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

Summary

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

Abstract

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 °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·mol_Co^-1·min^-1, and the specific hydrogen generation rate was determined to be 2447 mL H₂·g_Co^-1·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.

Introduction

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 operations^1,2

Protocol

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. Person....

Results

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 2θ of 44.2°, 51.5°, and 75.8° 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 2θ of around 26° corresponding .......

Discussion

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 at 800 °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 pathway f.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Dicyandiamide	Sigma Aldrich	D76609
Borane-ammonia complex	Aladdin	B131882-100g
Citric acid, 99%	Sigma Aldrich	C0759
Cobalt metal standard solution, traceable to SRM from NIST Co(NO3)2 in HNO3 0.5 mol/l 1000 mg/l Co Certipur	Sigma Aldrich	1.19785
Cobalt(II) acetylacetonate, ≥ 99%	Sigma Aldrich	727970
Hydrochloric acid, ACS reagent	Sigma Aldrich	320331-2.5L
ICP-OES			ICP-OES with dichroic spectral combiner (Agilent 5110)
Muffle furnace			High Performance Hybrid Muffle furnace, Chamber: (360 x 250 x 320) mm, Exterior: (610 x 545 x 500) mm, Power(3100W), Vulcan 3-1750)
Nitric acid, puriss. p.a., 65.0-67.0%	Sigma Aldrich	84378
Sulphuric acid, ACS reagent 95-98%	Sigma Aldrich	258105
Tubular furnace			OTF-1200X with tube size of 60 mm outer diameter (Hefei Kejing)
Ultrasonic bath			10L Digital Single Frequency 40 kHz Ultrasonic Cleaner (Biobase)