A method for protecting an indium- indium oxide heterojunction electrocatalyst with carbon nitride

Abstract

The application discloses a method for protecting an indium-indium oxide heterojunction electrocatalyst. First, indium oxide is synthesized by a simple solvothermal method, then a nitrogen-doped carbon layer is deposited on the surface of the indium oxide by a vapor deposition method, and finally, the indium oxide is in-situ formed into an indium-indium oxide heterojunction catalyst through an electrochemical in-situ reduction treatment. The indium and the nitrogen-doped carbon layer coated on the surface form a Schottky barrier to actively limit the excessive transmission of electrons to the indium oxide, optimize the local electron distribution, realize self-limiting reduction, stabilize the indium-indium oxide heterojunction, provide more active sites for a CO2 electrocatalytic reaction process, and realize excellent electrocatalytic activity and selectivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of CO2 electrocatalytic reduction, and particularly relates to a method for protecting an indium-indium oxide heterojunction electrocatalyst. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of providing an understanding of the general context of the application, and is not necessarily recognized as prior art by the patent practitioner.

[0003] The electrocatalytic carbon dioxide reduction technology (CO2RR) is attracting attention because of its dual benefits of converting CO2 into high-value carbon-based fuels (such as formic acid, ethylene, and other C1-C2 compounds) under mild conditions. Therefore, it is urgent to design advanced electrocatalysts with high activity to achieve efficient conversion and utilization of CO2.

[0004] The p-block metal indium has low toxicity and environmental friendliness, and its unique oxygenophilic property tends to adsorb formic acid intermediates, and is considered to be one of the most potential catalysts for the electrocatalytic synthesis of formic acid from CO2. Generally, its excellent activity is mainly attributed to the heterostructure formed by the metal and its oxide state, which can effectively inhibit the hydrogen evolution reaction and reduce the CO2 activation energy. However, the metal oxide will undergo self-reduction during the electroreduction process, and all of them will be converted into metal sites, which cannot maintain the stability of the metal-metal oxide heterostructure, resulting in a decrease in the number of active sites at the heterojunction, and a decrease in catalytic activity and product selectivity. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a method for protecting an indium-indium oxide heterojunction electrocatalyst, which combines chemical vapor deposition and electrochemical in-situ reduction technology to solve the problem that indium oxide is easily reduced to metal indium at the CO2 reduction potential, the metal-metal oxide heterostructure is unstable, the number of active sites at the heterojunction is reduced, and the CO2 electrocatalytic activity and selectivity are reduced.

[0006] The technical scheme adopted by the present application is as follows:

[0007] Firstly, the present application discloses a method for protecting an indium-indium oxide heterojunction electrocatalyst, comprising the following steps:

[0008] (1) Dissolve indium nitrate, citric acid and urea in deionized water in sequence, stir uniformly until a colorless transparent solution is formed, transfer the solution to a reaction kettle for hydrothermal reaction, and after natural cooling, centrifuge, wash and dry to obtain indium hydroxide nanospheres, which are placed in a muffle furnace for high-temperature calcination to obtain indium oxide nanospheres;

[0009] (2) Using chemical vapor deposition method, melamine and indium oxide nanospheres are respectively placed in the upstream and downstream positions of the nitrogen atmosphere tube furnace, and during the high-temperature calcination process, melamine is converted into nitrogen-doped carbon and deposited in situ on the surface of the indium oxide nanospheres, thereby obtaining nitrogen-doped carbon-coated indium oxide nanospheres;

[0010] (3) Using electrochemical in-situ reduction technology, the nitrogen-doped carbon-coated indium oxide nanospheres are dispersed in a water-ethanol mixed solution, and a Nafion binder is added to obtain an electrode slurry, which is coated on the surface of carbon paper as a cathode electrode. In a three-electrode system, the nitrogen-doped carbon-coated indium oxide nanosphere electrode sheet is subjected to in-situ electrochemical reduction treatment using chronopotentiometry, and a nitrogen-doped carbon-coated indium-indium oxide heterojunction electrocatalyst is obtained.

[0011] Further, in step (1), the mass ratio of indium nitrate to citric acid is 1:2, and the mass ratio of indium nitrate to urea is 1:2.5.

[0012] Further, in step (1), the hydrothermal reaction temperature is 140℃, and the reaction time is 12 h.

[0013] Further, in step (1), the washing refers to washing with water and ethanol in sequence, respectively.

[0014] Further, in step (1), the drying temperature is 60-80℃, and the drying time is 8-12h.

[0015] Further, in step (1), the muffle furnace calcination temperature is 500℃, and the time is 1h.

[0016] Further, in step (2), the mass ratio of melamine to indium oxide nanospheres is 30~10:10~1, preferably 20:1.

[0017] Further, in step (2), the tube furnace calcination temperature is 500℃, and the time is 1~3h, preferably 2h.

[0018] Further, in the vapor deposition method of step (2), during the high-temperature calcination process, the nitrogen atmosphere flow rate is 10~30 mL / min.

[0019] Further, in step (3), the volume ratio of water to ethanol in the water-ethanol mixed solution is 1:3, and the volume of the Nafion binder is 5~10% of the total volume of the water-ethanol mixed solution.

[0020] Further, the step (3) electrochemical reduction treatment adopts a three-electrode system, the nitrogen-doped carbon-coated indium oxide nanosphere electrode material is used as a working electrode, silver / silver chloride is used as a reference electrode, and a platinum plate is used as a counter electrode, an H-type electrolytic cell is used for in-situ electrochemical treatment, a Nafion 117 proton exchange membrane is used to separate the cathode and anode chambers, the electrolyte in the two chambers is 0.5 M potassium bicarbonate, CO2 is continuously introduced into the cathode, and a current of-10~-50 mA cm is applied by a chronopotentiometric method for 1 hour to obtain the nitrogen-doped carbon-coated indium-oxide nanosphere heterojunction electrocatalyst. -2

[0021] In a second aspect of the present application, the nitrogen-doped carbon-coated indium-oxide heterojunction electrocatalyst prepared by the above method is provided.

[0022] In a third aspect of the present application, the application of the nitrogen-doped carbon-coated indium-oxide heterojunction electrocatalyst in a CO2 catalytic reduction reaction is provided.

[0023] Compared with the related art known to the present inventors, one of the technical solutions of the present application has the following beneficial effects:

[0024] The present application provides a method for protecting an indium-oxide heterojunction electrocatalyst. First, a nitrogen-doped carbon layer is deposited on the surface of the oxide by chemical vapor deposition. During the subsequent in-situ electrochemical reduction process, when part of the In2O3 is reduced to In, a Schottky barrier is formed at the interface between In and the nitrogen-doped carbon layer coated on the surface of In2O3, which actively limits the excessive transfer of electrons to In2O3, achieving self-limiting reduction. The in-situ formed In interacts with the nitrogen-doped carbon layer, maintaining the dynamic balance of the In-In2O3 heterojunction, stabilizing the active sites of the CO2 electrocatalytic reaction, and achieving excellent electrocatalytic activity and selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments illustrated in the drawings, and their descriptions, serve to explain the present application without limiting it improperly.

[0026] Figure 1 SEM image of In2O3 prepared for Example 1 of the present application.

[0027] Figure 2 SEM image of NC@In2O3-L prepared for Example 2 of the present application.

[0028] Figure 3 SEM image of NC@In2O3-M prepared for Example 3 of the present application.

[0029] Figure 4 ​SEM image of NC@In2O3-H prepared in Example 4 of the present application.

[0030] Figure 5 XRD patterns of In2O3 and NC@In2O3-M prepared in Example 1, 3 of the present application, respectively.

[0031] Figure 6 XRD patterns of In and NC@In-In2O3-M prepared in Example 5, 7 of the present application, respectively.

[0032] Figure 7 Linear scan voltammetry curves of In and NC@In-In2O3-M prepared in Example 5, 7 of the present application, respectively, in N2 and CO2 saturated electrolyte.

[0033] Figure 8 Product Faradic efficiency plots of (a) In, (b) NC@In-In2O3-L, (c) NC@In-In2O3-M and (d) NC@In-In2O3-H prepared in Example 5-8 of the present application. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed description is merely exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0035] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0036] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with specific examples.

[0037] Example 1

[0038] (1) 1.5 g of In(NO3)3·4.5H2O (4 mmol in conversion) was dissolved in 50 mL of H2O, and then 3.0 g (15 mmol in conversion) of citric acid was weighed and added to the above solution, and stirred for 10 min. Subsequently, 3.75 g of urea (62.5 mmol in conversion) was weighed and added to the above homogeneous solution, and continuous stirring was performed until a colorless transparent solution was formed.

[0039] (2) The mixed solution was transferred to a 100 mL high-pressure reactor and reacted at 140 °C for 12 h. After natural cooling to room temperature, the obtained product was washed with ethanol and deionized water for several times and dried at 80 °C overnight to obtain a white precipitate of the precursor.

[0040] (3) The white precipitate of the precursor was transferred to a muffle furnace and calcined at 500 °C for 1 h in air at a heating rate of 4 °C / min. After natural cooling, In2O3 nanospheres were obtained.

[0041] The final material obtained in Example 1 is marked as "In2O3".

[0042] Example 2

[0043] 300 mg of melamine and 30 mg of In2O3 in Example 1 were transferred to a tube furnace and placed upstream and downstream of the N2 gas flow, respectively. Using a gas deposition method, the N2-doped carbon-coated In2O3 nanosphere material was obtained by calcining at 500 °C for 1 h under N2 protection atmosphere, with a N2 gas flow rate of 15 mL / min.

[0044] The final material obtained in Example 2 is marked as "NC@ In2O3-L".

[0045] Example 3

[0046] 600 mg of melamine and 30 mg of In2O3 nanosphere material in Example 1 were transferred to a tube furnace and placed upstream and downstream of the N2 gas flow, respectively. Using a gas deposition method, the N2-doped carbon-coated In2O3 nanosphere material was obtained by calcining at 500 °C for 1 h under N2 protection atmosphere, with a N2 gas flow rate of 15 mL / min.

[0047] The final material obtained in Example 3 is marked as "NC@ In2O3-M".

[0048] Example 4

[0049] 900 mg of melamine and 30 mg of In2O3 nanosphere material in Example 1 were transferred to a tube furnace and placed upstream and downstream of the N2 gas flow, respectively. Using a gas deposition method, the N2-doped carbon-coated In2O3 nanosphere material was obtained by calcining at 500 °C for 1 h under N2 protection atmosphere, with a N2 gas flow rate of 15 mL / min.

[0050] The final material obtained in Example 4 is marked as "NC@ In2O3-H".

[0051] Example 5

[0052] Using In₂O₃, the material prepared in Example 1 above, as a catalyst, it was dispersed in a water-ethanol (v / v=1 / 3) mixed solution. Then, 5% Nafion conductive binder was added, and the mixture was ultrasonically mixed to obtain catalyst ink. This ink was coated onto the surface of carbon paper as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The working electrode was electrochemically treated using a chronopotential method in a 0.5 M KHCO₃ electrolyte with continuous CO₂ aeration at -25 mA cm⁻¹. -2 The reaction was carried out at a current density for 1 hour to obtain an elemental indium catalyst.

[0053] The material obtained in Example 5 is labeled "In".

[0054] Example 6

[0055] Using the material prepared in Example 2 above as a catalyst, it was dispersed in a water-ethanol (v / v=1 / 3) mixed solution, followed by the addition of 5% Nafion conductive binder. After ultrasonic mixing, the catalyst ink was obtained and coated onto the surface of carbon paper as the working electrode. A platinum sheet was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. The working electrode was electrochemically treated using a chronopotentiometric method in a 0.5M KHCO3 electrolyte with continuous CO2 aeration at -25 mA cm⁻¹. -2 The reaction was carried out at the current density for 1 hour to obtain a nitrogen-doped carbon-coated indium-indium oxide heterojunction electrocatalyst.

[0056] The material finally obtained in Example 6 is labeled "NC@In-In2O3-L".

[0057] Example 7

[0058] Using the material prepared in Example 3 above as a catalyst, it was dispersed in a water-ethanol (v / v=1 / 3) mixed solution, followed by the addition of 5% Nafion conductive binder. After ultrasonic mixing, the catalyst ink was obtained and coated onto the surface of carbon paper as the working electrode. A platinum sheet was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. The working electrode was electrochemically treated using a chronopotentiometric method in a 0.5M KHCO3 electrolyte with continuous CO2 aeration at -25 mA cm⁻¹. -2 The reaction was carried out at the current density for 1 hour to obtain a nitrogen-doped carbon-coated indium-indium oxide heterojunction electrocatalyst.

[0059] The material finally obtained in Example 7 is labeled "NC@In-In2O3-M".

[0060] Example 8

[0061] The material prepared in Example 4 above was used as catalyst, dispersed in a water-ethanol (v / v = 1 / 3) mixed solution, followed by the addition of 5% nafion conductive binder, and after ultrasonic mixing to obtain a catalyst ink, which was coated on the surface of carbon paper as a working electrode, a platinum plate as a counter electrode, and an Ag / AgCl electrode as a reference electrode. The working electrode was electrochemically treated in a 0.5 M KHCO3 electrolyte with continuous CO2 aeration by chronoamperometry at -25 mA cm -2 at a current density for 1 h to obtain a nitrogen-doped carbon-coated indium-indium oxide heterojunction electrocatalyst.

[0062] The final material obtained in Example 8 is marked as "NC@In-In2O3-H".

[0063] The sample materials prepared in the above examples were characterized as follows:

[0064] Product detection:

[0065] The gaseous products after CO2 electro-reduction were detected online using a gas chromatograph. Every 20 minutes, the reacted gas was introduced into the gas chromatograph for qualitative and quantitative analysis. The KHCO3 electrolyte after reaction was analyzed using a nuclear magnetic resonance spectrometer. 0.5 mL of the electrolyte after reaction was mixed with 0.1 mL of deuterium oxide, and 100 μL of dimethyl sulfoxide with a concentration of 6 mmol / L was added as an internal standard, and the water peak method was used for measurement.

[0066] Characterization results:

[0067] From the scanning Figure 1 electron microscopy (SEM) images of the indium oxide nanospheres prepared in Example 1, it can be seen that the morphology of the prepared indium oxide nanospheres is uniform and the structure is complete, and the surface is composed of fine particles. The diameter of the nanospheres is about 550 nm. As shown in the transmission electron microscopy (TEM) image, the surface of the nanospheres is covered with irregular particles. Figure 2 As shown in the transmission electron microscopy (TEM) image, the surface of the nanospheres is covered with irregular particles. Figure 3 As the amount of melamine increases, the nitrogen-doped carbon particles on the surface of the nanospheres grow and form a uniform and smooth covering layer. Figure 4 When the amount of melamine continues to increase, the nitrogen-doped carbon layer on the surface of the indium oxide further thickens, and due to the stress effect, it is squeezed and broken, with a nanolayer thickness of about 20 nm, and the fragmented structure will affect the performance of the subsequent CO2 electrocatalytic reduction reaction.

[0068] As shown in the transmission electron microscopy (TEM) image, the surface of the nanospheres is covered with irregular particles. Figure 5As shown, In2O3 and NC@In2O3-M have similar diffraction patterns, with strong diffraction peaks appearing at 30.5°, 35.4°, 45.6°, 51.0°, and 60.6°, mainly attributed to In2O3 (JCPDS 06-0416). However, compared to the diffraction peaks of In2O3, no obvious nitrogen-doped carbon diffraction peaks were found in NC@In2O3-M, possibly due to the low amount of nitrogen-doped carbon. Figure 6 As shown, after electrochemical in-situ reduction, NC@In2O3-M exhibits strong diffraction peaks near 32.9°, 36.3°, and 39.1°, which are attributed to elemental In (JCPDS 05-0642). This is due to the reduction of most of In2O3 to metallic In at a negative potential. However, weak In2O3 diffraction peaks can still be observed in the spectrum. This is because when some In2O3 is reduced to elemental In, a Schottky barrier forms at the interface between In and nitrogen-doped carbon, hindering further electron transport into the In2O3 interior. This causes the reduction reaction to spontaneously terminate after a certain amount of In is formed, thus protecting the active In2O3 species and maintaining the In-In2O3 coexistence structure, ultimately yielding the NC@In-In2O3-M heterojunction electrocatalyst. After undergoing the CO2 electroreduction reaction, all the oxidation peaks in the spectrum of In2O3 without nitrogen-doped carbon protection disappeared, indicating that it was completely reduced to metallic In. This demonstrates the crucial role of the nitrogen-doped carbon layer in protecting the indium-indium oxide heterostructure.

[0069] Using NC@In-In2O3-M and In as working electrodes, linear sweep voltammetry was performed in N2 and CO2-saturated 0.5 M KHCO3 solutions, respectively. Figure 7 As shown, the current densities of both samples in CO2-saturated electrolyte were higher than those in N2, indicating significant catalytic activity for CO2 reduction. NC@In-In2O3-M exhibited a higher current density, reaching 23 mA / cm² when an applied voltage of -1.2 V was applied. -2 This indicates that it possesses higher electrocatalytic activity. Subsequently, CO2 potentiostatic electrolysis tests were performed on NC@In-In2O3-L, NC@In-In2O3-M, NC@In-In2O3-H, and In with different nitrogen-doped carbon layer thicknesses deposited on the In2O3 surface. Figure 8As shown, the main product of CO2 electro-reduction is HCOOH, and the formic acid Faraday efficiency of the electrode gradually increases with the increase of applied voltage, among which the NC@In-In2O3-M has the largest increase, and the maximum value is 91.2% at-1.1V, and the C1 product Faraday efficiency is as high as 95.4%, while the maximum formic acid Faraday efficiency of In is only 88%, and the C1 product is also lower than 90%. In addition, the maximum formic acid Faraday efficiency of NC@In-In2O3-L and NC@In-In2O3-H is 88.8% and 86.5% respectively, and the maximum C1 product Faraday efficiency is 91.7% and 90.7% respectively, which all show that NC@In-In2O3-M has excellent CO2 electro-catalytic activity. When the nitrogen-doped carbon layer deposited on the surface of In-In2O3 is less, it is difficult for In and nitrogen-doped carbon to form an effective Schottky barrier, and a large amount of electrons are transported to the surface of oxygen species, which are reduced, so that the In-In2O3 heterojunction interface is affected, the number of active sites is less, and the electro-catalytic performance is reduced. When the nitrogen-doped carbon layer deposited on the surface of In-In2O3 is thick, CO2 molecules are difficult to be effectively adsorbed on the In-In2O3 heterojunction interface, and cannot be fully activated, at the same time, the thick shell is broken under stress, exposing more In2O3, and the oxygen species cannot be effectively protected, the In and In2O3 heterojunction interface is damaged, leading to further reduction of CO2 electrochemical performance. The CO and H2 Faraday efficiency of NC@In-In2O3-M is obviously less than that of other electrodes, which further confirms the excellent electro-catalytic product selectivity of NC@In-In2O3-M. In summary, the excellent performance of NC@In-In2O3-M is due to the nitrogen-doped carbon layer which can effectively protect the In-In2O3 heterojunction, the Schottky barrier formed between In and nitrogen-doped carbon actively limits the excessive transmission of electrons to In2O3, realizes self-limiting reduction, prevents it from being completely reduced to metallic indium in the process of CO2 electro-reduction, the oxide species existing on the surface and metallic indium form a heterojunction, which provides rich active sites for the reaction, and at the same time inhibits the occurrence of hydrogen evolution reaction, thereby showing excellent electro-catalytic activity and product selectivity.

[0070] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, which are all included in the protection scope of the present application.

Claims

1. A method for protecting an indium-indium oxide heterojunction electrocatalyst with carbon nitride, characterized in that, Includes the following steps: (1) Dissolve indium nitrate, citric acid and urea in deionized water one by one, stir until a colorless and transparent solution is formed, transfer it to a reaction vessel for hydrothermal reaction, and after natural cooling, centrifuge, wash and dry to obtain indium hydroxide nanospheres. Place them in a muffle furnace and calcine at high temperature to obtain indium oxide nanospheres. (2) Melamine and indium oxide nanospheres were placed at the upstream and downstream positions in a nitrogen atmosphere tube furnace, respectively. During the high-temperature calcination process, melamine was converted into nitrogen-doped carbon and deposited in situ on the surface of indium oxide nanospheres, thus obtaining nitrogen-doped carbon-coated indium oxide nanospheres. (3) Nitrogen-doped carbon-coated indium oxide nanospheres were dispersed in a water-ethanol mixed solution, and Nafion binder was added to mix and obtain an electrode slurry. The slurry was coated on the surface of carbon paper as a cathode electrode. In a three-electrode system, the nitrogen-doped carbon-coated indium oxide nanosphere electrode sheet was electrochemically reduced by chronopotential method to obtain a nitrogen-doped carbon-protected indium-indium oxide heterojunction electrocatalyst. In step (2), the mass ratio of melamine to indium oxide nanospheres is 20:1; In step (3), the current applied by the chronopotential method is -10 to -50 mA cm⁻¹. -2 The time is 1 hour.

2. The method for protecting indium-indium oxide heterojunction electrocatalysts with carbon nitride as described in claim 1, characterized in that, In step (1), the mass ratio of indium nitrate to citric acid is 1:2; the mass ratio of indium nitrate to urea is 1:2.

5.

3. The method for protecting indium-indium oxide heterojunction electrocatalysts with carbon nitride as described in claim 1, characterized in that, In step (1), the hydrothermal reaction temperature is 140℃ and the reaction time is 12 h.

4. The method for protecting indium-indium oxide heterojunction electrocatalysts with carbon nitride as described in claim 1, characterized in that, In step (1), the drying temperature is 60-80℃ and the drying time is 8-12h; In step (1), the calcination temperature in the muffle furnace is 500℃ and the time is 1h.

5. The method for protecting indium-indium oxide heterojunction electrocatalysts with carbon nitride as described in claim 1, characterized in that, In step (2), the calcination temperature in the tubular furnace is 500℃, and the time is 1~3h; In step (2) of the vapor deposition method, the nitrogen atmosphere flow rate is 10~30 mL / min during the high-temperature calcination process.

6. The method for protecting indium-indium oxide heterojunction electrocatalysts with carbon nitride as described in claim 1, characterized in that, In step (3), the volume ratio of water to ethanol in the water-ethanol mixture is 1:3, and the volume of Nafion binder is 5 to 10% of the total volume of the water-ethanol mixture.

7. The method for protecting indium-indium oxide heterojunction electrocatalysts with carbon nitride as described in claim 1, characterized in that, Step (3) Electrochemical reduction treatment uses a three-electrode system. Nitrogen-doped carbon-coated indium oxide nanospheres are used as the working electrode, silver / silver chloride is used as the reference electrode, and platinum sheet is used as the counter electrode. An H-type electrolytic cell is used for electrochemical treatment. A Nafion 117 proton exchange membrane is used to separate the cathode and anode chambers. The electrolyte in both chambers is 0.5 M potassium bicarbonate, and CO2 is continuously introduced into the cathode to obtain a nitrogen-doped carbon-coated indium-indium oxide nanosphere heterojunction electrocatalyst.

8. The nitrogen-doped carbon-coated indium-indium oxide heterojunction electrocatalyst prepared by any one of claims 1 to 7.

9. The application of the nitrogen-doped carbon-coated indium-indium oxide heterojunction electrocatalyst of claim 8 in the catalytic reduction of CO2.

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