CoNiFe Oxide Nanostructure Catalyst and Its Use

Abstract

The present disclosure relates to CoNiFe nanostructured catalysts and the use of such catalysts in the electrochemical conversion of methane to methanol. In particular, the present disclosure relates to a nanocube catalyst having the formula Co 1-x Ni x Fe2O4.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority to U.S. Provisional Application No. 63 / 353,182, filed on June 17, 2022, the content of which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to CoNiFe nanostructured catalysts and the use of such catalysts in the electrochemical conversion of methane to methanol. In particular, the disclosure relates to nanocube catalysts having the formula Co 1-x Ni x Fe2O4.

Background Art

[0003] Methane (CH4) is not only the second most prominent greenhouse gas contributing to global warming 1 but also a potentially useful feedstock that can be converted into valuable chemicals for the chemical industry. 2-4 Considering the increasingly deteriorating environmental problems and the inevitable depletion of fossil fuels for energy, the development of efficient and environmentally friendly strategies for improving direct methane conversion (DMC) into value - added chemicals is urgently required. 5-7 The conventional Fischer - Tropsch method for methanol synthesis mainly relies on converting syngas (a mixture of CO and H2) into useful chemicals by energy - intensive reactions, which is difficult to achieve both economically and environmentally. 8 Also, the C - H activation of CH4 molecules and the over - oxidation of products also greatly limit the kinetics and selectivity of CH4 oxidation. 2 Therefore, in order to efficiently convert CH4, it is important to develop highly active catalysts with variable selectivity. In recent years, there has been an increasing interest in resource management and carbon capture for converting CH4 into oxygenates. Thus, numerous alternative strategies have been explored towards the development of DMC technologies using homogeneous reactions involving catalysts, 9 enzymatic catalysts, 10 biocatalysts, 11 photocatalysts, 8 and electrocatalysts. 12Since they are low-cost, reaction-controllable, and easy to scale up, electrode-catalyzed CH4 oxidation provides an attractive and environmentally friendly approach for efficiently producing valuable chemical products. An efficient electrode catalyst for CH4 conversion is essential for improving the thermodynamics and kinetics of the process against the competing oxygen evolution reaction (OER).

[0004] To promote the conversion of CH4 and its utilization at room temperature, great efforts have been devoted to the exploration of high-performance electrode catalysts, 13,14 the design of electrochemical reaction cells, 15,16 microorganisms 11,17 or the incorporation of solar cells, and 18,19 density functional theory (DFT) calculation techniques. 20,21 Despite the significant progress made in the field of CH4 conversion so far, one of the major remaining challenges towards the optimal oxidation of CH4 is the design of highly active electrode catalysts for C-H activation and product selectivity. In this regard, the development of effective electrode catalysts for oxygenating DMC is an important prerequisite.

Summary of the Invention

[0005] The present disclosure relates to CoNiFe nanostructure catalysts and the use of such catalysts in the electrochemical conversion of methane to methanol. In particular, the present disclosure relates to nanocube catalysts having the formula Co 1-x Ni x Fe2O4.

[0006] One embodiment of the present disclosure is (a) a ternary metal oxide represented by the following formula, and

Chemical formula

[0007] In one embodiment, the electrochemical catalyst of the present disclosure is used for the electrochemical oxidation of methane.

[0008] One embodiment of the present invention includes a method for producing methanol from methane in an electrochemical process, the process comprising: (a) introducing methane into the anode chamber of an electrochemical reactor, the anode chamber including an anode comprising an electrochemical catalyst of the present disclosure; (b) introducing a catholyte into the cathode chamber of the electrochemical reactor, the cathode chamber including a cathode; (c) oxidizing at least a portion of the methane to methanol by introducing a voltage between the anode and the cathode; (d) collecting the methanol from the anode chamber.

[0009] Other features and advantages of the present application will become apparent from the following detailed description. However, it should be understood that the detailed description and preferred embodiments are given by way of illustration only, while indicating specific embodiments of the present application, since various changes and modifications within the spirit and scope of the present application will become apparent to those skilled in the art.

[0010] The present invention will be described in more detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011]

Figure 1(a)

Figure 1(b)

Figure 1(c)

Figure 1(d)

[0012]

Figure 2

[0013]

Figure 3

[0014]

Figure 4

[0015]

Figure 5(a)

Figure 5(b)

[0016]

Figure 6(a)

Figure 6(b)

Figure 6(c)

Figure 6(d)

[0017]

Figure 7(a)

Figure 7(b)

Figure 7(c)

Figure 7(d)

Figure 7(e)

Figure 7(f)

[0018]

Figure 8(a)

Figure 8(b)

Figure 8(c)

Figure 8(d)

Figure 8(e)

Figure 8(f)

[0019]

Figure 9(a)

Figure 9(b)

Figure 9(c)

Figure 9(d)

Figure 9(e)

Figure 9(f)

[0020]

Figure 10(a)

Figure 10(b)

Figure 10(c)

Figure 10(d)

Figure 10(e)

Figure 10(f)

[0021]

Figure 11(a)

Figure 11(b)

Figure 11(c)

Figure 11(d)

Figure 11(e)

Figure 11(f)

[0022]

Figure 12(a)

Figure 12(b)

Figure 12(c)

Figure 12(d)

Figure 12(e)

Figure 12(f)

[0023]

Figure 13(a)

Figure 13(b)

[0024]

Figure 14(a)

Figure 14(b)

[0025]

Figure 15(a)

Figure 15(b)

Figure 15(c)

Figure 15(d)

Figure 15(e)

Figure 15(f)

[0026]

Figure 16

[0027]

Figure 17(a)

Figure 17(b)

Figure 17(c)

Figure 17(d)

[0028]

Figure 18

[0029]

Figure 19(a)

Figure 19(b)

Figure 19(c)

Figure 19(d)

[0030]

Figure 20(a)

Figure 20(b)

Figure 20(c)

Figure 20(d)

[0031]

Figure 21(a)

Figure 21(b)

Figure 21(c)

Figure 21(d)

[0032]

Figure 22

[0033]

Figure 23(a)

Figure 23(b)

Figure 23(c)

Figure 23(d)

Figure 23(e)

Figure 23(f)

Figure 23(g)

Figure 23(h)

Figure 23(i)

[0034]

Figure 24(a)

Figure 24(b)

[0035]

Figure 25

[0036]

Figure 26

[0037]

Figure 27

[0038]

Figure 28(a)

Figure 28(b)

Figure 28(c)

Figure 28(d)

[0039]

Figure 29(a)

Figure 29(b)

Figure 29(c)

Figure 29(d)

Embodiments for Carrying Out the Invention

[0040] (I) Definitions

[0041] As can be understood by those skilled in the art, unless otherwise specified, the definitions and embodiments described in this specification and other parts are intended to be applicable to all embodiments and aspects described in this specification.

[0042] The term "comprising" and its derivatives used in this specification are intended to be open-ended terms that identify the presence of the described features, elements, components, groups, integers, and / or steps, but do not exclude the presence of other un-described features, elements, components, groups, integers, and / or steps. The same applies to words with similar meanings such as the terms "including" and "having" and their derivatives.

[0043] As used herein, the term "consisting of" and its derivatives are intended to be closed terms that identify the presence of the recited features, elements, components, groups, integers, and / or steps, and that exclude the presence of other unrecited features, elements, components, groups, integers, and / or steps.

[0044] As used herein, the term "consisting essentially of" is intended to identify the presence of the recited features, elements, components, groups, integers, and / or steps, as well as the presence of those that do not substantially affect the basic and novel characteristics (s) of the features, elements, components, groups, integers, and / or steps.

[0045] Degree terms such as "substantially", "about", and "approximately" as used herein mean a reasonable deviation of the modified term such that the end result is not materially changed. These degree terms should be construed to include at least a ±5% deviation of the modified term, where such deviation does not negate the meaning of the modifying word.

[0046] As used in this application, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise.

[0047] In embodiments that include "additional" or "second" components, the second component as used herein is chemically different from the other components or the first component. The "third" component is different from the other components, the first and second components, and additional recited or "additional" components are likewise different.

[0048] As used herein, the term "and / or" means that the recited terms are present, or used alone or in combination. In fact, this term means that "at least one" or "one or more" of the recited terms is used or present.

[0049] As used herein, the term "nanocube" refers to a structural atomic arrangement of a cubic ternary metal oxide having a nanoscale size of, for example, about 10 nm to 1 μm.

[0050] As used herein, the term "carbon" includes both non-graphitic forms of carbon and graphitic forms of carbon.

[0051] As used herein, the term "adjacent" means that in the case of a carbon layer and a nanocube, the two are in close proximity to each other with little or no empty space therebetween.

[0052] As used herein, the term "layer" refers to a layer of carbon atoms or molecules on a substrate adjacent to or in close proximity to a ternary metal oxide nanocube.

[0053] (II) Electrochemical Catalyst

[0054] The present disclosure relates to a highly active electrochemical catalyst for effectively converting methane to methanol. Also, a similar catalyst is useful for the conversion of nitrogen gas to ammonia.

[0055] Accordingly, in one embodiment, the present disclosure is (i) a ternary metal oxide represented by the following formula,

Chemical formula

[0056] In one embodiment, the ternary metal oxide is Co 0.8 Ni 0.2 Fe2O4.

[0057] In one embodiment, the ternary metal oxide is Co 0.6 Ni 0.4 Fe2O4.

[0058] In one embodiment, the catalyst has XRD peaks at 18.28°, 26.15°, 35.69°, and 43.36°.

[0059] In a further embodiment, x is an integer between 0.01 and 0.99, or between 0.1 and 0.9.

[0060] In another embodiment, x is about 0.20, about 0.40, about 0.60, or about 0.80.

[0061] In one embodiment, the carbon is elemental carbon. In one embodiment, the carbon may contain other atoms that do not affect the catalytic activity of the electrochemical catalyst of the present disclosure, such as oxygen or nitrogen.

[0062] In one embodiment, the elemental carbon is graphite or graphene.

[0063] In one embodiment, the carbon is in the form of a layer adjacent to the nanocubes.

[0064] In one embodiment, the carbon, optionally in the form of a layer, is a structure of carbon atoms bonded to each other by covalent bonds, ionic bonds, or other strong intermolecular forces. The layer may be planar or uneven. In one embodiment, there may be multiple carbon layers held together via intermolecular forces such as van der Waals interactions. Examples of carbon layers include, but are not limited to, graphite layers, graphene sheets, and carbon films. The carbon layer may also refer to the carbonaceous material coating the outer surface of the nanocubes.

[0065] In one embodiment, the dimensions of the nanocubes with adjacent carbon layers are between 10 nm and 1000 nm.

[0066] In one embodiment, the dimensions of the nanocubes with adjacent carbon layers are between 500 nm and 700 nm.

[0067] In one embodiment, the size of the nanocube having adjacent carbon layers is between 600 nm and 700 nm.

[0068] In one embodiment, the size of the nanocube having adjacent carbon layers is 640 nm.

[0069] (III) Electrochemical process The present disclosure relates to an electrochemical catalyst that efficiently converts methane to methanol and nitrogen gas to ammonia. Accordingly, one embodiment of the present invention includes a method for producing methanol from methane in an electrochemical process, the process comprising (a) introducing methane into the anode chamber of an electrochemical reactor, the anode chamber including an anode comprising the electrochemical catalyst of the present disclosure; (b) introducing a catholyte into the cathode chamber of the electrochemical reactor, the cathode chamber including a cathode; (c) oxidizing at least a portion of the methane to methanol by introducing a voltage between the anode and the cathode; (d) collecting the methanol from the anode chamber.

[0070] In another embodiment, the process further produces isopropanol.

[0071] In one embodiment, the electrochemical catalyst is Co 0.6 Ni 0.4 Fe2O4.

[0072] In one embodiment, the voltage is between 0.5 V and 1.5 V.

[0073] In one embodiment, the present disclosure also relates to a method for producing ammonia from nitrogen gas (N2) in an electrochemical process, the process comprising (a) introducing ammonia into the cathode chamber of an electrochemical reactor, the cathode chamber including a cathode comprising the electrochemical catalyst of the present disclosure; (b) introducing an anolyte into the anode chamber of the electrochemical reactor, the anode chamber including an anode; (c) Introducing a voltage between the anode and the cathode to reduce at least a part of the nitrogen gas to ammonia; (d) Collecting ammonia from the cathode chamber.

[0074] In another embodiment, the electrochemical catalyst is Co 0.8 Ni 0.2 Fe2O4.

[0075] In one embodiment, the voltage is between 0.5 V and 1.5 V.

[0076] In another embodiment, the catalyst of the present disclosure has a dual use and is useful as an anode and a cathode in an electrochemical process for producing methanol from methane and ammonia from nitrogen gas in an electrochemical process. The process comprises: (a) Introducing methane into the anode chamber of an electrochemical reactor, wherein the anode chamber comprises an anode comprising the electrochemical catalyst of the present disclosure; (b) Introducing ammonia into the cathode chamber of the electrochemical reactor, wherein the cathode chamber comprises a cathode comprising the electrochemical catalyst of the present disclosure; (c) Introducing a voltage between the anode and the cathode to oxidize at least a part of the methane in the anode chamber to methanol and reduce at least a part of the nitrogen gas in the cathode chamber to ammonia; (d) Collecting methanol from the anode chamber and ammonia from the cathode chamber.

[0077] In one embodiment, the electrochemical catalyst in the anode chamber is Co 0.6 Ni 0.4 Fe2O4.

[0078] In one embodiment, the electrochemical catalyst in the cathode chamber is Co 0.8 Ni 0.2 Fe2O4.

[0079] In one embodiment, the voltage is between 0.5 V and 1.5 V.

[0080] Although the present disclosure has been described in conjunction with its specific embodiments, it will be apparent to those skilled in the art that many alternatives, modifications, and variations will be apparent. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims. In addition, any reference or identification of a reference in this application should not be construed as an admission that such reference is available as prior art to the present disclosure.

Examples

[0081] The operation of the present disclosure is shown by the following representative examples. It will be apparent to those skilled in the art that many details of the examples may be changed while practicing the disclosure described herein.

[0082] Experimental section

[0083] Chemicals

[0084] Nickel(II) nitrate hexahydrate (99%, Ni(NO3)2·6H2O), cobalt(II) nitrate hexahydrate (98%, Co(NO3)2·6H2O), sodium citrate (99%, Na3C6H5O7), potassium hexacyanoferrate(III) (99% + , K4Fe(CN)6), sodium sulfate (99%, Na2SO4), sodium carbonate (99% + , Na2CO3), sodium hydroxide (97% + , NaOH), sodium salicylate (99%, C7H5O3Na), sodium hypochlorite (5%, NaClO), sodium nitroferricyanide(III) (99% + , C5FeN6Na2O), hydrazine (98% + , N2H4), and ammonium chloride (99% + , NH4Cl) were purchased from Sigma-Aldrich Chemical Reagent Ltd. Nafion (1 wt%) solution, hydrogen peroxide (30%, H2O2), sulfuric acid (99% +) Methanol and ethanol were purchased from Aladdin Ltd. All reagents were of analytical grade and used without further purification. Also, the anion exchange membrane (AEM) was purchased from DuPont (N2050TX, thickness: 0.3 mm). The deionized (DI) water (18.2 MΩ cm) used in all experiments was obtained from a Nanopure Diamond™ ultrapure water system.

[0085] Synthesis of NiFe PBA NC template: Uniform Ni-Fe PBA nanocubes (NCs) were synthesized by the method reported by the inventors. 4 In a typical procedure, 6 mmol of Ni(NO3)2·6H2O and Na3C6H5O7 were dissolved in 200 mL of deionized (DI) water to form Solution A. At the same time, 4 mmol of K4Fe(CN)6 was dissolved in another 200 mL of DI water to form Solution B. Subsequently, Solution B was added dropwise to Solution A over 20 min while magnetically stirring. Then, the mixed solution was aged at room temperature for 24 h. Thereafter, it was centrifuged and collected, washed with water and ethanol, and the precipitate was dried at 60 °C overnight.

[0086] Synthesis of NiFe2O4 and NiFe2O4-N / C NC: Two as-prepared NiFe PBA samples (200 mg each) were further pyrolyzed at 350 °C for 2 h in air and Ar atmospheres, respectively, with a heating rate of 2 °C min -1 . After cooling, 110.8 mg and 112.4 mg of NiFe2O4 and NiFe2O4-N / C NC were obtained, respectively. The catalyst carbonization yield was calculated according to the following formula.

[0087] Catalyst yield (%) = (m 炭化 / m 触媒前駆体 ) * 100%

[0088] Synthesis of CoNiFe-x PBA NC template: CoNiFe-x PBA nanocubes (NCs) were synthesized in a similar way to the synthesis of NiFe PBA. In a typical route, the Ni ions in NiFe PBA were replaced with Co content so that the total of Co and Ni precursors was 6 mmol, where x refers to the Co content (x = 0.2, 0.4, 0.6, 0.8). For example, to prepare a sample with x = 0.2 and 4.8 mmol of Ni(NO3)2·6H2O, 1.2 mmol of Co(NO3)2·6H2O and 9 mmol of Na3C6H5O7 were dissolved in 200 mL of DI water to form solution A. On the other hand, 4 mmol of K4Fe(CN)6 was dissolved in 200 mL of DI water to form solution B. Subsequently, solution B was added dropwise to solution A over 20 min while being magnetically stirred. Then, the mixed solution was aged at room temperature for 24 h. The precipitate was separated and purified by centrifugation and washing with DI water and ethanol, and then dried overnight at 60 °C to obtain CoNiFe-0.2 PBA NC, CoNiFe-0.4 PBA NC, CoNiFe-0.6 PBA NC and CoNiFe-0.8 PBA NC samples.

[0089] Co y Ni 1-y Fe2O4 and Co y Ni 1-y Synthesis of Fe2O4 and Co -1 Ni 0.2 Fe2O4-N / C NCs: Two of the prepared CoNiFe-x PBA NCs (200 mg each) were further pyrolyzed at 350 °C for 2 h at a heating rate of 2 °C min 0.8 in air and Ar atmospheres, respectively. After cooling, in air atmosphere, Co 0.4 Ni 0.6 Fe2O4 NC, Co 0.6 Ni 0.4 Fe2O4 NC, Co 0.8 Ni 0.2 Fe2O4 NC and Co 0.2 Ni 0.8 Fe2O4-N / C NC, Co0.4 Ni 0.6 Fe2O4-N / C NC, Co 0.6 Ni 0.4 Fe2O4-N / C NC and Co 0.8 Ni 0.2 144.2 mg, 154.2 mg, 134.6 mg and 127.2 mg corresponding to Fe2O4-N / C NC were obtained.

[0090] Synthesis of CoFe PBA NC template: CoFe PBA nanocubes (NC) were synthesized in the same way as the synthesis of NiFe PBA. 6 mmol of Co(NO3)2·6H2O and Na3C6H5O7 were dissolved in 200 mL of DI water to form solution A. At the same time, 4 mmol of K4Fe(CN)6 was dissolved in another 200 mL of DI water to form solution B. Then, solution B was dropped into solution A over 20 min while being magnetically stirred. After that, the mixed solution was aged at room temperature for 24 h. Then, it was collected by centrifugation, washed with water and ethanol, and the precipitate was dried at 60 °C overnight. The obtained sample was named CoFe PBA NC.

[0091] Synthesis of CoFe2O4 and CoFe2O4-N / C NC: Two (200 mg) of the as-prepared CoFe PBA NC were further pyrolyzed at 350 °C for 2 h at a heating rate of 2 °C min -1 in air atmosphere and Ar atmosphere, respectively. After cooling, 107.8 mg and 124.2 mg of CoFe2O4 and CoFe2O4-N / C NC were obtained, respectively.

[0092] Electrochemical measurement: The as-prepared Co y Ni 1-y Fe2O4-N / C and Co y Ni 1-yThe electrochemical properties of the Fe2O4-N / C catalyst were evaluated in a single cell (30 mL) with a necessary gas inlet system using an electrochemical workstation (Voltalab Potentiostat PGZ301). Each of the 5 mg of the prepared samples was dispersed in a mixed solution of 480 μL of ethanol, 480 μL of water, and 40 μL of Nafion (0.5 wt%) for 60 min by continuous ultrasonic treatment. The obtained catalyst ink (10 μL) was applied to a well-polished and washed glassy carbon electrode (φ3 mm, 0.071 cm 2 ) as the working electrode. A saturated Ag / AgCl and a graphite rod (φ3 mm) were used as the reference electrode and the counter electrode, respectively. For the nitrogen reduction reaction (NRR), before the electrochemical experiment, ultrapure nitrogen gas (99.999%) was purged into the electrolyte for at least 20 min to saturate it. 0.1 M Na2SO4 was selected as the electrolyte for all electrochemical nitrogen reduction experiments. To test the CH4 oxidation activity, ultrapure CH4 gas (99.999%) was purged into a 0.5 M Na2CO3 solution used as the electrolyte for the CH4 oxidation reaction. To evaluate the hydrogen generation behavior and other interferences, measurements were carried out under argon saturation conditions and open circuit potential conditions, respectively.

[0093] Linear sweep voltammetry (LSV) was used to evaluate the catalytic activity under Ar saturation conditions, N2 saturation conditions, and CH4 saturation conditions (sweep rate: 20 mV s -1 ). To determine the electrochemical surface area (ECSA) of these catalysts, cyclic voltammograms (CV) of these electrode catalysts were recorded in the double layer region under different conditions and at different scan rates (10, 20, 30, 40, 50, 60, 70, 80, 90, 100 mV s -1 ) for NRR (electrolyte: 0.1 M Na2SO4) and CH4 reduction (electrolyte: 0.5 M Na2CO3), respectively. The charge transfer resistances of NRR and DMC were investigated using electrochemical impedance spectroscopy (EIS) (10 -2 ~10 5 Hz). All experiments were carried out at room temperature (20 ± 2 o °C).

[0094] As shown in Fig. 1a, the field emission scanning electron microscope (FE-SEM) image shows that the hollow Ni-Fe NCs were successfully synthesized with an average size of 208 nm by the Prussian blue analogue (PBA) method (Fig. 1b). The weight loss of the template was examined by thermogravimetric analysis. As shown in Fig. 1c, the first stage of weight loss at about 80 °C could be explained by the loss of surface water molecules. The weight loss in the second stage (340 °C) was considered to be due to the final conversion of the PBA structure to metal oxides. As shown in Scheme 1, by regulating different Co / Ni ratios and Co y Ni 1-y The thermal conversion of Fe-PBA converts the CN - groups of PBA into an N-doped carbon layer (N / C), where the Co, Ni, and Fe species are converted into CoNiFe oxides. 32 Also, with the increase in the Co doping amount, the color of the CoNiFeO-N / C-x (x refers to the Co ratio, 0, 0.2, 0.4, 0.6, 0.8, and 1) catalyst ink became dark brown (Fig. 1d). Considering the function of the carbon layer in the electrochemical reaction, catalysts without carbon were also examined, and Co y Ni 1-y These catalysts of Fe-PBA were aged at 350 °C under air conditions to form CoNiFeO-x catalysts.

Chemical formula

[0095] The morphology of the as-prepared CoNiFe catalysts was examined by FE-SEM. As shown in Figure 2, with the increase in Co content, they showed a similar morphology of nanocubes (NC) when treated under Ar conditions, but the dimensions (Figure 3) and microstructure of the CoNiFe-N / C-x catalysts changed significantly due to the growth of the carbon layer. On the other hand, when treated under air conditions, as shown in Figure 4, they maintained a similar skeleton, and the surface of the CoNiFe-x catalysts became cleaner without generating a carbon layer, suggesting that the carbon layer could be removed by air-conditioning treatment. All CoNiFe PBA samples showed higher yields when treated under Ar conditions than under air conditions (Table 1), and it was further confirmed that a carbon layer was formed on the surface of the CoNiFe catalysts by Ar pyrolysis. Naturally, with the increase in Co content, both yields showed a similar distribution trend, which is considered to be due to the metal-support interaction. 33 Also, the average size of the CoNiFe catalysts was calculated and analyzed in Figure 5a, which showed a positive relationship with the Co atomic content. As shown in Figure 5b, with the addition of Co, the dimensions of these NCs with carbon layers increased from 207 nm to 640 nm. Without a carbon layer, it expanded from 162 nm to 475 nm, indicating that the size variation was mainly due to the formation of the carbon layer. The elemental composition of the CoNiFe-N / C catalysts was examined using an energy-dispersive X-ray analyzer (EDS) (Table 2), which explained that N-doped carbon was generated from CoNiFe PBA.

[0096] To investigate the Co / Ni ratio catalysts for electrochemical oxidation-reduction performance, linear sweep voltammetry (LSV) was used to evaluate the electrochemical activity for NRR and DMC. As shown in Figures 6a and 6b and Figures 7 and 8, the cathodic scans of the LSV of a series of Co / Ni composition ratio catalysts were recorded in Ar-saturated and N2-saturated 0.1 M Na2SO4 solutions for comparison, revealing that the composition of CoNiFe and the carbon layer support strongly affected the NRR activity. Figures 7f and 8f show the current density difference of the LSV measured in N2-saturated electrolyte and Ar-saturated electrolyte, Co 0.8 Ni 0.2It was revealed that the Fe-N / C catalyst exhibited the highest catalytic activity towards NRR. On the other hand, regarding the performance of CH4 oxidation operating in Ar-saturated and CH4-saturated 0.5 M Na2CO3 electrolytes, in Figures 6c and 6d, both CoNiFe-N / C-0.6 and CoNiFe-0.6 showed high CH4 electrochemical oxidation behavior. As shown in Figures 9 and 10, the LSV curves also indicated that the anodic current density of the CoNiFe-N / C catalyst was significantly improved compared to the CoNiFe catalyst. Compared with the sample without a carbon layer, the calibrated curve further showed that the onset CH4 oxidation potential in CoNiFe-N / C was low, with a minimum of 0.49 V vs. Ag / AgCl for CoNiFe-0.4. The onset potential of CoNiFe-N / C was 0.54 V, which showed a significant anodic current density for CH4 oxidation. Overall, the CoNiFe-N / C-0.6 catalyst was used as the optimized electrode for the CH4 oxidation reaction. Based on the above data and analysis, the carbon layer support with CoNiFe oxide is advantageous, especially for improving the electrochemical performance of NRR and DMC.

[0097] To further investigate the crystal structures of these catalysts, transmission electron microscopy (TEM), crystal model construction, and X-ray diffraction patterns (XRD) were used. In the TEM images (Figure 11), the optimized CoNiFe-N / C-0.8 and CoNiFe-N / C-0.6 catalysts showed a cubic structure composed of nanoparticles, and the carbon film was also easily visible. The high-resolution TEM (HRTEM) images (Figures 11b and 11e) showed lattice fringes of 0.209 nm, 0.252 nm, and 0.482 nm, which could be attributed to the facets (002) of NiFe2O4, the facets (311) of Co y Ni 1-y Fe2O4, and the facets (111) of CoFe2O4, respectively. Furthermore, it was found that the lattice constant of the amorphous carbon was 0.342 nm at the edge of the cube corresponding to the (002) facet, which indicated that the crystal structure of the synthesized catalyst was Co y Ni 1-y Fe2O4-N / C. Co y Ni 1-The lattice fringes of yFe2O4 and CoFe2O4 intersected, indicating the occurrence of a heterojunction. Furthermore, the TEM mapping images demonstrated a uniform metal mixture of the Co, Ni, Fe composite material (Figs. 11c and 11f). This result verified that in the research of the present inventors, Co y Ni 1-y Fe2O4-N / C catalyst was successfully synthesized. Also, some lattice fringes were disrupted, suggesting the occurrence of some defects. Following these data, Co y Ni 1-y Fe2O4, Co y Ni 1-y Fe2O4-N / C and the corresponding adsorption models were constructed as shown in Fig. 12. In these models, the molecular linking group was considered as the main catalytic active site. Furthermore, the corresponding simulated XRD patterns were calculated and shown in Figs. 13a and 13b. As seen from Fig. 14a, the XRD patterns of the fabricated CoNiFe-N / C-x samples have characteristic peaks at 18.28°, 26.15°, 35.69° and 43.36° belonging to the facets (111) of CoFe2O4 (PDF # 22-1086), the facet (002) of N-doped carbon (PDF # 50-1249), the facets (311) and (400) of NiFe2O4 (PDF # 10-0325) respectively, which were consistent with the previous HRTEM results. Co y Ni 1-y Fe2O4-N / C catalyst was further examined by Raman spectroscopy (Fig. 14b). The two peaks at 2198 cm -1 and 2225 cm -1 of CoNiFe-x (except x≠1) were assigned to the vibrations of CN(Fe 2+ )-Ni 3+ / 2+ and CN(Fe 3+ )-Ni 2+ respectively, and the CoNiFe samples (except x≠0) have peaks at 2111 cm 2+ and 2143 cm 3+ / 2+ assigned to CN(Fe 3+ )-Co 2+ and CN(Fe -1 )-Co -1showed two similar signal peaks therein. Also, this corresponded to 1346 cm -1 and 1585 cm -1 which showed two weak signals.

[0098] Co y Ni 1-y The surface chemical state and bonding environment of the CoNiFe₂O₄-N / C samples were investigated using X-ray photoelectron spectroscopy (XPS) technology. In Fig. 15a, the full XPS survey of these catalysts determined the presence of Co, Ni, Fe, C, N, and O elements. The intensity of the Ni signal decreased with the increase in the Co ratio, which was consistent with the EDX analysis. The high-resolution XPS spectra of Co 2p, Ni 2p, Fe 2p, C 1s, and N 1s are shown in Figs. 15b - f. The binding energies of these metals clearly changed with the change in the Co / Ni ratio. The peaks of Co and Ni changed to lower binding energies while the Fe signal changed to higher binding energies, indicating a strong trimetallic interaction effect. For the carbon layer, the C 1s peak of the CoNiFe-x samples was affected by the Co atom content. In the corresponding N 1s analysis (Fig. 15f), the N 1s signal had little variation. As shown in Fig. 16, the four fitted peaks at 398.4, 399.5, 400.4, and 403.2 eV from Co y Ni 1-y NiFe₂O₄-N / C were derived from pyridine-N, metal-N, pyrrole-N, and oxidized-N, respectively, confirming the formation of the N-doped carbon layer. After quantitatively calculating the content of each N group (Fig. 17a), it was found that the higher the metal-N ratio, the more favorable it was for DMC and NRR, and the more pyridine-N species, the better the performance of DMC. In Fig. 17b, the O 1s plot showed significant changes in intensity and curve shape (Fig. 18). The O 1s signal corresponded to lattice oxygen (O Latt , O-I) with the metal, oxygen deficiency (O V , O-II), and surface-adsorbed oxygen (O ad, it could be divided into four peaks at 530.7, 531.9, 532.8, and 534.9 eV corresponding to O-III) and C-O-H (O-IV). Furthermore, the ratio of each oxygen species was calculated in Fig. 17c because the surface-adsorbed oxygen groups play an important role in the electrochemical performance. Vacancy engineering has shown to be a promising strategy for enhancing the activity of oxygen vacancies in the oxygen evolution reaction (OER). Surprisingly, in this study, an increase in oxygen vacancies did not seem to improve the performance of DMC. As shown in Fig. 17d, the ratio of the O Latt / O V curve shows a volcano-like trend, revealing that the maximum value of O Latt / O V is favorable for the improvement of NRR and DCM. This may be due to the internal regulation effect of the ternary metal that inhibits the OER performance.

[0099] To evaluate the rate-determining steps of NRR and DCM on the CoNiFe-N / C-x catalyst surface, electrochemical impedance spectroscopy (EIS) was performed to analyze the charge transfer under redox conditions. As shown in Figs. 19a - 19c, the CoNiFe-N / C-0.8 catalyst showed the smallest semicircle, suggesting excellent charge transfer on the electrode surface in electrochemical NRR. Using an equivalent circuit model (the inset in Fig. 19c), the EIS curve was fitted to the corresponding values listed in Table 3. Among different ratios of Co / Ni, the Co 0.8 Ni 0.2 Fe2O4-N / C catalyst showed the lowest charge transfer resistance (R 0.8 Ni 0.2 ), R ct , and R ct(CE) , demonstrating that the optimized Co ct(AE) Fe2O4-N / C catalyst has excellent electron transfer ability in electrochemical NRR. On the other hand, EIS measurements conducted in 0.5 M Na2CO3 electrolyte (Figs. 19d - 19f) revealed that Co 0.6 Ni 0.4 Fe2O4-N / C had a lower R ct compared to catalysts with other Co / Ni ratios. The CoNiFe-N / C-0.6 catalyst had the smallest Rct The value (Table 4) was consistent with the LSV measurement, where the highest anodic current density was obtained. Co y Ni 1-y The electrochemically active surface area (ECSA) of the Fe2O4-N / C catalyst was estimated based on their double-layer capacitance. Figures 20 and 21 show Co 0.8 Ni 0.2 Fe2O4-N / C > Co 0.6 Ni 0.4 Fe2O4-N / C > Co 0.4 Ni 0.6 Fe2O4-N / C and Co 0.6 Ni 0.4 Fe2O4-N / C > Co 0.4 Ni 0.6 Fe2O4-N / C > Co 0.8 Ni 0.2 Fe2O4-N / C in the order of. Co for NRR 0.8 Ni 0.2 Fe2O4-N / C and Co for DMC 0.6 Ni 0.4 Fe2O4-N / C showed the highest ECSA suggesting that they had the most electrochemically active sites for NRR and DMC respectively. These electrochemical results indicate that the optimized catalysts for N2 reduction and CH4 oxidation are Co 0.8 Ni 0.2 Fe2O4-N / C and Co 0.6 Ni 0.4 Fe2O4-N / C respectively.

[0100] To evaluate the electrochemical activity of the prepared CoNiFe-based catalysts for N2 reduction and CH4 oxidation, they were carried out in a self-made double-chamber with a graphite rod as the counter electrode at room temperature. Figure 22 shows the chronoamperometric curve of CoNiFe-NC-0.8 for NRR indicating that the current density increased with the increase of the cathode potential from -1.2 V to -1.6 V as shown in the LSV results in Figure 3a. As shown in Figure 23a, Co 0.8 Ni 0.2 Fe2O4-N / C was 52.35 μg h at -1.4 V vs. Ag / AgCl-1 mg cat. -1 showed the highest NH₃ yield rate and a minimum FE of 15.35% at -1.3 V vs. Ag / AgCl. Compared with the CoNiFe-N / C-x samples at a potential of -1.4 V vs. Ag / AgCl (Figure 23b), only the catalysts with x = 0.4, 0.6, and 0.8 showed catalytic activity towards NRR, where Co 0.8 Ni 0.2 Fe₂O₄-N / C showed the highest NRR performance. To investigate the effect of the carbon layer, CoNiFe-x was also tested at the same potential of -1.4 V vs. Ag / AgCl. As shown in Figure 23c, the highest NH₃ yield rate of 23.22 μg h -1 mg cat. -1 was obtained with a highest FE of 10.14% for CoNiFe-0.6, while obtained with CoNiFe-0.2. The above results suggest that the interaction between Co y Ni 1-y Fe₂O₄ (y = 0.4, 0.6, and 0.8) and the carbon layer was beneficial for the improvement of NRR activity. Using the Watt and Crisp method, the possible formation of by-product (N₂H₄) was further investigated. Figure 24a shows a plot with a series of standard N₂H₄ indicating that the absorbance of N₂H₄ increased linearly with the increase of its concentration. However, as shown in Figure 24b, the UV-vis spectra of the solutions after 2 h electrolysis under Ar-saturated and N₂-saturated conditions were almost the same, with no change in absorbance, which confirmed that no N₂H₄ was generated during NRR with Co 0.8 Ni 0.2 Fe₂O₄-N / C and N₂ was reduced to NH₃. On the other hand, the by-product H₂ was detected by gas chromatograph (GC), which indicated that a hydrogen evolution reaction occurred at the cathode during NRR. CoO QDs / rGO, 43 CoFe₂O₄ / rGO, 44 single-atom Co-N / C, 45 NiCo₂O₄-N / C, 46 single-atom Fe / N-O / C, 47 and Fe-N / C-carbon nanotubes 48Some of the promising Co / Ni / Fe-based catalysts recently reported for NRR are compared in Table 5, and it was shown that Co 0.8 Ni 0.2 Fe2O4-N / C exhibited excellent N2 reduction activity.

[0101] Regarding CH4 oxidation in the anode chamber, Co 0.6 Ni 0.4 Fe2O4-N / C catalyst was tested in the anode chamber. The DMC products were collected after electrolyzing a CH4-saturated Na2CO3 solution at a potential of 0.8 V vs. Ag / AgCl for 2 h, 1 and analyzed by 1H nuclear magnetic resonance spectroscopy ( 1 1H HNMR). Methanol and 2-propanol were detected at yields of 722.6 mmol g cat. -1 h -1 and 306.4 mmol g cat. -1 h -1 respectively, as shown in Table 6. To fully utilize both the anodic and cathodic reactions, an integrated electrochemical system was assembled as shown in Fig. 23g, and the NRR in the cathode chamber with Co 0.8 Ni 0.2 Fe2O4-N / C and the DMC in the anode chamber with Co 0.6 Ni 0.4 Fe2O4-N / C were simultaneously measured. As shown in Fig. 23d, the 1H-NMR spectra of the products collected after electrolyzing for 2 h at different potentials showed a strong peak attributed to methanol. The intensity of this peak increased with the increase in potential from 0.8 V to 1.1 V, however, its density decreased when the potential further increased to 1.2 V. The byproduct 2-propanol was also observed in Fig. 23d. To further confirm the results, a control experiment was carried out for 2 h under the same conditions at open circuit potential, and methanol and 2-propanol were obtained 1 1 ​It was not detected in the 1H-NMR spectrum. The methanol formation rate and the 2-propanol formation rate were determined after electrolysis for 2 hours at different applied electrode potentials. As shown in FIGS. 23e and 25, methanol had the highest yield rate of 5070.7 mmol g cat. -1 h -1 obtained at 1.1 V vs. Ag / AgCl, respectively, and the minimum selectivity of 82.8% at 0.8 V vs. Ag / AgCl with a yield of 1925.47 mmol g cat. -1 h -1 was the main product. The FE of the products of methanol and 2-propanol is shown in FIG. 23f. The highest FE (9.02%) of the methanol product was achieved at 0.8 V, while the highest FE (6.94%) of 2-propanol formation was obtained at 0.9 V. As shown in Table 6, the yield and FE of methanol had a weak improvement for 2-propanol, but increased by 2.7 times and 2.4 times, respectively, compared to the case without NRR. FIG. 23h showed that the anodic current density measured from the LSV was improved to some extent. In addition, the influence of the integrated electrochemical system on NRR was examined (Table 7), showing that the NH3 yield rate was improved by 1.6 times. The stability of the two integrated electrochemical processes was further tested (FIG. 23i), showing high stability during 12 hours of electrolysis. The above results showed that the integrated electrochemical system was efficient for NRR in the cathode chamber and DMC in the anode chamber simultaneously. TiO2, 18 Ni-based catalyst, 15,23 ZrO2-based catalyst, and 13,14,24 CuO / CeO2 catalyst and other various anode materials (Table 8) for DMC, compared with the published research on DMC, 19 Co 0.6 Ni 0.4 the Fe2O4-N / C catalyst showed the best conversion from CH4 to CH3OH.

[0102] The fabricated Co y Ni 1-y To investigate the electronic structure and appropriate Co / Ni molar ratio of the Fe2O4-N / C NC catalyst, density functional theory (DFT) calculations were performed for Co 0.6 Ni0.4 Fe2O4-N / C and Co 0.8 Ni 0.2 The adsorption energies of DMC and NRR on Fe2O4-N / C were clarified. Combining the obtained electron paramagnetic resonance (EPR) spectra (Figure 26) with previous studies, 9 superoxide radicals ((O2 - ) were determined to be the active species, which demonstrated that Co 0.6 Ni 0.4 Fe2O4-N / C could selectively activate CH4 to form CH3. Furthermore, the adsorption energies of CH4 on the surfaces of CoNiFe-x and CoNiFe-N / C-x were calculated by Eq.S11 in the supporting information. As shown in Figure 27, Co 0.6 Ni 0.4 Fe2O4-N / C catalyst showed the lowest CH4 adsorption energy, which confirmed that it could function as a feasible catalyst for the effective activation of CH4. As demonstrated by Ma et al. 24 and Park et al. 13 in their studies, when the methanol product was peroxidized to 1-propanol or 2-propanol, formaldehyde or acetaldehyde intermediates were 1 readily detected by 1H-NMR spectra, however, signals regarding the formation of these two by-products were not present. 1 Based on the 1H-NMR results and the information reported in the literature, 22 the simultaneous reaction routes of DMC and NRR were summarized as follows.

[0103] Integrated electrochemical system:

[0104] Anode

[0105] CH4 + 2OH - → CH3OH + H2O + 2e - (1)

[0106] 3CH4 + 6OH - → CH3CHOHCH3 + 5H2O + 6e - (2)

[0107] 4OH - →2H2O + O2 + 4e - (3)

[0108] Cathode

[0109] N2 + 6H2O + 6e - →2NH3 + 6OH - (4)

[0110] 2H2O + 2e - →H2 + 2OH - (5)

[0111] In this integrated system, CH4 is selectively oxidized to methanol and 2-propanol by active radicals (O2 0.6 Ni 0.4 ) on the Co - Fe2O4-N / C catalyst in the anode chamber, which is attributed to the ternary metal-carbon layer interaction. The electrons generated in the anodic oxidation reactions (1)-(3) migrate to the cathode Co 0.8 Ni 0.2 Fe2O4-N / C that promotes the cathodic reduction (4) and (5). Subsequently, the possible mechanism of the combined electrochemical system is shown in Scheme 2. The electron transfer pathway between CH4 and NRR on the optimized catalyst was also investigated in Figure 28. For the oxidation of CH4 on the surface of Co 0.6 Ni 0.4 Fe2O4-N / C, the partial density of states (PDOS) shows a high concentration of electrons, and the shape of the electron orbital distribution also changes significantly after the adsorption of CH4 molecules. The overlap of the Co 0.6 Ni 0.4 -3d band, Fe 3d band and O 2p band suggests a strong bond between the ternary metal and oxygen. Also, after the activation of CH4, the electron density difference (EDD) mapping shows that the generated electrons are Co 0.6 Ni 0.4It was shown that it rapidly moved to the atom. Furthermore, the PDOS of the carbon layer (Figs. 29a and 29b) revealed that N-doped carbon played an important role in electron transfer as it provided an efficient electron transfer channel. Therefore, Co 0.6 Ni 0.4 and Fe were used as the main catalyst centers of DMC. Under NRR conditions, compared with the bulk catalyst, Co 0.8 Ni 0.2 in Co 0.8 Ni 0.2 Fe2O4-N / C, the intensity of the main peak decreased due to electron transfer with N2 (Fig. 28d). On the other hand, the fluctuations and overlays of the Co 0.8 Ni 0.2 -3d band and O-2p band suggested that the N2 molecule could be easily activated by the Co 0.8 Ni 0.2 active site and active oxygen group, which was consistent with the EDS mapping where the electrons released from Co 0.8 Ni 0.2 moved to N2. In Figs. 29c and 29d, the PDOS of the carbon layer from the Co 0.8 Ni 0.2 Fe2O4-N / C catalyst revealed that the intensity of the N-2p band was improved by the adsorption of N2, indicating that it promoted electron transfer. The DFT results demonstrated that the interaction between the ternary metal CoNiFe and the carbon layer significantly improved the performance of CH4 oxidation and N2 reduction.

Chemical formula

[0112] Electrochemical activity evaluation

[0113] Using a two-compartment cell separated by a pretreated cation exchange membrane (CEM), the products in each compartment were examined. When examining one reduction or oxidation reaction in one compartment, the other compartment was inspected without gas bubbling. For the NRR experiment, a graphite rod was used as the counter electrode. In the cathode compartment with N2 gas, the production of ammonia (NH3) was measured and quantitatively analyzed by the modified indophenol blue method.1,2 As follows, 2 mL of the cathode effluent was collected, and then 2 mL of Solution A (10.0 g of salicylic acid and 10.0 g of sodium citrate dissolved in 0.32 M NaOH solution), 1 mL of 0.05 M NaClO, and 0.2 mL of 0.01 g / mL -1 C5FeN6Na2O were successively added dropwise to the test solution. After 2 hours, the concentration was measured at 655 nm using a UV-vis spectrophotometer (Varian Cary 50). The UV-vis absorbance corresponding to standard NH4Cl of 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 μg / mL -1 was used to generate a calibration curve, and a clear linear relationship (y = 0.113x + 0.013, R 2 = 0.999) was obtained in three parallel experiments. Each time, the open circuit and Ar saturation state of the NRR experiment were adopted as the baseline for NH3 yield calculation to avoid any exogenous sources of nitrogen compounds. The optimized generation of TIFF2025522425000006.tif58 was calculated as follows.

[0114]

Number

[0115] The NH3 yield was calculated by the following formula.

[0116]

Number

[0117] The Faradaic efficiency was determined as follows.

[0118]

Number

[0119] In the anodic chamber, the CH4 oxidation reaction was investigated. Pure CH4 gas was continuously purged into a 0.5 M Na2CO3 electrolyte solution at a flow rate of 5 mL min -1 All gas products were detected by gas chromatography. The liquid products of CH4 electrochemical oxidation were measured by 600 MHz 1H nuclear magnetic resonance spectrometer (Bruker) 1 1H nuclear magnetic resonance spectrum ( 1 1H NMR). Before measurement, a 0.35 mL sample from the anode mass was mixed in 0.05 wt% tetramethylsilane (TMS) and 0.35 mL of D2O. The yields, FEs, corresponding selectivities, and CH4 conversion rates of the products were calculated as follows.

[0120] Yield (mmol g cat. -1 h -1 ) = mmol of product / g of catalyst / h of reaction time (S4)

[0121] FE(CH3OH, %) = 0.1929 * n(CH3OH, μmol) * 100% / Q (S5)

[0122] FE(CH3CHOHCH3, %) = 0.1929 * n(CH3CHOHCH3, μmol) * 100% / Q (S6)

[0123] Selectivity of CH3OH = 100% * n(CH3OH) / (n(CH3OH) + n(CH3CHOHCH3) (S7)

[0124] Selectivity of CH3CHOHCH3 = 100% * n(CH3CHOHCH3) / (n(CH3OH) + n(CH3CHOHCH3) (S8) Here, Q is the total amount of charge.

[0125] The integrated reaction system was composed of two working electrodes and one reference electrode. Co 0.8 Ni 0.2 The Fe2O4-N / C catalysts and Co 0.6 Ni 0.4 The Fe2O4-N / C catalysts were used as working electrodes in the cathode chamber and the anode chamber, respectively. N2 gas and CH4 gas were purged into the corresponding electrolytes simultaneously. Considering the measurement of the current density, the reference electrode was used in the same chamber as the target reaction. After 2 hours of electrolysis, the corresponding anode electrolyte and cathode electrolyte were collected and further analyzed. Under open potential conditions, blank experiments including the blank GCE catalyst and the NiCoFe catalyst were conducted to eliminate interference.

[0126] Characterization of Nanomaterials

[0127] The morphologies of the CoNiFe-N / C catalyst and the CoNiFe catalyst were characterized using a field emission scanning electron microscope (FE-SEM) (FEI Quanta 250) and a high-resolution transmission electron microscope (HRTEM) (FEI Tecnai F30 electron microscope using an acceleration voltage of 200 kV). The crystal structure of the prepared catalyst was investigated using an X-ray diffractometer (D / max-2400, Japan, light source with a wavelength (λ) of 0.1541 nm) using Cu Kα radiation. Monochromatic Al K α X-ray photoelectron spectroscopy (XPS) (Scienta Omicron) with an x-ray source was used to analyze their chemical compositions and oxidation states. Raman spectra were recorded at 532 nm using a Raman spectrophotometer (Renishaw Canada Ltd.). Thermogravimetric (TG) analysis was performed using a QMA200M thermal analyzer (METTLER TOLEDO) under air conditions at a heating rate of 2 °C min -1 The radicals were detected via electron paramagnetic resonance (EPR) spectroscopy using a Bruker ECS106X band spectrometer (Bruker A200, Germany). The gas products were transferred using a gas-tight syringe (Hamilton) and examined using a gas chromatograph (GC, Shimadzu, GC-2014, column: silica gel) equipped with a thermal conductivity detector (TCD).

[0128] Theoretical calculation

[0129] To investigate the electronic structure and electron transfer in the NRR and CH4 oxidation systems, Co with one layer of the carbon structure model y Ni 1-y Fe2O4 and Co y Ni 1-y Fe2O4-N / C was constructed based on the NiFe2O4 template. The optimization of the constructed structure was enabled by CASTEP using the Perdew-Burke-Ernzerhof (PBE) function of the generalized gradient approximation (GGA). Also, the position of Co doping was considered as substituting Ni atoms with Co atoms. The A2×2×1 3D triclinic NiFe2O4 cell (a = 8.480 Å, b = 8.480 Å, c = 8.480 Å, α = β = γ = 90°) was used for doping and the addition of the carbon layer cell. A 2×1×1 k-point set and an energy cutoff of 320 eV were performed to optimize the geometric configuration of the model constructed with a medium k-point set. The convergence criteria were 1.0×10 -5 eV for energy and 0.05 eV Å for force -1 . The adsorption energy (E) was calculated as follows.

[0130]

Equation

[0131] The present disclosure has been described with reference to what are presently considered to be preferred examples, but it is to be understood that the application is not limited to the examples described herein. On the contrary, the present disclosure is intended to cover various modifications and equivalent configurations included within the spirit and scope of the appended claims.

[0132] All publications, patents, and patent applications mentioned in this specification are hereby incorporated by reference in their entirety, as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. In case a term in the present disclosure is defined differently in a document incorporated by reference into this specification, the definition provided in this specification shall function as the definition of that term.

[0133] Reference 1. Z. Wang, Y. Li, H. Yu, Y. Xu, H. Xue, X. Li, H. Wang and L. Wang, ChemSusChem, 2018, 11, 3480 - 3485.

[0134] 2. L. Xia, X. Wu, Y. Wang, Z. Niu, Q. Liu, T. Li, X. Shi, A. M. Asiri and X. Sun, Small Methods, 2018, 14, 1800251.

[0135] 3. S. Z. Andersen, V. Colic, S. Yang, J. A. Schwalbe, A. C. Nielander, J. M. McEnaney, K. Enemark - Rasmussen, J. G. Baker, A. R. Singh, B. A. Rohr, M. J. Statt, S. J. Blair, S. Mezzavilla, J. Kibsgaard, P. C. K. Vesborg, M. Cargnello, S. F. Bent, T. F. Jaramillo, I. E. L. Stephens, J. K. Norskov and I. Chorkendorff, Nature, 2019, 570, 504 - 508.

[0136] 4. L. Zeng, X. Li, S. Chen, J. Wen, W. Huang, and A. Chen, J. Mater. Chem. A, 2020, 8, 7339 - 7349.

[0137] 5. X. Han, C. S. Gerke, S. Banerjee, M. Zubair, J. Jiang, N. M. Bedford, E. M. Miller, and V. S. Thoi, ACS Energy Lett., 2020, 5, 3237 - 3243.

[0138] 6. K. Chu, Y.-p. Liu, Y.-b. Li, H. Zhang, and Y. Tian, J. Mater. Chem. A, 2019, 7, 4389 - 4394.

[0139] 7. M. I. Ahmed, S. Chen, W. Ren, X. Chen, and C. Zhao, Chem. Commun., 2019, 55, 12184 - 12187.

[0140] 8. J. Hou, M. Yang, and J. Zhang, Nanoscale, 2020, 12, 6900 - 6920.

[0141] 9. S. Luo, X. Li, B. Zhang, Z. Luo, and M. Luo, ACS Appl. Mater. Interfaces, 2019, 11, 26891 - 26897.

[0142] 10. B. Yang, W. Ding, H. Zhang, and S. Zhang, Energy Environ. Sci., 2021, 14, 672 - 687.

[0143] 11. K. Chu, Y.-p. Liu, Y.-b. Li, Y.-l. Guo, and Y. Tian, ACS Appl. Mater. Interfaces, 2020, 12, 7081 - 7090.

[0144] 12. K. Lu, F. Xia, B. Li, Y. Liu, I. B. Abdul Razak, S. Gao, J. Kaelin, D. E. Brown and Y. Cheng, ACS Nano, 2021.

[0145] 13. K. Zhao, X. Quan, Y. Su, X. Qin, S. Chen and H. Yu, Environ. Sci. Technol., 2021.

[0146] 14. F. Lai, J. Feng, X. Ye, W. Zong, G. He, C. Yang, W. Wang, Y.-E. Miao, B. Pan, W. Yan, T. Liu and I. P. Parkin, J. Mater. Chem. A, 2020, 8, 1652 - 1659.

[0147] 15. C. Ma, X. Yan, H. He, B. Liu and S. Yan, Sustain. Energy Fuels, 2021, 5, 2415 - 2418.

[0148] 16. J. H. Moon, M. Y. Lee, B. C. Park, Y. S. Jeon, S. Kim, T. Kim, M. J. Ko, K. H. Cho, K. T. Nam and Y. K. Kim, Small, 2021, e2103575.

[0149] 17. C. Li, Y. Fu, Z. Wu, J. Xia and X. Wang, Nanoscale, 2019, 11, 12997 - 13006.

[0150] 18. Y. Li, J. Li, J. Huang, J. Chen, Y. Kong, B. Yang, Z. Li, L. Lei, G. Chai, Z. Wen, L. Dai and Y. Hou, Angew. Chem. Int. Ed., 2021, 60, 9078 - 9085.

[0151] 19. W. Ye, Y. Yang, M. Arif, S. Yang, X. Fang, M. A. Mushtaq, X. Chen and D. Yan, ACS Sustain. Chem. Eng., 2020, 8, 15946 - 15952.

[0152] 20. Y. Wang, X. Cui, J. Zhao, G. Jia, L. Gu, Q. Zhang, L. Meng, Z. Shi, L. Zheng, C. Wang, Z. Zhang and W. Zheng, ACS Catal., 2018, 9, 336 - 344.

[0153] 21. W. Li, D. He, G. Hu, X. Li, G. Banerjee, J. Li, S. H. Lee, Q. Dong, T. Gao, G. W. Brudvig, M. M. Waegele, D. E. Jiang and D. Wang, ACS Cent Sci, 2018, 4, 631 - 637.

[0154] 22. Y. Song, Y. Zhao, G. Nan, W. Chen, Z. Guo, S. Li, Z. Tang, W. Wei and Y. Sun, Appl. Catal. B - Environ., 2020, 270, 118888.

[0155] 23. Z. Guo, W. Chen, Y. Song, X. Dong, G. Li, W. Wei and Y. Sun, Chinese J. Catal., 2020, 41, 1067 - 1072.

[0156] 24. Y. Liu, X. Zhu, Q. Zhang, T. Tang, Y. Zhang, L. Gu, Y. Li, J. Bao, Z. Dai and J.-S. Hu, J. Mater. Chem. A, 2020, 8, 8920 - 8926.

[0157] 25. M. Ma, C. Oh, J. Kim, J. H. Moon and J. H. Park, Appl. Catal. B - Environ., 2019, 259, 118095.

[0158] 26. M. Ma, B. J. Jin, P. Li, M. S. Jung, J. I. Kim, Y. Cho, S. Kim, J. H. Moon and J. H. Park, Adv. Sci., 2017, 4, 1700379.

[0159] 27. C. Oh, J. Kim, Y. J. Hwang, M. Ma, and J. H. Park, Appl. Catal. B - Environ., 2021, 283, 119653.

[0160] 28. J. Wu, J. H. Li, and Y. X. Yu, ACS Appl. Mater. Interfaces, 2021, 13, 10026 - 10036.

[0161] 29. J. Lee, J. Yang, and J. H. Moon, ACS Energy Letters, 2021, 893 - 899.

[0162] [Table 1]

[0163] [Table 2]

[0164] [Table 3]

[0165] [Table 4]

[0166] [Table 5]

[0167] [Table 6]

[0168] [Table 7]

[0169]

Table 8

Claims

1. 1. An electrochemical catalyst comprising: (i) a ternary metal oxide represented by the formula: 【Chemical 1】 wherein the catalyst is in the form of nanocubes, and x is an integer between 0.1 and 0.9 (ii) carbon.

2. The ternary metal oxide is Co ０．８ Ni ０．２ Fe ２ O ４ The electrochemical catalyst according to claim 1, wherein

3. The ternary metal oxide is Co ０．６ Ni ０．４ Fe ２ O ４ The electrochemical catalyst according to claim 1, wherein

4. 10. The electrochemical catalyst of claim 1, wherein the catalyst has XRD peaks at 18.28°, 26.15°, 35.69°, and 43.36°.

5. 2. The electrochemical catalyst of claim 1, wherein x is an integer between 0.01 and 0.

99.

6. 6. The electrochemical catalyst of claim 5, wherein x is about 0.20, about 0.40, about 0.60, or about 0.

80.

7. 10. The electrochemical catalyst of claim 1, wherein the carbon is elemental carbon.

8. 8. The electrochemical catalyst of claim 7, wherein the elemental carbon is graphite or graphene.

9. 10. The electrochemical catalyst of claim 1, wherein the carbon is in the form of a layer adjacent to the nanocubes.

10. 10. The electrochemical catalyst of claim 9, wherein the nanocubes with adjacent carbon layers have a dimension between 10 nm and 1000 nm.

11. 11. The electrochemical catalyst of claim 10, wherein the dimension of the nanocubes with adjacent carbon layers is between 500 nm and 700 nm.

12. 12. The electrochemical catalyst of claim 11, wherein the dimension of the nanocubes with adjacent carbon layers is between 600 nm and 700 nm.

13. 13. The electrochemical catalyst of claim 12, wherein the dimension of the nanocube with the adjacent carbon layers is between 640 nm.

14. 1. A method for producing methanol from methane in an electrochemical process, the process comprising: (e) introducing methane into an anode chamber of an electrochemical reactor, the anode chamber comprising an anode comprising the electrochemical catalyst according to any one of claims 1 to 13; (f) introducing catholyte into a cathode compartment of the electrochemical reactor, the cathode compartment containing a cathode; (g) oxidizing at least a portion of the methane to methanol by introducing a voltage between the anode and the cathode; (h) collecting the methanol from the anode chamber.

15. 15. The method of claim 14, wherein the process further produces isopropanol.

16. The electrochemical catalyst is Co ０．６ Ni ０．４ Fe ２ O ４ The method of claim 14, wherein

17. 15. The method of claim 14, wherein the applied potential is between 0.2 V and 2.5 V vs. Ag / AgCl.

18. Nitrogen gas (N ２ ), said process comprising: (e) introducing ammonia into a cathode chamber of an electrochemical reactor, the cathode chamber comprising a cathode comprising the electrochemical catalyst according to any one of claims 1 to 13; (f) introducing anolyte into an anode compartment of the electrochemical reactor, the anode compartment containing an anode; (g) reducing at least a portion of the nitrogen gas to ammonia by applying a voltage between the anode and the cathode; (h) collecting the ammonia from the cathode chamber.

19. The electrochemical catalyst is Co ０．８ Ni ０．２ Fe ２ O ４ 19. The method of claim 18, wherein:

20. 19. The method of claim 18, wherein the applied potential is between 0.0 V and −2.0 V vs. Ag / AgCl.

21. 1. A method for producing methanol from methane and ammonia from nitrogen gas in an electrochemical process, the process comprising: (e) introducing methane into an anode chamber of an electrochemical reactor, the anode chamber comprising an anode comprising the electrochemical catalyst according to any one of claims 1 to 13; (f) introducing ammonia into a cathode chamber of the electrochemical reactor, the cathode chamber comprising a cathode comprising the electrochemical catalyst according to any one of claims 1 to 13; (g) applying a voltage between the anode and the cathode to oxidize at least a portion of the methane in the anode chamber to methanol and reduce at least a portion of the nitrogen gas to ammonia in the cathode chamber; (h) collecting the methanol from the anode chamber and the ammonia from the cathode chamber.

22. The electrochemical catalyst in the anode chamber is Co ０．６ Ni ０．４ Fe ２ O ４ 22. The method of claim 21, wherein:

23. The electrochemical catalyst in the cathode chamber is Co ０．８ Ni ０．２ Fe ２ O ４ 22. The method of claim 21, wherein:

Images