A ruthenium-catalyzed material supported on cobalt phosphide / nitrogen co-doped carbon nanotubes, and its preparation method and application

Abstract

The present invention discloses a ruthenium-loaded catalytic material supported on cobalt phosphide / nitrogen co-doped carbon nanotubes, which is composed of cobalt phosphide / nitrogen-doped carbon nanotubes Co<subgt;2< / subgt;P / N-CNTs and Ru; N-CNTs are obtained by calcining and carbonizing CoZn-ZIFs to achieve nitrogen doping of CNTs; Co<subgt;2< / subgt;P is obtained by phosphating CoZn-ZIFs as a self-sacrificing template and sodium hypophosphite. CoZn-ZIFs use CNTs as a carrier and are self-grown on the surface of CNTs from polyvinylpyrrolidone, cobalt nitrate hexahydrate, and zinc nitrate hexahydrate; Ru is obtained by reducing and loading ruthenium hydrate trichloride. CoZn-ZIFs serve as a cobalt source, a zinc source, and a nitrogen source, and the zinc element volatilizes during the calcination process; sodium hypophosphite is a phosphorus source, and ruthenium hydrate trichloride is a ruthenium source. Its preparation method includes the following steps: 1. Preparation of CoZn-ZIFs / CNTs; 2. Preparation of Co / N-CNTs; 3. Preparation of Co<subgt;2< / subgt;P / N-CNTs; 4. Preparation of Ru / Co<subgt;2< / subgt;P / N-CNTs. As a catalytic application in the hydrolysis of ammonia borane for hydrogen production, the hydrogen evolution turnover frequency is 100 - 300 mol<subgt;H2< / subgt>·mol<subgt;Ru< / subgt;<supgt;–1< / supgt>·min<supgt;–1< / supgt>, the hydrogen evolution time by hydrolysis is 20 - 60 s, and the activation energy for catalytic hydrogen evolution is E <subgt; a

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic hydrogen production, and particularly relates to a ruthenium-catalyzed material supported on cobalt phosphide / nitrogen co-doped carbon nanotubes, a preparation method thereof, and an application thereof. Background Art

[0002] As an important application direction of ammonia borane hydrogen production, the catalytic performance of the hydrolysis hydrogen production catalyst mainly depends on the catalytically active metal and the carrier. In terms of metals, it is mainly divided into two categories: noble metal catalysts and non-noble metal catalysts; in terms of carriers, carbon materials have been widely studied and used due to their high specific surface area and high active sites.

[0003] For noble metal catalysts, as described in the existing literature 1 (Cui Z, Guo Y, Feng Z, et al. Ruthenium nanoparticles supported on nitrogen doped porous carbon as a highly efficient catalyst for hydrogen evolution from ammonia borane[J]. New Journal of Chemistry, 2019), an Ru / NC-Fe catalyst with nitrogen-doped porous carbon materials combined with ruthenium nanoparticles was prepared. In the catalytic hydrolysis hydrogen production of ammonia borane, the hydrogen evolution turnover frequency at room temperature was 102.9 mol H2 ·mol Ru -1 ·min -1 . The technical effect of this prior art, that is, the catalytic activity is relatively poor among the ruthenium-supported catalysts of the same type. However, it was proven in this literature that the nitrogen-doped carbon material has certain catalytic activity as a carrier; in addition, the addition of ferrocene carboxaldehyde in this technical solution forms iron oxide, making the catalyst magnetic and facilitating recovery. The technical problem solved by this technical feature has nothing to do with the present invention.

[0004] Non-noble metal catalysts, such as in the existing literature 2 (Zhou L, Jing M, Pan L, et al. Ultrasmall cobalt nanoparticles supported on nitrogen-doped porous carbon nanowires for hydrogen evolution from ammonia borane[J]. Materials Horizons, 2017), prepared a Co / NPCNW catalyst with nitrogen-doped porous carbon nanowires paired with cobalt nanoparticles, achieving a hydrogen evolution turnover frequency of 7.29 mol H2 ·mol Co −1 ·min −1 . This prior art also used nitrogen-doped carbon materials as carriers, but its technical effect was also relatively poor among catalysts with similar supported cobalt.

[0005] Based on the above-mentioned existing literature 1 and existing literature 2, the following conclusion can be drawn regarding metal catalysts: The catalytic performance of a single metal cannot meet the application requirements. The corresponding solution is to use a bimetal as the catalyst. For example, in the existing literature 3 (Liu Z, Yang X, Hu G, et al. Ru Nanocluster Coupled over Co / N Doped Carbon Nanotube Efficiently Catalyzed Hydrogen Evolution Reaction[J]. ACS Sustainable Chemistry & Engineering, 2020), by loading ruthenium nanoparticles on Co / N-doped carbon nanotubes, a Ru@Co / N-CNTs catalyst was prepared, achieving a hydrogen evolution turnover frequency of 33.6 mol H2 ·mol Ru -1 ·min -1 . This technical solution uses Co / N-doped carbon nanotubes with more active sites as carriers to load ruthenium nanoparticles, enabling better dispersion when loading cobalt nanoparticles. At the same time, the synergistic effect between the Ru and Co bimetals is achieved. However, in this technical solution, due to the problem of electron transfer limitation between the carrier and the metal, its catalytic activity still cannot meet the requirements. To solve the technical problems of the existing literature 3, it can be improved by adjusting the carrier.

[0006] Returning to the existing literature 1 and existing literature 2, the following conclusions can be drawn regarding the support: Under the premise of the same type of metal catalyst, the support has a significant impact on the catalytic performance. Combining with the existing literature 3, the research group of the inventors found in the previous research work, namely the existing literature 4 (CN114210343A[P]. 2022 A ruthenium-nickel bimetallic nanocluster catalytic material supported on reduced graphene oxide), that the current one-piece catalyst preparation method is to load ruthenium nanoparticles on the organic framework during synthesis, and then carry out phosphidation and carbonization. This technical feature directly results in fewer active sites on the catalyst surface, thereby reducing the catalytic performance. Therefore, in the existing literature 4, the research group of the inventors adopted the method of phosphidation first and then loading. By changing the metal catalyst from Co to Co2P, the technical effect of improving the electron transfer rate was achieved, thereby obtaining the technical effects of enhancing the adsorption of ammonia borane and water molecules and accelerating the cleavage of the B-N bond in ammonia borane, ultimately increasing the hydrolysis rate of ammonia borane and improving its catalytic activity. At the same time, this technical solution also utilized the characteristic of high-temperature evaporation of zinc, and adopted the technical feature of growing cobalt-zinc MOFs on the surface of carbon nanotubes. Through high-temperature calcination operation, while achieving carbonization, zinc was evaporated and vacancies were left, achieving the technical effect of increasing and regulating active sites. Finally, in the catalytic hydrolysis of ammonia borane to produce hydrogen, the hydrogen evolution turnover frequency at room temperature was 193.9mol H2 ·mol Ru -1 ·min -1 。In the subsequent research of the research group of the present invention, it was found that the technical solution of the existing literature 4 still has the following technical problems in the synthesis process: When directly combining ruthenium nanoparticles with the support, the active sites existing in the support cannot be effectively utilized, thereby affecting the dispersion of ruthenium on the support, and further unable to effectively improve the catalytic activity. Summary of the Invention

[0007] The object of the present invention is to provide a ruthenium catalyst supported on cobalt phosphide / nitrogen co-doped carbon nanotubes, its preparation method and application.

[0008] The basic principle of the present invention to solve the technical problems described in the background is that when preparing nitrogen-doped carbon nanotubes, high temperature is used to evaporate zinc to leave vacancies, and combined with the subsequent step-by-step treatment methods of carbonization and phosphidation, the nitrogen-doped carbon nanotubes have more and exposed active sites when used as a support. Therefore, when loading ruthenium nanoparticles, the ruthenium nanoparticles can obtain better dispersion, and finally the catalytic activity is improved.

[0009] The specific technical features involved include:

[0010] 1. By doping with nitrogen, the number of active sites of the carrier CNTs itself is increased. And taking advantage of the characteristic that zinc will evaporate during the high-temperature carbonization of the cobalt-zinc framework, more vacancies are left, enabling the loaded substances to be more evenly dispersed during loading, thereby improving the intrinsic activity of the catalyst.

[0011] 2. Adopt a preparation method of step-by-step carbonization and phosphidation, so that the carbonization and phosphidation are more complete, thus having more exposed active sites.

[0012] 3. Adopt a preparation method of first phosphidating and then loading ruthenium nanoparticles. When Co is phosphidated to Co2P, it does not affect the normal loading of ruthenium nanoparticles, improving the synergistic effect between cobalt and ruthenium bimetals, thereby improving its intrinsic activity.

[0013] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0014] A ruthenium-loaded cobalt phosphide / nitrogen co-doped carbon nanotube catalytic material is composed of Co2P, nitrogen-doped carbon nanotubes N-CNTs and Ru; wherein, N-CNTs are obtained by calcining and carbonizing CoZn-ZIFs to achieve nitrogen doping of CNTs; Co2P is obtained by phosphidating CoZn-ZIFs as a self-sacrificing template and sodium hypophosphite. The CoZn-ZIFs are supported on CNTs and are self-grown on the surface of CNTs by polyvinylpyrrolidone, cobalt nitrate hexahydrate and zinc nitrate hexahydrate; Ru is obtained by reducing and loading ruthenium chloride hydrate; the CoZn-ZIFs are a cobalt source, a zinc source and a nitrogen source, wherein zinc volatilizes during the calcination process; sodium hypophosphite is a phosphorus source, and ruthenium chloride hydrate is a ruthenium source.

[0015] A preparation method of a ruthenium-loaded cobalt phosphide / nitrogen co-doped carbon nanotube catalytic material includes the following steps:

[0016] Step 1, preparation of CoZn-ZIFs / CNTs. Carbon nanotubes CNTs, polyvinylpyrrolidone, cobalt nitrate hexahydrate and zinc nitrate hexahydrate are placed in methanol and ultrasonicated for a period of time to obtain solution A. At the same time, 2-methylimidazole is dissolved in a certain amount of methanol to obtain solution B. Then, under magnetic stirring conditions, solution B is slowly dropped into solution A. After dropping and mixing evenly, aging is carried out under certain conditions at room temperature to obtain a black-purple precipitate. After washing and centrifuging with methanol under certain conditions, drying is carried out under certain conditions to obtain cobalt-zinc bimetal ZIFs supported on carbon nanotubes, named CoZn-ZIFs / CNTs.

[0017] In the said step 1, the mass ratio of carbon nanotubes, polyvinylpyrrolidone, cobalt nitrate hexahydrate, zinc nitrate hexahydrate and 2-methylimidazole is 2:5:10:5:65.688.

[0018] In Step 1, the aging time is 10 - 36 h; the centrifugation conditions are a centrifugation speed of 8000 - 10000 revolutions per minute, a centrifugation time of 3 - 9 min, and the number of centrifugation times is 3 - 9 times; the drying conditions are a drying temperature of 60 - 90 °C and a drying time of 10 - 16 h;

[0019] Step 2: Preparation of Co / N-CNTs. Under certain conditions, the CoZn-ZIFs / CNTs obtained in Step 1 are subjected to the first calcination. Then, the obtained black product is washed, vacuum filtered, and vacuum dried to obtain cobalt / nitrogen co-doped carbon nanotubes, named Co / N-CNTs;

[0020] In Step 2, the conditions for the first calcination are that under nitrogen conditions, the first calcination temperature is 500 - 1000 °C and the first calcination time is 1 - 5 h;

[0021] Step 3: Preparation of Co2P / N-CNTs. Sodium hypophosphite and the Co / N-CNTs obtained in Step 2 satisfy a certain mass ratio, and phosphidation is achieved by the second calcination under certain conditions. Then, the obtained product is filtered, washed, and dried to obtain cobalt phosphide / nitrogen co-doped carbon nanotubes, named Co2P / N-CNTs;

[0022] In Step 3, the mass ratio of sodium hypophosphite to Co / N-CNTs is 1:1;

[0023] In Step 3, the conditions for the second calcination are that sodium hypophosphite is placed upstream and Co / N-CNTs are placed downstream. Under nitrogen conditions, the second calcination temperature is 500 - 1000 °C and the second calcination time is 1 - 5 h;

[0024] Step 4: Preparation of Ru / Co2P / N-CNTs. Co2P / N-CNTs and ruthenium(III) chloride hydrate are placed in deionized water and stirred for a period of time to obtain mixture C. Then, an aqueous solution of sodium borohydride is added to mixture C for a reduction reaction until no bubbles are generated. Finally, the obtained product is filtered, washed, and dried to obtain a ruthenium catalyst supported on cobalt phosphide / nitrogen co-doped carbon nanotubes, named Ru / Co2P / N-CNTs;

[0025] In Step 4, the mass ratio of Co2P / N-CNTs, ruthenium(III) chloride hydrate, and sodium borohydride is 3:19.

[0026] Catalytic application of a ruthenium catalyst supported on cobalt phosphide / nitrogen co-doped carbon nanotubes in the hydrolysis of ammonia borane for hydrogen production, with a hydrogen evolution turnover frequency of 100 - 300 mol H2 ·mol Ru –1 ·min–1 , the hydrolysis hydrogenation time is 20-60 s, and the activation energy of catalytic hydrogenation is E a =30-35 kJ·mol –1 ; At 25 °C, after 5 cycles, 40-45% of the initial catalytic activity was maintained.

[0027] The beneficial technical effects of the material obtained by the present invention can be seen from testing:

[0028] XRD analysis shows that Ru / Co2P / N-CNTs contains characteristic peaks of Co and C, as well as characteristic peaks of Co2P, but no characteristic peaks of Ru are detected, which is presumably due to the low loading of Ru.

[0029] EDS test shows that there are five elements, C, N, Ru, Co, and P, in Ru / Co2P / N-CNTs, among which Ru, Co, N, and C are relatively concentrated.

[0030] SEM examination showed that Ru / Co2P / N-CNTs showed a typical tubular microstructure;

[0031] The hydrogen production test shows that the hydrogen evolution conversion frequency provided at 25 ℃ is 193.9 mol H2 ·mol Ru –1 min –1 , the hydrolysis rate is 100%;

[0032] The reaction kinetics performance test shows that the apparent activation energy of the reaction E a = 32.4 kJ·mol –1 ;

[0033] The cyclic performance test showed that after 5 cycles at 25 °C, 42.5% of the initial catalytic activity was retained.

[0034] Therefore, the present invention has the following advantages over the prior art:

[0035] 1. The present invention uses nitrogen-doped carbon nanotubes as the initial carrier, utilizing the large number of active sites on its surface to improve the uniformity and dispersion of the load;

[0036] 2. The present invention uses MOFs as a self-sacrificial template, which completes nitrogen doping and Co doping during pyrolysis, and utilizes the synergistic effect between MOFs and Ru to improve the intrinsic activity;

[0037] 3. After phosphating the initial support by the calcination method in the present invention, it is beneficial to expose more active sites, further increase electron conduction, and thus improve the catalytic activity and stability.

[0038] 4. The present invention conducts carbonization and phosphating separately, making the carbonization and phosphating more complete, and having more exposed active sites compared with simultaneous carbonization and phosphating.

[0039] 5. The present invention adopts the preparation method of phosphating first and then loading ruthenium nanoparticles. When Co is phosphated to Co2P, it does not affect the normal loading of ruthenium nanoparticles, improves the synergistic effect between cobalt and ruthenium bimetals, and thus improves its intrinsic activity.

[0040] 6. The raw materials used in the present invention are all chemical raw materials that have been industrially produced, are commercially available, and are easily obtained. The synthesis process is simple, the reaction cycle is short, and the reaction process has low energy consumption and low pollution.

[0041] 7. As an application of a hydrogen production catalyst material, the ruthenium-loaded cobalt phosphide / nitrogen co-doped carbon nanotube catalyst material has high-performance catalytic ammonia borane hydrolysis hydrogen production performance, with a high hydrogen evolution conversion rate and a low reaction activation energy under the condition of 25 °C.

[0042] Therefore, compared with the prior art, the present invention has better hydrogen production catalytic performance and material stability performance, and has broad application prospects in the field of hydrogen production. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 SEM image of CNTs used in step 1 of Example 1;

[0044] Figure 2 XRD pattern of CoZn-ZIFs / CNTs prepared in step 1 of Example 1

[0045] Figure 3 XRD pattern of Co / N-CNTs prepared in step 2 of Example 1;

[0046] Figure 4 SEM image of Co / N-CNTs prepared in step 2 of Example 1.

[0047] Figure 5 XRD pattern of Co2P / N-CNTs prepared in step 3 of Example 1;

[0048] Figure 6 SEM image of Co2P / N-CNTs prepared in step 3 of Example 1;

[0049] Figure 7 XRD pattern of Ru / Co2P / N-CNTs prepared in step 4 of Example 1;

[0050] Figure 8 EDS test chart of Ru / Co2P / N-CNTs prepared in step 4 of Example 1.

[0051] Figure 9 SEM image of Ru / Co2P / N-CNTs prepared in step 4 of Example 1;

[0052] Figure 10 Performance test chart of Co2P / N-CNTs catalyzing ammonia borane hydrolysis prepared in step 3 of Example 1;

[0053] Figure 11 Performance test chart of Ru / Co2P / N-CNTs catalyzing ammonia borane hydrolysis prepared in step 4 of Example 1;

[0054] Figure 12 Performance test chart of Ru / Co2P / N-CNTs catalyzing ammonia borane hydrolysis cycle prepared in step 4 of Example 1;

[0055] Figure 13 Retention rate of Ru / Co2P / N-CNTs catalyzing ammonia borane hydrolysis cycle prepared in step 4 of Example 1;

[0056] Figure 14 Performance test chart of Ru / Co2P / N-CNTs catalyzing ammonia borane hydrolysis at different temperatures prepared in step 4 of Example 1;

[0057] Figure 15 Performance test chart of Ru / Co / N-CNTs catalyzing ammonia borane hydrolysis prepared in Comparative Example 1. Embodiment

[0058] The present invention further elaborates on the content of the present invention through examples in combination with the accompanying drawings of the specification, but it is not a limitation of the present invention. Example

[0059] A preparation method of a ruthenium-catalyzed material supported on cobalt phosphide / nitrogen co-doped carbon nanotubes includes the following steps:

[0060] Step 1, preparation of CoZn-ZIFs / CNTs, 0.2 g carbon nanotubes CNTs, 0.5 g polyvinyl pyrrolidone, 1.0 g cobalt nitrate hexahydrate, and 0.5 g zinc nitrate hexahydrate were placed in 200 mL methanol and ultrasonicated for 0.5 h to obtain solution A. At the same time, 6.5688 g dimethylimidazole was dissolved in 200 mL methanol to obtain solution B. Then, solution B was slowly added dropwise to solution A under magnetic stirring. After the addition was completed and mixed evenly, the solution was aged at room temperature for 24 h to obtain a black-purple precipitate, which was washed and centrifuged with methanol at a centrifugal speed of 8000 rpm and a centrifugal time of 5 min for 5 times. After drying at a drying temperature of 60 ° C and a drying time of 10 h, cobalt-zinc bimetallic ZIFs-loaded carbon nanotubes were obtained, named CoZn-ZIFs / CNTs;

[0061] In order to prove the composition of CoZn-ZIFs / CNTs obtained in step 1, that is, the successful preparation, XRD test was performed. The test results are as follows Figure 2 , CoZn-ZIFs / CNTs contain characteristic peaks of both ZIFs and C. The test results show that the preparation of CoZn-ZIFs / CNTs is successful.

[0062] Step 2, preparation of Co / N-CNTs: calcining the CoZn-ZIFs / CNTs obtained in step 1 for the first time under nitrogen conditions at a first calcination temperature of 900°C and a first calcination time of 5 hours. Then, the resulting black product is washed, vacuum filtered, and vacuum dried to obtain cobalt / nitrogen co-doped carbon nanotubes, named Co / N-CNTs;

[0063] In order to prove the composition of Co / N-CNTs obtained in step 2, that is, the successful preparation, XRD test was carried out. The test results are as follows Figure 3 As shown, the Co / N-CNTs contain characteristic peaks for both elemental Co and C. The characteristic peaks for ZIFs disappear, and no characteristic peaks for Zn are detected. These results indicate that during the first calcination, the ZIFs decompose, forming elemental Co. Furthermore, prior research by our research group and existing literature indicates that Zn volatilizes during calcination, doping the CNTs with nitrogen. This indicates that the Co / N-CNTs are prepared during calcination.

[0064] In order to verify the micromorphology of Co / N-CNTs obtained in step 2, SEM test was performed. The test results are shown in Figure 2. Figure 4 As shown, Co / N-CNTs present a tubular structure.

[0065] Step 3: Preparation of Co2P / N-CNTs. The mass ratio of sodium hypophosphite to Co / N-CNTs obtained in Step 2 is 1:1. Place sodium hypophosphite upstream in the tubular furnace and Co / N-CNTs downstream. Under nitrogen conditions, perform the second calcination at 900 °C for 5 h to achieve phosphidation. Then, after the obtained product is filtered, washed, and dried, cobalt phosphide / nitrogen co-doped carbon nanotubes, named Co2P / N-CNTs, can be obtained.

[0066] To prove the composition of Co2P / N-CNTs obtained in Step 3, that is, to successfully prepare it, XRD testing was carried out. The test results are as Figure 5 shown. In addition to the characteristic peaks of Co and C, Co2P also has characteristic peaks in Co2P / N-CNTs. The test results indicate that during the second calcination process, part of Co reacts with P to form Co2P, that is, phosphidation is achieved.

[0067] To prove the microscopic morphology of Co2P / N-CNTs obtained in Step 3, SEM testing was carried out. The test results are as Figure 6 shown. Co2P / N-CNTs still maintain a tubular structure, that is, the second calcination process does not change the microscopic morphology of the material.

[0068] Step 4: Preparation of Ru / Co2P / N-CNTs. Place 100 mg of Co2P / N-CNTs obtained in Step 3 and 6 mg of ruthenium(III) chloride hydrate in deionized water and stir for 6 h to obtain mixture C. Then, add an aqueous solution containing 38 mg of sodium borohydride to mixture C for a reduction reaction until no bubbles are generated. Finally, after the obtained product is filtered, washed, and dried, a ruthenium-loaded cobalt phosphide / nitrogen co-doped carbon nanotube catalyst material, named Ru / Co2P / N-CNTs, can be obtained.

[0069] To prove the composition of Ru / Co2P / N-CNTs obtained in Step 4, that is, to successfully prepare it, XRD testing was carried out. The test results are as Figure 7 shown. The XRD pattern of Ru / Co2P / N-CNTs has no obvious difference from that of Co2P / N-CNTs, that is, no characteristic peaks of Ru are detected.

[0070] Therefore, to further prove the successful loading of Ru, EDS testing was carried out. The test results are as Figure 8 shown. Ru / Co2P / N-CNTs contain Ru, N, Co, P, and C elements at the same time, that is, it is proved that Ru is successfully loaded.

[0071] To prove the microscopic morphology of Ru / Co2P / N-CNTs obtained in Step 4, SEM testing was carried out. The test results are as Figure 9As shown, Ru / Co2P / N-CNTs still maintain a tubular structure, that is, the process of loading Ru does not change the microscopic morphology of the material.

[0072] To prove that Ru / Co2P / N-CNTs have the performance as a catalyst for hydrogen production by ammonia borane hydrolysis, a hydrolysis performance test was carried out. The specific test method is as follows: Under standard atmospheric pressure and at 25 °C, 100 mg of the sample to be tested was placed in a wide-mouth bottle, 20 mL of deionized water was added and stirred well to disperse. Then, the wide-mouth bottle was connected to a metering tube filled with water in a constant temperature water bath. Under magnetic stirring conditions, 10 mL of an aqueous solution of ammonia borane with a concentration of 0.1 mmol / mL was injected. Finally, the volume of hydrogen generated was calculated by the water displacement method; among them, the hydrogen evolution turnover frequency was calculated through the hydrogen evolution time, which can reflect the reaction rate of hydrogen evolution during hydrolysis. At the same time, to prove the influence of loaded Ru on the performance, the hydrolysis performance test of Co2P / N-CNTs obtained in step 3 was carried out.

[0073] The hydrolysis performance test results of Co2P / N-CNTs are as Figure 10 shown, the hydrogen evolution time is 400 s, and the hydrogen evolution turnover frequency is 20.36 mol H2 ·mol metal –1 ·min –1 , and the hydrolysis rate is 70%. The test results show that Co2P / N-CNTs have catalytic performance, but the catalytic activity is very low.

[0074] The hydrolysis performance test results of Ru / Co2P / N-CNTs are as Figure 11 shown, the hydrogen evolution time for hydrogen evolution during hydrolysis is 40 s, and the hydrogen evolution turnover frequency is 193.9 mol H2 ·mol Ru –1 ·min –1 , and the hydrolysis rate is 100%. By comparing Co2P / N-CNTs and Ru / Co2P / N-CNTs, it can be seen that loading Ru can reduce the hydrogen evolution time during hydrolysis to 1 / 10, that is, significantly improve the hydrogen evolution rate during hydrolysis; at the same time, the hydrolysis rate is significantly improved, from 70% to 100%.

[0075] To prove the cycling performance of Ru / Co2P / N-CNTs, a cycling performance test was carried out. The specific test method is as follows: Repeatedly injecting an aqueous solution of ammonia borane for the hydrolysis performance test can achieve the cycling performance test. The cycling performance test results of Ru / Co2P / N-CNTs are as Figure 12 shown, after 5 cycles, the hydrogen evolution turnover frequency is 82.35 mol H2 ·mol Ru –1 ·min –1, the hydrolysis rate is 100%. The test results show that Ru / Co2P / N-CNTs has cycling performance.

[0076] To prove the influence of Ru / Co2P / N-CNTs on the kinetic performance of ammonia borane hydrolysis, the hydrolysis performance tests were carried out at different temperatures, and the test temperatures were 25 °C, 35 °C, 45 °C, and 55 °C respectively. The test results are as Figure 13 and Table 1 show that the activation energy can be calculated to be 32.4 kJ·mol -1 by fitting with the Arrhenius equation, which can prove that Ru / Co2P / N-CNTs significantly improves the kinetic performance of ammonia borane hydrolysis.

[0077] Table 1 Hydrogen evolution turnover frequency and time required to complete hydrogen evolution hydrolysis at different temperatures

[0078] Temperature (°C) 25 35 45 55 Time required to complete hydrogen evolution by hydrolysis (s) 40 24 16 11 <![CDATA[Hydrogen evolution conversion frequency (mol H2 ·mol Ru –1 ·min –1 )]]. 193.9 317.1 490.9 645.4

[0079] To prove the influence of the phosphidation in Step 3 on the performance, Comparative Example 1, Ru / Co / N-CNTs without phosphidation operation, is provided.

[0080] Comparative Example 1

[0081] A preparation method of Ru / Co / N-CNTs, the steps not specifically described are the same as those in Example 1, the difference is that: Step 3 is not carried out, and the Co / N-CNTs obtained in Step 2 are directly subjected to Step 4, and the obtained material is named Ru / Co / N-CNTs.

[0082] The hydrolysis performance test results of Ru / Co / N-CNTs are as Figure 14 shown, the hydrogen evolution time is 320 s, and the hydrogen evolution turnover frequency is 22.33 mol H2 ·mol Ru –1 ·min –1 , and the hydrolysis rate is 92.3%.

[0083] By comparing Example 1 and Comparative Example 1, it can be seen that phosphidation can significantly reduce the hydrogen evolution time and increase the hydrogen evolution turnover frequency, and the effect reaches 8 times. The above comparison can prove that phosphidation can significantly improve the catalytic activity by significantly increasing the electron transfer rate.

Claims

1. Application of a ruthenium-catalyzed material supported on cobalt phosphide / nitrogen co-doped carbon nanotubes in electrocatalytic hydrolysis of ammonia borane for hydrogen production, characterized in that, The preparation method of ruthenium supported on cobalt phosphide / nitrogen co-doped carbon nanotubes comprises the following steps: Step 1, Preparation of CoZn-ZIFs / CNTs: Carbon nanotubes CNTs, polyvinylpyrrolidone, cobalt nitrate hexahydrate, and zinc nitrate hexahydrate are placed in methanol and ultrasonicated for a period of time to obtain solution A. Meanwhile, dimethylimidazole is dissolved in a certain amount of methanol to obtain solution B. Then, under magnetic stirring conditions, solution B is slowly dropped into solution A. After dropping and mixing evenly, under room temperature conditions, aging is carried out under certain conditions to obtain a black-purple precipitate. After washing and centrifuging with methanol under certain conditions, drying is carried out under certain conditions to obtain cobalt-zinc bimetallic ZIFs supported on carbon nanotubes, named CoZn-ZIFs / CNTs; In the said Step 1, the mass ratio of carbon nanotubes, polyvinylpyrrolidone, cobalt nitrate hexahydrate, zinc nitrate hexahydrate, and dimethylimidazole is 2:5:10:5:65.688; In the said Step 1, the aging time is 10 - 36 h; the centrifugation speed is 8000 - 10000 revolutions per minute, the centrifugation time is 3 - 9 min, and the number of centrifugations is 3 - 9 times; the drying temperature is 60 - 90 °C, and the drying time is 10 - 16 h; Step 2, Preparation of Co / N-CNTs: Under certain conditions, the CoZn-ZIFs / CNTs obtained in Step 1 are subjected to the first calcination. Then, the obtained black product is washed, vacuum filtered, and vacuum dried to obtain cobalt / nitrogen co-doped carbon nanotubes, named Co / N-CNTs; In the said Step 2, the conditions for the first calcination are: under nitrogen conditions, the first calcination temperature is 1000 °C, and the first calcination time is 1 - 5 h; Step 3, Preparation of Co2P / N-CNTs: Sodium hypophosphite and the Co / N-CNTs obtained in Step 2 satisfy a certain mass ratio, and phosphidation is achieved by carrying out the second calcination under certain conditions. Then, the obtained product is filtered, washed, and dried to obtain cobalt phosphide / nitrogen co-doped carbon nanotubes, named Co2P / N-CNTs; In the said Step 3, the mass ratio of sodium hypophosphite to Co / N-CNTs is 1:1; In the said Step 3, the conditions for the second calcination are: sodium hypophosphite is placed upstream, Co / N-CNTs are placed downstream, under nitrogen conditions, the second calcination temperature is 500 - 1000 °C, and the second calcination time is 1 - 5 h; Step 4, Preparation of Ru / Co2P / N-CNTs: Co2P / N-CNTs and ruthenium chloride trihydrate are placed in deionized water and stirred for a period of time to obtain mixture C. Then, an aqueous solution of sodium borohydride is added to mixture C for a reduction reaction until no bubbles are generated. Finally, the obtained product is filtered, washed, and dried to obtain ruthenium supported on cobalt phosphide / nitrogen co-doped carbon nanotubes, named Ru / Co2P / N-CNTs; In the said Step 4, the mass ratio of Co2P / N-CNTs, ruthenium chloride trihydrate, and sodium borohydride is 50:3:

19.

2. The application according to claim 1, wherein: The obtained ruthenium supported on cobalt phosphide / nitrogen co-doped carbon nanotubes catalytic material consists of cobalt phosphide / nitrogen co-doped carbon nanotubes Co2P / N-CNTs and Ru; among them, N-CNTs are obtained by calcining and carbonizing CoZn-ZIFs to achieve nitrogen doping of CNTs; Co2P is obtained by phosphating CoZn-ZIFs as a self-sacrificing template and sodium hypophosphite. The CoZn-ZIFs are supported on CNTs and are self-grown on the surface of CNTs by polyvinylpyrrolidone, cobalt nitrate hexahydrate, and zinc nitrate hexahydrate; Ru is obtained by reducing and loading ruthenium hydrate trichloride; The CoZn-ZIFs serve as a cobalt source, a zinc source, and a nitrogen source. Among them, zinc elements volatilize during the calcination process; sodium hypophosphite serves as a phosphorus source, and ruthenium hydrate trichloride serves as a ruthenium source.

3. The application according to claim 1, wherein: The hydrogen evolution turnover frequency of the obtained ruthenium-catalyzed material supported on cobalt phosphide / nitrogen co-doped carbon nanotubes is 100 - 300 mol H2 ·mol Ru –1 ·min –1 , the hydrogen evolution time by hydrolysis is 20 - 60 s, and the activation energy for catalytic hydrogen evolution is E a = 30 - 35 kJ·mol -1 .

4. The application according to claim 1, wherein: The obtained ruthenium supported on cobalt phosphide / nitrogen co-doped carbon nanotubes catalytic material maintains 40-45% of its initial catalytic activity after 5 cycles at 25 °C.

Images