SPIN-POLARIZED ELECTROCATALYTIC REDUCTION REACTIONS, AND CATALYSTS THEREFOR

Abstract

A method of producing ethanol by electrocatalytic reduction of carbon dioxide, comprises reducing carbon dioxide in an aqueous electrolyte on an electrocatalyst with electricity. The electrocatalyst is exposed to a magnetic field of at least 400 Gauss, the electrocatalyst comprises at least one paramagnetic material, and an amount of ethanol produced by the reducing is greater than an amount of ethanol produced without the magnetic field. Also described is a system for electrocatalytic reduction of carbon dioxide, which comprises (a) and electrocatalyst, containing (i) copper and (ii) copper oxide, C60 and/or neodymium; (b) an aqueous electrolyte, in contact with the electrocatalyst; (c) a counter electrode, in ion-conductive contact with the electrocatalyst; (d) a magnet, for providing a magnetic field of at least 400 Gauss to the electrocatalyst; and (e) a power source, electronically connected to the electrocatalyst and the counter electrode.

Description

BACKGROUND

The bottleneck for economical decarbonization via electrochemical CO₂ reduction reaction (CO₂RR) is the breakeven point between input cost and value of the output products. The input electrical energy for CO₂RR is regulated by power=voltage×current, where voltage is the potential gap between cathode and anode. Besides lowering the voltage for reduced electrical power consumption, it is also crucial to guide the current flow towards high-value products in order to boost the economic viability of electrochemical CO₂RR. Organic products containing chemical bonds with high specific energy including C—H and one or more than one C—C or C═C bonds (C₂₊ products) generally possess more added value than products without these bonds (e.g., CO). However, current effort on directing the electrochemical CO₂RR towards high value C₂₊ compounds with high selectivity prejudicially rely on the development of new electrocatalysts or other chemical approaches (e.g., electrolytes).^1-3 In contrast, magnetic fields that have a fundamental relevance to species with orbital magnetic moment (orientation) and spin magnetic moment (e.g., radicals with unpaired electrons)^{4, 5} in CO₂RR has rarely been exploited.^6-8 For example, in Hao et al.⁷ a magnetic field was used to enhance electrochemical CO₂RR for formic acid, but no C₂₊ products such as ethanol were produced. Furthermore, the prior study was not carried out in a flow reactor which is more relevant to a practical, commercial or large scale system.

SUMMARY

In a first aspect, the present invention includes a method of enhancing the production of ethanol and ethylene (both are C₂₊ products), by electrocatalytic reduction of carbon dioxide, comprising reducing carbon dioxide in an aqueous electrolyte on an electrocatalyst with electricity. The electrocatalyst is exposed to a magnetic field of at least 400 Gauss, the electrocatalyst comprises at least one paramagnetic material, and amounts of ethanol and ethylene produced by the reducing are greater than the amounts of ethanol and ethylene produced without the magnetic field.

In a second aspect, the present invention includes a method of reducing of carbon dioxide electrocatalytically, comprising reducing carbon dioxide in an aqueous electrolyte on an electrocatalyst with electricity. The electrocatalyst is exposed to a magnetic field of at least 400 Gauss, and the electrocatalyst comprises (i) copper and (ii) copper oxide, C60 and/or neodymium.

In a third aspect, the present invention includes a system for electrocatalytic reduction of carbon dioxide, comprising (a) and electrocatalyst, containing (i) copper and (ii) copper oxide, buckminsterfullerene (C60) and/or neodymium; (b) an aqueous electrolyte, in contact with the electrocatalyst; (c) a counter electrode, in ion-conductive contact with the electrocatalyst; (d) a magnet, for providing a magnetic field of at least 400 Gauss to the electrocatalyst; and (e) a power source, electronically connected to the electrocatalyst and the counter electrode.

In a fourth aspect, the present invention includes a flow reactor for electrocatalytic reduction, comprising (a) and electrocatalyst, containing neodymium, (b) an aqueous electrolyte, in contact with the electrocatalyst, (c) a counter electrode, in ion-conductive contact with the electrocatalyst, (d) a magnet, for providing a magnetic field of at least 400 gauss to the electrocatalyst, and (e) a power source, electronically connected to the electrocatalyst and the counter electrode.

In a fifth aspect, the present invention includes a magnetically responsive electrocatalyst for an electrocatalytic reduction reaction, comprising (i) a substrate, (ii) neodymium, on the substrate, and (iii) a non-magnetically responsive electrocatalytic material, on the neodymium.

Definitions

A flow reactor is a system for hosting electrocatalyst, in which both reactants and products are continuously provided to, and removed from, the electrocatalyst. A flow reactor includes pumps and/or fans for flowing liquid and/or gaseous reacts and products, to and away from, the electrocatalyst.

A magnetically responsive electrocatalyst is an electrocatalyst that shows a change in product distribution and/or a change in Faradaic efficiency (FE) when subject to a magnetic field of at least 400 Gauss, as compared to the absence of the magnetic field, during an electrocatalytic reaction.

A non-magnetically responsive electrocatalytic material is an electrocatalyst that does not show a change in product distribution, nor a change in FE, when subject to a magnetic field of at least 400 Gauss, as compared to the absence of the magnetic field, during an electrocatalytic reaction.

The enhancement factor for a product or class of products means the ratio of the FE with magnetic field to FE without a magnetic field, for that product or class of products, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XRD patterns of the PTFE and CuO/Cu/PTFE nanofiber.

FIG. 2A is a low-magnification SEM image of CuO/Cu on PTFE.

FIG. 2B is EDX elemental mapping images of Cu, O and their overlap for CuO/Cu catalyst on PTFE.

FIG. 2C is a schematic of the cross-sectional structure of a CuO/Cu/PTFE nanofiber.

FIG. 2D is a STEM elemental mapping image.

FIG. 2E is STEM images of Cu, O, Au, and their overlap.

FIG. 2F is an HRTEM image of CuO/Cu catalysts.

FIG. 2G is a high-resolution Cu 2p spectra for CuO/Cu on PTFE.

FIG. 2H is a high-resolution O 1s spectra for CuO/Cu on PTFE.

FIG. 2I is an EPR spectra for PTFE and CuO/Cu on PTFE (the dash-dotted line is the fitting curve by EasySpin for CuO/Cu).

FIG. 3A is a graph of FE (Faradaic efficiency) values of C₂₊ products on CuO/Cu with (solid bars) and without (oblique line bars) various magnetic fields of ˜400, 800 and 1200 Gauss at 100 mA cm⁻². The error bars stand for the standard deviation of three independent measurements. The data are presented as mean values±standard deviation.

FIG. 3B is a graph of FE values comparisons of C₂₊ products on pure Cu and CuO/Cu with (solid bars) and without (oblique line bars) the magnetic field of ˜800 Gauss at 100 mA cm⁻². The error bars stand for the standard deviation of three independent measurements. The data are presented as mean values±standard deviation.

FIG. 3C is a graph of FE enhancement factor toward C₂₊ products on CuO/Cu over different magnetic fields of ˜400, 800 and 1200 Gauss at 100 mA cm⁻² and pure Cu with the magnetic field of ˜800 Gauss at 100 mA cm⁻², which is defined as the FE values ratio on CuO/Cu or pure Cu with/without magnetic field. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 4A is a graph of FE values of products on CuO/Cu with (solid bars) and without (oblique line bars) the magnetic field over different current densities. The error bars stand for the standard deviation of three independent measurements. The data are presented as mean values±standard deviation.

FIG. 4B is a graph of FE values comparisons of C₂₊ products on CuO/Cu with/without the magnetic field over different current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 4C is a graph of FE values comparisons of H₂ on CuO/Cu with/without the magnetic field over different current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 4D is a graph of FE values comparisons of ethanol on CuO/Cu with/without the magnetic field over different current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 4E is a graph of FE values comparisons of ethylene on CuO/Cu with/without the magnetic field over different current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 4F is a graph of FE values comparisons of the ratio of FE_ethanol to FE_ethylene (FE_ethanol/FE_ethylene) on CuO/Cu with/without the magnetic field over different current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 4G is a graph of FE_products enhancement factors toward C₂₊ products, H₂, ethanol, ethylene, and ethanol ethylene on CuO/Cu over different current densities, which is defined as the ratio of FE values on CuO/Cu with/without the magnetic field. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 5A is a graph of EE toward C₂₊ on CuO/Cu with/without the magnetic field over different applied current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 5B is a graph of SPCE toward C₂₊ on CuO/Cu with/without the magnetic field over different applied current densities. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 5C is a comparison of j_C2+, FE_C2+, EE_C2+, and SPCE_C2+ on CuO/Cu with/without the magnetic field at 400 mA cm⁻¹. The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 6A is a graph of partial current density values toward ethanol on CuO/Cu with/without the magnetic field of ˜800 Gauss over applied current densities from 100 to 400 mA/cm². The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 6B is a graph of partial current density values toward ethylene on CuO/Cu with/without the magnetic field of ˜800 Gauss over applied current densities from 100 to 400 mA/cm². The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 6C is a graph of partial current density values toward C₂₊ on CuO/Cu with/without the magnetic field of ˜800 Gauss over applied current densities from 100 to 400 mA/cm². The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 7 is a graph of EE factor comparisons toward to ethanol of the CuO/Cu catalyst with/without the magnetic field of ˜800 Gauss over different applied current densities from 100 to 400 mA/cm². The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 8 is a graph of SPCE factor comparisons to ethanol of the CuO/Cu catalyst with/without the magnetic field of ˜800 Gauss over different applied current densities from 100 to 400 mA/cm². The data stands for the mean value of three independent measurements. The data are presented as mean values.

FIG. 9 is a graph of FE values of products produced using a catalyst of 10 nm C₆₀ coated on 300 nm Cu catalysts on PTFE. The cathode is in 1M KOH.

FIG. 10 is a graph of FE values of products produced using a catalyst prepared by applying 400 nm Cu followed by coating 20 nm Nd then 50 nm Cu catalysts on PTFE. The cathode is in 1M KOH.

FIG. 11 is a schematic showing a flow reactor. Not included in the illustration are the pumps and/or fans used to flow the gaseous and liquid reactants, as well as the power source. The flow reactor, as illustrated, include NdFeB magnets for providing a magnetic field.

FIG. 12 is an illustration of a flow reactor.

DETAILED DESCRIPTION

By considering the wave nature of electrons, the electron transfer from catalysts to receptors (e.g., CO₂, H⁺ and intermediates) should exhibit dependence on the orbital and spin symmetry matching between the conduction electrons on catalysts and the lowest unoccupied molecular orbitals (LUMO) of their receptors. Thus, tuning such symmetry-dependent interactions between reactive radicals by magnetic field may eventually control the orientation of radical-radical coupling in CO₂RR preferentially towards C₂₊. Using a combination of a magnetic field and a magnetically responsive electrocatalyst, the electrocatalytic reduction can be enhanced, and/or controlled to produce more of the desired reduction product(s).

The examples below demonstrate that in a flow reactor, a magnetic field of at least 400 gauss may be used to suppress the hydrogen evolution reaction, increase the FE of a desired electrocatalytic reduction product, and/or change the relative amounts of electrocatalytic reduction reaction products. The system uses a magnetically responsive electrocatalyst. If the electrocatalytic material is not natively a magnetically responsive electrocatalyst, it may be made into a magnetically responsive electrocatalyst by applying it to a layer of paramagnetic or ferromagnetic material such as Nd, or by chemical modification of the electrocatalytic material to be paramagnetic or ferromagnetic.

Preferably, the magnetic field at the electrocatalyst is at least 100, at least 200, at least 400, at least 800, or at least 1200 gauss, for example 100-1200 gauss. The magnetic field may be produced using a permanent magnet, such NdFeB magnet, or may be produced using an electromagnet.

Preferably, the hydrogen evolution reaction (HER) is suppressed by the magnetic field in favor of CO₂RR. Preferably the FE of the HER (FE_H2) is decreased in the presence of the magnetic field, as compared to the FE_H2 without a magnetic field, by at least 8%, or by at least 27%, or by at least 27.8%, for example by 8.1 to 27.8%. Preferably, the enhancement factor for H₂ is at most 0.64-fold, or at most 0.24-fold, for example 0.64 to 0.24-fold.

In a CO₂RR, in which ethanol is produced, preferably the FE_ethanol is at least 22%, or at least 35%, or at least 35.8%, for example 26.1% to 35.8%, in the presence of the magnetic field. The enhancement factor for ethanol is preferably at least 1.63-fold, or at least 1.95-fold, for example 1.63 to 1.95-fold.

In a CO₂RR, in which ethanol is produced, preferably the enhancement factor for C₂₊ products in at least 1.28-fold, or at least 1.36-fold, for example 1.28 to 1.36-fold. Preferably, the FE_C2+ is at least 50.1%, at least 59.7%, or at least 60.9%, for example 50.1 to 60.9%, in the presence of a magnetic field.

EXAMPLES

Example 1: Spin Polarized Electrocatalytic CO₂ Reduction on CuO/Cu Paramagnetic Surface for Enhanced C—C Coupling

In this Example, we impart electrocatalysts with a net spin as a gripper for a magnetic field to modulate the spin exchange interaction between electrocatalysts and the radicals in CO₂RR, so as to alter the reaction pathways. We demonstrate the magnetic field effect (MFE) in promoting electrochemical CO₂RR towards C₂₊ organics, particularly towards those containing C—C σ-bond, e.g., ethanol catalyzed at a paramagnetic CuO/Cu interface. Bulk copper metal is diamagnetic because the unpaired electrons (4s¹) merge to form a sea of delocalized (itinerant) free conducting electrons (metallic bond, purely s-wave) throughout the entire metal, losing the unpaired nature. All the ten electrons in 3d¹⁰ are paired and localized, and do not contribute to conduction. In contrast, CuO is paramagnetic ascribed to the [Ar]3d⁹4s⁰ electron configuration of the Cu²⁺ in CuO, thus creating a localized spin in d orbital. CuO is a p-type semiconductor with its conduction originated from the electrons hopping through the Cu—O bonds.⁹ The resulting 4s-2p hybrid wave contains both gerade 4s wave of Cu and ungerade 2p wave of O, implying good overlapping, in terms of orbital symmetry with the LUMO (b2u* and/or b3u*) of a CO₂ molecule that contains both s and p components. When polarized by an external magnetic field, the magnetic moment of the localized d spins in Cu²⁺ are aligned preferentially along the field, which then partially polarize the otherwise randomized spins (if in absence of magnetic field) of the conducting 4s-2p electrons of CuO via sp-d exchange interaction. The injection of such spin-polarized conducting electrons to receptors results in spin polarized C1 radicals. Under magnetic field, besides the spin of the unpaired electron in C1 radical being in parallel alignment with the magnetic field, so is the axis of the p orbital in which this unpaired electron is accommodated. It is the magnetic field that aligns the reactive (i.e., containing one electron) p-orbital on these C1 radicals along the same direction, hence greatly enhances the effective collision of these C1 radicals for C—C coupling, forming a σ-bond. While not wishing to be limited by the theory, we show that magnetic field preferentially promotes the C—C coupling towards ethanol in which there is only one C—C σ-bond. In comparison, however, the formation of C═C coupling involves an additional π bond that is orthogonal to the C—C σ-bond, while only one of them can benefit from the alignment via the magnetic field. As such, we observed that CO₂RR towards ethylene is less responsive to magnetic field.

Synthesis and Characterization of CuO/Cu

We sought to construct CuO/Cu catalysts via evaporation deposition of a nanoparticulate layer of Cu on the surface of PTFE nanofibers, followed by an air-plasma treatment (FIGS. 2A, 2B and 2C) to form CuO layer. Energy-dispersive spectroscopy (EDS) elemental mapping images demonstrated that both Cu and O were uniformly distributed on the surface of the PTFE nanofibers (FIG. 2B). FIG. 2C is the illustration of the CuO/Cu structure on PTEF nanofibers. For conducting the scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) analyses, an external Au layer (ca. 20 nm) was sputtered on the surface of the CuO layer. As shown in FIG. 2D, a nanoparticulate CuO/Cu layer was observed between the Cu layer and the Au protection layer. The energy-dispersive spectroscopy (EDS) elemental mapping images (FIG. 2E) further confirms the presence of an oxygen-rich zone between Cu and Au, as shown in the overlap image of FIG. 2E. High-resolution transmission electron microscopy (HRTEM) (FIG. 2F) showed the lattice fringe of Cu with the lattice parameter of 0.21 nm matching well with the d-spacing of the (111) crystal plane of Cu. An obvious CuO/Cu layer comprising Cu, disordered CuO nanoparticles encircled by yellow circular ring, and a 1˜2 nm disordered CuO layer adjacent to Au layer was observed between Cu layer and Au layer.

Powder X-ray diffraction (XRD) pattern (FIG. 1) showed the presence of Cu, suggesting the bulk phase of the catalyst is metallic copper. Surprisingly, no crystalline CuO peak was observed, which is likely either due to the insufficient amount of CuO for XRD detection,¹⁰ or the dominant amorphous structure of the CuO layer as seen in TEM study. The oxidation state of CuO/Cu layer was determined by high-resolution X-ray photoelectron spectroscopy (XPS) Cu 2p and O 1s spectra (FIG. 2G and FIG. 2H). The XPS fine spectrum of Cu 2p (FIG. 2G) of CuO/Cu depicts Cu 2p_3/2 (˜933.6 eV) and Cu 2p_1/2 (˜953.6 eV) with a gap difference of ˜20 eV, which demonstrates the formation of CuO.^{11, 12} The peaks of the fitted curve at 932.7 eV (Cu 2 p_3/2) and 952.6 eV (Cu 2p_1/2) can be assigned to Cu (0) state, and the peaks at 934.3 eV (Cu 2p_3/2) and 954.4 eV (Cu 2p/2) are due to Cu (+2) state.^{10, 13-15} Two shake-up satellite peaks are observed at around 941.3, 943.7 eV and 962.1 eV, unique to CuO characteristic electronic structure, which reveals partially filled d-block (3d⁹) of Cu²⁺ ions.¹⁶ The O 1s spectrum of CuO/Cu in FIG. 2H is deconvoluted into three peaks, where the peaks at the binding energy of ˜529.7, 531.3, and 532.1 eV are attributed to the lattice oxygen (O_lattice), oxygen vacancy (O_vacancy) and the surface adsorbed moisture (O_absorbed), respectively.¹⁷ The paramagnetic feature of CuO/Cu was confirmed by electron paramagnetic resonance (EPR) spectroscopy. The observed resonance signal around 3293.596 gauss (g=2.0347) (FIG. 2I) and the fitted spectrum (dash-dotted line, fitted by Easyspin) is attributed to the paramagnetic Cu²⁺ ion arising from the electron configuration of 3d⁹ of CuO.^18-20 The resonance signal around 3340.470 gauss (g=2.006) and the fitted spectrum (dash-dotted line, fitted by Easyspin) can be assigned to the O²⁻ ions.^{21, 22} Compared with the results of CuO/Cu electrode, the backbone of PTFE (FIG. 2I) showed no paramagnetic signals.

We conducted the CO₂RR tests on the CuO/Cu electrode in a flow cell electrolyzer using 1M KOH as the electrolyte, a cell configuration similar to that implemented in a reported work,²³ except that a pair of permanent SmCo magnets are used to provide the magnetic field normal to the electrode surface. As shown in FIG. 3A, the FE (defined in Eq. 1 and Eq. 2 of Methods) toward C₂₊ production (FE_C2+) on CuO/Cu rises with the increased magnetic fields from 50.1% at ˜400 Gauss to 59.7% at ˜800 Gauss, and to 60.9% at ˜1200 Gauss. For comparison on the magnetic nature of the catalytic surface, we further conducted the CO₂RR tests using pure thus diamagnetic Cu electrodes with/without an external magnetic field of ˜800 Gauss at 100 mA/cm². As shown in FIG. 3B, the pure non-paramagnetic Cu electrodes demonstrated an FE_C2+ of 40.0% in the absence of magnetic field that is very close to the FE_C2+ of 40.4% under ˜800 Gauss magnetic field, all at 100 mA/cm².

In order to quantify the MFE on FE_C2+, we define an enhancement factor as the ratio of FE_C2+ with/without the external magnetic field. FIG. 3C shows that the enhancement factor on CuO/Cu catalyst is 1.11-fold, 1.32-fold, and 1.34-fold at various external magnetic field strengths of ˜400 Gauss, ˜800 Gauss, and ˜1200 Gauss, respectively. However, the FE_C2+ enhancement factor value of pure Cu electrodes is only 1.01-fold, indicating the absence of MFE on this diamagnetic surface. This comparison suggests that a spin polarized paramagnetic surface is relevant to the promoted C—C bond coupling, and the detailed mechanistic study is further conducted. In the following study, we lock the magnetic field strength at ˜800 Gauss as this value already represents the nearly same promotional effect on FE as that of ˜1200 Gauss, as well as for safely handling the strong permanent magnets.

To gain mechanistic insight, we further investigated the MFE on CO₂RR by varying the current density of CO₂RR at 100, 200, 300 to 400 mA/cm² while keeping the magnetic field strength at ˜800 Gauss or none for comparison. FIG. 4A shows the total FE values on the CuO/Cu. Explicitly, FE_C2+ on the CuO/Cu with the magnetic field of ˜800 Gauss are higher than that in the absence of the external magnetic field under the same applied current densities. To be clear, we plotted the values of FE_C2+ on CuO/Cu with/without the magnetic field of ˜800 Gauss over different current densities in FIG. 4B. The FE_C2+ with the magnetic field of ˜800 Gauss is notably greater than that in the absence of the magnetic field at all applied current density (from 100 to 400 mA/cm²). On the other hand, the FE_C2+ increased with the increased current densities from 100 to 400 mA/cm² in both the absence/presence of the magnetic field. The fact that rising current density within certain range promotes the FE_C2+ agrees with other's reports^{24, 25}. However, compared with the FE_H2 in the absence of an external magnetic field, the FE_H2 under the external magnetic field of ˜800 Gauss is notably suppressed over all measured current densities as shown in FIG. 4C. Specifically, the absolute values of FE_H2 decreased to 27.8%, 14.3%, 7.1% and 8.1% respectively at the current densities of 100, 200, 300 and 400 mA/cm² in the presence of magnetic field versus its absence.

To further evaluate the MFE on product distribution, we analyzed the difference in FE of the two main products, namely ethanol (FIG. 4D) and ethylene (FIG. 4D) with/without the magnetic field of ˜800 Gauss, respectively. As shown in FIG. 4D, with the increase of applied current density, the FE value of ethanol (FE_ethanol) improves as well. Specifically, without magnetic field, the FE_ethanol were 10.9, 13.4, 18.6, and 21.9% respectively at the applied current density of 100, 200, 300 and 400 mA/cm². Remarkably, under the external magnetic field of ˜800 Gauss, the FE_ethanol increased to 17.8, 26.1, 32.9 and 35.8% respectively at the applied current density of 100, 200, 300 and 400 mA/cm². Correspondingly, the partial current density (j, defined in Eq. 3 of Methods) toward ethanol (j_ethanol) on CuO/Cu catalysts also increased by the MFE. FIG. 6A shows that j_ethanol increased from 10.9, 26.8, 55.7, and 87.6 mA/cm² in the absence of magnetic field to 17.8, 52.1, 98.7 and 143.3 mA/cm² in the presence of magnetic field of 800 Gauss at the respective total applied current density of 100, 200, 300 and 400 mA/cm². Obviously, under the same current densities, CuO/Cu catalysts with the magnetic field of ˜800 Gauss deliver a greater FE_ethanol than that in the absence of the magnetic field, suggesting that the external magnetic field facilitates C—C coupling for ethanol.

In contrast, the response of FE of ethylene (FE_ethylene) to magnetic field is much weaker than that of FE_ethanol as shown in FIG. 4E. FIG. 4F clearly depicted a jump in the ratios of FE_ethanol to FE_ethylene (denoted as FE_ethanol/FE_ethylene), indicating the existence of promotional MFE on the selectivity of ethanol over ethylene in CO₂RR within the applied current densities. The MFE on partial current density to ethylene (j_ethanol, FIG. 6B) on CuO/Cu catalysts is relatively weak compared with j_ethanol. FIG. 4G quantified the MFE on FE of the CO₂RR on CuO/Cu at various current densities by the FE enhancement factor defined as the ratio of FE values on CuO/Cu with/without the magnetic field of ˜800 Gauss. The general enhancement factor for C₂₊ ranges between 1.28˜1.36-fold. The specific enhancement factor for ethanol ranges between 1.63˜1.95-fold in the applied current densities, notably greater than that of ethylene (1.05˜1.09-fold). The alternative indictor is the ratio of FE of ethanol to FE of ethylene, which ranges between 1.50˜1.83-fold. The enhancement factor for H₂ is markedly below 1, ranging between 0.24˜0.64-fold, suggesting the impeded hydrogen evolution reaction (HER) by MFE. Thus, it is clear that MFE promotes the production of ethanol over ethylene but suppresses the production of H₂. Accordingly, the MFE on the partial current density to C₂₊ (FIG. 6C) is mainly contributed from the MFE on ethanol.

While not wishing to be limited by the theory, the benefits from the magnetic field-oriented C—C δ bonding and the suppressed H₂ formation by Lorentz force are further embodied by EE (defined in Eq. 4 of Methods), an important indicator to evaluate the CO₂ electroreduction performance.^26-28 Similar to FE, the CuO/Cu demonstrated a promotional MFE on the EE toward ethanol (FIG. 7) and C₂₊ (FIG. 5A) and over a wide current densities from 100 to 400 mA/cm². Excitingly, the EE_C2+ on CuO/Cu catalysts reached 47.5% at 400 mA/cm² in the presence of magnetic field versus 36.8% at 400 mA/cm² in the absence of magnetic field.

To reduce energy demand of CO₂RR product separation, promoting single-pass carbon efficiency (SPCE, defined in Eq. 5 of Methods) of CO₂RR is becoming increasingly important.^29-31 By far, high SPCEs were reported in many acidic systems accounting for the fact that the acidic system can prohibit the carbonate formation and its crossover in bulk electrolytes, achieving high SPCE.^29-31 Though the SPCEs in alkaline systems were relatively low,^{32, 33} strong basic electrolyte using KOH can bring higher selectivity and EE for C₂₊ production.³⁴ Therefore, it is still valuable to assess the MFE on SPCE in this work. Obviously, our CuO/Cu showed a promotional MFE on the SPCE values toward ethanol (SPCE_ethanol, FIG. 8) and C₂₊ products (SPCE_C2+, FIG. 5B) over the applied current densities from 100 to 400 mA/cm². For instance, the CuO/Cu reach to 0.89% of SPCE_C2+ at 400 mA/cm² in the presence of magnetic field of ˜800 Gauss versus the 0.69% of SPCE_C2+ in the absence of magnetic field of ˜800 Gauss, a ˜30% improvement in SPCE.

FIG. 5C visualized these four important indicators (i.e., FE, j, EE, and SPCE) toward C₂₊ production on CuO/Cu catalysts with/without magnetic field of ˜800 Gauss at 400 mA/cm². Clearly, the promotional MFE on FE_C2+, j_C2+, EE_C2+ and SPCE_C2+ on CuO/Cu catalysts is systematically evident. Compared with the recent works, our CuO/Cu catalysts under MFE demonstrated an astonishing FE_C2+ of 86.7% and a EE_C2+ of 47.5% at the applied current density of 400 mA/cm².

Methods

Materials. Copper target was provided by the Kurt J. Lesker company. The PTFE membrane as a gas-diffusion layer was obtained from the same source as reported in literature.³ Cu was evaporated on PTFE membrane using an evaporation system (Auto 306, Edwards) at an evaporation rate of 0.5 Å/Sec at 10⁻⁶ torr. The desired thickness of Cu was 400 nm. The obtained 400 nm Cu/PTFE composite membrane was treated within 30 min in an air-plasma (Harrick Plasma, PDC-32G) to obtain CuO/Cu electrode. The obtained 400 nm Cu/PTFE composite membrane works as pure Cu electrodes. The SmCo block magnets are from MagnetShop.com. Ag/AgCl (3.0 M KCl) electrode was used as the reference electrode. Nickel foam with a thickness of 1.6 mm was used as the counter electrode in a flow cell. A Sustainion anion exchange membrane was purchased from Dioxide Materials. The KOH, dimethyl sulfoxide (DMSO), and phenol were purchased from Sigma-Aldrich. The chemicals were used as received without any further purification.

Characterization. X-ray diffraction patterns were collected on a Bruker D8-A25 powder X-ray diffractometer with Cu Kα irradiation (λ=1.5418 Å) over the angular range from 10° to 80°. The SEM, TEM and STEM for structure characterization were collected on a JEOL IT-800HL scanning electron microscope system, a JEOL-2100F transmission electron microscope system, and a FEI Talos F200X TEM/STEM system, respectively. Samples for the TEM and STEM analyses were placed on sample holders followed by sputter coating of a gold layer. The gold layer works for the protection of CuO layer when the TEM and STEM analyses. The oxidation state of Cu in the sample was measured by an ULVAC-PHI, PHI 5000 VersaProbe II X-ray photoelectron spectroscopy (XPS). The electron paramagnetic resonance (EPR) measurement was performed on a Bruker Elexsys E500 CW-EPR spectrometer.

Electrochemical measurements. Electrochemical measurements were conducted in a 3D printed flow-cell in this work according to the design of previous report²³. A PTFE-based GDE was fixed between the gas and catholyte compartment. The catalyst side of the PTFE-based GDE faces the cathode compartment, while the GDE layer of PTFE faces the gas compartment. An anion-exchange membrane was used to separate the catholyte and anolyte compartment. Silicone gaskets with a 1×1 cm² window were used for sealing. The active area of the PTFE-based GDE is 1×1 cm². Each compartment has an inlet and outlet connection to the gas or flow electrolyte. The catholyte (1M KOH) and anolyte (1M KOH) were circulated through the catholyte (flow rate of 4 mL/min) and anolyte (flow rate of 20 mL/min) compartment by two peristaltic pumps, respectively. Ultra-pure CO₂ gas (99.999%, research grade) was supplied continuously to the gas compartment with a flow rate of 50 mL/min controlled by a mass flow controller. All CO₂RR performance experiments were carried out using the chronopotentiometric method, with the power supplied by a potentiostat (Biologic, SP-150). The electrochemical impedance spectroscopy (EIS) analyses were used to determine the ohmic loss between the working and reference electrodes. All Ag/AgCl potentials after iR compensation (85%) were scaled to values relative to the reversible hydrogen electrode (RHE) using the following equation: E_RHE=E_Ag/AgCl+0.210V+0.0591×PH.

Product analysis. The products collected from the gas outlet went through a simplified cold trap that was used to separate gasified liquid and gas products. The gas-phase products were analyzed using a gas chromatograph (7890B, Agilent) equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD). The FE toward CO₂RR gas product was calculated using the following equation:³⁵

$\begin{array}{cc}{\mathrm{FE}}_x=\frac{n_x\times c_x\times v_{\mathrm{gas}}\times F}{j_{\mathrm{total}}{V}_m}& \left(\mathrm{Eq}.1\right)\end{array}$

where FE_x is the Faraday efficiency of product x, n_x is the number of electrons required for the gas products of CH₄, C₂H₄, C₃H₆ and H₂. C_x is the concentration of product x analyzed by gas chromatograph, v_gas stands for the CO₂ flow rate (50 mL/min), F donates the Faraday' constant (96,485 C/mol), and V_m equals 24.5 L/mol at room temperature, 1 atm.

Liquid products were quantified using a nuclear magnetic resonance (NMR) spectrometer (Ultrashield 500 Plus, Bruker) with dimethyl sulfoxide (DMSO) and phenol as the internal standards. The water suppression method was used. Standard curves for each liquid product (e.g., ethanol, acetate, n-propanol, formate) were prepared by the relative peak area ratio. The relative peak area (e.g., ethanol, formate) can be calculated using the following expression:^{36, 37}

$\mathrm{Relative}\mathrm{peak}\mathrm{area}\mathrm{ratio}\left(\mathrm{ethanol}\right)=\frac{\mathrm{Triplet}\mathrm{peak}\mathrm{area}\mathrm{at}1.1\mathrm{ppm}\left(\mathrm{ethanol}\right)}{\mathrm{Single}\mathrm{peak}\mathrm{area}\mathrm{at}2.6\mathrm{ppm}\left(\mathrm{DMSO}\right)}\mathrm{Relative}\mathrm{peak}\mathrm{area}\mathrm{ratio}\left(\mathrm{formate}\right)=\frac{\mathrm{Single}\mathrm{peak}\mathrm{area}\mathrm{at}8.3\mathrm{ppm}\left(\mathrm{formate}\right)}{\mathrm{Single}\mathrm{peak}\mathrm{area}\mathrm{at}7.2\mathrm{ppm}\left(\mathrm{phenol}\right)}$

The FE for the liquid products were calculated using the following equation:^{23, 37}

$\begin{array}{cc}{\mathrm{FE}}_x=\frac{n_x\times {\eta }_x\times F}{Q}& \left(\mathrm{Eq}.2\right)\end{array}$

where n_x is the number of electrons required for the liquid products of CH₃CH₂OH, CH₃COOH, CH₃CH₂CH₂OH, and HCOOH. η_x is the number of moles of product x, F is the Faraday' constant, and Q is the total charge passed during the CO₂ electrolysis.

The partial current densities (j) of the products were calculated as follows:²⁷

$\begin{array}{cc}{j}_x=\frac{j_{\mathrm{total}}\times {\mathrm{FE}}_x}{A}& \left(\mathrm{Eq}.3\right)\end{array}$

where j_x represents the partial current of product x, j_total represents the total current, FE_x is the Faraday efficiency of product x, A is the geometric area of 1 cm².

The half-cell energy efficiencies (EE) for the products were calculated as follows:^{27, 31, 38}

$\begin{array}{cc}{\mathrm{EE}}_x=\frac{\left(1.23-E_x^{\mathrm{theoretic}}\right)}{\left(1.23-E_x^{\mathrm{applied}}\right)}\times {\mathrm{FE}}_x& \left(\mathrm{Eq}.4\right)\end{array}$

where EE_x stands for the energy efficiency of product x, E_x^theoretic is the theoretic thermodynamic potential vs. RHE for product x, in which E_ethanol^theoretic is 0.09V,³⁹ E_ethylene^theoretic is 0.08V,³⁹ E_n-propanol^theoretic is 0.21V,³⁹ E_propylene^theoretic is 0.13V,⁴⁰ E_acetate^theoretic is ˜0.26V,³⁹ respectively. E_x^applied is the applied potential vs. RHE and FE, is the calculated FE of the product x.

The single pass carbon efficiency (SPCE) for the products were calculated as follows:^29-31

$\begin{array}{cc}{\mathrm{SPCE}}_x=\frac{\left(j_x\times 60s\right)/\left(n_x\times F\right)}{\left(v_{\mathrm{gas}}\times 1\min \right)/V_m}& \left(\mathrm{Eq}.5\right)\end{array}$

where SPCE_x denotes the single pass carbon efficiency of product x, j_x is the partial current of product x, n_x is the number of electrons required for the products, F stands for the Faraday' constant, v_gas is the CO₂ flow rate (50 mL/min), V_m is 24.5 L/mol.

Example 2: Spin Polarized Electrocatalytic CO₂ Reduction on Ferromagnetic C₆₀—Cu Surface for Enhanced C—C Coupling

Preparation of catalysts: 300 nm copper was coated on porous PTFE film via vacuum evaporation, followed by 10 nm C₆₀ coated onto the copper. The C₆₀—Cu interface is reported to be ferromagnetic.⁴¹

Performance of the catalysts: The liquid products via electrochemical reduction of CO₂ using the above catalysts is analyzed by the same methods as described in Example 1. The results show increase of C₂₊ liquid such as ethanol under magnetic field.

Example 3: Spin Polarized Electrocatalytic CO₂ Reduction on Paramagnetic Cu—Nd—Cu Surface for Enhanced C—C Coupling

Preparation of catalysts: 400 nm copper (Cu) was coated on porous PTFE film via vacuum evaporation, followed by 20 nm neodymium (Nd) coated onto the copper layer, followed by additional 50 nm Cu to cover the previous 20 nm Nd layer. The Nd layer is paramagnetic.

Performance of the catalysts: The liquid products via electrochemical reduction of CO₂ using the above catalysts is analyzed by the same methods as described in Example 1. The results show increase of C₂₊ liquid such as ethanol under magnetic field. It is also found that the switching the direction of the magnetic field does not have impact of the product selectivity, rather, it is the presence of the magnetic field that impacts the product selectivity.

REFERENCES

• 1. Gao, D.; Ardn-Ais, R. M.; Jeon, H. S.; Roldan Cuenya, B., Rational catalyst and electrolyte design for CO₂ electroreduction towards multicarbon products. Nature Catalysis 2019, 2 (3), 198-210.
• 2. Zhang, X.; Li, J.; Li, Y.-Y.; Jung, Y.; Kuang, Y.; Zhu, G.; Liang, Y.; Dai, H., Selective and High Current CO₂ Electro-Reduction to Multicarbon Products in Near-Neutral KCl Electrolytes. Journal of the American Chemical Society 2021, 143 (8), 3245-3255.
• 3. Zhao, Y.; Hao, L.; Ozden, A.; Liu, S.; Miao, R. K.; Ou, P.; Alkayyali, T.; Zhang, S.; Ning, J.; Liang, Y.; Xu, Y.; Fan, M.; Chen, Y.; Huang, J. E.; Xie, K.; Zhang, J.; O'Brien, C. P.; Li, F.; Sargent, E. H.; Sinton, D., Conversion of CO₂ to multicarbon products in strong acid by controlling the catalyst microenvironment. Nature Synthesis 2023, 2 (5), 403-412.
• 4. Staub, U.; Tanaka, Y.; Katsumata, K.; Kikkawa, A.; Kuramoto, Y.; Onuki, Y., Influence of stress and magnetic field on the orbital orientations in CeB6. Journal of Physics: Condensed Matter 2006, 18 (48), 11007.
• 5. Xu, J.; Wu, F.; Bao, J.-K.; Han, F.; Xiao, Z.-L.; Martin, I.; Lyu, Y.-Y.; Wang, Y.-L.; Chung, D. Y.; Li, M.; Zhang, W.; Pearson, J. E.; Jiang, J. S.; Kanatzidis, M. G.; Kwok, W.-K., Orbital-flop Induced Magnetoresistance Anisotropy in Rare Earth Monopnictide CeSb. Nature Communications 2019, 10 (1), 2875.
• 6. Pan, H.; Jiang, X.; Wang, X.; Wang, Q.; Wang, M.; Shen, Y., Effective Magnetic Field Regulation of the Radical Pair Spin States in Electrocatalytic CO₂ Reduction. The Journal of Physical Chemistry Letters 2020, 11(1), 48-53.
• 7. Hao, J.; Xie, S.; Huang, Q.; Ding, Z.; Sheng, H.; Zhang, C.; Yao, J., Spin-Enhanced C– C Coupling in CO₂ Electroreduction with Oxide-Derived Copper. CCS Chemistry 0 (0), 1-13.
• 8. Lin, C.-C.; Liu, T.-R.; Lin, S.-R.; Boopathi, K. M.; Chiang, C.-H.; Tzeng, W.-Y.; Chien, W.-H. C.; Hsu, H.-S.; Luo, C.-W.; Tsai, H.-Y.; Chen, H.-A.; Kuo, P.-C.; Shiue, J.; Chiou, J.-W.; Pong, W.-F.; Chen, C.-C.; Chen, C.-W., Spin-Polarized Photocatalytic CO2 Reduction of Mn-Doped Perovskite Nanoplates. Journal of the American Chemical Society 2022, 144 (34), 15718-15726.
• 9. Lee, W.-J.; Wang, X.-J., Structural, Optical, and Electrical Properties of Copper Oxide Films Grown by the SILAR Method with Post-Annealing. Coatings 2021, 11 (7), 864.
• 10. Xia, Y.; Zhang, Q.; Guo, F.; Wang, J.; Li, W.; Xu, J., Ag@Cu with Cu—CuO interface prepared by air cold-plasma promoting the electrocatalytic reduction of CO2 to low-carbon alcohols. Vacuum 2022, 196, 110767.
• 11. Selvanathan, V.; Aminuzzaman, M.; Tey, L.-H.; Razali, S. A.; Althubeiti, K.; Alkhammash, H. I.; Guha, S. K.; Ogawa, S.; Watanabe, A.; Shahiduzzaman, M.; Akhtaruzzaman, M., Muntingia calabura Leaves Mediated Green Synthesis of CuO Nanorods: Exploiting Phytochemicals for Unique Morphology. Materials 2021, 14 (21), 6379.
• 12. Sudha, V.; Murugadoss, G.; Thangamuthu, R., Structural and morphological tuning of Cu-based metal oxide nanoparticles by a facile chemical method and highly electrochemical sensing of sulphite. Scientific Reports 2021, 11(1), 3413.
• 13. Hui, L. S.; Whiteway, E.; Hilke, M.; Turak, A., Synergistic oxidation of CVD graphene on Cu by oxygen plasma etching. Carbon 2017, 125, 500-508.
• 14. Chusuei, C. C.; Brookshier, M. A.; Goodman, D. W., Correlation of Relative X-ray Photoelectron Spectroscopy Shake-up Intensity with CuO Particle Size. Langmuir 1999, 15 (8), 2806-2808.
• 15. Song, Y.; Cho, D.; Venkateswarlu, S.; Yoon, M., Systematic study on preparation of copper nanoparticle embedded porous carbon by carbonization of metal-organic framework for enzymatic glucose sensor. RSC Advances 2017, 7 (17), 10592-10600.
• 16. Singh, B. P.; Chaudhary, M.; Kumar, A.; Singh, A. K.; Gautam, Y. K.; Rani, S.; Walia, R., Effect of Co and Mn doping on the morphological, optical and magnetic properties of CuO nanostructures. Solid State Sciences 2020, 106, 106296.
• 17. Rajendran, K.; Yadav, J.; Khan, T. S.; Haider, M. A.; Gupta, S.; Jagadeesan, D., Oxygen Vacancy-Mediated Reactivity: The Curious Case of Reduction of Nitroquinoline to Aminoquinoline by CuO. The Journal of Physical Chemistry C 2023, 127 (18), 8576-8584.
• 18. Sekhar, H.; Narayana Rao, D., Preparation, characterization and nonlinear absorption studies of cuprous oxide nanoclusters, micro-cubes and micro-particles. Journal of Nanoparticle Research 2012, 14 (7), 976.
• 19. Lin, K.-S.; Wang, H. P., Byproduct Shape Selectivity in Supercritical Water Oxidation of 2-Chlorophenol Effected by CuO/ZSM-5. Langmuir 2000, 16 (6), 2627-2631.
• 20. Maurelli, S.; Ruszak, M.; Witkowski, S.; Pietrzyk, P.; Chiesa, M.; Sojka, Z., Spectroscopic CW-EPR and HYSCORE investigations of Cu2+ and O2− species in copper doped nanoporous calcium aluminate (12CaO·7Al2O3). Physical Chemistry Chemical Physics 2010, 12 (36), 10933-10941.
• 21. Che, M.; Tench, A. J., Characterization and Reactivity of Molecular Oxygen Species on Oxide Surfaces. In Advances in Catalysis, Eley, D. D.; Pines, H.; Weisz, P. B., Eds. Academic Press: 1983; Vol. 32, pp 1-148.
• 22. Sojka, Z., Molecular Aspects of Catalytic Reactivity. Application of EPR Spectroscopy to Studies of the Mechanism of Heterogeneous Catalytic Reactions. Catalysis Reviews 1995, 37 (3), 461-512.
• 23. Nguyen, T. N.; Chen, Z.; Zeraati, A. S.; Shiran, H. S.; Sadaf, S. M.; Kibria, M. G.; Sargent, E. H.; Dinh, C.-T., Catalyst Regeneration via Chemical Oxidation Enables Long-Term Electrochemical Carbon Dioxide Reduction. Journal of the American Chemical Society 2022, 144 (29), 13254-13265.
• 24. Wang, X.; Wang, Z.; Garcia de Arquer, F. P.; Dinh, C.-T.; Ozden, A.; Li, Y. C.; Nam, D.-H.; Li, J.; Liu, Y.-S.; Wicks, J.; Chen, Z.; Chi, M.; Chen, B.; Wang, Y.; Tam, J.; Howe, J. Y.; Proppe, A.; Todorovid, P.; Li, F.; Zhuang, T.-T.; Gabardo, C. M.; Kirmani, A. R.; McCallum, C.; Hung, S.-F.; Lum, Y.; Luo, M.; Min, Y.; Xu, A.; O'Brien, C. P.; Stephen, B.; Sun, B.; Ip, A. H.; Richter, L. J.; Kelley, S. O.; Sinton, D.; Sargent, E. H., Efficient electrically powered CO₂-to-ethanol via suppression of deoxygenation. Nature Energy 2020, 5 (6), 478-486.
• 25. Xie, Y.; Ou, P.; Wang, X.; Xu, Z.; Li, Y. C.; Wang, Z.; Huang, J. E.; Wicks, J.; McCallum, C.; Wang, N.; Wang, Y.; Chen, T.; Lo, B. T. W.; Sinton, D.; Yu, J. C.; Wang, Y.; Sargent, E. H., High carbon utilization in CO₂ reduction to multi-carbon products in acidic media. Nature Catalysis 2022, 5 (6), 564-570.
• 26. Zhong, M.; Tran, K.; Min, Y.; Wang, C.; Wang, Z.; Dinh, C.-T.; De Luna, P.; Yu, Z.; Rasouli, A. S.; Brodersen, P.; Sun, S.; Voznyy, O.; Tan, C.-S.; Askerka, M.; Che, F.; Liu, M.; Seifitokaldani, A.; Pang, Y.; Lo, S.-C.; Ip, A.; Ulissi, Z.; Sargent, E. H., Accelerated discovery of CO₂ electrocatalysts using active machine learning. Nature 2020, 581 (7807), 178-183.
• 27. Peng, C.; Yang, S.; Luo, G.; Yan, S.; Shakouri, M.; Zhang, J.; Chen, Y.; Li, W.; Wang, Z.; Sham, T.-K.; Zheng, G., Surface Co-Modification of Halide Anions and Potassium Cations Promotes High-Rate CO₂-to-Ethanol Electrosynthesis. Advanced Materials 2022, 34 (39), 2204476.
• 28. Wen, G.; Ren, B.; Park, M. G.; Yang, J.; Dou, H.; Zhang, Z.; Deng, Y.-P.; Bai, Z.; Yang, L.; Gostick, J.; Botton, G. A.; Hu, Y.; Chen, Z., Ternary Sn—Ti—O Electrocatalyst Boosts the Stability and Energy Efficiency of CO₂ Reduction. Angewandte Chemie International Edition 2020, 59 (31), 12860-12867.
• 29. Huang, J. E.; Li, F.; Ozden, A.; Sedighian Rasouli, A.; Garcia de Arquer, F. P.; Liu, S.; Zhang, S.; Luo, M.; Wang, X.; Lum, Y.; Xu, Y.; Bertens, K.; Miao, R. K.; Dinh, C.-T.; Sinton, D.; Sargent, E. H., CO₂ electrolysis to multicarbon products in strong acid. Science 2021, 372 (6546), 1074-1078.
• 30. Zhao, Y.; Hao, L.; Ozden, A.; Liu, S.; Miao, R. K.; Ou, P.; Alkayyali, T.; Zhang, S.; Ning, J.; Liang, Y.; Xu, Y.; Fan, M.; Chen, Y.; Huang, J. E.; Xie, K.; Zhang, J.; O'Brien, C. P.; Li, F.; Sargent, E. H.; Sinton, D., Conversion of CO₂ to multicarbon products in strong acid by controlling the catalyst microenvironment. Nature Synthesis 2023.
• 31. Li, L.; Liu, Z.; Yu, X.; Zhong, M., Achieving High Single-Pass Carbon Conversion Efficiencies in Durable CO₂ Electroreduction in Strong Acids via Electrode Structure Engineering. Angewandte Chemie 2023.
• 32. Garcia de Arquer, F. P.; Dinh, C.-T.; Ozden, A.; Wicks, J.; McCallum, C.; Kirmani, A. R.; Nam, D.-H.; Gabardo, C.; Seifitokaldani, A.; Wang, X.; Li, Y. C.; Li, F.; Edwards, J.; Richter, L. J.; Thorpe, S. J.; Sinton, D.; Sargent, E. H., CO₂ electrolysis to multicarbon products at activities greater than 1 A cm^{− 2}. Science 2020, 367 (6478), 661-666.
• 33. Dinh, C.-T.; Burdyny, T.; Kibria, M. G.; Seifitokaldani, A.; Gabardo, C. M.; Garcia de Arquer, F. P.; Kiani, A.; Edwards, J. P.; De Luna, P.; Bushuyev, O. S.; Zou, C.; Quintero-Bermudez, R.; Pang, Y.; Sinton, D.; Sargent, E. H., CO₂ electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface. Science 2018, 360 (6390), 783-787.
• 34. Nitopi, S.; Bertheussen, E.; Scott, S. B.; Liu, X.; Engstfeld, A. K.; Horch, S.; Seger, B.; Stephens, I. E. L.; Chan, K.; Hahn, C.; Nerskov, J. K.; Jaramillo, T. F.; Chorkendorff, I., Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chemical Reviews 2019, 119 (12), 7610-7672.
• 35. Wang, Y.; Wang, Z.; Dinh, C.-T.; Li, J.; Ozden, A.; Golam Kibria, M.; Seifitokaldani, A.; Tan, C.-S.; Gabardo, C. M.; Luo, M.; Zhou, H.; Li, F.; Lum, Y.; McCallum, C.; Xu, Y.; Liu, M.; Proppe, A.; Johnston, A.; Todorovic, P.; Zhuang, T.-T.; Sinton, D.; Kelley, S. O.; Sargent, E. H., Catalyst synthesis under CO₂ electroreduction favours faceting and promotes renewable fuels electrosynthesis. Nature Catalysis 2020, 3 (2), 98-106.
• 36. Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S., Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper(I) Oxide Catalysts. ACS Catalysis 2015, 5 (5), 2814-2821.
• 37. Xu, H.; Rebollar, D.; He, H.; Chong, L.; Liu, Y.; Liu, C.; Sun, C.-J.; Li, T.; Muntean, J. V.; Winans, R. E.; Liu, D.-J.; Xu, T., Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper. Nature Energy 2020, 5 (8), 623-632.
• 38. Wang, Z.; Li, Y.; Zhao, X.; Chen, S.; Nian, Q.; Luo, X.; Fan, J.; Ruan, D.; Xiong, B.-Q.; Ren, X., Localized Alkaline Environment via In Situ Electrostatic Confinement for Enhanced CO₂-to-Ethylene Conversion in Neutral Medium. Journal of the American Chemical Society 2023, 145 (11), 6339-6348.
• 39. Kuhl, K. P.; Cave, E. R.; Abram, D. N.; Jaramillo, T. F., New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy & Environmental Science 2012, 5 (5), 7050-7059.
• 40. Gao, J.; Bahmanpour, A.; Kröcher, O.; Zakeeruddin, S. M.; Ren, D.; Grätzel, M., Electrochemical synthesis of propylene from carbon dioxide on copper nanocrystals. Nature Chemistry 2023.
• 41. MaMari, F., Moorsom, T., Teobaldi, G. et al. Beating the Stoner criterion using molecular interfaces. Nature 524, 69-73 (2015). doi.org/10.1038/nature14621.

Claims

1. A method of producing ethanol by electrocatalytic reduction of carbon dioxide, comprising:

reducing carbon dioxide in an aqueous electrolyte on an electrocatalyst with electricity,

wherein the electrocatalyst is exposed to a magnetic field of at least 400 gauss,

the electrocatalyst comprises at least one paramagnetic and/or ferromagnetic material, and

an amount of ethanol produced by the reducing is greater than an amount of ethanol produced without the magnetic field.

2. The method of claim 1, wherein the electrocatalyst comprises copper.

3. The method of claim 2, wherein the electrocatalyst further comprises copper oxide, C60 and/or neodymium.

4. The method of claim 1, wherein the magnetic field is at least 800 gauss.

5. The method of claim 1, wherein the magnetic field is at least 1200 gauss.

6. The method of claim 1, wherein the magnetic field is produced using an electromagnet.

7. The method of claim 1, wherein the FE of the hydrogen evolution reaction (HER), FEH2, is decreased by at least 8%, as compared to FEH2 without a magnetic field.

8. The method of claim 1, wherein the FE of the hydrogen evolution reaction (HER), FEH2, is decreased by at least 27%, as compared to FEH2 without a magnetic field.

9. The method of claim 1, wherein the FE of ethanol, FEethanol, is at least 22%.

10. The method of claim 1, wherein the FE of ethanol, FEethanol, is at least 35%.

11. The method of claim 1, wherein the enhancement factor for ethanol is at least 1.63-fold.

12. The method of claim 1, wherein the enhancement factor for ethanol is at least 1.95-fold.

13. The method of claim 1, wherein the enhancement factor for C2+ products is at least 1.28-fold.

14. The method of claim 1, wherein the enhancement factor for C2+ products is at least 1.36-fold.

15. A method of reducing carbon dioxide electrocatalytically in a flow reactor, comprising:

reducing carbon dioxide in an aqueous electrolyte on an electrocatalyst with electricity,

wherein the electrocatalyst is exposed to a magnetic field of at least 400 gauss,

the electrocatalyst comprises (i) copper and (ii) copper oxide, C60 and/or neodymium, and

the faradaic efficiency (FE) is greater than the faradaic efficiency (FE) without the magnetic field.

16. The method of claim 15, wherein the magnetic field is at least 800 gauss.

17. The method of claim 15, wherein the magnetic field is at least 1200 gauss.

18-26. (canceled)

27. A flow reactor for electrocatalytic reduction of carbon dioxide, comprising:

(a) and electrocatalyst, containing (i) copper and (ii) copper oxide, C60 and/or neodymium,

(b) an aqueous electrolyte, in contact with the electrocatalyst,

(c) a counter electrode, in ion-conductive contact with the electrocatalyst,

(d) a magnet, for providing a magnetic field of at least 400 gauss to the electrocatalyst, and

(e) a power source, electronically connected to the electrocatalyst and the counter electrode.

28. A flow reactor for electrocatalytic reduction, comprising:

(a) and electrocatalyst, containing neodymium,

(b) an aqueous electrolyte, in contact with the electrocatalyst,

(c) a counter electrode, in ion-conductive contact with the electrocatalyst,

(d) a magnet, for providing a magnetic field of at least 400 gauss to the electrocatalyst, and

(e) a power source, electronically connected to the electrocatalyst and the counter electrode.

29. A magnetically responsive electrocatalyst for an electrocatalytic reduction reaction, comprising:

(i) a substrate,

(ii) neodymium, on the substrate, and

(iii) a non-magnetically responsive electrocatalytic material, on the neodymium.