This work was fully funded by Hong Kong University Grants Committee - Institutional Development Scheme (IDS) Collaborative Research Grant, grant number UGC/IDS(C)14/B(E)01/19, the Faculty Development Scheme (FDS), grant number UGC/FDS25/E08/20 and partially funded by the Institutional Development Scheme (IDS), grant number UGC/IDS(R)25/20.
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CAUTION: Readers are advised to carefully check the properties and toxicities of the chemicals described in this paper for the proper chemical handling from the relevant material safety data sheets (MSDS). Some of the chemicals used are detrimental to health, and special cares are to be taken. The impact of nanomaterials on human health is unknown and could pose safety and health risks. Inhalation and contact through the skin with these materials should be avoided. Safety precautions shall also be exercised, such as releasing the waste gas during the catalyst synthesis to the fume hood and catalyst performance evaluation with proper venting of the hydrogen gas. Personal protective equipment is advised to be worn at all times. Hydrogen is a potentially explosive gas with a very broad flammability range from 4%-74% in air. Care shall be taken to allow the hydrogen gas to vent properly to the atmosphere.
1. Synthesis of melem-C&#160;3N4 materials
<ol>
	<li>Weigh out 280 g of dicyandiamide (density = 1.4 g&#183;cm-3) into an 800 mL beaker.</li>
	<li>Place the beaker with the above solid into a muffle furnace and slowly raise the temperature from room temperature to 350 &#176;C with a ramp of 5 &#176;C&#183;min-1.</li>
	<li>Keep the temperature at 350 &#176;C for 2 h, cool down the furnace by natural cooling.</li>
	<li>Grind the obtained white solids into fine powder as the C3N4 materials in the melem form (DCD-350). 
	&#8203;NOTE: The yield is 175 g.</li>
</ol>
2. Annealing the melem-C&#160;3N4 and Co(acac)2 mixtures at different temperature
<ol>
	<li>Mix 10.0 g of melem-C3N4 with 0.218 g of Co(acac)2 [Co&#160;: melem-C3N4 = 1:200 (weight ratio)]. Grind and mix the two solids until the homogeneous color is observed.</li>
	<li>Add 6 mL of citric acid solution (water: ethanol = 1:1, citric acid = 10 g&#183;L-1) to the homogeneous mixture and further grind the materials.</li>
	<li>Dry the materials in an oven at 60 &#176;C for 6 h.</li>
	<li>Place the materials into a square-shaped crucible and then put it into a tubular furnace.</li>
	<li>Heat the materials at a heating rate of 2.6 &#176;C&#183;min-1 from room temperature to 800 &#176;C and keep for 2 h under an Ar flow of 100 mL&#183;min-1.</li>
	<li>Slowly cool down the furnace by natural cooling.</li>
	<li>Weight out the catalyst samples. Here, the yield was 0.65 g.</li>
</ol>
3. Measuring hydrogen release from ammonia borane hydrolysis
<ol>
	<li>Set up the water-filled inverted cylinder system (Supplementary Figure 1).</li>
	<li>Set up the 0.1 M H2SO4 washing solution.</li>
	<li>Connect the Schlenk flask with the washing solution and the water-filled inverted cylinder.</li>
	<li>Set the water bath temperature to 40 &#176;C.&#160;</li>
	<li>Place 0.04 g of the catalyst into the Schlenk flask.</li>
	<li>Prepare a solution of ammonia borane in water, with 0.04 g of ammonia borane in 0.948 mL of water (concentration = 0.04 g&#183;mL-1).</li>
	<li>Inject 1 mL of the NH3BH3 solution (40 mg&#183;mL-1) to the reactor to initiate the hydrolysis reaction.</li>
	<li>Monitor the drop in the water level as the reaction proceeds. Carefully record the production volume at designated times, e.g., each 5 s intervals.</li>
	<li>Plot the graph of volume of H2 production vs. time in minutes.</li>
</ol>
4. Kinetic studies
<ol>
	<li>Determination of the activation energy
	<ol>
		<li>Set the water bath temperature at 40 &#176;C.</li>
		<li>Place 0.04 g of the catalyst and 10 mL of water into the Schlenk flask and immerse into the water bath. Sonicate the solution at 40 kHz in an ultrasonic bath for 6 min.</li>
		<li>Inject 1 mL of the NH3BH3 solution (40 mg&#183;mL-1) to the reactor to initiate the hydrolysis reaction.</li>
		<li>Record the time for completion of the hydrogen release.</li>
		<li>Repeat steps 4.1.1-4.1.4 setting the water bath temperature at 35 &#176;C.</li>
		<li>Repeat the above experiment at 30 &#176;C and 25 &#176;C, respectively.</li>
		<li>Plot the specific rate constant versus time on a graph using the following equation. A plot of ln k and 1/T should yield a straight line. 
		<img alt="Equation 1" src="/files/ftp_upload/62965/62965eq01.jpg" /> 
		where ko denotes the specific rate constant (mol H2&#183;gCo-1&#183;min-1), R is the ideal gas constant (8.314 kJ&#183;mol-1), T represents the reaction temperature (K), and A is the pre-exponential factor (mol H2 gCo-1&#183;min-1).</li>
	</ol>
	</li>
	<li>Determination of the turnover frequency and specific hydrogen generation rate
	<ol>
		<li>Calculate the turnover frequency according to the following equation: 
		<img alt="Equation 2" src="/files/ftp_upload/62965/62965eq02.jpg" /> 
		where nH2 is the moles of hydrogen produced, &#916;t is the time required for complete hydrogen release and nM is the molar amount of metal in the catalyst.</li>
		<li>Calculate the specific hydrogen generation rate according to the following equation42,43: 
		<img alt="Equation 3" src="/files/ftp_upload/62965/62965eq03.jpg" /> 
		Where &#916;VH2 is the volume of hydrogen produced, t is the time required for the initiating and stabilizing stages (e.g., the time where 70 mL of hydrogen generated for 40 mg ammonia borane, the time where 140 mL of hydrogen generated for 80 mg ammonia borane) and &#969;&#8203;M is the mass of metal in the catalyst.</li>
	</ol>
	</li>
	<li>Determination of the relationship between [ammonia borane] and reaction rate
	<ol>
		<li>Set the water bath temperature at 40 &#176;C.</li>
		<li>Place 40 mg of the catalyst and 10 mL of water into the Schlenk flask and immerse into the water bath. Sonicate the solution at 40 kHz in an ultrasonic bath for 6 min.</li>
		<li>Inject 1 mL of the NH3BH3 solution (40 mg&#183;mL-1) to the reactor to initiate the hydrolysis reaction.</li>
		<li>Record the time for completion of the hydrogen release.</li>
		<li>Repeat step 4.3.3 injecting 2 mL of the NH3BH3 solution (i.e., 80 mg per 2 mL) to the reactor to initiate the hydrolysis reaction.</li>
		<li>Repeat steps 4.3.1-4.3.4 with 0.5 mL and 0.25 mL of the NH3BH3 solution (40 mg/mL) respectively to record the time for completion of the hydrogen release.</li>
		<li>Calculate the reaction rate according to the following equation44: 
		<img alt="Equation 4" src="/files/ftp_upload/62965/62965eq04.jpg" /> 
		where &#916;mlH2 is the volume of hydrogen produced, &#916;t is the time required for 70 mL of hydrogen release.</li>
		<li>Plot the ln rate vs. ln[ammonia borane] and determine the slope of the graph.</li>
	</ol>
	</li>
	<li>Determination of the relationship between [catalysts] and production rate
	<ol>
		<li>Set the water bath temperature at 40 &#176;C.</li>
		<li>Place 40 mg of the catalyst and 10 mL of water into the Schlenk flask and immerse into the water bath. Sonicate the solution at 40 kHz in an ultrasonic bath for 6 min.</li>
		<li>Inject 1 mL of the NH3BH3 solution (40 mg&#183;mL-1) to the reactor to initiate the hydrolysis reaction.</li>
		<li>Record the time for completion of the hydrogen release.</li>
		<li>Repeat steps 4.4.1-4.4.4 varying the amount of catalyst (20 mg, 40 mg, 60 mg, 80 mg) and inject 1 mL of the NH3BH3 solution (i.e., 40 mg&#183;mL-1) into the reactor to initiate the hydrolysis reaction.</li>
		<li>Record the time for completion of the hydrogen release for using the above various catalyst amounts.</li>
		<li>Calculate the reaction rate according to the following equation44: 
		<img alt="Equation 5" src="/files/ftp_upload/62965/62965eq04.jpg" /> 
		where &#916;mlH2 is the volume of hydrogen produced, &#916;t is the time required for 70 mL of hydrogen release.</li>
		<li>Plot the ln rate vs. ln[catalyst] and determine the slope of the graph.</li>
	</ol>
	</li>
</ol>
5. Cycling performance test
<ol>
	<li>Set the water bath temperature at 40 &#176;C.</li>
	<li>Place 0.04 g of the catalyst and 10 mL of water into the Schlenk flask and immerse into the water bath. Sonicate the solution at 40 kHz in an ultrasonic bath for 6 min.</li>
	<li>Inject 1 mL of the NH3BH3 solution (40 mg&#183;mL-1) to the reactor to initiate the hydrolysis reaction.</li>
	<li>Record the time for completion of the hydrogen release.</li>
	<li>Filter off the catalyst, washed with water (5 mL) three times, and then dry the catalyst in the oven (60 &#176;C) for 3 h.</li>
	<li>Place the catalyst in 10 mL of water and sonicate the solution at 40 kHz in an ultrasonic bath.</li>
	<li>Repeat steps 5.1.3-5.1.5 for ten times.</li>
	<li>Plot the hydrogen production volume, TOF and specific generation rate vs. cycles, respectively.</li>
</ol>
6. Leaching experiment for metal NPs to obtain pure metal SAs CNT
<ol>
	<li>Set the oil bath temperature at 80 &#176;C.</li>
	<li>Place 0.15 g of the catalyst and 50 mL of 0.5 M H2SO4 into the Schlenk flask and immerse into the oil bath.</li>
	<li>Stir the reaction for 2 h.</li>
	<li>Filter off the solid using a Buchner funnel and wash the solid with deionized water (3x in 10 mL each). Dilute the leachate further to 250 mL in a 250 mL volumetric flask.</li>
	<li>Collect the metal nanoparticles-leached solids (which contain only Co-doped CNT) and dry at 60 &#176;C in an oven.</li>
</ol>
7. Metal content determination using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)
<ol>
	<li>Determination of total cobalt metal content
	<ol>
		<li>Place approximately 0.02 g of as-prepared catalyst from section 2 into 50 mL of 2 M acid solution (HCl: HNO3 = 3:1 mole ratio)45,46 in a polytetrafluoroethylene-lined stainless-steel autoclave.</li>
		<li>Place the polytetrafluoroethylene-lined container into the stainless steel bomb and secure the cap.</li>
		<li>Place the bomb into an oven, set the temperature to 180 &#176;C, and heat the bomb for 12 h.</li>
		<li>Remove the bomb and empty the contents. Filter the solid and dilute the solute in a 250 mL volumetric flask with 200 mL of deionized water. 
		NOTE: The purpose of the dilution is to adjust the concentration of the ICP samples, which will fit into the metal standard concentration range, i.e., 0-40 ppm.</li>
		<li>Run the ICP-OES test of the solution and calculate the total amount of Co in wt%.</li>
	</ol>
	</li>
	<li>Determination of the cobalt atoms content on the CNT
	<ol>
		<li>Place approximately 0.02 g of as-prepared catalyst from step 6.5 into 50 mL of 2 M acid solution (HCl: HNO3 = 3:1 mole ratio)45,46 in a polytetrafluoroethylene-lined stainless-steel autoclave.</li>
		<li>Place the polytetrafluoroethylene-lined container into the stainless-steel bomb and secure the cap.</li>
		<li>Place the bomb into an oven, set the temperature to 180 &#176;C, and heat the bomb for 12 h.</li>
		<li>Remove the bomb and empty the contents. Filter the solid and dilute the solute in a 250 mL volumetric flask with 200 mL of deionized water. 
		NOTE: The purpose of the dilution is to adjust the concentration of the ICP samples, which will fit into the metal standard concentration range, i.e., 0-40 ppm.</li>
		<li>Run the ICP-OES test of the solution and calculate the amount of Co atom contents in wt%.</li>
	</ol>
	</li>
	<li>Determination of the cobalt nanoparticles (NPs) content
	<ol>
		<li>The difference between the metal content of 7.1.5 and 7.2.5 is the wt% of Co NPs.</li>
	</ol>
	</li>
</ol>

We have nothing to disclose.

The pyrolysis method has become one of the powerful strategies in the synthesis of one-dimensional nanomaterial on various heteroatom-doped solid supports with controlled sizes of NPs. For example, the nanospace-confined pyrolysis strategy was reported by Guo et al.56. Briefly, the pre-treated MWCNTs, cobalt, and phosphorus precursors were pyrolyzed&#160;at 800 &#176;C under N2 atmosphere, and the CoP NPs supported on N-CNT can be obtained. The presence of the micro-pores can act as the...

Developing low-cost and highly efficient catalysts for renewable energy production remains one of the most critical and challenging problems to relieve the energy crisis. However, it is far from practical applications due to several concerns, such as large-scale production methods with reliable performance, high production cost, and long-standing stability to extend the service life of catalysts. Industry sectors, like transport and logistics, require energy production for vehicles and equipment with long operation hours, high powered energy supply, and minimal refueling time in achieving efficient operations1,2,3. Therefore, effective strategies have been extensively exploited to address the above technical challenges. For example, by regulating the electronic structure of the metal active sites and catalyst supports, designing the specific architecture of the metal nano-catalysts, fine-tuning metal compositions, functional group modification of anchored support, and varying the morphology to increase the number of intrinsic active sites. In the past few decades, nanoparticles (NPs) have dominated the fields of various heterogeneous catalysis, and the catalytic activities can be effectively tuned by varying the size of the NPs. Only until in recent years, highly dispersed single-atom catalysts (SACs) emerged to have excellent properties towards many catalytic&#160;reactions due to their unique electronic structure and coordination environment. Particularly, SACs have already demonstrated superior performances in energy conversion such as electrochemical reactions (HER, ORR, OER) and electrochemical energy systems (e.g., supercapacitors, rechargeable batteries)4,5,6. While both NPs and SACs have their respective&#160;advantages and limitations in catalytic applications, there do exist reactions that require both NPs and SACs in order to boost catalytic reactivity. For example, Ru NPs supported on Ni- and N-co-doped carbon nanotube superstructure could facilitate the high catalytic wet air oxidation of acetic acid7. This synergistic effect was also demonstrated by Pd1+NPs/TiO2 catalysts for highly selective ketone and aldehydes hydrogenation at room temperatures8. In order to accelerate the field of synergistic NPs and SACs catalysis and explore more on their catalytic applications, a facile way of catalyst synthesis is highly desirable, and the introduction of high loadings of the atomically dispersed active site remains a challenge due to the high tendency of the aggregation of SACs9.
Several methods have been utilized to synthesize SACs for applications in the hydrogenation of nitroarenes10, oxygen reduction reaction and hydrogen evolution reaction11,12, lithium-oxygen batteries13.The most common strategy is the bottom-up approach, in which the metal precursors were absorbed, reduced, and immobilized on the defects of the corresponding support. Mononuclear metal complexes could also be first attached to the functional group of supports, followed by subsequent removal of the organic ligands, thus creating active metal sites for the catalytic process. Atomic layer deposition (ALD) is probably the most frequently used procedure for bottom-up fabrication by depositing a thin layer of film on the substrate with repeated exposure of reactants. Although the catalyst size could be precisely controlled and the reactivity could be greatly improved14, the purity of the substrate was rather demanding, and the metal loading was relatively low, thus resulting in high production costs for practical applications. Various methods such as direct impregnation, co-precipitation, and deposition-precipitation, have been employed to immobilize metal nanoparticles onto the support surfaces, such as metal oxide and nitride, through surface charging effects. However, increasing metal loading usually leads to significant agglomeration and cluster formation of the metal atoms or nanoparticles. Therefore, usually, a very diluted metal solution is required, thus leading to low SACs loadings of the catalysts15. Amine ligands such as phenanthroline have been employed to undergo pyrolysis with metal precursors to prepare atomically dispersed metal catalysts with highly active Co-Nx active sites for the selective dehydrogenation of formic acid. However, the metal loading was relatively low (2-3 wt%) due to the limited number of available N atoms in the amine precursors16.
In the past few decades, hydrogen has been regarded as a potential alternative to replace fossil fuels or hydrocarbons, such as coal, natural gas, and gasoline, due to the advantage of zero-emission of the former. Until now, about 94% of commercial hydrogen is still produced from the reforming process of fossil fuels, in which the process releases a great deal of greenhouse gas17. Therefore, hydrogen production from renewable resources such as water electrolysis is a way to solve the problem of depleted fossil resources and severe carbon emissions. However, the low hydrogen production efficiency has hindered their wider applications. Thus, to overcome this kinetic energy barrier for water-splitting, numerous efficient electrocatalysts have been discovered in the past decade18. Another issue is the storage problem due to the gaseous and explosive nature of hydrogen gas at ambient conditions. Physical storage methods such as compression will require the hydrogen to be compressed up to 700-800 bar, and cryogenic storage by liquefaction will require low temperature at -253 &#176;C19. Although commercialized hydrogen fuel cell-powered vehicles have been successfully demonstrated, the storage problem is yet to be solved if the technology is to be used in wider applications, such as miniature devices and mini-fuel cells. Thus, storage methods of using chemical H materials have been one of the hot focuses in hydrogen energy research. Some examples of chemical H storage materials are ammonia borane (AB)20, formic acid (FA)21, ammonia gas22, sodium alanate23, and magnesium hydride24. Among these, AB has a low molecular weight (30.7 g&#183;mol-1), high gravimetric and volumetric densities (196 gH2&#183;kg-1 and 146 gH2&#183;L-1, respectively). Besides, it is an air and moisture stable compound, non-toxic, and highly soluble in water. Metal nanoparticles on various supported materials have been widely used to release the three equivalents of hydrogen from AB, such as platinum- (Pt-), palladium- (Pd-), ruthenium- (Ru-), cobalt- (Co-), and nickel- (Ni-) based catalysts. Co-based heterogeneous catalysts supported on carbon materials are especially attracting much attention due to their low cost, high abundance, and ease of recovery. Several synthetic strategies have been reported, such as the Co NPs supported on branched polyethylenimine-decorated graphene oxide25. The 3D structure with a large surface area ensures the stabilization of Co NPs maintaining at the 2-3 nm size range and prevented the aggregation of NPs. Another strategy is to use N-doped carbon materials to support Co NPs with small sizes. Using Co(salen)26 and Co-MOF27 (metal organic framework) as the precursors, Co NPs of 9.0 nm and 3.5 nm supported on N-doped porous carbon materials have been prepared respectively. The stability towards AB hydrolysis are high and the reactivity can maintain over 95% of the initial activity after 10 reaction runs. Recently, catalysts with hollow micro/nanostructures have been exploited for AB hydrolysis. These materials are conventionally prepared by hydrothermal methods and have been widely used for lithium-ion batteries, supercapacitors, chemical sensors, and heterogeneous catalysis research. Thus, the copper-cobalt synergy towards AB hydrolysis has been demonstrated by the hollow CuMoO4-CoMoO428, which gives a high TOF of 104.7 min-1. Other highly structural-dependent examples include the core-shell CuO-NiO/Co3O429, the CoxCu1&#8722;xCo2O4@CoyCu1&#8722;yCo2O4 yolk-shell type30, and the Ni0.4Cu0.6Co2O4 nanoarrays31 were also found to be active towards AB hydrolysis. Another type of emerging materials known as heterostructured catalysts, such as MXenes and layered double hydroxides (LDHs), are increasingly being exploited for electrocatalytic and photocatalytic reaction32,33,34,35. These materials such as the NiFe-layered double hydroxide36,37 and the CoB-N materials having N-doped carbon-cobalt boride heterointerfaces38 are especially active for oxygen evolution and reduction reaction. In principle, they could be further exploited for hydrogen evolution reactions from hydrogen storage materials such as ammonia borane39. Maximizing the interaction between the catalysts and substrates is also another strategy for AB hydrolysis. Chiang et al. have utilized the surface oxide group of graphene oxide to form an initiated complex species with AB40, thus Ni0.8Pt0.2/GO and rGO demonstrated excellent reactivity towards AB hydrolysis. The use of &#945;-MoC as support for Co and Ni bimetallic catalysts assisted the activation of water molecules and achieved high TOF towards AB hydrolysis, which is four times higher than the commercial Pt/C catalyst41.
Taking advantage of high N contents of the dicyandiamide and related C3N4 materials, a protocol for achieving a facile synthesis of cobalt NPs supported on highly dispersed Co- and N-doped carbon nanotubes is presented herein. The gradual&#160;in-situ formation of Co NPs from the formed atomically dispersed Co during the pyrolysis of C3N4 materials ensure that 1) Co NPs and Co dopants are highly dispersed; 2) Co NPs can be strongly anchored on the doped carbon supports and 3) Co NPs size can be carefully controlled by the temperature and time of the pyrolysis. The as-prepared Co/Co-N-CNT, as a result of the strongly anchored Co NPs and the ability of the Co dopants to lower the adsorption energy of water molecules, was found to have superior stability towards the hydrolysis of AB for hydrogen production. The details of the synthetic protocol of the catalysts and the measurement of the hydrogen production will be the focal point of this report.

<table><tbody><tr><td>Dicyandiamide</td><td>Sigma Aldrich</td><td>D76609</td><td></td></tr><tr><td>Borane-ammonia complex</td><td>Aladdin</td><td>B131882-100g</td><td></td></tr><tr><td>Citric acid, 99%</td><td>Sigma Aldrich</td><td>C0759</td><td></td></tr><tr><td>Cobalt metal standard solution, traceable to SRM from NIST Co(NO&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; in HNO&lt;sub&gt;3&lt;/sub&gt; 0.5 mol/l 1000 mg/l Co Certipur</td><td>Sigma Aldrich</td><td>1.19785</td><td></td></tr><tr><td>Cobalt(II) acetylacetonate, &amp;ge; 99%</td><td>Sigma Aldrich</td><td>727970</td><td></td></tr><tr><td>Hydrochloric acid, ACS reagent</td><td>Sigma Aldrich</td><td>320331-2.5L</td><td></td></tr><tr><td>ICP-OES</td><td></td><td></td><td>ICP-OES with dichroic spectral combiner (Agilent 5110)</td></tr><tr><td>Muffle furnace</td><td></td><td></td><td>High Performance Hybrid Muffle furnace, Chamber: (360 x 250 x 320) mm, Exterior: (610 x 545 x 500) mm, Power(3100W), Vulcan 3-1750)</td></tr><tr><td>Nitric acid, puriss. p.a., 65.0-67.0%</td><td>Sigma Aldrich</td><td>84378</td><td></td></tr><tr><td>Sulphuric acid, ACS reagent 95-98%</td><td>Sigma Aldrich</td><td>258105</td><td></td></tr><tr><td>Tubular furnace</td><td></td><td></td><td>OTF-1200X with tube size of 60 mm outer diameter (Hefei Kejing)</td></tr><tr><td>Ultrasonic bath</td><td></td><td></td><td>10L Digital Single Frequency 40 kHz Ultrasonic Cleaner (Biobase)</td></tr></tbody></table>

synthesis of metal nanoparticles supported on carbon nanotube with doped co and n atoms and its catalytic applications in hydrogen production

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented herein. The novel strategy is based on a facile one-pot pyrolysis treatment of cobalt (II) acetylacetonate and nitrogen-rich organic precursors under Ar atmosphere at 800 &#176;C, resulting in the formation of Co- and N- co-doped carbon nanotube with earthworm-like morphology. The obtained catalyst was found to have a high density of defect sites, as confirmed by Raman spectroscopy. Here, cobalt (II) nanoparticles were stabilized on the atomically dispersed cobalt- and nitrogen-doped carbon nanotubes. The catalyst was confirmed to be effective in the catalytic hydrolysis of ammonia borane, in which the turnover frequency was 5.87 mol H2&#183;molCo-1&#183;min-1, and the specific hydrogen generation rate was determined to be 2447 mL H2&#183;gCo-1&#183;min-1. A synergistic function between the Co nanoparticle and the doped carbon nanotubes was proposed for the first time in the catalytic hydrolysis of ammonia borane reaction under a mild condition. The resulting hydrogen production with its high energy density and minimal refueling time could be suitable for future development as energy sources for mobile and stationary applications such as road trucks and forklifts in transport and logistics.

X-ray diffraction patterns (XRD) have been obtained to determine the crystallinity and size of the cobalt NPs. As shown in Figure 1, diffraction peaks corresponding to the (111), (200) and (220) planes (at 2&#952; of 44.2&#176;, 51.5&#176;, and 75.8&#176; respectively) of the cubic phase of metallic cobalt were present in agreement with the JCPDS (Joint Committee for Powder Diffraction Standards) power diffraction file (card # 15-0806)47. The broad peak at 2&#952; of ...

Watch this Scientific Journal Video about Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production at JoVE.com

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

Here, we present a protocol to synthesize Co nanoparticles supported on carbon nanotubes with Co- and N- dopants for hydrogen productions.

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented ...

synthesis-metal-nanoparticles-supported-on-carbon-nanotube-with-doped

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JoVE Journal

Chemistry

3.4K Views.  Technological and Higher Education Institute of Hong Kong (THEi). Dit protocol gaat over het ontwikkelen van goedkope en zeer efficiënte katalysatoren met betrouwbare prestaties en langdurige stabiliteit. De ontwikkelde katalysator kan worden gebruikt voor de productie van hernieuwbare energie en kan zelfs het probleem van de energiecrisis oplossen. Het voordeel van deze studie is om zowel deeltjes- als atomair dispergeeraal metaalatomen op dezelfde katalysatorsteunen te construeren, die synergetisch kunnen werken voor bepaalde soorten katalysatorreacties....

Video: Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Engineering

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates.

The study of methods to generate on-demand hydrogen for fuel cells continues to grow in importance. However, systems to measure hydrogen evolution from the reaction of chemicals with water can be complicated and expensive. This article details a simple, low-cost, and robust method to measure the evolution of hydrogen gas.

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic nanoparticles is developed. Guidelines for the replication of the reactor and its operation are provided in detail. Three different composite systems (Pt/graphene, Pt/TiO2, and Au/TiO2) with monodisperse and uniformly distributed particles are produced by this reactor, and the photodeposition mechanism, as well as the synthesis optimization strategy, are discussed. The synthesis methods and their technical aspects are described comprehensively. The role of the ultraviolet (UV) dose (in each excitation pulse) on the photodeposition process is investigated and the optimum values for each composite system are provided.

For a continuous and scalable synthesis of noble-metal-based nanocomposites, a novel photocatalytic reactor is developed and its structure, operation principles, and product quality optimization strategies are described.

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected.
Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 &#176;C to 130 &#176;C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of &#945;, &#946;-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

This protocol shows a convenient method for comparing the catalytic properties of supported platinum catalysts, synthesized by deposition of nanosized colloids or by impregnation. The hydrogenation of cyclohexene serves as a model reaction to determine the catalytic activity of the catalysts.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands ...

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

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