Microalloyed g-C3N4 catalyst modified MgH2 hydrolysis hydrogen production material and method

Abstract

The method comprises the following steps: step 1, selecting magnesium-rich MgZn powder, putting the magnesium-rich MgZn powder into a high-energy ball milling tank, introducing H2, carrying out ball milling, then transferring into a hydrogenation reaction kettle, introducing hydrogen, emptying air in the reaction kettle, and then heating to obtain a MgH2-Zn hydrolysis material; 2, urea, thiourea and melamine are selected as raw materials and put into corundum crucibles with covers respectively, then the corundum crucibles are sequentially put into a muffle furnace, after the reaction is finished, natural cooling is conducted to the room temperature, finally, the prepared sample is ground to obtain powder, and three kinds of g-C3N4 catalysts can be obtained; and step 3, simultaneously adding the MgH2-coated Zn hydrolysis material and the catalyst obtained in the step 2 into a ball milling tank in a nitrogen atmosphere, and mixing by using a high-energy ball mill to finally obtain three MgH2 hydrolysis materials. The method is helpful for promoting large-scale hydrogen production by magnesium-based hydrolysis in the future.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen production by hydrolysis, and particularly relates to a MgH2 hydrolysis hydrogen production material modified by micro-alloying and a g-C3N4 catalyst and a method. BACKGROUND

[0002] Current hydrogen production methods, such as water electrolysis and natural gas reforming, are still relatively high in cost. Water electrolysis requires a large amount of electrical energy, while natural gas reforming, although lower in cost, produces a large amount of carbon dioxide, and the energy conversion efficiency of existing hydrogen production technologies is limited. Magnesium-based hydrolysis materials (such as magnesium and magnesium alloys) as a new emerging hydrogen production technology have shown great advantages. The raw material cost of magnesium and its alloys is relatively low. The hydrogen production rate of magnesium-based hydrolysis reaction is relatively high, and the reaction conditions are relatively mild. No harmful by-products are produced during the hydrolysis process, and the safety is higher compared with traditional methods. Magnesium-based hydrolysis materials can be used in various environmental conditions and have wide adaptability.

[0003] Currently, the reaction rate of magnesium-based hydrolysis materials with water is slow, especially at low temperatures. For example, SeKwon Oh et al. http: / / dx.doi.org / 10.1016 / j.ijhydene.2016.01.067 studied the effect of temperature on the hydrogen production kinetics of Mg-2.7Ni hydrolysis in a 3.5wt.%NaCl solution. As the solution temperature increased from 30℃ to 70℃, the hydrogen generation rate increased from 24.2ml min -1 g -1 to 172.7ml min -1 g -1 The low temperature rate is slow, and high temperature will limit the large-scale use of hydrolysis and increase the cost. In addition, the magnesium hydroxide generated by the reaction will form a passivation layer on the surface of the magnesium-based material, hindering further hydrolysis reaction and reducing the hydrogen production rate. In order to improve the reaction rate of magnesium and water, it is usually necessary to increase the reaction temperature and catalyst, which will increase the energy consumption and complexity of the system. Moreover, the synthesis of the catalyst is generally complex and high in cost. At present, it is still necessary to explore and develop catalysts with low cost, high efficiency and green environmental protection characteristics to promote the low-temperature hydrolysis process of magnesium-based materials. The defects of the prior art are:

[0004] Firstly, the hydrogen production rate of MgH2 hydrolysis is slow. In order to improve the reaction rate, it is usually necessary to increase the temperature, which will increase the energy consumption, increase the cost, and affect the actual use scenario.

[0005] Secondly, in order to improve the performance, many MgH2 hydrolysis hydrogen production processes change the medium and introduce other metal salt solutions and weak acids to improve the hydrogen production performance, which will complicate the system, increase the cost, and introduce acid to cause rapid and large dehydrogenation. The reaction is too violent and there is a safety hazard.

[0006] Third, in order to improve the performance of MgH2 hydrolysis to produce hydrogen, catalysts are added. However, the preparation process of most catalysts is complicated and the yield is low.

[0007] Fourthly, the hydrolysis performance with added catalysts is still far from practical application. Summary of the Invention

[0008] In order to overcome the problems of the above-mentioned prior art, the purpose of the present invention is to provide a microalloyed and g-C3N4 catalyst-modified MgH2 hydrolysis hydrogen production material and method, which can promote the reaction of microelement batteries and improve the rate and conversion rate of hydrolysis. Based on the fact that g-C3N4 has a large number of defects, the defects have the ability to capture electrons, promote the transfer of electrons, and improve the catalytic hydrolysis performance. g-C3N4 is insoluble in water, non-toxic and harmless, and the reaction is pollution-free, which is conducive to the recovery and reuse of the catalyst, conforming to the design of green engineering. The preparation process is low-cost, the steps are simple and can be mass-produced, which will help promote the future large-scale hydrogen production by magnesium-based hydrolysis. After modification, the g-C3N4 / MgH2@Zn hydrolysis material obtains fast hydrolysis kinetics and almost 100% hydrogen yield.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] Microalloying and g-C3N4 catalyst-modified MgH2 hydrolysis hydrogen production materials, namely g-C3N4@MgH2@Zn composite materials, in which the Zn content of the hydrogenated MgH2@Zn is 5-10% and the MgH2 content is 90-95%. In situ generated g-C3N4 is used as the surface catalyst and g-C3N4 / MgH2@Zn is synthesized by high-energy ball milling. The g-C3N4 / MgH2@Zn has a Mg / MgH2 mass fraction of 80-95%, a Zn mass fraction of 5-10% by weight, and a g-C3N4 mass fraction of 0-10% by weight.

[0011] The 2D stacking morphology of g-C3N4 is used to disperse MgH2, and the abundant pores and surface defects of g-C3N4 are used to inhibit the coating of Mg(OH)2, increase the large number of active sites, and improve the rate and yield of hydrolysis.

[0012] The preparation method of a microalloyed and g-C3N4 catalyst-modified MgH2 hydrolysis hydrogen production material comprises the following steps:

[0013] Step 1, preparation of MgH2@Zn hydrolysis material

[0014] Commercially available magnesium-rich MgZn powder with a purity of ≥99.8% was selected and placed in a high-energy ball mill. H2 was introduced and milled, then transferred to a hydrogenation reactor, where hydrogen was introduced and the air inside the reactor was evacuated. The temperature was then raised to harvest the MgH2@Zn hydrolysis material.

[0015] Step 2: In situ preparation of g-C3N4 catalyst

[0016] Urea (AR, purity ≥99.8%), thiourea (AR, purity ≥99.8%), and melamine (AR, purity ≥99.8%) were selected from Sinopharm Group as raw materials. Equal amounts of urea and thiourea, equal amounts of urea and melamine, and equal amounts of thiourea and melamine were placed in a corundum crucible with a lid, and then placed in a muffle furnace in sequence. After the reaction was completed, the crucible was naturally cooled to room temperature. Finally, the obtained sample was ground into powder to obtain three kinds of g-C3N4 catalysts, namely U / T-C3N4, U / M-C3N4, and T / M-C3N4, where U represents urea, T represents thiourea, and M represents melamine.

[0017] Step 3, composite catalytic modification

[0018] The MgH2@Zn hydrolysis material obtained in step 1 and the three catalysts U / T-C3N4, U / M-C3N4, and T / M-C3N4 obtained in step 2 were simultaneously added to a ball mill under a nitrogen atmosphere, and the materials were mixed using a high-energy ball mill to finally obtain three MgH2 hydrolysis materials, namely g-C3N4@MgH2@Zn composite materials. The g-C3N4@MgH2@Zn composite materials are U / T-C3N4 / MgH2@Zn, U / M-C3N4 / MgH2@Zn, and T / M-C3N4 / MgH2@Zn, respectively.

[0019] The step 1 is specifically as follows:

[0020] After weighing the magnesium-rich MgZn powder, it was placed in a high-energy ball mill, and 0.2-2Mpa H2 was introduced. The ball-to-material ratio was 10-100:1, the ball mill speed was 300-1200rap / min, and the ball milling time was 0.5-12h. It was then sieved through a 200-mesh sieve and placed in a pre-prepared dry stainless steel tray. It was then transferred to a hydrogenation reactor, and 0.2-0.4Mpa hydrogen was introduced for 1-2 minutes. The air inside the reactor was evacuated, and the temperature was then raised to 200-350℃ and maintained for 4-72h to harvest the MgH2@Zn hydrolysis material.

[0021] In the magnesium-rich MgZn powder, the mass fraction of Zn accounts for 5 to 10 wt.%.

[0022] The step 2 is specifically as follows:

[0023] Weigh 10-30g of raw materials on an electronic balance, place them in a corundum crucible with a lid in a ratio of 1:1, and then place them in a muffle furnace. Set the heating rate of the muffle furnace to 2.5-20℃min -1The temperature was raised from room temperature to 500-650°C and maintained for 2-5 hours. After the reaction was completed, the mixture was naturally cooled to room temperature and the obtained sample was finally ground into powder to obtain three types of g-C3N4 catalysts: U / T-C3N4, U / M-C3N4, and T / M-C3N4 (U represents urea, T represents thiourea, and M represents melamine).

[0024] In step 3, the material mass ratio of the MgH2@Zn hydrolysis material to the g-C3N4 catalyst is 9:1.

[0025] In the step 3, the ball-to-material ratio is 10-100:1, the ball milling time is 30-240 min, and the ball mill speed is 300-1200 rap / min, so that the g-C3N4 catalyst and the MgH2@Zn hydrolysis material are evenly mixed, and the g-C3N4 is embedded in the surface of the MgH2@Zn to inhibit the coating of Mg(OH)2 on the surface. The porous carbon nitride also has abundant pores, which serve as channels for hydrogen transmission. In addition, g-C3N4 has good electrical conductivity, which can promote the progress of alloyed microelement batteries, accelerate the progress of the hydrolysis reaction, and achieve synergistic catalytic modification with microalloying to improve the hydrolysis hydrogen production performance.

[0026] The application of the g-C3N4@MgH2@Zn composite material is to select 0.1g g-C3N4@MgH2@Zn composite material in simulated seawater (3.5wt.% sea salt solution), where the sea salt comes from sun-dried sea salt and the sea area is Weihai, China. Hydrolysis hydrogen production test is carried out in a homemade hydrolysis hydrogen production system. The sea salt solution is 500ml and the hydrolysis hydrogen production temperature is 293-313K. The hydrolysis hydrogen production system automatically records the mass of hydrolysis hydrogen every 5s.

[0027] Beneficial effects of the present invention:

[0028] The present invention utilizes microalloying to construct a primary cell, and adds g-C3N4 prepared from mixed raw materials during the MgH2@Zn ball milling process. The alloying and the introduction of the green and harmless g-C3N4 catalyst synergistically catalyze the process to obtain excellent hydrolysis hydrogen production performance, thereby enabling large-scale and efficient hydrolysis hydrogen production.

[0029] First, by constructing a microalloying system, the hydrolysis reaction rate of MgH2 is improved. Under the premise of ensuring the total hydrogen production capacity of the MgH2 material, the steps are simple and the cost is controllable, so that the MgH2 material can achieve excellent hydrolysis performance at room temperature.

[0030] Secondly, the medium chosen in the MgH2 hydrolysis process is seawater, and the sun-dried sea salt solution used is more in line with actual seawater. In addition, some metal salts contained in seawater can also promote the hydrolysis reaction. my country's seawater resources are very rich and can be used for large-scale hydrogen production, which is easy to promote industrialization.

[0031] Third, the g-C3N4 catalyst used in the present invention has a simple synthesis method, low raw material price, and is a green and safe catalyst with good catalytic performance. It can improve the hydrolysis performance of g-C3N4@Mg / MgH2 composite materials, and the catalyst is efficient, controllable and easy to prepare. The different g-C3N4 catalysts in the present invention have different catalytic rates and conversion rates, making it easier to select suitable g-C3N4 catalysts based on actual needs and flexibly respond to actual scenarios.

[0032] Fourthly, the optimal g-C3N4@Mg / MgH2 composite material in the present invention can have an excellent hydrolysis hydrogen production rate and almost 100% conversion rate, and has good future application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 (a) is the SEM image of MgZn powder; Figure 1 (b) is the SEM image of MU-C3N4; Figure 1 (c) is the SEM image of MgH2@5Zn; Figure 1 (d) SEM image of MU-C3N4 / MgH2@5Zn;

[0034] Figure 1 (e)(f)(g)(h)(i) are EDS images of MU-C3N4 / MgH2@5Zn with different elements.

[0035] Figure 2 Graphs of hydrolysis hydrogen production and hydrolysis conversion rates for different samples. DETAILED DESCRIPTION

[0036] The present invention will be described in further detail below with reference to the accompanying drawings.

[0037] like Figure 1 As shown, microalloying and g-C3N4 catalyst modification of MgH2 hydrolysis hydrogen production materials, magnesium-rich MgZn alloy powder was selected, the Mg and Zn potentials in the MgZn alloy were different, and the electrochemical corrosion potential was used in simulated seawater hydrolysis to effectively form a galvanic cell reaction between the interfaces of the MgZn alloy. MgH2@Zn hydrogenated at high temperature and high pressure was used as the raw material. The Zn content in the hydrogenated MgH2@Zn was 5-10%, and the MgH2 content was 90-95%. In situ generated g-C3N4 was selected as the surface catalyst, and g-C3N4 / MgH2@Zn was synthesized by high-energy ball milling, in which the mass fraction of Mg / MgH2 accounted for 80-95%, the mass fraction of Zn accounted for 5-10wt.%, and the mass fraction of g-C3N4 accounted for 0-10wt.%.

[0038] Example 1

[0039] Commercial purity ≥99.8% metallic MgZn powder was selected, and the Zn mass fraction was 5wt.%. The raw materials for g-C3N4 catalyst preparation were purchased from Sinopharm Group. Thiourea (AR, purity ≥99.8%), urea (AR, purity ≥99.8%), and melamine (AR, purity ≥99.8%) were purchased from Sinopharm Group. The sea salt was derived from sun-dried sea salt in Weihai, China. Step 1, preparation of MgH2@Zn hydrolysis material. MgZn powder was selected, and the Zn mass fraction was 5wt.%. After weighing, it was placed in a high-energy ball mill and passed through 0.5Mpa H2, the ball-to-material ratio is 40:1, the ball mill speed is 350rap / min, the ball milling time is 1h, then it is sieved through a 200-mesh sieve and placed in a pre-prepared dry stainless steel tray. It is then transferred to a hydrogenation reactor and introduced with 0.2Mpa hydrogen for 1 minute. The air inside the reactor is evacuated and then heated to 350℃ and maintained for 48h to harvest the MgH2@Zn hydrolysis material.

[0040] Step 2, preparation of g-C3N4 catalysts with different raw materials

[0041] Urea, thiourea and melamine were used as raw materials. 20 g of each was weighed using an electronic balance. Two of them were placed in a corundum crucible with a 1:1 ratio. The crucibles were then placed in a muffle furnace. The heating rate of the muffle furnace was set at 10 °C / min. -1 The temperature was raised from room temperature to 550°C and maintained for 4 hours. After the reaction was completed, the mixture was naturally cooled to room temperature and the obtained sample was ground into powder to obtain three types of g-C3N4 catalysts: U / T-C3N4, U / M-C3N4, and T / M-C3N4 (U represents urea, T represents thiourea, and M represents melamine).

[0042] Step 3, composite catalytic modification

[0043] The MgH2@Zn hydrolysis material obtained in step 1 and the three catalysts U / T-C3N4, U / M-C3N4, and T / M-C3N4 obtained in step 2 were simultaneously added to a ball mill under a nitrogen atmosphere, and the materials were mixed using a high-energy ball mill with a ball-to-material ratio of 40:1, a ball milling time of 60 min, and a ball mill speed of 800 rap / min to uniformly mix the catalyst and the MgH2@Zn hydrolysis material, ultimately obtaining three MgH2 hydrolysis materials: U / T-C3N4 / MgH2@Zn, U / M-C3N4 / MgH2@Zn, and T / M-C3N4 / MgH2@Zn;

[0044] Step 4: Simulate seawater hydrogen production

[0045] 0.1 g of the g-C3N4 / MgH2@Zn composite material prepared in step 3 was placed in simulated seawater (3.5 wt.% sea salt solution) and subjected to a hydrolysis hydrogen production test in a homemade hydrolysis hydrogen production system. The sea salt solution was 500 ml, the hydrolysis hydrogen production temperature was 293 K, and the hydrolysis hydrogen production system automatically recorded the mass of hydrolysis hydrogen produced every 5 seconds.

[0046] Example 2

[0047] Commercially available metallic MgZn powder with a purity of ≥99.8% and a Zn mass fraction of 10 wt.% was used for g-C3N4 catalyst preparation. Thiourea (AR, purity ≥99.8%), urea (AR, purity ≥99.8%), and melamine (AR, purity ≥99.8%) were purchased from Sinopharm Group. Sea salt was sourced from sun-dried sea salt in Weihai, China.

[0048] Step 1, preparation of MgH2@Zn hydrolysis material: MgZn powder with a Zn mass fraction of 10 wt.% was selected, and after weighing, it was placed in a high-energy ball mill, and 0.6 MPa H2 was introduced. The ball-to-material ratio was 30:1, the ball mill speed was 600 rap / min, and the ball milling time was 2 h. Then, it was sieved through a 200-mesh sieve and placed in a pre-prepared dry stainless steel tray. It was then transferred to a hydrogenation reactor, and 0.3 MPa hydrogen was introduced for 1 minute. The air inside the reactor was evacuated, and then the temperature was raised to 300°C and maintained for 36 h to harvest the MgH2@Zn hydrolysis material.

[0049] Step 2, preparation of g-C3N4 catalysts with different raw materials

[0050] Urea, thiourea and melamine were used as raw materials. 30 g of each was weighed using an electronic balance. Two of them were placed in a corundum crucible with a 1:1 ratio. The crucibles were then placed in a muffle furnace. The heating rate of the muffle furnace was set at 5 °C / min. -1 The temperature was raised from room temperature to 600°C and kept at this temperature for 4 hours. After the reaction was completed, the mixture was naturally cooled to room temperature and the obtained sample was finally ground into powder to obtain three types of g-C3N4 catalysts: U / T-C3N4, U / M-C3N4, and T / M-C3N4 (U represents urea, T represents thiourea, and M represents melamine).

[0051] Step 3, composite catalytic modification

[0052] The MgH2@Zn hydrolysis material obtained in step 1 and the three catalysts U / T-C3N4, U / M-C3N4, and T / M-C3N4 obtained in step 2 were simultaneously added to a ball mill under a nitrogen atmosphere, and the materials were mixed using a high-energy ball mill with a ball-to-material ratio of 30:1, a ball milling time of 120 min, and a ball mill speed of 1000 rap / min to uniformly mix the catalyst and the MgH2@Zn hydrolysis material, ultimately obtaining three MgH2 hydrolysis materials: U / T-C3N4 / MgH2@Zn, U / M-C3N4 / MgH2@Zn, and T / M-C3N4 / MgH2@Zn;

[0053] Step 4: Simulate seawater hydrogen production

[0054] 0.1 g of the g-C3N4 / MgH2@Zn composite material prepared in step 3 was placed in simulated seawater (3.5 wt.% sea salt solution) and subjected to a hydrolysis hydrogen production test in a homemade hydrolysis hydrogen production system. The sea salt solution was 500 ml, the hydrolysis hydrogen production temperature was 303 K, and the hydrolysis hydrogen production system automatically recorded the mass of hydrolysis hydrogen produced every 5 seconds.

[0055] Example 3

[0056] Commercially available metallic MgZn powder with a purity of ≥99.8% and a Zn mass fraction of 5 wt.% was used for g-C3N4 catalyst preparation. Thiourea (AR, purity ≥99.8%), urea (AR, purity ≥99.8%), and melamine (AR, purity ≥99.8%) were purchased from Sinopharm Group. Sea salt was sourced from sun-dried sea salt in Weihai, China.

[0057] Step 1, preparation of MgH2@Zn hydrolysis material

[0058] MgZn powder with a Zn mass fraction of 5 wt.% was selected and weighed, and then placed in a high-energy ball mill, into which 0.8 MPa H2 was introduced, with a ball-to-material ratio of 60:1, a ball mill speed of 500 rap / min, and a ball milling time of 3 h. The powder was then sieved through a 200-mesh sieve and placed in a pre-prepared dry stainless steel tray. The powder was then transferred to a hydrogenation reactor, into which 0.2 MPa hydrogen was introduced for 1 minute, and the air inside the reactor was evacuated. The temperature was then raised to 400 ° C and maintained for 24 h to harvest the MgH2@Zn hydrolysis material.

[0059] Step 2, preparation of g-C3N4 catalysts with different raw materials

[0060] Urea, thiourea and melamine were used as raw materials. 25g of each was weighed using an electronic balance. Two of them were placed in a corundum crucible with a 1:1 ratio. The crucibles were then placed in a muffle furnace. The heating rate of the muffle furnace was set at 10℃ min. -1The temperature was raised from room temperature to 500°C and kept at this temperature for 3 hours. After the reaction was completed, the mixture was naturally cooled to room temperature and the obtained sample was finally ground into powder to obtain three types of g-C3N4 catalysts: U / T-C3N4, U / M-C3N4, and T / M-C3N4 (U represents urea, T represents thiourea, and M represents melamine).

[0061] Step 3, composite catalytic modification

[0062] The MgH2@Zn hydrolysis material obtained in step 1 and the three catalysts U / T-C3N4, U / M-C3N4, and T / M-C3N4 obtained in step 2 were simultaneously added to a ball mill under a nitrogen atmosphere, and the materials were mixed using a high-energy ball mill with a ball-to-material ratio of 60:1, a ball milling time of 240 min, and a ball mill speed of 900 rap / min to uniformly mix the catalyst and the MgH2@Zn hydrolysis material, ultimately obtaining three MgH2 hydrolysis materials: U / T-C3N4 / MgH2@Zn, U / M-C3N4 / MgH2@Zn, and T / M-C3N4 / MgH2@Zn;

[0063] Step 4: Simulate seawater hydrogen production

[0064] 0.1 g of the g-C3N4 / MgH2@Zn composite material prepared in step 3 was placed in simulated seawater (3.5 wt.% sea salt solution) and subjected to a hydrolysis hydrogen production test in a homemade hydrolysis hydrogen production system. The sea salt solution was 500 ml, the hydrolysis hydrogen production temperature was 293 K, and the hydrolysis hydrogen production system automatically recorded the mass of hydrolysis hydrogen produced every 5 seconds.

[0065] The optimal g-C3N4@Mg / MgH2 composite material in the present invention can have an excellent hydrolysis hydrogen production rate and an almost 100% conversion rate. According to the reaction equation of MgH2+2H2O→Mg(OH)2+2H2↑, the hydrogen production capacity of 0.1g of MgH2 under standard conditions is calculated to be 172.3ml·g -1 We added 5% Zn, and Zn hydrolyzes Zn+2H2O→Mg(OH)2+H2↑, and 0.1g is 34.5ml·g -1 The yield of 0.1g MgH2@5Zn is 172.3×0.95+34.5×0.05=165.41ml·g -1 Adding 10% of the catalyst does not hydrolyze, so the capacity is 165.41×0.9=148.869ml·g -1 The best sample is 148.42 ml·g -1 , the conversion rate was calculated to be 99.97%.

[0066] Figure 1Figure 2 is the SEM and EDS images of MgZn powder, MU-C3N4, MgH2@5Zn and MU-C3N4 / MgH2@5Zn. Figure (a) is the SEM image of MgZn powder. It can be seen that it is a uniformly distributed sphere with an average size of about 18.3μm. Figure (b) is the SEM image of MgZn powder after hydrogenation. It can be seen that the morphology has changed after hydrogenation, from spherical to irregular block, and the size has also increased. It is caused by the agglomeration of some of them after ball milling, and the chemical reaction process during the subsequent high-temperature hydrogenation. Its average size increased from 18.3μm to 29.9μm. Figure (c) is the SEM image of MU-C3N4. EM image shows that it is stacked in layers with abundant pores and cracks. After compounding with MgH2@5Zn, it can provide additional active sites for H2 in the hydrolysis reaction. The abundant pores can also become channels for H2 transmission, thereby improving the performance of hydrolysis. Figure (d) is the SEM image of MU-C3N4 / MgH2@5Zn. It can be seen that the size of MgH2@5Zn is further reduced after ball milling. The size reduction can increase the specific surface area and have more reaction active sites. In addition, MU-C3N4 is broken and refined in size after ball milling, and is evenly distributed around MgH2@5Zn. This can inhibit the coating of Mg(OH)2 during the hydrolysis process, thereby improving the conversion rate of hydrolysis. Figure (e) is the EDS graph of MU-C3N4 / MgH2@5Zn. It can be seen from the figure that Mg, Zn, C and N are evenly distributed in the sample. The appearance of Zn proves the existence of MgZn alloy. In addition, the uniform distribution of C and N elements indicates that MU-C3N4 and MgH2@5Zn are successfully composited, which shows that the MU-C3N4 / MgH2@5Zn sample has been successfully prepared.

[0067] Figure 2 The hydrolysis performance diagram of the composite sample, MgH2@5Zn and MgH2@5Zn after ball milling shows that the hydrolysis yields of different samples are different as the reaction proceeds. Among them, the hydrolysis effect of MgH2@5Zn is the worst, with a hydrogen production of 28.3 ml·0.1 g -1 The ball-milled MgH2@5Zn Balling increased by 2.3 times compared to the unmilled MgH2@5Zn, and the hydrogen production reached 65.56ml·0.1g -1, which shows that ball milling can improve some of the hydrolysis performance. This may be due to the holes and defects increased by ball milling. The holes increase the channels for hydrogen transmission during the hydrolysis process, and the defects increase the reaction active sites, which optimizes the hydrolysis reaction and thus improves some of the performance. As can be seen from the figure, after the introduction of g-C3N4, the rate and yield of hydrolysis have been greatly improved. This is because the unique 2D stacking morphology of g-C3N4 can well disperse MgH2 and due to the rich holes and surface defects of g-C3N4, it can further inhibit the coating of Mg(OH)2. The increased number of active sites also further improves the rate and yield of hydrolysis. Among them, MU-C3N4 / MgH2@5Zn has the best hydrogen production, reaching 148.42ml·0.1g -1 , and the conversion rate reached 99.97%, which was 5.2 times higher than that of MgH2@5Zn, greatly improving the hydrolysis rate and yield.

Claims

1. Microalloying and g-C3N4 catalyst modified MgH2 hydrolysis hydrogen production material, characterized in that, The g-C3N4@MgH2@Zn composite material comprises 5-10% Zn and 90-95% MgH2 in the hydrogenated MgH2@Zn. In situ generated g-C3N4 is used as a surface catalyst to synthesize g-C3N4 / MgH2@Zn by high-energy ball milling, wherein the mass fractions of Mg / MgH2 are 80-95%, the mass fraction of Zn is 5-10% by weight, and the mass fraction of g-C3N4 is 0-10% by weight. The 2D stacking morphology of g-C3N4 is used to disperse MgH2, and the abundant pores and surface defects of g-C3N4 are used to inhibit the coating of Mg(OH)2, increase the large number of active sites, and improve the rate and yield of hydrolysis.

2. A method for preparing a microalloyed and g-C3N4 catalyst-modified MgH2 hydrolysis hydrogen production material, characterized in that: The following steps are included: Step 1: Select magnesium-rich MgZn powder, place the magnesium-rich MgZn powder in a high-energy ball mill, introduce H2, and ball-mill, then transfer it to a hydrogenation reactor, introduce hydrogen, evacuate the air inside the reactor, and then heat it to harvest the MgH2@Zn hydrolysis material; Step 2: Select urea, thiourea, and melamine as raw materials, take equal amounts of urea and thiourea, equal amounts of urea and melamine, and equal amounts of thiourea and melamine, respectively, and put them into a corundum crucible with a lid, and then put them into a muffle furnace in sequence. After the reaction is completed, naturally cool to room temperature, and finally grind the obtained sample to obtain a powder to obtain three kinds of g-C3N4 catalysts, namely U / T-C3N4, U / M-C3N4, and T / M-C3N4, wherein U represents urea, T represents thiourea, and M represents melamine; Step 3, the MgH2@Zn hydrolysis material obtained in step 1 and the three catalysts U / T-C3N4, U / M-C3N4, and T / M-C3N4 obtained in step 2 are simultaneously added to a ball mill under a nitrogen atmosphere, and mixed using a high-energy ball mill to finally obtain three MgH2 hydrolysis materials, namely g-C3N4@MgH2@Zn composite materials. The g-C3N4@MgH2@Zn composite materials are U / T-C3N4 / MgH2@Zn, U / M-C3N4 / MgH2@Zn, and T / M-C3N4 / MgH2@Zn, respectively.

3. The method for preparing the microalloyed and g-C3N4 catalyst modified MgH2 hydrolysis hydrogen production material according to claim 2, characterized in that: The step 1 is specifically as follows: After weighing the magnesium-rich MgZn powder, it was placed in a high-energy ball mill, and 0.2-2Mpa H2 was introduced. The ball-to-material ratio was 10-100:1, the ball mill speed was 300-1200rap / min, and the ball milling time was 0.5-12h. It was then sieved through a 200-mesh sieve and placed in a pre-prepared dry stainless steel tray. It was then transferred to a hydrogenation reactor, and 0.2-0.4Mpa hydrogen was introduced for 1-2 minutes. The air inside the reactor was evacuated, and the temperature was then raised to 200-350℃ and maintained for 4-72h to harvest the MgH2@Zn hydrolysis material.

4. The method for preparing the microalloyed and g-C3N4 catalyst-modified MgH2 hydrolysis hydrogen production material according to claim 3, characterized in that: In the magnesium-rich MgZn powder, the mass fraction of Zn accounts for 5 to 10 wt.%.

5. The method for preparing the microalloyed and g-C3N4 catalyst modified MgH2 hydrolysis hydrogen production material according to claim 2, characterized in that: The step 2 is specifically as follows: Weigh 10-30g of raw materials on an electronic balance, place them in a corundum crucible with a lid in a ratio of 1:1, and then place them in a muffle furnace. Set the heating rate of the muffle furnace to 2.5-20℃min -1 The temperature was raised from room temperature to 500-650°C and maintained for 2-5 hours. After the reaction was completed, the mixture was naturally cooled to room temperature and the obtained sample was ground into powder to obtain three types of g-C3N4 catalysts: U / T-C3N4, U / M-C3N4, and T / M-C3N4 (U represents urea, T represents thiourea, and M represents melamine).

6. The method for preparing the microalloyed and g-C3N4 catalyst modified MgH2 hydrolysis hydrogen production material according to claim 2, characterized in that: In step 3, the material mass ratio of the MgH2@Zn hydrolysis material to the g-C3N4 catalyst is 9:

1.

7. The method for preparing the microalloyed and g-C3N4 catalyst modified MgH2 hydrolysis hydrogen production material according to claim 2, characterized in that: In step 3, the ball-to-material ratio is 10-100:1, the ball milling time is 30-240 min, and the ball mill speed is 300-1200 rap / min, so that the g-C3N4 catalyst and the MgH2@Zn hydrolysis material are evenly mixed, and the g-C3N4 is embedded in the surface of the MgH2@Zn to inhibit Mg(OH)2 from coating on the surface.

8. Application of the g-C3N4@MgH2@Zn composite material obtained by the method according to any one of claims 2 to 7, characterized in that: The g-C3N4@MgH2@Zn composite material is used for hydrolysis hydrogen production. 0.1 g g-C3N4@MgH2@Zn composite material is selected in simulated seawater, the sea salt solution is 500 ml, the hydrolysis hydrogen production temperature is 293-313 K, and the hydrolysis hydrogen production system automatically records the mass of hydrolysis hydrogen every 5 seconds.

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