Carbon electrode, preparation method thereof and hydrogen production process coupled with indirect oxidation of so2

Abstract

The application discloses a carbon electrode, a preparation method thereof and a hydrogen production process coupled with SO2 indirect oxidation reaction, and the carbon electrode is prepared by the following method: (1) performing plasma treatment on carbon paper to obtain an intermediate product; and (2) annealing the intermediate product for a set time. The process uses an electrolysis reaction device to electrolyze an electrolyte to produce hydrogen; the electrolysis reaction device is provided with a cathode working electrode and an anode working electrode; the electrolyte contains trivalent iron ions, and a reducing gas is continuously introduced into the electrolyte during electrolysis. The carbon electrode has the characteristics of large specific surface area, many surface active sites and strong surface hydrophilicity, and is particularly suitable for the hydrogen production process coupled with SO2 indirect oxidation reaction. The application continuously performs the oxidation-reduction reaction by using a special electrode, a reducing gas and Fe (III), and the oxidation-reduction reaction is coupled with the cathode, so that efficient hydrogen production can be realized at a low potential, the generation of oxygen is avoided, and the coupled production of waste gas treatment and hydrogen production is realized.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen energy, specifically relating to a carbon electrode, its preparation method, and a hydrogen production process coupled with SO2 indirect oxidation reaction. Background Technology

[0002] Currently, fossil fuels, as non-renewable energy sources, account for over 80% of total energy consumption, and this consumption process is accompanied by the emission of harmful gases (such as SO2) to the environment and humans. Industrial processes commonly use desulfurization technology to absorb SO2, utilizing ordinary activated carbon to adsorb SO2 or impregnating activated carbon or metal substrates with certain catalysts to cause a chemical reaction in the SO2, producing harmless substances such as salt and water. However, this method is costly.

[0003] Hydrogen possesses advantages such as high energy density, non-toxicity, and environmental friendliness, making it a promising renewable energy source. Water electrolysis is a commonly used technology for producing green hydrogen, where the integration of the anodic and cathodic reactions plays a crucial role in the efficient utilization of electrical energy throughout the electrocatalytic conversion process. The oxygen evolution reaction (OER) is a common anodic reaction in electrocatalysis, which can be coupled with cathodic reactions such as hydrogen evolution, carbon dioxide reduction, nitrogen reduction, and nitrate reduction. However, the kinetics of the anodic OER are slow, and water electrolysis requires a high potential (>1.23VRHE) to drive the OER, resulting in significant energy consumption and greatly limiting the overall electrocatalytic reaction rate.

[0004] Meanwhile, the carbon electrodes used in existing electrocatalytic hydrogen production processes have a small specific surface area, few surface active reaction sites, and poor hydrophilicity, making it difficult to meet the reaction requirements of hydrogen production processes. Summary of the Invention

[0005] In view of this, the purpose of this invention is to overcome the problems mentioned in the background art, such as the small specific surface area, few surface active reaction sites, and poor hydrophilicity of existing carbon electrodes, as well as the shortcomings and defects of excessive power consumption in traditional electrochemical hydrogen production processes. The invention provides a novel carbon electrode and an electrochemical hydrogen production process that can significantly reduce oxidation potential and overall production energy consumption while simultaneously treating waste gas.

[0006] The technical solution adopted by this invention to solve the technical problem is as follows:

[0007] A method for preparing a carbon electrode includes the following steps:

[0008] (1) The carbon paper is placed in a plasma reactor and subjected to plasma treatment using a radio frequency source in a protective atmosphere. After the treatment is completed, an intermediate product is obtained.

[0009] (2) Anneal the intermediate product in a protective atmosphere for a set time to obtain the processed carbon electrode.

[0010] The design concept of the above technical solution is that it uses plasma to treat and etch carbon paper. Electrons bombard neutral gas atoms, causing them to dissociate and generate plasma. Excited molecules, free radicals, and other active particles act on the surface of the carbon paper sample to produce an etching effect, roughening the surface of the carbon paper and forming many micro-pits. This increases the specific surface area of ​​the carbon paper and the number of active sites on the surface. At the same time, it enhances the hydrophilicity of the carbon paper surface, improves the wettability of the electrolyte on the electrode surface, and reduces the liquid junction resistance between the catalytic electrode interface and the electrolyte. This ensures that reactants can quickly reach the catalytic sites and undergo electrocatalytic reactions during the electrocatalytic process, making carbon paper a more suitable electrode for electrocatalytic hydrogen production processes.

[0011] As a further preferred embodiment of the above technical solution, the frequency of the radio frequency source in step (1) is 13.56MHz, the radio frequency power is 100~200W, and the plasma treatment time is 3~10min. The plasma treatment under the above parameters has the best etching effect on carbon paper.

[0012] As a further preferred embodiment of the above technical solution, the annealing temperature in step (2) is 300~600℃, and the annealing time is 1~2h. The annealing operation under the above parameters results in a more stable surface structure of the etched carbon electrode material.

[0013] As a further preferred embodiment of the above technical solution, the carbon paper is heat-treated at 350°C for 16 hours before plasma treatment. This pre-treatment process removes residual organic matter and other impurities from the surface of the carbon paper.

[0014] Based on the same technical concept, the present invention also provides a carbon electrode, which is prepared by the above-described preparation method.

[0015] Based on the same technical concept, the present invention also provides a process for producing hydrogen through indirect oxidation reaction coupling of SO2, which uses an electrolysis reactor to electrolyze an electrolyte to produce hydrogen; the electrolysis reactor is provided with a cathode working electrode and an anode working electrode; the electrolyte contains ferric ions, and a reducing gas is continuously introduced into the electrolyte during electrolysis; the anode working electrode is the aforementioned carbon electrode.

[0016] Based on the same technical concept, the present invention also provides a process for producing hydrogen through indirect oxidation reaction coupling of SO2, which uses an electrolysis reactor to electrolyze water to produce hydrogen; the electrolysis reactor is provided with a cathode working electrode and an anode working electrode, and the cathode working electrode and the anode working electrode are separated by a diaphragm; the anode electrolyte contains ferric ions, and a reducing gas is continuously introduced into the anode electrolyte during electrolysis; the anode working electrode is the aforementioned carbon electrode.

[0017] The design concept of the above technical solution is to address the problems of high power consumption and high cost in electrochemical hydrogen production processes caused by excessively high anodic oxidation potential and large potential difference between the two electrodes, as mentioned in the background technology. Existing technologies generally reduce the anodic oxidation potential by utilizing biomass oxidation. The working principle is that the electrochemical oxidation process of biomass can generate a lower anodic oxidation potential. The inventors discovered that the electro-oxidation process of metal ions often generates an anodic oxidation potential lower than that of conventional biomass oxidation. However, the oxidation process of these metal ions from low to high valence states is usually discontinuous, making... The electrochemical performance of the catalyst will continuously decline, thus failing to effectively solve the problem of excessively high anodic oxidation potential. This invention, however, by adding a reducing gas and ferric ions to the electrolytic cell, reduces ferric iron (Fe(III)) to ferrous iron (Fe(II)). Then, Fe(II) is electro-oxidized on the carbon electrode to obtain Fe(III), allowing the entire chemical chain oxidation reaction to proceed continuously. This replaces the oxygen evolution reaction, fundamentally changing the anodic reaction mechanism, reducing the electrolysis voltage, thereby improving energy utilization efficiency, reducing energy consumption and cost in hydrogen electrolysis, and avoiding oxygen generation, thus eliminating safety hazards at the source. However, the above reaction places high demands on the anodic electrode. If the electrode has a small specific surface area, insufficient active reaction sites, or poor hydrophilicity, it is difficult to achieve low-potential, high-current electro-oxidation performance. The carbon electrode prepared using the specific process described above has a large specific surface area, numerous surface active sites, and strong surface hydrophilicity, making it particularly suitable for the hydrogen production process described in this invention.

[0018] As a further preferred embodiment of the above technical solution, the reducing gas is waste gas containing sulfur dioxide, and the flow rate of the waste gas containing sulfur dioxide is 10-50 mL / min. Using waste gas containing sulfur dioxide as the reducing gas, SO2 waste gas can be used to assist the redox reaction of Fe(II) / Fe(III) metals with variable valence, removing pollutants from the waste gas while producing hydrogen. This achieves low-cost gas pollution control and has extremely high energy-saving and environmental protection value. This system also holds promise for integration with fuel cell systems, providing a new approach for developing low-energy-consumption, high-economic-value, and environmentally friendly low-carbon hydrogen production-fuel cell systems.

[0019] As a further preferred embodiment of the above technical solution, the concentration of ferric ions in the electrolyte is 0.1M.

[0020] As a further preferred embodiment of the above technical solution, the electrolysis voltage is set to 0.8V~1.3V during electrolysis.

[0021] As a further preferred embodiment of the above technical solution, the electrolyte is a sulfuric acid solution or a sodium sulfate solution, and the concentration of the electrolyte is 0.5M to 5M.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The carbon electrode prepared by the preparation method of the present invention has the characteristics of large specific surface area, many surface active sites and strong surface hydrophilicity, which is particularly suitable for use in the SO2 indirect oxidation reaction coupled hydrogen production process of the present invention.

[0024] (2) This invention utilizes a special electrode to reduce Fe(III) in the electrolyte to Fe(II) through substances with strong reducing properties such as SO2. Then, Fe(II) is electrolytically oxidized to obtain Fe(III). In this way, the Fe(II) / Fe(III) redox reaction can continue. When this reaction replaces the traditional oxygen evolution reaction and is combined with the hydrogen evolution reaction, efficient hydrogen production can be achieved at a low potential, avoiding the generation of oxygen and eliminating safety hazards from the source. This is of great significance to hydrogen energy research. At the same time, it can also achieve low-cost removal of SO2 polluting gas and realize the coupled production of waste gas treatment and hydrogen generation. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0026] Figure 1 This is a comparison diagram of the morphology of the carbon electrode in Example 1 and ordinary carbon paper;

[0027] Figure 2 The image shows a comparison of the X-ray photoelectron spectra of the carbon electrode in Example 1 and ordinary carbon paper.

[0028] Figure 3 Linear sweep voltammetry curves of the electrolytic systems of Example 1 and Comparative Example 1;

[0029] Figure 4 The graph shows the results of the Fe(II) electro-oxidation stability test in Example 1 and Comparative Example 1.

[0030] Figure 5 Linear sweep voltammetry curves of the electrolytic systems of Example 1 and Comparative Example 2;

[0031] Figure 6 Linear sweep voltammetry curves of the electrolytic systems of Example 2 and Comparative Example 3;

[0032] Figure 7This is a schematic diagram of the assembly of the flow electrolysis cell device in Example 3;

[0033] Figure 8 The graph shows the results of the Fe(II) electro-oxidation stability test in Example 3. Detailed Implementation

[0034] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0037] Example 1:

[0038] The carbon electrode in this embodiment is prepared by the following method:

[0039] (1) Place the cleaned carbon paper in a muffle furnace at 350°C for annealing for 16 hours (in air atmosphere).

[0040] (2) The carbon paper is placed in a plasma reactor and subjected to plasma treatment using a radio frequency source in a protective atmosphere. After the treatment is completed, an intermediate product is obtained. The frequency of the radio frequency source is 13.56MHz, the radio frequency power is 100W, and the plasma treatment time is 10min.

[0041] (3) The intermediate product is annealed at 300°C for 2 hours in a protective atmosphere to obtain the carbon electrode of this embodiment.

[0042] A comparison of the morphology of ordinary carbon paper (the carbon paper of step (1)) and the carbon electrode of this embodiment is as follows: Figure 1 As shown, the X-ray photoelectron spectroscopy of ordinary carbon paper (the carbon paper of step (1)) and the carbon electrode of this embodiment are compared as follows: Figure 2 As shown ( Figure 2 (b is a magnified view of a at the x-axis of 528-538 eV). The results show that after plasma treatment, the number of oxygen-containing functional groups on the surface of the carbon electrode increased significantly, and its hydrophilicity was significantly enhanced.

[0043] The SO2 indirect oxidation reaction coupled hydrogen production process of this embodiment includes the following steps: An H-type electrolytic cell is separated in the middle by an acidic membrane to form a cathode electrolytic cell and an anode electrolytic cell. 80 mL of 0.5 MH2SO4 electrolyte is added to both the cathode and anode electrolytic cells. Electrocatalysis is performed using a three-electrode system, with the carbon electrode (A-CP) of this embodiment as the working anode, a saturated calomel electrode as the reference electrode, and a carbon rod as the counter electrode. 0.1 MFeCl3 is added to the anode electrolytic cell, and waste gas containing sulfur dioxide (the flow rate is calculated based on the volume of sulfur dioxide as 10 mL / min) is introduced for electrolysis.

[0044] Table 1 shows the current density at different scan rates under a constant voltage of 1.2V relative to the hydrogen electrode. As can be seen from Table 1, the current density does not change significantly under the same voltage and different scan rates.

[0045] Table 1: Comparison of current densities at different scan rates

[0046] Voltage (Vvs.RHE) Scan rate (mVs⁻¹) Current density (mA / cm2) 1.2V 1mVs-1 62.81 1.2V 5mVs-1 69.98 1.2V 10mVs-1 67.35 1.2V 20mVs-1 67.95 1.2V 30mVs-1 68.25 1.2V 40mVs-1 68.86 1.2V 50mVs-1 69.56

[0047] This embodiment also investigated the current density of different concentrations of electrolyte in the SO2 indirect oxidation reaction coupled hydrogen production process under a constant voltage of 0.9V relative to the hydrogen electrode. The results are shown in Table 2. As can be seen from Table 2, under the same voltage conditions, the current density gradually increases with the increase of electrolyte concentration. When the electrolyte concentration exceeds 2.5 mol / L, the increase of current density is not obvious, and even the current density begins to decrease as the concentration increases. This may be due to the instability of the electrode surface caused by the high acid concentration.

[0048] Table 2: Comparison of current densities with different electrolyte concentrations

[0049] Voltage (Vvs.RHE) Electrolyte concentration (mol / L) Current density (mA / cm2) 0.9V 0 10.35 0.9V 0.0005 14.72 0.9V 0.005 18.78 0.9V 0.05 23.89 0.9V 0.5 41.79 0.9V 1.0 47.18 0.9V 1.5 51.64 0.9V 2.0 54.82 0.9V 2.5 63.09 0.9V 3.0 66.99 0.9V 3.5 69.96 0.9V 4.0 56.27 0.9V 4.5 57.86 0.9V 5.0 50.46

[0050] Comparative Example 1:

[0051] The carbon electrode, its preparation method, and the SO2 indirect oxidation reaction coupled hydrogen production process in this comparative example are basically the same as those in Example 1. The only difference is that SO2 is not introduced into the anolyte in the SO2 indirect oxidation reaction coupled hydrogen production process in this comparative example.

[0052] The linear sweep voltammetry curves of the electrolytic systems in this comparative example and Example 1 are as follows: Figure 3 As shown ( Figure 3The curves for FeCl3+SO2 are linear sweep voltammetry curves from Example 1, and for FeCl3 are linear sweep voltammetry curves from this comparative example. The results show that, between 0.7 and 1.3 V (vs. RHE), pure ferric ions have no electro-oxidation performance, and pure sulfur dioxide also has almost no performance. However, when ferric ions and sulfur dioxide combine, significant performance is obtained. This is attributed to the fact that sulfur dioxide can reduce ferric Fe(III) to ferrous Fe(II), and then Fe(II) is electro-oxidized on the carbon electrode to obtain Fe(III), thus exhibiting a higher current density.

[0053] The current density retention rates of Fe(II) electrooxidation stability tests in this comparative example and Example 1 are shown in Table 3 and... Figure 4 As shown.

[0054] Table 3: Comparison of current density retention rates between Example 1 and Comparative Example 1

[0055] Voltage (Vvs.RHE) Time (h) Current density retention rate Comparative Example 1 1.1V 16 15.8% Example 1 1.1V 16 85%

[0056] Comparative Example 2:

[0057] The SO2 indirect oxidation reaction coupled with hydrogen production process in this comparative example is basically the same as that in Example 1, the only difference being that a common carbon paper electrode (CP) is used as the working anode electrode in this comparative example. The linear sweep voltammetry curves of the carbon electrodes in this comparative example and Example 1 are shown below. Figure 5 As shown ( Figure 5 The CP curve in this example is the linear sweep volt-ampere curve of this comparative example, and the A-CP curve is the linear sweep volt-ampere curve of Example 1. (At a current density of 50 mA / cm²) -2 Under the conditions described, the potentials of the working anode relative to the hydrogen electrode in this comparative example and Example 1 are shown in Table 4.

[0058] Table 4: Comparison of current density at the anode working electrode in Example 1 and Comparative Example 2

[0059] Current density (mAcm⁻²) Voltage (Vvs.RHE) Comparative Example 2 50mAcm-2 1.13 Example 1 50mAcm-2 0.99

[0060] Example 2:

[0061] The carbon electrode in this embodiment is prepared by the following method:

[0062] (1) Place the cleaned carbon paper in a muffle furnace at 350°C for annealing for 16 hours (in air atmosphere).

[0063] (2) The carbon paper is placed in a plasma reactor and subjected to plasma treatment using a radio frequency source in a protective atmosphere. After the treatment is completed, an intermediate product is obtained. The frequency of the radio frequency source is 13.56MHz, the radio frequency power is 200W, and the plasma treatment time is 3min.

[0064] (3) The intermediate product is annealed at 600°C for 1 hour in a protective atmosphere to obtain the carbon electrode of this embodiment.

[0065] The SO2 indirect oxidation reaction coupled hydrogen production process of this embodiment is specifically implemented as follows: 80 mL of 0.5 M H2SO4 electrolyte is added to the two-electrode electrolytic cell. The carbon electrode (A-CP) of this embodiment is used as the anode working electrode, and CoP / CP (non-precious metal catalyst) is used as the cathode working electrode to assemble a two-electrode system. 0.1 M FeCl3 is added to the anode electrolytic cell and waste gas containing sulfur dioxide is introduced (the flow rate is calculated based on the volume of sulfur dioxide as 50 mL / min) for electrolysis.

[0066] Comparative Example 3

[0067] The SO2 indirect oxidation reaction coupled with hydrogen production process in this comparative example is basically the same as that in Example 2, the only difference being that a common carbon paper electrode is used as the working anode electrode in this comparative example. The scanning potential window is 0.5V to 1.4V, and the linear scanning curves of the electrolyte are recorded. The linear scanning voltammetric curves of the electrolysis systems in this comparative example and Example 2 are shown below. Figure 6 As shown ( Figure 6 The CP(+) / / CoP(-) curve is the linear scan voltammetry curve for this comparative example, and the A-CP(+) / / CoP(-) curve is the linear scan voltammetry curve for Example 2. Figure 6 It can be seen that after assembling the device, the current reaches 10 mA / cm. -2 Current density, voltage advance 0.19V.

[0068] Example 3

[0069] The carbon electrode in this embodiment is prepared by the following method:

[0070] (1) Place the cleaned carbon paper in a muffle furnace at 350°C for annealing for 16 hours (in air atmosphere).

[0071] (2) The carbon paper is placed in a plasma reactor and subjected to plasma treatment using a radio frequency source in a protective atmosphere. After the treatment is completed, an intermediate product is obtained. The frequency of the radio frequency source is 13.56MHz, the radio frequency power is 200W, and the plasma treatment time is 3min.

[0072] (3) The intermediate product is annealed at 600°C for 1 hour in a protective atmosphere to obtain the carbon electrode of this embodiment.

[0073] In this embodiment of the electrochemical hydrogen production process, the carbon electrode (A-CP) is used as the anode working electrode, and Pt / C (a commercial platinum-carbon catalyst) is used as the cathode working electrode, forming a flow electrolyzer (as shown in the schematic diagram of the flow electrolyzer assembly). Figure 7As shown in the figure, 0.5 M H2SO4 electrolyte was added to the cathode electrolytic cell and the anode electrolytic cell respectively, and 0.1 M FeCl3 was added to the anode electrolytic cell and sulfur dioxide was introduced (the flow rate was calculated based on the volume of sulfur dioxide as 30 mL / min) for electrolysis.

[0074] Under the premise of introducing sulfur dioxide, the retention rate of the current density test for the electro-oxidation stability of Fe(II) in this embodiment was tested, and the results are as follows: Figure 8 As shown, by Figure 8 It can be seen that under a voltage of 1.2V, after 90 hours of testing, the current density retention rate is 94%, which shows good stability.

[0075] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon electrode, characterized in that, Includes the following steps: (1) The carbon paper is placed in a plasma reactor and subjected to plasma treatment using a radio frequency source in a protective atmosphere. After the treatment is completed, an intermediate product is obtained. (2) Anneal the intermediate product in a protective atmosphere for a set time to obtain the processed carbon electrode.

2. The method for preparing a carbon electrode according to claim 1, characterized in that, The frequency of the radio frequency source in step (1) is 13.56MHz, the radio frequency power is 100~200W, and the plasma treatment time is 3~10min.

3. The method for preparing a carbon electrode according to claim 1, characterized in that, In step (2), the annealing temperature is 300~600℃ and the annealing time is 1~2h.

4. A carbon electrode, characterized in that, It is prepared by the preparation method according to any one of claims 1-3.

5. A process for producing hydrogen via indirect SO2 oxidation coupled with an electrolysis reaction, comprising using an electrolysis reactor to electrolyze an electrolyte to produce hydrogen; wherein the electrolysis reactor is provided with a cathode working electrode and an anode working electrode; characterized in that, The electrolyte contains ferric ions, and a reducing gas is continuously introduced into the electrolyte during electrolysis; the anode working electrode is the carbon electrode as described in claim 4.

6. A process for producing hydrogen via SO2 indirect oxidation coupled with an electrolysis reaction, comprising using an electrolysis reactor to electrolyze water to produce hydrogen; wherein the electrolysis reactor is provided with a cathode working electrode and an anode working electrode, and the cathode working electrode and the anode working electrode are separated by a diaphragm; characterized in that, The anolyte contains ferric ions, and a reducing gas is continuously introduced into the anolyte during electrolysis. The working anolyte is the carbon electrode as described in claim 4.

7. The SO2 indirect oxidation reaction coupled hydrogen production process according to claim 5 or 6, characterized in that, The reducing gas is sulfur dioxide waste gas, and the flow rate of the sulfur dioxide waste gas is calculated based on the volume of sulfur dioxide as 10~50 mL / min.

8. The SO2 indirect oxidation reaction coupled hydrogen production process according to claim 5 or 6, characterized in that, The concentration of ferric ions in the electrolyte is 0.01~0.1M.

9. The SO2 indirect oxidation reaction coupled hydrogen production process according to claim 5 or 6, characterized in that, During electrolysis, the electrolysis voltage is set to 0.7V~1.3V.

10. The SO2 indirect oxidation reaction coupled hydrogen production process according to claim 5 or 6, characterized in that, The electrolyte is a sulfuric acid solution or a sodium sulfate solution, and the concentration of the electrolyte is 0.5M to 5M.

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