode comprising nickel or carbon cloth disposed in the enclosure; anda eutectic electrolyte comprising triethylamine hydrochloride, iron chloride, and aluminum chloride,wherein the anode and the conductive electrode are in contact with the electrolyte, and carbon dioxide is introduced into the enclosure and the electrochemical cell is pressurized with carbon dioxide.

11. The method of claim 1, wherein the conductive electrode comprises a substrate in a pure form or a substrate having one or more materials deposited thereon by mechanical, electrochemical, or chemical deposition methods, the deposited materials comprising metal oxides, carbon-based materials, sulfides, or metal sulfides.

12. The method of claim 4, wherein the eutectic electrolyte composition is configured to dissolve carbon dioxide or carbon dioxide-containing gases.

13. The method of claim 1, further comprising converting carbon dioxide electrochemically within the electrochemical cell.

14. The method of claim 13, wherein converting carbon dioxide electrochemically within the electrochemical cell produces one or more carbon-containing products.

15. The method of claim 13, wherein converting carbon dioxide electrochemically within the electrochemical cell produces carbonate or bicarbonate species.

16. The method of claim 13, wherein converting carbon dioxide electrochemically within the electrochemical cell produces formate species.

17. The method of claim 13, wherein converting carbon dioxide electrochemically within the electrochemical cell produces carbon monoxide.

18. The method of claim 1, wherein hydrogen gas is generated during operation of the electrochemical cell.

19. The method of claim 1, wherein carbon dioxide capture and electrochemical energy storage occur simultaneously within the electrochemical cell.

20. The method of claim 1, wherein there is no separate carbon dioxide desorption step.

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