Catalyst for producing hydrogen by electrolyzing multiple types of sewage and preparation method of catalyst

Abstract

The invention relates to the technical field of hydrogen production through electrolysis of multiple water sources and synchronous realization of metal recovery in sewage, and discloses a sulfur-doped carbon-coated ultralow-iridium-loading particle catalyst, and iridium particles in the catalyst are uniform in size and are uniformly dispersed in sulfur-doped carbon nanosheets. The invention also provides a preparation method of the sulfur-doped carbon-coated ultralow-iridium-loading particle catalyst, which comprises the following steps: step 1, putting 12-18mg of iridium chloride trihydrate, 0.8-1.2 g of L-methionine and 0.15-0.25 g of sublimed sulfur into a ball milling tank, carrying out ball milling for 2 hours, collecting and drying, and then calcining in an inert atmosphere; and step 2, infiltrating the powder in a CS2 liquid, stirring for 2 hours, freeze-drying, and calcining in an inert atmosphere. The sulfur-doped carbon-coated ultralow-iridium-loading particle catalyst prepared by the preparation method disclosed by the invention is uniform in particle size, the particle size is less than 3nm, the particles are uniformly dispersed in sulfur-doped carbon nanosheets, meanwhile, the iridium loading capacity is only 9.81%, and the utilization rate of the iridium element is higher.

Description

Technical Field

[0001] The invention relates to the technical field of electrolyzing various water sources to produce hydrogen, and in particular to a catalyst for electrolyzing sewage to produce hydrogen and simultaneously recovering metals in the sewage, and a preparation method thereof. Background Art

[0002] Hydrogen production from water electrolysis is one of the effective ways to achieve the transformation of the global energy structure to a clean and low-carbon one. At present, the technology for hydrogen production from water electrolysis mainly uses alkaline electrolysis systems and proton exchange membrane electrolysis systems, but both technical routes rely on high-purity fresh water as the water source. However, fresh water accounts for a small proportion of the earth's water resources, and most of it is polluted water that cannot be used directly, such as domestic wastewater and industrial sewage. If hydrogen can be produced by direct electrolysis of polluted water, it can reduce the pressure on fresh water resources and alleviate the current energy and environmental crisis. However, polluted water is full of messy but not low-concentration metal ions and organic matter. As the electrolysis proceeds, the electrode materials suffer from severe corrosion. Therefore, the development of efficient and corrosion-resistant electrode materials for hydrogen production from polluted water electrolysis faces huge challenges.

[0003] In the process of electrolysis of contaminated water to produce hydrogen, the reduction effect of the cathode can reduce water to hydrogen. Because of the efficient reduction reaction, the pH of the catalyst surface area will change sharply, causing the metal ions to form insoluble precipitates. If a suitable catalyst can be developed to allow the cathode to carry out the above reaction efficiently and corrosion-resistantly, the metal ions in the electrolyte contaminated water containing a large amount of metal ions can be directly recovered. In the treatment of contaminated water and industrial treatment and recovery of contaminated water, several flocculation and precipitation and several disinfection treatments are required, which requires great costs. Therefore, the cathode reduction effect of electrolysis of water to produce hydrogen and the regional increase in pH to produce hydrogen while precipitating and recovering metals has a high practical application value, but this requires the cathode to be corrosion-resistant and highly stable.

[0004] Most of the catalysts that can meet the above requirements contain precious metal elements. Based on the demand to reduce the cost of catalytic materials, when using precious metal elements as synthetic raw materials, it is necessary to ensure high performance while reducing the precious metal element loading in the catalyst, thereby improving the utilization efficiency of the precious metal elements.

[0005] Therefore, developing an efficient and low-precious metal element-loaded catalyst that can simultaneously electrolyze multiple water sources to produce hydrogen and recover metal ions in polluted water is of great significance for the efficient utilization of polluted water resources, but it also faces major challenges. It also requires that the electrolysis equipment is simple and the catalytic material can electrolyze polluted water at low potential, high current density and high stability. Summary of the invention

[0006] In order to solve the technical problems raised in the background technology, the present invention provides a catalyst for producing hydrogen by electrolyzing sewage and a preparation method thereof.

[0007] The present invention is implemented by the following technical scheme: a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst, wherein the iridium particles in the catalyst are uniform in size and evenly dispersed in the sulfur-doped carbon nanosheets.

[0008] The present invention also proposes a method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst, comprising the following steps:

[0009] Step 1, 12-18 mg of iridium chloride trihydrate, 0.8-1.2 g of L-methionine and 0.15-0.25 g of sublimed sulfur are placed in a ball mill, and after ball milling for 2 hours, a light yellow product is collected and placed in a 60° C. vacuum drying oven for 12 hours; the light yellow powder obtained after drying is placed in a quartz boat and placed in a tube furnace, and calcined to obtain a black powder;

[0010] Step 2: soak the black powder in CS2 liquid, stir for 2 hours and then freeze-dry at -50°C for 12 hours; the dried black powder is placed in a quartz boat and calcined in a tube furnace, and the catalyst is obtained after cooling.

[0011] Preferably, under the condition that the mass ratio of L-methionine, sublimed sulfur and iridium chloride trihydrate is 200:40:3, increasing the dosage of the three can achieve large-scale synthesis.

[0012] Preferably, the calcination conditions in step 1 and step 2 are: in an Ar gas flow, the temperature is raised to 900° C. at a program heating rate of 5° C. / min and 20° C. / min, respectively, and the constant temperature calcination is performed for 60 min and 30 min.

[0013] The present invention provides a method for preparing an electrode material. 5 mg of a catalyst prepared by any method of claim 2-4 is weighed, and then dispersed in 0.5 mL of a mixed solution containing anhydrous ethanol and naphthol in a volume ratio of 47:3. Ultrasonic dispersion is performed for 60 minutes to obtain a uniformly dispersed mixed solution. The obtained mixed solution is uniformly dispersed and applied to an area of ​​0.5×0.5 cm 2 The carbon cloth is placed on the carbon cloth and the carbon cloth is dried.

[0014] The present invention provides an electrode material, which is prepared by the method according to claim 7.

[0015] The present invention proposes an electrolysis system for producing hydrogen from electrocatalytic polluted water, using the electrode materials described in claim 7 as working electrodes, a Pt sheet as a counter electrode, and an Ag / AgCl electrode as a reference electrode to form a three-electrode system for electrocatalytic water decomposition hydrogen production test. The sewage used in this scheme includes but is not limited to domestic sewage, seawater, and chlor-alkali wastewater; the recovered metals include but are not limited to magnesium, calcium, and iron.

[0016] Linear sweep voltammetry (LSV) was used to explore the electrocatalytic activity of the catalyst, and the constant potential method was used to test the change of current over time at a fixed potential to illustrate the stability of the catalyst.

[0017] The present invention proposes a method for electrolyzing contaminated water to prepare hydrogen and recover metals in the contaminated water, using the electrode materials described in claim 7 as working electrodes and counter electrodes, respectively, to form a dual-electrode system, using solar panels to generate electricity, and using an H-type electrolytic cell to explore its hydrogen production and metal precipitation activity.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention adopts a cheap and easy mass synthesis method to prepare the catalyst. The method of synthesizing sulfur-doped carbon-wrapped iridium particle catalyst by calcination and CS2 solution reprocessing is simple and efficient to operate, can realize mass synthesis, and has a broad application prospect in actual large-scale industrial applications.

[0020] The sulfur-doped carbon-wrapped ultra-low iridium loading granular catalyst prepared by the present invention has uniform particle size, all less than 3nm, and is evenly dispersed on the sulfur-doped carbon nanosheets. At the same time, the iridium loading is only 9.81%, achieving more efficient utilization of the iridium element.

[0021] The sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst proposed in the present invention can be used as a bifunctional electrocatalyst, showing excellent hydrogen evolution and metal recovery capabilities under contaminated water conditions. For the hydrogen evolution reaction, stability under high current can be achieved, and the overpotential of the neutral buffer solution prepared with contaminated water as an electrolyte is 0.9V vs RHE, and the current density is as high as 1000mA cm -2 At the same time, the pH in the cathode area changes sharply, inducing metal ion deposition and thus recovering metals, achieving efficient resource recovery and maintaining it stably for hundreds of hours. Its catalyst has high practical application value.

[0022] The solar hydrogen production device proposed by the present invention generates electricity from solar panels, and a neutral buffer solution prepared from polluted water is used as an electrolyte to realize renewable energy power generation, online electrolysis of polluted water to produce hydrogen, and metal recovery. It realizes efficient and stable catalytic cracking of polluted water to produce hydrogen while recovering metal ions, opening up a new path for efficient, low-cost, large-scale production of hydrogen and metal recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an optical photograph of a large number of synthesized sulfur-doped carbon-wrapped ultra-low iridium loading particle catalysts prepared by the present invention.

[0024] Figure 2 It is an X-ray diffraction (XRD) pattern of the sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst prepared by the present invention.

[0025] Figure 3 It is a transmission electron microscope (TEM) photograph of the sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst prepared by the present invention.

[0026] Figure 4 X-ray photoelectron spectroscopy (XPS) diagram of the sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst prepared by the present invention.

[0027] Figure 5 This is a thermogravimetric analysis diagram of the sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst prepared by the present invention.

[0028] Figure 6 It is a linear voltammetric scanning curve (LSV) diagram of the sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst prepared by the present invention in a contaminated water electrolyte.

[0029] Figure 7 The present invention is a curve of the current density variation over time (it) of the sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst prepared in the present invention in a contaminated water electrolyte.

[0030] Figure 8 The present invention is a schematic diagram of metal ion deposition in the sulfur-doped carbon-wrapped ultra-low iridium loading granular catalyst prepared by the present invention during the electrolysis of sewage. Figure a is an optical photograph of the cathode pool before the electrolysis experiment, Figure b is an optical photograph of the cathode pool during the electrolysis experiment, Figure c is an optical photograph of the cathode pool at the end of the electrolysis experiment, and Figure d is an optical photograph of the precipitation product obtained in the cathode pool after the electrolysis experiment.

[0031] Fig. 9 This is the XPS graph of the precipitation product obtained in the cathode cell after the electrolysis experiment.

[0032] Fig.10 It is a schematic diagram of the actual operation of the sulfur-doped carbon-wrapped ultra-low iridium loading granular catalyst prepared by the present invention on hydrogen evolution from wastewater under sunlight. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, in the event of any conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0034] Embodiment 1:

[0035] The chemical reagents used in the present invention are analytically pure L-methionine, iridium chloride trihydrate, sublimed sulfur, and CS2, and the purity of the inert gas (argon) used in step 1 is 99.999%. All carbon cloths were purchased from Taiwan, China. All sewage came from Hefei, China.

[0036] Embodiment 1:

[0037] A method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst comprises the following steps: 5 mg of iridium chloride trihydrate, 1 g of L-methionine and 0.2 g of sublimated sulfur are placed in a ball mill, and the ball mill is milled for 2 hours at a ball mill speed of 500 rpm. After the end, the light yellow product is collected and placed in a 60°C vacuum drying oven for drying for 12 hours. The light yellow powder obtained after drying is placed in a quartz boat and placed in a tube furnace, and the temperature is raised to 900°C at a program heating rate of 5°C / min in an Ar gas flow, and the temperature is calcined at a constant temperature for 60 minutes to obtain a black powder. The black powder is soaked in CS2 liquid, stirred for 2 hours, cooled with liquid nitrogen, frozen and placed at -50°C for freeze drying for 12 hours. The obtained black powder is placed in a quartz boat and placed in a tube furnace, and the temperature is raised to 900°C at a program heating rate of 20°C / min in an Ar gas flow, and the temperature is calcined at a constant temperature for 30 minutes to obtain a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst. Thermogravimetric testing determined that the iridium loading was only 9.81%.

[0038] Embodiment 2:

[0039] The present invention proposes an electrode made of sulfur-doped carbon wrapped with ultra-low iridium loading particle catalyst, and the preparation method thereof comprises the following steps: weighing 5 mg of the catalyst obtained in the above embodiment 1, dispersing it in 0.5 mL of a mixed solution containing anhydrous ethanol and naphthol in a volume ratio of 47:3, ultrasonically dispersing for 60 minutes to obtain a uniformly dispersed mixed solution, and then uniformly dispersing it on an area of ​​0.5×0.5 cm 2 The carbon cloth coated with the catalyst was directly used as the working electrode after drying, and the Ag / AgCl electrode was used as the reference electrode, the Pt electrode was used as the counter electrode, and the sewage was used as the electrolyte.

[0040] Embodiment 3:

[0041] This scheme uses the electrodes prepared in Example 2 as working electrodes, Pt electrodes as counter electrodes, and Ag / AgCl electrodes as reference electrodes to form a three-electrode system in an H-type electrolyzer. A neutral buffer solution prepared from sewage was used as an electrolyte to conduct an electrocatalytic sewage decomposition hydrogen production test. Linear sweep voltammetry (LSV) was used in the test to explore the electrocatalytic activity of the catalyst, and the constant potential method was used to test the change of current over time at a fixed potential to explore the stability of the catalyst. After testing, the current density was as high as 1000mA cm -2 It can be stable for 350h, which shows the high efficiency and stability of the catalyst.

[0042] Electrocatalytic recovery of metals from wastewater: The constant potential method in Example 3 was used to test the change in current over time at a fixed potential. The white precipitate at the bottom of the electrolyte was collected, centrifuged and filtered, and dried in a vacuum oven at 60°C for 5 h. After being ground into powder in a mortar, the main components were determined by XPS.

[0043] Embodiment 4:

[0044] This scheme proposes a method for electrolyzing wastewater to prepare hydrogen and recovering metal ions in contaminated water. The electrodes prepared in Example 2 are used as working electrodes and counter electrodes to form a dual-electrode system. Solar panels are used to generate electricity as a source of electrical energy, and a neutral buffer solution prepared from contaminated water is used as an electrolyte to achieve simultaneous electrolysis of contaminated water to prepare hydrogen and recover metals.

[0045] like Fig.10 As shown in the figure, establishing a solar electrolysis system for hydrogen production and metal recovery from sewage is undoubtedly the best way to promote the application of water splitting technology and sewage treatment. Using commercial solar panels as the power system, the electrolytic cell where the working electrode is located will produce bubbles violently during the actual assembly (inset). This shows that the device exhibits excellent electrocatalytic performance in hydrogen production from sewage.

[0046] Result analysis:

[0047] like Figure 1 The optical photographs show that by increasing the raw materials of the sulfur-doped carbon-wrapped ultra-low iridium loading granular catalyst prepared by the present invention, a large amount of catalyst can be obtained, indicating that the method for preparing the sulfur-doped carbon-wrapped ultra-low iridium loading granular catalyst of the present invention is simple and can be synthesized in large quantities.

[0048] like Figure 2 As shown, the catalyst was subjected to phase analysis using XRD, and the obtained diffraction peaks corresponded one to one with the metal iridium with the standard substance card number of JCPDS: 46-1044, indicating that the material synthesized by the present invention was metal iridium.

[0049] like Figure 3 As shown, according to the low-resolution TEM images, the iridium nanoparticles are evenly dispersed on the two-dimensional graphitic carbon, and the average size is less than 3 nm.

[0050] like Figure 4 As shown, according to the XPS full spectrum, it can be known that the carbon-encapsulated iridium particles contain Ir, S, and C elements, indicating that the carbon material obtained by the present invention is a sulfur-doped and modified carbon material, that is, a sulfur-doped carbon-encapsulated iridium nanoparticle material is prepared.

[0051] like Figure 5 As shown, according to thermogravimetric analysis, the iridium loading is only 9.81%, which is lower than the loading of common iridium catalysts on the market.

[0052] like Figure 6 As shown in the LSV test results, when the sulfur-doped carbon-wrapped ultra-low iridium loading granular catalyst prepared by the present invention is used to electrolyze sewage to produce hydrogen, the current density reaches 10 mA cm -2 The overpotential required is only 34 mV, which is lower than commercial Pt / C. In addition, when the overpotential is 950 mV, the current density is as high as 1000 mA cm -2 , which can achieve low voltage and high current hydrogen production effect.

[0053] like Figure 7 As shown in the figure, the current density versus time curve under constant potential shows that the catalyst can maintain a high current density (1000mA cm) for hundreds of hours in the sewage electrolysis test. -2) At the same time, by observing the metal precipitation in the cathode pool (such as Figure 8 As shown in Figure 2, it can be seen that precipitates are obviously precipitated from the catalyst. XPS detection (as shown in Figure 2 Fig. 9 As shown), mainly Ca 2+ Mg 2+ , Fe 3+ Elements (and trace amounts of other elements, mainly depending on the composition of metal ions in sewage) have high practical application value.

[0054] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A sulfur-doped carbon-coated ultra-low iridium loading particle catalyst, characterized in that: The iridium particles in the catalyst are uniform in size and evenly dispersed in the sulfur-doped carbon nanosheets.

2. The method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst according to claim 1, characterized in that: The steps include: Step 1, 12-18 mg of iridium chloride trihydrate, 0.8-1.2 g of L-methionine and 0.15-0.25 g of sublimed sulfur are placed in a ball mill, and after ball milling for 2 hours, a light yellow product is collected and placed in a 60° C. vacuum drying oven for 12 hours; the light yellow powder obtained after drying is placed in a quartz boat and placed in a tube furnace, and calcined to obtain a black powder; Step 2: soak the black powder in CS2 liquid, stir for 2 hours and then freeze-dry at -50°C for 12 hours; the dried black powder is placed in a quartz boat and calcined in a tube furnace, and the catalyst is obtained after cooling.

3. The method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst according to claim 1, characterized in that: Under the condition that the mass ratio of L-methionine, sublimed sulfur and iridium chloride trihydrate is 200:40:3, increasing the dosage of the three can achieve large-scale synthesis.

4. The method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst according to claim 1, characterized in that: The calcination conditions in step 1 and step 2 are as follows: in an Ar gas flow, the temperature is raised to 900° C. at programmed heating rates of 5° C. / min and 20° C. / min, respectively, and the temperature is kept constant for 60 min and 30 min, respectively.

5. The method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst according to claim 1, characterized in that A liquid sulfur source, such as carbon disulfide, is used to achieve resulfurization and enhance the hydrogen production activity of the iridium-based catalyst.

6. The method for preparing a sulfur-doped carbon-wrapped ultra-low iridium loading particle catalyst according to claim 1, characterized in that The iridium content in the iridium-based catalyst is the lowest, and the preparation of an iridium-based catalyst with a lower iridium content can be achieved.

7. A method for preparing an electrode material, characterized in that: Weigh 5 mg of the catalyst prepared by any of the methods of claims 2-5, and then disperse it in 0.5 mL of a mixed solution containing anhydrous ethanol and naphthol in a volume ratio of 47:3, and ultrasonically disperse it for 60 min to obtain a uniformly dispersed mixed solution. The obtained mixed solution is evenly dispersed and applied to an area of ​​0.5×0.5 cm 2 The carbon cloth is placed on the carbon cloth and the carbon cloth is dried.

8. An electrode material, characterized in that Prepared by the method as claimed in claim 6.

9. An electrolysis system for producing hydrogen from multiple water sources by electrocatalysis, characterized in that: The electrode materials described in claim 7 are used as working electrodes, Pt sheets are used as counter electrodes, and Ag / AgCl electrodes are used as reference electrodes to form a three-electrode system to catalyze water decomposition to produce hydrogen and simultaneously realize metal recovery in wastewater.

10. The electrolysis system for producing hydrogen from multiple water sources by electrocatalysis as claimed in claim 9, characterized in that: The water sources used include but are not limited to domestic sewage, chlor-alkali wastewater, seawater, and distilled water; the recovered metals include but are not limited to magnesium, calcium, and iron.

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