A preparation method of a bifunctional electrocatalyst based on cobalt metal loaded waste leather scraps

Abstract

A preparation method of a bimetallic cobalt catalyst based on waste leather scraps, taking chromium-containing waste leather scraps from a planing section of a leather factory as a carbon source, using an organic ligand 2-methyl imidazole as an intermediate, introducing metal cobalt on the surface of collagen fibers by an immersion stirring method, filtering and washing with ethanol, drying, and then preparing a chromium-cobalt bimetallic carbon-based catalyst through high-temperature calcination; the catalyst prepared in the application realizes resource utilization of chromium-containing waste leather scraps, more metal cobalt is introduced on the surface of fiber bundles by adding the intermediate, and the active center is increased; effective utilization of these leather wastes can relieve resource and environmental pressure and promote sustainable development of the leather industry and ecology; the preparation method is simple, conducive to further exploration of non-noble metal carbon-based catalysts, has bimetallic catalytic performance, saves resources, and has low energy consumption.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalytic material preparation, and particularly relates to a method for preparing a bifunctional electrocatalyst by loading cobalt on waste leather shavings. BACKGROUND

[0002] Hydrogen is expected to play an important role in the future energy landscape as a clean energy carrier with high combustion value. Since there is no original hydrogen on earth, the primary problem people face is how to produce hydrogen in an environmentally friendly way. Electrolysis of water is considered to have great application prospects as a green hydrogen production route, which has the following advantages: (1) water as a raw material for hydrogen production is abundant in nature and renewable, providing the possibility of sustainable hydrogen production; (2) the reaction products of electrolysis of water are environmentally friendly oxygen and hydrogen, which do not cause environmental pollution; (3) the required electric energy can be obtained by converting renewable energy such as solar and wind energy. Currently, electrolysis of water has become one of the most active and most advanced research topics in hydrogen production technology. Water splitting includes oxygen production (water oxidation, 2H2O→O2+4H + + 4e - ) and hydrogen production (water reduction, 2H + + 2e - →H2), both of which are endothermic reactions, i.e. the occurrence of the reaction needs to overcome a very high energy barrier, which is a high energy consumption process, making water splitting difficult to achieve in terms of thermodynamics and kinetics. Therefore, electrocatalytic materials must be developed to reduce the reaction energy barrier and thus promote the occurrence of the two half-reactions.

[0003] Currently, the most effective catalysts are still noble metal-based materials such as platinum, iridium, and ruthenium-based catalysts, but the high price and limited storage hinder their application. Therefore, it is of great significance to explore non-noble metal catalysts to reduce the amount of noble metal used or even replace noble metal catalysts. Recent research has shown that carbon materials, especially those prepared from biomass, have a series of advantages such as environmental protection and low cost, and non-noble metals have advantages such as abundant earth storage, low cost, and high stability compared to noble metals, so non-noble metal-doped carbon-based materials are expected to become an excellent substitute for noble metal catalysts.

[0004] In traditional tanning processes, only 20% of raw hides can be converted into leather products, and the rest is discarded as solid waste. China is the world's largest leather producer and consumer, and the tanning industry produces more than 1.4 million tons of solid waste per year, which has caused great pressure on the environment and also resulted in a huge waste of biomass resources. The resource utilization of tanning solid waste has become the lifeline of the development of the industry. SUMMARY

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the purpose of the present application is to provide a method for preparing a dual-functional electrocatalyst based on waste leather scraps loaded with metallic cobalt, which has the characteristics of dual-functional catalytic performance, resource saving and low energy consumption.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is a method for preparing a dual-functional electrocatalyst based on waste leather scraps loaded with metallic cobalt, comprising the following steps:

[0007] Step 1, pretreatment of waste chromium scraps: collect the chromium-containing waste leather scraps from the planing process of a leather processing plant, immerse them in a mixed solution of ethanol and water for 24-48 h, crush them with a homogenizer and wash them with water several times, dry them and sieve them with a mesh screen for use;

[0008] Step 2, add the pretreated chromium-containing waste leather scraps and intermediates from step 1 to a 15-40 ml mixed solution of methanol and deionized water to form solution A, then weigh cobalt salt and dissolve it in 5-20 ml deionized water to form solution B, stir at room temperature for 1 h, then pour solution B into solution A, stir for another 3-24 h, filter and wash with ethanol, and then dry in a 60℃ vacuum drying oven; obtain the catalyst precursor loaded with metallic cobalt.

[0009] Step 3, place the catalyst precursor loaded with metallic cobalt into a tube furnace and perform annealing treatment in a nitrogen atmosphere, then collect the obtained product after cooling to room temperature, i.e. obtain the chromium-cobalt-loaded carbon-based catalyst.

[0010] In the step 1, the ratio of chromium-containing waste leather scraps to mixed solution is 1:3; the mixing ratio of water to ethanol is 2-5:1; the crushing time with the homogenizer is 2-10 min; the drying temperature is 60-80℃; and the mesh size of the screen is 10-100 mesh.

[0011] In the step 2, the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride, the molar amount of cobalt salt is 0.1-2 mmol, and the intermediate is 2-methylimidazole; the ratio of 2-methylimidazole to cobalt salt is 6:1.

[0012] In the step 2, the mass of the pretreated chromium-containing waste leather scraps is 1-3 g; the mixing ratio of methanol to water is 2:1; the ethanol filtering and washing is performed 5 times; and the drying temperature is 60℃.

[0013] In the step 3, the calcination conditions are as follows: in a nitrogen atmosphere; the heating rate is 5℃ / min; the annealing temperature is 600-1000℃; and the holding time is 2-4 h.

[0014] The method for preparing a dual-functional electrocatalyst based on waste leather scraps loaded with metallic cobalt.

[0015] The application of the chromium-cobalt loaded carbon-based catalyst in an electrocatalytic water splitting reaction under 1M KOH alkaline conditions.

[0016] The present application has the following beneficial effects:

[0017] 1) The present application realizes direct resource utilization of waste leather scraps.

[0018] 2) The present application uses the abundant functional groups in waste leather scraps as active sites, coordinates metal particles through organic ligands, further increases the nitrogen content, and stably and uniformly fixes the metal on the biomass carbon through one-step calcination.

[0019] 3) The preparation process of the present application is simple, and the original collagen fiber bundle can be maintained, further increasing the active sites and improving the catalytic performance in water splitting.

[0020] 4) The chromium-based electrocatalyst synthesized by the present application has good hydrogen evolution reaction (HER) performance and oxygen evolution reaction (OER), providing a new idea for preparing high-performance and low-cost overall water splitting electrocatalysts.

[0021] The biomass carbon material is a carbon-rich porous solid material derived from the thermal decomposition of biomass at relatively low temperatures and limited oxygen conditions. The carbon precursor is provided by leather waste. Biomass carbon materials usually have rich porosity and surface functional groups (-C-O, -C=O, -COOH, and -OH, etc.), as well as N, P, S, Ca, Mg, and K minerals. These properties make biomass carbon materials can be directly used as adsorbents, catalysts and catalyst carriers. In addition, its high modifiability and easily adjustable surface function make functional materials based on biomass carbon materials widely used in the fields of catalysis, energy storage, pollutant removal and CO2 capture.

[0022] Metal element doping is an effective way to improve the performance of catalysts by changing the electronic structure of the catalyst surface. Through metal element doping, the conductivity of the catalyst can be enhanced, and additional active sites can be introduced to reduce the kinetic barrier of the reaction, thereby promoting the electrocatalytic water splitting reaction. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the oxygen evolution polarization curve of the carbon-based electrocatalyst prepared by different cobalt molar amounts of the present application.

[0024] Figure 2 is the hydrogen evolution polarization curve of the carbon-based electrocatalyst prepared by different cobalt molar amounts of the present application.

[0025] Figure 3 is the Nyquist plot of the chromium-cobalt double metal carbon-based electrocatalyst of the present application.

[0026] Figure 4 is the XRD pattern of the carbon-based electrocatalyst of the chromium-cobalt bimetal of the present application.

[0027] Figure 5 is the SEM image of the carbon-based electrocatalyst of the chromium-cobalt bimetal of the present application.

[0028] Figure 6 is the EDS area scan image of the carbon-based electrocatalyst of the chromium-cobalt bimetal of the present application. Specific implementation method

[0029] The technical solutions of the present application will be further described below in combination with the drawings and examples. The modes of realizing the present application include but are not limited to the following examples, which are used to illustrate the present application but not to limit the protection scope of the present application. If not specifically indicated, the technical means used in the examples are the conventional means familiar to those skilled in the art. The test methods in the following examples are the conventional methods, unless otherwise specified.

[0030] The present application is a method for a dual-functional electrocatalyst based on cobalt-loaded waste leather scraps, which is specifically carried out according to the following steps

[0031] Step 1, waste leather scrap pretreatment: collect the waste leather scraps from the shaving process of a leather processing factory, immerse them in a mixed solution of ethanol and water, crush them with a homogenizer, wash them with water several times, dry them, and sieve them for use.

[0032] The ratio of chromium-containing waste leather scraps to mixed liquid is 1:3; the ratio of water to ethanol in the mixed liquid is 2-5:1; the immersion time is 24-48 h; the crushing time with the homogenizer is 2-10 min; the drying temperature is 80°C, and the sieve mesh size is 10-100 mesh;

[0033] Step 2, add the treated waste leather scraps and 2-methylimidazole to a 30 ml mixed solution of methanol and deionized water to form solution A, then weigh cobalt nitrate and dissolve it in 10 ml deionized water to form solution B, stir at room temperature for a certain time, then pour solution B into solution A, stir for a certain time, filter and wash with ethanol, and then dry in a vacuum drying oven.

[0034] The mass of the pretreated waste leather scraps is 1-3 g; the mixing ratio of methanol to water is 2:1; the molar amount of cobalt salt is 0.1-2 mmol; the first stirring time is 1 h; the second stirring time is 3-24 h; the ethanol filtration and washing is performed 5 times; and the drying temperature is 60°C.

[0035] Step 3, place the cobalt-loaded catalyst precursor into a tube furnace and perform annealing treatment in a nitrogen atmosphere, then collect the obtained product after cooling to room temperature, to obtain a chromium-cobalt-loaded carbon-based catalyst.

[0036] The calcination conditions are: in nitrogen atmosphere; the heating rate is 5℃ / min; the annealing temperature is 600-1000℃; the holding time is 2-4h.

[0037] By using the abundant functional groups in chromium-containing waste leather shavings as active sites, direct impregnation of cobalt salt cannot successfully load it, but coordination through organic ligand connection metal cobalt can make metal cobalt uniformly loaded on chromium-containing waste leather shavings, and the presence of organic ligand can further increase the nitrogen content. By one-step calcination method, metal is stably and uniformly fixed on biomass carbon, which can reduce metal nanoparticle agglomeration to a certain extent and maximize the catalytic performance of non-noble metals. Embodiment

[0038] A preparation method of a bifunctional electrocatalyst based on waste leather shavings loaded with metal cobalt, comprising the following steps:

[0039] Step 1, waste chromium shavings pretreatment: collect chromium-containing waste leather shavings from the planing process of a leather processing plant, soak them in a mixed solution of ethanol and water for 24h, crush them with a homogenizer and wash them with water several times, dry them and sieve them with a mesh screen for use;

[0040] Step 2, add the pretreated chromium-containing waste leather shavings and intermediates in step 1 to a 15ml mixed solution of methanol and deionized water to form solution A, then weigh cobalt salt and dissolve it in 5ml deionized water to form solution B, stir at room temperature for 1h, then pour solution B into solution A, stir for another 3h, filter and wash with ethanol, then dry in a 60℃ vacuum drying oven to obtain a metal cobalt-loaded catalyst precursor.

[0041] Step 3, place the metal cobalt-loaded catalyst precursor into a tube furnace and perform annealing treatment in a nitrogen atmosphere, then collect the obtained product after cooling to room temperature, i.e. a chromium cobalt-loaded carbon-based catalyst.

[0042] In step 1, the ratio of chromium-containing waste leather shavings to mixed solution is 1:3; the mixing ratio of water to ethanol is 2:1; the crushing time with a homogenizer is 2min; the drying temperature is 60℃; and the mesh size is 10 mesh.

[0043] In step 2, the cobalt salt is cobalt nitrate / cobalt sulfate / cobalt chloride, the molar amount of cobalt salt is 0.1mmol, and the intermediate is 2-methylimidazole, the molar amount of 2-methylimidazole is 0.6mmol.

[0044] In step 2, the mass of the pretreated chromium-containing waste leather shavings is 1g; the mixing ratio of methanol to water is 2:1; the ethanol filtering and washing is performed 5 times; and the drying temperature is 60℃.

[0045] In step 3, the calcination conditions are: in nitrogen atmosphere; the heating rate is 5℃ / min; the carbonization temperature is 600℃; and the holding time is 2h. Embodiment

[0046] A preparation method of a bimetallic cobalt-based electrocatalyst loaded on waste leather scraps, comprising the following steps:

[0047] Step 1, waste chromium scrap pretreatment: collect chromium-containing waste leather scraps from the planing process of a leather processing factory, soak them in a mixed solution of ethanol and water for 36 h, crush them with a homogenizer, wash them with water several times, dry them, and then sieve them with a mesh screen for use;

[0048] Step 2, add the pretreated chromium-containing waste leather scraps and intermediates in step 1 to a 30 ml mixed solution of methanol and deionized water to form solution A, and then weigh cobalt salt and dissolve it in 10 ml deionized water to form solution B, stir solution B at room temperature for 1 h, then pour solution B into solution A, stir for another 12 h, filter and wash with ethanol, and then dry in a 60℃ vacuum drying oven; thus a cobalt metal-loaded catalyst precursor is obtained.

[0049] Step 3, place the cobalt metal-loaded catalyst precursor into a tube furnace, and perform annealing treatment in a nitrogen atmosphere, and then collect the obtained product after cooling to room temperature, thus a chromium cobalt-loaded carbon-based catalyst is obtained.

[0050] In the step 1, the ratio of chromium-containing waste leather scraps to the mixed solution is 1:3, the mixing ratio of water to ethanol is 3:1, the crushing time of the homogenizer is 6 min, the drying temperature is 70℃, and the mesh size of the sieve is 50 mesh.

[0051] In the step 2, the cobalt salt is cobalt nitrate / cobalt sulfate / cobalt chloride, the molar amount of the cobalt salt is 1 mmol, and the intermediate is 2-methylimidazole, the molar amount of 2-methylimidazole is 6 mmol.

[0052] In the step 2, the mass of the pretreated chromium-containing waste leather scraps is 2 g, the mixing ratio of methanol to water is 2:1, the ethanol filtering and washing is performed 5 times, and the drying temperature is 60℃.

[0053] In the step 3, the calcination conditions are as follows: in a nitrogen atmosphere, the heating rate is 5℃ / min, the carbonization temperature is 800℃, and the holding time is 3 h. Embodiment

[0054] A preparation method of a bimetallic cobalt-based electrocatalyst loaded on waste leather scraps, comprising the following steps:

[0055] Step 1, waste chromium scrap pretreatment: collect chromium-containing waste leather scraps from the planing process of a leather processing factory, soak them in a mixed solution of ethanol and water for 48 h, crush them with a homogenizer, wash them with water several times, dry them, and then sieve them with a mesh screen for use;

[0056] Step 2, the pretreated chromium-containing waste leather scraps and intermediates in step 1 are added into a 40ml mixed solution of methanol and deionized water to form solution A, and a cobalt salt is weighed and dissolved in 20ml deionized water to form solution B, after stirring at room temperature for 1h, solution B is poured into solution A, and then stirred for 24h, and then filtered and washed with ethanol, and then dried in a 60℃ vacuum drying oven to obtain a cobalt metal-loaded catalyst precursor.

[0057] Step 3, the cobalt metal-loaded catalyst precursor is placed in a tube furnace and annealed in a nitrogen atmosphere, and after cooling to room temperature, the obtained product is collected, i.e. a chromium-cobalt-loaded carbon-based catalyst is obtained.

[0058] In the step 1, the ratio of chromium-containing waste leather scraps to mixed solution is 1:3; the mixing ratio of water to ethanol is 5:1; the homogenizer crushing time is 10min; the drying temperature is 80℃; and the screen mesh size is 100 meshes.

[0059] In the step 2, the cobalt salt is cobalt nitrate / cobalt sulfate / cobalt chloride, the molar amount of cobalt salt is 2mmol, and the intermediate is 2-methylimidazole, the molar amount of 2-methylimidazole is 12mmol.

[0060] In the step 2, the mass of the pretreated chromium-containing waste leather scraps is 3g; the mixing ratio of methanol to water is 2:1; the ethanol filtering and washing is performed 5 times; and the drying temperature is 60℃.

[0061] In the step 3, the calcination conditions are: in a nitrogen atmosphere; the heating rate is 5℃ / min; the carbonization temperature is 1000℃; and the holding time is 4h.

[0062] Comparative Example

[0063] 100g of chromium-containing waste leather scraps from the shaving process of a leather processing plant are weighed, 200ml of water and 100ml of ethanol are added and soaked for 24h, then the mixture is poured into a homogenizer and crushed for 10min, then the crushed mixture is washed with water several times, dried in a 80℃ vacuum drying oven, and then passed through a 10 mesh screen. Then, it is placed in a tube furnace and heated to 900℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and held for 2h, and then cooled to room temperature, and the obtained black product is collected.

[0064] Figure 1 is the oxygen evolution polarization curve of the carbon-based electrocatalyst prepared by the present application with different molar amounts of cobalt under alkaline conditions of 1M KOH solution, Figure 2is the hydrogen evolution polarization curve of the carbon-based electrocatalyst prepared by different molar amounts of cobalt in the present application under alkaline conditions 1 M KOH solution. According to the test results, it is shown that the hydrogen evolution and oxygen evolution performance of the catalyst prepared by the waste leather crumb containing chromium without loading metal cobalt in the comparative example is very poor, and almost has no catalytic performance. It may be due to the fact that the metal chromium cannot play a catalytic effect alone. By loading metal cobalt, a certain active species is introduced to make it synergize with the chromium oxide therein. When the content of the introduced metal cobalt is 0.1 mM, the catalytic activity is still poor, but it is improved compared with the catalytic activity when the chromium oxide alone is used as the active species. When the amount of the metal cobalt is 1 mM, the catalytic activity of the hydrogen evolution and oxygen evolution reaction reaches the optimum, and the overpotential is 326 mV and 390 mV, respectively, when the current density is 10 mA cm -2 When the loaded metal cobalt is too much, the performance of the catalyst is reduced. The reason may be that the agglomeration occurs between the metal particles, which reduces the specific surface area of the reaction and affects the rapid transmission between the electrons, thereby hindering the progress of the catalytic reaction. The transmission kinetics of the chromium-cobalt bimetallic carbon-based electrocatalyst is analyzed by impedance. Figure 3 The semicircular diameter of the Nyquist plot of the transmission kinetics can further prove the charge transfer ability. As can be seen from the figure, the semicircular diameter of the catalyst with the content of 1 mM of cobalt is the smallest, which confirms the charge transfer ability of the OER.

[0065] In order to determine the composition of the catalyst, XRD component analysis is carried out, and it is shown by Figure 4 that the crystal composition formed in the calcination process at the same temperature is slightly different due to the different contents of the introduced metal cobalt. The XRD spectrum of CL / Co-0 shows that the diffraction peaks of 2θ = 37.6°, 43.7°, 63.5° and 76.2° belong to the characteristic peaks of PDF#76-2494-CrN, and the diffraction peaks of 2θ = 24.5°, 33.6°, 36.2°, 41.5°, 54.8°, 63.4° and 65.1° belong to the characteristic peaks of PDF#38-1479-Cr2O3. With the gradual increase of the content of the metal cobalt, the diffraction peaks of the metal cobalt (PDF#15-0806-Co) appear at 44.2°, 51.5° and 75.8° from CL / Co-0.5, and the diffraction peak of CrN corresponding to 37.6° gradually disappears. In CL / Co-0.1, the characteristic peak of the metal cobalt may not appear due to the too low concentration of the cobalt salt. The appearance of the characteristic peak of the metal cobalt is due to the increase of the concentration of the cobalt loaded on the surface. As can be seen from the SEM image of Figure 5 , the calcined waste leather crumb still maintains the original fiber bundle shape. As can be seen from the EDS area scan image of Figure 6 , the chromium element and the cobalt element are uniformly loaded on the carbon fiber substrate.

Claims

1. A method for the preparation of a bifunctional electrocatalyst based on cobalt metal supported on waste leather shavings, characterized by, It comprises the following steps: Step 1, waste chromium scrap pretreatment: collect the chromium-containing waste leather scrap from the shaving process of a leather processing plant, soak it in a mixed solution of ethanol and water for 24-36 h, crush it with a homogenizer, wash it with water several times, dry it, and sieve it with a mesh screen for use; In step 1, the ratio of chromium-containing waste leather scrap to mixed solution is 1:3; the mixing ratio of water to ethanol is 2-5:1; the homogenizer crushing time is 2-10 min; the drying temperature is 60-80℃; and the mesh size is 10-100 mesh; Step 2, add the pretreated chromium-containing waste leather scrap and intermediate of step 1 to a 15mL-40mL mixed solution of methanol and deionized water to form solution A, then weigh cobalt salt and dissolve it in 5mL-20mL deionized water to form solution B, stir at room temperature for 1h, then pour solution B into solution A, stir for another 3-24h, filter and wash with ethanol, and then dry in a 60℃ vacuum drying oven; obtain the cobalt-loaded catalyst precursor; The intermediate is 2-methylimidazole; Step 3, place the cobalt-loaded catalyst precursor into a tube furnace and perform annealing treatment in a nitrogen atmosphere, cool to room temperature, collect the resulting product, and obtain the chromium-cobalt-loaded carbon-based catalyst.

2. A method for preparing a dual functional electrocatalyst based on cobalt metal supported on waste leather shavings according to claim 1, characterized by, In step 2, the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride, and the molar amount of cobalt salt is 0.1-2mmol; the ratio of 2-methylimidazole to cobalt salt is 6:

1.

3. The method of claim 1, wherein the method is characterized by: In step 2, the mass of pretreated chromium-containing waste leather scrap is 1-3g; the mixing ratio of methanol to water is 2:1; the ethanol filtering and washing is performed 5 times; and the drying temperature is 60℃.

4. The method of claim 1, wherein the method is characterized by: In step 3, the calcination conditions are: in a nitrogen atmosphere; the heating rate is 5℃ / min; the annealing temperature is 600-1000℃; and the holding time is 2-4h.

5. A chromium-cobalt-loaded carbon-based catalyst prepared by the preparation method of a dual-functional electrocatalyst based on waste leather scrap loaded with cobalt metal according to any one of claims 1-4.

6. The application of the chromium-cobalt-loaded carbon-based catalyst of claim 5 in an electrocatalytic water splitting reaction under 1M KOH alkaline conditions.

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