AgCu Single-Atom Alloy Catalyst for Electrocatalytic CO2 Reduction

Description

CROSS REFERENCE TO PRIOR APPLICATIONS

The present application claims priority to U.S. Application No. 63/473,924, filed on Jul. 8, 2022, the entire contents of which are incorporated herein as if set forth in its entirety.

TECHNICAL FIELD

The present description relates to electrocatalytic CO₂ reduction into multicarbon products, in particular to a catalyst for use in a catalysis for producing multicarbon products from CO₂. More particularly, the present description relates to an AgCu single-atom nanoparticle (AgCu SANP) catalyst.

BACKGROUND

Electrocatalytic CO₂ reduction into valuable chemicals utilizing renewable electricity provides a sustainable route for CO₂ recycling and utilization, thus playing a critical role in realizing a carbon-neutral cycle. Electrocatalytic CO₂ reduction reaction (CO₂RR) has emerged as a strategy to enable efficient reduction of carbon emission while storing renewal electricity into chemical bonds in fuels or other chemicals. The design of a suitable catalyst for CO₂RR generally focuses on the catalyst's effect on the activity and selectivity of the reaction, for example, a high selectivity of CO₂ reduction products, lower overpotentials, high energy efficiencies, good stability, and/or low fabrication cost.

In the past decades, progress was made in the generation of single-carbon (C1) products (for example, carbon monoxide and formic acid) using electrocatalytic CO₂ reduction reactions (CO₂RR). However, the low value of C1 products severely limits the application potential of the electrocatalytic CO₂RR technology. Thus, it is desirable to produce multicarbon products by employing CO₂RR (Zhong, M., et al. Nature 581, 178-183 (2020)).

Hori et. al. first reported preparation of multicarbon products, including C₂H₄, C₂H₅OH, CH₃COOH, n-C₃H₇OH, at a copper (Cu) electrode (J. Chem. Soc., Faraday Trans. 1, 1989, 85, 2309-2326). In 1989, Cu was demonstrated to be a metal that could effectively catalyze CO₂ into multicarbon products. However, the C—C coupling kinetics over pure Cu surface were sluggish, thus severely hindering industrial-level productions of multicarbon products. Various catalyst design strategies have been developed to improve the multicarbon product performance of Cu-based catalysts, for instance, alloying/doping, surface modification, interface engineering, etc.

Peter et al. proposed a cascade catalysis strategy to improve the production of multicarbon products with an Ag@Cu core-shell structure catalyst, where the CO₂ can be reduced into CO on the Ag core and then transferred to the Cu shell for further reduction into multicarbon products (J. Am. Chem. Soc. 2019, 141, 36, 14093-14097).

Based on a similar tandem catalysis mechanism, Chen et al. reported an improvement on C₂₊ partial current over a Cu catalyst from 37 to 160 mA cm⁻² by adding Ag nanoparticles to the catalyst, suggesting the effectiveness of cascade catalysis under industrial current densities (Joule 4, 1688-1699 (2020)).

Zhang et al. applied a cascade catalysis mechanism to a gas diffusion electrode (GDE) design. The authors prepared elaborate segmented tandem electrodes, in which a CO-selective catalyst layer (CL) segment at the inlet prolonged CO residence time in the subsequent C₂₊ selective segment, resulting in 90% C₂₊ FE over Cu/Fe—N—C catalysts (Nat. Catal. 5, 202-211 (2022)).

Accordingly, it is possible to apply a cascade CO₂RR mechanism for C₂₊ production, which would involve an integration of two consecutive steps of CO₂-to-CO and CO-to-C₂₊ on two catalytic active sites. However, the C—C coupling kinetics are usually dominated by two factors, which are surface coverage of locally adsorbed carbon monoxide (*CO) and adsorption energy of *CO on the surface of a catalyst. Almost all of the reported catalyst designs in cascade CO₂RR systems focused on only improving the surface coverage of locally adsorbed *CO by enhancing a local CO concentration but ignoring the adsorption energy of *CO on a metal surface of the catalyst, for example, a Cu surface.

There is a need for a novel catalyst in a cascade CO₂RR catalysis for the production of multicarbon products. It is desirable such catalyst can improve the adsorption energy of *CO on active sites of a metal surface of the catalyst while maintaining the surface coverage of adsorbed *CO.

SUMMARY

In one aspect, the present description provides a novel AgCu SANP catalyst for producing multicarbon products.

In one aspect, there is provided a catalyst for producing a multicarbon product from CO₂, comprising a copper (Cu) substrate having at least one silver copper (AgCu) single-atom alloy (SAA), and silver (Ag) nanoparticles (NPs) on the Cu substrate or on the AgCu SAA, wherein the AgCu SAA comprises at least one single Ag atom dispersed into a surface of the Cu substrate, and the Ag nanoparticles comprise Ag-Ag bonds between the Ag nanoparticles. In some aspects, the ratio of the AgCu SAA to the Ag NPs in the catalyst is about 1:7.

In one aspect, the Cu substrate comprises Cu nanoparticles.

In another aspect, the Cu substrate is polycrystalline.

In yet another aspect, the catalyst exhibits at least about 94% Faradaic Efficiency (FE) towards the multicarbon product under about 720 mA cm⁻².

In yet another aspect, the multicarbon product comprises C2-C6 products or any mixtures thereof. In some aspects, the multicarbon product comprises ethanol, ethylene, acetic acid, n-propanol or any mixtures thereof.

BRIEF DESCRIPTION OF THE FIGURES

The features of certain embodiments will become more apparent in the following detailed description in which reference is made to the appended figures wherein:

FIG. 1 is a general scheme showing a synthesis process of Cu-based catalysts, including an AgCu SANP catalyst in accordance with one embodiment of the present description.

FIGS. 2A to 2D (collectively FIG. 2) are scanning transmission electron microscopy (STEM) images of the AgCu SANP catalyst in accordance with an embodiment of the present description. FIG. 2A: bright-field scanning transmission electron microscopy (BF-STEM) image of the AgCu SANP; FIG. 2B: high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the AgCu SANP; FIG. 2C: aberration-corrected HAADF-STEM (AC-HAADF-STEM) image of the AgCu SANP; and FIG. 2D: STEM and energy-dispersive X-ray spectroscopy (EDS) element mapping images of the AgCu SANP.

FIGS. 3A to 3F (collectively FIG. 3) illustrate X-ray diffraction and spectroscopic characterization of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP in accordance with an embodiment of the present description. FIG. 3A: X-ray diffraction (XRD) spectra of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP; FIG. 3B: Ag 3d core-level X-ray photoelectron spectroscopy (XPS) spectra of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP; FIG. 3C: Cu 2p core-level XPS spectra of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP; FIG. 3D: Ag K-edge X-ray absorption near-edge structure (XANES) spectra of AgCu SANP and Ag foil; FIG. 3E: Ag K-edge X-ray absorption fine structure (XAFS) experimental and fitting spectrum of AgCu SANP; and FIG. 3F: a schematic structure of the AgCu SANP and the ratio of Ag-Cu and Ag-Ag contribution from the fitting results (Ag SAC=Ag single-atom catalyst).

FIGS. 4A to 4G (collectively FIG. 4) illustrate electrocatalytic CO₂ reduction and CO reduction performance of the catalysts in accordance with an embodiment of the present description. FIG. 4A: a general scheme of the cascade catalysis mechanism over the AgCu SANP; FIG. 4B: FE results of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP catalysts towards CO₂RR at −0.65V; FIG. 4C: total current density of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP catalysts at −0.65V; FIG. 4D: performances comparison of the AgCu SANP and results reported in the literature; FIG. 4E: FE results of Cu NP, AgCu SAA and AgCu SANP towards CO reduction; FIG. 4F: long-term stability results of the AgCu SANP towards CO₂RR; and FIG. 4G: FE results of the AgCu SANP towards CO₂RR feeding with different CO₂ concentrations.

FIGS. 5A to 5C (collectively FIG. 5) illustrate mechanistic studies of the catalysts in the production of multicarbon products by density functional theory (DFT) calculations. FIG. 5A: comparison of the C—C coupling activation barrier for the *CHO and *CHO intermediates; FIG. 5B: the lowest free energy pathway for the formation of ethanol (CH₂CH₂OH), ethylene (CH₂CH₂) and acetic acid (CH₃COOH); and FIG. 5C: associated chemical formula for each elementary step.

FIGS. 6A to 6H (collectively FIG. 6) are scanning electron microscopy (SEM) images of Cu NP (FIGS. 6A and 6E), AgCu SAA (FIGS. 6B and 6F), AgCu SANP (FIGS. 6C and 6G), and Ag NP (FIGS. 6D and 6H) in accordance with an embodiment of the present description.

FIGS. 7A to 7G (collectively FIG. 7) illustrate STEM characterization of the catalysts in accordance with an embodiment of the present description. FIGS. 7A and 7B: BF-STEM images of AgCu SANP; FIGS. 7C and 7D: HAADF-STEM images of the AgCu SANP with representative Ag NP marked by a circle in FIG. 7D; FIG. 7E: HAADF-STEM image of the AgCu SANP, region 1 representing the Ag NP and region 2 representing AgCu SAA; FIG. 7F: r dispersive X-ray p EDX) of region 1 showing the apparent signal of Ag and Cu; and FIG. 7G: EDX of region 2, showing only the signal of Cu without Ag due to the low content of Ag in the AgCu SAA composition.

FIGS. 8A to 8E (collectively FIG. 8) illustrate STEM characterization of AgCu SAA in accordance with one embodiment of the present description. FIG. 8A: BF-STEM image of the AgCu SAA; FIGS. 8B and 8C: HAADF-STEM images with different magnifications of the AgCu SAA; FIG. 8D: AC-HAADF-STEM image of AgCu SAA, with bright dots marked by circles representing the Ag single-atoms; and FIG. 8E: STEM and EDS element mapping images of the AgCu SAA.

FIG. 9 shows XRD spectra of Cu NP, AgCu SAA, AgCu SANP and AgCu NP in accordance with an embodiment of the present description.

FIGS. 10A and 10B (collectively, FIG. 10) are spectra of an exemplary AgCu SANP catalyst of the present description. FIG. 10A: Cu K-edge XANES spectra of the AgCu SANP and Cu foil; and FIG. 10B: Ag K-edge extended X-ray absorption fine structure (EXAFS) experimental and fitting spectra of the AgCu SANP.

FIGS. 11A to 11F (collectively, FIG. 11) are experimental and fitting spectra of an exemplary AgCu SANP catalyst of the present description. FIGS. 11 A and 11B: experimental and fitting spectra of Ag K-edge in k space of the AgCu SANP and Ag foil respectively; FIG. 11C: experimental and fitting spectra of Ag K-edge in r space of the Ag foil; FIGS. 11D and 11E: experimental and fitting spectra of Cu K-edge in k space of the AgCu SANP and Cu foil respectively; and FIG. 11F: experimental and fitting spectra of Cu K-edge in r space of the Cu foil.

FIG. 12 is a schematic illustration of a flow cell in accordance with one embodiment of the present description.

FIGS. 13A to 13E (collectively FIG. 13) illustrate gas chromatography (GC) flame ionization detector (FID) studies of CO₂RR performance in accordance with an embodiment of the present description. FIG. 13A: representative GC FID spectrum for CO₂RR products; FIG. 13B: representative GC thermal conductivity detector (TCD) spectrum for the CO₂RR products; FIGS. 13C to 13E: standard curves of CH₄, C₂H₄ and CO respectively.

FIGS. 14A to 14E (collectively, FIG. 14) illustrate nuclear magnetic resonance (NMR) studies of CO₂RR performance of an exemplary AgCu SANP catalyst of the present description. FIG. 14A: representative NMR spectrum for CO₂RR products; and FIGS. 14B to 14E: standard curves of HCOO⁻·C₂H₅OH, CH₃COO⁻ and C₃H₇OH respectively.

FIGS. 15A to 15H (collectively FIG. 15) illustrate results of CO₂RR performance in accordance with an embodiment of the present description. FIGS. 15A to 15D: FE results of Cu NP, AgCu SAA, AgCu SANP, and AgCu NP under different potentials; and FIGS. 15E to 15H: Current density vs. time (l−t) curves of the Cu NP, AgCu SAA, AgCu SANP, and AgCu NP under different potentials. In each of FIGS. 15E to 15H, counting from the top, the lines denote −0.50V, −0.55V, −060V, −0.65V and −0.70V respectively.

FIGS. 16A to 16F (collectively FIG. 16) illustrate results of an exemplary AgCu SANP of the present description for CO₂RR feeding with different CO₂ concentrations. FIGS. 16A to 16C: FE results with different CO₂ concentrations; and FIGS. 16D to 16F: l−t curves with different CO₂ concentrations. In each of FIGS. 16D to 16F, counting from the top, the lines denote −0.50V, −0.55V, −060V, −0.65V and −0.70V respectively.

FIG. 17 illustrates possible mechanistic pathways for the formation of ethanol, ethylene, and acetic acid. The free energy of the reactions indicated in the arrows is in eV.

FIG. 18 illustrates projected d-bands for pure Cu and Ag-doped surfaces. The two lines at the bottom are the density of states (DOS) projected on the d-band of the atoms near the target Cu (in pure Cu) and Ag atom (in AgCu). In the insets. the target Cu and Ag atoms are indicated with “A” whereas the first-neighbour Cu atoms are indicated with “B”. The dashed lines indicate the d-band center of the pure Cu and AgCu surfaces, respectively. The dashed oval indicates the excess DOS in AgCu.

FIGS. 19A to 19D (collectively FIG. 19) illustrate CO adsorbed structures before and after optimization for the ontop and bridge sites on pure Cu surface (FIGS. 19A and 19B respectively) and on Ag doped-Cu surface (FIGS. 19C and 19D respectively).

DETAILED DESCRIPTION

For the purposes of the present specification, and unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained by the present description, inclusive of the stated value and has the meaning including the degree of error associated with measurement of the particular quantity. The term “about” generally refers to a range of numbers that one of ordinary skill in the art would consider as a reasonable amount of deviation to the recited numeric values (i.e., having the equivalent function or result).

The term “and/or” can mean “and” or “or”.

Unless stated otherwise herein, the articles “a” and “the”, when used to identify an element, are not intended to constitute a limitation of just one and will, instead, be understood to mean “at least one” or “one or more”.

In general, the present description provides a novel AgCu SANP catalyst suitable for the production of multicarbon products. Such production of the multicarbon products can be carried out in a cascade catalysis. The AgCu SANP catalyst comprises a Cu substrate having at least one AgCu SAA, and Ag NPs on the substrate or on the AgCu SAA, wherein the AgCu SAA comprises at least one single Ag atom dispersed into a surface of the Cu substrate, and the Ag nanoparticles comprise Ag-Ag bonds between the Ag nanoparticles. In some embodiments, the Cu substrate comprises Cu nanoparticles. In some embodiments, the multicarbon products comprise organic compounds having 2 to 6 carbons (generally referred to as C2 to C6 products) or any mixtures thereof. In another embodiment, the multicarbon carbon products comprise C2 and C3 products or any mixtures thereof.

In one embodiment, the AgCu SANP catalyst comprises at least one AgCu SAA and Ag nanoparticles, wherein the AgCu SAA is capable of promoting C—C coupling kinetics to produce multicarbon products from adsorbed CO and the Ag NP is capable of producing CO from CO₂. The AgCu SANP catalyst can exhibit a high FE towards multicarbon products. The terms “AgCu SANP” and “AgCu SANP catalyst” are used interchangeably throughout the present description. As would be understood by persons skilled in the art, the term “promote” is synonymous to facilitate or accelerate.

As would be understood by persons skilled in the art, the term “multicarbon product” or “C₂₊” refers to an organic compound having at least two carbons. For example, a C2 product refers to an organic compound having two carbons.

As would be understood by persons skilled in the art, the term “electrochemical” process or reaction describes a chemical process or reaction involving electron transfer.

As would be understood by persons skilled in the art, the term “cascade reaction”, refers to a chemical process that integrates at least two reactions, of which each subsequent reaction can start when the previous reaction step is completed. The term “cascade catalysis” or “catalytic cascade reaction” refers to a in-series process of different catalytic cycles, in which the product of the first cycle becomes the substrate of the second catalytic cycle and so on. Tandem reaction and domino reaction are generally understood to be subcategories of cascade reactions.

As would be understood by persons skilled in the art, the term “Faradaic Efficiency” (FE) can be used to describe the selectivity of a catalyst in an electrochemical reaction and is defined as the amount (moles) of collected product relative to the amount that could be produced from the total charge (i.e. electrons) transferred in the reaction. FE can be expressed as a fraction or a percent. For example, in the present description, FE is used to measure the selectivity of a catalyst towards multicarbon products.

As would be understood by persons skilled in the art, the term “single-atom catalyst” (SAC) generally refers to a catalyst having a single atom on its surface.

As would be understood by persons skilled in the art, the term “single-atom alloy” (SAA) can be used to refer to a catalyst in which atoms of one metal that serve as dopants are dispersed in the surface of a different metal that serves as the host. The metal host can also be understood as the metal substrate. For example, single Ag atoms in a Cu host would be referred to as an AgCu SAA. Also as would be understood by persons skilled in the art, “doping” is a way of introducing a small amount of one chemical material (which is generally known as a dopant) into a different host material such as a host chemical material. The term “alloying” would be generally understood by persons skilled in the art as a way of mixing different chemical materials together to form an alloy. In the present description, the terms “doping” and “alloying” are similarly used.

As would be understood by persons skilled in the art, the term “nanoparticle” generally refers to a particle having overall dimensions in the nanoscale, for example under 100 nm. As opposed to a single metal atom, a metal nanoparticle is generally understood to comprise a plurality of metal atoms present either as single atoms or in compound forms. Although the nanoparticles described herein are depicted as spheres in the Figures, it would be readily appreciated by persons skilled in the art, the nanoparticles can be in any shape known in the art.

The present description also provides using AgCu SANP in the production of multicarbon products.

As described herein, the inventors developed a novel AgCu SANP catalyst comprising an AgCu single-atom alloy (SAA) serving as a C—C coupling site and Ag nanoparticles (NP) producing local CO. Without being limited to any particular theory, it is postulated that the Ag single-atom doping of Cu NP can improve the adsorption energy of *CO on the Cu sites due to the asymmetric bonding of the Cu atom to the enamouring Ag atom, resulting in a much better C—C coupling ability than that of a pure Cu NP. As a result, in one example, the AgCu SANP catalyst comprising an AgCu single-atom alloy and Ag NPs (denoted as AgCu SANP) exhibited 94% FE towards multicarbon products under about 720 mA cm⁻² working current density in a flow cell.

According to density functional theory (DFT) calculations, it is postulated that the C₂₊ selectivity observed mainly originates from the cascade catalysis by the AgCu SAA and the Ag NPs in the cascade AgCu SANP catalyst disclosed herein.

The present description is further illustrated by the following examples.

Methods

Chemicals:

All solvents, unless otherwise mentioned, are American Chemical Society (ACS) grade. The water used was purified by a Milli-Q™ system with a resistivity of 18.2 MΩ cm. All pure gasses, for electrocatalysis and gas chromatography, were obtained from Praxair and Linde with the associated purities: CO₂ LaserStar™ 5.0 (99.999%), Air Zero (maximum 3 ppm water, 1 ppm total hydrocarbons), Helium 5.5 (99.9995%), Hydrogen 5.5 (99.9995%), Argon 5.0 (99.9995%). The gas mixture for GC calibration (Supelco™ 23462) was obtained from Sigma-Aldrich. For NMR tests, deuterium oxide (99.9 atom % D), dimethyl sulfoxide (99.5%), formic acid (98%), and 1-propanol (99.9%) were obtained from Sigma Aldrich. Ethylene glycol was obtained from VWR Chemicals (laboratory grade). 100 nm copper nanoparticles and silver nitrate (99%) were obtained from Sigma Aldrich. Nafion™ 117 containing solution (about 5% in a mixture of lower aliphatic alcohols and water) was obtained from Sigma Aldrich. Sigracet™ 36BB gas diffusion electrodes were purchased from Fuel Cell Store. Nickel foam (99.9%) was purchased from MTI Corporation. Potassium hydroxide (85%) was obtained from Sigma Aldrich.

Synthesis of AgCu SANP Catalyst:

20 mg Cu NPs and 2 mg AgNO₃ were firstly dispersed into 5 mL ethylene glycol and 0.2 mL H₂O, respectively. The two solutions were then combined together and put in an ultrasonic bath for the galvanic reaction for 30 min. After that, the resulting nanoparticles were washed with water and isopropanol (IPA) and collected using the centrifuge. The obtained nanoparticles contained both Ag single-atoms and nanoparticles, labeled as AgCu SANP.

The AgCu SAA and AgCu NP catalysts were prepared using a similar method, except for the different AgNO₃ usage (0.1 mg for the AgCu SAA and 20 mg for the AgCu NP).

Preparation of AgCu-Based Gas Diffusion Electrode (GDE):

AgCu-based nanoparticles, including AgCu SANP, AgCu SAA and AgCu NP, were firstly dispersed into IPA with a concentration of 5 mg mL⁻¹. The Nafion-117 solution was also added to the IPA solution containing the AgCu-based nanoparticles with 1% volume. After mixing under ultrasound conditions for 30 min, the catalyst ink was directly sprayed on the GDL (Sigracet 36 BB) using an airbrush. The final loading of the GDE was determined by balancing the weight difference before and after the airbrush step, which was about 0.5 mg cm⁻².

Material Characterization:

Scanning electron microscopy (SEM) images were captured on a Hitachi™ S4800 with a working accelerating voltage of 10 kV. Glancing-incidence X-ray diffraction (GIXRD) was measured on a PANalytical X'Pert Pro™ MRD diffractometer with Cu Kα radiation (1.54 Å) at an incidence angle of 0.3°. X-ray photoelectron spectroscopy (XPS) measurements were carried out on a Thermo-VG Scientific ESCALab™ 250 microprobes with a monochromatic Al Ka X-ray source (1486.6 eV). The obtained spectra were calibrated using C 1 s line. Aberration-corrected scanning transmission electron microscope (AC-STEM) tests were carried out on an FEI Titan™ 80-300 HB TEM equipped with energy-dispersive X-ray spectroscopy (EDS) at 200 kV. The HAADF-STEM images were recorded by FEI Titan 80-300 HB TEM/STEM with aberration corrector operating at 300 kV. Inductively coupled plasma-atomic emission spectrometry (ICP-MS) tests were carried out on X Series quadrupole, Thermo Scientific USA. Proton nuclear magnetic resonance (H-NMR) was measured on Bruker Avance Ill™ 300 MHz. GC tests were conducted on an Agilent™ 6890 machine with Carboxen (TCD) and Carbonplot (FID) columns. XAS measurements were carried out at the Advanced Photon Sources (APS) 20-ID-C and 20-BM beamline. The measurements at the copper K-edge and Ag K-edge were performed in fluorescence mode using a Lytle detector. The XAS data were analyzed using the software package Athena™.

Electrochemical CO₂RR Measurements:

All electrochemical tests were measured on Gamry Reference 3000™ electrochemical workstation at room temperature with IR compensation. A three-electrode system was fabricated with the prepared AgCu-based GDE, Ni foam, and Ag/AgCl electrode severing as working electrode, counter electrode, and reference electrode, respectively. A gas-tight, three-chamber flow cell equipped with a piece of Fumasep™ FAB-PK-130 anion exchange membrane (AEM) was employed to conduct the CO₂RR. The experiments were carried out under ambient conditions. Before the CO₂RR tests, the AEM was firstly activated in 1 M KOH solution for 12 h. The CO₂RR catalytic activities were evaluated using the potentiostatic technique under selective potential for 10 min in 1M KOH with flowing pure CO₂ gas. The flow rate of electrolyte and CO₂ gas was 18 mL min⁻¹ and 30 sccm, respectively. All the potential values are relative to the reversible hydrogen electrode (“RHE”) unless otherwise stated. The gas products were tested using online GC, liquid products are detected using ¹H-NMR.

Determination of Gas Products Using GC Method:

Standard curves of CH₄, CO, C₂H₂, C₂H₄, and C₂H₆ gases were firstly built using standard gas. In detail, different concentrations were prepared by diluting the mixture with CO₂ using mass flow controllers (Alicat Scientific™). The produced standard curves of CH₄, C₂H₄ and CO are shown in FIGS. 13C to 13E respectively. During the electrocatalytic CO₂R R, the gas products flew into the GC with the input CO₂ gas in the online tube. In experiments where CH₄ and C₂H₄ were the main gas products that could be detected in flame ionization detector (FID), CO was detected by the thermal conductivity detector (TCD).

Determination of Liquid Products Using the NMR Method:

Standard curves of ethanol, formate, acetate and propanol were firstly built using pure chemicals with known concentrations. NMR tubes were prepared by combining 70 μL D₂O and 30 μL of aqueous 5 6 mM DMSO internal standard with 630 μL sample. The produced standard curves of HCOO⁻, C₂H₅OH, CH₃COO⁻ and C₃H₇OH are shown in FIGS. 14B to 14E respectively. After electrocatalytic CO₂RR, the electrolyte was collected and mixed with the NMR detecting solution (DMSO internal standard DMSO, D₂O, as mentioned above). For ¹H-NMR tests, 128 scans were performed, with excitation sculpting used to suppress the water peak. As presented in FIG. 14A, ethanol, formate, acetate, propanol, and DMSO can be ascribed to the peaks located at 1.07 (triplet) and 3.55 (quartet), 8.35 (singlet), 3.44 (triplet), and 1.42 (sextet) and 0.77 (triplet), and 2.61 ppm, respectively. Signals from the OH proton in the alcohols were not observed, which is likely due to hydrogen-deuterium exchange.

DFT Calculations:

All DFT calculations were performed using the Vienna ab initio simulation package (VASP) with spin polarization. The generalized gradient approximation (GGA) exchange-correlation functional parametrized by Perdew, Burke, and Ernzerhof (PBE) for the electronic interactions and the projector-augmented wave (PAW) method for the core electrons was used. A cutoff energy of 600 eV was used for the plane-wave. The convergence criterion for the electronic self-consistent iteration was set at 10⁻⁶ eV. During the relaxation, it was assumed that the relaxation was achieved when the atomic forces were lower than 0.05 eV/Å. A Monkhorst-Pack grid was used with dimensions of 4×4×1 for sampling the first Brillouin zones. The DOS calculations were done using a 12×12×12 k-points grid, and the tetrahedron method with Blöchl corrections. The d-band center was calculated with an integration window of −10 to 10 eV. As the single crystal structure of copper is face centered cubic (FCC), the copper surface was modelled using a 2x 2 supercells of the (100) plane (fcc(100)) with four layers, for which only the bottom two layers were frozen, while the rest of the 2×2 supercell model system was allowed to relax. As would be understood by persons skilled in the art, the term “supercell” comprises at least two unit cells and hence, 2×2 supercells comprise four unit cells. The (100) plane of Cu (Cu(100)) was doped with Ag by substituting one Cu atom with Ag, which corresponded to a 3% Ag doping concentration in the Ag-doped Cu surface.

To ensure that the interactions between neighboring periodic images were negligible, a vacuum region along the z-direction was added so that the distance between two nearest surface atoms in neighboring images was at least 16 Å. The DFT-D3 Grimme method was employed for long-range dispersion interaction correction (Grimme, Stefan & Antony et al. J. Chem. Phys. 132, 154104 (2010). For the C—C coupling, a transition state search was carried out by automated relaxed potential energy surface scans (ARPESS).

The computational hydrogen electrode (CHE) model proposed by Norskov et al. was used to calculate the free energies of CO₂ reduction intermediates, based on which the free energy of an adsorbed species is defined as: ΔG_ads=ΔE_ads+ΔE_ZPE−TΔS_ads+∫C_PdT, where ΔE_ads is the electronic adsorption energy, ΔE_ZPE and TΔS_ads represent zero-point energy and entropy (difference between adsorbed and gaseous species), respectively, ∫C_PdT is the enthalpy correction and Tis at room temperature (J. Phys. Chem. B. 108, 17886-17892, (2004)).

Example 1: Characterization of Catalysts

The catalysts, including AgCu SANP, AgCu SAA and AgCu NP, were prepared through a galvanic replacement reaction between commercial Cu NPs and Ag⁺ as noted above under “Methods”, which was spontaneously driven by their reduction potential difference. As illustrated in the general synthesis scheme in FIG. 1 showing Ag as spheres of a darker shade than those of Cu, the dispersion of Ag atoms varies with increasing amounts of Ag⁺. As a result, the AgCu SAA, AgCu SANP, and AgCu NP were synthesized by tuning the amount of Ag⁺. In AgCu NP, all the Ag is present as NPs on the Cu NPs. In one embodiment, Cu NPs act as hosts for Ag doping to form AgCu SAA, and Ag NPs form on the AgCu SAA. Therefore, the Cu NPs act as substrate and as host materials for the Ag doping.

The scanning electron microscope (SEM) images (FIG. 6A) show that all the catalysts prepared presented a similar morphology of aggregation with a size between 100 nm to 200 nm. The bright-field scanning transmission electron microscopy (BF-STEM) images (FIG. 2A and FIGS. 7A and 7B) further proved the aggregation morphology. From the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images (FIG. 2B and FIGS. 7C to 7F), some small Ag NPs could be found in the AgCu SANP due to the Z contrast difference between Ag and Cu. Further aberration-corrected HAADF-STEM (AC-HAADF-STEM) images (FIG. 2C and FIG. 8D) showed many bright dots in the Cu crystal lattice, which were ascribed to Ag single-atoms. The HAADF-STEM images and energy-dispersive X-ray spectroscopy (EDS) element mapping demonstrated the existence of separated Ag NP and uniform dispersion of Ag and Cu elements in other parts of the AgCu SANP catalyst (FIG. 2D). These results confirm the co-existence of Ag NP and Ag single-atom in the AgCu SANP catalyst.

As a comparison, the Ag atoms appeared to be uniformly and atomically dispersed in the AgCu SAA (FIG. 8E).

To further study the structure and composition of the AgCu SANP catalyst prepared, grazing incidence X-ray diffraction (GI-XRD) was measured (FIG. 3A and FIG. 9). The intensity of Cu (111) and CuO (002) and (111) peaks gradually decreased with the increase of Ag in the samples, accompanying the increase of Ag (111) and (200) and Cu₂O (111) and (200) peak intensity. The AgCu SAA showed a similar XRD spectrum to Cu NP, indicating the high atomic dispersion of the Ag atoms in the AgCu SAA. There were both Ag and Cu peaks in the AgCu SANP, confirming the existence of the Ag NP and agreeing well with the STEM results. As shown in FIG. 9, all the samples contained Cu (111), (200), (220) reflections, which indicated Cu was polycrystalline.

X-ray photoelectron spectroscopy (XPS) was further carried out to study the elemental valence. Only the AgCu SANP and the AgCu NP showed apparent Ag peaks, which could be deconvoluted into the four peaks of 3d3/2, 3d5/2 of metallic Ag, and Ag oxide (as marked in FIG. 3B). It is postulated that the disappearance of the Ag XPS peak in the AgCu SAA might be caused by the low content of Ag, which was 0.04 wt. % determined by inductively coupled plasma mass spectrometry (ICP-MS). The core-level Cu 2p XPS peak could be deconvoluted into six peaks, corresponding to 2p_3/2, 2p_1/2 of Cu⁰, Cu²⁺, and shake-up peaks (as marked in FIG. 2C) (Appl. Surf. Sci. 257, 887-898 (2010); Cryst Eng Comm 18, 6055-6061 (2016)). In addition, the intensity of Ag and Cu XPS peaks also exhibited a similar trend to that of XRD spectra, in which Ag increased and Cu decreased with the increasing amount of Ag in the samples.

The above results also agreed well with the galvanic replacement reaction mechanism. ICP-MS results showed that the detailed content of Ag in the AgCu SAA, AgCu SANP, and AgCu NP increased from 0.04 w %, 1 wt % to 4 wt %.

The coordination structure of Ag species in the as-prepared AgCu SANP catalyst was further investigated by synchrotron-radiation-based X-ray absorption fine structure (XAFS) at the Advanced Photon Source (APS), Argonne National Laboratory, Lemont, IL, USA. As shown in the Ag K-edge X-ray absorption near-edge structure (XANES) spectral (FIG. 3D), the line of representing the AgCu SANP showed a slight shift to lower energy for the adsorption edge (E0) compared to that of the Ag foil, indicating electron transfer from Cu to Ag due to the formation of Ag-Cu bond. The positive shift of the AgCu SANP line in the Cu K-edge also demonstrated the electron loss of Cu (FIG. 10). Moreover, the Fourier transform (FT) of the k³-weighted extended X-ray absorption fine structure (EXAFS) curve of the Ag K-edge of the AgCu SANP showed both Ag-Ag and Ag-Cu coordination bonds (FIG. 3E). As shown in the schematic structure of the AgCu SANP in FIG. 3F, the ratio of Ag-Cu bonds to Ag-Ag bonds was estimated to be about 1:7 based on the extended X-ray absorption fine structure (EXAFS) fitting results (FIG. 11 and Table 1), which would be understood the ratio of the AgCu SAA to the Ag NP was about 1:7. These results indicated that the Ag existed in the AgCu SANP in both single-atom and NP form with both Ag-Cu and Ag-Ag coordination.

TABLE 1
Fitted EXAFS Parameters at the Cu and Ag K-
edge for AgCu SANP, Ag Foil, and Cu Foil

	AMP	ERROR	CN	error	R(Å)	ERROR	E0(eV)	σ2(Å2)	R-factor

AgCu SANP
Ag—Ag	0.50	0.05	7.32	0.73	2.859	0.009	2.4(7)	0.0080(1)	0.0103
Ag—Cu	0.12	0.01	1.03	0.09	2.810	0.048		0.0125(9)
Cu—O	0.53	0.09	2.12	0.36	1.952	0.170	8(2)	0.0019(5)	0.0204
Cu—O	0.53	0.09	1.06	0.18	2.689	0.077		0.0030(2)
Cu—Cu(oxide)	0.53	0.09	2.12	0.36	3.076	0.042		0.0118(1)
Cu—Cu(metal)	0.11	0.05	1.42	0.65	2.548	0.018		0.0012(8)
Cu—Ag	0.11	0.01	0.95	0.09	2.810	0.048		0.0008(5)
Ag Foil
Ag—Ag	0.82	0.04	12		2.866	0.003	2.1(3)	0.0092(4)	0.0021
Cu
Cu—Cu	0.93	0.05	12.00		2.544	0.003	4.5(5)	0.0090(4)	0.0011
Cu—Cu	0.93	0.05	6.00		3.595	0.022		0.0148(4)
Cu—Cu—Cu	0.93	0.05	48.00		3.848	0.046		0.0202(5)
Cu—Cu—Cu	0.93	0.05	48.00		4.373	0.032		0.0032(5)
Cu—Cu	0.93	0.05	24.00		4.418	0.018		0.0125(2)
AMP: amplitude reduction factor, CN: coordination number; R: distance; E0: energy shift; σ2: mean-square disorder; R-factor: goodness of EXAFS fitting. The numbers in the parentheses are the last digit error.

Combining the XANES and EXAFS analyses and AC-STEM images, the co-existence of Ag and Cu atoms in the AgCu SAA prepared was also confirmed.

Example 2: Performance of CO₂ Reduction and CO Reduction on Catalysts

To demonstrate the cascade catalysis concept on the C₂₊ production (FIG. 4A), the electrocatalytic CO₂RR performance of the AgCu SANP prepared and other catalyst samples listed in FIG. 4B (CuNP, AgCu SAA, AgCu NP) were tested in a flow cell with 1M KOH as an electrolyte. The testing system is schematically shown in FIG. 12. Generally, a potentiostatic test was conducted on the catalysts under different potentials. The gas products were collected and quantified by in-line gas chromatography (FIGS. 13A and 13B), while the liquid products were directly dissolved in the electrolyte and analyzed by NMR (FIG. 14A). The C₂₊ products were mainly ethylene and ethanol with minor acetate and n-propanol for all the catalysts (FIG. 4B and FIG. 15).

In one embodiment, the AgCu SANP exhibited a C₂₊ FE of 94% under −0.65V, which was much higher than that of the Cu NP (56%), the AgCu SAA (78%), and the AgCu NP (73%) (FIG. 4B). The apparent current density under −0.65 V of the AgCu SANP (720 mA cm⁻²) was also larger than that of the Cu NP (630 mA cm⁻²), the AgCu SAA (710 mA cm⁻²) and the AgCu NP (233 mA cm⁻²) (FIG. 4C). In another embodiment, the AgCu SANP exhibit at least about 94% FE for multicarbon products under about 720 mA cm⁻².

In addition, the C₂₊ production performance of the AgCu SANP as prepared was also superior to most of the reported catalysts listed in FIG. 4D and Table 2. This activity performance strongly confirmed the superiority of the AgCu SANP catalyst in the C₂₊ production, suggesting that the proposed cascade catalysis concept is valid. It is worthwhile to note that all the copper oxides in the as-synthesized AgCu SANP were reduced to the metallic state during the negative potential. The FE of the CO production was the least in the AgCu SANP catalyst, indicating that most of the CO was converted to C₂₊ products via a C—C coupling.

TABLE 2
Performances Comparison of AgCu SANP and Reported results in FIG. 4D

		jtotal mA
Catalysts	NO.	cm−2	C2+ FE	Reference

AgCu SANP	1	720	94	Example 2
La2−xCuO4−δ	2	51.3	41.5	Angew. Chem. Int. Ed. 2022, 61,
				e202111670
CuxOyCz	3	80	54	Angew. Chem. Int. Ed. 2021, 60,
				23427-23434
Cu—PzH	4	346	60	Angew. Chem. Int. Ed. 2021, 60,
				19829-19835
alkanethiol-modified Cu	5	255	64	J. Am. Chem. Soc. 2021, 143, 21,
				8011-8021
CuO/Al2CuO4	6	600	70.1	Energy Environ. Sci., 2022, 2022,
				15, 2397-2409
F—Cu	7	400	70.4	Green Chem., 2022, 2022, 24,
				1989-1994
Cu—CuI	8	700	71	Angew. Chem. Int. Ed. 2021, 60,
				14329-14333
Cu2P2O7	9	350	73.6	Angew. Chem. Int. Ed. 2022, 61,
				e202114238
Cu—SiOx	10	300	75	Nature Communications (2021)
				12: 2808
electrodeposited Cu	11	150	75	J. Am. Chem. Soc. 2021, 143, 8,
				3245-3255
Cu3—Ag3Au	12	230	77	Angew. Chem. Int. Ed. 2021, 60,
				2508-2518
B—Cu—Zn	13	200	79	Angew. Chem. Int. Ed. 2021, 60,
				9135-9141
Cu NPs with + 1	14	300	80	Adv. Energy Mater. 2021, 2101424
valence
CuNi	15	250	80.5	ACS Materials Lett. 2021, 3,
				1143-1150
Cu@Pb	16	400	81.6	ACS Nano 2021, 15, 1, 1039-1047
Cu3Nx	17	307	81.7	Adv. Mater. 2021, 2103150
Cu Nanoribbons	18	347.9	82.3	Adv. Energy Mater. 2021, 11,
				2102447
Oxide-Derived Copper	19	341.5	83.8	Chem. Sci., 2021, 2021,12,
				5938-5943
SHKUST-1	20	400	88.4	Angew. Chem. Int. Ed. 2022, 61,
				e202111700
Cu(OH)2-derived Cu	21	217	87	Angew. Chem. Int. Ed. 2021, 60,
				4879-4885
N—C/Cu	22	300	93	Nature Energy, 5, 478-486 (2020)

Without being limited to any particular theory, it was postulated that the AgCu SANP cascade catalysis disclosed herein would involve the promotion of the C—C coupling kinetics by the Ag single-atoms on the Cu nanoparticles and the production of local CO from CO₂ by the Ag nanoparticles on the Cu nanoparticles. To further prove this point, CO reduction experiments were carried out to study the C—C coupling kinetics.

As presented in FIG. 4E, the AgCu SAA presented a much higher FE than that of the Cu NP, strongly indicating the improvement of the C—C coupling kinetics by the Ag single-atoms in the Cu lattice. The low FE of the AgCu SANP for the CO reduction could be ascribed to the Ag NP composition, which excluded the adsorption of CO and hampered further CO reduction. This easy desorption of CO from the Ag nanoparticles was also confirmed by the density functional theory (DFT) calculation. It is worthy to note that the FE of ethanol and ethylene in the CO reduction (FIG. 4B) and CO₂ reduction (FIG. 4E) were comparable on the AgCu SAA and the Cu NP. In comparison, the FE of ethanol and ethylene in the CO reduction on the AgCu SANP significantly decreased from 87.1% (FIG. 4B) to 32.2% (FIG. 4E). It was postulated that this was due to the easy desorption of CO from the Ag NP, which was expected to decrease the local concentration of CO on the surface of the catalyst. The existence of Ag NP in the AgCu SANP and the cascade catalysis mechanism of the AgCu SANP for CO2RR were therefore also confirmed. The FE of acetate formation was similar for the CuNP, the AgCu SANP and the AgCu SAA in CO reduction (FIG. 4E), suggesting that the formation of acetate was on the Cu active sites, which was independent of Ag content.

To alleviate the flooding issue in the flow cell, long-term stability was tested using a pulse electrolysis method (working 90 s and off 30 s) with a polytetrafluoroethylene (PTFE)-based gas diffusion electrode (GDE) according to a previous report (ACS Energy Lett. 6, 809-(2021). Although the current density decreased due to the flooding problem, the C₂₊ FE only decreased from 98% to 88% during the 13 h test (total working time 9.75h) (FIG. 4F).

To better investigate the potential of the as-prepared AgCu SANP in practical CO₂ reduction applications in industry from flue gas, its catalytic activity with a diluted CO₂ gas feed was studied.

As shown in FIG. 4G and FIG. 16, the AgCu SANP still maintained a very high CO₂RR activity when the concertation of CO₂ feeding gas decreased to 20%, exhibiting 95% FE towards CO₂ reduction with 76% C₂₊ production FE. With decreasing CO₂ gas concentration, the C₂₊ FE decreased to 57% (70% for total CO₂RR) and 35% (43% for total CO₂RR) with 15% and 10% CO₂ gas concentrations, respectively. This performance strongly indicates a promising application of the AgCu SANP catalyst in practical conditions. Therefore, in some embodiments, CO₂ enrichment processes are needed to maximize the catalytic performance of AgCu SANP catalyst in converting flue gas. For example, in the CO₂ concentration is low, CO₂ enrichment is needed by using membrane technology, amine or other methods known in the art to increase the CO₂ concentration

Example 3: Mechanism Studies by Density Functional Theory Calculations

It has been found that ethanol and ethylene are the most common competing C₂ products on AgCu SANP with a slight amount of acetic acid. Both ethanol and ethylene are 12-1π electron reduced products, while acetic acid is 8-electron reduced product. To understand the CO₂ reduction reaction mechanism towards ethylene, ethanol, and acetic acid on the surface of the AgCu SANP, a detailed mechanistic study considering the possibility of forming different intermediates was carried out using density functional theory (DFT) calculations. The Cu was confirmed to be polycrystalline in experiments (FIG. 9). The (100) facet or plane of Cu was used for the simulations because it favours C2 products over the C1 products based on the known literature. The CO₂RR to C₂₊ products generally involve various intermediates with the C—C coupling being the rate-determining step. The possible intermediates in each elementary step across the reaction coordinate were examined as shown in FIG. 17. The minimum energy pathways are shown in FIG. 5C. Prior studies reported that on Cu electrodes, the C—C coupling could occur through *CO—*CO dimerization, *CO—*CHO, or *CO—*COH with *CO—*CO coupling being less feasible with a higher transition state (TS) barrier (>1 eV) (ACS Catal. 11, 9688-9701(2021); J. Am. Chem. Soc. 138, 483-486 (2016); Chem Cat Chem 5, 737-742 (2013)). The barriers for hydrogenation of *CO to *CHO and *COH on Cu(100) was found to be 0.64 and 3 0.94 eV respectively, which are more favoured than the direct CO—CO coupling (>1 eV). Thus, it was decided that the less energetic coupling barrier between *CO—*CHO and *CO—*COH on the Ag-doped Cu (100) surface should be investigated.

It has been postulated that the Ag doping creates a surface strain because of its larger atomic radius. In pure Cu(100) surface, the Cu-Cu bond length is 2.57 Å; however, after doping, this was compressed to 2.50 Å at the surface. The compressive strain created asymmetrical sites next to the Ag atom (i.e., first-neighbour atoms labelled as “B” in (FIG. 18), providing active sites for the C—C coupling. As shown in FIG. 5A, the TS values of the C—C coupling via *CO—*CHO and *CO—*COH reactions were 0.51 and 1.10 eV, respectively, which agreed well with the previously reported work on Cu(100) (ACS Catal. 11, 9688-9701, (2021)).

To understand the effect of Ag on the reactions, the transition state (TS) barrier of *CO—*CHO on the pure Cu(100) surface was calculated, and a 0.55 eV barrier was obtained, which was slightly higher than the Ag-doped Cu(100) surface. On the other hand, Ag is known to produce CO from CO₂ (Adv. Powder Mater. 1, 100012 (2022)). CO was not stable on the Ag atom and easily diffused to the next Cu atoms (see Table 3 and FIG. 19). These findings suggest that the Ag atoms can play at least the following two key roles: 1) they facilitate reduction of CO₂ to CO and ii) they facilitate the C—C coupling by spilling over the CO atom to this asymmetrical active site with reduced transition state energy.

TABLE 3
Gibbs Free Adsorption Energies (ΔGads) of CO on
Ag Doped-Cu Surface of AgCu SANP and Pure Cu Surface

Ag Doped-Cu Surface

Pure Cu Surface

	Site type	ΔGads (eV)	Site type	ΔGads (eV)

	On top of Cu	−0.75
	On top of Ag	−0.33	On top	−1.00
	Bridge Cu—Cu	−0.77	Bridge	−1.02
	Bridge Cu—Ag	unstable	Hollow	−1.05
	Hollow (4-fold)	unstable
	Note:
	the CO adsorption on the bridge between Cu—Ag and 4-fold symmetry (“4-fold”) hollow structure/sites is not stable (i.e. migrating to the nearby Cu sites).

Ethanol, Ethylene, and Acetic Acid Formation Paths:

The lowest energy pathways identified for ethanol, ethylene and acetic acid production are illustrated in FIGS. 5B and 5C. All the intermediates before the C—C coupling were the same for these three products, i.e., CO2→*COOH →*CO→*CHO→*CO—CHO.

Because of the lower TS barrier, all the elementary steps after the C—C coupling were investigated based on the *CO—CHO intermediate. The acetic acid path bifurcates at the sixth protonation step, while ethanol and ethylene share six hydrogen/electron transfer intermediates and bifurcate only at the seventh protonation step. The ethanol and ethylene *OCH—CHO*common intermediate (labelled as “7A” in FIG. 5C) is more favoured than the acetic acid intermediate (labelled as “7B” in FIG. 5C), indicating that the formation of ethanol and ethylene would occur before acetic acid. This mechanistic understanding supports the experimental finding in FIG. 4B, in which ethylene and ethanol were the major products and a negligible amount of acetate/acetic acid was formed from the CO₂RR. However, the formation of acetate from CORR was as equivalent to the formation of ethylene and ethanol (FIG. 4E). This can be due to the presence of a high amount of CO on the catalyst surface that expedites the C—C coupling step and thereby enables the formation of other products including the acetate/acetic acid. As shown in FIG. 5, the free energy of the acetic acid path (labelled as “7B” in FIG. 5B) is slightly higher (0.19 eV) than the ethanol and ethylene path (labelled as “7A” in FIG. 5B) and thus, the acetic acid/acetate pathway would be feasible as well. Comparing ethanol and ethylene (both of which are 12-electron reduction products), the free energy diagram analysis demonstrated that ethanol formation is favoured over ethylene (labelled as “8a” and “8b” respectively FIG. 5B). This finding appears to agree with the slightly higher percentage of ethanol over ethylene in the experimental results as shown in FIG. 4B for the AgCu SANP catalyst.

To get further insight into the impact of Ag doping on the electronic structure of copper surfaces, the density of states (DOS) of the pure Cu and Ag-doped Cu surfaces of AgCu SANP (in the absence of adsorbate). As shown in FIG. 18, the analysis was focused on the d-band, which has shown to be a good descriptor to understand the differences in catalytic activities (P. Natl. Acad. Sci. USA 108, 937-943 (2011)). The analysis showed that the d-band center in pure Cu(100) surface was shifted to lower values in the Ag-doped Cu, as indicated by the vertical dashed lines. It was postulated that this downshift originated from the excess of DOS in Ag-doped Cu (compared to pure Cu) with respect to the Fermi level. The projected DOS on the d orbitals of the Cu (labelled as “B” in FIG. 18) atoms near the target Cu atom and Ag atom (before and after Ag substitution, respectively) also showed a downshift of the d-band center upon Ag substitution. The downshift of the d-band center in the Ag-doped Cu surface indicates that Ag can reduce the bonding strength of the adsorbate at the surface, which is consistent with the weak adsorption of CO on the Ag-doped Cu surface, and the reduced reaction barriers to producing ethanol, ethylene and acetic acid molecules (FIGS. 5A and 5B).

CONCLUSIONS

As described herein, a novel AgCu SANP cascade catalyst has been developed and exhibited a high FE (for example, 94%) towards multicarbon products under about 720 mA 23 cm⁻² working current density in a. DFT calculations indicate that an excellent C₂₊ selectivity should be ascribed to the synergistic catalysis of the Ag NP and the AgCu SAA in the AgCu SANP, wherein the Ag NP is capable of generating local CO from CO₂ and the AgCu SAA is capable of promoting the C—C coupling kinetics to form the multicarbon products from the adsorbed CO. This work not only develops a highly effective catalyst for multicarbon products production, but also provides a new cascade catalysis strategy for future C₂₊ selective catalysts development.

Although the above description includes reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art. Any examples provided herein are included solely for the purpose of illustration and are not intended to be limiting in any way. Any drawings provided herein are solely for the purpose of illustrating various aspects of the description and are not intended to be drawn to scale or to be limiting in any way. The scope of the claims appended hereto should not be limited by the preferred embodiments set forth in the above description but should be given the broadest interpretation consistent with the present specification as a whole. The disclosures of all references in the present description herein are incorporated herein by reference in their entirety.